Fossil Nests and Eggs

"Thus nest construction, egg-laying, and nurture of juveniles occurred at this locality three times.  If one cycle of this sort is difficult to fit into the Flood year, the establishment of three successive nesting colonies one after the other surely strains the imagination, notwithstanding that the growth rate of baby dinosaurs was rapid." — Paul Garner, young-earth geologist, 1996¹

"Our results show unexpectedly slow incubation (2.8 and 5.8 mo) like those of outgroup reptiles." — Gregory Erickson and colleagues, counting daily growth lines in embryonic dinosaur teeth, 2017²

"The only viable conclusion is that the dinosaurs laid their eggs in haste." — Michael Oard, 2013³

Summary

A fossil egg is a body fossil.  A fossil nest is a trace fossil:  it records an animal alive on that surface, choosing a place, digging, laying, waiting and, if the eggs hatched, the young walking about on the same ground.  This article asks what the best-studied dinosaur nesting grounds record, and whether that record fits inside a Flood year.  The sibling articles cover tracks, coprolites, and the one young-earth answer offered for all of them, Michael Oard's Briefly Exposed Diluvial Sediments (BEDS).  BEDS is argued in full there.  Here it is stated in Oard's words and then priced against what the nests require of it.

The young-earth position, in its own words.  Oard holds that every dinosaur egg, nest and track in the Mesozoic was made on Flood sediment that was briefly above water, between Day 40 and about Day 120 of the Flood, by dinosaurs that swam or floated to it and "laid their eggs in haste," after which the next rise of water buried everything.⁴  He reads the rarity of rimmed nest structures, the rarity of preserved vegetation, and the porous eggshell as signs of abnormal conditions, and he reads stacked egg levels as repeated oscillations of the water.³  Brian Thomas of ICR summarises the 2011 book:  the dinosaurs' "final hours or days" were spent on the freshly exposed surface.⁵  Not every creationist agrees.  Paul Garner surveyed the nest literature in 1996 and concluded that nests "on several successive horizons" stretch the Flood chronology "beyond breaking point," and placed the whole Mesozoic after the Flood instead.¹  Chad Arment, writing in Answers Research Journal in 2023, rejected Oard's "briefly" for stacked burrow horizons with soils between them.⁶  So the young-earth camp has two answers that contradict each other, and the organisations publish both.

What the sites record.  At Egg Mountain in Montana, Jack Horner's crews found clutches of one egg type on each of three fossil horizons in a three-metre section, with a "trampled, muddy soil surface clearly preserved" on each;⁷  the Willow Creek Anticline next to it has three separate Maiasaura nesting horizons;⁸  the one undisputed rimmed nest, holding 24 Troodon eggs, sits "within a moderately well-developed micritic paleosol;"⁹  and the whole Egg Mountain section is stacked calcretes and calcareous siltstones riddled from bottom to top with wasp and beetle cocoons, which the ichnologists read as "slow, relatively continuous distal floodplain deposition" on "well-drained and workable soils with extended periods of subaerial exposure," with no single depositional event thicker than ten centimetres.¹⁰  At Devil's Coulee in Alberta, nests of the hadrosaur Hypacrosaurus lie in caliche-bearing mudstones in the uppermost hundred metres of a 650-metre formation, and the embryos inside them are the ones whose teeth were counted.¹¹  At Auca Mahuevo in Argentina, the excavators mapped six separate egg-beds, some traceable for kilometres, holding about four hundred in-place clutches, and concluded that the titanosaurs returned to "the same nesting site at least six separate times" and laid their eggs "in excavated depressions without burying them."¹²  In the Spanish Pyrenees, one locality exposes nine egg horizons, and the three-dimensional shape of the clutches records an asymmetric dug hole.¹³  In Romania the Tustea eggs sit above a mudstone with "small calcretes, plant rootlets, and vertical burrows."¹⁴  In India, 92 titanosaur clutches with 256 eggs show hatching windows and shell piles.¹⁵

The clock.  In 2017 Erickson, Zelenitsky, Kay and Norell counted the daily growth lines in the teeth of near-hatching embryos.  The count is not a radiometric date;  it is the same kind of count as tree rings, made on lines that form once a day in crocodile and human teeth.  The teeth of the Devil's Coulee Hypacrosaurus embryo record 99.45 days of growth and those of a Protoceratops embryo 48.23.  Adding the time before the first tooth, modelled from living crocodiles, gives at least 171 and 83 days in the egg, and every uncertainty the authors list makes the true figures longer.²²  Oard's whole window for egg-laying is about eighty days.⁴  A single incubation at Devil's Coulee is longer than the window, before any nest is dug, any hatchling walks, any soil forms, or any second horizon is laid down.

Where the young-earth side is right.  The excavators themselves say that floods buried most of these clutches.  At Auca Mahuevo, "Flooding of shallow stream channels deposited overbank silt and mud on the eggs, killing the embryos."¹⁶  The Troodon nest was sealed by an overbank mudstone.⁹  The Javkhlant colony in Mongolia was blanketed by a flood after most of it had hatched.¹⁷  Rimmed nest structures really are rare, and at Auca Mahuevo the excavators say the few in egg-bed 4 are "the only reliable evidence" of nest architecture there.¹²  Most eggs hold no embryo.  The brooding oviraptorids of the Gobi were buried alive, though by collapsing wet dune sand rather than water.¹⁸  And the science corrected itself twice at Egg Mountain:  the "hypsilophodont" eggs became Troodon eggs, and Horner's lake limestone became a calcrete soil.

Verdict.  BEDS gets the burial right and the clock wrong.  Every nesting ground this article examines records, in its own rock, an exposure measured in months:  nests dug into soils, eggs incubated for a quarter to half a year, hatchlings on the surface, insect cocoons through the whole section, and the same ground reused three to nine times with sediment and soil formed between.  A model that allows eighty days for all of it, worldwide, cannot hold one incubation at Devil's Coulee.  Garner's alternative, a post-Flood Mesozoic, fits the nests but is rejected by the rest of Flood geology for other reasons.  The honest position is that fossil nests are an unsolved problem for the one-year Flood, and that the young-earth literature's own best writer on nests said so in 1996.

Part 1: The young-earth position, in its own words

Michael Oard is the young-earth author who has written most on dinosaur eggs, and the one whose model the creationist organisations now carry.  His position has been stable since 1995, so it can be stated from his own papers before anything is said against it.

The problem as Oard states it

Oard does not hide the difficulty.  In 1999 he put it this way:  "The dinosaur features strongly imply that the dinosaurs were living at the time the features were made.  This is the problem for creationists: since the sedimentary rocks that entomb the dinosaurs were deposited in the global Genesis Flood, how could thousands of dinosaurs have been alive, laying eggs and walking around, in the midst of the catastrophic activity of that same Flood?"¹⁹  In 2010 he called the Mesozoic's "billions of dinosaur tracks and millions of dinosaur eggs" evidence of "live dinosaurs that must have perished by Day 150."²⁰  And in 1997, after working through Egg Mountain in detail, he wrote that "Dinosaur eggs, nests, and babies at first glance appear to contradict the hypothesis of briefly exposed sediments during the Flood.  However, many unknowns still surround this fascinating evidence of in situ dinosaur activity."²¹

The answer: briefly exposed diluvial sediments

The answer is a strip of freshly deposited Flood sediment that stood briefly above the water.  In 1995, writing about Egg Mountain:  "As thousands of dinosaurs landed on this newly arisen strip of land, many females were undoubtedly pregnant.  They would anxiously lay their eggs, either in a makeshift nest or in the mud."²²  The same paper fixes the clock:  "It is not clear from Genesis whether every air breathing animal died in 40 days or 150 days.  Because of dinosaur tracks on thousands of meters of Flood sediments and baby dinosaurs hatched from eggs, I favor 150 days before all air breathing animals on land died."²²  By 2010 the mechanism had a name:  tracks, eggs and burrows "represent animal activity during the Flood, before Day 150.  Such tracks were made on 'briefly exposed diluvial sediments' (BEDS) during fluctuations in relative sea level during the Flooding Stage."²⁰  Brian Thomas of ICR, reviewing the 2011 book that argues it in full, quotes its definition:  "If there were places that were submerged, covered by sediment, and then re-emerged for a short time, then all the dinosaur data can be explained by their final hours or days being spent on the freshly-laid-and-then-exposed flat Flood sediments."⁵  Thomas's own summary of the picture is dinosaurs "truly on their last legs, treading water for perhaps hours before finally being able to step in submerged mud when waters lowered."⁵

The window narrowed over time.  In 1995 it was the first 150 days.  By 2016 it was "between Day 40 and about Day 120 of the Flood.  If they were laid during the first 40 days of heavy rain, the rain would have washed away the tracks and eggs."⁴  The popular version says the same:  "The dinosaur activity can be placed between Day 40 and Day 120 of the 370-Day Flood."²³  That is about eighty days for every egg, nest, track and hatchling in the Mesozoic, on every continent.

