Figure 1 - uploaded by Zhe-Xi Luo
Content may be subject to copyright.
Phylogenetic relationships of main taxa of therian tribosphenic mammals.The Australosphenida (Box A) and Boreosphenida (Box B) are both monophyleticand separate from each other. a, Primary analysis: the strict consensusof 18 equally parsimonious and shortest trees from the 55 dental and mandibularcharacters that are known for the southern tribosphenic mammals (see Supplementary Information). b, Extended analysis: thestrict consensus of eight equally parsimonious and shortest trees from anexpanded analysis including cranial and postcranial data for the better preservedtaxa (118 informative characters; see Supplementary Information). Placement of the australosphenidan clade on the mammalian tree isconsistent, whether it is based on just the dental and mandibular featuresknown for southern taxa (a), or on combined data of the dentition,mandible, plus cranium23,24 and postcranium25–27 (b). Apomorphies supporting the main cladogram nodes are presentedin Supplementary Information (see Methods for details).
Source publication
Marsupials, placentals and their close therian relatives possess complex (tribosphenic) molars that are capable of versatile occlusal functions. This functional complex is widely thought to be a key to the early diversification and evolutionary success of extant therians and their close relatives (tribosphenidans). Long thought to have arisen on no...
Contexts in source publication
Context 1
... analysis of the available evidence from the dentition and mandible ( Fig. 1; also see Methods) places the tribosphenic mam- mals Ambondro 6 and Ausktribosphenos 7,8 , together with the earliest known monotreme Steropodon 6 (Australia, Early Cretaceous), in a monophyletic group, which we term the Australosphenida (concept modi®ed from Ausktribosphenida 7 ; seèSystematic Palaeontol- ogy'). This group is ...
Context 2
... when com- pared with other Jurassic/Early Cretaceous holotherians. Notably, Ausktribosphenos retains plesiomorphies of the jaw as seen in stem mammals 9 , and we provisionally recognize some of these primitive characters to be preserved also in Steropodon. By contrast, the Boreosphenida, a clade of northern mammals with tribosphenic molars 10±12 (Fig. 1), have distinctive cingulid cuspules (cuspule e, cuspule f, or both) but lack a continuous mesial cingulid. The mesial cingulid does not wrap around or extend to the lingual side of the molars. Furthermore, boreosphenidans and proximal relatives, such as Henkelotherium, are more derived in that they have a mandibular angle far more ...
Context 3
... may have af®nities with the northern holo- there Shuotherium 19±21 (Fig. 1), some unknown early``early``symmetro- donts'' 9 , or the holotherian Dryolestidae 14 . However, by any previous interpretation they are independent from boreospheni- dans and their proximal relatives, including Henkelotherium 19 and pre-tribosphenic Peramus 17,22 . The clade of Ausktribosphenos, Ambondro and the monotreme Steropodon ...
Context 4
... (Fig. 1), some unknown early``early``symmetro- donts'' 9 , or the holotherian Dryolestidae 14 . However, by any previous interpretation they are independent from boreospheni- dans and their proximal relatives, including Henkelotherium 19 and pre-tribosphenic Peramus 17,22 . The clade of Ausktribosphenos, Ambondro and the monotreme Steropodon (Fig. 1), as inferred from mandibular and postcanine tooth morphology, is consistent with the phylogenies established by independent studies of basicranial 23,24 and postcranial 25±27 features of the main Mesozoic mammal groups documented by well-preserved fossils. In our expanded analysis (Fig. 1b), we added the cranial and postcranial ...
Context 5
... Ausktribosphenos, Ambondro and the monotreme Steropodon (Fig. 1), as inferred from mandibular and postcanine tooth morphology, is consistent with the phylogenies established by independent studies of basicranial 23,24 and postcranial 25±27 features of the main Mesozoic mammal groups documented by well-preserved fossils. In our expanded analysis (Fig. 1b), we added the cranial and postcranial features for those better-preserved taxa (for example, Morganucodon, Jeholodens and Henkelotherium). The simultaneous analysis (Fig. 1b) of cranial and postcranial data, together with the dental and mandibular characters, corroborates the australosphe- nidan clade and the boreosphenidan clade. ...
