Dewclaws and Carpal Pads

Senter, Phil, and John G. Moch.  “A critical survey of vestigial structures in the postcranial skeletons of extant mammals.”  PeerJ 3:e1439.  Nov 24, 2015.  A survey of 578 mammal skeletons and skins from 293 species, drawn from 98 of the 139 living mammal families, looking for structures that have lost a major ancestral function and are usually much reduced in size.  Its authors set three tests for vestigiality and apply them to each structure.  The article relies on those three tests and on the survey's finding that the front dewclaw fails all three.

1. 1a.

   Section Methods:  “The first criterion for vestigiality is that in comparison to its state in the sister groups the structure exhibits extreme reduction.  For this study, we considered this criterion met if the structure was reduced to one-third its size relative to adjacent skeletal structures, in comparison with its state in the sister groups.”  “The second criterion is that the structure has lost the specialized morphology that it exhibits in the sister groups.”  “The third criterion is that the structure has lost a salient ancestral function.” ↩

2. 1b.

   Section Results, Hand and fingers:  “Ancestrally, the mammalian hand has five digits with two phalanges in the thumb and three phalanges in each other finger”.  Section Results, Foot and toes:  “Ancestrally, the mammalian foot has five digits with two phalanges in the first toe and three phalanges in each other toe”. ↩ ↩ ↩

3. 1c.

   Section Results, Hand and fingers:  “In the Canidae and Felidae the thumb (Figs. 8D and 8E) is called the dewclaw.  It is shorter than the other digits and does not contact the ground.  Some authors consider it vestigial (e.g., Eldredge, 2007), but it is not reduced enough to satisfy the first criterion for vestigiality.  Also, it retains a claw and therefore does not satisfy the second criterion.  Nor does it satisfy the third criterion, because it retains the typical function of a finger with a sharp, curved ungual and claw: prehension.  Its use is an important part of prey capture in felids (Londei, 2000), and we have personally observed that domestic dogs use the dewclaw to snag and maintain a grip on objects.  Its shortening is therefore not the reduction of an unused organ.”  Figure 8 shows a domestic cat and a golden jackal. ↩ ↩ ↩ ↩

4. 1d.

   Section Results, Hand and fingers:  “A vestigial dewclaw is present in Hyaena (striped hyena and brown hyena) and Crocuta (spotted hyena).  In both, the metacarpal is reduced to a small block, the distal phalanx is lost, and the proximal phalanx is reduced.”  “The hyaenid Proteles cristata (aardwolf) has an unreduced dewclaw (Fig. 8F).” ↩

5. 1e.

   Section Results, Foot and toes:  “For other extant mammal taxa, the phylogenetic distribution of character states (Fig. 1) indicates that the first toe became vestigial independently at least five times: in the Dasyuridae, Thryonomyidae, Canidae, Hyaenidae, and Rhinocerotidae + Tapiridae.  It was independently lost eight times in mammals other than rodents: in Chaeropus, Thylacinus, Hyracoidea, Macroscelidea, sloths, Lagomorpha, Felidae, and Perissodactyla + Cetartiodactyla.” ↩

6. 1f.

   Section Results, Foot and toes:  “Most members of the Carnivora retain all five toes.  Exceptions are the families Canidae, Felidae, and Hyaenidae.  In the Canidae the first toe is vestigial.  Its metatarsal is tiny, and its toe has only one phalanx, which is reduced to a small spike or nubbin (Figs. 12O–12Q).  In the Felidae the first toe is lost and its metatarsal is vestigial (Flower, 1870) (Figs. 12R and 12S).”  Figures 12O to 12Q show a collie, a coyote and a red fox. ↩ ↩

Park, Kyoungtag et al.  “Canine polydactyl mutations with heterogeneous origin in the conserved intronic sequence of LMBR1.”  Genetics 179(4):2163–2172.  2008.  A genetics study by a team of Korean researchers that traced the gene behind extra hind toes in dogs, mapping it in the Korean Sapsaree breed and testing the altered DNA in a laboratory assay and in mouse embryos.  They found two single-letter DNA changes, one in the Sapsaree and one in Western breeds, each of which acts as a dominant mutation, so one changed copy of the gene is enough to produce the trait.  The article uses it to show that in these dogs the hind dewclaw follows a mutation near a DNA switch for the Sonic hedgehog gene.

