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Lukousaurus: The first “raptor”?

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In either the late 1930s or in the year 1940, the front half of a fossilized skull was discovered in Huangchiatien (also called Dahungtien), Yunnan Province, China. It was named and described as Lukousaurus yini by Chung Chien Young in the year 1940 (Young, Chung Chien. “Preliminary notes on the Lufeng vertebrate fossils”. Bulletin of the Geological Society of China, 20 (3-4) (1940). Pages 235-239), and it was described further in 1948 (Young, Chung Chien. “Further notes on Gyposaurus sinensis Young. Bulletin of the Geological Society of China, 28 (1-2) (1948). Pages 91-103). The holotype specimen is housed within the Institute of Vertebrate Paleontology and Paleoanthropology, which is located in Beijing, China, and it has been given the identification code of “IVPP AS V.23”.

Below is a drawing of the partial skull made by Tracy Ford.

Partial skull of Lukousaurus yini. Illustration by Tracy Ford. From The Dinosaur Society Dinosaur Encyclopedia, written by Don Lessem and Donald F. Glut. New York: Random House, Inc., 1993. Page 279. Image used with permission.

Lukousaurus lived during the early Jurassic Period, approximately 195 million years ago (MYA). Based upon the size of its remains, which consist only of the front half of its skull, it may have been six to eight feet long.

Some may cite Lukousaurus for its old age, but what grabbed my attention was when I read that the teeth had serrations only on the back edge. I had been told that this is a feature that is only found in the carnivorous dinosaurs commonly called “raptors”, more properly known as Deinonychosauria. This clade is divided into two families: Dromaeosauridae and Troodontidae. According to this source, all dromaeosaurids had teeth which were serrated only along the posterior (back) edge, and some troodontids had this feature as well. Although all raptor dinosaurs are found during the Cretaceous Period, paleontologists have hypothesized for years, based upon phylogenic analysis, that the ancestor of the raptors appeared millions of years earlier during the Jurassic Period. It may well be that Lukousaurus is that ancestor. Could it be that Lukousaurus is the oldest-known “raptor”?

Unfortunately, the information which I had read concerning raptor tooth serrations was later shown to be incorrect. I proposed this idea of Lukousaurus being a basal raptor on an online paleontology forum. In response, I was contacted by Jim Kirkland, a well-known paleontologist from Utah, who corrected me by saying that Deinonychosaurians actually DO have serrations on both the front and back edges of their teeth, but their anterior (front) serrations are much smaller than the posterior (back) serrations. In fact, in many specimens, the front serrations are so small that they are practically non-existent – you need a microscope to see them. This shows the danger of basing a hypothesis upon incorrect information, because this taints your reasoning and your conclusions.

I myself have not seen the actual specimen of Lukousaurus, nor do I know anyone who has. The claim is that Lukousaursus had absolutely no serrations on the front edge of their teeth. However, it was also claimed in another source that raptor dinosaurs didn’t have any serrations on the front edges of their teeth either – a statement that was proven false. Is it true that Lukousaurus had no anterior tooth serrations, or are the serrations so tiny that they cannot be seen with the naked eye?

If it is true that Lukousaurus had absolutely no serrations on the front edges of its teeth and only had serrations on the back edges of its teeth, then this invalidates the hypothesis that it might be a basal Deinonychosaurian, and it must belong to some other dinosaur group, if indeed it is a dinosaur at all; it has been proposed by at least one person that it might, in fact, be a crocodilian. However, what if Lukousaurus possessed teeth that are similar to raptors, with prominent serrations on the posterior edge, and miniscule serrations on the anterior edge, serrations that are so small that they were not noticed? If this is the case, then it is possible that Lukousaurus might, in fact, be a very primitive raptor dinosaur.

Evidence to back up this claim is very thin. But let’s assume for the time being that it is a dinosaur. Is there any evidence which suggests that Lukousaurus might be a member of Deinonychosauria, or perhaps a close relative?

The first piece of evidence to support the hypothesis that Lukousaurus is a very primitive raptor is its age. Paleontologists have speculated that raptors appeared during the Jurassic Period, specifically either the early or middle Jurassic. The reason why is because birds are believed to have been descended from raptors, and the oldest-known birds come from the late Jurassic – therefore, raptors must have appeared earlier. Lukousaurus comes from the early Jurassic.

The second bit of evidence is geographic location. Raptors are believed to have originated in Asia and then spread elsewhere. Lukousaurus comes from China, specifically the Lower Lufeng Formation in Yunnan Province, China. It would have shared the landscape with the prosauropods Gyposaurus, Lufengosaurus, and Yunnanosaurus. It would have also lived alongside the early carnosaur Sinosaurus and the ornithischian Tatisaurus (we’re not sure if it was an ornithopod or an early thyreophoran; it might have looked similar to Scutellosaurus).

The third piece of evidence, which I have already mentioned before, is tooth structure. Lukousaurus’ teeth are very thin and blade-like, and are sharply recurved backwards. What is especially noteworthy is that it is claimed that the teeth have serrations only on the posterior edge. This feature was stated to also be present in raptors, but as I said earlier, this was dis-proven.

This brings about the fourth piece of evidence, although this is subject to intense debate – taxonomy. It has been hypothesized that Lukousaurus was a coelurosaur, and the coelurosaurs were the ancestors of Maniraptora. This clade includes the ornithomimids, the therizinosaurs, the oviraptorosaurs, and the raptors. However, due to the incredibly fragmentary nature of Lukousaurus – it is, after all, known only from one fragmentary snout – its phylogenic position is uncertain. Yes, it has been classified as a coelurosaur, but it has also been classified as a ceratosaur, and even as a crocodilian. So, using taxonomy as evidence is incorrect; it’s more likely an opinion rather than evidence.

Lukousaurus might be an early raptor, but personally, I think it is an advanced coelurosaur which shows the beginning of raptor-like traits. This would make Lukousaurus a borderline coelurosaur-maniraptoran. Until more material from this particular species is uncovered, any assertions made as to which clade this creature belongs to will always be tinged with uncertainty.

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