Tyrannosaurus rex is without a doubt the most famous dinosaur in the world, and one of the lasting questions people have about this amazing dinosaur is what it was like as a teenager before it was full grown. A paper I co-authored with Bruce Rothschild, a former research affiliate with the University of Kansas Biodiversity Institute, now published online in the journal Cretaceous Research addresses this interesting question.
A nearly complete dinosaur skeleton labeled as BMR P2002.4.1, but more affectionately referred to as 'Jane' in honor of the woman who discovered it, has been the center of a decades long dispute over the validity of a dinosaur called Nanotyrannus lancensis. Nanotyrannus was named by a team led by the famous paleontologist Bob Bakker as a 'pygmy tyrannosaur' from the Late Cretaceous of Montana1. Not all dinosaur paleontologists are convinced of this assessment, and many prominent studies have asserted that Nanotyrannus—specifically 'Jane', the original holotype fossil skull at the Cleveland Museum of Natural History, and a handful of other isolated remains—are instead remanants of immature T. rex. In fact, if you visit wikipedia's page for Tyrannosaurus rex, you will find a proudly displayed image of 'Jane' from the Burpee Museum of Natural History. While paleontologists in this debate have focused on the number of teeth in the jaws2, the overall shape and proportion of the skull3, and whether the texture of the bone is more similar to that of adults of immature individuals4, we observed an isolated character on the skeleton of 'Jane' that shed some additional insight on this debate.
A portion of 'Jane's' lower jaw (called the dentary bone) is marked by a deep groove containing numerous small openings. Bruce Rothschild, who is an expert on ancient diseases and has looked at many jaws from theropod dinosaurs, was unaccustomed to seeing such a feature in a tyrannosaur, and thought this groove was possibly a sign of some disease. It turns out that the other specimens of the embattled genus Nanotyrannus also shared this feature, so it likely wasn't evidence of a disease. After examining additional dinosaur fossils, we found out that, in fact, this groove is found on nearly all theropod dinosaurs outside of the tyrannosauroid group (the group more closely related to T. rex than other meat-eaters like Allosaurus, Spinosaurus, and Coelophysis). Among tyrannosaurs, however, we found an opposite trend: only 7 of 18 tyrannosaurs had this feature, and half of those occurences were found in the group of the earliest tyrannosaurs. We further investigated this question by examining known T. rex material, ranging in age from "baby" all the way to full grown adult, and found that none of these fossils showed the groove we found on 'Jane'!
So what does this mean? It could be that 'Jane' and all the other fossils we call Nanotyrannus really are juvenile T. rex, and they are undergoing a really dramatic bodily transformation during their growth into adults (puberty sure is rough!), but this is unlikely given that none of the undisputed T. rex fossils we investigated have this feature. This groove is a passageway for nerves and blood vessels to move through the bones of the skull, and short of saying that the nerves and veins of the head dramatically changed their placement as the animal grew, if a baby has no groove, a sub-adult has no groove, and a full-grown adult has no groove, one would logically not expect a juvenile to have a groove either. To us (and some of the other scientists arguing in favor of Nanotyrannus), this is evidence that Nanotyrannus is a different dinosaur from T. rex, and they likely preferred different environments and prey even though they lived at the same time.
What does this mean about how Nanotyrannus fits in to the dinosaur family tree? Even though Nanotyrannus has been variously proposed to be a young T. rex or a closely related species, our phylogenetic analysis actually places Nanotyrannus as a close relative of the albertosaurine tyrannosaurs (moderate-sized theropods that lived in what is now Canada). We obtained this result because they are the only group of advanced tyrannosaurs to possesses the groove we studied. This result was interesting, however, because Charles Gilmore, the paleontologist that described the original Nanotyrannus on display at the Cleveland Museum5, thought it was an example of a new species of Gorgosaurus, one of the types of albertosaurines. History seems to have come full circle.
So now what? Well to the fan club of Nanotyrannus, we have some additional evidence that this was in fact a separate dinosaur species. And for now, the hunt is back on for a complete fossil that shows us what the mighty T. rex was like as a teenage terror.
1. Bakker et al., 1988. Nanotyrannus, a new genus of pygmy tyrannosaur, from the Latest Cretaceous of Montana. Hunteria 1:1-28.
2. Larson, P. 2013. The case for Nanotyrannus. Pp. 14-53 in Parish et al. (eds.), Tyrannosaur Paleobiology. Indiana University Press.
3. Carr, T. 1999. Craniofacial anatomy in Tyrannosauridae (Dinosauria, Coelurosauria). Journal of Vertebrate Paleontology 19:497-520.
4. Currie, P. 2003. Cranial anatomy of tyrannosaurid dinosaurs from the Late Cretaceous of Alberta, Canada. Acta Palaeontologica Polonica 48:191-226.
