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Transition from synapsid reptiles to mammals (Talk.Origins)

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Response Article

This article (Transition from synapsid reptiles to mammals (Talk.Origins)) is a rebuttal regarding a supposed transitional form published by the Talk.Origins Archive under the title Transitional Vertebrate Fossils FAQ.

Response to Transition from synapsid reptiles to mammals

CreationWiki response:

The presence of a dentary-squamosal jaw joint has been arbitrarily selected as the defining trait of a mammal.

Note that the compiler of the list on Talk.Origins has chosen one admittedly arbitrary trait to separate mammals from reptiles. It needs to be noted that the actual defining traits of mammals—hair and milk—would not tend to show up in fossils, and as such it is possible that actual defining traits are not available.

  • Paleothyris (early Pennsylvanian) ...
  • Protoclepsydrops haplous (early Pennsylvanian) ...
  • Clepsydrops (early Pennsylvanian) ...
  • Archaeothyris (early-mid Pennsylvanian) ...

All of these reptiles are classified as early Pennsylvanian and as such they would be contemporaries on the evolutionary time scale, making their order arbitrary. Therefore there is no progression, only a case of placing fossils in an arbitrary order that favors evolution.

In addition Archaeothyris and Paleothyris look more alike than their so-called intermediate form Ophiacodontidae. This represents a problem for Talk.Origins' arbitrary order. Finally, Clepsydrops seems to be reconstructed from fragmented remains.

  • Varanops (early Permian) -- Temporal fenestra further enlarged. Braincase floor shows first mammalian tendencies & first signs of stronger attachment to rest of skull (occiput more strongly attached). Lower jaw shows first changes in jaw musculature (slight coronoid eminence). Body narrower, deeper: vertebral column more strongly constructed. Ilium further enlarged, lower-limb musculature starts to change (prominent fourth trochanter on femur). This animal was more mobile and active. Too late to be a true ancestor, and must be a "cousin".

At least Talk.Origins is admitting that Varanops is not an actual ancestor of mammals, but the existence of that ancestor is assumed. This is a typical case of taking a fossil out of its order in the Geologic Column and placing it where their theory says it should be. What they really have here is a gap, which Talk.Origins is just filling in with an animal that they moved from a different location on their timescale.

Not only areHaptodus, Dimetrodon and Sphenacodon dated as older than Varanops, but they would also be contemporaries. Furthermore, Sphenacodon seems to be the same kind of animal as Haptodus.

  • Biarmosuchia (late Permian) ... Upper jaw bone (maxillary) expanded to separate lacrymal from nasal bones, intermediate between early reptiles and later mammals. ... had just one canine, like mammals, and stopped replacing the canine after reaching adult size. Jaw hinge more mammalian in position and shape, jaw musculature stronger (especially the mammalian jaw muscle). The amphibian-like hinged upper jaw finally became immovable. ... more mammalian femur & pelvis....

First of all, there is an unacknowledged gap of geologic time here, since there is no reference to the mid Permian. Furthermore, there are significant differences between Biarmosuchia and Haptodus, Dimetrodon and Sphenacodon that one could not make a case for a relationship without numerous intermediates. What we have here is a classic mosaic; this is a reptile that has some mammal-like parts and some amphibian-like parts. Given the lack of any transition from any earlier types, all it shows is that their traits are not unique to mammals.

  • Procynosuchus (late latest Permian) -- The first known cynodont -- a famous group of very mammal-like therapsid reptiles, sometimes considered to be the first mammals. Probably arose from the therocephalians, judging from the distinctive secondary palate and numerous other skull characters. Enormous temporal fossae for very strong jaw muscles, formed by just one of the reptilian jaw muscles, which has now become the mammalian masseter. The large fossae is now bounded only by the thin zygomatic arch (cheekbone to you & me). Secondary palate now composed mainly of palatine bones (mammalian), rather than vomers and maxilla as in older forms; it's still only a partial bony palate (completed in life with soft tissue). Lower incisor teeth was reduced to four (per side), instead of the previous six (early mammals had three). Dentary now is 3/4 of lower jaw; the other bones are now a small complex near the jaw hinge. Jaw hinge still reptilian. Vertebral column starts to look mammalian: first two vertebrae modified for head movements, and lumbar vertebrae start to lose ribs, the first sign of functional division into thoracic and lumbar regions. Scapula beginning to change shape. Further enlargement of the ilium and reduction of the pubis in the hip. A diaphragm may have been present.

