Mammal-like reptiles were a very diverse, widely spread group of reptiles that had a number of characteristics that are found in mammals. Taking evolution as a fact and that mammals evolved from reptiles, evolutionists logically assume that the presence of these mammalian characteristics supports the theory that mammals originated from one or more groups of creatures within the group of these mammal-like reptiles.
Creationist scientists, of course, do not accept these assumptions. They emphasize that vertebrates are extremely diverse. Some weigh less than 90 grams, while others weigh many tons. Some are limited to life on land, with significant differences in the way they move. Others are skilled fliers, while some live exclusively in the sea. It would be truly surprising if vertebrates from different classes did not share many common characteristics.
Looking at this problem from a broad perspective, we must say that all evidence supports the creationist view, as there is no evidence in the fossil record linking vertebrates to any presumed ancestor among invertebrates. If vertebrates themselves did not evolve, as it certainly seems they did not, the evolutionary theory is dead, and it is pointless to speculate about the evolution of groups within vertebrates, or within any other part. If we look at the problem from a more limited perspective, if we focus our attention on reptiles, mammal-like reptiles, and mammals, then there is evidence supporting every viewpoint.
Evolutionary view on the evidence
Let us first explore the evidence that supports the assumption that mammals evolved from reptiles. In doing so, let us look at the geological column and time differences through the eyes of evolutionists, as must be done if the evidence is to be evaluated within the assumptions of the evolutionary model. “Primitive” mammal-like reptiles appear simultaneously in the fossil record with “reptile-like” reptiles in the late Upper Carboniferous period. From the beginning, these creatures had characteristics that are now associated with mammals, but other mammal-like characteristics, such as the secondary palate and the double occipital joint, are missing. Later, in the Permian and Triassic periods, “advanced” mammal-like reptiles appeared that had these and other mammalian characteristics, including highly differentiated teeth and a single enlargement of the dental bone, as well as a reduction in the size of other bones in the lower jaw. Finally, at the Triassic-Jurassic boundary, or approximately 180 million years ago according to the evolutionary geological timescale, there was a creature that possessed many of these mammal-like characteristics and that, although it still had a fully functional reptilian type of jaw joint (quadrate-articular), also had, alongside this reptilian jaw joint structure, a mammalian type jaw joint structure (squamosal-dental). Then, we had a creature that evolutionists designate as the first mammal.
Some general observations
All mammal-like reptiles are placed in the subclass Synapsida. Evolutionists believe that these creatures form a natural group, where all share a common ancestor, and this ancestor appeared very early in the history of reptiles. They are actually a diverse group of creatures. The only diagnostic feature common to all members was the presence of a lateral opening in the temporal region, which is a condition found only in this group. Mammal-like reptiles are further divided into two orders, Pelycosauria, which constitutes what is considered the earliest members of mammal-like reptiles, and Therapsida, which evolutionists believe constitute more advanced types. Pelycosauria were found in large numbers only in the Texas red layers (Lower Permian), although a few were found in Europe. Therapsida were found mainly in South America, Russia, and in the Karoo Supergroup of South Africa. Romer calls this arrangement in these two orders illogical, but convenient. Within these two orders, families, genera, and species are arranged in a sequence that is believed to represent, or at least generally, the order in which these reptiles were created.
Does this sequence represent the true temporal sequence of the origin of these creatures, or is this sequence arranged so as to fit the pre-conceived ideas about evolution? It seems that there is at least some basis for doubt that many of these creatures are placed in this sequence according to the demands of evolutionary theory. Then, this sequence is presented as evidence for this theory!
A few quotes from literature can be cited to document the above-mentioned doubt. Kemp argues that:
“The record is also geographically patchy, and no locality provides more than a short segment of the history of mammal-like reptiles, and in many cases, one region contains fossils from only one period. Similarly, no taxonomic group of synapsids occurs worldwide, although it is almost certain that at least one of them had a wide distribution during life.”
It seems quite clear that since no locality provides more than a short segment of the so-called history of mammal-like reptiles, different segments must be compared with an imagined evolutionary sequence, or at least according to some scheme determined by assumptions based on indirect evidence.
Especially suggestive is Kemp’s statement that: “…synapsids are also of use to geologists as stratigraphic indicators of the relative age of the continental rocks in which they were found…” In other words, fossils, in this case, fossils of mammal-like reptiles, are used to date rocks. But how do we know the relative age of mammal-like reptiles if we use them to determine the age of rocks? By their order in the evolutionary scheme adopted by evolutionists, of course!
