Cranial and mandibular morphology of Middle Pleistocene cave bears (Ursus deningeri): implications for diet and evolution

ABSTRACT

Deninger’s bears (Ursus deningeri) have been studied less frequently than Ursus spelaeus s.l. Our objective is to present, for the first time, an analysis of the skull shape of U. deningeri.

Bear crania and mandibles were digitised with a Microscribe or CT-scanned and the surface models subsequently landmarked. The landmarks were chosen based on a compromise between functional morphology and sample size.

Results show that U. deningeri and U. spelaeus mandibles display very similar morphologies and allometric trajectories, both to each other and to Ailuropoda melanoleuca. It is inferred that masticatory adaptations to a herbivorous diet were already present in the Middle Pleistocene. U. deningeri displays a cranial morphology that is similar to that of U. spelaeus when comparing all species, but U. deningeri has a relatively narrower and dorsoventrally lower zygomatic arch than U. spelaeus, although the masticatory signal is less strong in the skull.

We observe intraspecific differences between different populations of U. deningeri, which could parallel the genetic diversity found in U. spelaeus. The intraspecific differences found within U. deningeri may be temporal and/or geographical in nature and could be related to the evolution of the Late Pleistocene cave bear, but this hypothesis remains to be tested.

KEYWORDS:

• Geometric morphometrics
• masticatory system
• skull
• mandible

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Acknowledgments

Specimens were studied in the following museums: Arkeologi Museoa, Bilbao, Spain; Haus der Natur, Salzburg, Austria; Landesmuseum Joanneum, Graz, Austria; Musée de Préhistoire de Tautavel; Museu de Ciències Naturals, Barcelona, Spain; Museum am Löwentor, Germany; Museum für Naturkunde, Leibnitz-Institut für Evolutions- und Biodiversitätsforschung and der Humboldt Universtität, Berlin, Germany; Museum of Zoology and Natural History La Specola, Firenze, Italy; Natural History Museum, London, United Kingdom; Natural History Museum, University of Oslo, Oslo, Norway; Naturhistorisches Museum Wien, Vienna, Austria; Royal Belgian Institute of Natural Sciences, Brussels, Belgium; Universität Tübingen, Tübingen, Germany; Universität Wien, Vienna, Austria; Université de Liège, Liège, Belgium. The authors would like to thank the curators at these institutions for granting permission to study the fossils. We would especially like to thank Prof. Evaggelia Tsoukala for giving permission to use the Petralona specimen. This research received support from the SYNTHESYS Project http://www.synthesys.info/ to AHvH, which is financed by European Community Research Infrastructure Action under the FP6 ‘Structuring the European Research Area’ Programme. This research was partly funded by internal grant 37913 and a 3-year bursary from the University of Roehampton to AHvH. This work was supported by the Spanish Ministerio de Economía y Competitividad under grant CGL2015–65387-C3–2-P-MINECO/FEDER); the Eusko Jaurlaritza-Gobierno Vasco under Research Group IT1044–16; and the Universidad del País Vasco-Euskal Herriko Unibertsitatea under Group PPG17/05. Research at Santa Isabel de Ranero (SIR; Karrantza, Biscay) and with the collections from this site were possible thanks to the funding provided by the Diputación Foral de Bizkaia-Bizkaiko Foru Aldundia.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

This work was supported by the Euskal Herriko Unibertsitatea [PPG17/05];Ministerio de Economía y Competitividad [CGL2015–65387-C3–2-P-MINECO/FEDER];Diputación Foral de Bizkaia-Bizkaiko Foru Aldundia [NA];Eusko Jaurlaritza-Gobierno Vasco [IT1044–16];Sixth Framework Programme [NA];University of Roehampton [37913].