You won't find the dinosaur known as Xixianykus terrorizing people in Jurassic Park.
The species, which lived more than 80 million years ago, is estimated by scientists to have been about the size of a cat, covered with feathers and to have dined on ants and termites. Nonetheless, it was part of the theropod family of meat-eating dinosaurs that ranged in size from the bus-sized听T. rex,听to the dog-sized听Velociraptor, to the birds we know today.
Why did theropods vary so much in size? 成人动漫网站’s Michael D’Emic, PhD, associate professor of biology, is the lead author of a new study published in the journal听Science听that听answers this question, which has eluded scientists for years. His research also has implications on how environmental or other factors affect the growth patterns of other species鈥攑ast and present.
A Window Back in Time
鈥淢ost animals are thought to evolve to be larger or smaller by growing faster or slower than their ancestors, but this study shows that it’s just as likely that bigger or smaller animals grew for longer or shorter periods of time during growth spurts,” said Dr. D’Emic.
The bones of many animals, including dinosaurs, slow or pause growth every year, leaving marks like tree rings that indicate the animal’s age and growth rate. 鈥淲idely spaced rings indicate faster growth and narrowly spaced rings tell us that an animal was growing more slowly,” he explained.
Dr. D’Emic and a team of international researchers measured about 500 such growth rings in about 80 different theropod bones. 鈥淲e found that there was no relationship between growth rate and size,” said Dr. D’Emic. 鈥淪ome gigantic dinosaurs grew very slowly, slower than alligators do today. And some smaller dinosaurs grew very fast, as fast as mammals that are alive today.”
Dr. D’Emic was interviewed about his work on听听on February 26. He also maintains a听听that offers a more in-depth look at his research,听, and features the students who get to partner and work with him.
Students Dig Into Dinosaur Research
Students from Adelphi as well as other institutions get to work alongside Dr. D’Emic. Thomas Pascucci, MS ’19, adjunct faculty member at Adelphi, contributed to this latest project as a co-author. He said the findings made sense to him: 鈥淓xtinct animals like dinosaurs inspire awe because of how different they seem from those in our modern world, but they were animals that grew under constraints and environmental factors similar to those that exist today.”
The research team found that it was just as common for meat-eating dinosaurs to evolve changes to how听fast听they grew as it was to evolve changes to how听long听they grew.
鈥淭his has really important implications because changes in rate versus timing can correlate to many other things, like how many or how large your offspring are, how long you live or how susceptible to predators you are,” Dr. D’Emic said. 鈥淗opefully this research spurs investigations into other groups, both alive and extinct, to see what developmental mechanisms are most important in other types of animals.”
Riley Sombathy, MS 鈥�21, co-author and Ohio University graduate student hopes to take up some of those investigations, adding, 鈥淥ne of the things that interests me about the results of our project is the apparent decoupling between growth rate and body size.鈥�
This study opens the door to future investigations of how animals regulate their growth. According to study co-author and professor at Ohio University Patrick O’Connor, PhD, 鈥淎lteration of different growth control mechanisms, at molecular or genetic levels, probably account for the range of developmental strategies our team observed in theropod dinosaurs. Future studies of living organisms provide an opportunity to elucidate mechanisms related to the evolution of body size in vertebrates more generally.”
The paper, 鈥淒evelopmental strategies underlying gigantism and miniaturization in non-avialan theropod dinosaurs,” was also co-authored by Patrick O’Connor, PhD, and Riley Sombathy of Ohio University; Ignacio Cerda of Consejo Nacional de Investigaciones Cient铆ficas y T茅cnicas (CONICET) and Universidad Nacional de R铆o Negro in Argentina; David Varricchio, PhD, of Montana State University; Diego Pol, PhD, of CONICET-Museo Paleontol贸gico Egidio Feruglio in Argentina; Rodolfo Coria of Museo Carmen Funes in Argentina; and Kristina A. Curry Rogers, PhD, of Macalester College in Minnesota.