The description seems to indicate that Procynosuchus had so many mammalian traits that it was probably a mammal. Apparently some paleontologists think it was a mammal. The reptilian features seem to be in the lower jaw so most likely Procynosuchus was a mammal. Furthermore, Procynosuchus is based on a sufficiently incomplete skeleton as to raise some questions about the details of its reconstruction. It leaves plenty of room for evolutionary assumptions in its interpretation. And there is a sudden appearance of these mammalian traits; it goes from reptiles with a few mammalian traits to mammals with a few reptilian traits, in one step. That shows a real gap not in time but in traits between mammals and reptiles.

  • Dvinia [also "Permocynodon"] (latest Permian) -- Another early cynodont. First signs of teeth that are more than simple stabbing points -- cheek teeth develop a tiny cusp. The temporal fenestra increased still further. Various changes in the floor of the braincase; enlarged brain. The dentary bone was now the major bone of the lower jaw. The other jaw bones that had been present in early reptiles were reduced to a complex of smaller bones near the jaw hinge. Single occipital condyle splitting into two surfaces. The postcranial skeleton of Dvinia is virtually unknown and it is not therefore certain whether the typical features found at the next level had already evolved by this one. Metabolic rate was probably increased, at least approaching homeothermy.

Dvinia is based only on a skull and not a complete one at that, and some teeth. Its only reptilian traits seem to be in the jaw as with Procynosuchus, suggesting that they too were mammals.

  • Thrinaxodon (early Triassic) ... Number of toe bones is, intermediate between reptile number ( and mammalian (, and the "extra" toe bones were tiny ... NOTE on hearing: The eardrum had developed in the only place available for it -- the lower jaw, right near the jaw hinge, supported by a wide prong (reflected lamina) of the angular bone.
  • Cynognathus (early Triassic, 240 Ma; suspected to have existed even earlier) ... There is possible evidence for fur in fossil pawprints.
  • Diademodon (early Triassic, 240 Ma; same strata as Cynognathus)... Lower jaw almost entirely dentary, with tiny articular at the hinge. Still a double jaw joint. Ribs shorten suddenly in lumbar region, probably improving diaphragm function & locomotion. Mammalian toe bones (, with closely related species still showing variable numbers.

While Thrinaxodon had an extra bone in two of its toes, there is no evidence of a loss process of two bones after it or before it. Even if Thrinaxodon did hear the way described above, there is no evidence of its development or succession. All three seem to be mammal with some reptilian jaw traits, but nothing else hinting at a connection to reptiles. Besides, they are all evolutionarily dated as being contemporaries so there is no objective evidence of a succession. In addition, the differences between Thrinaxodon and Cynognathus show significant difference in general body shape making any relationship doubtful without intermediates.

  • Probelesodon (mid-Triassic; South America) ...
  • Probainognathus (mid-Triassic, 239-235 Ma, Argentina) ...
  • Exaeretodon (mid-late Triassic, 239Ma, South America) ...

Probelesodon, Probainognathus and Exaeretodon are evolutionarily dated as contemporaries. Therefore the order they are placed on this list is arbitrary, and hence there is no objective evidence of descent here.

GAP of about 30 my in the late Triassic, from about 239-208 Ma. ...Bear in mind that both these groups were almost fully mammalian in every feature, lacking only the final changes in the jaw joint and middle ear.

This shows that rather than being an actual transition, these are just mammals with a few reptilian traits.

  • Oligokyphus, Kayentatherium (early Jurassic, 208 Ma) ... Probably cousin fossils (?), with Oligokyphus being more primitive than Kayentatherium. Thought to have diverged from the trithelodontids during that gap in the late Triassic. There is disagreement about whether the tritylodontids were ancestral to mammals (presumably during the late Triassic gap) or whether they are a specialized offshoot group not directly ancestral to mammals.