1. 2a.

   Section Abstract:  “Canine preaxial polydactyly (PPD) in the hind limb is a developmental trait that restores the first digit lost during canine evolution.”  “Unlike the previously characterized cases of PPD identified in the mouse and human ZRS regions, the canine mutations in pZRS lacked the ectopic expression of sonic hedgehog in the anterior limb bud, distinguishing its role in limb development from that of the ZRS.” ↩ ↩

2. 2b.

   Section Results:  Under the heading "Mutational heterogeneity for canine PPD in the MCS region of LMBR1 intron 5".  For DC-1 in the Sapsaree, 144 heterozygous and 6 homozygous affected dogs carried the change and 65 unaffected dogs did not.  For Western breeds,  “The DC-2 mutation was identified in 26 affected individuals of Western breeds with either heterozygosity (G/A in 14) or homozygosity (A/A in 12), whereas the 23 unaffected individuals were homozygous (G/G).”  The DC-2 change lies.  “246 bp downstream of DC-1.” ↩ ↩

3. 2c.

   Section Results, "The MCS region serves as a transcriptional enhancer":  “When we introduced DC-1 or DC-2 mutations in the wild-type ZRS region, >50% reduction in enhancer activity was evident (Figure 3A).”  In transgenic mice,  “The stained region was broader in the DC-1 embryos”.  and.  “extended to the position of the second digit”.  in the hind limb bud.  Section Discussion, paragraph second:  “Instead, the enhancing activity was extended toward the anterior side by the PPD mutation”. ↩

4. 2d.

   Section Discussion, paragraph first:  “However, the canine PPD studied here appears to be a reversion from the evolutionary loss of the first digit.” ↩

5. 2e.

   Section Discussion, paragraph first:  “the external morphology of hind-limb-specific canine PPD is slightly different from other polydactylies in that only the claw is observed as having an extra digit with fibrous tissue connecting the region between the tarsal and the first metatarsal bones, which either is reduced in size or is incomplete with a lesser deposit of bony material”. ↩

6. 2f.

   Section Discussion, paragraph third:  “The two independent origins of canine PPD mutation may reflect its rather frequent incidence, perhaps due to a developmental constraint.” ↩

7. 2g.

   Section Discussion, paragraph fourth:  “In fact, even in Great Pyrenees, the association with Alx4Δ51 alleles is genetically ambiguous, whereas DC-1 or DC-2 associations are clearly Mendelian with an autosomal-dominant mode of inheritance.” ↩

Sisson, Septimus.  The Anatomy of the Domestic Animals.  W. B. Saunders, Philadelphia.  2nd edition.  1914.  A veterinary anatomy of the domestic animals by a professor of comparative anatomy at Ohio State University, illustrated with 725 figures, many in color.  The article uses its descriptions of the dog's front and hind feet, the bones of the first digit and the muscles of the thumb.

1. 3a.

   Page 201, section Skeleton of the dog:  “The five digits have three phalanges each, except the first, which has two.  The third and fourth digits are the longest; the first is very short and does not come in contact with the ground in walking.” ↩

2. 3b.

   Page 200:  “Five metacarpal bones are present.  The first is much the shortest; the third and fourth are the longest”. ↩

3. 3c.

   Page 373, section Muscles of the dog's forearm:  “The extensor carpi obliquus or abductor pollicis longus arises from the lateral border and dorsal surface of the ulna, the interosseous ligament, and the proximal part of the lateral border of the radius.  It is inserted into the first metacarpal bone by a tendon which contains a small sesamoid bone.  It abducts the first digit.” ↩

4. 3d.

   Page 373:  “The extensor of the first and second digits (M. extensor pollicis longus et extensor indicis proprius) is small ... The delicate medial branch ends on the first digit, while the larger lateral one ends with the tendon of the common extensor for the second digit.” ↩

5. 3e.

   Page 374:  The subject is the common tendon of the deep digital flexor.  “passes down through the carpal canal, gives off a branch to the first digit, and divides into four branches.” ↩

6. 3f.

   Page 375:  “The abductor pollicis brevis et opponens pollicis, a very small pale muscle, arises on the fibrous band which connects the superficial flexor tendon with the medial carpal sesamoid, and ends on the distal end of the first metacarpal bone and the first phalanx of the first digit.  It abducts the first digit.”  “The flexor pollicis brevis arises on the volar carpal ligament over the second metacarpal bone, and ends on the volar sesamoid of the first digit.”  “The adductor pollicis, situated lateral to the preceding, is the largest of the thumb muscles.” ↩ ↩

7. 3g.

