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Masticatory musculature of Asian taeniolabidoid multituberculate mammals

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Gambaryan P. P., Kielan-Jaworowska Z.

Acta Palaeontologica Polonica

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1995

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tom 40

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nr 1

The backward chewing stroke in multituberculates (unique for mammals) resulted in a more anterior insertion of the masticatory muscles than in any other mammal group, including rodents. Multituberculates differ from tritylodontids in details of the masticatory musculature, but share with them the backward masticatory power stroke and retractory horizontal components of the resultant force of all the masticatory muscles (protractory in Theria). The Taeniolabididae differ from the Eucosmodontidae in having a more powerful masticatory musculature, expressed by the higher zygomatic arch with relatively larger anterior and middle zygomaticridges and higher coronoid process. It is speculated that the bicuspid, or pointed upper incisors, and semi-procumbent, pointed lower ones, characteristic of nontaeniolabidoid multitliberculates were used for picking-up and killing insects or other prey. In relation to the backward power stroke the low position of the condylar process was advantageous for most multituberculates. In extreme cases (Sloanbaataridae and Taeniolabididae), the adaptation for crushing hard seeds, worked against the benefit of the low position of the condylar process and a high condylar process developed. Five new multituberculate autapomorphies are recognized: anterior and intermediate zygomatic ridges: glenoid fossa large, flat and sloping backwards (forwards in rodents), arranged anterolateral and standing out from the braincase; semicircular posterior margin of the dentary with condylar process forming at least a part of it; anterior position of the coronoid process; and anterior position of the masseteric fossa. The postorbital process in those multituberculates studied is situated on the parietal and the orbit is very large.

2

Were mammals originally venomous?

84%

Hurum J. H., Luo Z. X., Kielan-Jaworowska Z.

Acta Palaeontologica Polonica

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2006

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tom 51

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nr 1

The extratarsal spur in extant monotremes consists of an os calcaris and a cornu calcaris. A poisonous extratarsal spur occurs only in the platypus (Ornithorhynchus); a possibly secondarily non−poisonous spur is present in echidnas (Tachyglossus and Zaglossus). Some therian mammals (e.g., bats), reptiles (Chamaeleo), and amphibians have a spur−like structure in the ankle, but this is not homologous to the extratarsal spur of monotremes. Among fossil mammals, the co−ossified os calcaris and ossified cornu calcaris have been found in the eutriconodontan Gobiconodon and in the spalacotheroid “symmetrodontan” Zhangheotherium. Here we describe the os calcaris in several multituberculate mammals from the Late Cretaceous of the Gobi Desert, Mongolia. The multituberculate os calcaris is a large, flat bone, generally similar to that in males of the extant monotreme species, but the cornu calcaris is not ossified. In Gobiconodon and Zhangheotherium the ossified cornu calcaris is fused to the os calcaris probably to provide the bony support for the keratinous spur. We hypothesize that the os calcaris in these Mesozoic mammal groups is homologous to that of monotremes. However, the extratarsal spur has not been found in non−mammalian cynodonts nor in other synapsids. A platypus−like os calcaris might be an apomorphic characteristic of basal Mesozoic mammals and is secondarily lost in crown therians; the os calcaris is confirmed to be absent in well−preserved tarsal structures of the earliest known crown therian mammals. We speculate that the os calcaris, the cornu calcaris, and its associated venom gland might have served the function of a defensive structure during the “dark ages” of mammalian history, when dinosaurs ruled the Earth. This structure is a plesiomorphic character retained in extant monotremes and cannot be used as an autapomorphy of Monotremata.

3

The Gashatan [Late Paleocene] mammal fauna from Subeng, Inner Mongolia, China

84%

Missiaen P., Smith T.