The three signs of haste

Oard's positive case rests on three observations, each of which he reads as a sign of abnormal conditions.  First, rimmed nest structures are rare:  "There are very few dinosaur nests in the world; most eggs are simply found on bedding planes."²⁴  He reads this as a hurry:  "One would certainly not expect the vast majority of eggs to have been simply laid out in the open on the surface of the sediment, i.e. on a bedding plane.  This evidence indicates that the dinosaurs likely laid their eggs in a hurry, and points to abnormal conditions of worldwide extent."²⁴  Second, vegetation is rarely preserved with eggs.  Third, dinosaur eggshell is porous like reptile eggshell, which in living animals means a buried or mounded nest, so eggs on an open bedding plane are a contradiction:  "Very rare nest structures and almost complete lack of evidence for vegetation means that dinosaur eggs have been laid on flat bedding planes.  The embryo inside the egg would quickly dry out.  This situation contradicts the environmental deduction of the porous eggs."³  His conclusion:  "They did not have time to dig a hole or add vegetation, possibly because there was no vegetation to be found.  This means the eggs were laid in an unnatural environment and on flat sediment surfaces with subsequent rapid burial by watery flows—worldwide."³

How Oard handles the hard cases

Oard has answered the two observations that cut hardest against him, and his answers should be stated.  On eggs at several levels in one place:  "Just having eggs at different stratigraphic levels is really not a problem in a Flood paradigm, in which portions of exposed land were periodically inundated."²¹  "Since sedimentation was rapid, and the Flood level oscillated repeatedly, it would not be unusual for eggs to be laid at multiple levels in the same area."²³  Of Auca Mahuevo's stacked egg levels he even turns the point around:  "The same type of dinosaur laid the eggs on all four BEDS.  In the uniformitarian model, the sequence should be an accumulation of sediment over hundreds of thousands of years.  How probable is it for the same type of dinosaur to frequent the same spot hundreds of thousands of years later?"⁴  On hatching:  "Eggs with broken tops can simply be due to sediment compaction or scavenging.  It is possible some embryos hatched, although this would be rare."²³  On the Egg Mountain babies specifically:  "Third, the eggs may or may not have hatched.  Just because the tops of many eggs were broken, does not necessarily mean the dinosaurs hatched. … The tops of the eggs could have been broken by scavengers, for which there is abundant evidence in the area."²¹

Two other creationist answers circulate.  Walter Barnhart, in Creation Research Society Quarterly, examined published clutch drawings and concluded that the eggs "were all laid into a watery environment in which sedimentation was often actively taking place," so that the nests "show life existed at the survival level under highly stressed conditions."²⁵  And a 2023 Creation magazine piece on Maiasaura offers the only creationist answer this article could find to incubation time:  "Some pregnant dinosaurs under stress may have retained fertilized eggs longer than usual, allowing the embryo to reach the point of hatching shortly after being laid," adding that "Infrequently, an uplifted surface could have stayed exposed for long enough to allow the hatchlings to develop for a time."²⁶

The dissent inside the camp

Not every young-earth geologist accepts this.  In 1996 Paul Garner, of the Biblical Creation Society in Britain, surveyed the whole nest literature in the same journal Oard publishes in, and he began by refusing the easy way out:  "I should state plainly at the outset that it is not possible to resolve this difficulty by denying the relative position of the Mesozoic sediments in the stratigraphic record. … In other words, the geological column is a reality."¹  His abstract states the finding:  "in situ dinosaur nests occur at multiple levels throughout the Mesozoic.  These nests stratigraphically overlie thousands of metres of Flood-deposited Palaeozoic sediments.  Creationist arguments that attempt to accommodate multiple periods of nest building and nurture of juveniles within the limited time available during the Flood have not proven convincing.  The nests are strong evidence that the Mesozoic host sediments are post-Flood."¹  He aimed directly at Oard's 1995 paper:  "Even more damaging to Oard's thesis are the localities where nests occur on several successive horizons. … How are we to accommodate several successive nest-building periods within 150 days, remembering that we also have to leave sufficient time for the rest of the Mesozoic, the entire Palaeozoic, and possibly a considerable portion of the Proterozoic to be deposited before the dinosaurs can even begin to build the first nest?  Examples such as these stretch Oard's Flood chronology beyond breaking point."¹  And he asked the question a skeptic would ask:  "He postulates thousands of dinosaurs floating and swimming in the Flood waters for hundreds of miles, before finally lighting upon temporary strips of land to make tracks and build their nests.  What terrestrial animals could really have survived in these conditions?  And if the Flood was sufficiently tranquil to allow this to happen — and to leave the nest horizons largely uneroded — why did not some dinosaurs survive the Flood altogether, just as they did up to the end of the Cretaceous?"¹

Garner's own answer is that the Flood ended before the Triassic and that every Mesozoic nest records post-Flood recolonisation.¹  That answer is a minority view.  Oard rejects it, ICR's Flood model buries the dinosaurs in the Flood, and the Flood boundary articles on this site set out why most Flood geologists put the boundary in the Cenozoic.  So the camp holds two incompatible positions on nests.  A third creationist voice shows the test this article applies is not a secular one.  Chad Arment, in Answers Research Journal in 2023, examined the stacked burrow horizons of Nebraska's Palaeocastor beavers, found Oard's BEDS answer applied to them, and wrote:  "Clearly, extensive plant growth, episodic and vertically staggered burrow formation, and a large terrestrial beaver population demonstrate that this phenomenon didn't 'briefly' occur during the Flood."⁶  Burrows belong to another article;  the point here is that a young-earth author applied the same test to the same model and failed it.

What the nests require of BEDS

Stated as requirements, BEDS must supply, at each nesting ground, dry workable ground that stays exposed for the full time the rock records:  long enough for a hole to be dug into a soil, for a clutch to be incubated to hatching, for hatchlings to move about and trample the surface, and for the whole cycle to repeat on the same ground as many times as there are nesting horizons, with sediment and soil formed between.  All of that must fit between Day 40 and Day 120, and all of the sediment beneath the lowest horizon must already be in place.  The rest of this article measures each requirement against the sites.  The BEDS article argues the mechanism itself.

Part 2: Egg Mountain and the Willow Creek Anticline, Montana

The first dinosaur nesting ground anyone excavated is still the best documented, and it is the one Oard and Garner both argue over.  It lies in the upper Two Medicine Formation west of Choteau, Montana, in a small fold called the Willow Creek Anticline, and the facts come from the people who dug it:  John Horner and Robert Makela's 1979 report of a nest of fifteen juvenile Maiasaura,²⁷ Horner's 1982 report of colonial nesting on several horizons,²⁸ his 1988 book with James Gorman, his 1994 chapter on the taphonomy of the nesting horizons, and the Montana State University work of David Varricchio, Frankie Jackson and their students from 1997 to the present.

What Horner found

Horner describes the setting plainly in Digging Dinosaurs:  "The anticline is about 160 feet thick, and it has seven distinct, fossil-rich rock layers. … It was from a spot on the bottom horizon, in the scooped-out center of the anticline, on a pebble-strewn nub of dirt and rock, that Bob and I dug up the first nest of baby maiasaurs.  And it was on this same horizon that, over the next few years, we were able to find eight more maiasaur nests."⁷  His 1994 chapter counts the horizons:  "Three Maiasaura peeblesorum nesting horizons have been discovered, all in the area of the Willow Creek Anticline, Teton County, Montana.  On the lower horizon, eight nest sites were found, two of which contained babies (Horner & Makela, 1979; Horner, 1982).  Randomly strewn over the nesting horizon were the isolated skeletal remains of baby hadrosaurid dinosaurs presumed to be Maiasaura peeblesorum."⁸  The nestlings in the 1978 nest were about a metre long, and their teeth were worn;  Garner, reading Horner and Makela, records that some "were worn along more than three-quarters of their length," and he concedes the point against his own side's Flood reading:  "It is difficult to see how this sequence of events can be accommodated within the year of the Flood."¹

Egg Mountain itself is a hill two kilometres away with a different egg type.  Horner:  "We had found each kind of egg on each of three different fossil horizons."  He describes the horizons as "essentially two-foot-thick layers of an unbelievably hard mixture of calcium carbonate and silica, a kind of limestone."⁷  Then the sentence that matters most for a trace-fossil argument:  "Even before we'd begun to take Egg Mountain apart, we thought these different horizons might each represent a nesting season.  For one thing, we could see the trampled, muddy soil surface clearly preserved.  And all the eggs were at the same depth in the limestone."⁷  Oard's own 1995 paper counts more:  the mound "is composed of three meters of green mudstone where multiple nests of Orodromeus makelai have been unearthed in five horizons," with 25 clutches and about 400 eggs in the Egg Mountain vicinity and 45 Maiasaura nests or clutches a little to the north.²²  Horner's 1994 maps label the levels:  "Nesting Horizon B on Egg Mountain."⁸

The eggs on Egg Mountain were first assigned to the small ornithopod Orodromeus, whose skeletons litter the horizons.  Embryos later showed the eggs belong to the theropod Troodon,²⁹ and in 1999 Varricchio, Jackson and Clive Trueman described the one nest on the hill that every side accepts as a built structure:  "a bowl-shaped depression with an internal area of ~1m2 surrounded by a distinct rim.  A clutch of 24 tightly-placed eggs sat in the center … The trace occurs within a moderately well-developed micritic paleosol.  A physically and chemically distinct mudstone covered the nest and represents overbank deposition.  The nest protected the eggs by creating a suitable micro-environment during the lengthy egg-laying and incubation periods."⁹  Oard accepts this one:  "This nest is the one on the top of Egg Mountain."²⁴  Note what the excavators record in one sentence:  a nest dug into a soil, and a flood that sealed it.  Both sides of this argument are in that sentence, and the rest of the site decides between them.

