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The Mammal-like reptiles | |
Duane T. Gish, Ph.D.
IMPACT
No. 102, December 1981
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Introduction
The "mammal-like" reptiles were a highly varied, widely distributed group ofreptiles that had a number of characteristics that are found in mammals.Assuming evolution to be a fact and that mammals must have arisen fromreptiles, evolutionists thus quite logically assume that the presence ofthese mammal-like characteristics provide support for the theory thatmammals arose from one or more groups of creatures within these mammal-likereptiles.
Creationists do not accept these assumptions, of course. They point out that
the vertebrates are extremely varied. Some weigh less than an ounce, whileothers weigh several hundred tons. Some are restricted to the land, withconsiderable differences in mode of locomotion. Others are skillful fliers,while others live exclusively in the sea. Evolution or no, it would besurprising indeed if vertebrates from different classes did not share manycharacteristics in common.
Looking at the problem with a broad overview, we would have to say that theevidence is all in favor of the creationist view, since there is not a shredof evidence in the fossil record to link the vertebrates to any supposedancestor among the invertebrates. Even though this transition is supposed tohave taken 100 million years, not a single intermediate has ever beendiscovered. If vertebrates themselves have not evolved, as seems certain,evolution theory is dead, and it is foolish to speculate about evolution ofgroups within the vertebrates, or within any other division. If we look atthe problem with a more limited perspective, if we confine our attention tothe reptiles, mammal-like reptiles, and mammals, then there is evidencewhich supports each viewpoint.
The Evolutionary View of the Evidence
Let us first examine the evidence which supports the assumption that mammalshave evolved from reptiles. In doing so, we will look at the geologicalcolumn and time spans through the eyes of evolutionists, as must be done ifthe evidence is to be evaluated within the assumptions of the evolutionmodel. "Primitive" mammal-like reptiles appear simultaneously in the fossilrecord with the "reptile-like" reptiles in the late Pennsylvanian Period.From the start these creatures possessed certain characteristics which arenow associated with mammals, but other mammal-like characteristics, such asa secondary palate and a double occipital condyle, were lacking. Later, inthe Permian and then in the Triassic "advanced" mammal-like reptilesappeared that possessed these and other mammalian characteristics, includinghighly differentiated teeth and an enlargement of the dentary bone of thelower jaw and a reduction in size of the other bones of the lower jaw.Finally, at about the Triassic-Jurassic boundary, or approximately 180million years ago on the evolutionary geological time scale, a creatureexisted, it is maintained, which possessed all of these mammal-likecharacteristics and which, though it still retained a fully-functionalreptilian type (quadrate-articular) jaw-joint, also possessed, side-by-sidewith this reptile jaw-joint, a mammalian type (squamosal-dentary) jaw-joint.We then had a creature which evolutionists designate as the first mammal.
Some General Observations
When evolutionists wish to cite evidence for evolution, they almost alwayspoint to the alleged reptile-to-mammal transition, Archaeopteryx (a supposedintermediate between reptile and bird) and the horse series. Gould andEldredge exclude Archaeopteryx as a transitional form, calling it a strangemosaic which doesn't count as a transitional form [1], and Eldredge, althoughhe does believe that horses have evolved, states that there are notransitional forms between the different types of fossil horses. [2] Thus,there seems to be pitifully little evidence for evolution if indeed millionsof species have gradually evolved through hundreds of millions of years. Ifthis has happened, our museums should be overflowing with vast numbers ofunquestionable transitional forms. There should be no room for question, nopossibility of doubt, no opportunity for debate, no rationale whatsoever forthe existence of the Institute for Creation Research. Instead of these vastnumbers of undoubted transitional forms that should exist, however, the casefor evolution rests on a very few doubtful examples, one of which is thealleged reptile to mammal transition.
Let us now look at the so-called reptile to mammal transition from acritical viewpoint. We wish first to make some general observations. Doesthe possession by a creature of some characteristics which are possessed bya second class of creatures necessarily indicate that it is transitionalbetween these two classes? To answer that question in the negative, we cancite numerous examples. Seymouria was a creature that possessed somecharacteristics found in amphibians and some characteristics found inreptiles. It should therefore constitute a "perfect transitional form"between amphibians and reptiles. It could not possibly have been such anintermediate, however, since it first appeared at about the beginning of theMiddle Permian, which is at least 20 million years too late on theevolutionary time scale to be the ancestor of the reptiles, which hadalready made their appearance in the preceding Pennsylvanian Period.
