I recently read an article in the Institute for Creation Research's periodical Acts & Facts titled "Devils, Dinosaurs, and Squirrel Fossils," by Brian Thomas. Normally, as a creationist, I am very supportive of ICR's publication but, in this case, it would seem that Thomas' presuppositional expectations have trumped his biological research training. The article begins with the statement: "The concept of dinosaurs living in a distant time populated by unique and now mostly extinct plants and animals has captured generations of students and moviegoers, but actual fossil finds keep contradicting this view." Unfortunately, this first sentence is not true, taken the way it is meant. The ecosystems of dinosaurs were "populated by unique and now mostly extinct plants and animals." The key word there being "mostly." It is actually kind of obvious. The vast majority of vertebrates uncovered from dinosaur-bearing fossil sites are, well, dinosaurs. And the habitats of the dinosaurs, dominated by tree ferns and cycads, are unlike most modern ecosystems. It is true that many of the plants and invertebrates found with dinosaurs are alive today, but the assemblages seen in the fossil record are completely unlike those of today. For some examples of a complete list of taxa found in a dinosaur ecosystem, see my paleobiology blog. But to say dinosaur ecosystems were "unique," is a very subjective and relative opinion.
My real beef with the article was Thomas' examples of animals that have been found with dinosaur fossils and are still alive today. He apparently believes that these animals should be synonymous with today's mammals, but that is a very naive assumption. First, he mentions the remarkable Repenomamus robustus fossil, found with young dinosaurs inside its stomach. In Thomas' article, it is implied that Repenomamus is an extinct representative of the Tasmanian devil. Ecologically, perhaps it is. But taxonomically, it is certainly not. Repenomamus has no living relatives and the osteology (features of the bones) are most like that of other extinct mammals (triconodonts). Perhaps Thomas' misinterpretation of the animals identity is due to the fact that it is often illustrated to look something like a Tasmanian devil externally. It probably did, but the bones deny any taxonomic affinity.
Next on Thomas' list are the Euharamiyida. Once again, this is a taxonomically distinct group that superficially resembled squirrels in some ways. Thomas claims that they are indeed "plain old squirrels," but that is untrue. Thomas seems to look no further than the artistic renderings of these creatures. Osteologically, euharamiyidans are most similar to multituberculate mammals, another completely extinct group known for their somewhat rodent-like incisors (but entirely unique molars). Both euharamiyidans and multituberculates looked like rodents superficially, but rodents supposedly outcompeted those groups before the Ice Age.
Thomas briefly mentions "shrew-like" mammals that lived alongside dinosaurs, but wisely avoids concluding that they really were shrews. Rather, they only "closely resemble treeshrews." Closely may be to strong a word. I am personally not familiar with any treeshrew-like mammals from dinosaur-bearing fossil sites, but I am aware that the shrew or hedgehog-like tenrec, which is alive today in Madagascar, has been found in dinosaur-bearing sediments. I'm surprised Thomas didn't mention an indisputable example of a "living fossil" mammal like the tenrec.
Castorocauda was described as analogous to modern beavers in a Science article, as Thomas points out. However, Thomas suggests that "it was a beaver." This is again a misinterpretation of an animals that only superficially resembles a beaver. Really, the tail is the only resemblance to a beaver: the teeth are more like those of a seal. In fact, it is about as far a mammal can be from a beaver as any. As a member of the Cynodontia, it is not often considered a mammal proper but, rather, a "mammal-like reptile" or a "mammaliafrom." It is believed that mammals evolved from creatures like Castorocauda but calling Castorocauda a mammal at all may be stretching things. It possessed many characteristics of reptiles. It just seems that the media is more excited about the animal's beavertail than anything else, so they forgot to mention that it isn't even a true mammal.
The final fossil on Thomas' list is Vintana. He quotes the media authoritatively as they declare an "ancient groundhog-like mammal discovered in Madagascar." And groundhog-like it was. But to say it was a groundhog is extremely speculative at best. First, only a skull is known for the species. As far as one can tell from a single skull, it's resemblance to groundhogs begins and ends with the incisors. A quick look at the skull shatters any hope that it is at all related to a groundhog. Even the way its muscles would be forced to move for operating its jaws is vastly different from any rodent. The skull actually looks very little like a groundhog's, comparatively speaking. Vintana was a unique animal with only a couple relatives, known exclusively from the fossil record. Like some of Thomas' other misidentified mammals, it was similar to the extinct multituberculate group.
Tracks are not usually a good point of evidential proof for living mammals alongside dinosaurs, but Thomas mentions some that he believes were opossum tracks, to his "non-expert eye." I am grateful that he is honest enough to admit that he is not an expert on the subject. And indeed he is not. I don't think Thomas intended to be dishonest or deceptive in any way for the writing of his article, but it demonstrated an appalling lack of thorough research. It is a warning to all of us creationists: we should never to be to quick to find "evidence" for our beliefs. "Evidence" seldom points clearly in any given direction--it is our interpretation that does the pointing. In Thomas' eagerness to find his expected and anticipated evidence for creationism (or his understanding of creationism), he potentially deceived many trusting readers who will parrot his false information to others. When word reaches secular scientists' ears, they will marvel at the ignorance of creationists. Let's avoid any misunderstandings and be more careful with our own presuppositions. In conclusion: "Squirrels, treeshrews, beavers, Tasmanian devils, and other rodent kinds" are not known as "fossils with dinosaurs." It might make you feel better to believe that, but there is no evidence for it. I wanted to let everyone know to avoid any potentially embarrassing conversations in the future.
References for Repenomamus:
Averianov, A.O., and A.V. Lopatin. 2011. "Phylogeny of Triconodonts and Symmetrodonts and the Origin of Extant Mammals." Doklady Biological Sciences 436(1): 32-35.
Li, J., Y. Wang, Y. Wang, and C. Li. 2001. "A New Family of Primitive Mammal from the Mesozoic of Western Liaoning, China." Chinese Science Bulletin 46(9): 782-785.
Montellano, M., J.A. Hopson, and J.M. Clark. 2008. "Late Early Jurassic Mammaliaforms from Huizachal Canyon, Tamaulipas, Mexico." Journal of Vertebrate Paleontology 28(4): 1130-1143.
Reference for the Euharamiyida:
Bi, S., Y. Wang, J. Guan, X. Sheng, and J. Meng. 2014. "Three New Jurassic Euharamiuidan Species Reinforce Early Divergence of Mammals." Nature 514: 579-584.
References for Castorocauda
Ji, Q., Z.X. Luo, C.X. Yuan, A.R. Tabrum. 2006. "A Swimming Mammaliaform from the Middle Jurassic and Ecomorphological Diversification of Early Mammals." Science 311(5764): 1123-1127.
References for Vintana
Krause, D.W., S. Hoffmann, J.R. Wible, E.C. Kirk, J.A. Shultz, W. von Koenigswald, J.R. Groenke, J.B. Rossie, P.M. O'Connor, E.R. Seiffert, E.R. Dumont, W.L. Holloway, R.R. Rogers, L.J. Rahantarisoa, A.D. Kemp, and H. Andriamialison. 2014. "First Cranial Remains of a Gondwanatherian Mammal Reveal Remarkable Mosaicism." Nature 515: 512-517.
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