What the rock between the eggs records

Horner thought the hard limestone layers were the bed of a shallow alkaline lake that dried out between nesting seasons.  The Montana State ichnologists who re-excavated the hill from 2010 have overturned that reading, and the correction cuts against BEDS harder than the original.  William Freimuth and Varricchio quarried a 7 by 11 metre area in 12.5-centimetre slices through 1.5 metres of section and found insect cocoons in every slice.  Freimuth's thesis summarises the result:  "The locality consists of stacked calcareous siltstones and calcretes, interpreted as bioturbated, well-drained paleosols."¹⁰  And:  "Fossil insect cocoons and dwelling traces are recovered throughout the measured section and suggest incipient, cumulative pedogensis and slow, relatively continuous distal floodplain deposition … The occurrence of invertebrate traces throughout the measured section suggests a lack of large (> 10 cm) depositional events (Freimuth and Varricchio, 2019).  Insect traces also suggest well-drained and workable soils with extended periods of subaerial exposure (Genise, 2016; Freimuth and Varricchio, 2019).  Limestones were interpreted as lacustrine by Horner (1987), but the abundance of insect traces precludes an aquatic origin; limestones instead likely represent calcretes, cemented by infiltrating subsurface waters."¹⁰  The published paper puts the environmental conclusion in one sentence:  "Abundant wasp trace fossils indicate a sparsely vegetated subaerial environment with workable, well-drained soil conditions favorable for both fossorial insect pupation and oviparous vertebrate nesting."³⁰  The cocoons are those of ground-nesting wasps and probably beetles, which dig into soil to pupate;  a wasp cocoon is itself a trace fossil of weeks spent in dry ground.  The paper also says what the burial agent was:  "Egg Mountain deposition and infilling of insect nests may have been brought on by seasonal flooding."³⁰

Kenneth Carpenter, who dug baby dinosaurs in the Lance Formation while Horner dug Montana, makes the same point from the colour of the rock:  "In the vicinity of Egg Mountain, there are even pale reddish rocks caused by an oxidized form of iron.  Not surprisingly, plant debris is rare.  All of this evidence indicates that during the Late Cretaceous the landscape was well drained."³¹  Gregory Paul noted that the colonies lacked trees:  "These nesting sites appear to have been used repeatedly for many years. … Such an interpretation is supported by the apparent absence of large plant roots in the colony sites."³²  So Oard's observation that vegetation is rare at nesting sites is correct, and the excavators had already explained it:  open, well-drained, sparsely vegetated ground, which is exactly where living ground-nesting birds and crocodilians choose to nest.

Oard's reading of Egg Mountain

Oard worked through Egg Mountain in 1997 and his answers are three.  The levels are oscillations:  "Just having eggs at different stratigraphic levels is really not a problem in a Flood paradigm, in which portions of exposed land were periodically inundated."²¹  The nests are mostly not nests:  "Actually, nests on Egg Mountain are rare; the eggs were mostly laid in a spiral on limestone with the pointed end down."²¹  And the broken egg tops are scavenging, not hatching.²¹  He also noticed, correctly, that the "Orodromeus" eggs had become Troodon eggs, and that the 20 to 25 Orodromeus skeletons on the horizons had not hatched from those clutches.²¹

Take the answers in turn.  The oscillation answer explains why there could be more than one level.  It does not explain what lies between them:  a calcrete soil with wasp cocoons through its whole thickness, and no bed thicker than ten centimetres laid down in one event.  An oscillating Flood that laid "three meters of green mudstone" in pulses would leave event beds, and the ichnologists looked for them slice by slice and found none.  The spiral of eggs with pointed ends down is not evidence against nesting;  it is the posture of eggs set upright in a substrate, and the 1999 nest shows the same eggs steeply inclined inside a rimmed bowl.  The porosity statistics of Kohei Tanaka, Darla Zelenitsky and François Therrien put troodontid eggs with the brooders that "still partially buried their eggs in sediment."³³  The scavenging answer is possible for any one egg, and Troodon teeth are indeed common on the horizons.  It does not reach the Maiasaura horizon two kilometres north, where metre-long nestlings with worn teeth lay in and around a nest and smaller skeletons with femora from six to nineteen centimetres were "randomly strewn" across the surface.⁸  Horner's later synthesis has the hatchlings leaving the nest "near the time of their first linear doubling,"³⁴ which for a hadrosaur hatching at about half a metre is a metre.  Those animals hatched, fed and grew on that ground.  Garner saw that in 1996 and said it could not fit.  Nothing published since has answered him on it.

The sum for this one hill, on the excavators' numbers:  at least three nesting horizons, each a soil, each trampled, in a three-metre section;  a built nest in a developed paleosol;  wasp cocoons through the whole 1.5 metres quarried;  a Maiasaura colony on three more horizons nearby with nestlings that grew to double their hatching length.  Oard's whole budget for all of it is eighty days, and one Troodon incubation, by the method of Part 7, would already take two of the three months.

Part 3: Devil's Coulee, Alberta

Devil's Coulee is the Canadian half of the same nesting ground.  It lies on the Milk River Ridge in southern Alberta, a few hours' drive north of Choteau, in rock the Alberta geologists assign to the Oldman Formation and Horner's 1994 list assigned to the Two Medicine.³⁵  Wendy Sloboda found the eggshell in 1986 as a high-school student;  Philip Currie's Royal Tyrrell Museum crew found the nests the next summer.  The museum's own account of the discovery gives the scale:  "Over the course of a week, the crew found more than a dozen eggshell-producing sites across the area … Excavation revealed eight more nests with embryos, and dozens of isolated bones."³⁶  The embryos belong to a new lambeosaurine hadrosaur, Hypacrosaurus stebingeri, named by Horner and Currie in 1994.

Horner and Currie place the nests in the section:  "All of the described and referred specimens, including the holotype of this new species of lambeosaurid, were found in the uppermost 100 of the 650-m thick Two Medicine Formation.  A bentonite located within a few meters of the Devil's Coulee sites has been dated at 75.05 ±0.08 Ma (D. Eberth & A. Deino, personal communications, 1992).  The nests and isolated bones from Montana and Alberta were found in greenish-grey mudstones, some of which contained abundant caliche.  Terrestrial gastropods and small wood fragments are common on the Montana nesting horizons."¹¹  The radiometric date is not used in this article;  the series argues from superposition alone.  The caliche is used:  it is a soil carbonate, the same material the Egg Mountain ichnologists re-identified as calcrete, and it forms in ground that has been dry for a long time.  Land snails and wood on the nesting surfaces are what one expects of ground that supported snails and plants.

The nests are spread across several sites rather than one hill:  "Devil's Coulee in southern Alberta has yielded several nests from a variety of sites.  Most of the specimens used in this study of embryonic individuals came from a single nest (No. 2) at a locality known as Little Diablo's Hill. … Little Diablo's Hill has yielded four additional nests, two of which contain embryonic specimens, whereas the remaining two contain eggs without embryonic material.  One of these nests (RTMP 89.79.53) contained eight eggs (Fig. 21.2). … Two other sites in Devil's Coulee (North Baby Butte and Kiddie's Corner) have also yielded embryonic material."¹¹  The eggs are nearly spherical, about 18.5 by 20 centimetres, with a volume of about 3,900 millilitres, among the largest dinosaur eggs known.¹¹  A second egg type nested on the same ground:  Zelenitsky and Hills described "A clutch of 12 eggs and numerous eggshell fragments recovered from the Oldman Formation at Devil's Coulee" as the elongate theropod-type egg Prismatoolithus levis.³⁷  Two kinds of dinosaur, one a four-tonne hadrosaur and one a small theropod, chose the same ground.

