Part 6: The Gulf Between Reptiles and Mammals

Alan Feuerbacher

Beginning on page 80 the Creation book speaks of the gulf between reptiles and mammals. It explains some ways reptiles and mammals are different from one another, and implies they have always been different. But here again it treats the fossil record inaccurately. The record shows that in late Permian times a group of animals called therapsids (synapsids), which had many mammal-like characteristics, appeared rather suddenly, flourished for about ten million years, and then died out in a wave of mass extinction.¹⁵¹ Then, at the beginning of the Triassic Period, another group of therapsid "protomammals" appeared in the fossil record for a few million years, and were extinguished. Then another group appeared. A group of animals called thecodonts appeared about the same time as the third wave of therapsids, and as the Triassic Period wore on the therapsids diminished in number and the thecodonts increased. At the end of the Triassic, and the beginning of the Jurassic Period, most of the therapsids and thecodonts disappeared in another great wave of extinction. True dinosaurs then appeared. They experienced several waves of flowering and extinction, with the greatest extinction closing the Jurassic Period. During the following Cretaceous Period, birds appeared in the fossil record. At the end of the Cretaceous, dinosaurs became extinct, birds became far more numerous, and the Age of Mammals began.¹⁵²

A scientist, L. Beverly Halstead, said concerning the intermediate forms between mammals and reptiles:¹⁵³

There are two aspects of the theory of evolution which are all too frequently, and one suspects deliberately, confused: evidence of the processes by which it took place, the how of evolution, and the historical evidence of it actually having taken place...

Regarding the transition from reptile to mammal, [creationist author Duane] Gish writes:

'The two most easily distinguishable osteological differences between reptiles and mammals, however, have never been bridged by transitional series. All mammals, living or fossil, have a single bone, the dentary, on each side of the lower jaw, and all mammals, living or fossil, have three auditory ossicles or ear bones, the malleus, incus, and stapes. In some fossil reptiles the number and size of the bones of the lower jaw are reduced compared to living reptiles. Every reptile, living or fossil, however, has at least four bones in the lower jaw and only one auditory ossicle, the stapes.'

'There are no transitional forms showing, for instance, three or two jaw bones, or two ear bones. No-one has explained yet, for that matter, how the transitional form would have managed to chew while his jaw was being unhinged and rearticulated, or how he would hear while dragging two of his jaw bones up into his ear.'

That is very good, quite amusing, but this transition is in fact very well known; the functional reasons for it were worked out in the early 1960s by Professor A. W. Crompton of Yale University. The splitting of the main jaw-closing muscles into two blocks, the masseter and temporalis, had the effect of reducing the pressure on the jaw joint, and in consequence the bones became reduced in size. In the early growth stages these bones were loose in the region of the ear apparatus, and Dr. J. Hopson in 1966 showed exactly how this process of the jaw bones becoming incorporated as sound-amplifying bones in the middle ear took place.

This same process can actually be seen today taking place in kangaroos and hedgehogs during their embryological development. The exact transition between the reptilian and mammalian jaw joint was described some years ago by Professor Romer from new fossils discovered in the Argentine. The new jaw articulation was already functioning while the other was becoming defunct.

Another author, Michael Archer,¹⁵⁴ gives extensive evidence for the existence of intermediate forms between mammals and reptiles. His discussion is extremely detailed, and contains clear illustrations of the fossils that are being discussed. Particularly striking are the illustrations of the fossils showing the intermediate structures in the jaw and ear of a series of animals said to show the transition between reptile and mammal. Please take careful note of the fossil evidence:

Table 6.2 shows character pairs which separate modern mammals from modern reptiles. All of the structures listed, except the last six, involve parts of the skeleton and might, as a result, be expected to have some sort of fossil record. That being the case, if the evolutionary concept includes, as it does, the hypothesis that mammals evolved from reptiles (a hypothesis that was originally developed from study of living animals only), we might expect some evidence from the fossil record for transitional forms. Are they known? In grand abundance.

