TITLE:
The most northerly record of the sirenian Protosiren and the possible polyphyletic evolution of manatees and dugongs
AUTHORS:
Cajus G. Diedrich
KEYWORDS:
Sirenian Remains; Early Middle Eocene; Palaeobiogeography; Oldest Sirenians of the Proto-North Sea Basin of Central Europe
JOURNAL NAME:
Natural Science,
Vol.5 No.11,
November
4,
2013
ABSTRACT: Newly discovered remains of the early Middle Eocene
(Lutetian) sirenian Protosiren (Protosirenidae) in shark tooth rich
conglomerates from a coastal delta environment northwest of the European
Rhenish Massif at Fürstenau (northwestern Germany), represent the most
northerly occurrence of this genus whose global distribution was generally
restricted to warm waters. Its presence of the remains so far north can be explained
by seasonal inflow of warm Tethys surface water into the cool, upwelling-influenced,
basin. The existence of two discrete centers of sirenian evolution can be
explained by the opening of the Atlantic and the upwelling that separated the
North American warm water faunal province from those of Africa and Eurasia. A
slightly modified evolutionary model is presented in which the oldest Early
Eocene manatee sirenians evolved in the Caribbean of Central America. Protosiren, however, appears to have
developed polyphyletically along the African coastline of the Tethys, and
represents the oldest known dugong ancestor. Younger (Oligocene) European
sirenian skeletons of Halitherium and Anomotherium are included in the
phylostratigraphic model in which sirenians had generally reduced their teeth
by 28 Ma as an adaptation for feeding on sea-plants (macroalgae/seagrass).
Teeth from early megatooth sharks, which preyed on sirenians, have been
recorded from shallow marine Eocene and Oligocene coastlines of the southern
proto-North Sea Basin, and shark bite marks have been found on sirenian
skeletons.