Home | Feedback | Links | Books

Reappraising the “Crown Jewel”

volutionists claim that the fossil record establishes beyond a reasonable doubt that reptiles evolved into mammals. Indeed, the reptile-to-mammal transition is so frequently cited as proof of megaevolution that one writer labeled it “the crown jewel of the fossil evidence for Darwinism.” (Johnson, 75.) The purpose of this article is to suggest that the evidence for this alleged transition is much weaker than evolutionists would have one believe. (Conventional dating is assumed arguendo throughout the article.)

Anapsida to Synapsida

The reptile-to-mammal story begins with what are termed “primitive” amniotes, reptiles belonging to the “stem” subclass Anapsida. (Carroll, 199-200.) The distinguishing feature of this group is the absence of openings behind the eye socket in the cheek region. Though the origin of these first reptiles is technically not a part of the reptile-to-mammal transition, it is noteworthy that their alleged descent from amphibians is not documented in the fossil record.

According to Robert Carroll, “The earliest known amniotes [i.e., the first reptiles] are immediately recognizable as members of this assemblage because of similarities of their skeleton to those of primitive living lizards.” (Carroll, 193.) He also states, “The early amniotes are sufficiently distinct from all Paleozoic amphibians that their specific ancestry has not been established.” (Carroll, 198.) Even so fierce an opponent of creation theory as Stephen Gould must admit that “no fossil amphibian seems clearly ancestral to the lineage of fully terrestrial vertebrates (reptiles, birds, and mammals).” (Gould, 25.)

Evolutionists believe that synapsids (amniotes having a single temporal opening) evolved from within the Protorothyridae, a family in the order Captorhinida in the subclass Anapsida. (Carroll, 199-201.) According to the fossil record, however, synapsids and anapsids appear simultaneously. The remains of a synapsid, Protoclepsysdrops (order Pelycosauria), have been found which are as old as the oldest anapsid (lower Pennsylvanian). (See, Carroll, 361-362, 615, 622.) Carroll states, “The ancestors of mammals [which he makes clear on the next page refers to synapsids] are identified from the same horizon and locality as the earliest conventional reptile, Hylonomus, in the early Pennsylvanian of Joggins, Nova Scotia.” (Carroll, 361.) Hylonomus is a protorothyrid. (Carroll, 193, 615).

Of course, one can always argue that anapsids actually preceded synapsids and that their contemporaneous appearance in the fossil record is due to the vagaries of fossilization, but it should be acknowledged that in doing so one has moved from data to speculation. One could just as easily claim that synapsids preceded anapsids.

Pelycosauria to Therapsida

Regarding the origin of Therapsida, an order in the subclass Synapsida, conventional wisdom among evolutionists is that they arose from the earlier synapsid order, Pelycosauria. More specifically, it is believed they arose from within the pelycosaurid family, Sphenacodontidae.

After pointing out that the members of the subfamily Sphenacodontinae are too specialized to be ancestors of therapsids, Carroll says, “However, the more primitive genus Haptodus could have filled this role. The lineage leading to therapsids may have diverged from animals that were similar to Haptodus at any time between the late Pennsylvanian and the middle Permian, a period of at least 25 million years” [Emphasis added]. (Carroll, 369.)

The reason Carroll is left to speculate regarding the origin of the first therapsids is that there are no fossils from which any plausible lines of descent from pelycosaurids to therapsids can be constructed. This is crucial because the issue is not whether evolutionists can imagine species from one order (Pelycosauria) evolving into species from another order (Therapsida) but whether that is in fact what occurred. The fossils provide no support for the claim. As Carroll frankly acknowledges, “The transition between pelycosaurs and therapsids has not been documented.” (Carroll, 397.)

The lack of fossil evidence for this alleged transition cannot be excused by trivializing the differences between pelycosaurs and therapsids. According to Carroll, “The therapsids are clearly advanced over the pelycosaurs when they appear in the Upper Permian, particularly in the specializations of the postcranial skeleton” [Emphasis added]. (Carroll, 369.) The two orders have some similarities in cranial structure, but there are also many differences (all the more if one limits the comparison to Haptodus; see, Carroll, 366, 370). And as Romer and Price acknowledge, much of the resemblance in cranial structure might be discounted as due the result of convergent evolution rather than common descent (though they doubt this can account for all of it). (Romer and Price, 193-194.)

