By Daniel Dunaief In a compelling discovery in Montana, two dinosaurs were locked in a fierce battle for their lives. On one side was a mighty Triceratops, with its two distinctive horns and neck plate. On the other was a predatory creature that looked like a smaller version of the fearsome Tyrannosaurus rex. Standing at about 7 feet and about 18 feet long, was this other creature indeed a younger member of the distinctive apex predator or was it a member of another species? James Napoli, Research instructor in the Department of Anatomical Sciences in the Renaissance School of Medicine at Stony Brook University, had known of the “dueling dinosaurs,” as this finding was called, for years. He eventually got to sink his cognitive teeth into identifying the other dinosaur in this fierce battle frozen in time for 66.9 million years. Working with Lindsay Zanno, Associate Research Professor at North Carolina State University, Napoli confirmed last year in a paper published in the prestigious journal Nature that this predator was not a T rex, but, rather was from a different genus, Nanotyrannus. Now, several months later, Napoli has published another paper, this time in Paleobiology, that offers a new way to differentiate vertebrate fossil remains between the juvenile of a species that scientists may already know well and a smaller and perhaps similar looking dinosaur. Distinguishing between a smaller species and the juvenile of one that would get larger provides important clues about evolution, while also offering a clearer picture of the species living, competing and hunting in earlier epochs. Refining the number of recognized species “changes the way we think about the fossil record,” Napoli explained, particularly because the species is the fundamental unit of evolution. Scientists typically develop a hypothesis about evolution and test it using an understanding of the classification of life. Changing the number of species, where they occur and what interactions they have can change the narrative about their lives, niches and evolutionary roles. Beyond DNA In theory, DNA can help researchers identify the species to which an individual belongs. In practice, however, DNA is limited, particularly for creatures that existed before the last ice age. DNA degrades over time, leaving fossils without enough evidence of their signature and distinctive genetic material. To develop a new model that might help, Napoli started with two different types of modern living reptiles, the American Alligator and the Chinese Alligator. As a model system, the two alligators present similar conundrums to the ones paleontologists face when they find bones with similar configurations but different sizes. Reaching as long as 11 feet, the American alligator is around twice the size of the Chinese alligator, which is about five feet long. The two alligators were not only a relevant model to study because of the relative similarities, but also because they and crocodiles are modern living relatives of dinosaurs. By studying these alligators and their development over time, Napoli found that characteristics of the anatomy of their blood vessels, nerves and sinuses were unlikely to change as they grew. The skeletal indications of soft tissue anatomy and of different types of interlocking bone sutures remains consistent through life, which makes it easier to pinpoint these species-specific characteristics. Indeed, this approach could have recognized Nanotyrannus as a distinct species, without relying on the methods Napoli used, which included looking at bone microstructure and growth rings that demonstrated that the predator had reached 20 years old when its life ended. The standard practice paleontologists had used almost always underestimated diversity, sometimes incorrectly indicating smaller creatures were juveniles and not different species. In other efforts to create a framework for differentiating species, previous researchers used large sample sizes to develop quantitative techniques that could reveal changes to the anatomy and skull shape as a creature grows. Napoli demonstrated that these methods didn’t work when used in the context of modern animals such as the alligators. To be sure, Napoli acknowledged the possibility that some variation might not represent a new species so much as a mutations that could reflect a variation within a species. He called trying to understand variation that’s not assignable to growth as the “next frontier” in this research. Some animals, including humans and cats, can have a mutation that causes extra fingers or toes. Anatomical differences like these, however, would not change as an individual grows. This difference, he explained, reflects a genetic, not a developmental, change. The framework and then the dinosaur Napoli had started considering ways to develop a new framework for identifying vertebrates even before he had the opportunity to study the Nanotyrannus. At that time, he didn’t imagine he’d become a part of analyzing a beast whose battle with a Triceratops would become the subject of ongoing debate. Even when he was studying this fossil, Napoli developed this framework in parallel. As for life outside of dinosaurs, the Setauket native has been excited by much more recent history. He has been enjoying the celebration of the 250th anniversary of the United States and has a passport from the Three Village Historical Society. While he only has a handful of stamps, he hopes to add to that collection now that Paleobiology has published this paper. He also recently went whale watching off the coast of Montauk, where he spotted several humpbacks with their calves. He was amazed that these enormous creatures, who lineage traces back 50 million years ago, are in such close visual proximity to developed areas on land. This summer, Napoli is teaching human anatomy courses to physical therapy and PA students in a course totaling about 160 students. He is pleased that his current work contributes a new approach that could provide an understanding of vertebrate evolution.
SBU’s James Napoli offers new approach to identifying animal fossils
