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Determining scapular position is a major issue in reconstructing the skeletal systems of extinct quadruped archosaurs and mammals, because the proximal portion of the scapulae has no direct skeletal joint with the vertebrae or ribs. When quadrupeds stand or walk, their trunk is suspended between the forelimbs by the serratus muscles, which arises from the lateral sides of the "thoracic" ribs and inserts into the proximal portion of the costal surface of the scapula. Therefore, the "thoracic" ribs are subjected to a static or dynamic vertical compression between the lifting force from the muscle and the gravitational force from the vertebral column. To investigate the body support function of the ribs, we analyzed the mechanical strength of the ribs of extant tetrapods by the two-dimensional finite element method, and compared the degree of strength through their craniocaudal scapular positions. The result of this simulation showed that the "thoracic" ribs of quadrupeds, to which the serratus muscles attach, have a relatively higher strength against compaction than the other ribs. In bipeds, however, we did not find a similar correlation between the strength of ribs and the serratus muscle. This implies that the location of robust ribs is associated with the arrangement of the serratus muscle, and provides a probable candidate for determination of the scapular position for extinct quadruped archosaurs and mammals.

Osteological characteristics of extant, quadrupedal, aquatic or amphibious mammals are compared and used to determine the presence and state of development, or absence, of aquatic adaptations in the order Desmostylia. The specimens compared include seventeen bones from in each species four higher taxa: Rodentia, Carnivora, Mustelidae and Artiodactyla. The aquatic form is compared with its terrestrial counterpart within each group. Quantitative evidence of convergence is used to sort out characters that are adaptive in relation to aquatic habits. Aquatic conformations or tendencies are identified as those characters, displayed by aquatic forms in different taxonomic groups, that have more in common with each other than with corresponding characters of land animals in the same taxa. About 80% of the 49 aquatic adaptive characters identified are also found in desmostylians. This analysis documents the gradual evolutionary transition of desmostylians to an aquatic mode of life. Furthermore, the results show t...

There have been many research attempts to infer the track‐maker from a fossil footprint. However, it does not seem that prediction of the footprint from a mounted skeleton has yet been attempted. The body form of the desmostylian is hypothesized to have a peculiar lateral‐type limb posture. If fossil desmostylian footprints were to be found, this hypothesis on reconstruction of the desmostylian skeleton could be tested. In order to stimulate such a discovery, the presumed footprint and trackway of Desmostylus are postulated here. The footprint and trackway are inferred from skeletons and comparisons with some living mammals. They are characterized by a short, wide footprint with four divergent toes and pad, short stride and wide trackway.

International audience; Background: The paleoecology of desmostylians has been discussed controversially with a general consensus that desmostylians were aquatic or semi-aquatic to some extent. Bone microanatomy can be used as a powerful tool to infer habitat preference of extinct animals. However, bone microanatomical studies of desmostylians are extremely scarce.Methodology/Principal Findings: We analyzed the histology and microanatomy of several desmostylians using thin-sections and CT scans of ribs, humeri, femora and vertebrae. Comparisons with extant mammals allowed us to better understand the mode of life and evolutionary history of these taxa. Desmostylian ribs and long bones generally lack a medullary cavity. This trait has been interpreted as an aquatic adaptation among amniotes. Behemotops and Paleoparadoxia show osteosclerosis (i.e. increase in bone compactness), and Ashoroa pachyosteosclerosis (i.e. combined increase in bone volume and compactness). Conversely, Desmostylus differs from these desmostylians in displaying an osteoporotic-like pattern.Conclusions/Significance: In living taxa, bone mass increase provides hydrostatic buoyancy and body trim control suitable for poorly efficient swimmers, while wholly spongy bones are associated with hydrodynamic buoyancy control in active swimmers. Our study suggests that all desmostylians had achieved an essentially, if not exclusively, aquatic lifestyle. Behemotops, Paleoparadoxia and Ashoroa are interpreted as shallow water swimmers, either hovering slowly at a preferred depth, or walking on the bottom, and Desmostylus as a more active swimmer with a peculiar habitat and feeding strategy within Desmostylia. Therefore, desmostylians are, with cetaceans, the second mammal group showing a shift from bone mass increase to a spongy inner organization of bones in their evolutionary history.

