A Loon Leg (Aves, Gaviidae) with Crocodilian Tooth from the Late Oligocene of Germany GERALD MAYR1* AND MARKUS POSCHMANN2 1Forschungsinstitut Senckenberg, Sektion Ornithologie, Senckenberganlage 25, D-60325 Frankfurt am Main, Germany 2Generaldirektion Kulturelles Erbe RLP, Direktion Landesarchäologie, Referat Erdgeschichte, Große Langgasse 29, D-55116 Mainz, Germany *Corresponding author; E-mail: [email protected] Abstract.—The first late Oligocene fossil record of a loon (Gaviiformes) is described from the lacustrine depos- its of the German locality Enspel. The specimen is an isolated foot, which is associated with a crocodilian tooth. The fossil belongs to a species about half the size of the smallest extant loon, and is morphologically most similar to the Paleogene taxon Colymboides. In all probability it constitutes the prey remains of a crocodilian, which is of particular significance because the distribution ranges of loons and crocodilians hardly overlap today. The Enspel palaeocli- mate was warm-temperate and subtropical, and the Enspel specimen and other Paleogene fossils of gaviiform birds raise the, as yet, unanswered question of why loons largely disappeared from inland habitats of the warmer regions. Received 22 July 2008, accepted 30 December 2008. Key words.—Colymboides, crocodilian tooth, fossil waterbirds, Gaviiformes, palaeoecology. Waterbirds 32(3): 468-471, 2009 In recent years, the Enspel fossil site anglicus Lydekker, 1891 from late Eocene (Westerwald, Germany) has yielded several lacustrine deposits of England is represent- birds of late Oligocene age (MP 28, i.e. 24.7 ed by a coracoid (the holotype), and a re- million years ago; Mertz et al. 2007). The fos- ferred humerus and frontal portion of the siliferous sediments originated in a small skull (Harrison and Walker 1976). The mate- maar lake, and the avian remains described rial assigned to C. belgicus Mayr and Smith, so far belong to a cormorant-like and a galli- 2002, from an early Oligocene lacustrine fos- form bird (Mayr 2001, 2007; Mayr et al. sil site in Belgium, consists of a proximal car- 2006). Here we report a new bird fossil from pometacarpus and a distal ulna (Mayr and this locality, which can be assigned to the Smith 2002). Only Colymboides metzleri Mayr, Gaviiformes (loons). 2004, which has been found in an early Oli- The four extant species of loons breed on gocene marine locality in southern Germa- northern freshwater lakes in the subantarc- ny, is known by a partial, albeit strongly disso- tic and boreal zones, but winter along sea ciated skeleton (Mayr 2004). coasts or on large lakes in temperate areas Most early Neogene loons were assigned (Carboneras 1992). Putative loons are to Colymboides minutus Milne-Edwards, 1867, known from late Cretaceous marine locali- which has been reported from the early Mi- ties of Chile and Antarctica, but their identi- ocene of France and the Czech Republic fication needs to be bolstered with addition- (Mlíkovsky 2002). From the early Miocene of al material (Olson 1992; Chatterjee 2002). the Czech Republic, a putative representa- Paleogene, i.e. early Cenozoic, loons were tive of the extant taxon Gavia was described found in fossil sites of both marine and lim- as G. egeriana by Svecˇ (1982). nic origin, but the fossils are still scarce (Mayr 2009). With the exception of the DESCRIPTION North American species Gaviella pusilla (Shufeldt 1915), whose holotype is a proxi- The specimen described in the present mal carpometacarpus of unknown, possibly note (Fig. 1) is a right foot with the collec- Oligocene (Wetmore 1940), age, all remains tion number PW 2007/5157-LS, which is de- stem from European deposits. Colymboides posited in the Generaldirektion Kulturelles 468 LATE OLIGOCENE LOON 469 Figure 1. Right foot of a loon from the late Oligocene of Enspel in Germany (Generaldirektion Kulturelles Erbe RLP, Mainz, Germany, PW 2007/5157-LS). Abbreviations: croc – crocodilian tooth; mt 2 – tarsometatarsal trochlea for second toe; peb – pebble; phal – isolated pedal phalange. Specimen coated with magnesium oxide. Erbe RLP, Direktion Landesarchäologie, Re- sponds to the tarsometatarsus of these two ferat Erdgeschichte, Mainz, Germany, and species, whereas that of the extant taxon Ga- will later be transferred to the Landessam- via is proportionally more elongated and mlung für Naturkunde Rheinland-Pfalz, more mediolaterally compressed. Even the Mainz. The fossil stems from a short-legged smallest extant loon, the Red-throated Diver diving bird with a mediolaterally compressed (Gavia stellata) is almost twice as large as the tarsometatarsus and a plantarly deflected fossil species, with the mean tarsometatarsus trochlea for the second toe. In these features length, based on measurements of ten indi- and in overall morphology, the tarsometatar- viduals, being 72.6 ± 3.3 mm. As in other Gavi- sus corresponds to that of the Gaviiformes iformes, there is a bulge on the medial sur- and