Another example is the living duck-billed platypus. This creature is amammal, and yet it has a duck-bill, webbed feet, and lays eggs, in additionto possessing other characteristics that might be called reptilian. It hascharacteristics of mammals, reptiles and birds, and perhaps could be calleda "primitive" mammal. It could not possible be ancestral to mammals,however, because it appeared very recently, about 150 million years too lateto be the ancestor of mammals! In fact, this unique combination ofstructural features renders it impossible to suggest that it arose from anyparticular class of vertebrates or that it could have been an intermediatebetween any two classes. Many similar examples could be cited. Thus theexistence in a single creature of characteristics possessed by animals oftwo different types does not necessarily indicate that this creature is anintermediate between these two types.
Mammal-like reptiles appeared supposedly right at the start of the reptiles,gradually became more mammal-like through the Permian and Triassic, andfinally culminated in the appearance of the first real mammals at the end ofthe Triassic. At this time the mammal-like reptiles essentially becameextinct, even though earlier they had been amongst the most numerous of allreptiles, world-wide in distribution. Since evolution is supposed to haveinvolved natural selection, in which the more highly adapted creaturesreproduce in larger numbers and thus gradually replace the less fit, wewould now expect the mammals, triumphant at last, to flourish in vastnumbers and to dominate the world. A very strange thing happened, however.For all practical purposes, the mammals disappeared from the scene for thenext 100 million years! During this supposed vast stretch of time, the"reptile-like" reptiles, including dinosaurs and many other land-dwellingcreatures, the marine reptiles, and the flying reptiles, swarmed over theearth. As far as the mammals were concerned, however, the "fittest" thatreplaced the mammal-like reptiles, they were almost nowhere to be found.Most of the fossil remains of mammals recovered to date from the Jurassicand Cretaceous Periods, allegedly covering more than 100 million years,could be contained in two cupped hands. Most such mammals are represented bya few teeth. If evolution is supposed to involve survival of the fittest,and the fittest are defined as those that reproduce in larger numbers, theorigin of mammals represents something very strange, indeed. Since theysurvived in very few numbers, evolution apparently occurred by survival ofthe unfit!
Now another very strange event (from an evolutionary viewpoint) took place.Very suddenly (on an evolutionary geological time scale), most reptiles,including all the dinosaurs, marine reptiles and flying reptiles,disappeared and were abruptly replaced by a great variety of land-dwelling,flying, and marine mammals, which appear fully-formed. As documented in anearlier Impact article (No. 87—"The Origin of Mammals", September 1980),each specific type of mammal, such as bats, whales, primates, hoofedmammals, rodents, carnivores, insectivores, and monotremes (duck-billedplatypus and spiny anteater) appear in the fossil record with their basiccharacteristics complete at the very start. It is strange that all that canbe produced to document the evolution of the mammals are some generalizedforms, but not one shred of evidence can be produced to document theevolution of a single specific mammal, such as bats, whales, rodents orprimates.
A Critical Review of the Evidence
The Jaw-joint
Now let us consider the two creatures, Morganucodon and Kuehneotherium thatsupposedly represent the most definitive transitional forms between reptilesand mammals. These are the creatures that, it is claimed, possessed themammal-type jaw-joint side by side with the reptile-type jaw-joint. Inmammals there is a single bone in each half of the lower jaw, called thedentary, since it bears the teeth, and this bone articulates directly withthe squamosal area of the skull. Reptiles have six bones in each half of thelower jaw. Articulation of the jaw with the skull is indirect, with thearticular (one of the bones of the jaw) articulating with the quadrate boneof the skull, a bone not found in mammals. Another fundamental differencebetween reptiles and mammals is the fact that all reptiles, living orfossil, have a single bone in the ear, a rod-like bone known as thecolumella, which connects the eardrum to the tympanum. Mammals possess threebones in the ear, the stapes, malleus and incus which connect the drum tothe tympanum. Evolutionists maintain that the stapes corresponds to thecolumella and that the quadrate and articular bones of the reptile somehowmoved into the ear to become, respectively, the incus and malleus bones ofthe mammalian ear. No explanation is given how the intermediates managed tohear while this was going on.
Another difficulty with the above notion is the fact that while thousands offossil reptiles have been found which possess a single ear bone and multiplejaw bones, and thousands of fossil mammals have been found which possessthree ear bones and a single bone in the jaw, not a single fossil creaturehas ever been found which represents an intermediate stage, such as onepossessing three bones in the jaw and two bones in the ear.
