discerning the Different Species of Cretaceous-Paleogene Multituberculate Genus Mesodma

Species Discrimination of Co-Occurring Small Fossil Mammals: A Case Study of the Cretaceous-Paleogene Multituberculate Genus Mesodma

Authors:

Smith et al

Abstract:

The mammalian fossil record is largely composed of isolated teeth and tooth-bearing elements. In vertebrate microfossil assemblages with closely related, co-occurring species of mammals, it can be difficult to identify isolated teeth to species level because morphological differences among species may be slight and based on a single tooth position. Here we investigate the utility of the allegedly diagnostic lower fourth premolar (p4) for species-level identification in the genus Mesodma (Multituberculata, Neoplagiaulacidae). We conducted linear and geometric morphometrics on 86 p4s representing four Cretaceous-Paleogene (K-Pg) species of Mesodma that are common in deposits of the western interior of North America. Although Mesodma has been extensively discussed in the literature, these four species overlap considerably in p4 size and shape, making species-level identifications challenging. Using linear measurements, landmarks, and semilandmarks, we quantified p4 size and shape to understand morphological variation across the genus and uncover practical sources of morphological differentiation among the species represented here. Our results indicate (1) size is more important than shape for identifying p4s of Mesodma species; p4 shape varies across the genus, but cannot be used alone to identify isolated p4s to species; (2) M. garfieldensis and M. thompsoni cannot be distinguished from each other using p4 size or shape; we therefore subsume M. garfieldensis within M. thompsoni; and (3) M. formosa increased in size across the K-Pg boundary. In light of these results, we recommend that taxonomic diagnoses relying on isolated teeth incorporate quantitative analyses of morphology whenever possible to increase the accuracy of species-level identifications and paleofaunal studies that employ them.

Yubaartar zhongyuanensis: a Large multituberculate mammal From Late Cretaceous China

Largest known Mesozoic multituberculate from Eurasia and implications for multituberculate evolution and biology

Authors:

Xu et al

Abstract:

A new multituberculate, Yubaartar zhongyuanensis gen. and sp. nov., is reported from the Upper Cretaceous of Luanchuan County, Henan Province, China. The holotype of the new taxon is a partial skeleton with nearly complete cranium and associated lower jaws with in situ dentitions. The new species is the southern-most record of a Late Cretaceous multituberculate from outside of the Mongolian Plateau in Asia and represents the largest known Mesozoic multituberculate from Eurasia. The new specimen displays some intriguing features previously unknown in multituberculates, such as the first evidence of replacement of the ultimate upper premolar and a unique paleopathological case in Mesozoic mammals in which the animal with a severely broken right tibia could heal and survive in natural condition. The phylogenetic analysis based on craniodental characters places Yubaartar as the immediate outgroup of Taeniolabidoidea, a group consisting of a North American clade and an Asian clade. This relationship indicates at least a faunal interchange of multituberculates before the K-Pg transition. The new evidence further supports the hypothesis that disparity in dental complexity, which relates to animal diets, increased with generic richness and disparity in body size, and that an adaptive shift towards increased herbivory across the K-Pg transitional interval.

Triconodont and Multituberculate Mammals Found in Lower Cretaceous Japan

New mammalian specimens from the Lower Cretaceous Kitadani Formation, Tetori Group, Fukui, Japan

Authors:

Miyata et al

Abstract:

New specimens of two non-therian (non-tribosphenidan) mammals are described from the Lower Cretaceous Kitadani Formation in the upper part of the Tetori Group, Katsuyama, Fukui Prefecture, Japan. Despite their poor preservation, these specimens represent undescribed species from Japan, suggesting additional mammalian diversity in the Tetori Group. Previously, four mammal taxa had been formally described from this rock unit: a spalacotheriid ‘symmetrodont’, two eobaatarid multituberculates and a eutriconodont mammal. One of the new specimens is a damaged left p4 of a ‘plagiaulacidan’ grade multituberculate assignable to the family Eobaataridae. The Kitadani eobaatarid is a large species distinguished from the two previously described eobaatarids, Tedoribaatar and Hakusanobaatar, which are known from the stratigraphically lower Kuwajima Formation of the Tetori Group, Hakusan, Ishikawa Prefecture, Japan. It also differs from Sinobaatar, Heishanobaatar and Liaobaatar described from the Early Cretaceous of China. Another specimen, a partial right dentary with a faint Meckelian groove, is assigned to a eutriconodontan that is larger than and morphologically distinguishable from the eutriconodont Hakusanodon from the Kuwajima Formation. The Kitadani eutriconodontan is potentially related to the family Triconodontidae. The additional specimens from the Kitadani Formation shed new light on Early Cretaceous mammalian faunal change and dispersal in East Asia.

