Early Jurassic dinosaur embryos tell an ancient tooth tale

Professor Robert Reisz
Monday, May 11, 2020 - 12:52pm

Early Jurassic dinosaur fetal dental development and its significance for the evolution of sauropod dentition, Article in Nature Communications

Dinosaur embryos are a prized find for palaeontologists. But a recent discovery of embryonic bones and teeth from the Early Jurassic period of Yunnan, China has given researchers an even rarer glimpse into the early days of tooth formation in a baby dinosaur.

An international research team, led by Academician Robert Reisz, Professor in Biology at University of Toronto Mississauga (UTM) studied the excellently preserved embryonic jawbones of an early sauropodomorph dinosaur called Lufengosaurus – a distant relative of the giant, long-necked sauropod dinosaurs. These embryonic dinosaur skeletons are among the oldest in the world and even preserve several jaws with teeth still inside.

“Embryonic teeth are very rare in the fossil record, but they can provide crucial insights into vertebrate development and evolution” said Reisz. “These unique fossils allowed us to compare for the first time the development of embryonic teeth to both hatchlings and adult teeth of the same kind of dinosaur”.

 

The fossils were originally collected during an expedition led by Timothy Huang of the National Chung Hsing University in Taiwan, and were carefully prepared by Diane Scott, a preparator at UTM. Subsequently, CT work by Professor Hillary Maddin at Carleton University in Ottawa, Canada, and histological thin sections by Dr. Aaron LeBlanc, then a PhD student at UTM, revealed multiple generations of developing, unerupted teeth in embryos of this early dinosaur. 

“Surprisingly we found that tooth development was rapid in the unhatched embryos, with multiple generations of teeth coexisting in each tooth position in a wide jaw” added Reisz. This condition was unexpected, because tooth development in the embryos was different from that of hatchlings and adults of Lufengosaurus.

Reisz and his team were very excited to discover that the early embryonic teeth of this early sauropodomorph dinosaur were actually more like the teeth of some of their descendants, the giant sauropods that had massive batteries of teeth as adults for processing plant material. “The evolutionary history of sauropods is fascinating, because they are a group of large to gigantic dinosaurs that survived throughout the Age of Dinosaurs and evolved complex dental batteries several times to deal with the highly resistant plant materials they consumed.”

This discovery allowed the team to propose that the evolution of complex dental batteries and the pencil-shaped adult teeth in the giant herbivorous sauropod dinosaurs may have evolved through paedomorphosis: the retention of embryonic developmental stages in adults. The similarities between embryonic Lufengosaurus teeth and those of much later-occurring species show that paedomorphosis was a common theme in the evolution of sauropods, the largest and longest-lived land dwelling animals of all time. 

Early Jurassic dinosaur fetal dental development and its significance for the evolution of sauropod dentition
Robert R. Reisz, Aaron R. H. LeBlanc, Hillary C. Maddin, Thomas W. Dudgeon, Diane Scott, Timothy Huang, Jun Chen, Chuan-Mu Chen & Shiming Zhong 
Nature Communications volume 11, Article number: 2240 (2020) Cite this article

https://doi.org/10.1038/s41467-020-16045-7

https://reiszlab.weebly.com/