Alistair R. Evans (2016)
What is ‘Pseudo’ in Pseudotribosphenic Teeth?
Memoirs of Museum Victoria 74: 93-96
The discovery of a ‘pseudotribosphenic’ lower tooth row in 1982, with a basin anterior to the trigonid rather than posterior, caused a large stir in mammalian palaeontology. This indicated that a tooth shape of equivalent complexity to the tribosphenic tooth form could evolve more than once. The upper tooth predicted to occlude with the pseudotribosphenic molar was reconstructed with a ‘pseudoprotocone’ to occlude with the pseudotalonid basin. Here I discuss the relative merits of naming the major upper lingual cusp of pseudotribosphenic molars as ‘protocone’ due to its likely similar developmental and functional relations as the protocone of tribosphenic molars. The use of a different name implies greater morphological distance between tribosphenic and pseudotribosphenic upper molars than is perhaps warranted, and likely exaggerates the perception of the difficulty in evolving both tribospheny and pseudotribospheny. The choice between the evolution of the alternative forms of tribospheny may in fact be related to the degree of anterior-posterior bias in lower molar development – tribospheny with a posterior bias, while pseudotribospheny with an anterior one.
Rebecca Pian, Michael Archer, Suzanne J. Hand, Robin M.D. Beck and Andrew Cody (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.
Ralph E. Molnar and Felipe Mesquita de Vasconcellos (2016)
Cenozoic dinosaurs in South America – revisited.
Memoirs of Museum Victoria 74: 363-377
Of course there were Cenozoic dinosaurs (theropods) in South America, phorusrhacid (‘terror’) birds among others, but that is not the subject here. Why did anyone think there were Cenozoic (non-avian) theropods in South America? Because of a misinterpretation of Ameghino’s belief that derived mammals lived along with dinosaurs in Late Cretaceous Argentina. But also because isolated theropod teeth were found associated with derived (Eocene) mammal fossils. These turned out to be the teeth of Sebecus icaeorhinus. This is a small crocodylomorph, skull length c. 450 mm. More recently discovered sebecosuchians were substantially larger: Barinasuchus arveloi had an (estimated) skull length of c. 1000 mm, similar to that of Daspletosaurus (1000 mm). These crocodylomorphs are generally believed to have been terrestrial animals, presumably preying on large mammals. Thus, although there were no large non-avian theropods in Cenozoic South America, there were crocodylomorphs that seem to have been ecological vicars of large theropods. The reconstruction of terrestrial trophic networks for large terrestrial tetrapods after the Cretaceous-Paleogene extinctions seems to have been slower than often supposed. At (or near) the Cretaceous-Paleogene boundary, large herbivores turned over from archosaurs to mammals, but turnover of large carnivores was slower. In South America, dinosaur-size crocodylomorphs lived as late as the Miocene. Thus modern terrestrial ecosystems do not, trophically, reflect those of even the Early Neogene in some southern continents. Sebecosuchians, at least in South America, seem to have been unaffected by the Cretaceous-Paleogene extinctions.