Curator of Paleontology
New Mexico Museum of Natural History and Science
1801 Mountain Road, NW
Albuquerque, NM 87104-1375

Adjunct Assistant Professor

Department of Earth and Planetary Science
University of New Mexico

Ph.D., University of New Mexico, Department of Earth and Planetary Sciences

M.S., University of New Mexico, Department of Geology

B.S., cum laude, University of Massachusetts, Amherst, Department of Geology

Vertebrate Paleontology, Geology, Stratigraphy

3D visualization of fossil specimens has in the past decade revolutionized the study of fossils by allowing paleontologists to gain important insights into the anatomy, development, and preservation of important specimens (Cunningham et al., 2014). We have been working with scientists at the Los Alamos Neutron Science Center (LANSCE) to use  X-ray (XCT)and neutron computed tomography (NT) (e.g., Vontobel et al., 2005) to scan important Late Cretaceous and Paleogene vertebrate fossils collected from the San Juan Basin, northwestern New Mexico. CT and NT scanning allow the nondestructive imaging and characterization of fossils in 3D. These models are useful, not only because they reveal new anatomical features, but because they enhance the ability to compare different fossil specimens, to visualize certain anatomical features in a new way (particularly internal structures like the brain and ear regions, which are inaccessible to the naked eye), and allow functional analysis using computer modeling with methods such as finite element analysis (see Rayfield, 2007) and 3D morphometric analysis (e.g., Fabre et al., 2014). They also allow data on unique and irreplaceable fossil specimens to be shared more easily between colleagues, as well as communicated to the general public. Neutron scanning is of special interest because it has only rarely been applied to vertebrate fossils, promises complementing information to the X-ray CT due to its contrast originating from the nuclear interaction of the probe with the sample, and has the potential to allow internal imaging of fossils impregnated with dense, iron rich minerals that are difficult or impossible to image with X-ray scanning techniques. We recently scanned the skull of the tyrannosaur Bistahieverser sealeyi with both high-energy x-rays and neutrons to produce one of the highest resolution computed tomography datasets of a tyrannosaur skull (see youtube video: http://www.youtube.com/embed/Nh82o0Ax4KM). Preliminary results were presented at the 2017 meeting of the Society of Vertebrate Paleontology (Schroeder et al., 2017).

Cunningham, J.A., Rahman, I.A., Lautenschlager, S., Rayfield, E.J., Donoghue, P.C.J., 2014. A virtual world of paleontology. Trends in Ecology & Evolution.

Fabre, A.-C., Cornette, R., Perrard, A., Boyer, D.M., Prasad, G.V.R., Hooker, J.J., Goswami, A., 2014. A three-dimensional morphometric analysis of the locomotory ecology of Deccanolestes, a eutherian mammal from the Late Cretaceous of India. Journal of Vertebrate Paleontology 34, 146-156.

Schroeder, K., T. E. Williamson, S. L. Brusatte, M. A. Espy, C. Gautier, J. Hunter, A. Losko, R. O. Nelson, S. Vogel. 2017. Neutron computed tomography of Cretaceous tyrannosauroid dinosaur Bistahieversor sealeyi and Paleocene phenacodontid mammal Tetraclaenodon puercensis reveals detail not easily visible with x-ray computed tomography. Journal of Vertebrate Paleontology, Program and Abstracts. 2017:191.

Vontobel, P., Lehmann, E., Carlson, W.D., 2005. Comparison of X-ray and neutron tomography investigations of geological materials. IEEE Transactions on Nuclear Science 52, 338341. 

A small, incomplete bird skeleton, Tsidiiyazhe abine (from the Navajo, meaning "small morning bird") from the lower Paleocene of the Nacimiento Formation, northwestern New Mexico, represents among the oldest skeletons of a crown bird. Tsidiiyazhi is closely related to extant mousebirds (family Coliidae, order Coliiformes), a group found today only in sub-Saharan Africa. Tsidiiyazhi is near the base of the crown bird family tree and can be dated to be about 62.5 million years in age, indicating that the initial diversification of crown birds happened prior to this, probably within the first few million years following the end-Cretaceous mass extinction.

Ksepka, D. T., T. A. Stidham, and T. E. Williamson. 2017. Early Paleocene mousebird supports rapid phylogenetic and morphological diversification of crown birds after the K-Pg mass extinction. Proceedings of the National Academy of Science. DOI: 10.1073/pnas.1700188114. 


An incomplete skeleton of a Torrejonia wilsoni, small plesiadapiform (stem primate) from the lower Paleocene of the Nacimiento Formation (about 62.5 million years old) represents the oldest plesiadapiform skeleton. The skeleton shows numerous specializations for arboreality. 