5. Gilmore, C. 1946. A new carnivorous dinosaur from the Lance Formation of Montana. Smithsonian Miscellaneous Collections 106:1-19.
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.
- 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.
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.”
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.
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.
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.
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.
A fundamental part of being a scientist is publishing your research. Scientists ask questions, formulate hypotheses, rigorously test these hypotheses, and publish their research and their results. Other people can then read these results and build off of these studies, either to question or refute the findings, or to use the findings to ask other questions. It is how science grows and evolves.
What almost all scientific publications lack, however, is the flair, the backstory, and general behind-the-scenes action that is part of everyday research. Scientific publications are whittled down to the most concentrated version, filled with the jargon of the discipline, and stripped of any extraneous behind-the-scenes anecdotes. So while any given scientific paper can be exciting to a scientist who wants to learn more about the organism or the methods addressed, they can be a bit unfriendly to a general reader.
So for fun, I have decided to tell some behind-the-scenes stories of the research I do, in the context of my published papers. Hopefully I give you a sense of what it is really like to be a paleontologist, and the work that is involved.
I’ll begin with my two solo-authored papers that I published in 2013. The papers can be found here and here, and if you cannot access those journals, please contact me at email@example.com and I will send you a PDF.
These two papers establish a new genus and two new species of fishes within a group called semionotiforms. Semionotiforms are an extinct group of fishes, but are closely related to living gar, and like gar, their bodies were covered with thick enamel scales (ganoid scales). Semionotiforms are found in geologic deposits worldwide, and range in age from Middle Triassic (~237 million years ago) to Early Cretaceous (~145 million years ago). A lot of variety occurs in semionotiforms in the shape of the body, the characteristics of the skull, the teeth, etc., and part of my research is to figure out what makes these particular fishes different from other species that have been described in the literature by other scientists. So you could say that my hypothesis for these studies is that these fishes represent new species, and I am testing that hypothesis by comparing the anatomy and morphology of these fishes to other semionotiform fishes to see if my hypothesis is correct or incorrect.
Some of the fossil specimens I work on are from museum collections, such as the American Museum of Natural History (AMNH) and the Smithsonian and were collected in the 1950s and 1960s, yet remained in these collections unstudied and undescribed for decades. I began working on these fishes in 2006, when I worked at the St. George Dinosaur Discovery Site (SGDS) as an undergraduate student intern and later as the prep lab and collections manager. The crew of staff and volunteers from SGDS had just gone out to a site in southeastern Utah and collected hundreds of fossils (outlined in Milner et al., 2006), but most of these fishes were not identified. So as I started cleaning the fossils (fossil prep—to be discussed in a later blog!), I started looking for characteristics that defined them as either new or belonging to a described species of semionotiform fish. While I worked on the new specimens, I looked at older literature, in particular a (1967) paper by an AMNH paleontologist Bobb Schaeffer, who mentioned collecting many semionotiforms from the same area but didn't describe them or give them names. So, in 2008, I went to the collections of the AMNH to look at those old specimens collected decades before and reexamined them, seeing which of them could be the same species as the new specimens the SGDS crew had just collected. I identified at least two different species, though there are likely more than that.
Now, identifying a new species is more than just a “Eureka!” moment. A scientist cannot know what is new unless he/she knows what already exists, and so scientists have to be very familiar with other scientists’ work in the field. An inordinate amount of any scientist’s time is spent reading books and papers, and I spent months pouring over scientific literature, some as old as 1820, to find the characteristics of other semionotiforms. As I looked at each bone on the fossil fishes from the AMNH and those newly collected from SGDS, I compared it to the same bones in other semionotiform fishes, and I had to look for similarities and differences. Eventually, I found a suite of anatomical and morphological characters that distinguished these fishes from all other semionotiform fishes, and I had enough to publish two papers on two distinct species. In these papers, I had to give an exhaustively detailed description of every single bone, and I mean EVERY bone (these fishes have hundreds of bones, dozens in their skull alone!) that I could see on the specimens, because other scientists, when trying to identify new species of their own, may turn to my work for comparison, and so my papers have to be provide as much anatomical detail as possible!
Next time….naming a new species!!
Milner, A.R.C., Mickelson, D.L., Kirkland, J.I., and Harris, J.D. 2006. Reinvestigation of Late Triassic fish sites in the Chinle Group, San Juan County, Utah: new discoveries. In: A Century of Research at Petrified Forest National Park: Geology and Paleontology (Eds. Parker, W.G., Ash, S.R., and Irmis, R.B.). Museum of Northern Arizona Bulletin 62: 163–165.
While a recent discovery may change textbooks and the way that many scientists think about bird and dinosaur evolution, it comes as no surprise us.