The fossil record shows evidence for a transition between reptiles and mammals. The evidence is based on detailed studies of jaw articulation in reptiles and mammals (both living and fossil) and the development of the bones of the mammalian middle ear, three of which appear to be the same as bones that help to articulate the reptilian jaw.

Soon after the 'true' (rather than transitional) reptiles had made their appearance, two distinctive subgroups of reptiles began to dominate the ecosystems of the day: the more conventional reptilian forms known as diapsids (such as dinosaurs, lizards and snakes) and the somewhat less conventional synapsids or mammal-like reptiles.

The oldest synapsids known are from the Carboniferous (i.e. about 315,000,000 years in age). They were small (50 cm) reptiles distinguished from others of their day most conspicuously by the presence of a temporal space in the cheek region of the skull. The subsequent 100 million years of synapsid evolution is represented by many thousands of fossils that document a number of different evolutionary trends within the group. Synapsids declined at the end of the Triassic, about 215 million years ago, at about the same time that primitive mammals made their first appearance in the fossil record. One synapsid group, however, survived until the Middle Jurassic. With extinction of this group the synapsids as such disappeared, although there is incontrovertible evidence from the fossil record that the first mammals were their descendants.

We can trace the development of mammalian characteristics in the synapsids by examining the skulls and other skeletal parts found at stratigraphic levels corresponding to successively younger times...

Synapsids from the Late Triassic such as Oligokyphus major had strikingly mammalian skeletons. Their features are so mammal-like that there has been debate as to whether they should be regarded as reptiles or mammals.

All of these features found in synapsids are standard equipment in living mammals but unknown in living reptiles. In other features, such as the relatively small brain and poor differentiation of the cheek teeth row into molars as well as premolars, synapsids are more reptile-like than mammal-like. This mixture of mammalian and reptilian features in synapsids is precisely what one would expect to find in a group of organisms transitional between reptiles and mammals.

The history of synapsids demonstrates very plainly that they were a group of reptiles that, for the first time, was experimenting with mammalian features. From their beginnings in the Carboniferous, they display ever-increasing degrees of 'mammal-ness' until, by the end of the Triassic, some lineages were clearly on the borderline between more advanced synapsids and primitive mammals (Figure 6.5).

In fact, the questions being debated now amongst vertebrate palaeontologists are not whether or not mammal-like reptiles were structural and temporal intermediates between reptiles and mammals but rather which particular group of synapsids gave rise to mammals. And even here, debates... are not any wider than the choice between [three types], all Middle-to-Late Triassic synapsids which were alive and kicking before the first primitive mammals appeared...

As noted above, the modern reptilian and mammalian jaw articulation systems are radically different. In the former, the articular bone of the lower jaw hinges with the quadrate bone of the skull. In modern mammals, the lower jaw consists of one bone, the dentary, which hinges against the squamosal bone of the skull. Skulls showing the synapsid-to-early mammal transition demonstrate that the mammalian condition was gradually acquired by posterior enlargement of the dentary bone until it contacted the squamosal bone (Figure 6.6).

The posterior extension of the dentary developed around the outside of the articular-quadrate system and (as the fossil record of synapsids and early mammals demonstrates), as the dentary-squamosal articulation enlarged, the articular-quadrate system diminished.

Archer then describes the fossils that show the changes from the reptile style jaw-earbone system to the mammalian.

Clearly, the first mammals to be recognized as such... are only marginally distinct from the structurally more primitive synapsids. Because of the fossil record, it is clear that the boundary between reptiles and mammals has no significant qualitative borderlines. There is a continuum of fossil forms from basically primitive reptiles, to primitive synapsid reptiles, to advanced mammal-like reptiles, to primitive reptile-like mammals, to advanced mammals of the kind that survive today. The fossil record clearly supports the predictions of the evolutionary model that intermediates between reptiles and mammals would be found.