Acta Palaeontologica Polonica

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2008

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tom 53

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nr 3

The Paleocene–Eocene boundary is of particular importance for the evolution of mammals and the poorly known Asian mammal faunas from this period have received much attention. The late Paleocene Subeng site in Inner Mongolia (China) has come under study only recently, and here we present the first complete description of its mammal fauna. Two new species are described, the neoplagiaulacid multituberculate Mesodmops tenuis sp. nov. and the praolestine nyctitheriid Bumbanius ningi sp. nov., representing stratigraphic range extensions of the respective genera into the Paleocene. Previously unknown parts of the dentition are described here for the eurymylid Eomylus bayanulanensis, the sarcodontid Hyracolestes ermineus, the cimolestid Tsaganius ambiguus, the carpolestid Subengius mengi, as well as the femur of the mesonychid Dissacus serratus. For most taxa, the new specimens from Subeng provide new phylogenetic and/or biostratigraphic information. We confirm the inclusion of Hyracolestesin the Sarcodontinae and elevate this group to the rank of family, the Sarcodontidae, separate from Micropternodontidae. In the case of Subengius mengi an updated cladistic analysis of carpolestids supports the hypothesis that Subengius is derived from an evolved Elphidotarsius−like ancestor in the early to middle Tiffanian of North America. A total of 17 species is identified, including well−known biostratigraphic markers for the late Paleocene Gashatan Asian Land Mammal Age such as Lambdopsalis bulla, Prionessus sp., Palaeostylops iturus, Pseudictops lophiodon, Tribosphenomys minutus, and Dissacus serratus. We propose that the Gashatan faunas are less endemic than previously thought, and result from a significant exchange with North American faunas from the late Paleocene.

4

Multituberculate mammals from near the Early-Late Cretaceous boundary, Cedar Mountain Formation, Utah

84%

Eaton J. G., Cifelli R. L.

Acta Palaeontologica Polonica

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2001

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tom 46

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nr 4

Herein we describe the oldest well-sampled multituberculate assemblage from the Cretaceous of North America. The fauna is dated at 98.37 Ma and thus approximates the Albian-Cenomanian (Early-Late Cretaceous) boundary. The multituberculate fauna is diverse. Two of the multituberculates (Janumys erebos gen. et sp. n. and an unidentified taxon) are provisionally placed among 'Plagiaulacida'. Another taxon, Ameribaatar zofiae gen. et sp. n., is of uncertain subordinal affinities. The remaining multituberculates appear to represent the advanced suborder Cimolodonta and fall within the 'Paracimexomys group'. We rediagnose Paracimexomys on the basis of the type species, P. priscus, and refer to other species as cf. Paracimexomys (including cf. P. perplexus sp. n.). A revised diagnosis is also provided for Cenomanian Dakotamys. A previously-described species from the Cedar Mountain Formation is placed in Cedaromys gen. n. as C. bestia, together with C. pawus sp. n. Bryceomys is represented in the fauna by B. intermedius sp. n. Relationships of Paracimexomys-group to later taxa remain obscure. However, Bryceomys and Cedaromys share a number of features with Cimolodontidae. Given these resemblances, together with the fact that Cimolodontidae retain certain plesiomorphies (stout lower incisor, gigantoprismatic enamel) with respect to Ptilodontoidea (to which they are commonly referred), we suggest that Cimolodontidae may have arisen from a clade within the 'Paracimexomys group', independent of ptilodontoids.

5

New specimens of the multituberculate mammal Sphenopsalis from China: Implications for phylogeny and biology of taeniolabidoids

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Mao F.-Y., Wang Y.-Q., Meng J.

Acta Palaeontologica Polonica

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2016

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tom 61

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nr 2

Multituberculates are the most diverse and best known group of Mesozoic mammals; they also persisted into the Paleogene and became extinct in the Eocene, possibly outcompeted by rodents that have similar morphological and presumably ecological adaptations. Among the Paleogene multituberculates, those that have the largest body sizes belong to taeniolabidoids, which contain several derived species from North America and Asia and some species with uncertain taxonomic positions. Of the known taeniolabidoids, the poorest known taxon is Sphenopsalis nobilis from Mongolia and Inner Mongolia, China, represented previously by a few isolated teeth. Its relationship with other multituberculates thus has remained unclear. Here we report new specimens of Sphenopsalis nobilis collected from the upper Paleocene of the Erlian Basin, Inner Mongolia, China, during a multi-year field effort beginning in 2000. These new specimens document substantial parts of the dental, partial cranial and postcranial morphologies of Sphenopsalis, including the upper and lower incisors, partial premolars, complete upper and lower molars, a partial rostrum, fragments of the skull roof, middle ear cavity, a partial scapula, and partial limb bones. With the new specimens we are able to present a detailed description of Sphenopsalis, comparisons among relevant taeniolabidoids, and brief phylogenetic analyses based on a dataset consisting of 43 taxa and 102 characters. In light of the new evidence, we assess the phylogenetic position of Sphenopsalis and re-establish the family Lambdopsalidae. The monophyly of Taeniolabidoidea is supported in all our phylogenetic analyses. Within Taeniolabidoidea the Asian lambdopsalids and the North American taeniolabidids represent two significantly different trends of adaptations, one characterized by shearing (lambdopsalids) and the other by crushing and grinding (taeniolabidids) in mastication, which supports their wider systematic separation, as speculated when Sphenopsalis was named.