On the Montana side of the border the same species gives the clearest picture of what happened after hatching.  At the Blacktail Creek nesting horizon Horner mapped a bone bed of Hypacrosaurus juveniles washed a short distance by a stream:  "The fluvially concentrated elements, representing at least twelve individuals, have femora lengths ranging from 16 cm to 23 cm … Although these specimens were transported to some degree by water, there is no indication of any abrasion."  Compare the nesting area itself:  "Femora from the nesting area range in length from 4.5 to 9 cm (adult femora are about 120 cm long).  The absence of larger juveniles may show that the volcanic ash prematurely terminated the use of the nesting ground."⁸  Two things are in those lines.  The juveniles in the bone bed have femora two to five times the length of the embryonic femora, so they lived for a long time after hatching in the same area.  And the burial agent Horner names for the nesting ground is volcanic ash, not water.  Gregory Paul adds that the Hypacrosaurus sites "in Montana and Alberta were closer to the coastline" than Egg Mountain and so under a milder climate.³²

Devil's Coulee matters for one more reason.  When Erickson and colleagues chose embryos whose teeth they could section for growth lines, the large-egg end of their sample came from here:  the eggs "were found in nests containing embryonic skeletons discovered by field parties of the Royal Tyrrell Museum of Paleontology, Drumheller, Alberta, Canada, from 1987 to 1999 in fluvial overbank deposits of the late Campanian Oldman Formation at Devil's Coulee in southernmost Alberta."²  Part 7 gives the count.  The number to carry forward from this site is that a Hypacrosaurus embryo's teeth had been growing for 99.45 counted days when the clutch was buried, and on the authors' full estimate it had been in its egg for at least 171.

Part 4: Auca Mahuevo, Argentina

Auca Mahuevo, in Neuquén Province in the foothills of the Andes, is the largest sauropod nesting ground known and the first place sauropod embryos were found inside their eggs.  Luis Chiappe, Rodolfo Coria and Lowell Dingus reported the embryos in Nature in 1998.³⁸  Oard wrote it up for his own journal within the year, and his reading has not changed since:  the site is a temporary refuge east of the Andes, and when Chiappe says floods buried the eggs, "Chiappe of course believes in a local flood, but the Genesis Flood will do."¹⁹  This site is where the young-earth side's strongest point and its weakest point sit side by side, so it is worth taking slowly.

The section

Dingus and colleagues measured the local section in 2000:  "The 5 m thick interval of overbank mudstones containing the fossilized eggs and embryos occurs near the middle of a 35 m sequence of thin, fluvial, concretionary sandstones and thicker units of silty sandstone.  Flooding of shallow stream channels deposited overbank silt and mud on the eggs, killing the embryos and initiating the process of fossilization."¹⁶  They add that "The eggs and embryos are exclusively preserved in the thickest and finest-grained overbank sediments in the section," and that the quarry's concentration of embryos "suggests that entire clutches may have been buried by a natural disaster, such as a flood."¹⁶  That is the young-earth side's fair point, in the excavators' words:  the embryos were buried alive by water.

The wider survey, written by Chiappe, Coria, Frankie Jackson and Dingus in 2003, gives the count of levels:  "Six different egg-beds, some of which are laterally continuous for several kilometers, are contained within the 85-meter-thick stratigraphic section of Auca Mahuevo (Fig. 1).  These egg-beds occur in uniform mudstones representing overbank deposits on an alluvial plain (Dingus et al., 2000).  Clutches from egg-bed 3 occur in paleovertisols, a type of soil common in areas that experience wet-dry climatic cycles under semi-arid to sub-humid conditions.  A network of slickensides affecting the integrity of the eggs and egg-clutches suggests these were laid prior to the complete formation of the soil."¹²  Alberto Garrido's 2010 sedimentological study traced the egg layers for 25 kilometres to the Los Barreales locality and found that "a higher concentration of egg-clutches occur into paleosols and abandoned channel deposits developed at ancient levee and meander belt areas," in a "semiarid climatic condition, with marked alternations of wet and dry seasons," with "Exceptional muddy sheet-floods burying the eggs and nests with a thick bed of mud, facilitating their preservation."³⁹

Three numbers from those paragraphs carry the argument.  Six egg-beds, not four:  Oard's 2016 paper counts "four levels of eggs within the finer-grained siltstone and mudstone layers within a 40 m vertical interval,"⁴ which is Jackson, Schmitt and Oser's 2013 count for one measured interval;  the site as a whole has six.  Eighty-five metres of section:  the lowest egg-bed and the highest are separated by tens of metres of floodplain sediment, and every metre of it had to be deposited between one nesting season and another.  And a vertisol:  a vertisol is a clay soil that cracks when it dries and swells when it wets, and the slickensides the excavators describe are the polished shear surfaces that form as the clay grinds against itself through repeated wet and dry cycles.  A vertisol is a record of seasons, and the eggs sit inside one.

The nests

The excavators are candid that most Auca Mahuevo clutches show no nest structure, and Oard quotes them for it.  Their own words:  "Several egg-clutches laid on the surface of an abandoned channel are contained within egg-bed 4.  These egg-clutches provide the only reliable evidence of nest architecture in sauropod dinosaurs (Chiappe et al., in press) (Table 1).  These egg-clutches are contained in large, rimmed depressions in sandstone, although the eggs are entombed by mudstone. … The structureless rim surrounding each of these egg-filled depressions has been interpreted as the debris produced during the excavation of the nest, and the mudstone encasing the eggs as the result of flooding (Chiappe et al., in press).  The fact that in none of these depressions are the eggs entombed by sandstone indicates that the eggs were laid on the surface of the substrate."¹²  The criteria they set for calling a depression a nest are a depression that truncates the bedding of the host rock, eggs or articulated juveniles inside it with no sign of transport, and "Elevated ridge of massive sediment surrounding the depression."¹²  Those are field tests anyone can apply.

Oard's 2013 reply is that the six rimmed structures "have turned out to be dinosaur tracks and the eggs probably floated into the tracks," which "reduces the number of nest structures in the rock record to probably less than a dozen."³  His source is a 2012 paper by Gerald Grellet-Tinner, who was a co-author of the 2004 nest-structure paper⁴⁰ and later reinterpreted the depressions as footprints.  That paper could not be obtained for this article, so the dispute is reported, not judged.  Two things can be said without it.  A titanosaur footprint large enough to hold a clutch of twenty to forty eggs, with eggs floated into it, would need the water to lift eggs the size of footballs and set them down in one depression without breaking them, and the excavators say the eggs in the depressions show "no evidence of transport."  And the dispute is about six clutches out of about four hundred;  whichever way it falls, the six egg-beds, the vertisol and the 85 metres of section remain.

Oard's reading, and its cost

Oard reads the whole site through BEDS:  "This mystery of the many eggs but few nests is easily solved if the dinosaurs did not have time to make nests."⁴  On the soils:  "The Auca Mahuevo paleosols contain expansive clays and can be classified as vertisols, but clays are not necessarily proof of ancient soils."⁴  On the mudstone:  "Today, major floods are known to deposit no more than a few metres of sediment, whereas the fine-grained sediments found at the site are about 5–10 m thick and homogeneous."⁴  And on the levels:  "The same type of dinosaur laid the eggs on all four BEDS.  In the uniformitarian model, the sequence should be an accumulation of sediment over hundreds of thousands of years.  How probable is it for the same type of dinosaur to frequent the same spot hundreds of thousands of years later?"⁴

Each claim can be checked against the excavators.  Clays alone are not proof of a soil;  slickensides, cracks and the wet-dry fabric of a vertisol are, and that is what Chiappe and Jackson describe.  The egg-bearing mudstone is not homogeneous:  Dingus describes a light grey micaceous sandstone near its middle and "numerous, irregular vein-like and nodular zones of greenish mudstone" through it, with root traces rarely preserved.¹⁶  "Hundreds of thousands of years" between levels is Oard's figure, not the excavators';  nobody has published a duration for the 85 metres, and Chiappe's own wording is that "Each egg-bed could preserve eggs laid during more than one closely occurring nesting season but stratigraphic resolution to discriminate among these possible nesting events is lacking."¹²  Returning to the same ground is what nesting animals do;  the excavators call it site fidelity and say "one sauropod species appears to have nested at this site at least six separate times."¹²  The question "how probable" is answered by the animals' habit, not by the age of the rock.

Two more observations cut both ways and should be stated.  The excavators found "little or no parental care, an inference consistent with the absence of evidence of trampling,"¹² so Auca Mahuevo does not supply the trampled surfaces Egg Mountain does.  And of "nearly 400 in situ clutches in egg-beds 2 and 3," only six held abnormal multilayered eggs,¹² a pathology rate of about one and a half per cent, which is low for a population Oard describes as laying under stress;  his 1995 paper had argued that "many dinosaur eggs are unusually thin and pathological," and cited it as a sign of "unusual and stressful conditions."²²  The eggshell porosity he relies on is also lower here than he says:  Jackson and colleagues measured the Auca Mahuevo egg's water vapour conductance at 341 milligrams per day per torr, two times a bird egg of the same size "but lower than in eggs of most modern reptiles," with "47 times fewer pores" than the Spanish megaloolithid egg.⁴¹  Oard rejects that measurement on the strength of a 2012 re-examination this article could not obtain.