Context 6
... by independent studies of basicranial 23,24 and postcranial 25±27 features of the main Mesozoic mammal groups documented by well-preserved fossils. In our expanded analysis (Fig. 1b), we added the cranial and postcranial features for those better-preserved taxa (for example, Morganucodon, Jeholodens and Henkelotherium). The simultaneous analysis (Fig. 1b) of cranial and postcranial data, together with the dental and mandibular characters, corroborates the australosphe- nidan clade and the boreosphenidan clade. Hence, the hypothesis of a diphyletic origin for tribosphenic mammals is supported by morphological characteristics other than teeth and ...
Context 7
... of the lower molar shows that Ausktribosphenos and Steropodon are grouped together ( Fig. 3; Ambondro is not suf®ciently complete for inclusion). These australosphenidans occupy their own morphospace and are distinct from the stem taxa of boreosphenidans, metatherians and euther- ians (Fig. 3). Both parsimony analysis of discrete characters ( Fig. 1) and shape analysis (Fig. 3) suggest that Ausktribosphenos does not belong to the crown group of therians 9,15 , and that it may have close af®nities to the monotreme Steropodon 15,28 ...
Context 8
... lower and more excavated, despite their convergent resemblance in other aspects of the talonid. Given the evidence for monophyletic grouping of Steropodon, Ambondro and Ausktribosphenos, it is equally plausible that the mortar-to-pestle occlusion on the talonid developed independently in Ausktribosphenos 7,8 and Ambondro 6 in australosphenidans (Fig. 1a), or that the hypertrophied transverse crests evolved secondarily in place of a functional basin on the talonid in Steropodon 13 and the earliest ornithorhynchid Obdurodon 13,14,28 . Correspondingly, the hypertrophied crests also developed seconda- rily in place of a functional protocone on the upper molars, as seen in Obdurodon 13,14 . ...
Context 9
... propose a new model: mammals with the mortar-to-pestle structure of the talonid (tribosphenic condition) underwent vicariant and diphyletic evolution on Gondwanan and Laurasian continents, respectively (Fig. 1). We suggest that the Australo- sphenida represent an endemic radiation of mammals on southern continents during the Jurassic/Early Cretaceous, surviving through the Tertiary 22,28,39 as the extant ...
Context 10
... of relationships among tribosphenic mammals is based on PAUP (3.1.1, Swofford, 1993) analyses of 21 selected taxa (see Supplementary Information). Our primary analysis (Fig. 1a) concentrated on 55 dental and mandibular characters that are preserved in many southern taxa (Ambondro, Ausktribosphenos and Steropodon). We grouped the southern and northern tribosphenic mammals into independent clades, by the strict consensus of 18 equally parsimonious and shortest trees. Our extended analysis (Fig. 1b) added 70 ...
Context 11
... Our primary analysis (Fig. 1a) concentrated on 55 dental and mandibular characters that are preserved in many southern taxa (Ambondro, Ausktribosphenos and Steropodon). We grouped the southern and northern tribosphenic mammals into independent clades, by the strict consensus of 18 equally parsimonious and shortest trees. Our extended analysis (Fig. 1b) added 70 cranial and postcranial characters (from refs 23±27) that are preserved in the more complete taxa in our dataset to the 55 dental and mandibular characters known for the southern mammals, with requisite missing values coded for the taxa known only by teeth and jaws. The australosphenidan clade (including monotremes) and ...
Context 12
... with requisite missing values coded for the taxa known only by teeth and jaws. The australosphenidan clade (including monotremes) and boreosphenidan clade (including extant therians) are supported by simultaneous analyses of 118 parsimony-informative characters of dentition, skull and skeleton for the well- preserved taxa of early mammals 23±27 (Fig. 1b), and with 125 characters in additional tests of 26 ...
Context 13
... australosphenidan clade is a more robust node (that takes more steps to collapse) than many widely accepted clades, such as the boreosphenidan clade (Kielantherium plus extant therians), the extant therian clade and the eutherian clade (Fig. 1). Apomorphies for each node of the cladograms are listed in Supplementary ...
