Vertebrate Paleontology

Friday, November 20, 2015

Dinner or Dinosaur? Both!


This Thanksgiving, don’t think of the yearly tradition as just carving up a turkey. In reality, you’re dissecting your very own dinosaur.

KU Paleontologist David Burnham studies ancient raptors of all sizes. Studying these ancient relatives fills the gaps between raptors of the past and the turkeys we eat today. Upon studying this lineage, one can see that turkeys and raptors have much more in common than you may think, despite differences in how we traditionally picture a “bird.”

“The public’s perception of what a bird may be might not be the definition a scientist would use,” said Burnham.

The public largely defines birds by their feathers and flight capabilities. By comparison to their ancestors, not only do both prehistoric raptors and modern birds share feathers, but many living birds also either rarely or never use flight including ostriches, emus, cassowaries and turkeys. 

“The loss of flight has evolved several times throughout that lineage,” said Burnham. “If we want to draw a line when theropod dinosaurs became strictly avian, well, we’re still refining that even today due to the enormous amount of new discoveries.”

What’s important to remember is that dinosaurs never fully became extinct. The ones that survived mass extinction merely changed. Birds such as turkeys and chickens share their lineage with theropods, or two-legged meat-eating dinosaurs. The skeletal structures of turkeys and extinct theropods such as Velociraptor, Bambiraptor and Microraptor retain several similarities in particular. 

Here are some points to look for while dissecting your “dinosaur” this Thanksgiving:

  • Wishbone - The furcula, or wishbone, is a major connection between the turkey and its ancient theropod ancestors. The furcula is made up of two formerly separate collarbones, fused together. This evolutionary change aided in flight capabilities of ancient raptors such as Microraptor, and continues to help modern birds, such as turkeys, reach liftoff.
  • Wings - The turkey wing deserves careful inspection. The fleshed-over tip is where claws protruded from theropod arms such as those of Velociraptor, Bambiraptor, and even the massive Dakotaraptor. Imagine those on your dinner plate! As theropod dinosaurs evolved, their arms became longer and those claws were covered by flesh forming wings suitable for extended flight – an easily recognizable feature of avian species we see today.

  • The fleshed-over tip of a turkey wing, where raptor claws once protruded to snatch prey
  • Thighs and drumsticks - These are often the most sought after pieces of the feast, and still quite similar to the legs of theropods. This leg structure allowed raptors to reach impressive ground speeds; Velociraptor is thought to have been able to run as fast as 40 miles per hour! The turkey on your table is no slowpoke either thanks to this ancient design, with a top running speed of 25 miles per hour. 

Turkey hips (left) as compared to  those of a pre-historic raptor (right)

While the turkey still possesses many remarkable features harkening back to its raptor relatives, there are some things we can be thankful were lost during evolution.

“Of course, turkeys don’t have teeth,” said Burnham, “and that’s probably a good thing.”

Wednesday, February 18, 2015

New Paper: Evolution of multicuspid teeth in a Triassic fish from Utah

the holotype of Hemicalypterus, USNM V 23425, composite image of the part and counterpart.

Just yesterday, my newest paper was published online in the journal The Science of Nature: Naturwissenschaften about a rather unusual fish from the Upper Triassic Chinle Formation of southeastern Utah. The fish, Hemicalypterus weiri, was a deep-bodied, disc-shaped fish, with enameled ganoid scales covering the anterior portion of its flank, and a scaleless posterior half, which presumably aided in flexibility while swimming. Although Hemicalypterus was first described in the 1960s (Schaeffer, 1967), recent collecting trips recovered many new specimens of Hemicalypterus, and I decided to reinvestigate this enigmatic fish as part of my dissertation research.

While cleaning specimens of Hemicalypterus at the University of Kansas Vertebrate Paleontology prep lab, I noticed rather unusual teeth on the lower jaw that I had exposed from the rock matrix. These teeth look like a mouthful of little forks, and there were at least six individual teeth on the lower jaw. As I prepared other specimens, I found that these teeth were also on the premaxillae. Each tooth has a long cylindrical base and a flattened, spatulate edge with four delicate, individual cusps. I hadn't seen anything like this before in other fossil fishes, and so I started searching the literature and talking to other ichthyologists.

The multidenticulate teeth on the premaxilla of one of the specimens

Well, as it turns out, this tooth morphology has evolved multiple times in several independent lineages of teleost fishes, and quite often fishes with similar dentition scrape algae off of a hard substrate. These teeth indeed act like little forks (or "sporks" might be more appropriate) for these herbivorous/omnivorous fishes. Examples of extant fishes with similar teeth include freshwater forms such as the algae-scraping cichlids and characiforms, as well as many marine forms that are key in controlling algae growth in coral reef environments, such as acanthurids (surgeonfishes, tangs) and siganids (rabbitfishes). Of course, these modern-day fishes also feed on other things (e.g., phytoplankton), but algae is often the primary staple, and these fishes use this specialized dentition for a specific feeding behavior.

The same teeth as above, but under fluorescent lighting

So while it is impossible to prove definitively what a species of fish that lived over 200 million years ago fed upon (without gut contents being preserved....or a time machine), it is still safe to infer that Hemicalypterus occupied an ecological niche space similar to algae-scraping cichlids or other modern-day herbivorous fishes and may have scraped algae off of a hard substrate, based on this unusual tooth morphology and its similarity to modern forms. 

The multidenticulate teeth of a modern-day algae-scraping cichlid, Labeotropheus

This discovery also extends evidence of herbivory in fishes clear back to the Early Mesozoic, whereas prior to this discovery it was assumed that herbivory evolved in the Middle Cenozoic in marine teleost fishes. Frankly, there was no evidence to say otherwise, as most Mesozoic fishes have general caniniform or styliform (peg-like) teeth, or they have heavy crushing or pavement-like teeth consistent with crushing hard-shelled organisms. The teeth of Hemicalypterus are very delicate, and wouldn't really do well with durophagy. This is the first potential evidence of herbivory in the Mesozoic, and in a non-teleost, ray-finned fish.

Original Source: Gibson, S.Z. 2015. Evidence of a specialized feeding niche in a Late Triassic ray-finned fish: evolution of multidenticulate teeth and benthic scraping in †Hemicalypterus. The Science of Nature — Naturwissenschaften 102:10. 

Also cited: Schaeffer, B. 1967. Late Triassic fishes from the western United States. Bulletin of the American Museum of Natural History 135: 289–342.