A new unusual Monachinae from the Neogene of the Atlantic Coastal Plain (Maryland, USA)

ABSTRACT

To date, for the family Phocidae, only two fossil genera of the subfamily Monachinae (Monotherium and Terranectes) and two fossil genera of the subfamily Phocinae (Prophoca and Leptophoca) have been described from the Western Shore of the Chesapeake Bay (Maryland, USA). This study presents the first description of a new fossil partial seal skull from the St. Mary’s Formation (late Miocene, 8.5–7.5 MYA) in Maryland, USA. The new skull exhibits both primitive and derived features. Morphological assessment of this new skull supports classifying it within the subfamily Monachinae (based on numerous diagnostic characters). However, the presence of unique characters that do not match with any known genera of Monachinae led to the naming of a new genus and species, Magnotherium johnsii. This is now the third taxon of the subfamily Monachinae described from this locality. Some key characters of the Magnotherium johnsii (sp. nov.) skull include the presence of six incisors (similar to seals of the subfamily Phocinae), a long rostrum, and long concavity of the preorbital area of the maxilla.

KEYWORDS:

• Phocidae
• Monachinae
• Neogene
• Maryland

Acknowledgments

We would like to express our deepest appreciation to Walt Johns for having donated parts of CMM-V-5350 to the Calvert Marine Museum, and to all those who found and donated subsequent parts of this skull to the CMM as well. We are also indebted to the Museum Curators and Collections Managers who allowed us to study specimens in their care. We want to thank the reviewers and journal editor for improving our manuscript. Christopher R. Smith helped with the Latin rendering of the new specific name, many thanks.

Funding for J.R.N. came from the Clarissa and Lincoln Dryden Endowment for Paleontology at the Calvert Marine Museum. Additional funding for both S.J.G. and J.R.N. came from the Citizens of Calvert County, Maryland, and the County Board of Calvert County Commissioners for funding the Calvert Marine Museum.

Disclosure Statement

No potential conflict of interest was reported by the author(s).