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Perot Dinosaur Grows Up

Just 20 months after announcing their discovery of a new species found in Alaska called the Pachyrhinosaurus perotorum, paleontologists from the Perot Museum of Nature and Science in Dallas have since uncovered a juvenile specimen that came from the same hole in the ground. The scientific paper describing the find – entitled An immature Pachyrhinosaurus perotorum (Dinosauria: Ceratopsidae) nasal reveals unexpected complexity of craniofacial ontogeny and integument in Pachyrhinosaurus” –  was posted late yesterday on the prestigious science journal PLOS ONE, an international, peer-reviewed, open-access online publication featuring reports on primary research from all scientific disciplines. Dallas paleontologist Anthony R. Fiorillo, Ph.D., the Perot Museum’s curator of earth sciences, and Ronald S. Tykoski, Ph.D., fossil preparator at the Museum, co-authored the report. To read Dr. Fiorillo and Dr. Tykoski’s entire manuscript, go to PLOS ONE at http://dx.plos.org/10.1371/journal.pone.0065802.
 

Series of Pachyrhinosaurus perotorum skullsA series of Pachyrhinosaurus perotorum skulls (on the left) and stylized life reconstructions (on the right) at three (of a proposed six) different life stages. Stage 2 skull is based on juveniles of the closely related species Pachyrhinosaurus lakustai from southern Alberta. The Stage 4 skull represents a ‘partially grown’ or ‘early adolescent’ individual, based on the new specimen (DMNH 21460) described in the PLOS ONE paper. The Stage 6 skull is that of a mature adult, based on DMNH 22558, a nearly complete Pachyrhinosaurus perotorum skull described by Fiorillo and Tykoski in 2012 and currently on public exhibit in the Perot Museum of Nature and Science. The ‘fleshed-out’ reconstructions are based on previously published ideas of Pachyrhinosaurus skin structures, but modified to reflect new information revealed by the new specimen (DMNH 21460). Light tan indicates ‘normal’ skin, while dark brown indicates cornified (= thickened, hardened, horn-tissue-covered) scales, horns, sheaths, or other cornified tissue. Scale bar equals 50 cm.

“In our early years of work, we initially thought we had only had one age profile – that of an adult. But as the preparation work has continued in recent years on the additional blocks from that same Alaskan expedition site, it was a true ‘aha’ moment to find the younger skull as well,” said Dr. Fiorillo.

Dr. Fiorillo discovered the adult version of the Pachyrhinosaurus perotorum during a return excavation in 2006 to the North Slope (Prince Creek Formation: Maastrichtian) of Alaska, many miles north of the Arctic Circle. In October 2011, the species was formally named Pachyrhinosaurus perotorum in recognition of the Perot family (Margot and Ross Perot and their children) for their long history of commitment and support for science and science education.

After transporting more than 12,000 pounds of cargo by air and highway from Alaska to the Museum’s paleontology labs in Dallas, the jackets were handed over to Dr. Tykoski, who handles and oversees all the preparation work at the Perot Museum. He and his team of staff and volunteers began the painstakingly slow task of meticulously whittling away the 70 million-year-old sediment that entombed the dinosaur bones.

The discovery of the juvenile came in 2012 when Dr. Tykoski was working on a smallish block about the size of a football focusing on a strip of bone about an inch wide exposed at the surface. One of the key diagnostic features of the Pachyrhinosaurus perotorum is the top of the nose. The juvenile specimen has a small, narrow horn on the snout that, after puberty, grows and thickens into a lumpy, battering ram-like bulge, a mark that distinguishes the Pachyrhinosaurus perotorum.

“After a couple weeks of working on it, our question was ‘what on earth is this?’ It had features on it that looked like the big adult skull of the Pachyrhinosaurus perotorum that we had originally found, yet it was very narrow and skinny and didn’t have the big expanded nose of the adult,” said Dr. Tykoski. “After ruling out all of the possibilities through the process of elimination, we realized this was a juvenile specimen. This provided us a snapshot in the development of the species – and that’s not common – so this was a very exciting moment for us.”

