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The World's Oldest Fossil Seal Record Vol.3, No.11, 914-920 (2011) Natural Science http://dx.doi.org/10.4236/ns.2011.311117 The world’s oldest fossil seal record Cajus Diedrich PaleoLogic, Research Institute, Halle, Germany; [email protected] Received 12 September 2011; revised 22 October 2011; accepted 28 October 2011. ABSTRACT appeared about 28 m.y. ago during the North American Oligocene [1], but more recent reports claim to have A femur fragment with an Early Lutetian (early found an even younger (Miocene) “missing link” between Middle Eocene) age is the world’s oldest fossil terrestrial mammals and the basal pinnipeds in the Arctic record from a seal, and, is described as Pra- [2]. DNA analyses on pinnipeds have, however, sug- ephoca bendullensis nov. gen. nov. spec. This gested an older (Eocene) age for their ancestors [3,4], find pushes back the earliest evolution of seals but until now without any supporting fossil evidence. into the Paleocene epoch. The femur has ple- A newly discovered seal femur from a recently exca- siomorphic terrestrial mammal characteristics vated site at Fürstenau-Dalum in north-west Germany but has a morphology that is already closer to (Figures 1(a) and (b)) [5] and a review of other rare that of Miocene and present day seals. The Eo- European remains of Oligocene age from the pre-North cene seal femur was found at Fürstenau-Dalum Sea basin have now combined to suggest a different in north-west Germany, in a conglomerate rich scenario from that proposed by previous authors, who in shark teeth that was deposited in a coastal have suggested a basal pinniped evolution starting in, or delta environment to the north-west of the cen- along the coastline of, the North American landmass [4]. tral European Rhenish Massif mainland, in the Neither the palaebiogeography nor the suggested (but southern pre-North Sea Basin. This discovery unproven) Eocene age for the beginning of the evolution has led to a revision of the theory that phocids of evolution of earless seals (phocids) [3,4,6,7] can be originated along the coastline of the North supported by the evidence from this new fossil seal site American continent. Instead they can now be in Germany. This vertebrate-rich site has been the sub- interpreted to have originated in the tropical ject of interdisciplinary studies; it contains mainly shark Eocene climate of central Europe. Although the remains but also a variety of marine mammals [5]. Con- fossil records of pinnipeds in Europe during the vincing evidence has been identified from this site of a Eocene, Oligocene and Miocene are extremely “missing link” seal with a Middle Eocene or even older sparse, they appear to have inhabited the pre- (Lower Eocene) age [5]. North-western Germany also North Sea basin, within the influence of tem- provides insights into both the palaeoenvironment (Fig- perate and arctic upwellings. The distribution of ure 1(b)) and the palaeoecology of these, the earliest abundant teeth from white and megatooth sharks (and already fully developed) seals in the world, as well of two different lineages appears to correlate as into their main predators, the ancestors of present-day with that of the seals, which the sharks most white sharks and megatooth sharks [5]. probably hunted; providing supporting evidence Central Europe experienced a tropical climate during that the phocids were already adapted as shal- the Middle Eocene and many terrestrial mammal groups low marine coastal inhabitants by this time. were already well developed at this time. These are, to date, mainly known from the German fluvial and freshwater Keywords: Oldest Seal Remains; Praephoca lake sites at Messel and Geiseltal (Figure 1(a)) [8], from bendullensis Nov. Gen. Nov. Spec.; Giant Shark which no seal ancestors have been recorded, nor have Predation; Middle Eocene; Shallow Marine Coastal any early phocids been reported from other Eocene ma- Deltaic Influenced Habitats; Pre-Northsea Basin of rine vertebrate fossil localities of the European pre-North Central Europe Sea basin in France, Belgium, or England (Figure 1(a)). 1. INTRODUCTION 2. MATERIALS AND METHODS The oldest seals on planet Earth were thought to have A two-day excavation of a field site at Dalum was Copyright © 2011 SciRes. OPEN ACCESS C. Diedrich / Natural Science 3 (2011) 914-920 915915 (a) (b) (c) Figure 1. (a) Important Eocene marine and terrestrial vertebrate fossil sites in Europe; (b) Middle Eocene seal delta and beaches on the north-western Rhenish Massif, in the southern pre-North Sea basin; (c) Modern common seal Phoca vitulina Linnaeus, 1758 colony on the German Helgoland Düne sand bank (Photo A. Trepte). Copyright © 2011 SciRes. OPEN ACCESS 916 C. Diedrich / Natural Science 3 (2011) 914-920 performed in May 2011, using large earth-moving ma- Holotype. Half right femur (Figure 1(a)). chinery [5]. Sections were drawn up as part of strati- Type