What BEDS must deliver at Auca Mahuevo, then, is six separate exposures of the same ground, each long enough for a sauropod to dig and lay, the lower ones long enough for a clay soil to crack and shear, with tens of metres of floodplain mud laid down between, all inside eighty days.  The flood that killed the embryos is real and the excavators say so.  It is the only part of the sequence that was fast.

Part 5: The Pyrenees, Hateg and the Lameta beds

Three more regions supply the same kinds of evidence with different details.  They are treated briefly, with the numbers that matter.

The Spanish Pyrenees: nine horizons at one village

Dinosaur eggs have been known from the latest Cretaceous of southern France since 1859 and from the Spanish side of the Pyrenees since the 1990s.  The first widely reported Spanish site was Bastús, in the Arén Sandstone, published by José Luis Sanz and colleagues in Nature in 1995 under the title "Dinosaur nests at the sea shore."⁴²  Garner summarised it the next year:  "abundant egg and bone material from the Arenisca de Aren Formation of the southern Pyrenees.  The material is distributed over an area of about 15 km2, and many closely-spaced, well-preserved nests occur in a two-metre-thick red sandstone layer at the top of the formation.  Each nest contains one to seven eggs; most have only two or three.  The abundance of the material suggests that the area was a nesting ground, and that dinosaurs may have returned to this area during several reproductive seasons."¹  Oard noted the same site in 1997:  "A new discovery from Spain suggests a whopping 300,000 eggs packed into a rock volume of about 12,000 cubic metres.  These rocks are probably within marine sandstone, so according to the uniformitarian paradigm the nests are automatically said to have been laid at the seashore."²¹  A beach is a place where living sea turtles lay eggs in sand, and the Bastús sandstone is a coastal deposit;  nothing in a beach nesting ground is a difficulty for either side.

The site that matters for stacking is inland, in the red continental beds of the Tremp Formation near Coll de Nargó.  In 2010 Bernat Vila, Frankie Jackson and colleagues modelled the clutches there in three dimensions.  Their abstract sets the site in the southern Pyrenees and gives the count:  "Nine horizons containing Megaloolithus siruguei clutches are exposed near the village of Coll de Nargó."¹³  The setting is a floodplain soil:  "Three lithofacies identified at the Pinyes locality include pedogenically modified massive, calcareous silty mudstones, very fine to fine-grained sand bodies, and medium to coarse-grained sandstone [52,53].  The rocks comprising the local section are interpreted as sedimentary deposits of a fluvial environment that were located some distance from an active stream channel."¹³  And the clutches themselves record the nest that held them:  "Linear and grouped eggs occur in three superimposed levels and form an asymmetric, elongate, bowl-shaped profile in lateral view."  The authors' conclusion:  "The distinct clutch geometry at Pinyes and other localities likely resulted from the asymmetrical, inclined, and laterally compressed titanosaur pes unguals of the female, using the hind foot for scratch-digging during nest excavation."¹³  The eggshell agrees.  Jackson's conductance study found the Spanish Megaloolithus siruguei egg had a water vapour conductance of 3,979 milligrams per day per torr, ten times a bird egg of its size, "supporting previous inferences of egg burial."⁴¹  Here is the answer to Oard's porosity contradiction in one locality:  the eggs are porous, and they were buried in dug holes in a soil, which is why there is no rim and no preserved vegetation.  Nine times, at one village, in a section of pedogenically modified mudstone.

Hateg, Romania: eggs on a rooted soil, under a conglomerate

In the Hateg Basin of Transylvania a rockfall in 1988 exposed a nest at Tustea.  Dan Grigorescu and colleagues described it in 1994.  The locality "produced not only hatched and unhatched eggs, but also embryonic and hatchling skeletal material."¹⁴  The eggs' position in the section is the point:  "The specimens, split into polyhedral fragments, were found in a 0.5 m thick, red, massive, silty mudstone.  This unit is intercalated between a lower 1.2-m thick, reddish mudstone that contains small calcretes, plant rootlets, and vertical burrows, and an upper 4 m thick cross-bedded conglomerate with a friable matrix."¹⁴  Read as a sequence of events:  a soil formed, with carbonate nodules, plant roots and animal burrows;  the dinosaurs laid on it;  hatchlings emerged;  a flood strong enough to carry gravel buried the lot under four metres of conglomerate.  The flood is what BEDS predicts.  The rooted, burrowed, carbonate-bearing soil under the eggs is what it cannot afford.  Later work on the same site, which pairs megaloolithid eggs with hadrosaur hatchlings and reconstructs the nesting horizon across a quarry floor, could not be obtained for this article and is listed in the literature review.

The Lameta beds, India: 92 clutches and hatching windows

The Lameta Formation of central India holds the largest number of titanosaur nesting sites in the world.  Dhananjay Mohabey's 1998 systematics paper opens with the scale:  "A large number of dinosaur nesting sites have been documented from the Upper Cretaceous (Maestrichtian) Lameta Formation of India."  He notes, as Oard does for other sites, that "Many eggs are unhatched and completely preserved."⁴³  Garner, from the 1986 Kheda report:  "Some individual horizons contained several regularly spaced clutches and appear to have been nesting grounds.  At Rahioli at least 11 clutches were found within an area of about 1,200 m2."¹

The most recent survey, by Harsha Dhiman, Guntupalli Prasad and Vishal Verma in 2023, documents "256 eggs and three clutch patterns (viz. circular, combination, linear) that are assignable to six oospecies" from 92 clutches in the Dhar district.¹⁵  The rock is a soil-like marsh deposit:  "The presence of grainy intraclastic fabric, alveolar-septal fabrics, brecciation and shrinkage cracks observed in the clutch-bearing rocks are indicative of a low energy-low gradient palustrine depositional condition in a fluvial/alluvial setting."¹⁵  Shrinkage cracks are drying cracks.  The authors infer burial in dug pits:  "Since we have not found many evidences of plant remains we assume nesting in a shallow pit as a more suitable nesting habitat of titanosaurs of the studied areas. … The clutch P1, showing many eggs touching each other, must have been buried together as a group in a shallow pit."¹⁵  They describe hatching windows, the missing upper surfaces where a hatchling broke out, and piles of shell, and they conclude:  "we envisage that a few egg clutches of this area were laid close to lake/pond margins while most were laid away from the lake/pond margins, and thus, were hatched."¹⁵  They are also honest about what the Lameta outcrops cannot show:  "In the absence of a well-developed vertical section, it is difficult to assess the number of nesting cycles, site fidelity, and colonial nesting behaviour."¹⁵  India therefore gives hatching and drying, but not stacking;  the stacking comes from Montana, Argentina and Spain.

Part 6: The Gobi: brooding oviraptorids and a colony that hatched

The Gobi Desert supplies the two nesting finds that no flood explains, and it is the one region where the young-earth side's burial agent is plainly wrong.  Both should be said.

Buried alive on the nest

In 1995 Mark Norell, James Clark, Luis Chiappe and Demberelyin Dashzeveg reported an oviraptorid skeleton crouched over a ring of eggs at Ukhaa Tolgod, its limbs folded around the clutch in the posture of a brooding bird;⁴⁴ Clark, Norell and Chiappe described it fully in 1999,⁴⁵ and a second specimen in the same posture came from Bayan Mandahu in Inner Mongolia.⁴⁶  An animal that dies on its clutch and is buried where it sits was buried fast.  Oard, writing in 1997, drew the obvious inference and then went one step further:  "It is doubtful a sandstorm could freeze-frame a brooding dinosaur.  Usually any little disturbance will cause an animal to leave its eggs.  There is the added question of how the dinosaurs are to be fossilised in a desert.  It is more likely this powerful sandstorm was a 'giant watery sandwave' in a catastrophic flood."²¹