The gait of several extant mammals was analyzed so as to provide basic data for the restoration of the terrestrial locomotion of extinct animals. An attempt has been made to establish the correlation between the gaits and the morphological data, as the latter can be obtained even from fossils. Animals walking naturally were recorded on videotape, appropriate frames were then printed for analysis. Five kinds of gaits are illustrated here with supporting graphs. In addition, some diagrams were drawn using variables of the gait cycle, the rhythm of limb work, the rhythm of locomotion and the hindlimb length ratio to the trunk. Changes in the four joint angles during a gait cycle were measured and graphed for comparison with each limb joint among mammals with four typical foot postures. The kind of gait was determined in relation to the limb length ratio, the gait cycle and the position of the center of gravity. The joint angle of limbs is in relation to foot posture. The wrist joint in walking is analogous to the knee joint in the degree, direction and timing of flexion.

Desmostylians from the Pacific coasts of Japan and North America are compared and taxonomy and adaptations in the mammalian order Desmostylia discussed. The taxonomy is based mainly on teeth and skulls. Feeding adaptations and habitat are discussed using teeth and restored skeletons, respectively. In the extinct order two families, six genera and 10 species can now be recognized. Each genus is distinguished by a set of tooth characters. The three species of the genus Paleoparadoxia have different body sizes. Two species of the genus Desmostylus can be distinguished on morphological differences in the cranium. As a result it is clear that both species, D. hesperus, which had long been recognized only in North America, and D. japonicus, which has hitherto been recognized only in Japan, inhabited both coasts of the Pacific. All genera of the Order Desmostylia share a common and distinctive body form, interpreted by Inuzuka as having a laterally placed limb posture. Based on this body form, the optimum habitat is thought to have been an intertidal sandy beach. The dental morphology is variable, and derived species show an adaptation for wear by an abrasive diet. In conclusion, we theorize that the Order Desmostylia was adapted for a coastal habitat from its inception, with each genus adapting to a different sort of herbivorous diet.

The scalenus anterior muscle was found to pass behind the left subclavian artery and the first thoracic nerve in a 95-year-old Japanese woman. The scalenus anterior muscle originates from the fifth and sixth cervical vertebrae and inserts on the first rib more dorsal than typical. It is innervated by the fifth and seventh cervical nerves. The muscle belly is thin. The scalenus minimus was not found. The left vertebral artery originates from the aortic arch and enters the transverse foramen of the fifth cervical vertebra. The primary vertebral artery arises from the costocervical artery. The internal thoracic artery originates from the subclavian artery more distally than typical. The axillary artery crosses the brachial plexus between the eighth cervical and first thoracic nerves. Because the first thoracic nerve joins the brachial plexus more distally than usual, the plexus has no typical inferior trunk. Comparative anatomy shows that the muscles, nerves and arteries of the lateral cervical region of the present case maintains primitive characteristics. From the functional viewpoint, the mechanical efficiency of the scalenus anterior muscle is probably lower than usual due to the lower point of origin and the dorsal shift of the insertion.

In this paper, the eleven molars of four Asiatic elephants (Elephas maximus LINNE) in two zoos are described. They were found in the straw where the elephants slept, except one premolar, artificially removed just before shedding.Compared with the molars in function, the shed molars exihibit the following: smaller number of lamellae, shorter crown length, lower crown height by abrasion, resorbed roots, smooth mesial wearing surface with shallow dentin inlets and indistinct enamel foldings and broad distal facette. Root resorption is more evident in the mesial portion than in the distal; the buccal and lingual third parts are more resorbed than the intermediate third portion, on the buccal side in the upper molar and on the lingual side in the lower molar, than the opposite sides in basal aspect.It is shown in specimens no. 6 and 7 that the crown height decreased by 14-15mm through abrasion during three years (P1. I, 1-4). It was noted that the distal lamellae, (specimen no.11) were shed three months earlier than the mesial ones (specimen no.10, P1. I, 5-7)

In 1973, fossil elephant bones were yielded from the sandy formation, at Kamibessho, Sakura-shi, Chiba Prefecture, Kwanto Regeon of Central Japan.The formation, belonging to the lower part of Narita Formation also yielded many other molluscan fossils characterized by Glycymeris yessoensis, Diplodonta usta etc. The molluscan assemblage is closely related to that of Kamiiwahashi fossil beds of Narita Formation in other area except for a few remarkable characteristics, that is; containing less number of the genera than the other Kamiiwahashi beds and being found in thin fossil beds.The fossil materials of the elephant include a lower jaw with the left second molar in situ, and a right tusk separated into three pieces. The mandible is rather large as P. naumanni of M2 stage and the shape of it generally resembles to the holotype of P. naumanni. The features observed on the grinded tooth indicate that the materials belong to the molar of P. naumanni, which is steno-crown type with distinct loxodont plica. The incisor is more thick and stout, suggesting that it belongs to male individual.