Morganucodon [3] and Kuehneotherium [4] each possessed a full complement of thereptilian bones in its lower jaw. Furthermore, there was no reduction in thefunctional importance of the reptilian (quadrate-articular) jaw-joint, eventhough these creatures are supposed to be intermediates between reptiles andmammals, allegedly possessing a mammalian (squamosal-dentary) jaw-joint inaddition to the reptilian jaw-joint. Kermack, et al., state "The moststriking characteristic of the assessory jaw bones of Morganucodon is their cynodont character. Compared with such a typical advanced cynodont asCynognathus, the accessory bones present show no reduction, either in sizeor complexity of structure. In particular, the actual reptilian jaw-jointitself was relatively as powerful in the mammal, Morganucodon, as it was inthe reptile Cynognathus. This was quite unexpected." [5] (We would interjecthere that we emphatically reject the idea of calling Morganucodon a mammal.)
These authors relate that it has long been generally held by evolutioniststhat there was a progressive weakening of the jaw joint in passing fromearly to late cynodonts, which weakening continued into the first mammals(the cynodonts were "advanced" mammal-like reptiles). This is what one wouldpredict if mammals evolved from reptiles and there was thus a gradualevolutionary replacement of the reptilian jaw-joint by the mammalianjaw-joint. Kermack and his co-workers now reject this idea since thereptilian jaw-joint of Cynognathus was extremely powerful and the lower jawof Morganucodon closely resembled that of Cynognathus.
There is no doubt whatsoever therefore, that Morganucodon had a powerfulstandard reptilian type jaw-joint. Although almost all of the availablematerial related to Morganucodon consists of disarticulated bones (theindividual bones are scattered about) and almost all of the individual bonesconsist of fragments, a fragment of a jaw was recovered with the quadratebone still in contact with the articular bone, leaving no doubt about theexistence of a reptilian jaw-joint in this creature. But did Morganucodonand Kuehneotherium have, in addition to this reptilian jaw-joint, a point ofcontact between the dentary and squamosal and, if so, does this indicate theincipient formation of a mammalian type jaw-joint?
Kermack and his colleagues certainly believe that this has been establishedfor Morganucodon and Kuehneotherium (it is also said to have beenaccomplished in several other groups of mammal-like reptiles [6]). What is thebasis for this belief? Regardless of how strongly this belief is held, itrests on inference. The evidence is extremely fragmentary and no fossils areavailable showing the dentary in actual contact with the squamosal of theskull. In fact, not even a single intact lower jaw is available, all suchspecimens being reconstructed from fragments.
What is the evidence for a squamosal-dentary joint in these creatures? Thisevidence consists of an alleged condyle on the dentary. A condyle is arounded process at the end of a bone forming a ball and socket joint withthe hollow part (termed the fossa) of another bone. In mammals there is avery prominent condyle on the posterior end of the dentary which articulatesto the squamosal bone of the skull. The squamosal contains a fossa for thereception of the condyle and the contact forms the jaw-joint. WithMorganucodon and Kuehneotherium, the dentary extends sufficientlyposteriorly to encourage the belief that it made contact with the squamosaland the alleged point of contact on the dentary is called the condyle.
Whether the dentary bone of these creatures actually made contact with thesquamosal can only be inferred. But if there had been a real contact betweenthe dentary and squamosal, could it be said that this constituted amammalian jaw-joint which existed alongside the reptilian jaw-joint? We mustremember that these creatures had a fully-developed, powerful reptilianjaw-joint. The anatomy required for such a jaw-joint, including thearrangement and mode of attachment of musculature, must be quite differentfrom that required for a mammalian jaw-joint. How then could a powerful,fully-functional reptilian jaw-joint be accommodated along with a mammalianjaw-joint?
The Reptilian vs. the Mammalian Ear
Furthermore, we cannot divorce the evidence related to the jaw-joint fromthat related to the auditory apparatus. As mentioned earlier, evolutionistsbelieve that as the bones in the reptilian jaw, except for the dentary,gradually became relieved of their function in the jaw they were now freeeither to evolve out of existence or to assume some new function. Thus, thequadrate and articular bones of the jaw became free (they were, by the way,firmly attached to the dentary in Morganucodon) and somehow worked their wayinto the middle ear to eventually become the incus and malleus, respectively.
Now the anatomical problems associated with such a postulated process arevastly greater than merely imagining how two bones precisely shaped toperform in a powerfully effective jaw-joint could detach themselves, forcetheir way into the middle ear, reshape themselves into the malleus andincus, which are precisely engineered to function with a remodeled stapes ina vastly different auditory apparatus, while all at the same time thecreature continues to chew and to hear! As insuperable as this problemappears to be, it pales into relative insignificance when we consider thefact that the essential organ of hearing in the mammal is the organ ofCorti, an organ not possessed by a single reptile, nor is there any evidencethat would provide even a hint of where this organ came from.