By the Middle Jurassic (approximately 175 million years ago),... [all] three surviving groups of mammals, the monotremes, the marsupials and the placentals, lack postdentary bones attached to the dentary but have four small 'free' bones [which make up the mammalian middle ear]... These sound-transmitting middle-ear bones are adjacent to the posterior edge of the dentary in exactly the same relationship as the synapsid and primitive mammalian angular, articular, quadrate and incus (Figure 6.8). That they are the same four bones, performing in part the same function of sound transmission, is an inescapable conclusion.

In this regard, studies of the embryological development of the modern mammal jaw articulation system and middle ear are very interesting. Palmer (1913) followed their development in a bandicoot... When the young are born they are in effect two-week-old embryos. At this stage the young has a functional quadrate-articular jaw joint -- a normal reptilian system -- and uses it to open its tiny mouth very wide to grasp a teat in the pouch (Figure 6.8c). As the embryonic bandicoot develops in the pouch, the embryonic articular and quadrate become the malleus and incus of the middle ear. The angular matures between the articular and the dentary to become the ectotympanic for support of the developing tympanic membrane. The dentary develops posteriorly and the squamosal bone 'overgrows' the small malleus and incus to make contact with the dentary. By the time (less than sixty days later) that the young bandicoot first releases its grip on the teat it has, like all living mammals (Figure 6.8b) and most fossil mammals since the Middle Jurassic, a fully functional dentary-squamosal jaw articulation system and four 'free' bones in its middle ear.

While it is inappropriate to interpret ancestral adult conditions from the embryological conditions of descendants..., this embryological evidence strongly suggests that there is in living mammals an intimate developmental relationship between the jaw articulation system and the bones of the middle ear. This developmental relationship is precisely mirrored by what one finds in the fossil record of the reptile-to-mammal transition.

To recapitulate, from the fossil record there is clear evidence that the transition from the reptilian to the mammalian jaw articulation system was gradual and that it went bone-in-bone, as it were, with simultaneous changes in the middle ear. The net effect, from the modern mammal point of view, was that the dentary and squamosal replaced the articular and quadrate as the bones involved in articulation of the lower jaw to the skull. The replacement was gradual and involved an intermediate condition, represented by some of the most advanced synapsids as well as by some of the most primitive mammals, in which both sets of bones simultaneously provided support for the lower jaw. Three postdentary bones, the angular and articular of the lower jaw and the quadrate of the upper jaw, functioned simultaneously as transmitters of sound to the stapes which then passed the vibrations on to the inner ear. As the postdentary bones reduced in size and lost their commitment to jaw support, their capacity to transmit high-frequency sounds increased. Subsequent evolution amongst later mammals resulted in eventual confinement of the angular (as the ectotympanic which supports the tympanic membrane), the articular (as the malleus or 'hammer'), the quadrate (as the incus or 'anvil') and the stapes (the 'stirrup') to the middle ear in a position just behind the posterior end of the dentary. The embryological development of the jaw articulation system and the middle-ear region in modern mammals indicates the intimate developmental relationship between the bones which articulate the lower jaw and those which transmit sound, a relationship that is essentially the same as that demonstrated by advanced synapsids.

Clearly, the fossil record most definitely provides evidence in support of the existence of former 'links' between what are today significantly different kinds of organisms. In this case, the Triassic synapsids and morganucodontids firmly bridge two otherwise quite distinct classes of vertebrates, the reptiles and the mammals.

Now note what Creation said concerning the "evolution" of the mammalian jawbone-earbone assemblage, on page 80, in paragraph 24:

Mammals also have three bones in their ears, while reptiles have only one. Where did the two "extras" come from? Evolutionary theory attempts to explain it as follows: Reptiles have at least four bones in the lower jaw, whereas mammals have only one; so, when reptiles became mammals there was supposedly a reshuffling of bones; some from the reptile's lower jaw moved to the mammal's middle ear to make the three bones there and, in the process, left only one for the mammal's lower jaw. However, the problem with this line of reasoning is that there is no fossil evidence whatsoever to support it. [italics added] It is merely wishful conjecture.

Creation claims there is no fossil evidence for the reshuffling of the bones. Yet the above references cite many examples from the fossil record showing a sequence in time of animals that had bones that looked like they were in the process of being reshuffled. Some of this information goes back to the mid-1960s, yet Creation was published in 1985. Is the author of Creation really not aware of the fossil record? Who is really guilty of wishful conjecture?

