Palaeodiversity 3: 235–239; Stuttgart 30 December 2010. 235 The fi rst record of a beaver – Trogontherium (Euroxenomys) minutum – in the Höwenegg fauna (Miocene, southern Germany) SAMUEL GIERSCH, WOLFGANG MUNK & REINHARD ZIEGLER Abstract The fi st record of a beaver from the Late Miocene (MN 9) Höwenegg fauna, a dentary fragment with all teeth, is described in detail. It likely represents Trogontherium (Euroxenomys) minutum. The taxonomic affi nities of the species are discussed. The Late Miocene fauna correlates with the Neogene mammal unit MN 9. K e y w o r d s : Beaver, systematics, Höwenegg, Late Miocene, MN 9. Zusammenfassung Der Erstnachweis eines Bibers in der obermiozänen (MN 9) Höwenegg-Fauna wird detailliert beschrieben. Er gehört wahrscheinlich zu Trogontherium (Euroxenomys) minutum. Die taxonomischen Probleme werden diskutiert. 1. Introduction The dentary is housed in the Staatliches Museum für Naturkunde Karlsruhe (SMNK) under the catalogue The Upper Miocene fossil site at the Höwenegg (north- number SMNK-Pal. 6601. All measurements were taken ern Hegau district, Southwest Germany) was discovered on the occlusal surface and are given in mm. The termi- in the 1930s and elaborately excavated for several decades nology of the dental elements follows STIRTON (1935). (TOBIEN 1986, JÖRG & ROTHAUSEN 1991, HEIZMANN et al. 2003). The site is renowned for its excellently preserved Acknowledgements complete mammalian skeletons, including females with We would like to thank the Revealing Hominid Origins In- foetuses. The tridactyl horse Hippotherium primigenium, itiative (NSF grant BCS-0321893 awarded to R.L. BERNOR by the project directors F.C. HOWELL and T.D. WHITE, University of the rhinoceros Aceratherium incisivum, and the archaic California, Berkeley) for funding the excavations at Höwenegg antelope Miotragocerus pannoniae are known from multi- 2005–2009. We are also grateful to K. WOLF-SCHWENNINGER for ple skeletons. Muntiacine and tragulid deers are represent- preparing the photo, C. STEFEN for reviewing the manuscript and ed by partial skeletons. However, remains of small mam- R. SCHOCH and R. BÖTTCHER for editorial work. mals are extremely rare. The few fi nds sampled in the last appr. 50 years will be published elsewhere. So far 9 spec- imens have been found, and only the lagmomorphs can 2. Systematic palaeontology be determined to species level. The ongoing excavation at the Höwenegg site by the SMNK staff yielded a dentary Family Castoridae HEMPRICH, 1820 fragment of a small beaver in April 2009. This is the fi rst Genus Trogontherium FISCHER VON WALDHEIM, 1809 record of a castorid in the Höwenegg fauna. The discovery Subgenus Euroxenomys SAMSON & RĂDULESCO, 1873 of fossil beaver remains at Höwenegg is not unexpected, given that the fauna was deposited in a lacustrine environ- Trogontherium (Euroxenomys) minutum ment. The lacustrine deposits of the Höwenegg-Formation (VON MEYER, 1838) are a sequence of white or grey marl-layers alternating Figs. 1–2 with reddish-brown layers that are interpreted to be tuf- 40 39 M a t e r i a l : Fragmentary horizontal ramus of right den- faceous mudfl ows. A Ar/ Ar dating of the deposits indi- tary with i, p4–m3, partly broken, labially embedded in matrix, cates an age of 10.3 ± 0.19 Ma. The Höwenegg-Fauna is bi- SMNK-Pal. 6601 (Figs. 1–2). ostratigraphically correlative with the European Mammal M e a s u r e m e n t s : p4 4.45 × 3.93; m1 2.91 × 3.81; m2 Unit MN 9 (Lower Pannonian) (MUNK et al. 2007). 2.80 × 3.90; m3 3.11 × 3.38. The castorid dentary described herein was extracted D e s c r i p t i o n . – The right dentary fragment pre- from the layer Höw 03/I, 12-top, which represents a tuf- serves most of the horizontal ramus and is partly embed- faceous mudfl ow. Here, we present a description of the ded in matrix with its labial side. Only the cheek teeth can specimen, discuss its taxonomic attribution, and compare be seen in occlusal view. The inferior margin and a part of it with other records of the species from localities in the the lingual side below m1-m2 were broken during the ex- wider vicinity, older and younger. cavation. The tooth row is not in line, with the m2 being 236 PALAEODIVERSITY 3, 2010 Fig. 1. Trogontherium (Euroxenomys) minutum (VON MEYER, 1838); right dentary fragment with I, p4–m3, matrix virtually removed; Late Miocene, MN 9, Höwenegg. – a. Lingual view. b. Occlusal view of the tooth row. Fig. 2. Trogontherium (Euroxenomys) minutum (VON MEYER, 1838), occlusal view of the tooth row; Late Miocene, MN 9, Höwenegg. dislocated inferiorly and posteriorly. Hence, the length of is labially embedded in matrix, no measurements can be the tooth row cannot be accurately measured. There are taken. two vertical