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Download Full Article 1.5MB .Pdf File Memoirs of Museum Victoria 74: 97–105 (2016) Published 2016 ISSN 1447-2546 (Print) 1447-2554 (On-line) http://museumvictoria.com.au/about/books-and-journals/journals/memoirs-of-museum-victoria/ The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei REBECCA PIAN1,2,3, MICHAEL ARCHER1,*, SUZANNE J. HAND1, ROBIN M.D. BECK1,4 AND ANDREW CODY5 1 PANGEA Research Centre, School of Biological, Earth and Environmental Sciences, University of New South Wales, Sydney, New South Wales 2052, Australia ([email protected]) 2 Division of Paleontology, American Museum of Natural History, New York, NY 10024, USA ([email protected]) 3 Department of Earth and Environmental Sciences, Columbia University, New York, NY 10026 USA 4 School of Environment & Life Sciences, University of Salford, Salford M5 4WT, England 5 The National Opal Collection, 119 Swanston St, Melbourne, Victoria 3000, Australia *To whom correspondence should be addressed. E-mail: [email protected] Abstract Pian, R., Archer, M., Hand, S.J., Beck, R.M.D. and Cody, A. 2016. The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei. Memoirs of Museum Victoria 74: 97–105. Mesozoic mammals from Australia are rare, so far only known from the Early Cretaceous, and most are poorly represented in terms of dentitions much less cranial material. No upper molars of any have been described. Kollikodon ritchiei is perhaps the most bizarre of these, originally described on the basis of a dentary fragment with three molars. Here we describe a second specimen of this extremely rare taxon, one that retains extraordinarily specialised upper cheekteeth (last premolar and all four molars). Each molar supports rows of bladeless, rounded cuspules many of which exhibit apical pits that may be the result of masticating hard items such as shells or chitin. Reanalysis of the phylogenetic position of this taxon suggests, based on a limited number of apparent synapomorphies, that it is an australosphenidan mammal and probably the sister group to Monotremata. This reanalysis also supports the view that within Monotremata, tachyglossids and ornithorhynchids diverged in the early to middle Cenozoic. Keywords New South Wales, Mesozoic, Albian, Australosphenida, Monotremata, Ausktribosphenidae. Introduction placed ausktribosphenids and monotremes within a larger Gondwanan radiation termed Australosphenida (Luo et al., Mesozoic mammals from Australia were unknown until the 2001, 2002, 2007a; Martin and Rauhut, 2005; Rougier et al., description in 1985 of the holotype and only known specimen 2011; Wood and Rougier, 2005), together with the early Jurassic of the monotreme Steropodon galmani (Archer et al., 1985), a partial right dentary with all three molars, from the Early (Toarcian) (Cúneo et al., 2013) South American Asfaltomylos Cretaceous (Albian) Griman Creek Formation at Lightning (Rauhut et al., 2002) and Henosferus (Rougier et al., 2007), and Ridge, New South Wales. This was followed by discovery at the middle Jurassic (Bathonian) Ambondro mahabo (Flynn et Lightning Ridge of Kollikodon ritchiei (Flannery et al., 1995), al., 1999) from Madagascar. Some authors, however, have known from a single partial right dentary with three molars in questioned the inclusion of monotremes within Australosphenida situ and alveoli for the posterior two premolars and a fourth (Pascual et al., 2002; Rich et al., 2002; Rowe et al., 2008; molar. Since then, additional Early Cretaceous mammals have Woodburne, 2003). been described from sites in southern Victoria and New South Archer et al. (1985) described Steropodon galmani as a Wales. These include: from the Aptian Flat Rocks locality in plesiomorphic, toothed monotreme in the monotypic family Victoria, the ausktribosphenids Ausktribosphenos nyktos (Rich Steropodontidae, an assignation that has been widely accepted et al., 1997) and Bishops whitmorei (Rich et al., 2001a), the (Kielan-Jaworowska et al., 1987; Musser, 2006; Phillips et al., monotreme Teinolophos trusleri (Rich et al., 1999, 2001b), and 2009). Inclusion of Teinolophos trusleri within Monotremata is the multituberculate Corriebaatar marywaltersae (Rich et al., also uncontested, despite some debate over placement within 2009); from the Albian Dinosaur Cove locality in Victoria, the the stem or crown group (Phillips et al., 2009; Rich et al., 2001b; partial humerus of (the possible monotreme) Kryoryctes Rowe et al., 2008). Flannery et al., (1995) described Kollikodon cadburyi (Pridmore et al., 2005); and from Lightning Ridge in ritchiei as a possible monotreme, placing it in its own monotypic New South Wales a very large, mammal-like isolated tooth family, the Kollikodontidae. This assignation has proved more (Clemens et al., 