The Iron Toothed Multituberculate Mammal From Maastrichtian Cretaceous Transylvanian “Haţeg Island”

Red Iron-Pigmented Tooth Enamel in a Multituberculate Mammal from the Late Cretaceous Transylvanian “Haţeg Island”

Authors:

Smith et al

Abstract:

Mammals that inhabit islands are characterized by peculiar morphologies in comparison to their mainland relatives. Here we report the discovery of a partial skull associated with the lower jaws of a Late Cretaceous (≈70 Ma) multituberculate mammal from the Carpathian “Haţeg Island” of Transylvania, Romania. The mammal belongs to the Kogaionidae, one of the rare families that survived the Cretaceous—Paleogene mass extinction in Europe. The excellent preservation of this specimen allows for the first time description of the complete dentition of a kogaionid and demonstration that the enigmatic Barbatodon transylvanicus presents a mosaic of primitive and derived characters, and that it is phylogenetically basal among the Cimolodonta. Another peculiarity is the presence of red pigmentation in its tooth enamel. The red coloration is present on the anterior side of the incisors and on the cusps of most of the teeth. Energy-dispersive X-ray spectrometry (EDS) analysis reveals that the pigmented enamel contains iron, as in living placentals. Such a red pigmentation is known in living soricine shrews and many families of rodents, where it is thought to increase the resistance of the enamel to the abrasion that occurs during “grinding” mastication. The extended pattern of red pigment distribution in Barbatodon is more similar to that in eulipotyplan insectivores than to that in rodents and suggests a very hard diet and, importantly, demonstrates that its grasping incisors were not ever-growing. As inferred for other endemic Transylvanian vertebrates such as dwarf herbivorous dinosaurs and unusual theropod dinosaurs, insularity was probably the main factor of survival of such a primitive mammalian lineage relative to other mainland contemporaries of the Northern hemisphere.

How Mesozoic Mammals Moved

A multivariate approach to infer locomotor modes in Mesozoic mammals

Authors:

Chen et al

Abstract:

Ecomorphological diversity of Mesozoic mammals was presumably constrained by selective pressures imposed by contemporary vertebrates. In accordance, Mesozoic mammals for a long time had been viewed as generalized, terrestrial, small-bodied forms with limited locomotor specializations. Recent discoveries of Mesozoic mammal skeletons with distinctive postcranial morphologies have challenged this hypothesis. However, ecomorphological analyses of these new postcrania have focused on a single taxon, a limited region of the skeleton, or have been largely qualitative.

For more comprehensive locomotor inference in Mesozoic mammals, we applied multivariate analyses to a morphometric data set of extant small-bodied mammals. We used 30 osteological indices derived from linear measurements of appendicular skeletons of 107 extant taxa that sample 15 orders and eight locomotor modes. Canonical variate analyses show that extant small-bodied mammals of different locomotor modes have detectable and predictable morphologies. The resulting morphospace occupation reveals a morphofunctional continuum that extends from terrestrial to scansorial, arboreal, and gliding modes, reflecting an increasingly slender postcranial skeleton with longer limb output levers adapted for speed and agility, and extends from terrestrial to semiaquatic/semifossorial and fossorial modes, reflecting an increasingly robust postcranial skeleton with shorter limb output levers adapted for powerful, propulsive strokes. We used this morphometric data set to predict locomotor mode in ten Mesozoic mammals within the Docodonta, Multituberculata, Eutriconodonta, “Symmetrodonta,” and Eutheria. Our results indicate that these fossil taxa represent five of eight locomotor modes used to classify extant taxa in this study, in some cases confirming and in other cases differing from prior ecomorphological assessments. Together with previous locomotor inferences of 19 additional taxa, these results show that by the Late Jurassic mammals had diversified into all but the saltatorial and active flight locomotor modes, and that this diversification was greatest in the Eutriconodonta and Multituberculata, although sampling of postcranial skeletons remains uneven across taxa and through time.

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).

Barbatodon oardaensis: A new Kogaionid Multituberculate Mammal From Maastrichtian Cretaceous Romania

A new kogaionid multituberculate mammal from the Maastrichtian of the Transylvanian Basin, Romania

Authors:

Codrea et al

Abstract:

The Latest Cretaceous (Maastrichtian) terrestrial sedimentary sequences of the Haţeg Basin in Transylvania are well known for the so-called “Haţeg Island” vertebrate faunas, which evolved in endemic (insular?) conditions. In addition to frogs, lizards, turtles, crocodilians, birds and dinosaurs, peculiar multituberculate mammals have been recorded, all belonging to the family Kogaionidae. Here, a new species of the genus Barbatodon is reported from the Maastrichtian Şard Formation in the Transylvanian Basin (Alba County, Romania). Barbatodon oardaensis n. sp. is characterized by M1 cusp formula 3:4:2 and is much smaller than the two other Maastrichtian kogaionids from Transylvania, Barbatodon transylvanicus and Kogaionon ungureanui. The origin and paleobiogeography of kogaionids are discussed.