Regarding the postcranial skeleton, Carroll states that “[t]he structure of the girdle and limbs [in the early therapsids] indicates a posture much advanced above the level of the pelycosaurs” [Emphasis added]. (Carroll, 370.) The most Romer and Price can say is that the girdles and limbs (appendicular skeleton) of sphenacodontids “in at least a few details show the beginning of therapsid features.” (Romer and Price, 193.) As for the axial skeleton, Romer and Price state, “The axial skeleton presents no strong argument for a particularly close genetic connection between the two groups but on the other hand offers no obstacles.” Ibid.

The bottom line is that when therapsids first appear they differ significantly from pelycosaurs and there are no intermediate species plausibly connecting any known species from the two orders. The claim that therapsids descended from pelycosaurs is based on the assumption of evolution and the belief that, among creatures known to precede therapsids in the fossil record, pelycosauria is the most likely (or least objectionable) source of the ancestral species. That is a far cry from having established descent from pelycosaurids.

Origin of Cynodontia

Cynodontia is the particular suborder of the order Therapsida from which evolutionists believe mammals evolved. They are the only therapsids to “show a significant approach to the mammalian condition in their general morphology.” (Carroll, 378.) There is, however, no fossil record of the ancestry of the cynodonts.

As Carroll freely admits:

Two much more advanced groups of carnivorous therapsids, the therocephalians and cynodonts, appear in the Upper Permian of Russia and southern Africa. We have not established the specific origin and interrelationships of these groups. They may have evolved separately from primitive carnivorous therapsids. (Carroll, 377.)

The fact of the matter is that all six suborders of Therapsida appear virtually simultaneously in the fossil record (in the Upper Permian), already bearing the distinctive features of at least ten infraorders, 42 families, and scores of genera. (Carroll, 362, 397, 623-24.) Thus, there is no known earlier therapsid stock from which cynodonts could have arisen. They are among the earliest therapsids and, according to T. S. Kemp, when they appear they are already “unmistakably at the cynodont level of evolution.” Kemp, 180. Kemp is driven by such evidence to suggest a “very rapid evolution”:

The sudden appearance of new higher taxa, families and even orders, immediately after a mass extinction, with all the features more or less developed, implies a very rapid evolution. . . . It is possible that this is an artifact, and that the new taxa had long histories before they appeared in the fossil record, during which they gradually acquired their characteristic features. However, in no case is such a long history known by even a single specimen, and therefore it is much more reasonable to accept that very high rates of morphological evolution characteristically occur following a mass extinction [Emphasis added]. (Kemp, 327.)

Several genera of the family Galesauridae (infraorder Procynosuchia, suborder Cynodontia) are among the cynodonts appearing in the Upper Permian. (Carroll, 624.) However, the best known example of the galesaurids, Thrinaxodon, dates from the Lower Triassic (slightly later). Though galesaurids are sometimes contrasted to more “primitive” therapsids (e.g., Carroll, 381-386; but see, 396, Fig. 17-47 where Thrinaxodon is called a primitive cynodont), “primitive” in that case refers to morphology rather than to age and is defined in terms of the assumed evolutionary development.

Cynodontia to Mammalia

Evolutionists acknowledge that they “cannot yet recognize the specific [cynodont] lineage that led to mammals.” (Carroll, 398.) That is why Roger Lewin, summarizing a scientific conference on the matter for the journal Science (1981), wrote: “The transition to the first mammal, which probably happened in just one or, at most, two lineages, is still an enigma.” (Lewin, 1492.)

The best Carroll can say is that “[i]t is reasonable to believe that the ancestors of mammals can be found among cynodonts such as the chiniquodontids or galesaurids that reduced their body size, probably in relationship to an insectivorous diet” [Emphasis added]. (Carroll, 410.) However, as Carroll points out, the chiniquodontids and galesaurids of the Lower to Middle Triassic reveal only “the initial stages in the origin of most of the features that characterize the mammalian skeleton.” (Carroll, 392.)

This inability to trace the transition from cynodont to mammal is usually blamed on the paucity of fossils. Carroll writes, “Unfortunately, the record of the immediate ancestors of mammals becomes less complete in the Upper Triassic.” (Carroll, 392.) There are, however, fossils of at least two superfamilies, three families, and seven genera of “advanced” cynodonts from the Upper Triassic. (Carroll, 624.) It just so happens that none of them are suitable as transitions to mammals.