6

Postcranial skeleton of a Cretaceous multituberculate mammal Catopsbaatar

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Hurum J. H., Kielan-Jaworowska Z.

Acta Palaeontologica Polonica

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2008

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tom 53

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nr 4

We describe an incomplete postcranial skeleton of Catopsbaatar catopsaloides from the ?late Campanian red beds of Hermiin Tsav I, in the Gobi Desert, Mongolia. The skeleton is fragmentary and the preservation of bone surface does not permit reconstruction of the musculature. The studied skeleton contains some parts not preserved or incompletely known in other multituberculate genera, such as a long spinous process in a single lumbar vertebra, which together with long transverse processes preserved in Nemegtbaatar, might indicate that at least some multituberculates had jumping ability. The calcaneus of Catopsbaatar is unusual, differing from most other multituberculates (where known) and other mammals by having a short tuber calcanei, with a large proximal anvil−shaped process strongly bent laterally and ventrally, arranged obliquely with respect to the distal margin of the calcaneus, rather than arranged at 90° to it, as in other mammals. This suggests the presence of strong muscles that attached to the tuber calcanei, perhaps further attesting to jumping abilities in Catopsbaatar. We also describe an unfused pelvic girdle and the first extratarsal spur bone (os cornu calcaris) known in multituberculates.

7

Second specimen of Corriebaatar marywaltersae from the Lower Cretaceous of Australia confirms its multituberculate affinities

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Rich T. H., Krause D. W., Trusler P., White M. A., Kool L., Evans A. R., Morton S., Vickers-Rich P.

Acta Palaeontologica Polonica

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2022

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tom 67

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nr 1

8

An Australian multituberculate and its palaeobiogeographic implications

67%

Rich T. H., Vickers-Rich P., Flannery T. F., Kear B. P., Cantrill D. J., Komarower P., Kool L., Pickering D., Trusler P., Morton S., Van Klaveren N., Fitzgerald E. M. G.

Acta Palaeontologica Polonica

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2009

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tom 54

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nr 1

1-6

A dentary fragment containing a tiny left plagiaulacoid fourth lower premolar from the Early Cretaceous (Aptian) of Victoria provides the first evidence of the Multituberculata from Australia. This unique specimen represents a new genus and species, Corriebaatar marywaltersae, and is placed in a new family, Corriebaataridae. The Australian fossil, together with meagre records of multituberculates from South America, Africa, and Madagascar, reinforces the view that Multituberculata had a cosmopolitan distribution during the Mesozoic, with dispersal into eastern Gondwana probably occurring prior to enforcement of climatic barriers (indicated by marked differentiation in regional floras) in the Early Cretaceous.

9

A new species of the plagiaulacoid multituberculate mammal Eobaatar from the Early Cretaceous of southern Britain

67%

Sweetman S. C.

Acta Palaeontologica Polonica

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2009

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tom 54

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nr 3

373-384

Until recently, the only mammal remains to be obtained from the Early Cretaceous (Barremian, Wealden Group) Wessex Formation of the Isle of Wight, southern England were a poorly preserved left m2 and a well preserved left I2 crown representing one or possibly two plagiaulacoid multituberculate species. These were recovered in the early 1970s but despite subsequent efforts by a number of workers to recover additional Mesozoic mammal remains none were forthcoming until comprehensive bulk screening of the Wessex Formation was undertaken in a study commenced in 2002. This study resulted in the recovery of a number of new specimens representing an assemblage of at least six taxa. Among these are a well−preserved plagiaulacoid multituberculate left m1 and a similarly preserved left I3. The former permits diagnosis of a new species of eobaatarid, Eobaatar clemensisp. nov. The previously recovered left m2 is also tentatively assigned to the same taxon. In addition, another left m1, somewhat worn as a result of dietary attrition, was recently obtained by a private collector. This is of very similar morphology to the holotype of E. clemensi but slightly larger. It is undoubtedly referable to the same taxon and provides some insight into intraspecific size, and other minor morphological variations in the teeth of the new species. The I3 may also be referable to the new species, in which case it is the first well preserved I3 of a member of Eobaataridae to be fully described.