Note that even Talk.Origins doesn't think that Oligokyphus and Kayentatherium are mammal ancestors. These are clearly 100 percent mammals with no evidence of reptilian traits.

  • Pachygenelus, Diarthrognathus (earliest Jurassic, 209 Ma) ... These are probably "cousin" fossils, not directly ancestral (the true ancestor is thought to have occurred during that late Triassic gap). Pachygenelus is pretty close, though.

Pachygenelus, and Diarthrognathusm are dated as older than Oligokyphus, and Kayentatherium and as such they are simply being presented in the order evolution dictates and not how they are actually dated. Note that even Talk.Origins doesn't think that Pachygenelus and Diarthrognathusm are mammal ancestors. These are clearly 100 percent mammals with no evidence of reptilian traits.

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  • Adelobasileus cromptoni (late Triassic; 225 Ma, west Texas)...Also note that this fossil dates from slightly before the known tritylodonts and trithelodonts, though it has long been suspected that tritilodonts and trithelodonts were already around by then. Adelobasileus is thought to have split off from either a trityl. or a trithel., and is either identical to or closely related to the common ancestor of all mammals.

|} Adelobasileus cromptoni is dated as nearly 20 MA older than Pachygenelus, Diarthrognathusm, Oligokyphus, and Kayentatherium. So Pachygenelus, Diarthrognathusm, Oligokyphus, and Kayentatherium cannot be the ancestors of Adelobasileus cromptoni and other mammals. This helps to show that the entire series is a sham. They claimed a gap, but it has a full mammal whose placement there simply does not fit the theory.

  • Sinoconodon (early Jurassic, 208 Ma) ... Reptilian jaw joint still present, though tiny.

Sinoconodon is actually dated as contemporary with the "earlier" types Oligokyphus, and Kayentatherium. It is interesting that to connect them, Talk.Origins' places three "older" types between them. Talk.Origins claims that Sinoconodon had a tiny reptilian jaw joint but no independent information is available on this—not even a picture—so it is possible that this is an interpretation of a feature that has nothing to do with a jaw joint.

  • Kuehneotherium (early Jurassic, about 205 Ma) -- ...
  • Eozostrodon, Morganucodon, Haldanodon (early Jurassic, ~205 Ma) ...

These are dated as contemporary, so the order is arbitrary and based solely on evolutionary assumptions.

  • Kuehneotherium

Kuehneotherium only known from fragmentary jaw remains and teeth from fissure fillings in Wales.

The fact is that not only are there no known post-cranial bones for Kuehneotherium, but there is only a fragmented jaw and some teeth. This makes its use as evidence for evolution a joke. Its placement is based only on the fact that its teeth are similar to what evolutionists think mammal teeth evolved from.

  • Eozostrodon, Morganucodon, Haldanodon

Eozostrodon, Morganucodon, and Haldanodon seem to be the same kind of animal, possibly varieties of mouse. They are also dated by evolutionary methods as contemporary with Kuehneotherium. As such, placing Kuehneotherium first is arbitrary and based entirely on evolutionary assumptions.

  • Peramus (late Jurassic, about 155 Ma) -- A "eupantothere" (more advanced placental-type mammal). The closest known relative of the placentals & marsupials. Triconodont molar has with more defined cusps. This fossil is known only from teeth, but judging from closely related eupantotheres (e.g. Amphitherium) it had finally lost the reptilian jaw joint, attaing(sic) a fully mammalian three-boned middle ear with excellent high-frequency hearing. Has only 8 cheek teeth, less than other eupantotheres and close to the 7 of the first placental mammals. Also has a large talonid on its "tribosphenic" molars, almost as large as that of the first placentals -- the first development of grinding capability.

Note that Peramus is known only from some teeth. Yet from just its teeth they know what its jaw joint and other bones are like and how it reproduced? Now these teeth may resemble those of some other type of placental mammal, but if that is the case why can't it just be a variety of that type? The argument is a little far-fetched, and reminds one of Nebraska Man. Furthermore, there is no reference to any finds from the mid-Jurassic, so there is no connection with other types. It is a gap that according to evolutionary dating methods is 50 million years.