   Pages 205–206, section Skeleton of the dog's hind foot:  “Five metatarsal bones are present.  The first is commonly very small and has the form of a blunt cone, somewhat compressed laterally.  It articulates with the first tarsal and furnishes insertion to the tibialis anterior muscle.  In some cases it fuses with the first tarsal”. ↩ ↩

8. 3h.

   Page 206:  “The first digit is often absent.  When present, its development varies and it contains one or two phalanges.  In other cases — especially in very large dogs — a sixth digit is present; it does not articulate with the metatarsus, but is attached by fibrous tissue.” ↩

9. 3i.

   Pages 381–382, section Muscles of the dog's hind foot:  “In case the skeleton of the first digit is well developed, there are three muscles which are homologous with those of the same digit in the forelimb.  These are the abductor hallucis, adductor hallucis, and flexor hallucis brevis.” ↩

10. 3j.

    Page 903, section Skin of the dog:  “On the flexion surface of the carpus and digit there are hairless, cushion-like pads.  The carpal pad (Torus carpalis) is situated medial and distal to the accessory carpal bone.  The metacarpal and metatarsal pads (Torus metacarpalis, metatarsalis) are the largest ... The metapodio-phalangeal joints rest on them when the paw supports the weight.  The digital pads (Toruli digitales) are oval and are much smaller; they similarly support the second digital joints.” ↩

Evans, Howard E., and George C. Christensen.  Miller's Anatomy of the Dog.  W. B. Saunders, Philadelphia.  2nd edition.  1979.  A second-edition anatomy of the dog, quoted for its account of the dog's first digit on the front and hind feet and for the carpal pad.  The article uses it for its definition of the dewclaw, which applies to the first digit of the hind foot and not to the front one, and for its description of the front digit.

1. 4a.

   Page 195:  “Unlike the first metatarsal bone of the hindpaw, the first metacarpal bone of the forepaw is usually present, although it is by far the shortest and most slender of the metacarpal bones.  It bears the first digit, which does not quite reach the level of the second metacarpophalangeal joint.” ↩

2. 4b.

   Page 367:  “The special muscles of digit I.  The rudimentary first, or medial, digit has three special muscles: an outward rotator, a flexor, and an inward rotator.” ↩

3. 4c.

   Page 222:  “The term "dewclaw" is applied to the variably developed first digit of the hindpaw of the dog.  It should not be applied to the first digit of the forepaw because that appendage, although rudimentary, is always present.  Some breeds are recognized by the American Kennel Club (1975) as normally possessing fully developed first digits on their hindpaws.  Many individuals of the larger breeds of dogs possess "dewclaws" in various degrees of development (Kadletz 1932).  In the most rudimentary condition an osseous element bearing a claw is attached only by skin to the medial surface of the tarsus.” ↩ ↩ ↩

4. 4d.

   Page 222:  “Occasionally, two claws of equal size are present on the medial side of the hindpaw.  These supernumerary digits probably have no phylogenetic significance.” ↩

5. 4e.

   Page 222:  “Although the dewclaw may be lacking, a rudiment of the first metatarsal is occasionally seen as a small, flattened osseous plate which lies in the fibrous tissue on the medial side of the tarsus.” ↩

6. 4f.

   Page 407, section Muscles of the hindpaw:  “When the first digit (dewclaw) is lacking, its muscles are also lacking”. ↩

7. 4g.

   Page 374, section Fascia of the forepaw:  “From the cushion of the carpal pad an especially strong band of the fascia extends directly laterally and a little proximally toward the distal end of the ulna”.  Page 702, section Median artery:  “A small branch to the carpal pad arises from the median just distal to the carpal canal.” ↩ ↩

Sellon, Debra C. et al.  “A survey of risk factors for digit injuries among dogs training and competing in agility events.”  Journal of the American Veterinary Medical Association 252(1):75–83.  2018.  An internet survey of 1,081 agility dogs, reported by their handlers, comparing 207 that had injured a digit with 874 that had not.  Dogs without front dewclaws had higher odds of injury (odds ratio 1.9), but a veterinarian did not have to confirm the injury and the authors warn of recall bias.  The article uses it as the strongest data on dewclaws and toe injury, and treats it as a lead rather than proof.

