The mandible and dentition of the Early Cretaceous monotreme Teinolophos trusleri

Abstract

Rich, T.H., Hopson, J.A., Gill, P.G., Trusler, P., Rogers-Davidson, S., Morton, S., Cifelli, R.L., Pickering, D., Kool, L., Siu, K., Burgmann, F.A., Senden, T., Evans, A.R., Wagstaff, B.E., Seegets-Villiers, D., Corfe, I.J., Flannery, T.F., Walker, K., Musser, A.M., Archer, M., Pian, R. & Vickers-Rich, P., June 2016. The mandible and dentition of the Early Cretaceous monotreme Teinolophos trusleri. Alcheringa 40, xx–xx. ISSN 0311-5518.

The monotreme Teinolophos trusleri Rich, Vickers-Rich, Constantine, Flannery, Kool & van Klaveren, 1999 from the Early Cretaceous of Australia is redescribed and reinterpreted here in light of additional specimens of that species and compared with the exquisitely preserved Early Cretaceous mammals from Liaoning Province, China. Together, this material indicates that although T. trusleri lacked a rod of postdentary bones contacting the dentary, as occurs in non-mammalian cynodonts and basal mammaliaforms, it did not share the condition present in all living mammals, including monotremes, of having the three auditory ossicles, which directly connect the tympanic membrane to the fenestra ovalis, being freely suspended within the middle ear cavity. Rather, T. trusleri appears to have had an intermediate condition, present in some Early Cretaceous mammals from Liaoning, in which the postdentary bones cum ear ossicles retained a connection to a persisting Meckel’s cartilage although not to the dentary. Teinolophos thus indicates that the condition of freely suspended auditory ossicles was acquired independently in monotremes and therian mammals. Much of the anterior region of the lower jaw of Teinolophos is now known, along with an isolated upper ultimate premolar. The previously unknown anterior region of the jaw is elongated and delicate as in extant monotremes, but differs in having at least seven antemolar teeth, which are separated by distinct diastemata. The dental formula of the lower jaw of Teinolophos trusleri as now known is i2 c1 p4 m5. Both the deep lower jaw and the long-rooted upper premolar indicate that Teinolophos, unlike undoubted ornithorhynchids (including the extinct Obdurodon), lacked a bill.

Thomas H. Rich [[email protected]], Sally Rogers-Davidson [[email protected]], David Pickering [[email protected]], Timothy F. Flannery [[email protected]], Ken Walker [[email protected]], Museum Victoria, PO Box 666, Melbourne, Victoria 3001, Australia; James A. Hopson [[email protected]], Department of Organismal Biology & Anatomy, University of Chicago,1025 East 57th Street, Chicago, IL 60637, USA; Pamela G. Gill [[email protected]], School of Earth Sciences, University of Bristol, Bristol BS8 1RJ, U.K. and Earth Science Department, The Natural History Museum, Cromwell Road, London SW7 5BD, UK; Peter Trusler [[email protected]], Lesley Kool [[email protected]], Doris Seegets-Villiers [[email protected]], Patricia Vickers-Rich [[email protected]], School of Earth, Atmosphere and Environment, Monash University, Victoria 3800, Australia; Steve Morton [[email protected]], Karen Siu [[email protected]], School of Physics and Astronomy, Monash University, Victoria 3800, Australia; Richard L. Cifelli [[email protected]] Sam Noble Oklahoma Museum of Natural History, University of Oklahoma, Norman, OK 73072, USA; Flame A. Burgmann [[email protected]], Monash Centre for Electron Microscopy, 10 Innovation Walk, Monash University, Clayton, Victoria 3800, Australia; Tim Senden [[email protected]], Department of Applied Mathematics, Research School of Physical Sciences and Engineering, The Australian National University, Canberra, Australian Capital Territory 0200, Australia; Alistair R. Evans [[email protected]], School of Biological Sciences, Monash University, Victoria 3800, Australia; Barbara E. Wagstaff [[email protected]], School of Earth Sciences, The University of Melbourne, Victoria 3010, Australia; Ian J. Corfe [[email protected]], Institute of Biotechnology, Viikinkaari 9, 00014, University of Helsinki, Finland; Anne M. Musser [[email protected]], Australian Museum, 1 College Street, Sydney NSW 2010 Australia; Michael Archer [[email protected]], School of Biological, Earth, and Environmental Sciences, University of New South Wales, Sydney, NSW 2052, Australia; Rebecca Pian [[email protected]], Division of Paleontology, American Museum of Natural History, Central Park West at 79th Street, New York, NY 10024-5192, USA. Received 7.4.2016; accepted 14.4.2016.

Key words:

• Monotremata
• Teinolophos
• TMME
• Cretaceous
• Australia
• dentition
• mandible

Dedication::

• This paper is warmly dedicated to the memory of Zofia Kielan-Jaworowska, one of the foremost pioneers and all-time authorities on Mesozoic mammals

Disclosure statement

No potential conflict of interest was reported by the authors.

Acknowledgements

First and foremost, the literally hundreds of volunteers who participated in the field work at the Flat Rocks site between 1993 and 2008 are thanked for their hard work and discoveries. The Committee for Research and Exploration of the National Geographic Society and the Australian Research Council provided much of the funding needed for the fieldwork carried out at the Flat Rocks locality. Permits to carry out the excavations in the Bunurong Marine Park were issued by National Parks Victoria. Useful discusions were had with Edgar Allin, Alexander Averianov, Zofia Kielan-Jaworowska and Guillermo Rougier. Averianov and Rougier completely unbeknownst to one another, each suggested that NMV P229194 might be the upper premolar of Teinolophos. Jin Meng and one anonymous reviewer provided useful comments on the manuscript. Andrew Russos, Wheelers Hill, Victoria, Australia and Atlas Copco, Sjöbodavägen, Stockholm, Sweden provided essential facilities and assets. Digimorph scans were provided by Timothy Rowe. Draga Gelt provided critical assistance with the graphics at short notice. Suzanne Hand organized the loan of isolated upper premolars of Obdurodon dicksoni. We acknowledge travel funding provided by the International Synchrotron Access Program managed by the Australian Synchrotron and funded by the Australian Government. We also thank Museum Victoria, Monash University and the Australian Synchrotron for the use of facilities and equipment.