Context 14
... extant platypus (Ornithorhynchus) is nested in the australosphenidan clade. Bootstrap majority consensus trees from separate searches of the 55 dental and mandibular data partitions and the total 125 morphological characters have replicated both the australosphenidan clade and the boreosphenidan clade (Supplementary Information). These analyses (Fig. 1) and other independent morpho- logical analyses 2,23±27 have all shown that monotremes (herein considered to be a part of the australosphenidan clade) are more distant from the living therians than the non-tribo- sphenic symmetrodonts (Zhangheotherium) and eupantotheres ...
Similar publications
The squamates (lizards, snakes, and relatives) today comprise more than 10,000 species, and yet their sister group, the Rhynchocephalia, is represented by a single species today, the tuatara. The explosion in squamate diversity has been tracked back to the Cretaceous Terrestrial Revolution, 100 million years ago (Ma), the time when flowering plants...
Eutherian mammals (Placentalia and all mammals phylogenetically closer to placentals than to marsupials) comprise the vast majority of extant Mammalia. Among these there is a phenomenal range of forms and sizes, but the origins of crown group placentals are obscure. They lie within the generally tiny mammals of the Mesozoic, represented for the mos...
Paleoophiocordyceps coccophagus, a fungal parasite of a scale insect from the Early Cretaceous (Upper Albian), is reported and described here. This fossil not only provides the oldest fossil evidence of animal parasitism by fungi but also contains morphological features similar to asexual states of Hirsutella and Hymenostilbe of the extant genus Op...
A new Jurassic species of the very rare and incompletely known synechodontiform shark, Welcommia, is described. The new species, Welcommia cappettai, is represented only by a single tooth, precluding reconstruction of its dentition in detail. Nevertheless, this specimen provides sufficient information and characteristics to establish its taxonomic...
Pterosaurs were a unique clade of flying reptiles that were contemporaries of dinosaurs in Mesozoic ecosystems. The Pterodactyloidea as the most species-diverse group of pterosaurs dominated the sky during Cretaceous time, but earlier phases of their evolution remain poorly known. Here, we describe a 160 Ma filter-feeding pterosaur from western Lia...
Citations
... However, not all hoofed mammals have molarized premolars, as basal ungulates show distinct regionalization of the premolars and molars (Prothero and Foss 2007). This establishes molarized premolars as a strongly homoplastic character, unsurprising given the fast rates of evolution in mammalian crown complexity in comparison with the rest of the mammalian skull (Butler 1952(Butler , 1956; Janis and Lister 1985; Luo et al. 2001;Couzens et al. 2021; Goswami et al. 2023). Some hoofed mammals have retained regional differences between premolars and molars, while other groups have evolved molariform premolars (Fig. 1). ...
Molariform teeth have fascinated zoologists for as long as the field of evolutionary biology has existed, but few mammalian groups show as much morphological variation as hoofed mammals. Ungulate premolars and molars function together as the post-canine unit in grinding mastication. The degree of similarity of the premolars to the molars in crown complexity varies wildly across dietary ecologies and similar morphologies are refered to as molarized. However, the vast majority of dental complexity evolution research over the past 30 years has focused on molar crown morphogenesis evolution rather than interregional dental phenomena such as molarization. Dental crown complexity in vertebrates is controlled by signalling centers known as enamel knots in all regions of the jaw. In this study we tested whether applying current knowledge of enamel knot driven crown morphogenesis to shape covariation across the premolar molar boundary would inform potential mechanisms of molarization in hoofed mammals. We used 2D geometric morphometrics to study enamel-knot driven covariation at the lower premolar molar boundaries of 16 artiodactyl and 18 perissodactyls species. Phylogenetically informed modularity analyses were used to test several a-priori morphogenetic hypotheses describing different developmental interactions between the premolars and molars. Our results showed artiodactyls and perissodactyls significantly differ in their premolar molar boundary covariation caused by heterochronic shifts between premolar and molar development. To our knowledge, our study is the first to contribute a comprehensive yet accesible 2D morphometric method to produce heuristic results for further investigating the evolution of molarized premolars.
... Finally, we have not undertaken a phylogenetic analysis of the Lightning Ridge monotreme fossils because our interests principally lie in taxonomy and zoogeography. The outgroup to Monotremata is disputed, with two very different mammalian groups having been put forward-Southern Hemisphere tribosphenids (Luo et al. 2001), and dryolestids (Archer et al. 1993). This makes determinations of character state polarity (e.g., molar number) uncertain. ...
