EXCEPTIONALLY PRESERVED OCTOBRACHIA COLEOIDS FROM THE FIRST EARLY JURASSIC LAGERSTÄTTE IN NORTH AMERICA

Lagerstätten are rare, exceptional fossil deposits that preserve soft tissue and poorly calcified or uncalcified organisms. Such deposits capture information about organism physiology typically not preserved (e.g.,cephalopod soft parts) and provide extraordinary opportunities to study morphology, ecology, taphonomy, and organism interactions. Here we will present a study of a new deposit, known as the Ya Ha Tinda Lagerstätte, that is both the first North American Jurassic lagerstätte and the first Early Jurassic lagerstätte from outside of Europe.

The Toarcian Oceanic Anoxic Event (T-OAE, ~182 Ma) in the Early Jurassic is accompanied by a globally recognized negative carbon isotope excursion. A chemostratigraphic analysis of the Ya Ha Tinda site confirms the occurrence of the T-OAE within the lagerstätte strata. This indicates that the Ya Ha Tinda deposit is time correlative to the well-studied Posidonia Shale in Germany and, thus, for the first time, provides the opportunity to describe contemporaneous Early Jurassic lagerstätten from opposite sides of the earth.

Octobrachiates (e.g., modern octopods, extinct loligosepiids, teudopseids and prototeuthinids, etc.) are found in abundance from the T-OAE intervals in the Posidonia Shale and other European T-OAE deposits. However, there have been few taxa described outside of these European specimens; to date, Early Jurassic Octobrachia coleoids are only represented by two North American and two South American specimens. Our excavations at Ya Ha Tinda have uncovered more than ten new Octobrachiate fossils. Several specimens preserve internal organs (e.g., ink sacs) and subtle growth lines, which can be used to make taxonomic determinations. Our study identifies and describes these new Octobrachia coleoids and will compare this fauna to those found in the coeval deposits in Europe. Finally, the Octobrachiate distribution and the potential influence of the T-OAE on this distribution will be discussed to provide a global picture of their paleobiogeography during the Early Jurassic.