Kollikodon ritchiei Flannery, Archer, Rich and Jones, 1995

Pian, Rebecca, Archer, Michael, Hand, Suzanne J., Beck, Robin M. D. & Cody, Andrew, 2016, The upper dentition and relationships of the enigmatic Australian Cretaceous mammal Kollikodon ritchiei, Memoirs of Museum Victoria 74, pp. 97-105 : 98

Kollikodon ritchiei Flannery, Archer, Rich and Jones, 1995

Holotype. AM F96602 ( Australian Museum Palaeontological Collection , Sydney, Australia,), right dentary fragment preserving m1-3 and alveoli for two premolars and m4.

Referred specimen. Opalised right skull fragment preserving part of the maxilla, which retains the posterior premolar (possibly P4) and M1-4, and possibly also part of the palatine ( Figs 1–2 ). A 35μm voxel Xradia microCT data file of the specimen has been lodged with the Museum of Victoria in Melbourne. Detailed 3D prints of this specimen can be made from the scan data. Solid casts taken from a mould of the complete upper dentition are also available; one ( AM F140201) is registered in the collections of the Australian Museum. Although the original specimen, which is a natural glass cast without internal structure of any kind, is less informative than the microCT scan data (given that it reveals structures in undercut areas not visible via conventional microscopy) and no more informative than 3D prints and hard casts, this specimen is available for further examination as part of the National Opal Collection, on application to its Director, Andrew Cody ([e-mail]).

Locality and age. Griman Creek Formation; Early Cretaceous (Middle Albian) ( Flannery et al., 1995). The type locality is claim 30226, Moonshine area of the Cocoran opal field, Lightning Ridge, New South Wales, Australia ( Flannery et al., 1995). The new skull fragment described here comes from an unnamed mine on the Cocoran opal field.

New diagnosis of clade containing Kollikodon and monotremes. Kollikodon ritchiei and definitive monotremes (ornithorhynchids, tachyglossids, Steropodon and Teinolophos ) differ from other groups variously regarded as australosphenidans (ausktribosphenids, Ambondro , Asfaltomylos and shuotheriids), in so far as they are known, in having no paraconid on the first lower molar, an extremely abrupt discontinuity in size between the ultimate premolar and the first molar in the upper and lower dentitions, and in the presence of an enlarged dentary canal.

Revised specific diagnosis. Kollikodon ritchiei is a large (by Mesozoic standards) mammal (estimated body mass approximately 1935 g based on m1 area ( Legendre, 1986)) that differs from definitive monotremes that retain a functional dentition in exhibiting the following combination of features: bunodont molars with no vertical blades (lophs or crests) of any kind; broadly crescentic upper molars with unique cusp arrangement; reduced or absent posterior cingula/cingulids on all molars; markedly convex curve of the buccal edge of the upper and (to a lesser extent) lower molar rows.

Figures

Figure 1. Kollikodon ritchiei right maxillary fragment and molar row preserving Px, M1, M2, M3 and RM4. Stereopair occlusal view. ant, anterior; bucc, buccal.

Figure 2. Kollikodon ritchiei right maxillary fragment and molar row preserving Px, M1, M2, M3 and M4. (A) Stereopair oblique-occlusal view. (B) Stereopair lingual view. (C) Stereopair buccal view. ant, anterior.