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Paläontologische Zeitschrift

, Volume 90, Issue 1, pp 153–171 | Cite as

Digital reconstruction of the inner ear of Leptictidium auderiense (Leptictida, Mammalia) and North American leptictids reveals new insight into leptictidan locomotor agility

  • Irina Ruf
  • Virginie Volpato
  • Kenneth D. Rose
  • Guillaume Billet
  • Christian de Muizon
  • Thomas Lehmann
Research Paper

Abstract

Leptictida are basal Paleocene to Oligocene eutherians from Europe and North America comprising species with highly specialized postcranial features including elongated hind limbs. Among them, the European Leptictidium was probably a bipedal runner or jumper. Because the semicircular canals of the inner ear are involved in detecting angular acceleration of the head, their morphometry can be used as a proxy to elucidate the agility in fossil mammals. Here we provide the first insight into inner ear anatomy and morphometry of Leptictida based on high-resolution computed tomography of a new specimen of Leptictidium auderiense from the middle Eocene Messel Pit (Germany) and specimens of the North American Leptictis and Palaeictops. The general morphology of the bony labyrinth reveals several plesiomorphic mammalian features, such as a secondary crus commune. Leptictidium is derived from the leptictidan groundplan in lacking the secondary bony lamina and having proportionally larger semicircular canals than the leptictids under study. Our estimations reveal that Leptictidium was a very agile animal with agility score values (4.6 and 5.5, respectively) comparable to Macroscelidea and extant bipedal saltatory placentals. Leptictis and Palaeictops have lower agility scores (3.4 to 4.1), which correspond to the more generalized types of locomotion (e.g., terrestrial, cursorial) of most extant mammals. In contrast, the angular velocity magnitude predicted from semicircular canal angles supports a conflicting pattern of agility among leptictidans, but the significance of these differences might be challenged when more is known about intraspecific variation and the pattern of semicircular canal angles in non-primate mammals.

Keywords

Leptictida Leptictidium Inner ear Bony labyrinth Semicircular canals Locomotion 

Abbreviations

AMNH

Division of Paleontology, American Museum of Natural History, New York, USA

F-AM

Frick Collection, Division of Paleontology, American Museum of Natural History, New York, USA

SMF

Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Germany

SMF-ME

Senckenberg Forschungsinstitut und Naturmuseum Frankfurt, Germany, Messel Collection

SZ

Zoologische Schausammlung, Tübingen, Germany

USNM

Department of Paleobiology, National Museum of Natural History, Smithsonian Institution,Washington DC, USA

Kurzfassung

Leptictida sind basale Eutheria aus dem Paläozän bis Oligozän von Europa und Nordamerika, die Arten mit hochspezialisiertem Postcranialskelett umfassen; so haben manche Arten deutlich verlängerte Hinterbeine. Hierzu gehört die europäische Form Leptictidium, die möglicherweise ein bipeder Läufer oder Hüpfer war. Da die Bogengänge des Innenohres die Winkelbeschleunigung des Kopfes detektieren, kann deren Morphometrie genutzt werden, um die Agilität fossiler Säuger zu rekonstruieren. Erstmals werden hier die Innenohranatomie und – morphometrie der Leptictida vorgestellt, die auf hochauflösenden Computertomografiescans eines neuen Exemplares von Leptictidium auderiense aus dem mittleren Eozän der Grube Messel (Deutschland) sowie weiteren Exemplaren der nordamerikanischen Formen Leptictis und Palaeictops basieren. Generell zeigt die Morphologie des Innenohres, dass die untersuchten Arten zahlreiche plesiomorphe Säugermerkmale zeigen, wie z. B. ein sekundäres Crus commune. Leptictidium ist vom Grundplan der Leptictida abgeleitet, da es keine Lamina spiralis ossea secundaria besitzt und proportional größere Bogengänge als die anderen untersuchten Leptictida aufweist. Es zeigt sich, dass Leptictidium ein recht agiles Tier mit Agilitätswerten von 4.6 bzw. 5.5 war, die mit denen der Macroscelidea und rezenten biped hüpfenden Placentalia vergleichbar sind. Leptictis und Palaeictops haben geringere Agilitätswerte (3.4 bis 4.1), wie bei den meisten rezenten Säugern, die einen eher generalisierten Lokomotionstyp (z. B. terrestrisch, cursorial) aufweisen. Im Gegensatz dazu zeigt die Berechnung der Winkelbeschleunigungs-Magnitude, die von den Winkeln zwischen den Bogengängen abgeleitet wird, ein gegenteiliges Agilitätsmuster innerhalb der Leptictida, wobei diese Unterschiede weiterer Überprüfungen bedürfen, sobald mehr über die intraspezifische Variabilität der Bogengangwinkel in Nicht-Primaten bekannt ist.

Schlüsselwörter

Leptictida Leptictidium Innenohr knöchernes Labyrinth Bogengänge Lokomotion 

Notes

Acknowledgments

The authors wish to express their gratitude for the effort and enthusiasm of the excavation and preparation team from Senckenberg Forschungsinstitut und Naturmuseum Frankfurt (Abteilung Paläoanthropologie und Messelforschung) and Messel Research Station; in particular, M. Ackermann, M. Groppo, and M. Müller, who discovered and prepared the new specimen of Leptictidium auderiense. The Palaeictops specimen was collected under a permit from the U.S. Bureau of Land Management and with support from the U.S. National Science Foundation to KDR. Sincere thanks are given to J. Meng and J. Galkin (American Museum of Natural History, New York) as well as E. Weber (Zoologische Schausammlung Tübingen) for the loan of specimens. We are also grateful to P. Hornberger (Fraunhofer Anwendungszentrum CTMT, Deggendorf) and M. Heath (Werth Messtechnik GmbH, Gießen) for excellent technical assistance with the µCT scans of Leptictidium. C. Pfaff (Institut für Paläontologie, Universität Wien), M. Scheske (Steinmann-Institut, Bonn), and U. Menz (Senckenberg Forschungsinstitut und Naturmuseum Frankfurt) helped us with technical support. We thank T. Macrini, M. Silcox, and an anonymous reviewer whose comments greatly improved the manuscript. This study was funded by a Deutsche Forschungsgemeinschaft (DFG) grant to TL and VV (Le 2730/1-1). This article is dedicated to the memory of our friend and colleague Marion Groppo.

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Copyright information

© Paläontologische Gesellschaft 2016

Authors and Affiliations

  • Irina Ruf
    • 1
    • 2
  • Virginie Volpato
    • 1
    • 3
  • Kenneth D. Rose
    • 4
  • Guillaume Billet
    • 2
    • 5
  • Christian de Muizon
    • 5
  • Thomas Lehmann
    • 1
  1. 1.Abteilung Paläoanthropologie und MesselforschungSenckenberg Forschungsinstitut und Naturmuseum FrankfurtFrankfurt am MainGermany
  2. 2.Steinmann-Institut für Geologie, Mineralogie und PaläontologieRheinische Friedrich-Wilhelms-Universität BonnBonnGermany
  3. 3.Department of GeosciencesUniversity of FribourgFribourgSwitzerland
  4. 4.Center for Functional Anatomy and EvolutionJohns Hopkins University School of MedicineBaltimoreUSA
  5. 5.Muséum national d’Histoire naturelle, CR2P - UMR 7207 CNRS, MNHNUniv Paris 06, Sorbonne UniversitésParisFrance

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