Dr. Fiorillo added that “discoveries like this help us to realize that this unique polar dinosaur isn’t just a trophy on the wall, but was a living, breathing animal.”

“The finding of this juvenile implies that the Artic, which was believed to be too harsh a climate for dinosaurs to survive, was an environment not only ripe for productivity, but shows that the species of Pachyrhinosaurus perotorum was reproducing and living there contentedly,” added Dr. Fiorillo. 

Below is an excerpt from the report:

A new specimen attributable to an immature individual of Pachyrhinosaurus perotorum (Dinosauria, Ceratopsidae) from the Kikak-Tegoseak Quarry in northern Alaska preserves a mix of features that provides refinement to the sequence of ontogenetic stages and transformations inferred for the development of the nasal boss in Pachyrhinosaurus. The new specimen consists of an incomplete nasal that includes the posterior part of the nasal horn, the dorsal surface between the horn and the left-side contacts for the prefrontal and frontal, and some of the left side of the rostrum posteroventral to the nasal horn. The combination of morphologies in the new specimen suggests either an additional stage of development should be recognized in the ontogeny of the nasal boss of Pachyrhinosaurus, or that the ontogenetic pathway of nasal boss

development in P. perotorum was notably different from that of P. lakustai. Additionally, the presence of a distinct basal sulcus and the lateral palisade texture on the nasal horn of the specimen described here indicate that a thick, cornified horn sheath was present well before the formation of a dorsal cornified pad. A separate rugose patch on the nasal well posterior to the nasal horn is evidence for a cornified integumentary structure, most likely a thick cornified pad, on the posterior part of the nasal separate from the nasal horn prior to the onset of nasal boss formation in P. perotorum.

A display featuring the adult Pachyrhinosaurus perotorum currently is installed in the T. Boone Pickens Life Then and Now Hall, a 14,000-square-foot hall in the Perot Museum of Nature and Science, which opened December 1, 2012, near downtown Dallas. On view are the actual skull and grill fossils that Dr. Fiorillo found on Alaska’s North Slope along with a 3D model of the animal and a richly colored, wall-sized illustration created by artist Karen Carr.

The discovery of both the adult and juvenile specimens has further ignited the two paleontologists’ passion to keep plugging away at the thousands of pounds remaining in the jackets, which are stored in collection spaces at the Perot Museum’s Fair Park campus.

Neither of the two scientists have slowed down with Dr. Fiorillo returning to Alaska twice this summer to continue various expeditions. And Dr. Tykoski will continue working on the North Slope jackets, especially since just 2,000 of the 12,000 lbs. of rock have been prepped to date.

“Who knows what will show up tomorrow? All we know is that any time we can learn about how extinct animals grew up, how they lived and breathed, then that gives us a better understanding of the history of life, the history of organisms, the patterns of growth,” said Dr. Tykoski. “Finds like this juvenile Pachyrhinosaurus perotorum also revise our understanding and previously held notions of how ancient creatures lived. They force us to rethink and re-examine … and that’s what keeps us searching.” 

To learn more about the Perot Museum of Nature and Science, visit perotmuseum.org.

About the Perot Museum of Nature and Science. Accredited by the American Alliance of Museums, the Perot Museum of Nature and Science is a nonprofit educational organization located in Dallas, Texas, with campuses in Victory Park and Fair Park. In support of its mission to inspire minds through nature and science, the Perot Museum delivers exciting, engaging and innovative visitor and outreach experiences through its education, exhibition, and research and collections programming for children, students, teachers, families and life-long learners. The $185 million Victory Park museum, designed by 2005 Pritzker Architecture Prize Laureate Thom Mayne and his firm Morphosis Architects, opened to the public December 1, 2012. The Perot Museum is named in honor of Margot and Ross Perot, the result of a $50 million gift made by their five adult children. To learn more about the Perot Museum, please visit perotmuseum.org