Kimmeridgian Jurassic Postcranial Mammal Fossils From Portugal

Mammalian postcranial bones from the Late Jurassic of Portugal and their implications for forelimb evolution

Author:

Thomas Martin

Abstract:

Isolated bones of forelimb and pelvic girdle (two humeri, five ulnae, and an ilium) recovered from the Late Jurassic (Kimmeridgian) Guimarota coal mine in western central Portugal are attributed to the docodont Haldanodon exspectatus, dryolestoids, and a ?paulchoffatiid multituberculate. The larger of the two humeri is assigned to the dryolestid Dryolestes leiriensis based on size and shape. It clearly exhibits an incipient trochlea at the distal joint, suggesting that this derived character was well established among Late Jurassic dryolestidans, including Henkelotherium. Plesiomorphic characters are the prominent spherical radial condyle and the weakly developed ulnar condyle. An incipient medial keel is present in distal aspect of the humerus trochlea. The shallow olecranon fossa of the humerus corresponds to the small anconeal process of the radius. The smaller humerus with damaged distal joint is 50% smaller and cannot be assigned to a specific dryolestoid taxon. It is in the size range of the smaller Guimarota dryolestoids Krebsotherium, Drescheratherium, and Henkelotherium. One ulna differs from the dryolestoid ulnar shape by the nearly semicircular articular surface for the ulnar condyle of the humerus, the asymmetric olecranon with medial overhang, as well as the prominent anconeal process and is tentatively attributed to a paulchoffatiid multituberculate.

Another Awesome Theropod vs Multituberculate Picture

Stunning Picture of a Feathered Theropod Chasing a Rugosodon

Wow.  I got it from here which links to the title link.

Rugosodon eurasiaticus: An Oxfordian Jurassic Multituberculate, Early Example of the Wildly Successful Mammal Clade

The 160 million-year-old fossil of an extinct rodent-like creature from China is helping to explain how multituberculates—the most evolutionarily successful and long-lived mammalian lineage in the fossil record—achieved their dominance.

This fossil find—the oldest ancestor in the multituberculate family tree—represents a newly discovered species known as Rugosodon eurasiaticus. The nearly complete skeleton provides critical insights into the traits that helped such multituberculates thrive in their day. For example, the fossil reveals teeth that were adapted to gnawing plants and animals alike, as well as ankle joints that were highly adept at rotation.

In light of these findings, researchers suggest that R. eurasiaticus paved the way for later plant-eating and tree-dwelling mammals.

Chong-Xi Yuan from the Chinese Academy of Geological Sciences in Beijing, China, along with Chinese and American colleagues, report their analysis of the fossil in the 16 August issue of Science.

The multituberculates flourished during the Cretaceous era, which ended over 60 million years ago. Much like today's rodents, they filled an extremely wide variety of niches—below the ground, on the ground and in the trees—and this new fossil, which resembles a small rat or a chipmunk, possessed many of the adaptations that subsequent species came to rely upon, the researchers say.

"The later multituberculates of the Cretaceous [era] and the Paleocene [epoch] are extremely functionally diverse: Some could jump, some could burrow, others could climb trees and many more lived on the ground," explained Zhe-Xi Luo, a co-author of the Science report. "The tree-climbing multituberculates and the jumping multituberculates had the most interesting ankle bones, capable of 'hyper-back-rotation' of the hind feet."

"What is surprising about this discovery is that these ankle features were already present in Rugosodon—a land-dwelling mammal," he said. (Such highly mobile ankle joints are normally associated with the foot functions of animals that are exclusively tree-dwellers—those that navigate uneven surfaces.)

Additionally, R. eurasiaticus could eat many different types of food, according to the researchers. The fossil—particularly its dentition, which reveals teeth designed for shearing plant matter—confirms a 2012 analysis of tooth types that suggested multituberculates consumed an animal-dominated diet for much of their existence, later diversifying to a plant-dominated one.

Multituberculates arose in the Jurassic period and went extinct in the Oligocene epoch, occupying a diverse range of habitats for more than 100 million years before they were out-competed by more modern rodents. By the end of their run on the planet, multituberculates had evolved complex teeth that allowed them to enjoy vegetarian diets and unique locomotive skills that enabled them to traverse treetops. Both adaptations helped them to become dominant among their contemporaries.