Romer’s statement is equally indicative:
“Although correlation with marine stages is possible in most cases, the general evolutionary theory about therapsids and other included forms suggests that layers with pelicosaurs should be considered as early Permian, the Tapinocephalus zone of Bofora and early Russian horizons as middle Permian, the Endothiodon and Cistecephalus zones of Bofora and their equivalents as late Permian. Olson proposed that one middle term be eliminated, and that the entire stretch of Russian and African layers (Double Mountain or Pease River American finds) be called late Permian. This seems like an uneven division, and the usual early-middle-late Permian terminology is more in line with a broad view of the Permian evolutionary picture.”4
Thus, it appears that Romer’s arrangement of these various deposits in a proposed time sequence is determined by “the general evolutionary story of therapsids” and “a broad view of the Permian evolutionary picture.” It is no surprise, then, that what is presented in the literature, especially in textbooks, as a temporal sequence for mammal-like reptiles generally aligns with the temporal expectations. This is precisely constructed to match those.
However, it can be suggested that the methods of radiometric dating used for dating fossils represent a method independent of any assumed stratigraphic correlation or evolutionary story. Derek Ager, a professor of geology at University College, Swansea, Wales, reacted angrily to such claims. He says:
“My frustrations as a geologist were brought to the boiling point by an article by David Challinor on historical natural history museums (New Scientist, September 29, 1983, p. 959), and especially his comment that ‘Originally, paleontologists dated fossils by identifying the geological layers in which they were found. Today, the age of fossils is determined by measuring the decay of radioactive carbon or through the decay of their radioactive potassium into argon’… Since William Smith at the beginning of the 19th century, fossils have still been the best method for dating and correlating the rocks in which they occur… As for the fact that this trust has been transferred to physicists and the measurement of isotopic decay, this leads to rage! It is certain that such studies give dates over millions of years, with large error margins… I cannot imagine cases of radioactive decay being used for dating fossils.”5
Thus, it seems that fossils are used for dating rocks, not the methods of radiometric dating. This seems to lead us back in a circle, because how do we date fossils? In the final analysis, everything seems to be based on an assumed evolutionary sequence.
Since mammal-like reptiles are supposedly advanced from very early reptilian forms to very mammal-like forms and finally to mammals, it would be assumed that these changes resulted in more or less stable progress from reptiles to mammals. In fact, mammal-like reptiles possessed a mosaic pattern of traits found in both reptiles and mammals. For example, Colbert noted that:
“It is not easy to determine the exact line of mammal ancestors among theriodont reptiles. Some theriodonts are very advanced towards mammals in certain traits, but relatively primitive in others. Among all theriodonts, the mix of advanced and conservative characteristics is so diverse that it is impossible to point to any particular group and define it as the one progressing most positively toward mammals.”6
In other words, although one of these so-called mammal-like reptiles might possess certain characteristics that are said to be mammalian, such as, for example, a secondary palate and differentiated teeth, it could also possess characteristics considered primitive reptilian. According to Colbert, this mix of “advanced” and “primitive” traits was so characteristic of theriodonts (“advanced” mammal-like reptiles) that it is impossible to select any one as the actual ancestor line leading to mammals.
“Does the possession by one creature of some characteristics that are also found in another species inevitably indicate that it is a transitional form between those two species? In support of a negative answer to this question, we can quote numerous examples. Seymouria was one creature that possessed some characteristics found in amphibians and some characteristics found in reptiles. It would therefore be supposed to constitute a ‘perfect transitional form’ between amphibians and reptiles. It probably could not have been such an intermediary, as was earlier shown in this chapter.
Another example is the living platypus. This creature is a mammal, yet has a duck-like bill, feet with flippers, and lays eggs, along with possessing other characteristics that can be called reptilian. It has characteristics of mammals, reptiles, and birds, and could perhaps be called a ‘primitive’ mammal. It probably could not have been the ancestor of mammals because it appeared very recently, about 150 million years too late to be the ancestor of mammals! In fact, this unique combination of structural traits makes it impossible to suggest that it arose from any specific class of vertebrates or that it could have been an intermediary between any two species. Many similar examples can be cited. Thus, the existence in one creature of characteristics possessed by animals of two different types does not inevitably indicate that it is an intermediary between those two types.