This week, Xing Xu, H. You, K. Du and F. Han published in the journal Nature a reanalysis of early bird evolution. The analysis knocks Archaeopteryx off its perch as a grandfather to later birds.
KU has been the central hub for the discovery of the fossil bird beds in the Early Cretaceous of China with the description of the primitive bird, Confuciusornis, and has continued to be involved with all the new discoveries coming out of this region in part through an alumnus of the KU vertebrate paleontology program.
The alumnus, Zhonghe Zhou, presently leads Chinese studies in that region and was recently elected to the prestigious National Academy of Sciences. Zhou and one of the paper’s authors, Xing Xu, had already precipitated a revolution in our understanding of bird evolution with the discovery of the four-winged gliding bird/dinosaur, Microraptor. With Microraptor, they showed that bird flight began with gliding.
Zhou has a long-term collaboration with KU vertebrate paleontology researchers at the Biodiversity Institute. Preparator David Burnham, collection manager Desui Miao and I regularly visit China to work on early birds. Our research also has suggested that Archaeopteryx along with other archaic birds represents a side branch that split off much earlier than the new bird, Xiaotingia, and its sister Anchiornis, another four-winged gliding animal.
While the recent paper in Nature calls these animals “feathered dinosaurs,” we think that they and their common ancestor with modern birds can be best considered true birds. Rather than removing Archaeopteryx from Aves because its avian features were shared with birdlike dinosaurs, we place a stronger emphasis on these features thereby pulling the dinosaur-like birds into Aves. This limits these flying, feathered animals to the Class Aves and pushes the origin of birds into the Early Jurassic or Late Triassic at about the same time as the dinosaurs themselves.
This past month I co-chaired a technical session at the national Geological Society of America conference in Denver. The session was entitled "Paleontology, Paleobiogeography, and Stratigraphy of the Late Cretaceous North America Seas: A Tribute to Bill Cobban." Dr. Cobban is a scientist at the US Geological Survey who has over 60 years of experience working on the statigraphy and paleontology of the Late Cretaceous Western Interior Seaway. The Western Interior Seaway (WIS) ran through the middle of the U.S. during the Cretaceous (about 65-100 million years ago) and was home to some amazing seafaring creatures, including the mosasaur that hangs over the doorway to the KU Natural History Museum.
I gave a talk entitled "Using GIS to investigate bias in the fossil record: a case study of the Late Cretaceous Western Interior Seaway of North America." In that talk I presented some tests that I performed to assess how good the fossil record in the WIS is. I was curious if the fossil record is biased in any way that would prevent us from mapping out the ranges of prehistoric species. The factors that I'm particularly interested in are competition, environmental change, and whether biological interactions between species are more or less important than environmental changes in determining which species go extinct and which do not.
I relate my research to the current biodiversity crisis: when you are trying to understand how invasive species, habitat fragmentation, and climate change are going to affect species in the future, there is a WEALTH of information (~544 million years in fact) in the fossil record that provides exactly that. The fossil record tells stories of how critters responded to species invasions and habitat loss and it teaches us about the effects of climate change and sea level fluctuations. These are the very factors that conservationists consider when attempting to save habitats and species.
One of the symposium's invited talks was by Neil Landman, a renowned cephalopod paleontologist from the American Museum of Natural History. He spoke eloquently on the life history of scaphite ammonites. Scaphites are shelled cephalopods (similar looking to modern Nautilus, also related to squid and octopi), but instead of having a properly coiled shell (like the Nautilus, their shell straightens out a bit at the end. Neil is probably one of the world's expert on scaphites. His talk described his latest interpretation of how these animals caught prey, what kind of prey, how they swam, at what orientation they held their body in the water column, how they reproduced, etc. Late Cretaceous cephalopds got SUPER weird, so this sort of talk is *really* exciting for folks like me who are into cephalopods and life in general in the WIS.
Overall, we had a very nice day talking about the current status of Late Cretaceous WIS research from a variety of geologically related fields: geochronology (age-dating the rocks), biology (mostly cephalopods, but also foraminifera, mosasaurs, sharks, etc.), biogeography, mapping, stratigraphy, and biostratigraphy. We are still working to better understand a number of the animal groups and how they might be used to date rocks. The great news is that it looks like the fossil and rock records are good enough to test many of our questions!
The word “fossil” often conjures images of Tyrannosaurus rex skulls, mammoth femurs, or other large bones. But those aren’t the only ones that survive through the millennia, and certainly aren’t the only ones that have importance.
KU Biodiversity Institute graduate students Sarah Spears and Kathryn Mickle study prehistoric fishes. Their fossils are so small that, in order to get them ready for study, Sarah and Kathryn have to use tiny tools to remove excess rock. Sometimes, even metal tools are too rough and inexact, so they switch over to porcupine quills — just sharp and flexible enough to clean tiny fish bones.