10

Limb posture in early mammals: Sprawling or parasagittal

67%

Kielan-Jaworowska Z., Hurum J. H.

Acta Palaeontologica Polonica

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2006

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tom 51

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nr 3

The limb posture in early mammals is a matter of controversy. Kielan−Jaworowska and Gambaryan presented arguments for a sprawling posture in multituberculates, based mainly on three characters of the hind limbs (deep pelvis, mediolateral diameter of the tibia larger than the craniocaudal, and position of MtV, which fits the peroneal groove on the calcaneus and is not aligned with the axis of tuber calcanei). Here we present two more arguments for sprawling hind limbs in early mammals. One is the presence of an os calcaris, supporting the probably venomous spur in hind legs of docodontans, multituberculates, eutriconodontans, and “symmetrodontans”, similar to those of extant monotremes. We argue that early mammals (except for boreosphenidans) had sprawling limb posture and venomous spur; acquisition of the parasagittal stance was apparently characteristic only of boreosphenidans, in which the spur has not been found. The second argument is based on taphonomic evidence from lacustrine conditions (e.g., Early Cretaceous Jehol Biota), in which the mammalian skeletons, except for boreosphenidans (Sinodelphys and Eomaia), have been preserved compressed dorso−ventrally, suggesting sprawling stance. In similar conditions of the Eocene Messel Biota the skeletons of boreosphenidan mammals (except for bats and pangolins) are preserved lying on flanks, suggesting parasagittal stance. Sereno argued that forelimbs in multituberculates were parasagittal, based on the stated presence of a ventrally facing glenoid, a mobile shoulder joint, and an elbow joint with enhanced flexion−extension capability. However, these characters are not unequivocally indicative of parasagittalism. We demonstrate that the structure of the distal end of the multituberculate humerus is condylar, with no tendency for developing a trochlea. We reconstruct multituberculates and other early mammals with sprawling stance in resting position as plantigrade.

11

The braincase of two Late Cretaceous Asian multituberculates studied by serial sections

67%

Hurum J. H.

Acta Palaeontologica Polonica

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1998

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tom 43

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nr 1

21-52

The braincase structure of two Late Cretaceous Mongolian djadochtatherian multituberculates Nemegtbaatar gobiensis and Chulsanbaatar vulgaris from the ?late Campanian of Mongolia is presented based on the two serially sectioned skulls and additional specimens. Reconstructions of the floor of the braincase in both taxa are given. The complete intracranial sphenoid region is reconstructed for the first time in multituberculates. Cavum epiptericum is a separate space with the taenia clino-orbitalis (ossified pila antotica) as the medial wall, anterior lamina of the petrosal and possibly the alisphenoid as the lateral wall, and the basisphenoid, petrosal and possibly alisphenoid ventrally. The fovea hypochiasmatica is shallow, tuberculurn sellae is wide and more raised from the skull base than it is in the genus Pseudobolodon. The dorsal opening of the carotid canal is situated in the fossa hypophyseos. The taenia clino-orbitalis differs from the one described in Pseudobolodon and Lambdopsalis in possessing just one foramen (metoptic foramen). Compared to all extant mammals the braincase in Nemegtbaatar and Chulsanbaatar is primitive in that both the pila antotica and pila metoptica are retained. In both genera the anterior lamina of the petrosal is large with a long anterodorsal process while the alisphenoid is small. A review is given of the cranial anatomy in Nemegtbaatar and Chulsanbaatar.

12

New teeth of allotherian mammals from the English Bathonian, including the earliest multituberculates

67%

Butler P. M., Hooker J. J.