In case the reader wishes to see for himself the graphic fossil evidence for all this change, he may consult the article "The Mammal-like Reptiles." This article, by the above referenced Dr. J. Hopson, contains many drawings showing how the skeletal structure of the mammal-like reptiles changed through time, as discussed above. In particular, it illustrates the changes from the fully reptilian jaw-earbone system to the fully mammalian. It seems incredible that such odd structures existed in animals, but they are in the fossil record for all to see. Typical of the information presented are Hopson's comments about above mentioned creationist author Duane Gish:¹⁵⁵

... Gish (1973) argues that fossils have never been found showing an intermediate stage between the reptilian many-boned lower jaw and single-boned middle ear and the mammalian single-boned jaw and three-boned ear. He writes: "There are no transitional forms showing, for instance, three or two jaw bones or two ear bones"... In this he is correct, of course; intermediates such as he describes never did exist. But his argument is a "red herring," intended, it would seem, to mislead the uninformed. As we have seen, the four reptilian jaw bones were incorporated into the mammalian middle ear mechanism as a unit.

Gish further objects to this proposed evolutionary transition because: "no one has explained yet,... how the transitional form would have managed to chew while its jaw was being unhinged and rearticulated or how it would hear while dragging its jaw bones up into its ear"... His tactic here is to discredit the idea of an evolutionary transformation by emphasizing the adaptive improbability or impossibility of the intermediate stages. But to do this he grossly misrepresents how the transformation actually occurred. As I have shown above, the lower jaw never was "unhinged"; it went from having one hinge (reptilian) to two hinges lying side-by-side (reptilian plus mammalian) back to a single hinge (this time, mammalian). Likewise, the post-dentary bones of the lower jaw were already connected to the stapes via the quadrate even in the earliest mammal-like reptiles...

In all the comings and goings of animal species, two things stand out: most of the time new animals that show up in the fossil record are not terribly different from those which came immediately before, and almost never are any fossils found where individual features appear to have been in some sort of transition state. So evolutionists have a major problem in explaining how novel structures come about, because they have very little evidence for it, yet new animals keep appearing in the fossil record, slightly different from those previous, giving an "appearance" of evolution. The Creation book, as well as all other Watchtower publications, denies there is a more or less continuous sequence of animal groups, one after the other, in the fossil record. In reading Creation, one gets the impression that everything paleontologists say about succession in the fossil record is spurious merely because they can't explain how new animals come about. In the section "The Gulf Between Reptile and Mammal" there is not one word about this succession. It is as if the Society does not want readers who are ignorant of the facts of paleontology to find out that there really was a succession of animals. At any rate, Creation's contention that no transitional links between major kinds of living things have ever been found in the fossil record (page 59) is merely a rhetorical device that obscures the real issues. That the book often quotes out-of-date reference material in support substantiates this contention.

The ignorance apparent in Creation with regard to the fossil record of the structural similarities between reptiles and early mammals is well illustrated by the two pages of quotations on pages 68-69, under the title "What the Fossil Evidence Says... about the Origin of Living Things." Under the sub-title "On Reptiles Becoming Mammals" the following is cited:

"There is no missing link [that connects] mammals and reptiles." -- The Reptiles

This quotation implies clearly, within the context of Creation's argument, that there are no intermediate forms between reptiles and mammals. But the context of the quotation shows something quite different. After talking about how clearly the ancient bird Archaeopteryx, shows a structure intermediate between reptiles and birds, The Reptiles says:¹⁵⁶

The record of the derivation of mammals from reptiles is both far longer and far more detailed than the history of birds -- and also, unfortunately, it is far less clear. It begins with the pelycosaurs of the late Carboniferous -- a group not far removed from the old stem reptiles. From these there radiated a great array of types known as mammal-like reptiles, and during the late Paleozoic and early Mesozoic these creatures were the dominant vertebrates on the land.

