Hide and Seek: How Sampling Bias May Lead to Our Limited Understanding of the Geographic Distribution of Ordovician Edrioasteroids

Edrioasteroids (Echinodermata) have a fossil history spanning over 300 million years, from the Early Cambrian through the Late Permian. The ease of post-mortem disarticulation necessitates rapid burial for the preservation of articulated specimens creating a taphonomic artifact that belies their longevity and contributes to our limited understanding of their global dispersal patterns. Here we collect and synthesize geographic distribution data for Ordovician Edrioasteroids from published faunal reports. Only Edrioasterida and Isorophida were considered for this study.

The Early Ordovician Iapetus Ocean was bounded to the north by Laurentia (later North America), to the east by Baltica, and to the south by Gondwana and the peri-Gondwandan constituent, Avalonia (later England and New England). Edrioasterids appear to be endemic to the North American continent with recorded distribution in modern day Utah, Michigan, Kentucky, New York, Oklahoma, and Ontario. Isorophids, on the other hand, appear to have a more cosmopolitan geographic distribution including Utah, eastern North America, peri-Gondwandan Europe, and Morocco. Enigmatic cyathocystids are known from North America and Baltica. Stalked rhenopyrgids first appear in Avalonia and Baltica and later become cosmopolitan. These findings suggest that Isorophids: (1) were better at larva dispersal; and (2) had a greater ecological range than edrioasterids.

The vast majority of Ordovician Edrioasteroid occurrences have been recorded in North America and Europe. We infer that this may purely be a sampling artifact as much of the Ordovician of Gondwana remains unsampled, including Antarctica, Australia, South America, India, and sub-Saharan Africa. Although Cambrian and Silurian/Devonian edrioasteroids are found in Australia and other undescribed Cambrian and Silurian edrioasteroids are found in China and South America, no Ordovician taxa have come forward from these areas. We hope that the compilation of these data will help us to better predict localities where additional specimens of Ordovician Edrioasteroids may be found.