The most northerly record of the sirenian Protosiren and the possible polyphyletic evolution of manatees and dugongs

Cajus G. Diedrich
2013 Natural Science  
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,
more » ... 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. Figure 2. (A) Newly discovered and most northerly record of Protosiren (rib), and large teeth of Otodus megatooth sharks (all coll. HF), from the north-western German site at Fürstenau. (B) Map after [6]. (C) Stratigraphic position of the sirenian and shark-rich vertebrate conglomerate layer at the two Fürstenau sites. Figure 3. Global paleobiogeography of Eocene sirenians, which was dependent on the distribution of warm waters and on ocean upwelling (after [6-40,47,48]), with the Protosiren genus having the widest range. The distribution of the sirenians overlapped with that of the early megatooth shark Otodus [8]. [12] Siegfried, P. (1965) Anomotherium langewieschei n.g. n.sp. (Sirenia) aus dem Ober-Oligozän des Dobergs bei
doi:10.4236/ns.2013.511142 fatcat:7hyep4vv4fazrhmdhhl2rh2cmi