... Many dryolestoids have five or more molars, implying that this state may be plesiomorphic for Monotremata. Luo et al. (2001), however, countered that southern hemisphere tribosphenids, which have three molars, form a clade with monotremes, implying that the presence of five molars may be a secondary reversion. ...
... AM F161197 and AM F97263 add considerably to knowledge of the Meckelian groove in Steropodon galmani. AM F66763 is widely considered to have possessed a Meckelian groove (e.g., Luo 2007, Luo et al, 2001, 2007, Kielan-Jaworowska et al. 2004, Rougier et al. 2007, Wible et al. 2009), but recent re-examination has revealed post-mortem damage to the dentary above the Meckelian groove suggesting that this feature is actually a crack (see Flannery et al. 2022a). Notably, AM F161197 and AM F97263 both lack corresponding structures, although they do possess corresponding shallow depressions on the lingual sides of their dentaries. ...
... For instance, the pseudotalonids of shuotheriids and docodontans are no longer a result of convergent evolution 9,10,14,35 ; instead, they are shared and derived features supporting the new clade Docodontiformes. Although the composition of 'australosphenidans' remains controversial 16,18,36 , with the removal of shuotheriids, this southern tribosphenic group is no longer associated with a northern pseudotribosphenic sister group. ...
Shuotheriids are Jurassic mammaliaforms that possess pseudotribosphenic teeth in which a pseudotalonid is anterior to the trigonid in the lower molar, contrasting with the tribosphenic pattern of therian mammals (placentals, marsupials and kin) in which the talonid is posterior to the trigonid1–4. The origin of the pseudotribosphenic teeth remains unclear, obscuring our perception of shuotheriid affinities and the early evolution of mammaliaforms1,5–9. Here we report a new Jurassic shuotheriid represented by two skeletal specimens. Their complete pseudotribosphenic dentitions allow reidentification of dental structures using serial homology and the tooth occlusal relationship. Contrary to the conventional view1,2,6,10,11, our findings show that dental structures of shuotheriids can be homologized to those of docodontans and partly support homologous statements for some dental structures between docodontans and other mammaliaforms6,12. The phylogenetic analysis based on new evidence removes shuotheriids from the tribosphenic ausktribosphenids (including monotremes) and clusters them with docodontans to form a new clade, Docodontiformes, that is characterized by pseudotribosphenic features. In the phylogeny, docodontiforms and ‘holotherians’ (Kuehneotherium, monotremes and therians)¹³ evolve independently from a Morganucodon-like ancestor with triconodont molars by labio-lingual widening their posterior teeth for more efficient food processing. The pseudotribosphenic pattern passed a cusp semitriangulation stage⁹, whereas the tribosphenic pattern and its precursor went through a stage of cusp triangulation. The two different processes resulted in complex tooth structures and occlusal patterns that elucidate the earliest diversification of mammaliaforms.
... To date, the evolution and functional morphology of molar crowns have been examined extensively for early mammals, including dryolestids (Crompton 1971;Crompton & Jenkins, 1968;Schultz & Martin 2014). The advent of key innovations such as the tribosphenic molar and precise dental occlusion are just two examples of how changes in dental morphology can increase biomechanical efficiency of mastication and facilitate more versatile feeding adaptations (Davis, 2011;Grossnickle et al., 2019;Luo, 2007;Luo et al., 2001;Martin et al., 2020;Schultz & Martin, 2011. However, before CT scanning became widely available to examine the root structures inside the jaws (Self, 2015a, b), few studies have fully explored the evolutionary morphology of tooth roots or investigated the functional relationship between crown and root structures (but see Sulej et al., 2020). ...
... teeth in living mammals are remarkably diverse in size and shape (Ungar, 2010). The molars of all marsupials and placental mammals, but not monotremes, are thought to have evolved from tribosphenic molars, which appeared in the common ancestral lineage of marsupials and placental mammals in the Middle Jurassic (Luo et al., 2001(Luo et al., , 2002(Luo et al., , 2011. Early fossil species with tribosphenic molars and their descendants are classified in the clade Tribosphenida (or Boreosphenida) (Kielan-Jaworowska et al., 2004;Luo, 2007). ...
