Unique fossils of adult animal and its embryo provide first evidence
of live birth among these prehistoric marine reptiles
Thursday, Aug. 11, 2011
HUNTINGTON, W.Va. – Marshall University paleontologist Dr. F. Robin O’Keefe and Dr. Luis Chiappe, director of the Natural History Museum (NHM) Dinosaur Institute in Los Angeles, have determined that a unique specimen now displayed in the museum’s Dinosaur Hall is the fossil of an embryonic marine reptile contained within the fossil of its mother.
Their findings will be published tomorrow in the journal Science.
The 78-million-year-old, 15.4-foot-long adult specimen is a Polycotylus latippinus, one of the giant, carnivorous, four-flippered reptiles known as plesiosaurs that lived during the Mesozoic Era. The embryonic skeleton contained within shows much of the developing body, including ribs, 20 vertebrae, shoulders, hips and paddle bones. The research by O’Keefe and Chiappe establishes that these dual fossils are the first evidence that plesiosaurs gave birth to live young, rather than hatching their offspring from eggs on land.
Although live birth (or viviparity) has been documented in several other groups of Mesozoic aquatic reptiles, no previous evidence of it has been found in the important order of plesiosaurs. O’Keefe and Chiappe have also determined that plesiosaurs were unique among aquatic reptiles in giving birth to a single, large offspring, and that they may have lived in social groups and engaged in parental care.
“Scientists have long known that the bodies of plesiosaurs were not well suited to climbing onto land and laying eggs in a nest,” said O’Keefe, who is an associate professor of biology at Marshall. “So the lack of evidence of live birth in plesiosaurs has been puzzling. This fossil documents live birth in plesiosaurs for the first time, and so finally resolves this mystery. Also, the embryo is very large in comparison to the mother, much larger than one would expect in comparison with other reptiles. Many of the animals alive today that give birth to large, single young are social and have maternal care. We speculate that plesiosaurs may have exhibited similar behaviors, making their social lives more similar to those of modern dolphins than other reptiles.”
Plesiosaurs have no known living relatives, but were common in the world’s oceans during the Age of Dinosaurs. They were among the top predators in the Western Interior Seaway, the vast, tropical body of water that split North America during the Cretaceous when waters from the Arctic Ocean and the Gulf of Mexico flooded onto the continent and met.
The remarkable NHM specimen was discovered in 1987 by Charles Bonner on the Bonner Ranch in Logan County, Kan. Virtually complete except for parts of the adult’s neck and skull, the “mother” specimen and her baby were given extensive conservation by NHM and then mounted for display by Phil Fraley Productions (Patterson, N.J.) with the supervision of O’Keefe and Chiappe. The specimen is currently on display in the Dinosaur Hall, the new 14,000-square-foot exhibition at NHM featuring more than 300 fossils and 20 complete mounts of dinosaurs and sea creatures.
O’Keefe’s research on plesiosaurs has taken him around the globe in search of these prehistoric creatures. He is credited with the discovery of a new plesiosaur, Tatenectes laramiensis, a type of marine animal that lived during the late Jurassic age when large dinosaurs, including apatosaurus, stegosaurus and allosaurus, roamed the Earth. O’Keefe made the discovery in what is now the Devils Tower National Monument in Wyoming.
O’Keefe has taught biology and paleontology at Marshall University since 2006. He teaches human anatomy and comparative vertebrate anatomy and serves as a graduate adviser. He received his bachelor’s degree in biology from Stanford University and his doctorate in evolutionary biology from the University of Chicago. He has published numerous scientific publications, and has served as a scientific adviser for National Geographic, IMAX and the Discovery Channel.
1. Plesiosaur giving birth. (Illustration by S. Abramowicz, courtesy of Natural History Museum of Los Angeles County.)
2. Detail of Polycotylus latippinus embryo on display at the Natural History Museum of Los Angeles County. (Courtesy of Natural History Museum of Los Angeles County.)
3. Dr. F. Robin O’Keefe, Marshall University. (Courtesy of Marshall University.)