Furthermore, mammal-like reptiles are not just mosaics that include characteristics generally associated with reptiles and mammals, but many possessed structures that are not found in living quadrupeds, either mammals or reptiles. Thus, Kemp says:
‘For a fossil structure, it is unlikely that it will resemble a living structure in any major detail, yet the differences themselves may indicate important functional differences. Indeed, in many cases concerning mammal-like reptiles, there are structures that simply have no reasonable analogies among living quadrupeds.’
Clearly, all such creatures would be too specialized to be ancestors of mammals (or any other creature, for that matter).
In fact, the gaps in the supposed evolutionary line leading from reptiles to mammals are so systematic that no creature can be considered a direct ancestor of another. This holds true whether we are talking about lower taxonomic levels (species and genus) or higher categories (families and orders). Thus, Kemp writes:
‘The gaps in the lower taxonomic level, species and genera, are virtually universal in the fossil record of mammal-like reptiles. There is not a single adequately documented case in which it would be possible to trace a transition, species by species, from one genus to another.’
Regarding gaps at higher taxonomic levels, Kemp argues:
‘The apparent speed of morphological change in major lineages of mammal-like reptiles varies. The sudden appearance of new higher taxa, families, and even orders, immediately after a mass extinction with all characteristics more or less developed, implies a very rapid evolution.’
‘The sudden appearance of new taxa… with all characteristics more or less developed’ is precisely what would be expected based on the creationist model of creation, but evolutionists must attempt to explain this contradictory evidence by using “ad hoc” assumptions of “very rapid evolution” (such as “punctuated equilibrium” or “punctuated equilibrium”).”
The Great Gap in Mammal Evolution
Mammal-like reptiles appeared, supposedly, exactly at the beginning of the appearance of reptiles, they gradually became more and more like mammals through the Permian and Triassic periods, and finally culminated with the appearance of the first true mammals at the end of the Triassic. At this time, the mammal-like reptiles disappeared, although they had previously been the most numerous among all reptile species, and were spread all over the world. Since evolution is presumed to involve natural selection, in which better-adapted creatures reproduce in greater numbers and thus gradually replace the less adapted ones, we would now expect mammals, who eventually triumph, to thrive in great numbers and dominate the world.
However, something very strange happened. Namely, mammals disappeared from the scene for the next 120 million years! During this long period of supposed time, “reptile-like” reptiles, including dinosaurs and many other land creatures, sea and flying reptiles, flooded the earth. As for mammals, however, the “most adapted” ones who replaced the mammal-like reptiles could hardly be found anywhere. Most of the fossil remains of mammals discovered to date, from the Jurassic and Cretaceous periods, which supposedly spanned over 120 million years, could fit into two hands. Most of these mammals are represented by only a few teeth.
If evolution is presumed to involve the survival of the best-adapted, and among them are those who reproduce in greater numbers, the origin of mammals represents something very strange, indeed. Since they survived in very small numbers, evolution obviously occurred through the survival of the unadapted!
Evolutionists would like us to believe that the evolution of mammals continued for 120 million years. For 120 million years, according to evolutionary theory, mammals, who obviously existed during that very long period of time in extremely small numbers, remained evolutionarily hidden as rather small generalized forms. Then, in an instant of geological time, most reptiles, including dinosaurs, disappear, and suddenly, 32 orders of mammals appeared, all highly specialized, so that they could be classified as primates, whales, bats, rodents, odd-toed ungulates, even-toed ungulates, etc.
In case it is suspected that we might have exaggerated this case due to creationist bias, let’s consider the comments on this matter by George Gaylord Simpson, one of the leading world evolutionary scientists. He says:
“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 though a curtain suddenly fell on a scene where reptiles, especially dinosaurs, held all the leading roles, in great numbers and bewildering diversity, and was immediately lifted again revealing the same scene, but with a completely new division in which dinosaurs do not appear at all, other reptiles are supernumerous, and all leading roles are held by species of mammals that had only been hinted at in the previous acts.”
Again, we could emphasize that the previous acts covered 120 million years on the evolutionary time scale. To prevent any evolutionist from pretending there is no serious problem here, we will remind them that Simpson says this is the most puzzling period in Earth’s history. The problem disappears, of course, if the assumption of evolution is rejected and the creationist model of origin is accepted.
