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 past August, I returned to the University of Kansas – and Natural History Museum and Biodiversity Institute – becoming the new Collections Manager in the Division of Herpetology. August couldn’t have made for a better homecoming, as KU was celebrating 100 years of herpetological research by hosting the annual SSAR (Society for the Study of Amphibians and Reptiles) meeting. The meeting offered a perfect opportunity to connect with so many whom have helped build this division into one of the greatest centers for herpetological research in the country, if not the world.
Over these few first, short months I’ve received nothing but support from students and colleagues, making the transition from student to employed researcher nearly seamless. This support has afforded me the flexibility to take on the responsibilities associated with managing a collection of more than 340,000 herpetological natural history specimens, while simultaneously wrapping up dissertation work towards a Ph.D. in Evolutionary Biology.
With the aid of a stellar group of undergraduate volunteers, an incredible curatorial assistant, and a cohort of graduate students that are second to none, we’ve been able to close outstanding loans of material that are years and even decades past due. We’ve also accessioned and incorporated into our collections several thousand specimens of amphibians and reptiles from the Philippines, Kansas (US), and Madagascar. Over the next few months, we’ll be doing the same for recent collections from the Solomon Islands, Indonesia, Malaysia, and Cameroon. Additional projects on the horizon include continued digitization of specimen photographs, calls, and other ancillary data, and a complete inventory of our tissue and dry collections.
I’m very much looking forward building on the storied history of herpetology at the University of Kansas. From modernizing the use of the collection, to maintaining it’s availability for researchers in the international community, and even contributing to it directly through my own research endeavors, I hope to play an integral roll in the future of herpetology here at KU.
Today we had a day of fieldwork capped off with an insightful talk discussing ecotourism as a tool for conservation. It was conducted by the general manager of the University of Georgia-Costa Rica, Fabricio Comacho. He presented with passion, as he is heavily involved with sustainable development in his home country of Costa Rica. Fabricio touched upon how ecotourism in Costa Rica is an integral part of the country’s income. He stressed how sustainable attractions impact the very environment tourists come to see. Water stress, for example, was a key issue that Fabricio said became more problematic than other issues in recent times. As development increases in rural regions of Costa Rica, the demand for water stresses many of the fragile ecosystems surrounding large resorts or hotels, and therefore also stresses the organisms trying to survive in those areas. Fabricio also mentioned other important component of sustainable development, including the creation of biological corridors, and the nationwide switch to renewable sources of energy. Costa Rica currently boasts approximately %90 of its energy as strictly renewable and aims to be %100 carbon independent by 2030. Seeing this level of respect for the natural environment in the people I met in Costa Rica made me realize what is possible when there is a nation-wide effort in maintaining the health of the environment. From the standpoint of an American living in a much larger and carbon-hungry nation, I felt saddened and more aware of the apparent apathy the U.S. as a whole applies to the concept of environmental sustainability.
While researching my previous blog A Dry Rainforest? I learned that Costa Rica is having a more extreme dry season than most and is actually experiencing a drought. To the untrained eye (like mine and most tourists) the forest appears fine; the plants are green and the lack of rain is assumed to be due to the dry season. For those familiar with rainforests, however, the signs are everywhere. Plants have fewer new growths than usual, deciduous trees have lost many of their leaves, and there have been many days with no precipitation at all. The cloud forest in Monteverde, normally a place of constant precipitation even in dry seasons, has received no precipitation for the past five days.
The drought has consequences reaching far beyond the rainforest. Hydroelectric dams generate approximately 82% of Costa Rica’s energy. The dropping water levels caused by the drought result in less water pressure to power the dams, reducing their total hydroelectric power. Costa Ricans must compensate by shifting to fossil fuels, hindering their goal to become the world’s first carbon neutral nation by 2021. It is believed that this drought is the result of a severe El Niño – the same weather system bringing floods to southern California – but the effect is exacerbated by recent climate trends. Global climate change has affected the region by increasing the number of completely dry days during the dry season. Since 2011 the area began experiencing over 100 dry days a year. Ironically, Costa Rica’s forced use of more fossil fuels only exacerbates the issue. If they are to achieve carbon neutral status, Costa Ricans (and the entire global population) will need to find a way to avoid regressing towards using fossil fuels.
In class I learned to classify a rainforest as a forest that receives ample precipitation throughout the year. I was confused then to find out that the Carara National Forest, while still a vibrant green, is currently in its dry season. We learned that there are different formations, or classifications, of rainforests that depend on factors including climate, soil, and elevation. Carara, for example, is a seasonal forest because it experiences a wet and dry season.