... Early fossil species with tribosphenic molars and their descendants are classified in the clade Tribosphenida (or Boreosphenida) (Kielan-Jaworowska et al., 2004;Luo, 2007). Monotremes are thought to have evolved from a separate lineage of Mesozoic mammals with tribosphenic-like molars (Australosphenida) (Luo et al., 2001(Luo et al., , 2002. Tribosphenic molars were originally described by Simpson (1936) as multi-cusped teeth that have two occlusal functions: shearing and grinding of food between the uppers and lowers ( Figure 1A.5 and B.5). ...
Phylogenetically, the tribosphenic molars—prototypes of multi-cusped cheek teeth in marsupial and placental mammals—are derived from the single-cusped conical teeth of reptiles through the addition of cusps. Ontogenetically, mammalian molars are formed through the interface between the dental epithelium and mesenchyme (future enamel–dentin junction), becoming geometrically complex by adding epithelial signaling centers, called enamel knots, which determine future cusp positions. To re-evaluate cusp homologies in Mesozoic mammals from an ontogenetic perspective, this study tracked molar development in a living placental mammal species, the house shrew (Suncus murinus), whose molars are morphologically the least derived from tribosphenic prototypes. The development of shrew molars proceeded as if it replayed the evolutionary process of tribosphenic molars. The first formed enamel knots gave rise to the evolutionarily oldest cusps—upper paracone and lower protoconid. The order of formation of other enamel knots and their location in development seemed to trace the order of cusp appearance in evolution. The parallel relationship between ontogeny and phylogeny of mammalian molars, if any, suggests that a change in the timing between developmental events rather than a change in the morphogenetic mechanism itself, should have been a major causal factor for the evolutionary transformation of tooth morphology.
... In this paper we examine the three-dimensional hemimandibular kinematics of mastication in D. virginiana. Didelphis retains an unfused mandibular symphysis and has tribosphenic molars similar to those of Mesozoic mammals [40][41][42][43][44][45][46][47]. Our objectives are threefold. ...
Didelphis virginiana (the Virginia opossum) is often used as an extant model for understanding feeding behaviour in Mesozoic mammaliaforms, primarily due to their morphological similarities, including an unfused mandibular symphysis and tribosphenic molars. However, the three-dimensional jaw kinematics of opossum chewing have not yet been fully quantified. We used biplanar videofluoroscopy and the X-Ray Reconstruction of Moving Morphology workflow to quantify mandibular kinematics in four wild-caught opossums feeding on hard (almonds) and soft (cheese cubes) foods. These data were used to test hypotheses regarding the importance of roll versus yaw in chewing by early mammals, and the impact of food material properties (FMPs) on jaw kinematics. The magnitude of roll exceeds that of yaw, but both are necessary for tooth-tooth or tooth-food-tooth contact between complex occlusal surfaces. We confirmed the utility of the four vertical kinematic gape cycle phases identified in tetrapods but we further defined two more in order to capture non-vertical kinematics. Statistical tests support the separation of chew cycle phases into two functional groups: occlusal and non-occlusal phases. The separation of slow close into two (occlusal) phases gives quantitative kinematic support for the long-hypothesized multifunctionality of the tribosphenic molar.
This article is part of the theme issue ‘Food processing and nutritional assimilation in animals’.
... Ausktribosphenos nyktos has been variously interpreted as a placental , eutherian (Rich et al. 2001a, Rich et al. 2002, Woodburne 2003, or a convergent non-therian (Kielan-Jaworowska et al. 1998, Archer et al. 1999) related to monotremes (Luo et al. 2001, Luo et al. 2002, Rauhut et al. 2002, Kielan-Jaworowska et al. 2004. Flannery et al. (2022a) alternatively argued against monotreme affinities, and classified A. nyktos as a Gondwanan representative of Tribosphenida (Flannery et al. 2022b). ...
... Flannery et al. (2022a) alternatively argued against monotreme affinities, and classified A. nyktos as a Gondwanan representative of Tribosphenida (Flannery et al. 2022b). Nonetheless, to maintain a phylogenetically justifiable taxonomy (and consistency with the corresponding online auFNSL: Travouillon et al. 2021), we retain A. nyktos within Australosphenida as defined by Luo et al. (2001). Kryoparvus Rich, Trusler, Kool, Pickering, Evans, Siu, Maksimenko, Kundrat, Gostling, Morton, & Vickers-Rich, 2020c. ...
