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First Mesozoic mammal from Australia - An early Cretaceous monotreme

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Abstract

Here we describe Australia's first known Mesozoic mammal and the first known early Cretaceous mammal from Gondwanaland. Steropodon galmani n. gen. and sp., discovered in early Cretaceous sediments at Lightning Ridge, New South Wales, Australia, appears to represent an ornithorhynchid-like monotreme. This discovery represents the first record of a fossil mammal from Australia that is older than 22.4±0.05 Myr1,2 and the specimen is, by more than 85Myr, the oldest known monotreme. As the oldest monotreme, it will necessitate a radical revision of present understanding about dental homology in the middle Miocene Obdurodon insignis, the only fossil monotreme previously known to have had teeth3. The structure of S. galmani supports one current view4 that monotremes, one of three groups of living mammals (the other two being marsupials and placentals), are phylogenetically close to the other groups of living mammals.
© Nature Publishing Group1985
© Nature Publishing Group1985
© Nature Publishing Group1985
© Nature Publishing Group1985
... 7, Ausktribosphenos, 8, Bishops, 9, Kryoparvus, and 10, Teinolophos, Lower Cretaceous (Aptian), Flat Rocks locality, southern Victoria, Australia (Rich et al., 1997(Rich et al., , 1999(Rich et al., , 20012020c). 11, Steropodon, 12, Kryoryctes, and 13, Stirtodon, Lower Cretaceous (Albian), Lightning Ridge locality, New South Wales, Australia (Archer et al.,1985;Rich et al., 2005;2020a).14, Obdurodon, Upper OligoceneePliocene, several sites in the Lake Ngapakaldi to Lake Palankarinna Fossil Area in South Australia, and Riversleigh, in northern Australia (Woodburne and Tedford 1975;Archer et al.,1992).15, ...
... From the same locality that has yielded Ausktribosphenos and Bishops, Flat Rocks in southeastern Victoria, the monotreme australosphenidan Teinolophos trusleri has been described (Rich et al., 1999). Of early Cenomanian age is the ornithorhynchid monotreme Steropodon galmani from Lightning Ridge in New South Wales (Archer et al., 1985) (Fig. 1). The Gondwanan record of australosphenidans further comprises besides Ambondro mahabo from the Middle Jurassic of Madagascar (Flynn et al., 1999) also an undescribed isolated lower molar from the LowereMiddle Jurassic from India preliminarily considered as a new taxon (Prasad et al., 2015) (Fig. 1). ...
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... Upper dentitions are not known for Ausktribosphenos and Bishops, but the lower molar wear pattern of Ausktribosphenos suggests a similar occlusal pattern like in Ambondro and the South American taxa. The Early Cretaceous monotreme Steropodon from Australia (Archer et al. 1985) is represented by a mandible fragment with three molars. The molars have a dilambdodont pattern, formed by trigonid and talonid. ...
... Not all of the larger Mesozoic taxa are represented by crania or even complete dentaries, thus precluding precise comparisons, but even fairly complete jaws are sufficient to reveal the presence of many species larger than brown rats (Rattus norvegicus, average ∼400 g; Nowak, 1991) and, in some cases, even guinea pigs (Cavia porcellus, average ∼1 kg; Nowak, 1991). These taxa include, for instance, Steropodon galmani and Kollikodon ritchei from the Early Cretaceous of Australia (Archer et al., 1985;Flannery et al., 1995;Pian et al., 2016); Vincelestes neuquenianus from the Early Cretaceous of Argentina (Rougier, 1993); Repenomamus robustus and Laioconodon hui from the Early Cretaceous of China (Li et al., 2001;Hu et al., 2005;Meng et al., 2011); Catopsbaatar catopsaloides and Mangasbaatar udanii from the Late Cretaceous of Mongolia (Kielan-Jaworowska et al., 2005;Rougier et al., 2016); Yubaatar zhongyuanensis from the Late Cretaceous of China (Xu et al., 2015); Gobiconodon ostromi and Cifelliodon wahkarmoosuch from the Early Cretaceous of the U.S.A. (Jenkins and Schaff, 1988;Huttenlocker et al., 2018); Didelphodon vorax from the Late Cretaceous of Canada and the U.S.A. (Gordon, 2003;Wilson et al., 2016); and Schowalteria clemensi from the Late Cretaceous of Canada (Fox and Naylor, 2003). ...