Acta Palaeontologica Polonica

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2005

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tom 50

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nr 2

Twenty one isolated multituberculate−like teeth are described from the Forest Marble (late Bathonian) of Oxfordshire and Dorset, England. Eighteen are additional to the teeth described as Eleutherodon oxfordensis by Kermack et al. (1998), and three of those are placed in new taxa. Six new molars of Eleutherodon provide further information on variation in size, proportion and root pattern. Millsodon superstes gen. et sp. nov. (family indeterminate), based on first and last lower molars and a referred upper molar, has resemblances to Haramiyidae and Theroteinidae. Kirtlingtonia catenata gen. et sp. nov. (family indeterminate), based on last upper molars and a probable upper premolar, has a slight resemblance to Eleutherodon, and also to M2 of some paulchoffatiid multituberculates. Kermackodon multicuspis gen. et sp. nov. (family Kermackodontidae nov.) and Hahnotherium antiquum gen. et sp. nov. (family Hahnotheriidae nov.) are based on second upper molars, recognised as multituberculate by their horizontal wear and inferred occlusal displacement with respect to m2. A lower molar referred to H. antiquum confirms this. A blade−like lower premolar and an upper premolar with conical cusps, referred to Kermackodon, are multituberculate−like, but distinctive. Divergence between the two Bathonian multituberculates indicates that the order originated much earlier, more probably from a haramiyid than from a morganucodontid source. Mojo is regarded as probably a haramiyid. The Hahnodontidae, which have basined wear, are removed from the Multituberculata to the “Haramiyida”.

13

New Late Cretaceous mammals of southern Kazakhstan

67%

Averianov A. O.

Acta Palaeontologica Polonica

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1997

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tom 42

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nr 2

Mammalian remains from the lower part of the Darbasa Formation (lower Campanian) at the 'Grey Mesa' locality in the Alymtau Range, southern Kazakhstan, are described. They include ?Bulganbaatar sp. (Multituberculata), Deltatheridium nessovi, sp. n. (Deltatheroida), and four eutherians: an undeterminated ?otlestid kennalestoid (?Otlestidae), ?Alymlestes sp. (Zalambdalestidae), ?Aspanlestes sp. (Zhelestidae), and an undeterminated eutherian. This new Cretaceous fauna is most similar to that from the Djadokhta Formation in Mongolia and may tentatively confirm an early Campanian age for the latter.

14

Early Cretaceous multituberculate mammals from the Kuwajima Formation [Tetori Group], central Japan

67%

Kusuhashi N.

Acta Palaeontologica Polonica

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2008

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tom 53

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nr 3

Hakusanobaatar matsuoi gen. et sp. nov. and Tedoribaatar reini gen. et sp. nov. are multituberculate mammals recovered from the Lower Cretaceous (Barremian to lower Aptian) Kuwajima Formation of the Tetori Group in the Shiramine district, Hakusan City, Ishikawa Prefecture, central Japan. Hakusanobaatar matsuoi is an eobaatarid multituberculate characterized by a P4 with cusp formula 3:5, and a P5 with cusp formula 2:6:?2. One of the specimens of H. matsuoi has the best preserved upper premolar series among known eobaatarid specimens. Based on the dentition of H. matsuoi, it is highly probable that the cimolodontan P4 is homologous with the “plagiaulacidan” P5. Tedoribaatar reini is also tentatively attributed to Eobaataridae, and shows a single−rooted p3 and loss of at least the permanent p2. On the basis of these apomorphic features, T. reini is considered to be the “plagiaulacidan” multituberculate that is most closely related to cimolodontans.

15

New multituberculate teeth from the Early Cretaceous of Morocco

67%

Hahn G., Hahn R.

Acta Palaeontologica Polonica

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2003

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tom 48

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nr 3

Three new multituberculate teeth are described from the Early Cretaceous of Morocco. Denisodon moroccensis gen. et sp. nov. is established for a second lower molar which differs from that of Hahnodon taqueti, from the same locality, by a preserved posterior buccal cusp, a smaller posterior lingual cusp and the less indented lingual wall of the crown. The second tooth is a posterior upper premolar. It is represented by the posterior portion of its crown on which is present only one row of cusps, similar to the conditions in Kielanodon, Eobaatar, Bolodon, and the Pinheirodontidae. The third tooth is a lower incisor, similar to that in Kuehneodon. Both teeth are grouped as „Hahnodontidae, gen. et sp. indet.” Paulchoffatioidea new superfamily is established for the Paulchoffatiidae, Hahnodontidae, and Pinheirodontidae. It is characterized by the following autapomorphies: premolarisation of I2−C, presence of a third row of cusps on the posterior upper premolars and the basin−like structure of the m2. Hahnodontidae and Hahnodon are redefined.