Unbeaten gap between reptiles and mammals Two mammal-like reptiles, Morganucodon (also known as Eozostrodon) and Kuehneotherium, supposedly represent the most defined transitional forms between reptiles and mammals. Thousands of fragments have been found representing many individuals of Morganucodon. The material consists of teeth, jaws, and fragments of the skull and postcranial skeleton from Wales, a complete skull and jaw from the Lufeng red deposits in China, as well as material from two similar genera found in the red deposits of the Karoo Supergroup in South Africa. Only isolated teeth and jaw fragments of Kuehneotherium have been discovered from Wales. These creatures were very small, about 10 cm in length. All this material is placed in the upper Triassic on the geological column.
There are creatures that are, it is claimed, possessed of a jaw joint of the mammalian type alongside the jaw joint of the reptilian type. In mammals, there is one bone in each half of the lower jaw, called the dental, because it carries the teeth, and this bone directly connects with the squamous region of the skull. Reptiles have six bones in each half of the lower jaw. The connection of the jaw to the skull is indirect, via the articular (one of the jaw bones), which connects to the quadrate bone, and which is not found in mammals.
Another fundamental difference between reptiles and mammals is that all reptiles, living or fossil, have one bone in the ear, resembling a stick, known as the columella. Mammals have three bones in the ear: the ossicle, hammer, and anvil.
Evolutionists support that the ossicle corresponds to the columella, and that the quadrate and articular bones of reptiles somehow shifted to the ear, becoming respectively the hammer and anvil of the mammalian ear. No explanation is given as to how intermediaries could hear while this was happening.
The next difficulty with the above idea is the fact that when thousands of reptilian fossils are found to possess one ear bone and multiple jaw bones, and thousands of mammalian fossils are found to possess ear bones and one jaw bone, no fossil creature has ever been found that would represent an intermediate stage, such as one that would have three bones in the jaw and two bones in the ear.”**
This translation is a direct word-for-word translation, with no omissions or alterations. Let me know if you need further assistance!
Morganucodon and Kuehneotherium had fully developed reptilian bones in their lower jaw. Furthermore, there was no reduction in the functional significance of the reptilian (quadrate-articular) jaw joint, although these creatures are presumed to be intermediates between reptiles and mammals, allegedly possessing a mammalian (squamosal-dental) jaw joint along with a reptilian jaw joint. Kermack argues:
“The strangest characteristic of the extra-jaw bones of Morganucodon is their cynodont character. In comparison with such an advanced cynodont as Cynognathus, the present extra bones show no reduction, neither in size nor in the complexity of structure. In fact, the actual reptilian jaw joint was relatively as powerful in mammals, Morganucodon, as it was in the reptile Cynognathus. This was completely unexpected.”
These authors say that evolutionists have long believed that there was a progressive weakening of the jaw bone in the transition from early to late cynodonts, and this weakening continued in the first mammals (cynodonts were “advanced” mammal-like reptiles). This is what would be predicted if mammals evolved from reptiles and there was a gradual evolutionary replacement of the reptilian jaw joint with a mammalian jaw joint. Kermack and his associates now reject this idea because the reptilian jaw joint of Cynognathus was exceptionally strong, and the lower jaw of Morganucodon closely resembled that of Cynognathus.
In any case, there is no doubt that Morganucodon had a powerful standard jaw joint of the reptilian type. Although almost all the available material related to Morganucodon consists of disarticulated bones (individual bones made up of fragments), a part of the jaw found with the quadrate bone was still in contact with the articular bone, leaving no doubt about the existence of a reptilian jaw joint in this creature. But, did Morganucodon and Kuehneotherium, with this reptilian jaw joint, also have a point of contact between the dental and squamosal bones, and if so, does this indicate the initial formation of a mammalian type jaw joint?
Kermack and his colleagues certainly believe that this is established for Morganucodon and Kuehneotherium (for this, it is said that it has been achieved in several other groups of mammal-like reptiles14). What is the basis for this belief? Regardless of how strongly this belief is held, it is based on inference. The evidence is extremely fragmentary, and fossils showing the dental bone in actual contact with the squamosal bone of the skull are not available. In fact, not even a single intact lower jaw is available, but all these specimens are reconstructed from fragments.
What is the evidence for a dental-squamosal joint in these creatures? This evidence consists of a supposed condyle on the dental bone. A condyle is a round protruding part at the end of a bone and forms a ball and socket joint with the hollow part (called a fossa) of the other bone. In mammals, there is a very prominent condyle on the rear part of the dental bone that connects it with the squamosal bone of the skull. The squamosal bone contains a fossa to receive the condylar bone, and this contact forms the jaw joint. In Morganucodon and Kuehneotherium, the dental bone is sufficiently wide to encourage the belief that it made contact with the squamosal bone, and the supposed point of contact with the dental bone is called the condyle.