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Adalatherium hui is a latest Cretaceous (Maastrichtian) gondwanatherian mammal based on only a single specimen, a virtually complete, articulated, and well-preserved skull and postcranial skeleton. The specimen is the most complete and best preserved of any mammaliaform from the Mesozoic of the southern supercontinent Gondwana. It was discovered in the Anembalemba Member of the Maevarano Formation in the Mahajanga Basin of northwestern Madagascar. The holotype specimen includes the only complete lower jaw and the only postcranial remains known for Gondwanatheria, which, other than the cranium of Vintana sertichi (also from the latest Cretaceous of Madagascar), are represented only by isolated teeth and fragmentary dentaries. Despite being represented by an immature individual, A. hui is third only to V. sertichi and Coloniatherium cilinskii as the largest Mesozoic mammaliaform (based on body fossils) from Gondwana. Here, we (1) review the paucity of mammaliamorph skull and postcranial skeletal material from the Mesozoic of Gondwana relative to the record from Laurasia; (2) review the systematic paleontology of A. hui; (3) provide an overview of the history of discovery of the holotype specimen; (4) detail the preservation of the holotype, its preparation history, and the imaging techniques used to study it; (5) provide an overview of the geological context of A. hui, which indicates that the species lived close to the end-Cretaceous extinction event in a highly seasonal, semiarid climate; and (6) estimate the body mass of A. hui in the context of other Mesozoic mammaliaforms.
... The fauna from the Griman Creek Formation is amongst the most diverse of contemporaneous formations in Australia. In addition to sauropods, the vertebrate fauna includes aspidorhynchid teleosts (Bell et al. 2019b), lamniform chondrichthyans (Bell et al. 2019b), several dipnoans (Kemp 1993;Kemp 1997a,b), chelid and possible meiolaniform turtles (Smith 2010), leptocleidid plesiosaurs (Kear 2006), megaraptorid (Bell et al. 2016), carchardodontosaurid (Brougham et al. 2019) and noasaurid theropods (Bell et al. 2016;Brougham et al. 2020), iguanodontian and non-iguanodontian ornithopods (Molnar & Galton 1986;Bell et al. 2018;Kitchener et al. 2019), crocodylomorphs (Molnar 1980Hart et al. 2019), anhanguerian pterosaurs (Brougham et al. 2017), enantiornithine birds (Molnar 1999), and both stem and crown monotreme mammals (Archer et al. 1985;Rich et al. 1989;Clemens et al. 2003); see Bell et al. (2019b) for a thorough review of the vertebrate fauna). ...
Article
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Chapter
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Chapter
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Chapter
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The Synapsida is the mammal-like ramus of the Amniota, the sister group of the Sauropsida (or Reptilia of Gauthier et al., 1988). Synapsids are characterized by the possession of a lateral temporal fenestra (Fig. 1A), among other features (see Gauthier, this volume). Of all the great transitions between major structural grades within vertebrates, the transition from basal amniotes to basal mammals is represented by the most complete and continuous fossil record, extending from the Middle Pennsylvanian to the Late Triassic and spanning some 75 to 100 million years. Structural evolution of particular functional systems has been well investigated, notably the feeding mechanism (Barghusen, 1968; Crompton, 1972; Crompton and Parker, 1978; Crompton and Hylander, 1986) and the middle ear (Hopson, 1966; Allin, 1975, 1986; Allin and Hopson, 1992), and these studies have demonstrated the gradual nature of these major adaptive modifications.
Chapter
An isolated upper premolar from the Early Cretaceous (late Albian) Griman Creek Formation of Lightning Ridge, NSW, Australia, represents a new genus and species of a toothed monotreme that is much larger than any known from there or elsewhere.
Article
A PRELIMINARY study has been carried out on fossil remains (unearthed in the British Museum) from a travertine deposit in Tasmania. Regardless of the precise taxonomic assignments ultimately given to this material, the evidence we present that a diverse fauna of diprotodont marsupials existed in Australia in late Oligocene time is of considerable importance. This evidence gives tangible support to the hypothesis that marsupials have been residents of the Australian continent since the early Tertiary at least. The basic differentiation of herbivorous Diprotodonta from Marsupicarnivora (Ride, 1964) very likely took place before the separation of Australia from Antarctica. By late Oligocene time Tasmania was situated near 52°S latitude1 bathed by warmer seas2 and the travertine accumulated in an equable warm-temperate to subtropical environment supporting a rich forest vegetation3-5 the closest living equivalents of which occur in the uplands of New Guinea and New Caledonia. Present-day representatives of some of the fossil marsupials from the travertine still inhabit such tropical environments in northern Australia and New Guinea.
Chapter
Periodically it is worthwhile to assess our knowledge and understanding of mammalian phylogeny and one of its expressions, classification. This short paper is yet another attempt to do so, taking into account the results of recently published paleontological research and drawing heavily on work in progress by many researchers in many fields and in various parts of the world. Concepts of mammalian phylogeny and classification have changed markedly during the last few years. A good many of the ideas expressed here are frankly speculative, but they are presented anyway in order to determine how well they will stand scrutiny, especially by nonpaleontologists. A few years ago I prepared a paper with a similar aim (McKenna, 1969), but that paper is now outdated. In the present offering I attempt to update certain aspects of my previous review by taking into account research published since 1969, as well as work being incorporated into a new classification of the Mammalia now being prepared which wall deal with all taxonomic levels down to the subgeneric level in essentially the same style as Simpson’s (1945) classification.
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