The seasonal changes in Carara are not due to Earth’s axial tilt, like the seasons we are used to in temperate climates. Instead, the seasons are a result of wind patterns over the mountainous continental divide. During the summer strong trade winds drive clouds from the Caribbean side of Costa Rica over the continental divide to the Pacific side. On their journey up the mountains the clouds lose much of their precipitation and create a rain shadow effect in Pacific forests like Carara. In the winter, the trade winds die down and allow clouds from the Pacific side to rise up over the central mountains, thus beginning the wet season.
Photo credit: Tracey Funk
On a night hike at the University of Georgia field station, I encountered a hairy friend, Edith. Edith is a Costa Rican Orange-Kneed Tarantula (Brachypelma smithi) that has inhabited a miniature triangular cave for the past year. Female tarantulas live up to 20 years, and occupy a cave or burrow where they wait to ambush unsuspecting prey.
Bradley Hiatt, our night hike guide and a resident naturalist, explained that Edith had been sitting on her egg sac for 6 months. Only one baby tarantula could be found beneath Edith’s wooly legs, the rest left the burrow after their first molt. The male tarantulas pursue females, so they have a lower survival rate than the females who wait in their burrows.
Costa Rican Orange-Kneed Tarantulas are omnivorous and will eat anything, from insects to small rodents. Irritating hairs on the tarantula’s body are used for protection and to catch prey. When attacked, a tarantula will flick the hairs off into a cloud of dust and hairs so it can quickly escape. Edith has been attacked and used these flicking hairs; the evidence is the bald spot on her abdomen. If the tarantula is backed into a corner, it will perform a threat display before biting its attacker with its malicious fangs. This tarantula species’ bite is not lethal to humans but you may have a nasty wound or allergic reaction.
Edith is one of many extraordinary creatures I observed in Costa Rica. Seeing Edith in her natural habitat positively impacted my perception of peculiar or misinterpreted organisms.
On Tuesday morning we traveled to hike at Carara National park, near Punta Leona. Our nature guide for the day, Maurice Vasquez told us about his line of work and its required education. Maurice has worked in the park for 18 years. He explained the challenging path to become a nature guide in Costa Rica. Certified guides have a unique I.D. indicating they received proper training in Costa Rican biology and culture, environmental and social ethics, communication, first aid, and education. This impressive array of communicative skills was gained while working toward a post-bachelor's degree in a biological field for three years, which is required to become a guide. Maurice told us he is fluent in Spanish, English, German, and French. He explained that he attended university in Hamburg and took up German there. Maurice's dedication to his career and to wildlife was contagious, and he stopped and taught anyone he could while on the trails. I think he is the embodiment of Costa Rica's motto "pure life." He really seemed to embrace the astounding biodiversity of the country with pride.
En route to Jaco from San Jose there is a bridge over the Rio Tarcoles made famous from the large population of American Crocodiles (Crocodylus acutus) that gather down below. The bridge has become a popular ecotourist stop, and after going there I see why. The bridge is just wide enough that people can exit their cars and walk alongside the road. We counted 26 enormous crocodiles in the water below us!
The reason for the large population is unclear, but their presence is evidence of the respect Costa Ricans hold for the environment. The crocodiles thrive because they are protected by the Costa Rican government. In 2012, a law was unanimously passed to ban all sport-hunting in Costa Rica. Not only was this the first law of its kind in the Americas, but it was also the first bill in Costa Rica to be proposed by popular initiative. Because of the widespread value Costa Ricans place on their environment, there is a large public movement to protect wildlife. The petition for the law submitted to Congress had 177,000 signatures.
Chaboo taking the zany zip-lining plunge in Costa Rica.
In June 2015, I visited Costa Rica with 14 KU undergraduates for the annual field course. The research part, funded by KU’s Office of International Programs, was to examine the arthropod communities of Zingiberales host plants (bananas and ginger are the most familiar examples). I personally enjoyed the country so much, that I returned with my family for Christmas holidays, spending the week at the spectacular Manuel Antonio National Park in the Pacific coastal town of Quepos. We enjoyed the adventurous personality of Costa Rica, with beaches, hiking, and zip-lining. Then came my eight KU undergraduates for the field course and new adventures in this beautiful country.
I am Luke Schletzbaum from Overland Park, Kansas and I’m a Junior majoring in Organismal Biology. Some of the things that inspired me to enter my field are habitat loss, species conservation, and science education. I chose to go on this field biology trip with Dr. Chaboo mostly due to the location and the ability to conduct fieldwork in a location renowned for its incredible biodiversity. Over the course of the trip I hope to gain experiences locating and obtaining specimens and how to categorize and prepare them for study.
When I entered KU I heard many things about how great the study abroad program is.I waited until an opportunity intrigued me, and this was the one!