... Rich et al. (2020c) assigned the taxon to Ausktribosphenidae, which was reiterated by Flannery et al. (2022b), who also posited tribosphenidan affinities. We otherwise retain K. gerriti with A. nyktos in Australophenida (sensu Travouillon et al. 2021) to follow the most widely accepted phylogenetic taxonomy (see Luo et al. 2001, Luo et al. 2002, Rauhut et al. 2002, Kielan-Jaworowska et al. 2004 Holotype NMV P210075, a left dentary with pm2-pm6 and m1-m3 (Fig. 11H). ...
In 2020, the Australasian palaeontological association Australasian Palaeontologists (AAP) joined the Australian government-supported Australian National Species List (auNSL) initiative to compile the first Australian Fossil National Species List (auFNSL) for the region. The goal is to assemble comprehensive systematic data on all vertebrate, invertebrate and plant fossil taxa described to date, and to present the information both within a continuously updated open-access online framework, and as a series of primary reference articles in AAP’s flagship journal Alcheringa. This paper spearheads these auFNSL Alcheringa publications with an annotated checklist of Australian Mesozoic tetrapods. Complete synonymy, type material, source locality, geological age and bibliographical information are provided for 111 species formally named as of 2022. In addition, chronostratigraphically arranged inventories of all documented Australian Mesozoic tetrapod fossil occurrences are presented with illustrations of significant, exceptionally preserved and/or diagnostic specimens. The most diverse order-level clades include temnospondyl amphibians (34 species), saurischian (13 species) and ornithischian (12 species) dinosaurs (excluding ichnotaxa), and plesiosaurian marine reptiles (11 species). However, numerous other groups collectively span the earliest Triassic (earliest Induan) to Late Cretaceous (late Maastrichtian) and incorporate antecedents of modern Australian lineages, such as chelonioid and chelid turtles and monotreme mammals. Although scarce in comparison to records from other continents, Australia’s Mesozoic tetrapod assemblages are globally important because they constitute higher-palaeolatitude faunas that evince terrestrial and marine ecosystem evolution near the ancient South Pole. The pace of research on these assemblages has also accelerated substantially over the last 20 years, and serves to promote fossil geoheritage as an asset for scientific, cultural and economic development. The auFNSL augments the accessibility and utility of these palaeontological resources and provides a foundation for ongoing exploration into Australia’s unique natural history.
... Didelphid molars retain an overall basic and primitive tribosphenic pattern typical of early mammals, capable of both shearing and crushing food. It has been suggested that despite some specializations, molars of living species of opossums, particularly Didelphis, are similar to the ancestor tribosphenic pattern (Crompton and Hiiemäe 1970;Luo et al. 2001). Its persistence is taken as evidence of its high adaptive value, as it suits to processing foods of different textures (Goin et al. 1992). ...
... Tribosphenic molars in opossums ( Fig. 1) will crush food through the compression of the protocones onto the talonids basin of the corresponding lower molar (e.g., M1 onto m1). Shear occurs through contact of the anterior wall of each trigon with the posterior wall of the corresponding trigonid (M1 against m1), and contact of the posterior wall of each trigon with the anterior wall of the subsequent molar (e.g., M1 against m2) (Solé and Ladevèze 2017), with the latter (metacrista  paracristid) being the largest shearing surface (Crompton and Hiiemäe 1970;Luo et al. 2001). During mastication, initial masticatory strokes result in gross food processing, first with the crushing of food pieces between the upper protocones and the talonids, and then, as food pieces become smaller, contacts between crests increase, for finer food processing (Crompton and Hiiemäe 1970;Goin et al. 1992). ...
... The Patagorhynchus m2 exhibits a distinct morphology that easily identifies it as a monotreme. This includes a unique lophid and cusp structure resulting in the presence of two mesiodistally compressed lobes that are sub-equally in shaped and size each consisting of three cusps, twinned paraconid and metaconid, wrapping cingulid, hypsodont lobes, and un-basined talonid 12,14,15 . ...
