Researchers at the Hopkins School of Medicine recently described the fossil of an armored dinosaur hatchling. Discovered in 1997 by amateur fossil hunter Ray Stanford, the dinosaur is the youngest nodosaur ever discovered and the first hatchling of any dinosaur species discovered in the eastern United States.
Stanford discovered the dinosaur impression in a riverbed near College Park, Maryland, after an extensive flood. According to Stanford, the hatchling was lying on its back, and the depression was filled with silt. When the silt was brushed out, he found the ribcage and a cast of the upper right arm and the foot.
Stanford classified the fossil as a nodosaurus based on the impressions of the arm bones. He said that due to the amount of weight they have to carry, nodosaurs have a characteristic curve on the humerus.
The tiny, five-inch fossil is a new species of Ankylosauria, a group of large armored herbivores that lived from the early Jurassic to the Cretaceous Era. The adults were quadrupeds and had bony plates covering their backs and often had spikes down their shoulders or sides.
The dinosaurs inhabited a large geographic range, appearing on every continent except for Africa. This particular specimen lived about 110 million years ago, in a swampy area that is now Maryland. The fossil is only 13cm long, which is very small compared to the 20 to 30-foot long adult nodosaurs.
David Weishampel, an anatomy professor at the Hopkins School of Medicine, says that the specimen closely resembles more well-known armored dinosaurs, such as Panoplosaurus, except for its small size and elongated limbs. Now named Propanoplosaurus marylandicus, the specimen also seems to have a larger braincase and a smaller snout than other ankylosaurs.
A paleontologist and expert in dinosaur systematics, Weishampel and his colleagues had confirmed the fossil's identity using a distinctive pattern of bumps and grooves in the skull. The research team then performed a computer analysis of the skull shape and compared its proportions to those of 10 skulls from different species of ankylosaurs, a group that includes nodosaurs.
The fossil was formed after the dinosaur hatchling drowned in a flood and ended belly-up in a lake. When the body sank, it landed in the sediment on the lake bottom, forming an impression of the skull top, ribcage, and part of the forelimbs and hind limbs. While individual bones are discernible, the fossil differs from a traditional fossil in that there are no mineralized or petrified remains.
The researchers determined the dinosaur's age by analyzing the degree of development at the bone ends. Scientists were able to deduce the porosity of the bones given that young bones are not fully solid.
Weishampel estimated the specimen's age at less than a year old, making it the youngest armored dinosaur ever found. He believed that the dinosaur was a hatchling, rather than an embryo, because of some small nodosaur footprints found nearby.
While there was no evidence of an eggshell, Weishampel believes that the hatchling would not have traveled far from its nesting area due to its small size. He says that it may be possible to find nests or egg casings near the area where the fossil was found.
The fossil also presents an opportunity to learn more about limb and skull development in early dinosaur life, dinosaur parenting and reproductive biology, and the lives of Maryland dinosaurs in general.
The study was published in the September 9th issue of the Journal of Paleontology, and was funded by the Hopkins Center of Functional Anatomy and Evolution. Stanford has donated the nodosaur to the Smithsonian National Museum of Natural History in Washington, D.C.
