The most northerly record of the sirenian &amp;lt;i&amp;gt;Protosiren&amp;lt;/i&amp;gt; and the possible polyphyletic evolution of manatees and dugongs

Cajus G. Diedrich

doi:10.4236/ns.2013.511142

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 Furstenau (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.

Highlights

Extant manatees and dugongs, together with the recently extinct Steller’s seacow, are three distinct types of modern sirenian [1] that have their earliest origins in the Late Palaeocene to Early Eocene (Figure 1) [2,3,4]
The most primitive skeletons of quadrupedal sirenians (Ypresian, Early Eocene) ever found in the shallow marine palaeoenvironments of the Middle American Caribbean are of the primitive Prorastomus and the slightly more evolved Pezosiren (Figure 1) [5]
The material was compared with a Protosiren fraasi skeleton from the Stuttgart State Museum for Natural History (SMNS), with skeletons or bones of Halitherium schinzii from the Senckenberg Museum in Frankfurt (SMF), and with Anomotherium langewieschei remains from the Dobergmuseum Geological Museum of Ostwestfalen-Lippe in Bünde (DMB)

Summary

Introduction

Together with the recently extinct Steller’s seacow, are three distinct types of modern sirenian [1] that have their earliest origins in the Late Palaeocene to Early Eocene (Figure 1) [2,3,4]. Middle Eocene (Lutetian) sirenian remains from the new sirenian locality at Dalum, near Fürstenau (north-western Germany, Figure 2) are considered . The shallow coastal and slightly carbonatic Eocene sands at this locality have been bioturbated by crustaceans and are interrupted by a transgressive conglomerate bed in which phosphorite nodules and vertebrate remains are concentrated [6]. Those conglomerates within the Fürstenau Formation are extraordinarily rich in shark teeth, and contain coprolites from several different sharks, including megatooth and white shark forms [6,7,8].

Methods

Results

Conclusion