1. 5a.

   Section Abstract, Results:  “Factors associated with significantly increased odds of injury included Border Collie breed (OR, 2.3; 95% confidence interval [CI], 1.5 to 3.3), long nails (OR, 2.4; 95% CI, 1.3 to 4.5), absence of front dewclaws (OR, 1.9; 95% CI, 1.3 to 2.6), and greater weight-to-height ratio (OR, 1.5; 95% CI, 1.1 to 2.0).”  Section Abstract, Conclusions:  “Results should be cautiously interpreted because of potential respondent and recall bias and lack of review of medical records.  Nevertheless, results suggested that retaining healthy dewclaws, maintaining lean body mass, and trimming nails short for training and competition may decrease the likelihood of digit injuries.” ↩ ↩ ↩ ↩

2. 5b.

   Section Results, footnote to Table 1:  “Only 110 of the 207 dogs were reported to have front dewclaws.  Of the dogs with dewclaws, 8 (7.3%) reportedly had injuries to that digit.” ↩

3. 5c.

   Section Discussion, third paragraph:  “The front dewclaws are proposed to have a functional role in preventing torque on the limb, and as such, their removal may predispose to injury.  Video and photographic images of exercising dogs clearly show that the metacarpophalangeal joint undergoes hyperextension when a dog is moving at speed with quick turns.  Hyperextension increases the forces on the metacarpophalangeal pads and allows digit 1 to make contact with the running surface.  The musculotendinous attachments to the dewclaws, including the extensor pollicis longus and flexor digitorum profundus muscles, allow these digits to grip the surface, stabilizing the foot and decreasing rotational forces on the other digits.”  The first sentence cites Zink's note (reference 18). ↩

4. 5d.

   Section Abstract, Conclusions:  “results suggested that retaining healthy dewclaws, maintaining lean body mass, and trimming nails short for training and competition may decrease the likelihood of digit injuries.”  Section Discussion, third paragraph:  “As such, we would advise against elective surgical removal of forelimb dewclaws for dogs training and competing in agility activities.” ↩

Ciucci, Paolo et al.  “Dewclaws in wolves as evidence of admixed ancestry with dogs.”  Canadian Journal of Zoology 81(12):2077–2081.  2003.  A genetic study of three dewclawed wolves from Tuscany, central Italy, from 1993 to 2001.  The authors tested 18 DNA markers and found that the wolves were not uniquely assigned to the Italian wolf population, but appeared to be second or later generation backcrosses of wolf–dog hybrids.  The article uses it to show that wild canids normally lack hind dewclaws, and that a dewclaw in a wolf points to dog ancestry.

1. 6a.

   Section Abstract:  “Vestigial first toes (dewclaws) on the hind legs are common in large dog (Canis lupus familiaris) breeds but are absent in wild canids, including wolves (Canis lupus).”  “Based on 18 microsatellite markers, dewclawed wolves were not uniquely assigned to the Italian wolf population but appeared to be second or later generation backcrosses of wolf–dog hybrids.” ↩ ↩

American Kennel Club.  Official Standard of the Briard.  Feb 8, 1975.  Page 2:  “Dewclaws two dewclaws are required on each rear leg, placed low on the leg, giving a wide base to the foot. ... Ideally the dewclaws form additional functioning toes.  Disqualification - anything less than two dewclaws on each rear leg.”  The official written standard for the Briard dog breed, the ideal description that the American Kennel Club approved.  The article uses it to show that the breed requires two dewclaws on each hind leg. ↩ ↩

Reighard, Jacob, and H. S. Jennings.  Anatomy of the Cat.  Henry Holt, New York.  1901.  A 1901 anatomy of the cat, quoted for the cat's thumb, its rudimentary first hind bone and the reduction of its first digit in the leg muscles.  The article uses it to show that the cat's first digits are built like the dog's.

1. 8a.

   Page 72:  “The first digit of the hand is called the pollex (thumb) ... The first digit has two phalanges, each of the others three phalanges.” ↩

2. 8b.