The organ of Corti is an extremely complicated organ. It is suggested thatthe reader consult one of the standard texts on anatomy for a description.One cannot help but marvel at this complex and wondrously designed organ. Ithas no homologue in reptiles. There is no possible structure in the reptilefrom which it could have been derived. It would have had to have beencreated de novo, since it was entirely new and novel.
According to evolution theory, all evolutionary changes occur as the resultof mistakes during the reproduction of genes. These are called mutations,and each change brought about by such mutations which survived must havebeen superior to preceding forms. Thus, if evolution is true, we mustbelieve that a series of thousands and thousands of mistakes in amarvelously coordinated fashion gradually created the organ of Corti tofunction in an ear which at the same time had to be reengineeredaccordingly while dragging in two bones from the jaw which had to beredesigned. Furthermore, each intermediate stage not only had to be fullyfunctional but actually must have been superior to the preceding stage. Andafter all this was accomplished, we still have reptiles and birds today withthe same old-fashioned reptilian auditory apparatus which is just asefficient as the corresponding mammalian apparatus [7]).
Other Required Changes
Furthermore, while all of the above miraculous changes were occurring, thesecreatures also invented (by genetic mistakes) many other marvelous newphysiological and anatomical organs and processes, including a new mode ofreproduction, mammary glands, temperature regulation, hair, and a new way ofbreathing.
The structure of the thoracic girdle of the mammal differs fundamentallyfrom that of the reptile. In the reptile it articulates with the breastboneby means of the coracoid bones and forms part of the thorax. This is not thecase with mammals. In reptiles the fore part of the thorax is rigid andincapable of expansion. In mammals the thorax is expansible. In mammals thethoracic and abdominal cavities are partitioned by the diaphragm, afibro-muscular organ. Since reptiles have no diaphragm, their thorax is nota closed box. As a consequence of the above, reptiles cannot breathe asmammals do. They cannot alternately expand and contract the thorax as is thecase with mammals. They must breathe buccally.
There is no structure in a reptile that is in any way similar or homologousto the mammalian diaphragm. There is no structure found in a reptile fromwhich it could have been derived. Again, a complicated structure had to becreated de novo (and by mistake!) to perform a function that was alreadybeing very satisfactorily performed in a different manner in the assumedreptilian ancestor.
Summary
Whatever one chooses to call them, Morganucodon and Kuehneotherium possessedthe full complement of reptilian bones in the jaw, a powerful,fully-functional reptilian jaw-joint and the standard single-bone reptilianear. On the other hand, all mammals, living or fossil, have a singlejawbone, a fully developed mammalian jaw-joint, and a vastly differentauditory apparatus involving three bones in the middle ear and a totallyunique and extremely complex structure, the organ of Corti. As describedbriefly above, there are many other fundamental differences between reptilesand mammals. It is argued here that these changes could not possibly haveoccurred gradually, and thus the notion that a reptile gradually evolvedinto a mammal is scientifically unacceptable.
| References
[1] S.G. Gould and Niles Eldredge, Paleobiology, V. 3, p. 147 (1977). Return to Text
[2] Niles Eldredge, as quoted by Boyce Rensberger (New York Times News Service) in the Houston Chronicle, Sec. 4, November 5, 1980, p. 15. Return to Text
[3] K.A. Kermack, F. Mussett and H.W. Rigney, Zool J. Linn. Soc., V. 53, No. 2 p. 157 (1973). Return to Text
[4] D.M. Kermack, K.A. Kermack and F. Mussett, Zool. J. Linn. Soc., V. 47, No. 312 p. 418 (1968). Return to Text
[5] Ref. 3, p. 119. Return to Text
[6] A.W. Crompton and F.A. Jenkins, Jr., "Origin of Mammals" in Mesozoic Mammals, J.A. Lillegraven, et al., Eds., U. of California Press, Berkeley, 1979, p. 62. Return to Text
[7] G.A. Manley, Evolution, V. 26, No. 4 p. 608 (1972). Return to Text
Other articles that may be consulted: A.W. Crompton and F.A. Jenkins, Jr., "Mammals from Reptiles: A Review of Mammalian Origins", Ann. Rev. Earth and Plan. Sci., V. 1, pp. 131-153 (1973). A.W. Crompton and Pamela Parker, "Evolution of the Mammalian Masticatory Apparatus", Am. Sci., V. 66, pp. 192-201 (1978).
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"Vital Articles on Science/Creation"
September 1980
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