The Geology and Vertebrate Paleontology of Calvert Cliffs, Maryland, USA – Volume 2: Turtles and Toothed Whales

Abstract

This volume is a follow-on to a work published by Smithsonian Institution Scholarly Press in 2018 on the Miocene vertebrate fauna from Calvert Cliffs, Maryland, USA. Two chapters are included in this compendium, one on turtles (chelonians) and the other on toothed whales (odontocetes). It is anticipated that two more volumes will be needed to complete the taxonomic review. Robert E. Weems details the occurrence of 19 kinds of chelonians that have been discovered in the Miocene and Pliocene marine strata of Delaware, Maryland, and Virginia, USA, 13 of them in the Calvert Cliffs. The most commonly found remains are those of an extinct sea turtle, Trachyaspis lardyi. Remains of four other marine turtles, Procolpochelys grandaeva, Lepidochelys sp., a generically indeter¬minate cheloniid, and a leatherback turtle (Psephophorus polygonus), are far less common. The other 14 chelonian taxa are nonmarine forms that inhabited the land, rivers, and marshes west of the Mid-Atlantic Seaboard during the Miocene. They were washed into the coastal marine environments that were then accumulating the sediments exposed today as the strata in the Calvert Cliffs. Stephen J. Godfrey and Olivier Lambert review the taxonomically diverse odontocete fauna of 29 named species. Nine of these Miocene taxa represent newly named species. Fragmentary remains hint at even greater diversity. Reviewed taxa are restricted to those known from along the Calvert Cliffs and other Miocene age deposits on the Atlantic Coastal Plain in Maryland and Virginia, USA. They range in age from approximately 22 to 8 Ma and derive from the Calvert, Choptank, and St. Marys Formations. This fauna preserves one of the most abundant and diverse assemblages of extinct toothed whales known. None of the named odontocete species included in this review are known from beyond the North Atlantic Ocean. In terms of their chronostratigraphic distribution, collectively, they range in age from the Aquitanian through the Tortonian, with the large majority occurring within the Burdigalian, Langhian, and Serravallian stages (the latter two being the most speciose). The greatest taxonomic diversity occurred during the Miocene Climate Optimum, a time (ca. 17–15 Ma) when global average temperatures were as much as 4°C to 5°C above today’s average temperatures, at least for much of that interval.