Podicipediformes (grebes). In contrast face of the trochlea for the third toe. to grebes, which have no Paleogene fossil In the new specimen, pedal phalanges of record in Europe (Mayr 2005), the distal ar- a fossil loon are for the first time preserved ticulation surfaces of the trochleae for the in articulation (note, the tarsometatarsus is second and third toes bear distinct sulci. The rotated from its life position, so that the tarsometatarsi of some procellariiform birds fourth toe lies next to the tarsometatarsal are also mediolaterally compressed with a trochlea for the second toe). Morphological- plantarly deflected trochlea for the second ly, they match the corresponding phalanges toe, but are less stout and proportionally of extant loons. The second toe is completely more elongated. preserved, and as in extant loons its proxi- The preserved length of the tarsometatar- mal phalanx is the longest of all phalanges, sus is 37.7 mm. The proximal end is broken, whereas in most other birds it is the proximal and the total length is estimated at 41.6 mm. phalanx of the third toe, which exceeds the The bone is thus larger than the tarsometatar- others in length. The ungual phalanx of the sus of C. metzleri, which has a length of 34.5 second toe also resembles that of extant mm (Mayr 2004), and that of C. minutus, Gaviiformes and is not greatly widened as in which measures 30.7-33.0 mm (Cheneval grebes and their sister taxon, the Phoenicop- 1984). Morphologically, however, it corre- teriformes (flamingos) (Manegold 2006). 470 WATERBIRDS DISCUSSION gareda et al. 1989; Tucker et al. 1996; Schweiz- er et al. 2006). The association of a crocodil- The Enspel loon is the first late Oli- ian tooth with a loon leg is, however, remark- gocene fossil record of the Gaviiformes and able, because the extant distribution ranges fills a temporal gap between the known Pa- of loons and crocodilians only overlap in the leogene and early Neogene specimens of southern parts of North America and China. this taxon. The preservation of the fossil In these areas loons are usually found on the does not allow an unambiguous taxonomic sea, whereas crocodilians are restricted to identification beyond the “family”-level, but freshwater sites. The chance that an extant in overall morphology it is clearly more sim- loon is attacked by a crocodilian is thus min- ilar to the Paleogene taxon Colymboides than imal at best, and the fossil is a vivid example to extant loons. for the profound differences between late The new specimen is of particular inter- Oligocene and extant ecosystems in Central est, because it is preserved together with a Europe. The specimen further places a cave- small crocodilian tooth, probably of the alli- at on ecological interpretations based on gatorid Diplocynodon. Both isolated crocodil- comparisons with the closest extant relatives ian teeth and bird remains are rare in the of fossil taxa, because, taken separately, the Enspel fossil site, and it is very unlikely that crocodilian, an indicator of a warm climate, placement of the tooth right above or below and the loon, whose extant relatives are den- the loon leg is coincidental. A random asso- izens of the subantarctic zones, would have ciation caused by bottom currents is consid- led to very different conclusions concerning ered unlikely as well, because in this case the the paleoenvironment of the fossil locality. fossils are expected to rather show a lateral Clearly, the Enspel palaeoclimate was warm- accretion. Furthermore, insect taphonomy temperate and subtropical based on analyses studies suggest that there were hardly any wa- of both plant (Köhler 1997; Herrmann ter movements at the bottom of Enspel Lake 2007) and insect (Wedmann 2000) taphoc- (Wedmann 1998). In crocodilians the roots oenoses, and future studies will have to iden- of the teeth are reduced before they are shed tify the factors which led to the retreat of (Njau and Blumenschine 2006). Because the loons from extant inland habitats of the tooth associated with the Enspel loon has a warmer regions. reduced root, we assume that it fell out dur- ing feeding shortly before it would have ACKNOWLEDGMENTS been naturally lost, which is not an unusual event (Hertner 2006). Dismemberment of We thank M. Wuttke (GDKE RLP, Mainz) for allow- ing access to material in his care, and R. W. Elner and the carcass into pieces that could be swal- two anonymous referees for comments on the manu- lowed is often achieved by vigorous shaking script. of the prey item (Franzen and Frey 1993; Njau and Blumenschine 2006). In the course LITERATURE CITED of this action, the loon leg may have become detached and sunk to the inhospitable lake Carboneras, C. 1992. Family Gaviidae (Divers). Pages 162-172 in Handbook of the Birds of the World, vol. 1 bottom, where it was embedded in the sedi- (J. del Hoyo, A. Elliott and J. Sargatal, Eds.). Lynx Edi- ment together with the tooth sticking in the cions, Barcelona.