  • Endotherium (very latest Jurassic, 147 Ma) -- An advanced eupantothere. Fully tribosphenic molars with a well- developed talonid. Known only from one specimen. From Asia; recent fossil finds in Asia suggest that the tribosphenic molar evolved there.

All that Talk.Origins mentions about Endotherium are teeth. Has anything else been found?

  • Kielantherium and Aegialodon (early Cretaceous) -- More advanced eupantotheres known only from teeth. ...

Once again these are known only from teeth, so this is all based on some teeth coupled with evolutionary assumptions. Clearly Talk.Origins has learned NOTHING from Nebraska man.

  • Vincelestes neuquenianus (early Cretaceous, 135 Ma) -- A probably-placental mammal with some marsupial traits, known from some nice skulls. Placental-type braincase and coiled cochlea. Its intracranial arteries & veins ran in a composite monotreme/placental pattern derived from homologous extracranial vessels in the cynodonts.

Vincelestes is only known from its skull. While this is better than Kielantherium and Aegialodon, since all three are classified as early Cretaceous they would have been contemporaries. This means that the order is based entirely on evolutionary assumptions.

  • Pariadens kirklandi (late Cretaceous, about 95 Ma) -- The first definite marsupial. Known only from teeth.

Where is the mid-Cretaceous? There are no references to fossils from the mid-Cretaceous. Pariadens is classified as "late Cretaceous" and Vincelestes is classified as "early Cretaceous." Why is there no reference to this gap? Could it be that relevant fossils that are classified as the mid-Cretaceous did not fit the assumptions of evolution? This is the case with Adelobasileus cromptoni of the "late Triassic gap". In its case Talk.Origins simply moved it to where they wanted it to be.

Again, note that according to Talk.Origins all that has been found of Pariadens kirklandi are some teeth. How do they know it was a marsupial? Teeth have nothing to do with reproduction, so it would impossible to tell just from the teeth. The only answer they provide is that the teeth resemble those of a known marsupial. If that is the case then why can't it be that marsupial? The only possible reason for not drawing such a conclusion is the assumption that evolution occurred.

  • Kennalestes and Asioryctes (late Cretaceous, Mongolia) -- Small, slender animals; eyesocket open behind; simple ring to support eardrum; primitive placental-type brain with large olfactory bulbs; basic primitive tribosphenic tooth pattern. Canine now double rooted. Still just a trace of a non-dentary bone, the coronoid, on the otherwise all-dentary jaw. "Could have given rise to nearly all subsequent placentals." says Carroll (1988).

The only available references to Kennalestes fossils are of teeth. Is it also based only on teeth?

Asioryctes is known only from its skull and fragmentary post cranial bones, making any reconstruction of Asioryctes questionable at best.

The evidence on which both Kennalestes and Asiorycte—as well as their immediate alleged ancestors—are based is too little evidence to draw any legitimate conclusions. The fact is that there is almost nothing to compare. They are classified as late Cretaceous as is its alleged immediate ancestor Pariadens kirklandi, which is itself also based only on teeth.

  • Cimolestes, Procerberus, Gypsonictops (very late Cretaceous) -- Primitive North American placentals with same basic tooth pattern.

There is no clear information on how much of Cimolestes, Procerberus and Gypsonictops have been found in the fossil record, but it seem that they are based only on teeth. Given the fact how little evidence there seems to be for their alleged ancestors there would nothing to compare them to even if complete skeletons are available.


When one can look at the entire animal there is no evidence of a transition here. Even though they can point to apparent trends in some features, there are many more for which there is no evidence of a trend at all. There are several cases were the alleged trend from reptile to mammal does not follow the evolutionary dating scheme. In other cases the evidence is so fragmentary as to make the existence of these taxons questionable. Once again when the available evidence is looked at without assuming evolution, no evidence is found that it took place. Yes, there are some reptiles with a few mammal-like traits and some mammals with a few reptile-like traits, but from Biarmosuchia to Procynosuchus there is a clear and sudden change in dominance from reptile to mammal traits. So rather than the smooth transition Talk.Origins wants you to think exists, there is a sudden shift from reptile to mammal as creationists would expect.


See Also