16

A new reconstruction of multituberculate endocranial casts and encephalization quotient of Kryptobaatar

67%

Kielan-Jaworowska Z., Lancaster T. E.

Acta Palaeontologica Polonica

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2004

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tom 49

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nr 2

Multituberculate and eutriconodontan endocasts differ from those of primitive therian mammals in their lack of visible midbrain exposure on the dorsal side and in having a vermis−like triangular bulge (recognized herein as the cast of a large sinus—the superior cistern) inserted between the cerebral hemispheres. As the shape and proportions of multituberculate, eutriconodontan, and Cretaceous eutherian endocasts are otherwise similar, one might speculate that the multituberculate and eutriconodontan brains did not differ essentially from those of primitive eutherian and marsupial mammals, in which the midbrain is exposed dorsally. This conclusion might have important phylogenetic implications, as multituberculates and eutriconodontans may lay closer to the therians sensu strico, than hitherto believed. We describe an endocast of the Late Cretaceous multituberculate Kryptobaatar, which differs from those of other multituberculates (Ptilodus, Chulsanbaatar, and Nemegtbaatar) in having unusually long olfactory bulbs and the paraflocculi elongated transversely, rather than ball−shaped. We estimate the encephalization quotient (EQ) of Kryptobaatar, using: 1) Jerison’s classical equation (1) based on estimation of endocranial volume and body mass; 2) McDermott et al.’s derived body mass estimation equation (2) using upper molar lengths; and 3) estimation of body mass based on new equations (3a, 3b, 3c, and 3d₁₋₉), which we propose, using measurements of the humerus, radius, ulna, femur and tibia. In both Jerison’s method and a mean of our series of derived formulae, the EQ varies around 0.71, which is higher than estimated for other multituberculate mammals. It remains an open question whether the evolutionary success of Kryptobaatar(which was a dominant mammal during the ?early Campanian on the Gobi Desert and survived until the ?late Campanian) might have been related to its relatively high EQ and well developed sensorimotor adaptations, in particular olfaction and coordinated movements.

17

Review of the early allotherian mammals

67%

Butler P. M.

Acta Palaeontologica Polonica

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2000

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tom 45

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nr 4

Comparison of the early allotherian genera, Haramiyavia, Thomasia, Theroteinus, and Eleutherodon shows that their molariform teeth are variants of a common pattern, justifying the inclusion of these genera in a single order Haramiyida. Haramiyavia is made the type of a new family Haramiyaviidae. The order Haramiyida is divided into two suborders: (1) Theroteinida (only family Theroteinidae), and (2) Haramiyoidea (families Haramiyaviidae, Haramiyidae, Eleutherodontidae). Dental resemblances support the hypothesis that the Multituberculata originated within the Haramiyida, in which case the Haramiyida would be paraphyletic. Derivation of multituberculates from within the Mammaliaformes would involve a highly improbable transformation of the dentition. It is therefore postulated that allotherian (Haramiyida + Multituberculata) and non-allotherian mammaliaform clades separated before the Mammaliaformes developed a shearing dentition with unilateral occlusion and transverse jaw movements. This hypothesis implies that the two clades evolved to a large extent in parallel, to account for the apparent synapomorphies of multituberculates and therians.

18

First ? cimolodontan multituberculate mammal from South America

67%

Kielan-Jaworowska Z., Ortiz-Jaureguizar E., Vieytes C., Pascual R., Goin F. J.