   Page 85:  The subject is the medial cuneiform bone.  “bears on its distal end the rudimentary first metatarsal.”  “The metatarsals are five in number.”  “The first metacarpal (1) is rudimentary and conical.”  Sic: "metacarpal" for metatarsal in the section on the foot. ↩ ↩

3. 8c.

   Page 207, section M. flexor longus digitorum:  “Owing to the reduction of the first digit in the cat the tendon of the flexor longus hallucis ... has become united to that of the flexor longus digitorum ..., so that the two might be considered separate heads of a single muscle.” ↩

Wang, Xiaoming.  “Transformation from plantigrady to digitigrady: functional morphology of locomotion in Hesperocyon (Canidae: Carnivora).”  American Museum Novitates (3069):1–23.  Sep 9, 1993.  A museum paper that measures the limb bones of Hesperocyon, the earliest known canid, and compares them with its relatives among the early carnivorans.  It concludes that Hesperocyon was plantigrade (it walked on its whole palm and sole) and probably climbed trees.  The article uses it to show the order of the canid fossils, from a first toe that still worked to a bare nub in living dogs.

1. 9a.

   Page 1, section Abstract:  “This combination of cursorial and noncursorial characters shows that Hesperocyon represents a transitional stage from its arboreal plantigrade ancestors to its cursorial digitigrade descendants.”  “I have concluded that Hesperocyon was plantigrade in posture and probably scansorial in life.”  The abstract also dates Hesperocyon.  “from the late Eocene to early Oligocene”. ↩ ↩

2. 9b.

   Page 13, section Metapodials:  “All of the early canids in this study remain pentadactyl, i.e., a functional first metapodial is present on the fore and hind feet.  The extremely reduced first digits in living canids are thus a derived condition within the subfamily Caninae.”  “The reduction of metatarsus I and metacarpus I, lost in living canids (Ginsburg, 1961), has already become apparent in Hesperocyon, although the length of these digits is still more than half that of the metapodials III or IV”. ↩ ↩

3. 9c.

   Page 14:  On a hind foot of Leptocyon vafer from the Tesuque Formation, Early Barstovian.  “The first metatarsus is reduced to less than half the length of metatarsus III and is more slender than the rest of the digits.” ↩ ↩

Nilsson, B. Y., and C. R. Skoglund.  “The tactile hairs on the cat's foreleg.”  Acta Physiologica Scandinavica 65(4):364–369.  1965.  A physiology study of the hairs at the wrist of the cat's foreleg, which examined their structure and recorded the nerve signals they send.  Each hair follicle has a large blood sinus, with Pacinian corpuscles (nerve endings that respond to vibration) close by, and bending a hair made the nerve discharge rise sharply.  The article uses it to show that the whiskers above a cat's carpal pad are a working touch organ.

1. 10a.

   Section Abstract:  “The vibrissae-like hairs at the wrist of the cat's foreleg have been studied morphologically and physiologically.  Each hair follicle contains a large blood sinus close to which a number of Pacinian corpuscles are situated.” ↩ ↩

Eager, Diane.  “DEW CLAWS ON DOGS? Are they evidence of evolution?”  Creation Research, Ask John Mackay.  May 12, 2015.  A question-and-answer page in which Diane Eager of Creation Research answers a reader who had heard that dewclaws are vestigial.  She argues that the dewclaw is functional in many breeds, where muscle and tendon attach it to the leg bones, and that a dewclaw without them is degenerate rather than evidence for evolution.  The article calls it the one direct creationist treatment of the dewclaw.

1. 11a.

   Paragraph second:  “In many dog breeds it is attached to the leg bones by muscle and tendons, and is therefore a functional structure.  When the dog runs it can make contact with the ground, and the dog uses it when making quick turns.” ↩

2. 11b.

   Paragraph fifth:  “In some breeds the dewclaw is present but lacks the muscle and tendons needed to make it useful, and in these cases it could be called "vestigial".  However, this is not evidence for evolution.  It just means that a functional claw has become degenerate and lost part of its structure, and is no longer useful.  In other words, it is a reminder that, like all living things, dogs are going downhill, not evolving upwards.” ↩ ↩

Wood, Todd Charles.  “Mitochondrial DNA analysis of three terrestrial mammal baramins (Equidae, Felidae, and Canidae) implies an accelerated mutation rate near the time of the Flood.”  Proceedings of the Seventh International Conference on Creationism.  Creation Science Fellowship, Pittsburgh.  2013.  A conference paper by Todd Charles Wood of the Core Academy of Science, a creationist researcher, that compares published mitochondrial DNA (the DNA kept in the cell's energy-making structures) from ancient and modern horses, cats and dogs.  It finds that the ancient sequences fall within the range of modern ones, which the author takes to mean that modern diversity was already in place soon after the Flood.  The article uses it because Wood reports that creationist researchers have classed the dog family as one baramin, a created kind.