The geologists who mapped Ukhaa Tolgod answered the burial question in 2008, and the answer is neither a sandstorm nor water.  Lowell Dingus, David Loope and colleagues identified a facies of structureless sandstone that lies against the steep lee faces of fossil dunes:  "Loope et al. (1998, 1999) interpret this facies to represent mass flows that buried lee slopes and (with intermixed fluvial deposits) filled interdunes during mesic intervals when the dunefield was stabilized."¹⁸  It is the richest facies at the site:  "This facies is the most fossiliferous at Ukhaa Tolgod.  Oviraptorid skeletons preserved on nests of well-arranged eggs, along with perfectly articulated skeletons of tiny mammals and lizards are present."¹⁸  Wet sand on a dune face slumps as a mass, and it buries whatever is at the base of the slope without first disturbing it.  That is how a brooding animal stays on its nest.  The same rocks show what the dunes were like between slumps:  "Within the distinctly cross-stratified eolian sandstone are numerous deformed zones that represent vertical cross sections of dinosaur tracks—the first such tracks known from the Late Cretaceous rocks of the Gobi Desert and clear evidence that dinosaurs traversed actively migrating dunes (Loope et al., 1998).  Bioturbation and accumulation of clay and pedogenic carbonates in the fossiliferous eolian facies support the sandslide interpretation of the laterally adjacent structureless sandstones.  Together, these lines of evidence indicate that the large dunes of the Late Cretaceous landscape were stabilized for long periods of time, and, when active, migrated by deposition of wind-ripple strata and thin grain flows."¹⁸  At the nearby Bayn Dzak locality the dunes carry fossil roots:  "The large rhizoliths in eolian strata at Bayn Dzak (Loope and Dingus, 1999) appear to record the presence of dune plants—their roots lie parallel to cross-strata."¹⁸  At Tugrikin-Shireh, the Protoceratops locality, David Fastovsky's team found the same thing:  dune cross-strata dipping east-northeast under westerly winds, bedding planes "dominated by a complex calcite- and iron-oxide-cemented ichnofauna," and animals that in some cases died "by suffocation during sand storms, but in other cases, by less dramatic processes."⁴⁷

So the honest statement is this.  The brooders were buried alive, and fast, as Oard says.  They were buried by dune sand in a desert that had been dry long enough to grow plants on the dunes, carry dinosaur traffic across them, form soil carbonate in them, and cement burrows on their surfaces.  A "giant watery sandwave" would not leave a dune field with its cross-strata, wind ripples, tracks and roots intact;  the sand that buried the nests came off the slope above them.  Nothing in the Gobi record is a flood, and the Gobi is where the Mesozoic's best brooding evidence comes from.  The Protoceratops embryos whose teeth Erickson counted (Part 7) come from this same Djadokhta Formation.

What the brooders were doing

What posture the oviraptorids were in and what it means has been argued among the excavators themselves, and the argument is worth reporting because Oard uses it.  Tzu-Ruei Yang and colleagues reconstructed five oviraptorid clutches from China in 2019 and found "a partially-open oviraptorid nest that contains 3–4 rings of paired eggs (more than 15 pairs total) whose blunt end points toward the center devoid of eggs at an angle of 35–40°."  They argue the architecture "further contradicts the TCI hypothesis in oviraptorids, hindering sufficient heat transfer to the inner (lower) ring(s) of eggs," and that complete clutches of more than thirty eggs are larger than the clutches found under adults.⁴⁸  Tanaka's porosity study put oviraptorids and troodontids among the first dinosaurs to leave eggs partly exposed and sit on them, while noting that "they still partially buried their eggs in sediment."³³  Whether the adult was warming the eggs or guarding them is open.  That it was on the nest when the sand came is not.

A colony that hatched before the flood

The sharpest single test of BEDS in the Gobi is a site Oard has answered directly.  In 2019 Kohei Tanaka, Yoshitsugu Kobayashi, Darla Zelenitsky, François Therrien and Yuong-Nam Lee described a nesting site in the Javkhlant Formation of the eastern Gobi:  "A new nesting site discovered in the Upper Cretaceous Javkhlant Formation of the eastern Gobi Desert, Mongolia, preserves at least 15 egg clutches laid by a probable non-avian theropod, and provides strong evidence for colonial nesting in a non-avian dinosaur.  The occurrence of the clutches at the top of a common paleosurface, the distribution of eggshell fragments within clutches, the presence of a consistent two-layer sediment infill within eggs, and a thin marker lithologic unit blanketing all the clutches indicate the clutches were laid and hatched in a single nesting season.  Despite the absence of sedimentologic evidence indicative of nest structure, statistical analyses of egg characteristics and facies association reveal the clutches were likely incubated in covered or buried nests.  Based on the number of hatched clutches, the hatching success rate of the colony was high (60%), similar to that of extant crocodylian populations and bird species that attend and/or protect their nests during the incubation period."¹⁷

Oard's reply accepts most of it.  "The inference that the eggs were all laid at the same time is a good deduction because of the two layers of mudstone in the eggs."  "The authors admit that the eggs were buried in a flood.  Although they automatically think it is a local flood because of their assumptions, it could easily have been continued flooding after sediments were briefly exposed in the Genesis Flood."  His disagreements are with the soil and the hatching:  "the caliche particles could have simply been eroded from a carbonate layer, since there were other indications of erosion such as mud clasts, pebbles, and volcanic fragments.  The soil and organic-rich substrate is an inference that appears to have little or no evidence."  And:  "But why would a large eggshell fragment be found within the egg if the hatchling pushed the shell outward?"⁴⁹

Set the two accounts side by side.  Both agree the clutches were laid in one season on one surface and buried by one flood.  The excavators' evidence for hatching is not only the open tops;  it is that the eggs were open before the marker bed arrived, so that the red marker mud is found inside them, and that eggshell fragments of hatching-window size lie inside and around the clutches.  A shell fragment inside an egg is what is left when a hatchling pushes a cap outward and part of it falls back in;  it is not what a flood leaves, since a flood that broke the eggs would fill them with mud, not with their own caps.  Nine clutches with at least one hatched egg out of fifteen is a hatching rate like a living crocodile colony's.  And a hatched colony is a colony that sat on exposed ground for a full incubation, which for a theropod egg of this size is, by the counts in Part 7, on the order of three months.  Oard's own window is eighty days for the whole Mesozoic.  This one colony in one season uses most of it.

Part 7: How long the eggs took: a growth-line count, not a date

Every argument so far has been about what a surface records.  This part is about a number.  How long did a dinosaur egg take to hatch?  Until 2017 the answer was a guess from bird eggs.  Since 2017 it has been a count.

The method

Teeth grow by adding dentine a layer at a time, and in crocodiles and humans the layers are laid down once a day, as rings called the incremental lines of von Ebner.  In 2017 Gregory Erickson, Darla Zelenitsky, David Kay and Mark Norell showed that the same daily lines are present in the teeth of dinosaur embryos still inside their eggs, and counted them.  They chose two species at the two ends of the egg-size range:  the small horned dinosaur Protoceratops andrewsi, from "a nest composed of 12 eggs discovered in Campanian sediments of the Upper Cretaceous Djadochta Formation from the Gobi Desert of Mongolia," which is "a bilobed depression in the sandstone,"² and the Devil's Coulee Hypacrosaurus of Part 3, whose eggs are 76 per cent of the largest dinosaur egg known.²  The count gives the days the oldest tooth took to form.  Tooth formation does not begin at laying, so the authors added the time before tooth initiation using the lowest value seen in living crocodiles, 42 per cent of incubation:  "The time elapsed in forming the oldest tooth in the dentition, determined from the total number of incremental lines represented in the tooth, is 48.23 d.  As described below (Materials and Methods), hatchling teeth were conservatively modeled as initiating at 42% of the incubation period (34.93 d).  The sum of these values reveals a minimum incubation period of 83.16 d for the P. andrewsi embryo."²  For the hadrosaur:  "Again, because the hatchling teeth conservatively began formation at 42% of incubation time (72.02 d), this reveals a minimum incubation period of 171.47 d."²

This is the kind of measurement the young-earth side usually trusts.  It involves no decay constant, no assumed initial condition and no correlation across basins.  It is a count of layers that form once a day, exactly like counting tree rings, done on the animal itself.

The result

"Our results show unexpectedly slow incubation (2.8 and 5.8 mo) like those of outgroup reptiles."²  The authors compare it with what the bird-based guess had been:  "Dinosaur incubation periods have been estimated to be very rapid, assuming typical extant avian values.  Regression of incubation period versus egg size in extant birds predict 40 d for small P. andrewsi eggs and 82 d for large H. stebingeri eggs (12) (Fig. 3).  Our analyses show considerably slower development, respectively 83 and 171 d."²  The small dinosaur's figure is almost exactly a crocodile's:  "Among reptilian clades, the P. andrewsi incubation period is just 3.5% longer than typical for Crocodylia (83.16 vs. 80.20 d)."²

Every direction of error the authors list makes the real figures longer, not shorter:  "(ii) it is indeterminable how many days away from hatching near-term embryos were, which inherently produces underestimated incubation periods; and (iii) there is a level of uncertainty regarding when in development hatchling teeth initiate [typically 42–52% in extant sister taxon Crocodylia (3) and 51–67% in distant outgroup Squamata (64–69)], with higher percentages leading to longer incubation period estimation."²  Only the counted days are hard floors, though:  48.23 days for Protoceratops and 99.45 for Hypacrosaurus.  The rest of each figure is the time before the first tooth, modelled at the lowest value seen in living crocodiles, so 83 and 171 days are soft floors.²²

Priced against the Flood

Oard's window for all dinosaur egg-laying is Day 40 to about Day 120 of the Flood, about eighty days.⁴  His older and more generous figure was 150 days.²²  Put the two embryos against both.