Chester, S. G. B., T. E. Williamson, J. I. Bloch, M. T. Silcox, E. J. Sargis. 2017. Oldest skeleton of a plesiadapiform provides evidence for an exclusively arboreal radiation of stem primates in the Paleocene. Royal Society Open Science. 4:170329. http://dx.doi.org/10.1098/rsos.170329

New Fossil tells of survival and rapid evolution for ancient group of mammals

Williamson, T. E., S. L. Brusatte, R. Secord, and S. Shelley. 2015. A new taeniolabidoid multituberculate (Mammalia) from the middle Puercan of the Nacimiento Formation, and a revision of taeniolabidoid systematics and phylogeny. Zoological Journal of the Linnean Society. doi: 10.1111/zoj.12336.

·        Kimbetopsalis was  rated at #5 of the top ten fossil discoveries of 2015 (http://www.eartharchives.org/articles/top-ten-fossil-discoveries-of-2015/) at Earth Archives and one of the Eight Best Extinct Species Discovered in 2015 (“Best Mammal”) by Motherboard (http://motherboard.vice.com/read/the-eight-best-extinct-species-discovered-in-2015).

·         Articles about the discovery appeared in BBCLive Science, the Washington PostNational GeographicDiscovery NewsCBS NewsFox NewsTime, the Daily Mail, the Mirror, the Express, the Scotsman, the Herald, the National, the Motherboard blog at Vice, The Daily Beast, the International Business TimesRed Orbit, the Christian Science Monitor, the Lincoln Journal StarNature World Report, and Forbes. Wire stories were put out by Reuters and UPI. I was interviewed for NPR’s Morning Edition.

The work was supported by the US National Science Foundation, the US Bureau of Land Management, the European Commission, and the Natural Environment Research Council.

Asteroid that wiped out dinosaurs may have nearly knocked off mammals, too



The classic story is that mammals rose to dominance after the dinosaurs went extinct, but a new study shows that some of the most common mammals living alongside dinosaurs, the metatherians (extinct relatives of living marsupials), were also nearly wiped out when an asteroid hit the planet 66 million years ago. This study was authored by an international team of paleontologists and published in the open access journal ZooKeys.

 Main Body:

The extinction of the dinosaurs 66 million years ago is thought to have paved the way for mammals to dominate, but a new study shows that many mammals died off alongside the dinosaurs.

Metatherian mammals—the extinct relatives of living marsupials (“mammals with pouches”, such as opossums) thrived in the shadow of the dinosaurs during the Cretaceous period. The new study, by an international team of experts on mammal evolution and mass extinctions, shows that these once-abundant mammals nearly followed the dinosaurs into oblivion.

When a 10-km-wide asteroid struck what is now Mexico at the end of the Cretaceous and unleashed a global cataclysm of environmental destruction, some two-thirds of all metatherians living in North America perished. This includes more than 90% of species living in the northern Great Plains of the USA, the best area in the world for preserving latest Cretaceous mammal fossils.

In the aftermath of the mass extinction, metatherians would never recover their previous diversity, which is why marsupial mammals are rare today and largely restricted to unusual environments in Australia and South America.

Taking advantage of the metatherian demise were the placental mammals: species that give live birth to well-developed young. They are ubiquitous across the globe today and include everything from mice to men.

Dr. Thomas Williamson of the New Mexico Museum of Natural History and Science, lead author on the study, said: “This is a new twist on a classic story. It wasn’t only that dinosaurs died out, providing an opportunity for mammals to reign, but that many types of mammals, such as most metatherians, died out too – this allowed advanced placental mammals to rise to dominance.”

Dr. Steve Brusatte of the University of Edinburgh’s School of GeoSciences, an author on the report, said: “The classic tale is that dinosaurs died out and mammals, which had been waiting in the wings for over 100 million years, then finally had their chance. But our study shows that many mammals came perilously close to extinction. If a few lucky species didn’t make it through, then mammals may have gone the way of the dinosaurs and we wouldn’t be here.”

The new study is published in the open access journal ZooKeys. It reviews the Cretaceous evolutionary history of metatherians and provides the most up-to-date family tree for these mammals based on the latest fossil records, which allowed researchers to study extinction patterns in unprecedented detail.

The work was supported by the US National Science Foundation and the European Commission. Dr. Gregory Wilson of the University of Washington also took part in the study.

Williamson, T. E., S. L. Brusatte, and G. P. Wilson. 2014. The origin and early evolution of metatherian mammals: the Cretaceous record. ZooKeys 465:1-76.

Dinosaurs fell victim to perfect storm of events, study shows

Brusatte, S. L., R. J. Butler, P. M. Barrett, M. T. Carrano, D. C. Evans, G. T. Lloyd, P. D. Mannion, M. A. Norell, D. J. Peppe, P. Upchurch, and T. E. Williamson. 2014. The extinction of the dinosaurs. Biological Reviews.

Updated September, 2017

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