Acta Palaeontologica Polonica

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2007

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tom 52

|

nr 2

We describe a Cretaceous ?cimolodontan multituberculate p4 from South America, for which we erect the new genus and species Argentodites coloniensis. This new taxon is represented by an isolated ?left p4 from the Upper Cretaceous (?Campanian or Maastrichtian) La Colonia Formation of Patagonia (Fig. 1). It has a strongly convex anterior margin and prismatic enamel, which attest to its cimolodontan nature, while the previously known p4 (MACN−RN 975) from the Late Cretaceous Los Alamitos Formation is roughly rectangular, suggesting “plagiaulacidan” affinity. The presence of normal prismatic enamel in Argentodites suggests similarities to Ptilodontoidea. However, it differs from the Late Cretaceous and Paleocene Laurasian cimolodontans (including Ptilodontoidea) in having a long, straight posterior margin, a nearly straight dorsal margin, characteristic of some “Plagiaulacida”, and in having the lingual side close to the mirror image of the labial side, the character that poses difficulties in establishing whether it is a right or left tooth. Because of these differences we assign Argentodites to ?Cimolodonta, tentatively only, superfamily and family incertae sedis.

19

Skull structure in Catopsbaatar and the zygomatic ridges in multituberculate mammals

67%

Kielan-Jaworowska Z., Hurum J. H., Lopatin A. V.

Acta Palaeontologica Polonica

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2005

|

tom 50

|

nr 3

The late Campanian djadochtatherioid multituberculate Catopsbaatar catopsaloides was originally known from three skulls from Hermiin Tsav in the Gobi Desert (Mongolia). Three more skulls from Hermiin Tsav are now available, associated with parts of the previously unknown postcranial skeleton, which will be described separately. We describe herein the skull and dentition of C. catopsaloides, based on all available material, housed in PIN, PM, and ZPAL collections. The genera Catopsbaatar, Djadochtatherium, and Kryptobaatar share several characters, unknown in Tombaatar, such as very long postorbital processes directed postero−laterally and downwards, parietal ridges extending from the posterior margins of the postorbital processes postero−medially, and nuchal crests with prominent lateral wings, incurved anteriorly in the middle, so that the skull in dorsal view is shorter in the middle than laterally. Catopsbaatar shares with Djadochtatherium a very high and prominent anterior zygomatic ridge, and presence of the masseteric protuberance, but differs from it and from other djadochtatherioid genera in having the orbit situated more posteriorly, the intermediate zygomatic ridge adhering to the anterior ridge, and a smaller trapezoidal (rather than crescent−shaped) p4 without ridges; it differs from Kryptobaatar and Djadochtatherium in having three upper premolars (P2 being lost) and shares this last character with Tombaatar. Catopsbaataris known not only from Hermiin Tsav, but also from Baruungoyot Formation of Khulsan, represented there by a single m2. We demonstrate that the separation of the masseter superficialis into two parts, the origins of which leave scars on the lateral wall of the zygomatic arch surrounded by zygomatic ridges, occurs in all the multituberculates (beginning with Paulchoffatiidae), and is regarded as a multituberculate autapomorphy.

20

Bone microstructure and growth patterns of early mammals

67%

Chinsamy A., Hurum J. H.

Acta Palaeontologica Polonica

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2006

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tom 51

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nr 2

We present results of the first studies of the bone microstructure of early mammals, based on the Early Jurassic Morganucodon, the Late Cretaceous multituberculates, Kryptobaatar and Nemegtbaatar, and the Late Cretaceous eutherians Zalambdalestes and Barunlestes. Our results show that the two eutherian taxa grew relatively slowly with periodic pauses in growth indicated by the presence of rest lines, while the multituberculates and Morganucodon had a faster rate of bone formation that suggests an overall rapid growth rate that slowed down later in ontogeny. Comparisons of the early mammalian bone microstructure with that of non−mammalian cynodonts, extant monotremes, and placentals are also made, and significant differences in the rate of osteogenesis in the various groups are documented. Our findings suggest differences in the growth rate between the multituberculates and the Mesozoic eutherians, and moreover, both groups appear to have slower growth rates as compared to modern monotremes and placentals. Our results further suggest that the determinate growth strategy typical of extant mammals evolved early in the evolution of the non−mammalian therapsids. We speculate that the sustained, uninterrupted bone formation among the multituberculates may have been an adaptive attribute prior to the K−T event, but that the flexible growth strategy of the early eutherians was more advantageous thereafter.

Ograniczanie wyników

Masticatory musculature of Asian taeniolabidoid multituberculate mammals

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Bone microstructure and growth patterns of early mammals