Whether the dental bone of these creatures actually made contact with the squamosal can only be inferred. But, if there was actual contact between the dental and squamosal bones, could it be said that this constitutes a mammalian type of jaw joint coexisting with the reptilian jaw joint? We must remember that these creatures had a fully developed, powerful reptilian jaw joint. The anatomy required for such a jaw joint, including the arrangement and method of attachment of the musculature, the arrangement of blood vessels and nerves, etc., must be quite different from that required for a mammalian jaw joint. How then could a powerful, fully functional reptilian jaw joint coexist with a mammalian jaw joint?
It is significant that similar claims regarding the existence of a double jaw joint in Probainognathus and Diarthrognathus have been questioned. Probainognathus and Diarthrognathus are presented as very close, hypothetically direct, ancestors of mammals. Regarding Probainognathus, Kemp claims:
“Another much-cited characteristic of Probainognathus that links it with mammals is the secondary contact between the dental and squamosal bones. In fact, there is some doubt as to whether there is any actual contact between them (Crompton and Jenkins, 1979)…”15
Regarding Diarthrognathus, Gow claims:
“The ichthyosaurus Diarthrognathus, from the Clarens Formation (Cave Pescari) (Crompton, 1958), is generally considered to fulfill a morphological step intermediate between cynodonts and mammals; more specifically, it is thought to have both a mammalian and a reptilian jaw joint. However, several of Crompton’s interpretations of the morphology of the lower jaw and its connection with the skull were incorrect. Some, but not all of these, appeared in print (Crompton, 1972).”16
Thus, we see that the idea that there existed both a mammalian and a reptilian jaw joint in these creatures has been questioned within evolutionary circles. These creatures are all extinct. All that remains is extremely fragmentary fossil material. The way these creatures are reconstructed and their function visualized is often influenced by preconceived ideas of what should be expected. Evolutionists feel confident that reptiles evolved into mammals. This would then require the replacement of a reptilian jaw joint with a mammalian one. With extremely fragmentary and incomplete material available, it is possible that what is “seen” is what is desired to be seen before it is truly evident. Finally, and this is conclusive, not a single intermediary has been found between an animal with a powerful, fully functional reptilian jaw joint and an animal with a single, powerful, fully functional mammalian jaw joint. All reptiles, whether Morganucodon, Kuehneotherium, or whichever, had fully completed reptilian bones in the jaw, and all mammals, whether fossils or living, have a single bone on each side of the lower jaw. No intermediaries have been found.
Reptilian vs Mammalian Ear
Further, we cannot separate the evidence related to the jaw joint from that related to the auditory apparatus. As previously mentioned, evolutionists believe that since the bones in the reptilian jaw, except for the dental bone, gradually became freed from their function in the jaw, they were now free either to disappear or to take on some new function. Thus, the square and articular bones became free (they were, by the way, firmly attached to the dental bone in Morganucodon) and somehow found their way into the middle ear to ultimately become the hammer and anvil, in sequence. This would require that the stapes (columella) of the reptile become freed from its attachment to the tympanum (eardrum), and that the retroarticular part of the articular bone become attached to the eardrum (since the articular bone of the reptile supposedly became the hammer of the mammal, which is attached to the eardrum). Somehow, as all this was happening, the square bone of the reptilian ancestor must have gained freedom, moved into the middle ear, and inserted itself between the stapes and the hammer. As all this maneuvering took place, all of these bones had to somehow reshape and rearrange in the most marvelous way so that they could function in a completely new auditory apparatus.
Anatomical problems associated with such a proposed process are far greater than simply imagining how two bones, precisely shaped to form a powerful and efficient jaw joint, could move into the middle ear and be reshaped into the hammer and anvil, which are precisely designed to function with the modified stapes in a very different auditory apparatus, while the creature continues to chew and swallow all the while! No matter how insurmountable this problem might seem, it pales into relative insignificance when considering the fact that the essential organ of hearing in mammals is the organ of Corti, which no reptile possesses, nor is there any evidence that it could even hint at where this organ might have come from.
The organ of Corti is an extraordinarily complex organ. It is recommended that the reader consult one of the standard anatomy texts for its description. There is no help, except for amazement, before this complex and marvelously designed organ. It has no homolog in reptiles. There are no possible structures in reptiles from which it could have originated. It must have been created de novo, as it was completely new.