2003). Most recent phylogenetic analyses have controversial, with suggestions that it may be a basal 98 R.Pian, M. Archer, S.J. Hand, R.M.D. Beck & A. Cody mammaliaform rather than a monotreme and as such more Systematic Palaeontology appropriately placed outside crown-group Mammalia (Musser, 2003). This controversy rejects in part the limited morphological Mammalia Linnaeus, 1758 information available on the basis of the previously only known specimen, a partial dentary with three highly autapomorphic, Australosphenida Luo, Cifelli and Kielan-Jaworowska, 2001 bunodont molars. Discovery of an additional specimen of K. ritchiei, a partial maxilla with one premolar and four molars, Kollikodontidae Flannery, Archer, Rich and Jones, 1995 now provides significant additional information about the structure and likely evolutionary relationships of this enigmatic Kollikodon Flannery, Archer, Rich and Jones, 1995 taxon. This specimen also represents the first maxilla with teeth known for any Australian Mesozoic mammal. Kollikodon ritchiei Flannery, Archer, Rich and Jones, 1995 Here we describe this specimen and test the evolutionary relationships of K. ritchei via phylogenetic analysis based on a Holotype. AM F96602 (Australian Museum Palaeontological comprehensive morphological character matrix. Collection, Sydney, Australia,), right dentary fragment preserving m1-3 and alveoli for two premolars and m4. Materials and Methods Referred specimen. Opalised right skull fragment preserving Measurements of the specimen were taken to the nearest 0.01 part of the maxilla, which retains the posterior premolar (possibly mm using a Leica M205 C microscope and integrated Leica P4) and M1-4, and possibly also part of the palatine (Figs 1–2). A DFC290 camera. Tooth lengths were measured along the long 35μm voxel Xradia microCT data file of the specimen has been axis of the molar row. Widths were measured from the widest lodged with the Museum of Victoria in Melbourne. Detailed 3D transverse points across the tooth, perpendicular to the long axis. prints of this specimen can be made from the scan data. Solid Kollikodon ritchiei was added to a revised version of the casts taken from a mould of the complete upper dentition are also character matrix of Luo et al. (2011), which is in itself a available; one (AM F140201) is registered in the collections of modified version of earlier matrices (Luo et al., 2001, 2002, the Australian Museum. Although the original specimen, which 2007b; Luo & Wible, 2005). Revisions to the matrix were is a natural glass cast without internal structure of any kind, is made on the basis of corrections and criticisms by Woodburne less informative than the microCT scan data (given that it reveals et al. (2003), Rougier et al. (2007), Rowe et al. (2008) and structures in undercut areas not visible via conventional microscopy) and no more informative than 3D prints and hard Phillips et al. (2009). The final matrix included 104 taxa and casts, this specimen is available for further examination as part 438 characters. 62 multistate characters representing plausible of the National Opal Collection, on application to its Director, morphoclines were ordered. The topologies of the consensus Andrew Cody ([email protected]). trees derived through the ordered and unordered analyses were very similar, and as such only the ordered analyses are Locality and age. Griman Creek Formation; Early Cretaceous included here (Wiens, 2001). (Middle Albian) (Flannery et al., 1995). The type locality is Maximum parsimony analyses were conducted using the claim 30226, Moonshine area of the Cocoran opal field, computer program PAUP* (Phylogenetic Analysis Using Lightning Ridge, New South Wales, Australia (Flannery et al., Parsimony and Other Methods) version 4.0b10 (Swofford, 1995). The new skull fragment described here comes from an 2002). 1,000 heuristic replicates were initially carried out, unnamed mine on the Cocoran opal field. saving 10 trees per replicate, followed by a second heuristic New diagnosis of clade containing Kollikodon and monotremes. search within the trees obtained from the first search. Zero- Kollikodon ritchiei and definitive monotremes length branches were then collapsed. Strict and 50% majority- (ornithorhynchids, tachyglossids, Steropodon and Teinolophos) rule consensus trees were derived from the most parsimonious differ from other groups variously regarded as australosphenidans trees recovered for each analysis. Bootstrap analysis was used (ausktribosphenids, Ambondro, Asfaltomylos and shuotheriids), to assess nodal support. To calculate bootstrap values, 250 in so far as they are known, in having no paraconid on the first bootstrap replicates were run, with a time limit of 60 seconds lower
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