1. 12a.

   Page 2, section Introduction:  “I here examine published mitochondrial DNA sequences of three well established baramins: Equidae, Felidae, and Canidae.  As terrestrial baramins, we may hypothesize that they have descended from a single pair preserved by Noah on the Ark.”  “Finally, the hybridization of canids has been reviewed by Siegler (1974), Crompton (1993), and Pendragon (2011).  Each author classified Canidae as a baramin.” ↩ ↩

Beddard, Frank E.  “Observations upon the carpal vibrissae in mammals.”  Proceedings of the Zoological Society of London 1:127–136.  1902.  A 1902 survey of the tuft of stiff whiskers on the wrist (the carpal vibrissae) across the mammal orders, by the zoologist Frank Beddard, who examined a large number of mammals.  The article uses it because it is the source for the claim that cats have this wrist tuft and dogs do not.

1. 13a.

   Page 127:  “That these structures must be of some use to their possessors seems to be obvious, and yet is not easy to prove.  I have watched various animals, and cannot see that they make any use of the tuft of hairs upon the wrist for touching objects, except in the possible case of the Raccoon (Procyon lotor)”. ↩

2. 13b.

   Page 130:  “The Carnivora as a group are apparently characterized by the existence of this organ.  I have found it in representatives of the Aeluroidea (Domestic Cat, Lion, ...), the Arctoidea (Putorius, Otter, Mustela, the Coati) but I do not find it in the Dogs.” ↩ ↩

3. 13c.

   Page 136, section Summary point 6:  “With the marked exception of the Anthropoidea, there seems to be a certain relation between the presence of the tuft of carpal vibrissae and the nature of the fore limbs.  When the fore limbs are purely ambulatory limbs, the carpal vibrissae are absent.” ↩

Zink, M. Christine.  Do the Dew(claws)?  Apr 10, 2013.  A one-page note, revised 10 April 2013, by a veterinarian who rehabilitates injured canine athletes.  She reports that of over 30 dogs with carpal (wrist) arthritis she had seen, only one had dewclaws, and she argues that the dewclaw touches the ground in a gallop and helps prevent twisting of the leg on turns.  The article uses it as the clinical evidence that the dewclaw touches the ground when a dog runs.

1. 14a.

   Paragraph first:  “Of the over 30 dogs I have seen with carpal arthritis, only one has had dewclaws.” ↩

2. 14b.

   Paragraph second:  “you will see that there are 2 major, functioning tendons attached to the dewclaw.”  Figure 1:  Caption:  “Anatomical diagram viewing the medial side of a dog's left front leg demonstrating the five tendons that attach to the dewclaw.” ↩

3. 14c.

   Paragraph third:  “Those muscles indicate that the dewclaws have a function.  That function is to prevent torque on the leg.  Each time the foot lands on the ground, particularly when the dog is cantering or galloping (see Figure 2), the dewclaw is in touch with the ground.  If the dog then needs to turn, the dewclaw digs into the ground to support the lower leg and prevent torque.” ↩

Gonyea, William, and Robert Ashworth.  “The form and function of retractile claws in the Felidae and other representative carnivorans.”  Journal of Morphology 145(2):229–238.  1975.  An anatomy study of the mechanism that draws cat claws back and forth, described in 15 felid species and compared with other carnivores.  It found that the claws are retracted by elastic ligaments, not by the forearm extensor muscles, and that in the other carnivore families the jaws, not the forelimbs, are the main tool for seizing prey.  The article uses it to show that in cats the forelimb is the main tool for catching prey.

1. 15a.