According to the theory of evolution, all evolutionary changes occur as a result of errors during gene reproduction. Every change brought about by such mutations, if the form survived, must have been superior to the previous forms. Thus, if evolution is true, we must believe that a series of thousands and thousands of errors in a wonderfully coordinated manner created the organ of Corti to function in the ear, which at the same time had to be rebuilt, accordingly, while retaining the two bones from the jaw, which had to be redesigned. Furthermore, each intermediate step not only had to be especially functional, but it had to be superior to the previous step. And after all this had been achieved, we still have reptiles and birds today with the same old-fashioned reptilian and avian auditory apparatuses, which are just as efficient as the corresponding mammalian apparatuses.
Other Necessary Changes
Further, while all these above-mentioned wondrous changes were happening, these creatures also invented (through genetic errors) many other wondrous new physiological and anatomical organs and processes, including a new method of reproduction, mammary glands, temperature regulation, hair, and a new method of breathing.
The structure of the thoracic cage in mammals fundamentally differs from that of reptiles. In reptiles, it connects with the sternum via the coracoid bones and forms part of the rib cage. This is not the case in mammals. In reptiles, the front part of the sternum is solid and incapable of expansion. In mammals, the sternum can expand. In mammals, the thoracic and abdominal cavities are separated by the diaphragm, a fibrous-muscular organ. Since reptiles do not have a diaphragm, their sternum is not a closed box. As a consequence of the above, reptiles cannot breathe like mammals. They cannot alternately expand and contract the sternum as mammals do. They must breathe through their mouth.
In reptiles, there is no structure that is in any way similar to or homologous with the mammalian diaphragm. In reptiles, no structure has been found from which a diaphragm could have developed. A complex structure had to be created “de novo” (and through a series of errors!) in order to perform a function that was already satisfactorily carried out in a completely different way by the presumed reptilian ancestor.
Summary
Whatever they may be called, Morganicodon and Kuehneotherium, they possessed fully complete reptilian bones in the jaw, a powerful, fully functional jaw joint, and, as standard, a single-bone reptilian ear. On the other hand, all mammals, living or fossil, have one jaw bone, a fully functional mammalian jaw joint, and a very different hearing apparatus, which includes three bones in the middle ear and a completely unique and extremely complex structure – the Corti organ. As briefly described earlier, there are many other fundamental differences between reptiles and mammals. It is argued here that the changes could not have happened gradually and that the idea that a reptile gradually evolved into a mammal is scientifically unsustainable. Thus, a thorough, detailed, and objective analysis of the anatomy, physiology, and paleontology of reptiles and mammals best supports the thesis that these two types of vertebrates have always been separate and distinct, with no genetic connection between them.
- Literature
- Ref 1. A. S. Romer, Vertebrate Paleontology, 3rd ed., U. of Chicago Press, Chicago, 1966.
- Romer, Ref. 1, p. 173.
- T. S. Kemp, Mammal-Like Reptiles and the Origin of Mammals, Academic Press, New York, 1982, p. 3.
- Kemp, Ref. 26, p. 4.
- A. S. Romer, Bull. Indian Geol. Assoc. 2(1-2):17 (1969).
- D. Ager, New Scientist 100:425 (1983).
- E. H. Colbert, Evolution of the Vertebrates, John Wiley and Sons, New York, 1980, p. 246.
- Kemp, Ref. 26, p. 9.
- Kemp, Ref. 26, p. 319.
- Kemp, Ref. 26, p. 327.
- G. G. Simpson, quoted in Life Before Man, Time-Life Books, New York, 1972, p. 42.
- Kemp, Ref. 26, p. 255.
- K. A. Kermack, F. Mussett, and H. W. Rigney, Zool. J. Linn. Soc. 53(no. 2):157 1973.
- D. M. Kermack, K. A. Kermack, and F. Mussett, Zool. J. Linn. Soc. 47(No. 312):418 1968.
- A. W. Crompton and F. A. Jenkins, Jr., “Origin of Mammals” in Mesozoic Mammals, J. A. Lillegraven, Z. Kielan-Jaworowska, and W. A. Clemens, eds., University of California Press, Berkley, 1979, p. 62.
- Kemp, Ref. 26, p. 271.
- C. E. Gow, Paleontologia Africana, 24:15 (1915).