Monotremata is a clade of egg-lying mammals, represented by the living platypus and echidnas, which is endemic to Australia, and adjacent islands. Occurrence of basal monotremes in the Early Cretaceous of Australia has led to the consensus that this clade originated on that continent, arriving later to South America. Here we report on the discovery of a Late Cretaceous monotreme from southern Argentina, demonstrating that monotremes were present in circumpolar regions by the end of the Mesozoic, and that their distinctive anatomical features were probably present in these ancient forms as well.
... The discovery of Mesozoic tribosphenic mammals from India (Prasad et al. 2015) and South America (Rauhut et al. 2002, Rougier et al. 2007) subsequently demonstrated that Mesozoic, tribosphenic mammals were widely distributed in Gondwana (Fig. 1). Luo, Cifelli & Kielan-Jaworowska (2001) advanced a higher-level classification of mammals that included the Mesozoic Southern Hemisphere tribosphenidans. Luo et al. (2001) discarded the infraclass Tribosphenida (McKenna, 1975) and instead advocated a division of the subclass Holotheria (sensu Wible et al. 1995) into Boreosphenida (for the metatherians and eutherians originating in the Northern Hemisphere) and Australosphenida (for the Southern Hemisphere Mesozoic tribosphenidans and monotremes). ...
... Luo, Cifelli & Kielan-Jaworowska (2001) advanced a higher-level classification of mammals that included the Mesozoic Southern Hemisphere tribosphenidans. Luo et al. (2001) discarded the infraclass Tribosphenida (McKenna, 1975) and instead advocated a division of the subclass Holotheria (sensu Wible et al. 1995) into Boreosphenida (for the metatherians and eutherians originating in the Northern Hemisphere) and Australosphenida (for the Southern Hemisphere Mesozoic tribosphenidans and monotremes). To demonstrate this hypothesis, Luo et al. (2001) presented a parsimony-based phylogenetic analysis of morphological data. ...
... Luo et al. (2001) discarded the infraclass Tribosphenida (McKenna, 1975) and instead advocated a division of the subclass Holotheria (sensu Wible et al. 1995) into Boreosphenida (for the metatherians and eutherians originating in the Northern Hemisphere) and Australosphenida (for the Southern Hemisphere Mesozoic tribosphenidans and monotremes). To demonstrate this hypothesis, Luo et al. (2001) presented a parsimony-based phylogenetic analysis of morphological data. At that time, only dentaries and lower dentitions were available for Southern Hemisphere tribosphenic Mesozoic mammals . ...
A review of the Southern Hemisphere Mesozoic tribosphenic mammal fossil record supports the hypothesis that Tribosphenida arose in the Southern Hemisphere during the Early Jurassic, around 50 million years prior to the clade’s reliably dated first appearance in the Northern Hemisphere. Mesozoic Southern Hemisphere tribosphenic mammals are known from Australia, Madagascar, South America and the Indian subcontinent, and are classified into three families: Bishopidae (fam. nov.), Ausktribosphenidae and Henosferidae. These are stem therians, and considerable morphological evolution occurred within the lineage between the Jurassic and late Early Cretaceous. Important dental modifications include a graduated transition between premolars and molars, development of molar wear facets V and VI, loss of facets for postdentary bones, reduction in the Meckelian groove and development of a true dentary angle. Previous classifications of Southern Hemisphere tribosphenic mammals are ambiguous because information from the upper dentition has been lacking. Upper molars attributed to the late Early Cretaceous (Albian) Southern Hemisphere group Bishopidae fam. nov. are now known to possess a prominent protocone and stylar cusp C. We thus consider bishopids to be the sister group to Theria.
Timothy F. Flannery [tim.flannery@textpublishing.com.au], Kristofer M. Helgen [Kris.Helgen@Australian.Museum], Australian Museum, 1 William St Sydney 2000, Australia; Thomas H. Rich [trich@museum.vic.gov.au], Museums Victoria, PO Box 666, Q28 Melbourne, Victoria 3001, Australia; Patricia Vickers-Rich [pat.rich@monash.edu; prich@swin.edu.au], School of Earth, Atmosphere and Environment, Monash University, Victoria 3800, Australia; Swinburne University of Science and Technology, Department of Chemistry and Biotechnology, Hawthorn, Victoria 3122, Australia; Elizabeth Grace Veatch [elizabeth.veatch@gmail.com], National Museum of Natural History, Smithsonian Institution, Washington, DC 20013, USA.
