We describe a fragmentary tooth of a rhinocerotid perisso-dactyl recovered from the middle unit o... more We describe a fragmentary tooth of a rhinocerotid perisso-dactyl recovered from the middle unit of the upper Miocene Oiso Formation, Japan. Although the specimen is fragmen-tary and heavily worn, it is worth describing because the
Abstract The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in t... more Abstract The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in the Middle-Late Pleistocene is known for its rich marine fauna that accommodated both the warm and cold water taxa brought by the Kuroshio and Oyashio Currents, respectively. However, little is known on the paleoichthyofauna in this area and the processes shaping the marine ichthyofauna of modern southern Kanto. We used fossil fish otoliths and teeth discovered in the Sha’ana Tuffaceous Sand Member belonging to the Chibanian Miyata Formation, exposed at Sha’ana-dai, Miura City, Kanagawa Prefecture, Japan, to reconstruct the paleoichthyofauna and its associated paleoenvironment and explore the content of fish assemblages during this period. The Sha’ana Tuffaceous Sand Member was composed of upper sandy mud and lower muddy sand horizons at the exposure. A total of 1,675 fish remains were collected from this site, of which 1,389 were assigned to 62 distinct taxa (20 orders, 31 families). The taxonomic composition revealed taxa from various environments, including shallow continental shelf, epi- to meso-pelagic settings, and the majority were from a generally temperate climatic zone. Paleoenvironmental analyses suggested that the fish assemblages were from the continental shelf (approximate depth of 100–200 m) in a temperate sea where both warm Kuroshio and cold Oyashio Currents had an influence on the biota. The analysis also showed that two boreal fishes, namely Clupea pallasii and Theragra chalcogramma, once had a wider distribution that extended to the southwestern areas of the Paleo-Tokyo Bay. This study provides a more complete view of the related paleobiogeography of marine fishes during the Chibanian and is essential for reconstructing the evolutionary processes of the rich ichthyofauna in the southern Kanto.
ABSTRACT The cervical and thoracic regions including vertebrae, spinal nerves, and brachial plexu... more ABSTRACT The cervical and thoracic regions including vertebrae, spinal nerves, and brachial plexus were examined by macroscopic and three-dimensional computed tomography observational scans in the two-toed sloth (Choloepus didactylus). This species possesses seven cervical vertebrae unlike closely related sloths, which possess varying number of cervical vertebrae ranging from five to ten. The large axis and the partially vestigial third cervical vertebra are morphologically characteristic of C. didactylus. In addition, the spinal nerve branches of C5, C6, C7, C8, and T1 contributed to the brachial plexus, whereas C4 and T2 did not supply nerves to the plexus. Histological data showed that the branches of C5, C6, C7, and C8 were obviously thicker than that of C4 and T1. The most notable observation was that only the two-toed sloth unlike other sloth species is conservative in these morphological characteristics regarding the cervical vertebrae spinal nerves. By comparing the morphological patterns of the cervical and thoracic spine and the brachial plexus of the two-toed sloth with ancestral morphological patterns and related species, which have derived a repatterned and variable morphology of these structures, it is possible to elucidate the morphological evolution of the cervical and thoracic regions in the evolutionary history of these mammals.
We describe a fragmentary tooth of a rhinocerotid perisso-dactyl recovered from the middle unit o... more We describe a fragmentary tooth of a rhinocerotid perisso-dactyl recovered from the middle unit of the upper Miocene Oiso Formation, Japan. Although the specimen is fragmen-tary and heavily worn, it is worth describing because the
Abstract The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in t... more Abstract The Paleo-Tokyo Bay (Kanto Plateau) that persisted during the transgression periods in the Middle-Late Pleistocene is known for its rich marine fauna that accommodated both the warm and cold water taxa brought by the Kuroshio and Oyashio Currents, respectively. However, little is known on the paleoichthyofauna in this area and the processes shaping the marine ichthyofauna of modern southern Kanto. We used fossil fish otoliths and teeth discovered in the Sha’ana Tuffaceous Sand Member belonging to the Chibanian Miyata Formation, exposed at Sha’ana-dai, Miura City, Kanagawa Prefecture, Japan, to reconstruct the paleoichthyofauna and its associated paleoenvironment and explore the content of fish assemblages during this period. The Sha’ana Tuffaceous Sand Member was composed of upper sandy mud and lower muddy sand horizons at the exposure. A total of 1,675 fish remains were collected from this site, of which 1,389 were assigned to 62 distinct taxa (20 orders, 31 families). The taxonomic composition revealed taxa from various environments, including shallow continental shelf, epi- to meso-pelagic settings, and the majority were from a generally temperate climatic zone. Paleoenvironmental analyses suggested that the fish assemblages were from the continental shelf (approximate depth of 100–200 m) in a temperate sea where both warm Kuroshio and cold Oyashio Currents had an influence on the biota. The analysis also showed that two boreal fishes, namely Clupea pallasii and Theragra chalcogramma, once had a wider distribution that extended to the southwestern areas of the Paleo-Tokyo Bay. This study provides a more complete view of the related paleobiogeography of marine fishes during the Chibanian and is essential for reconstructing the evolutionary processes of the rich ichthyofauna in the southern Kanto.
ABSTRACT The cervical and thoracic regions including vertebrae, spinal nerves, and brachial plexu... more ABSTRACT The cervical and thoracic regions including vertebrae, spinal nerves, and brachial plexus were examined by macroscopic and three-dimensional computed tomography observational scans in the two-toed sloth (Choloepus didactylus). This species possesses seven cervical vertebrae unlike closely related sloths, which possess varying number of cervical vertebrae ranging from five to ten. The large axis and the partially vestigial third cervical vertebra are morphologically characteristic of C. didactylus. In addition, the spinal nerve branches of C5, C6, C7, C8, and T1 contributed to the brachial plexus, whereas C4 and T2 did not supply nerves to the plexus. Histological data showed that the branches of C5, C6, C7, and C8 were obviously thicker than that of C4 and T1. The most notable observation was that only the two-toed sloth unlike other sloth species is conservative in these morphological characteristics regarding the cervical vertebrae spinal nerves. By comparing the morphological patterns of the cervical and thoracic spine and the brachial plexus of the two-toed sloth with ancestral morphological patterns and related species, which have derived a repatterned and variable morphology of these structures, it is possible to elucidate the morphological evolution of the cervical and thoracic regions in the evolutionary history of these mammals.
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Papers by Hajime Taru