A Protoceratops clutch at Ukhaa Tolgod had sat in its sandstone depression for about 83 days on the authors' full estimate when the dune face slumped onto it.  That is just over the eighty-day window, but only 48 of those days are counted in the tooth, so this clutch alone does not break the window.  The Hypacrosaurus clutch at Devil's Coulee does.  Its embryo's teeth had been growing for 99.45 counted days when the flood sealed it in its caliche-bearing overbank mudstone, almost three weeks longer than the eighty-day window.  The full estimate of 171 days is longer than the 150-day window by three weeks.  It is a single incubation of a single clutch, before any nest was dug, before any sediment was laid down under it, and before the uppermost hundred metres of the formation around it were deposited.  No oscillation of water level makes a clutch hatch faster.

The one creationist answer this article could find is egg retention:  "Some pregnant dinosaurs under stress may have retained fertilized eggs longer than usual, allowing the embryo to reach the point of hatching shortly after being laid."²⁶  That does not shorten the count;  it moves part of it inside the mother.  The growth lines record the days the embryo's teeth were forming wherever the egg was, so the 171 days stand, and what the answer requires is a four-tonne hadrosaur carrying a clutch of football-sized shelled eggs for months while, on Oard's account, swimming or floating in the Flood.  Retaining shelled eggs through most of development is a lizard and snake habit;  it is unknown in birds, crocodilians and turtles, which lay their eggs early and let the nest do the rest, and Erickson's comparison rests on that:  "Most reptiles have two functional oviducts, and the eggs of an entire clutch are formed then laid at the same time."²  No creationist paper has argued that dinosaurs did otherwise.

The comparison with the sibling article on tracks shows why nests are the harder case.  A track needs its surface to stay firm for about a day, and the measured survival of sharp footprints on a modern lake margin averages 1.3 days;  BEDS has the right ingredients on the wrong clock even for that (Fossil Tracks and Trackways).  A nest needs its surface to stay dry for three to six months, and then it needs the hatchlings to have somewhere to walk.

Part 8: Where the young-earth side has a fair point

An article that only listed failures would be misleading, because several things Oard says are true and the excavators say them too.

Floods buried most of these clutches.  The Auca Mahuevo embryos died when "Flooding of shallow stream channels deposited overbank silt and mud on the eggs."¹⁶  Garrido describes "Exceptional muddy sheet-floods burying the eggs and nests with a thick bed of mud."³⁹  The Egg Mountain Troodon nest was sealed by a mudstone that "represents overbank deposition."⁹  The Javkhlant colony was blanketed by a marker bed after a flood.¹⁷  The Tustea eggs lie under four metres of conglomerate.¹⁴  A reader who has been told that the mainstream account is slow and gentle should know that the excavators' account of the burial is a flood every time, and that this is why embryos are preserved at all.  What the excavators add is that the flood came at the end of a long dry interval the rock also records.  BEDS keeps the flood and discards the interval.

Rimmed nest structures are rare.  Oard's 2005 note is right that most clutches lie in sediment with no visible nest, and the Auca Mahuevo team says of its six rimmed depressions that they "provide the only reliable evidence of nest architecture in sauropod dinosaurs."¹²  The reason, on the evidence of Parts 2 to 5, is that most of these eggs were buried in dug pits or covered nests, which leave the eggs in a hole and no rim at all;  Tanaka's porosity statistics make covered nests the primitive condition for dinosaurs.³³  Rarity of rims is therefore evidence for burial of the eggs by the parent, not for haste.  But Oard's observation stands, and he was quoting the excavators correctly when he made it.

Eggshell fragments alone prove nothing, and whole eggs can move.  Garner conceded both in 1996, citing a tumbling experiment in which chicken eggshell survived the equivalent of 68 kilometres of transport without measurable abrasion, and a storm-surge deposit in Argentina with transported eggs.¹  This article has used no eggshell-only locality for any argument.

Most eggs hold no embryo, and Oard is right that this needs explaining.  His 1997 paper calls it "rather strange" that of thousands of eggs, embryos are extremely rare.²¹  The excavators' explanation is in the same paragraph:  egg contents leak or rot unless burial is immediate.  The sites with embryos are the sites where a flood came while eggs were still full.  That is a point for rapid burial, which both sides accept, not for a short exposure.

Pathological eggs exist.  Multilayered eggs are real and Oard reads them as stress.  At Auca Mahuevo the measured rate is six clutches in 393.¹²  Whether one and a half per cent is a stressed population or a normal one cannot be settled from this article's sources;  Jackson and colleagues say previous links between abnormal shells and dinosaur physiology "are incomplete in terms of taphonomy, taxonomic identification, and lack rigorous statistical methods."⁵⁰

The Gobi brooders were buried alive.  Oard is right that an animal preserved on its nest was buried at once.  Part 6 shows the burial agent was a slide of wet dune sand, not water, in a dune field with roots, tracks and soil carbonate.  The speed is his;  the medium is not.

The science corrected itself, twice, at Egg Mountain.  The eggs first assigned to Orodromeus are Troodon eggs, and the limestone Horner read as a dry lake bed is a calcrete soil.  Oard noticed the first correction in 1997 and used it fairly.  Both corrections are in the direction of more time on dry ground, not less, but a reader is entitled to know that the site's interpretation has changed and may change again.

Garner's reading of the geological column is the one this site uses.  His 1996 insistence that "the methods used by geologists to assign a relative geological age are sound" and that "the geological column is a reality"¹ is the superposition-only rule this whole series argues from.  His post-Flood Mesozoic is a minority view, but his method is not.

Part 9: What the nesting record requires of BEDS

The BEDS article argues the mechanism:  how much dry, firm ground a one-year Flood can afford and for how long.  This article hands it a bill.  For the nesting record to fit, BEDS must deliver, at a minimum:

1. Exposure measured in months at each site, not hours or days. The floor is set by the embryos themselves: 48 counted days of tooth growth at Ukhaa Tolgod and 99 at Devil's Coulee, and about 83 and 171 days once the time before the first tooth is added.²² Thomas's "final hours or days"⁵ is short by two orders of magnitude.
2. Soils. Calcrete and caliche at Egg Mountain and Devil's Coulee,¹⁰ a vertisol with slickensides at Auca Mahuevo,¹² pedogenically modified mudstone at Pinyes,¹³ calcrete with rootlets and burrows at Tustea,¹⁴ shrinkage cracks in the Lameta beds.¹⁵ Each formed on the surface the eggs were laid on or in.
3. Insects. Wasp and beetle cocoons through every 12.5-centimetre slice of the Egg Mountain section, with no depositional event thicker than ten centimetres.¹⁰ A soil-nesting wasp needs dry workable ground for its own development, and the cocoons are there from the bottom of the section to the top.
4. Dug nests. The rimmed Troodon bowl in a paleosol,⁹ the excavation-debris rims at Auca Mahuevo,¹² the scratch-dug asymmetric pits at Pinyes,¹³ the shallow pits of the Lameta beds.¹⁵
5. Hatching and the young on the surface. Trampled soil at Egg Mountain,⁷ metre-long nestlings with worn teeth and juveniles with femora up to 23 centimetres on the Montana horizons,⁸ sixty per cent of clutches hatched at Javkhlant,¹⁷ hatching windows and shell piles in India.¹⁵
6. Repetition on the same ground, with sediment between. Three horizons in three metres at Egg Mountain and three Maiasaura horizons nearby;⁷ six egg-beds in 85 metres at Auca Mahuevo;¹² nine at Pinyes.¹³ Each repeat is another full cycle of items 1 to 5, and the sediment between the horizons must be deposited after the lower cycle and before the upper one.
7. All of it inside eighty days, on top of every metre of sediment beneath the lowest horizon. Neither source gives that thickness at Devil's Coulee. Horner and Currie put the Hypacrosaurus specimens "in the uppermost 100 of the 650-m thick Two Medicine Formation," the Montana unit, while Erickson's team maps the Devil's Coulee nests in the Oldman Formation of Alberta,¹¹² so the 650 metres cannot be read as the section beneath these nests.

Items 1 and 6 alone are fatal to the stated window.  Devil's Coulee overruns eighty days on its counted days alone.  Eighty days leave 27 days for each of the three horizons at Egg Mountain and at the Willow Creek Maiasaura site, about half the 48 days counted in the smaller of the two embryos Erickson's team measured.  Auca Mahuevo's embryos died in the egg, so each of its six beds needs only their age at burial, not a full incubation, and no one has counted growth lines in a titanosaur embryo.  But eighty days leave 13 days per bed for sauropods to dig, lay, and grow embryos with skeletons, six times over;  nine beds at Pinyes leave 9.  Lengthening the window to 150 days, Oard's 1995 figure, gives Devil's Coulee room for its counted days but not for its full 171, and leaves 50 days per horizon at Egg Mountain, 25 per bed at Auca Mahuevo and 17 at Pinyes.