   Section Abstract:  “Recent behavioral studies have shown the primary organ of prehension used in capturing prey to be the claw equipped forelimbs.”  “For the other families of carnivorans, the jaws and not the forelimbs are used as the primary organ of prehension”. ↩

Pocock, R. I.  “On the feet and other external features of the Canidae and Ursidae.”  Proceedings of the Zoological Society of London, 913–941.  1914.  A survey of the feet of the dog family and the bear family by R. I. Pocock, Curator of Mammals, drawn from the specimens he examined.  He finds that the feet of the typical dogs closely resemble those of cats, with the first digit set back on the front foot and absent from the hind foot.  The article uses it to show that wild canids typically lack a hind first toe.

1. 16a.

   Page 913:  “The feet of the typical Canidae are highly specialised, and show a close adaptive resemblance to those of the Felidae in the form of the plantar pad, the strong curvature of the line of the pads of digits two to five, in the backward position of the first digit of the fore foot, its absence from the hind foot, the hairiness of the area behind the plantar pads, and the persistence of the single carpal pad on the fore feet.” ↩ ↩

2. 16b.

   Page 915:  On the bush dog Speothos:  “to decide whether the peculiarity of the feet in the matter of the low position of the first digit and carpal pad is a secondarily acquired adaptation to conditions or whether it is a retained primitive character.  I incline to the latter opinion, because these peculiarities are present in the newly born pups of species of dogs with normal feet when adult”. ↩ ↩

3. 16c.

   Page 917:  On Lycaon pictus:  “The main peculiarity about the feet of this dog, namely, the suppression of the first digit of the fore foot, is well known”. ↩

American Kennel Club.  Official Standard of the Beauceron.  Aug 8, 2006.  Page 2:  “Dewclaws - Double dewclaws form well separated "thumbs" with nails, placed rather close to the foot.  Disqualification - Anything less than double dewclaws on each rear leg.”  The official written standard for the Beauceron dog breed, effective 1 October 2006, as the American Kennel Club approved it.  The article uses it to show that the breed disqualifies any dog with fewer than double dewclaws on each rear leg. ↩

American Kennel Club.  Official Standard of the Great Pyrenees.  Jun 12, 1990.  Page 2:  “Double dewclaws are located on each rear leg.”  “Fault - Absence of double dewclaws on each rear leg.”  The official written standard for the Great Pyrenees dog breed, effective 1 August 1990, as the American Kennel Club approved it.  The article uses it to show that the breed counts missing double dewclaws on the rear legs as a fault. ↩

Fondon, John W. III, and Harold R. Garner.  “Molecular origins of rapid and continuous morphological evolution.”  PNAS 101(52):18058–18063.  2004.  A comparative genomic study of short DNA stretches that repeat in a row inside developmental genes, across 92 dog breeds.  The number of repeats in the Alx-4 and Runx-2 genes tracked differences in limb and skull shape, and the Great Pyrenees with extra rear toes carried a shortened Alx-4 repeat in both copies.  The article uses it to link the double dewclaws of the Great Pyrenees to a change in one gene.

1. 19a.

   Section Results and Discussion:  “The Alx-4Δ51 allele occurred in homozygosity in the Great Pyrenees breed (Fig. 1).  An official characteristic of this breed is bilateral rear first digit polydactyly.  All four Great Pyrenees with bilateral polydactyly examined were homozygous for this repeat contraction.” ↩

2. 19b.

   Section Results and Discussion:  “it has been shown that deletion of this PQn repeat (but not other portions of the protein) specifically destroys the ability of Alx-4 to bind with lymphoid enhancer binding factor-1 and drive target gene expression in limb bud mesenchyme (19).” ↩

Galis, Frietson et al.  “Why five fingers? Evolutionary constraints on digit numbers.”  Trends in Ecology and Evolution 16(11):637–646.  2001 (edition of 2002).  A review of why animals with limbs rarely gain or lose digits, by three researchers at Leiden University and the International Institute for Applied Systems Analysis.  Its authors argue that digit numbers are tightly constrained, because a mutation that changes the number of limb bones usually has side effects on other body parts (pleiotropic effects), and they note that amphibians with aquatic larvae vary more in toe number.  The article uses it for two points: that a St Bernard's extra hind toe is an atavism, a throwback to an ancestral first digit, and that the digit reduced first in evolution is usually the one formed last.

1. 20a.

   Page 2, figure 1:  “(b) Foot of St Bernard dog with five toes, including an atavistic first digit (arrow).  In wolves and most other canids, the first toe is reduced, and they only have four toes.” ↩

2. 20b.

