Studying Arboroharamiya Suggests Haramiyidans Closely Related to Multituberculates

Dental and Mandibular Morphologies of Arboroharamiya (Haramiyida, Mammalia): A Comparison with Other Haramiyidans and Megaconus and Implications for Mammalian Evolution

Authors:

Meng et al

Abstract:

Background

Two recent studies published in the same issue of Nature reached conflicting conclusions regarding the phylogeny of early mammals: One places the clade containing haramiyidans and multituberculates within the Mammalia and the other separates haramiyidans from multituberculates and places the former outside of the Mammalia. These two contrasting results require that the minimally oldest divergence time of the Mammalia was within the Late Triassic or the Middle Jurassic, respectively. Morphological descriptions of the species named in the two papers were brief, and no comparisons between the newly named species were possible.

Principal Findings

Here we present a detailed description of the dentary bone, teeth, occlusal and wear patterns of the haramiyidan Arboroharamiya and compare it with other haramiyidans and Megaconus. Using this new information, we suggest that tooth identifications and orientations of several previously described haramiyidan species are incorrect, and that previous interpretations of haramiyidan occlusal pattern are problematic. We propose that the published upper tooth orientation of Megaconus was problematic and question the number of upper molars, the length of dentition and mandible, and presence of the mandibular middle ear in Megaconus.

Conclusions

The additional morphological descriptions and comparisons presented here further support the view that Arboroharamiya, as a derived haramiyidan, shows similarity to multituberculates in tooth and mandible morphologies. Our comparison also suggests that Megaconus lacks many diagnostic features for the family Eleutherodontidae and that its close affinity with multituberculates cannot be ruled out. The detailed morphological data demonstrate that haramiyidans are more similar to multituberculates than to any other mammaliaforms.

Ectoypodus arctos: a new, northernmost Eocene Paleogene Multituberculate From Ellesmere Island

Northernmost global record for Multituberculata from the Eocene of Ellesmere Island, Arctic Canada

Authors:

Beard et al

Abstract:

Multituberculates are non-therian mammals that are reasonably well documented in Middle Jurassic to late Eocene terrestrial ecosystems, particularly in the Northern Hemisphere (Kielan-Jaworowska and Hurum, 2001; Yuan et al., 2013). In terms of their generic-level diversity, North American multituberculates reached their zenith during the early Paleocene (Puercan and Torrejonian North American land mammal ‘ages’ or NALMAs), although the group retained much of this diversity into the succeeding Tiffanian NALMA (Krause, 1986; Fox, 2005; Scott, 2005; Secord, 2008). Possibly as a result of ecological competition with rodents, which colonized North America at the beginning of the Clarkforkian NALMA (Dawson and Beard, 1996), multituberculate diversity decreased dramatically by the early Eocene Wasatchian NALMA (Krause, 1982, 1986; Krishtalka, 1984). As a result, although certain early Wasatchian sites yield surprisingly abundant samples of multituberculates (e.g., Silcox and Rose, 2001), only three genera of multituberculates have been reported from the Wasatchian of North America. Two of these, Ectypodus and Parectypodus, are members of the Neoplagiaulacidae, whereas the third, Neoliotomus, is referred to the Eucosmodontidae. By the late Wasatchian (Lostcabinian), multituberculates are rarely encountered, and only one species of Ectypodus has been reported from this interval in mid-latitude regions of North America (Stucky and Krishtalka, 1982). Multituberculates have not yet been described from the early middle Eocene Bridgerian NALMA, although the group is known to have persisted in North America until the late Eocene Chadronian NALMA (Krishtalka et al., 1982; Ostrander, 1984).

Fossil mammals from the Eocene Eureka Sound Group on Ellesmere and Axel Heiberg islands in the Canadian Arctic archipelago were first reported by Dawson et al. (1976). Subsequent work has greatly expanded our knowledge of the mammalian fauna from this rock unit, which remains the northernmost occurrence of early Cenozoic terrestrial vertebrates known globally (West and Dawson, 1977, 1978; West et al., 1977; McKenna, 1980; Dawson, 1990, 2001, 2012; Dawson et al., 1993; Eberle and McKenna, 2002; Rose et al., 2004; Eberle, 2005, 2006; Eberle and Greenwood, 2012). Among the more poorly documented mammalian taxa known from the Eureka Sound Group on Ellesmere Island is a single species of neoplagiaulacid multituberculate, which has been cited in faunal lists as Neoplagiaulax sp. for several decades (West et al., 1977; West and Dawson, 1978; McKenna, 1980). These references to Neoplagiaulax in the fauna from the Eureka Sound Group, which is widely regarded as late early Eocene in age (e.g., Eberle and Greenwood, 2012), conflict with the biostratigraphic distribution of Neoplagiaulax elsewhere in North America, where its youngest known occurrence is during the late Paleocene (specifically, late Tiffanian biozone Ti-5a of Secord, 2008:fig. 8). Here we describe the only known multituberculate specimen from the Eureka Sound Group in order to assess its affinities more precisely than has been the case previously. Subsequently, we comment briefly on the paleobiogeographic significance of this northernmost record for Multituberculata.  Dental terminology and measurements follow Scott (2003, 2005) and Secord (2008:fig. 2).

Vintana sertichi: A Remarkable Skull From a Maastrichtian Cretaceous Gondwanatheria Allotherian From Madagascar

First cranial remains of a gondwanatherian mammal reveal remarkable mosaicism

Authors:

Krause et al

Abstract:

Previously known only from isolated teeth and lower jaw fragments recovered from the Cretaceous and Palaeogene of the Southern Hemisphere, the Gondwanatheria constitute the most poorly known of all major mammaliaform radiations. Here we report the discovery of the first skull material of a gondwanatherian, a complete and well-preserved cranium from Upper Cretaceous strata in Madagascar that we assign to a new genus and species. Phylogenetic analysis strongly supports its placement within Gondwanatheria, which are recognized as monophyletic and closely related to multituberculates, an evolutionarily successful clade of Mesozoic mammals known almost exclusively from the Northern Hemisphere. The new taxon is the largest known mammaliaform from the Mesozoic of Gondwana. Its craniofacial anatomy reveals that it was herbivorous, large-eyed and agile, with well-developed high-frequency hearing and a keen sense of smell. The cranium exhibits a mosaic of primitive and derived features, the disparity of which is extreme and probably reflective of a long evolutionary history in geographic isolation.

Chinese Oxfordian Jurassic Euharamiyidan Mammals Suggest Allotheria Split From Other Mammals at the Rhaetian/Norian Triassic Boundary

Three new Jurassic euharamiyidan species reinforce early divergence of mammals

Authors:

Bi et al

Abstract:

The phylogeny of Allotheria, including Multituberculata and Haramiyida, remains unsolved and has generated contentious views on the origin and earliest evolution of mammals. Here we report three new species of a new clade, Euharamiyida, based on six well-preserved fossils from the Jurassic period of China. These fossils reveal many craniodental and postcranial features of euharamiyidans and clarify several ambiguous structures that are currently the topic of debate. Our phylogenetic analyses recognize Euharamiyida as the sister group of Multituberculata, and place Allotheria within the Mammalia. The phylogeny suggests that allotherian mammals evolved from a Late Triassic (approximately 208 million years ago) Haramiyavia-like ancestor and diversified into euharamiyidans and multituberculates with a cosmopolitan distribution, implying homologous acquisition of many craniodental and postcranial features in the two groups. Our findings also favour a Late Triassic origin of mammals in Laurasia and two independent detachment events of the middle ear bones during mammalian evolution.