There is no missing link between mammals and reptiles, nor any single fossil type which, as Archaeopteryx does for birds, stands out clearly as half reptile, half mammal. If each mammalian feature could be traced to its point of origin, we might hope to put a finger on the first mammals. As it is, the case rests mostly on bones and teeth, and relying on such skeletal characters alone, we only see the ancestral forms slowly acquiring the skeleton and dentition that today we associate with mammals. We can only deduce the scheduling of the less solid attributes not susceptible to preservation in the rocks.

What The Reptiles actually says is consistent with the information on transitional forms presented in the last few pages -- there are so many intermediate forms that no single one can be assigned as a "missing link." This is opposite to what Creation says, and is consistent with what evolutionists have said all along -- there was a progression of life forms from reptile to mammal. Furthermore, The Reptiles was written in 1963, and from what we have seen previously, many more "intermediate forms" have been discovered since then.

The other quotation under the sub-title "On Reptiles Becoming Mammals" further shows how Creation's quoting out of context is misleading. It quotes the following:

"Fossils, unfortunately, reveal very little about the creatures which we consider the first true mammals." -- The Mammals

Speaking about the various forms of life that show skeletal structure intermediate between reptiles and mammals, The Mammals actually says:¹⁵⁷

Evolution works by infinitely slow stages, so there is no one point where we can say that, as if at the blowing of a trumpet, mammals were born from the parent reptile stock. An important early approach to mammalian structure was taken by lizardlike creatures known as pelycosaurs, which date back 280 million years or more -- long before the appearance of true mammals...

Related to the pelycosaurs was a group of even more mammal-like reptiles called therapsids, most of which were aggressive meat eaters. These had skulls and teeth which in many ways were quite similar to those of mammals, and limbs which were shifting from the sprawling "out-to-the-side" position of early amphibian and some land-dwelling reptiles to the fore-and-aft position of typical mammals...

The structure of the teeth, among other features, shows that pelycosaurs and therapsids, although not necessarily the direct ancestors of mammals, may certainly be regarded as their ancient uncles and aunts. The fossil record does not tell us whether therapsids were warm-blooded, whether they had hair instead of scales and whether they nursed their young. But judging from the progressive modifications of their hard parts, they may possibly have been developing these typically mammalian characteristics.

Fossils, unfortunately, reveal very little about the creatures which we consider the first true mammals. From the few remains which have been discovered -- mainly teeth and jaws -- we know that they were mostly tiny animals no bigger than rats and mice...

So Creation's quotation from The Mammals, which was written in 1963, is speaking of animals that could be considered the first true mammals -- animals that clearly display fully mammalian features, with no hint of "reptile-ness." This is quite different from what Creation implies. Again the full context of the quotation, and up-to-date information, says the opposite of what Creation does.

The Evolution of Man

The question of man's origin has been a controversial subject ever since Charles Darwin published The Origin of Species in 1859. The Society presents its views on the evolution of man in the seventh chapter of the Creation book, "'Ape-Men' -- What Were They?" The book discusses several topics: the small quantity of fossil bone bearing on the evolution of man, the claim that there are no "missing links," the difficulties paleoanthropologists have in reconstructing man's "family tree," how the interpretation of fossil evidence has changed in the course of time, what sort of creatures the various primate and hominid fossils really represent, and how dating methods conflict with the Society's interpretation of Genesis. Creation's seventh chapter clearly illustrates the Society's ignorance of what science really says and shows how the Society only presents evidence that supports its views, while suppressing negative information. To prove this we will look at the current state of knowledge of human evolution, and then discuss how the Creation book ignores or misinterprets the evidence bearing on this knowledge.