Early Mammals to Modern Mammals

Morganucodontids, kuehneotheriids, and haramiyids are considered by evolutionists to be the oldest fossil mammals. They appear in the Upper Triassic and range into the lower Jurassic (with the possible exception of some teeth from the Middle Jurassic). Each of these families is from a distinct subclass (Prototheria, Allotheria, and Theria) of the class Mammalia. (Carroll, 414-415, 627.) Morganucodontids are by far the best known, but they are not believed to be related to any living mammals. (Carroll, 415.)

Morganucodontids (about four inches long to tail base) do indeed have a number of mammalian skeletal features, but they also have a fully-functional reptilian jaw joint (quadrate-articular) which distinguishes them from all living mammals. Evolutionists believe that over time the quadrate and articular bones of creatures such as morganucodontids worked their way into the middle ear to become the mammalian incus and malleus. There is, however, no fossil record of this transition. According to Carroll, “It is not yet certain when the malleus and incus became incorporated into the middle ear, but the grooves on the medial surface of the dentary that indicate their position of attachment in early Jurassic mammals are missing in Upper Jurassic genera.” (Carroll, 395.) Likewise, Kemp states, “The exact stage at which the therian ossicles evolved is unknown. Kuehneotherium, the earliest and most primitive therian, must have lacked them, for a groove to house the post-dentary bones is still present on the inner face of the dentary.” (Kemp, 293.)

Furthermore, the alleged migration and coordinated transformation of the quadrate and articular bones of the reptilian jaw into the incus and malleus of the mammalian middle ear is believed by evolutionists to have occurred separately in the Protherian (monotremes) and Therian (marsupials and placentals) lineages. Though Kemp suggested in the early 1980's that monotremes did not diverge until the Upper Jurassic, until after the hypothesized incorporation of the quadrate and articular into the middle ear, Carroll (p. 421) explains why this is unlikely. Thus, one finds Kermack and Kermack stating, “Since the Theria and the Atheria [now Protheria] separated from each other before the changes in the middle ear had taken place, these two major groups must have evolved mammalian auditory ossicles independently. This is a most surprising fact” [Emphasis supplied). (Kermack and Kermack, 64.)

The fossil record does not document the origin of any living orders of mammals: monotremes (Subclass Prototheria; Order Monotremata), marsupials (Subclass Theria; Infraclass Metatheria; Order Marsupialia), or orders of the placentals (Subclass Theria; Infraclass Eutheria; 20 or so orders). Regarding monotremes, Carroll says, “The skull of the platypus and echidnas are highly specialized in a manner divergent from those of all other groups of mammals, fossil or living.” (Carroll, 420.) The phylogeny at Carroll, 415 shows the Order Monotremata ending in question marks in the Lower Cretaceous. (The Lower Cretaceous find is a lower jaw that is described only as a possible monotreme. [Carroll, 421.] The next fossil evidence, some molar teeth and a partial lower jaw, is dated to about 100 million years later! [Carroll, 414, 421, 627.]) It is no wonder Carroll says, “The fossil record of monotremes provides little help in establishing their specific affinities.” (Carroll, 421.)

Marsupials and placentals (eutherians) are both known from the Upper Cretaceous, though isolated teeth dating to the Lower Cretaceous have been assigned to each group. (Carroll, 415, 431, 440, 445.) Carroll states, “We assume that marsupials and placentals diverged essentially simultaneously from a common ancestry that is represented by the early [Early Cretaceous] therians of metatherian-eutherian grade” [Emphasis added]. (Carroll, 430.) This assumed common ancestor is represented in the fossil record by only jaw parts and teeth. (Deltatherium is represented by a partial skull, but it dates from the Upper Cretaceous.) (Carroll, 429-430.) Regarding these teeth, Carroll says they “may belong to an ancestral stock that existed before the divergence of the modern infraorders” [Emphasis added]. (Carroll, 429.) Yet, other tribosphenic molars that cannot be classified as marsupialian or eutherian (“in between” teeth) appear contemporaneously with marsupials and placentals and are not considered to have belonged to ancestral creatures. (Ibid.)

