Dinosaur Park

New research sheds light on Maryland's ostrich dinosaurs

2 Digs

Above: an "advanced"-type ornithomimosaur claw.

New research on fossils found at Dinosaur Park was published yesterday in the open access journal PeerJ. Author Chase Brownstein, a research associate at the Stamford Museum of Stamford, Connecticut, has found evidence that two distinct ornithomimosaur (or “ostrich dinosaur”) species were present in Early Cretaceous Maryland.

Smithsonian paleontologist Charles Gilmore first identified ornithomimosaur remains among the fossils recovered from the Arundel Clay in 1920. Many subsequent finds have also been attributed to this group, but until now they had never been compared to one another in detail.

When Brownstein visited the Dinosaur Park collections last November, he inspected all the available fossils, and picked out those that he could confidently identify as belonging to ornithomimosaurs. These included two ends of a humerus (upper arm bone) found by Park visitors Chris C. and Jackson C., as well as a number of claws, one of which was found by visitor Rebecca W. Next, Brownstein carefully recorded every detail of the fossils, from the angle of every curve to the depth of every depression.

By comparing this dataset to similar measurements from ornithomimosaur fossils found elsewhere, Brownstein was able to draw some interesting conclusions. The toe claws came in two shapes: some were more triangular at the base, while others were more rounded. This may sound like a subtle difference, but it’s important. The triangular claws strongly resemble those of more advanced ornithomimosaurs from the Late Cretaceous of North America, like Struthiomimus. By comparison, the round claws are similar to primitive ornithomimosaurs from Asia, like Harpymimus. Likewise, the humerus is more like primitive ornithomimosaurs than advanced ones.

The significance of this discovery is twofold. First, two distinct types of ornithomimosaurs means that the Dinosaur Park fauna was more diverse than we previously thought. More important, however, are the implications of primitive and advanced ornithomimosaurs living side by side. It’s likely that ornithomimosaurs as a group originated in Asia, with animals like Harpymimus. At some point during the Cretaceous, they migrated to North America, along with other groups like the ceratopsians and oviraptorids. Indeed, over the course of the Cretaceous we see wholesale replacement of dinosaur groups shared with Europe (like sauropods and ankylosaurs) with Asian groups. The Atlantic Ocean was widening at this time, so it makes sense that migration between America and Europe would have been harder. Apparently, a land bridge formed with Asia around the same time, which allowed eastern dinosaurs to enter the Americas. However, the presence of primitive and advanced ornithomimids in Maryland makes things more complicated. It suggests that there may have been multiple migrations of Asian dinosaurs, separated by millions of years!

Research like this is the reason museum collections like ours exist. The process of discovery doesn’t end with finding the fossil. There’s always more to learn by studying known fossils in new ways. Museums hold important specimens and objects in the public trust, so that people can continue to learn new things from them far into the future.

References

Brownstein, C.D. 2017. Description of Arundel Clay ornithomimosaur material and a reinterpretation of Nedcolbertia justinhofmanni as an “ostrich dinosaur.” PeerJ 5e3110.

Gilmore, C.W. 1920. Osteology of the carnivorous Dinosauria in the United States National Museum, with special reference to the genera Antrodemus (Allosaurus) and Ceratosaurus. Bulletin of the United States National Museum 60: 1-154.