First, it must be stated that while paleoanthropologists do not agree on many details of human evolution, they do agree that man evolved from an apelike ancestor. This disagreement on details has not been made generally known to people outside the profession, although there have been some excellent books written about some of the difficulties.^{158, 159} Many books have been written by non-professionals, with varying degrees of competence.^{160, 161, 162} A common theme in the non-professional books is that the ancestry of man in evolutionary terms cannot be proven rigorously. They mean in the sense of being able to perform repeatable experiments, or to prove in the sense of a court trial, and few evolutionists would disagree. But in the same way, the ancestry of man in the Biblical view cannot be proven. The reader should keep these particular notions of proof in mind, because many creationists, as well as the Creation book, avoid defining what they mean by "proof." While there is much about the supposed evolution of man that cannot be satisfactorily explained, there is a great deal of circumstantial evidence that is consistent with it and that creationists have not dealt with satisfactorily. It is this sort of evidence that Creation fails to give due credence and generally misrepresents.

Second, it must be stated that many people become emotionally involved in questions regarding human origins, and for very good reasons. This has caused many paleontologists to go astray or become overly dogmatic about current theories. This emotionalism is at the heart of the evolution/creation controversy. Roger Lewin, a paleontologist and science writer, put it nicely:¹⁶³

Given the exquisite sensitivity of the topic, it is perhaps not surprising that the study of human origins, palaeoanthropology, is more emotional, more intense, and more given to flights of fancy than are most sciences. Although no science is the cool objective Baconian pursuit often idealistically portrayed, palaeoanthropology has been characterized by a distinctly greater-than-average level of eccentricity and private and public squabbles. And, just as any science reflects to some extent the current interests of the society in which it is being practised, so too has palaeoanthropology manifested passing fashions that can be traced to societal fads.

The latest thinking about the evolution of man is based on a combination of fossil and molecular evidence. Fossil evidence consists of bones, footprints, tools and such. Molecular evidence comes from studying the differences among the proteins and DNA of living animals and using this to catalog the "genetic distance" between various types of animals. As Blueprints said:¹⁶⁴

The best current knowledge of how we evolved depends on a blend of fossil and molecular evidence. It produces a better understanding of our ancestry than either could have done by itself. There is a bone story to be told; then it must be edited by molecules.

The fossil and molecular evidence are fairly consistent with one another in pointing to evolutionary relationships among fossil and living animal groups,¹⁶⁵ although molecular studies have revealed some surprises. The evidence can be interpreted as consistent with a creator who reused genetic material, albeit one who worked very differently from what fundamentalists infer from the Bible.

Footnotes

¹⁵¹ Bakker, op cit, pp. 406-414.

¹⁵² ibid, pp. 415-424.

¹⁵³ Ashley Montagu, ed., Science and Creationism, p. 247, Oxford University Press, New York, 1984.

¹⁵⁴ D. R. Selkirk and F. J. Burrows, editors, Confronting Creationism: Defending Darwin, pp. 82-92, New South Wales University Press, Kensington NSW Australia, 1988.

¹⁵⁵ James A. Hopson, "The Mammal-like Reptiles: A Study of Transitional Fossils," The American Biology Teacher, vol. 49, no. 1, p. 25, January, 1987.

¹⁵⁶ Archie Carr, The Reptiles, pp. 40-41, Time-Life Books, 1963.

¹⁵⁷ Richard Carrington, The Mammals, pp. 36-37, Time- Life Books, 1963.

¹⁵⁸ Niles Eldredge & Ian Tattersal, The Myths of Human Evolution, Columbia University Press, New York, 1982.

¹⁵⁹ Roger Lewin, Bones of Contention, Simon and Schuster, New York, 1987.

¹⁶⁰ William R. Fix, The Bone Peddlers: Selling Evolution, Macmillan Publishing Company, New York, 1984.

¹⁶¹ Phillip E. Johnson, Darwin On Trial, Regnery Gateway, Washington, DC, 1991.

¹⁶² Marvin L. Lubenow, Bones of Contention, Baker Book House, Grand Rapids, Michigan, 1992.

¹⁶³ Roger Lewin, Human Evolution: An Illustrated Introduction, p. 25, W. H. Freeman and Company, New York, 1984.

¹⁶⁴ Maitland A. Edey and Donald C. Johanson, Blueprints, p. 325, Penguin Books, New York, 1989.

¹⁶⁵ ibid, p. 358.