Objections and responses

"The eggs at different levels may lie on one surface that cuts across the bedding, so there was only one nesting episode."  Oard raised this for the Maiasaura site in 1997:  "Local erosion or soft sediments while the sediments were briefly exposed during the Flood could account for eggs on two of three stratigraphic horizons.  In other words, it is possible that the dinosaurs laid eggs on a surface that cuts through the stratigraphy."²¹  He concedes it is "possible," and for a site where the lateral stratigraphy is "confused" it deserves a hearing.  It does not reach Egg Mountain, where the horizons are distinct hard calcrete layers with mudstone between, each with its own trampled surface, and where Horner notes that "all the eggs were at the same depth in the limestone;"⁷ nor Auca Mahuevo, where the egg-beds are "laterally continuous for several kilometers;"¹² nor Pinyes, where nine horizons are drawn on a measured section.¹³  One cross-cutting surface cannot be continuous for kilometres inside the same bed.

"Growth lines in dinosaur teeth may not have been daily."  The lines are daily in the living crocodilians, which are the closest living relatives of dinosaurs, and in humans;  that is the basis of the method, and Erickson's team is explicit about it.²  The objection also does not help the Flood.  If the lines formed faster than daily the incubation was shorter, but to bring 171 days under 80 the lines would have to form more than twice a day, and the Protoceratops result would then be less than half a crocodile's incubation for an egg of the same size, which no living archosaur achieves.  Any rate that keeps the dinosaurs within the range of living egg-layers keeps Devil's Coulee past the window.

"The eggs could have been retained in the mother and laid near hatching."  This is the 2023 Creation magazine suggestion.²⁶  Part 7 answers it:  retention does not shorten the count, and no living bird, crocodilian or turtle retains shelled eggs through development.  It also requires gravid dinosaurs to carry clutches for months while, on Oard's own account, swimming or floating in the Flood.  The objection has not been developed by anyone beyond that one sentence.

"Vertisols and caliche are just clay and carbonate;  they need not be soils."  Oard says of Auca Mahuevo that "clays are not necessarily proof of ancient soils."⁴  True of clay alone.  The excavators do not rest on clay alone:  they describe slickensides, the shear surfaces produced by repeated swelling and shrinking, and cite them as the reason eggs were displaced within the soil.¹²  At Egg Mountain the calcretes are riddled with wasp cocoons, and an insect does not pupate in a bed that is forming under water.³⁰  What the young-earth side needs is a published mechanism that makes slickensided clay and cocoon-bearing calcrete in days;  the buried-soils article prices that claim for paleosols generally.

"Broken egg tops are compaction or scavenging, not hatching."  Oard's standing answer.²³  Compaction crushes an egg from above and leaves the shell in place;  a hatching window removes a cap and leaves a hole with the fill of the next bed inside it, which is what the Javkhlant and Lameta excavators describe.¹⁷  Scavenging is possible at any one egg.  It does not produce metre-long nestlings with worn teeth lying in a nest, nor juveniles with femora two to five times embryo length in the same beds.⁸  The young-earth side has not offered an account of the juveniles.

"Most clutches have no nest structure, so the eggs were dumped in a hurry."  The excavators agree on the first half and this article concedes it in Part 8.  The second half fails on the eggshell:  high-conductance eggs are buried eggs, as Seymour showed in 1979 and Deeming confirmed across the whole dataset in 2006,⁵¹⁵² and buried eggs leave a clutch in a hole with no rim.  Oard's porosity argument and his rarity-of-nests argument cancel each other:  the porosity says the eggs were covered, and covered eggs are exactly the ones that show no structure.  Tanaka's 2015 statistics draw the same conclusion from 127 living species.³³

"The article concedes flood burial;  doesn't that concede the Flood?"  No.  A crevasse-splay flood on a river floodplain, a sheet flood after a dry season, a conglomerate from a flash flood, and a slide of wet dune sand are the burial agents the excavators name, and each is a local event on a surface that had been dry for months.  The question is not whether water buried the eggs;  both sides say it did.  The question is how long the ground had been dry before it did, and the rock answers that in soils, cocoons, incubations and hatchlings.

"The 75-million-year bentonite dates are doing the work."  They are not used.  Every argument here is from one section at a time:  what lies under the eggs, what lies between the horizons, and what the embryos' own teeth count.  The dates appear in quotations because the excavators print them, and are left in so the quotations are complete.

"Garner is one creationist;  the organisations have moved on."  They have not answered him.  Oard's 1997 paper engages Garner directly and concedes that nests, eggs and babies "at first glance appear to contradict" his model;²¹ nothing published since has addressed the three Maiasaura horizons or the worn teeth, and Arment's 2023 paper in AiG's own journal applies Garner's test to burrows and gets Garner's answer.⁶  The organisations publish both positions.

"Why not just take Garner's post-Flood Mesozoic?"  It solves the nests.  It costs the rest of Flood geology:  the Mesozoic holds most of the world's coal, oil source rocks and megasequence sediment, which the boundary articles on this site show the major Flood models need inside the Flood.  A reader is free to prefer Garner;  the point of this article is that the nests force a choice the camp has not made.

Issues and unanswered questions

• Sources not read. Horner and Makela 1979 and Horner 1982, the two Nature papers that founded the Egg Mountain literature, are paywalled and no open copy exists; their content is taken from Horner's 1988 book, his 1994 chapter and Garner's redrawing of the 1982 figure. Chiappe and colleagues' 2004 Palaios paper on nest-structure criteria, Grellet-Tinner's 2012 reinterpretation of the Auca Mahuevo depressions as tracks, Jackson, Schmitt and Oser's 2013 vertisol paper, Sanz 1995, Grigorescu 2010 and Botfalvai 2017 on Tustea, and Lorenz and Gavin's 1984 field-guide geology of the Willow Creek Anticline were not obtained. Oard's 2011 book is read through Thomas's review and Oard's own journal papers, which state the same positions.
• How many horizons at Egg Mountain. Horner says three; Oard's 1995 figure caption says five. The difference does not affect the verdict and is not resolved here.
• Egg retention. The article states from general herpetology that no living bird, crocodilian or turtle retains shelled eggs through embryonic development. A primary citation for that sentence should be added; Andrews and Mathies 2000 in BioScience is the standard review and could not be opened.
• Devil's Coulee stratigraphy. No source read gives the number of nesting horizons through the section there; "several nests from a variety of sites" is a count of sites, not of levels. The incubation count is the site's contribution.
• The Auca Mahuevo nest dispute. Whether the six rimmed depressions are nests or titanosaur footprints is argued among the excavators and is reported, not settled. It does not touch the six egg-beds.
• Auca Mahuevo's duration. Oard's "hundreds of thousands of years" between levels is his figure; the excavators publish none. The article's case does not need one; it needs the vertisol and the six returns.
• No creationist budget exists. No young-earth paper has computed how many days of exposure BEDS must supply at any nesting site. Part 9 gives the bill; the BEDS article should pay it or decline it.
• Trampling at Auca Mahuevo. The excavators report no trampling and infer little parental care. The article's hatching evidence therefore rests on Montana, Javkhlant and India, not Argentina.

Verdict

The nesting grounds are the clearest trace fossils in the Mesozoic, and they say the same thing at every site that has a measured section.  Dinosaurs dug nests into soils, laid eggs in them, left them for a quarter to half a year, and in most places came back to the same ground and did it again, three, six or nine times, with floodplain sediment and new soil formed between.  The ground between the nesting horizons at Egg Mountain is a calcrete full of wasp cocoons with no event bed thicker than a hand's width.  The ground under the Tustea eggs has roots and burrows in it.  The ground holding the Auca Mahuevo clutches is a cracked and sheared clay soil.  And the embryos in their eggs carry a day count:  48 and 99 counted days of tooth growth for the small one and the large one, and at least 83 and 171 once the time before the first tooth is added.

The young-earth side's model for all of this is BEDS, and BEDS allows eighty days for the whole Mesozoic.  Its author is right that floods buried the eggs;  the excavators say so in every paper.  He is right that rimmed nests are rare and that most eggs hold no embryo.  He is wrong about the clock, and the error is not small:  one incubation at Devil's Coulee is longer than his window, and the stacked horizons multiply it.  The one young-earth writer who worked the problem in full, Paul Garner, said in 1996 that the nests cannot be fitted into the Flood year and moved the Flood below the Triassic to keep them out of it.  His solution is a minority one, but his statement of the problem has not been answered in thirty years.  The honest verdict is the one this series gives to the whale and to the tracks:  the pattern is real, the standard rebuttal fails, and the model does not yet have an answer.

Sources