   Page 7:  Box 3:  “The digit reduced first during evolution is usually the one formed last.” ↩

Lettice, Laura A. et al.  “Point mutations in a distant sonic hedgehog cis-regulator generate a variable regulatory output responsible for preaxial polydactyly.”  Human Molecular Genetics 17(7):978–985.  2008.  A laboratory study of domestic cats with extra toes, looking at the DNA switch (the ZRS) that controls the Sonic hedgehog gene in the developing limb.  The authors found single-letter DNA changes in that switch in the polydactylous cats, and a test in transgenic mouse embryos showed that these changes switch the gene on at an unusual site.  The article uses it to show that cats reach extra toes by a different route from the dog mutations described by Park's team.

1. 21a.

   Section Abstract:  “Here, we show that populations of domestic cats which manifest extra digits, including the celebrated polydactylous Hemingway's cats, also contain mutations within the ZRS.”  “A mouse transgenic assay shows that these single nucleotide substitutions operate as gain-of-function mutations that activate Shh expression at an ectopic embryonic site”. ↩

Wikipedia.  Paw.  Sep 28, 2025.  Section Lead:  “A carpal pad is also found on the forelimb which is used for additional traction when stopping or descending a slope in digitigrade species.”  The lead of an online encyclopedia article on the paw, as it stood in its revision of 28 September 2025.  The sentence carries no reference.  The article cites it only as the source of the claim it tests, not as evidence. ↩ ↩

New World Encyclopedia.  Cat.  2026.  Retrieved Sep 27, 2026.  “This special feature of the front paws, on the inside of the wrists, is the carpal pad, also found on the paws of dogs.  It has no function in normal walking, but is thought to be an anti-skidding device used while jumping.”  An online encyclopedia entry about cats.  The passage gives no reference for its claim about the carpal pad.  The article cites it only as the source of the claim it tests, not as evidence. ↩ ↩

Nilsson, B. Y.  “Structure and function of the tactile hair receptors on the cat's foreleg.”  Acta Physiologica Scandinavica 77(4):396–416.  1969.  A physiology study of the same wrist hairs, which moved each hair at set speeds and distances with a mechanical stimulator while recording the nerve fibers.  It found that the hairs are supplied by free nerve endings and Merkel cell complexes, and that each nerve fiber supplies only one hair.  The article cites it, alongside the earlier Nilsson and Skoglund study, for how the cat's wrist hairs sense movement.

1. 24a.

   Section Abstract:  “The cat's carpal sinus hairs are shown to be supplied by free nerve endings”.  and by Merkel cell complexes.  “Each fiber supplies only one hair.” ↩

Catchpoole, David.  “The Australian dingo, a wolf in dog's clothing.”  Creation 27(2):10–15.  Mar 2005.  A magazine article by David Catchpoole of Creation Ministries International about the Australian dingo.  It first appeared in Creation in March 2005 and went online on 1 February 2006.  The article quotes it because it is one Creation Ministries International text that mentions dewclaws, and it does so only in passing.

1. 25a.

   Section Body:  “They are different from most dogs in that they don't bark, only howl; breed only once a year; and have no dew claws on their hind legs.”  Section Note 1:  “In dogs, the 'dew claw' is the 'toe' hanging loosely attached to the skin, on the rear of the leg.” ↩

Sarfati, Jonathan, and Don Batten.  “'Vestigial' organs: what do they prove?”  Creation Ministries International.  Feb 14, 2006.  A short article by two writers for Creation Ministries International, answering the claim that some organs are useless.  It says no organ can be proved useless, because a use may be found later, and that losing an organ would show devolution rather than evolution.  The article cites it for that devolution argument, which it says the creation model allows.

1. 26a.

   On the argument's logic.  “Second, even if the alleged vestigial organ were no longer needed, it would prove devolution not evolution.  The creation model allows for deterioration of a perfect creation.” ↩

Coyne, Jerry A.  Why Evolution Is True.  Viking, New York.  2009.  A general book by Jerry A. Coyne on the case for evolution.  The article quotes it for a definition of vestigial that sets function aside, and sets this against the stricter test of Senter and Moch.

1. 27a.

   Page 58:  “Evolutionary theory doesn't say that vestigial characteristics have no function.  A trait can be vestigial and functional at the same time.  It is vestigial not because it's functionless, but because it no longer performs the function for which it evolved.” ↩