fractural lines between p4/m1 and between The p4 is by far the largest tooth. The mesofl exid is still m1/m2, respectively. open lingually and not closed to a mesofossettid. The mes- The incisor is chisel-shaped, slightly curved upwards, ostriid is still 0.46 mm high, terminating well above the and with a smooth enamel band on its frontal side. As it alveolar margin of the dentary. The parafossettid is wide GIERSCH ET AL., MIOCENE BEAVER FROM HÖWENEGG 237 in labio-lingual direction. Hypofl exid and metafossettid (1978), SAVAGE & RUSSELL (1983) and MCKENNA & BELL are directly adjacent to each other. The hypostriid extends (1997). HUGUENEY (1999) downgraded it to a subgenus of down to the crown base. The condition of the striids and Trogontherium. She was followed by STEFEN & RUMMEL fl exids shows that the p4 is only moderately worn. (2003), DAXNER-HÖCK (2004) and DAXNER-HÖCK & BERNOR In the m1 the mesio-lingual part and the whole para- (2009) in this allocation, whereas KORTH (2001) ranked fossettid are broken off. But enough of the anterior margin Euroxenomys at genus level. of the tooth is preserved to allow for a reliable measure- We believe that the differences between the early Mid- ment of length. The tooth is worn down to a closed mes- dle to Late Miocene species minutum and the Pleistocene ofl exid. The hypostriid terminates above the tooth base type species cuvieri are suffi ciently taken into account by and is only 0.27 mm high. The hypofl exid extends over ranking minutum as the subgenus Euroxenomys of the ge- more than half of the occlusal surface and is directly adja- nus Trogontherium. The absence of striation and rugosity cent to the metafossettid. in the incisors of the small T. (E.) minutum may be due to its In the slightly less worn m2 the mesostriid is just vis- small size, as this character occurs in large sized, but sys- ible, and the mesofl exid is short before closure to a meso- tematically unrelated beavers as T. cuvieri, Castoroides, fossettid. The hypostriid extends halfway down the crown and Anchitheriomys, as STEFEN & RUMMEL (2003) point- base with a height of 0.48 mm. Metafossettid and hypofl ex- ed out. In her phylogenetic analysis RYBCZYNSKI (2007) id are directly adjacent to each other. showed, that these large beavers belong to different lin- According to the height of the striids p4 and m3 are in eages. A hint of granulation in the incisors of the large- the same stage of wear. m3 is less worn than m1 and m2 sized subspecies T. (E.) minutum rhenanum from Dorn- as the mesofl exid is more open. The hypofl exid extends Dürkheim (FRANZEN & STORCH 1975) may underscore the nearly down to the alveolar margin, and the mesofl exid is relationship between large size and striation of incisors. 0.39 mm high. As in the other teeth metafossettid and hy- Other authors, e. g. ENGESSER (1972), STEFEN (1997) and pofl exid are directly adjacent to each other. GIERSCH (2004) used the nomen Steneofi ber minutus for D i s c u s s i o n . – The taxonomic assignment of this this small Miocene beaver referring to the fact that mate- small Miocene beaver is a matter of continuous debate. rial lacking M3 is diffi cult to distinguish from Steneofi ber The discussion is reviewed here in order to substantiate (STEFEN 1997, HUGUENEY 1999). STEFEN & RUMMEL (2003) the determination of the Höwenegg specimen. assumed the presence of another Miocene lineage of a The species minutus was described by VON MEYER small beaver besides T. (E.) minutum. This form differs (1838) as Chalicomys minutus on the basis of a dentary from T. (E.) minutum by showing upper molars of equal with p4–m2 from the brown coal of Elgg in Switzerland, size and therefore indicating a relation to Steneofi ber. But which is fi gured in SCHLOSSER (1884, pl. 10, fi g. 15). The a defi nite characterisation is still pending. However, the fi gure is only a very sketchy drawing, but it shows the p4 length of striids might support the identifi cation of lower strongly enlarged with respect to the subequal m1 and m2. jaw elements: Steneofi ber does not show any striae/ striids The species was referred to different genera: Chalicomys which reach the crown base (STEFEN 1997). In Trogon- KAUP, 1832, Steneofi ber GEOFFROY-SAINT-HILAIRE, 1833, therium at least the hypostriid of p4 shows the tendency Monosaulax STIRTON, 1935, and Trogontherium FISCHER, to extend down to the base of the crown. This elongated 1809. striid is present in T. (E.) minutum rhenanum from Dorn- The genus Trogontherium is best known from its Pleis- Dürkheim, MN11 (FRANZEN & STORCH 1975), and in the tocene species T. cuvieri FISCHER, 1809, which was pains- sample from Azelsdorf, MN 9 (DAXNER-HÖCK & BERNOR takingly described by SCHREUDER (1929).