Carroll notes, “A gap of approximately 20 million years separates these rare, early therians of metatherian-eutherian grade [the assumed common ancestor] from the comparatively rich fossil record of the Upper Cretaceous” (when marsupials and placentals unquestionably appear). (Carroll, 430.) The family Peramuridae, which is the assumed ancestor of the early therians of metatherian-eutherian grade, is itself known only from jaw parts and teeth. The only certain representative of Peramuridae (Peramus) appears about 25 million years before the appearance of the early therians of metatherian-eutherian grade (Late Jurassic vs. Aptian age of Early Cretaceous). (Carroll, 415, 428-429.) The presumed ancestor of the peramurids, Kuehneotherium, is again known from only jaw parts and teeth, which date from about 50 million years before the first peramurids (Sinemurian age of Early Jurassic vs. Late Jurassic). (Carroll, 414-415, 426.)

So according to Carroll, the origin of marsupial and placental mammals looks like that illustrated in Figure 1. Nearly all the living orders of eutherian mammals first appear in the fossil record between the Middle Paleocene and the Lower Eocene, a window of about 10 million years. (Carroll, 449.) (A tooth from the Upper Cretaceous has been classified as belonging to a primate. Ibid.) At least 30 distinct families are recognized by the Middle Paleocene. Ibid. Edwin Colbert describes the appearance of these diverse mammals as an “evolutionary explosion.” (Colbert, 280.)

Carroll believes that “[a]nimals with an anatomy like Kennalestes and Asioryctes [two Upper Cretaceous eutherian genera] could have given rise to nearly all subsequent placentals” [Emphasis added]. (Carroll, 447.) In other words, he sees nothing in these genera that eliminates them as possible ancestors. There is, however, no fossil evidence linking these genera to the multitude of families and orders that suddenly appear. As Carroll explains it, “The incomplete fossil record in the latest Cretaceous and early Cenozoic makes it very difficult to establish the nature of the interrelationships among the many groups of eutherians found in the later Tertiary.” (Carroll, 449.) (Tertiary is the first sub-era of the Cenozoic Era and comprises five epochs—paleocene through pliocene.)

George Gaylord Simpson casts the matter in a somewhat different light:

The most puzzling event in the history of life on earth is the change from the Mesozoic, the Age of Reptiles, to the Age of Mammals. It is as if the curtain were rung down suddenly on the stage where all the leading roles were taken by reptiles, especially dinosaurs, in great numbers and bewildering variety, and rose again immediately to reveal the same setting but an entirely new cast, a cast in which the dinosaurs do not appear at all, other reptiles are supernumeraries, and all the leading parts are played by mammals of sorts barely hinted at in preceding acts [Emphasis added]. (Kerwin, 42.)

Elsewhere Simpson notes:

The earliest and most primitive members of every order already have the basic ordinal characters, and in no case is an approximate continuous series from one order to another known. In most cases, the break is so sharp and the gap so large that the origin of the order is speculative and much disputed. (Simpson, 106.)

Given that mammals are considered the best documented case of megaevolution, one wonders how Carroll can declare, “modern amniotes are linked to their Paleozoic ancestors by a relatively complete sequence of intermediate forms” [Emphasis added]. (Carroll, 393.) Creationists and evolutionists really do see the world through different eyes.

Sources

Carroll, Robert L. 1988. Vertebrate Paleontology and Evolution. W. H. Freeman. New York.

Colbert, Edwin. 1980. Evolution of the Vertebrates. 3d ed. John Wiley & Sons. New York.

Gould, Stephen Jay. 1991. Eight (or Fewer) Little Piggies. Natural History 100 (no. 1, Jan.): 22-29.

Johnson, Phillip E. 1991. Darwin on Trial. Regnery Gateway. Washington, DC.

Kemp, T. S. 1982. Mammal-like Reptiles and the Origin of Mammals. Academic Press. New York.

Kermack, D. M. and K. A. Kermack. 1984. The Evolution of Mammalian Characters. Kapitan Szabo Publishers. Washington, DC.

Kerwin, Carlotta and others (editors). 1972. Life Before Man. Time-Life Books. New York.

Lewin, Roger. 1981. Bones of Mammals' Ancestors Fleshed Out. Science 212 (no. 6): 1492.

Romer, A. S. and L. W. Price. 1940. Review of the Pelycosauria. Geological Society of America Special Papers 28: 1-538.

Simpson, G. 1944. Tempo and Mode in Evolution. Columbia University Press. New York.

---

Home | Feedback | Links | Books | Donate | Back to Top

© 2024 TrueOrigin Archive.  All Rights Reserved.
  powered by Webhandlung