stratum. Marine transgression gravels of the Für- graphic and sedimentological studies on the Fürstenau stenau Formation, Early Lutetian, early Middle Eocene, Formation sequence at Dalum, which has been dated as Paleogene, 45 - 49 Ma. Early Eocene (Ypresian) to basal Middle Eocene (Lu- Type locality. Dalum, north-west Germany, southern tetian). A total of 180 cubic meters of phosphorite con- pre-North Sea basin. glomerate from the early Lutetian transgression was ob- Holotype name. Genus after the ancestor of Phoca, tained for sieving three size fractions using 1 and 4 mm and species after the collector J. Bendull. sieves, the finer fraction being discarded. Only 0.1% of Description and differential diagnosis. Only the upper the recovered material has yet been sieved [5], but this half of the right femur is preserved (Figure 1). Com- has already yielded 14,440 fossils, of which 95% are pared with Oligocene, but mainly with Miocene to pre- sharks’ teeth. Half of these 13,690 selachian teeth could sent-day phocid pinniped femora (Figures 2.2-2.4) the be identified at species level. Less well represented are femur joint is much more prominent and its plesiomor- the teeth and fin spines of rays and the teeth and bones phic character relates more to terrestrial mammals such of bone fish. The finer material (less than 4 mm) con- as the Eocene mammals from Messel [8]. This promi- tains many additional species that remain to be examined nence generally reduces during the evolution of phocids, in the future. Less then 0.1% of the fossils are from as an aquatic adaptation (Figures 2.2-2.4) [10]. The dou- mammals and these are mostly highly fragmented and ble-headed and narrower trochanter tertius of the Eocene rounded usually rendering them impossible to identify. femur still has a low angle with the axis of the femur Several terrestrial mammals that were identified just (10˚), compared to the much larger angle (30˚ - 40˚) in from their teeth are similar to those in the Messel fauna the Miocene to present-day phocids (Figures 2.2 and and of similar age; they include early horses and tapirs 2.3), which also have a flattened trochanter tertius. The [9]. Marine mammals have now also been identified, Trochanter tertius of P. bendullensis has the plesiomor- although only from their postcranial bones. At least one phic characteristics of terrestrial mammals. The already unidentified distal humerus fragment from a pachyos- flattened and widened femur shaft (Figure 2.1(b)) is the totic, marine mammal was found during this program, main apomorphic character and is typical of highly proving the significance of this site with regard to the evolved phocids that are already adapted to aquatic en- evolution of marine mammals. The femur illustrated in vironments, as well as being found in Miocene to pre- Figure 2 was actually found was actually found in these sent-day pinnipeds (Figures 2.2-2.4) [10,11]. Overall this gravels during the 1980s, and has prompted a major new Eocene femur reflects an intermediate stage be- program seeking to understand the biodiversity of ma- tween terrestrial mammals and the Miocene pinnipeds, rine vertebrates in Europe during the Eocene, in relation already exhibiting well-developed phocid characteristics. to that of the terrestrial vertebrates. This femur, together Quite similar in shape to this Eocene femur are those of with all material from the 2011 excavations, is housed in the modern arctic Phoca hispida Schreber, 1775 (Figure the Shark Center at Bippen (SCB) in north-west Ger- 2.4), and in particular, the common seal Phoca vitulina. many, a public visitor center and museum in the UNESCO- Both of these present-day seals have a less distinct femur supported “Geo and Naturpark TERRA. Vita”. Other seal head, and are distally wider with a smaller distal tibia/ femora [10] have also been studied with respect to their fibula articulation surface (Figures 2.3 and 2.4). measurements [11], including bone material in the Uni- versity of Alaska Museum (UAM), Oligocene remains 4. DISCUSSION housed in the Dobergmuseum, Bünde (DMB) in Ger- many, Miocene material from the Oertijdmuseum de 4.1. The Evolutionary Beginnings of the Groene Poort, Boxtel (MAB) in the Netherlands, and Earliest Phocids finally, modern seal remains from the southern North The seal femur (Figure 2) is possibly even a little older Sea Basin at the Seehundstation, Friedrichskoog (SFI) in than Middle Eocene, and may derive from reworked Germany. Lower Eocene marine sands [5], which would push back 3. THE WORLD’S EARLIEST PHOCID the evolution of pinnipeds at least into the Paleocene. FOSSIL The femur has been compared osteologically and morphologically to those of Eocene terrestrial mammals Suborder Pinnipedia Illiger, 1811 and Oligocene to present-day aquatic seals. It represents Family Phocidae Gray, 1821 an intermediate stage but has already developed a very Genus Praephoca nov.
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