First Multituberculate Fossil Found in India

The first multituberculate mammal from India

Authors:

1. Varun Parmar (a)
2. Guntupalli V. R. Prasad (b)
3. Deepak Kumar (a)

Affiliations:

a. Department of Geology, University of Jammu, Jammu 180006, India

b. Department of Geology, Centre for Advanced Studies, University of Delhi, Delhi 110007, India

Abstract:

Mesozoic deposits of the former Gondwanaland are depauperate in early mammals, in general, and multituberculate mammals, in particular. Until now, the oldest multituberculate mammals known from the Gondwanan continents come from the Early Cretaceous of Morocco, NW Africa. Here, we report the presence of a new multituberculate mammal, Indobaatar zofiae gen. et sp. nov., from the Lower/Middle Jurassic Kota Formation, Pranhita-Godavari valley in peninsular India. This is the first record of a multituberculate from the Mesozoic rocks of India and possibly predates the oldest known multituberculates from Gondwanan continents. The new specimen, representing an upper premolar (P4), compares well with the upper premolar morphology of Eobaatariinae multituberculates known from the Early Cretaceous of Mongolia, China, England, and Spain. Together with the recent findings of cimolodontan multituberculates from the Early Cretaceous of Australia and Late Cretaceous of South America, the new discovery indicates a wide temporal and spatial distribution for multituberculate mammals in the former Gondwanaland.

New Maryland Multituberculate Mammal From the Aptian Cretaceous

New multituberculate mammal from the Early Cretaceous of eastern North America

Authors:

1. Richard L. Cifelli (a)
2. Cynthia L. Gordon (b)
3. Thomas R. Lipka (a)

Affiliations:

a. Sam Noble Museum, 2401 Chautauqua Ave. Norman, OK 73072, USA.

b. Department of Biology, University of Oklahoma, Norman, OK 73019, USA.

Abstract:

Multituberculates, though among the most commonly encountered mammalian fossils of the Mesozoic, are poorly known from the North American Early Cretaceous, with only one taxon named to date. Herein we describe Argillomys marylandensis, gen. et sp. nov., from the Early Cretaceous of Maryland, based on an isolated M2. Argillomys represents the second mammal known from the Arundel Clay facies of the Patuxent Formation (Lower Cretaceous: Aptian). Though distinctive in its combination of characters (e.g., enamel ornamentation consisting of ribs and grooves only, cusp formula 2:4, presence of distinct cusp on anterobuccal ridge, enlargement of second cusp on buccal row, central position of ultimate cusp in lingual row, great relative length), the broader affinities of Argillomys cannot be established because of non-representation of the antemolar dentition. Based on lack of apomorphies commonly seen among Cimolodonta (e.g., three or more cusps present in buccal row, fusion of cusps in lingual row, cusps strongly pyramidal and separated by narrow grooves), we provisionally regard Argillomys as a multituberculate of “plagiaulacidan” grade. Intriguingly, it is comparable in certain respects to some unnamed Paulchoffatiidae, a family otherwise known from the Late Jurassic – Early Cretaceous of the Iberian Peninsula.

Barbatodon transylvanicus: A Cretaceous Multituberculate Mammal from Romania

What I find interesting is the reported use of iron to strengthen the teeth.  Do we have extent examples of this?

There Was Gnawing

Paleontologists have discovered the oldest mammalian tooth marks yet on the bones of ancient animals, including several large dinosaurs. They report their findings in a paper published online June 16 in the journal Paleontology.

Nicholas Longrich of Yale University and Michael J. Ryan of the Cleveland Museum of Natural History came across several of the bones while studying the collections of the University of Alberta Laboratory for Vertebrate Palaeontology and the Royal Tyrrell Museum of Palaeontology. They also found additional bones displaying tooth marks during fieldwork in Alberta, Canada. The bones are all from the Late Cretaceous epoch and date back about 75 million years.

The pair discovered tooth marks on a femur bone from a Champsosaurus, an aquatic reptile that grew up to five feet long; the rib of a dinosaur, most likely a hadrosaurid or ceratopsid; the femur of another large dinosaur that was likely an ornithischian; and a lower jaw bone from a small marsupial.

The researchers believe the marks were made by mammals because they were created by opposing pairs of teeth—a trait seen only in mammals from that time. They think they were most likely made by multituberculates, an extinct order of archaic mammals that resemble rodents and had paired upper and lower incisors. Several of the bones display multiple, overlapping bites made along the curve of the bone, revealing a pattern similar to the way people eat corn on the cob.

The animals that made the marks were about the size of a squirrel and were most likely gnawing on the bare bones for minerals rather than for meat, said Longrich. "The bones were kind of a nutritional supplement for these animals."

kewl! no time!