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Matsui, Kumiko; Kawabe, Soichiro
(detail)
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2015 |
The oldest record of Paleoparadoxia from the Northwest Pacific with an implication on the early evolution of Paleoparadoxiinae (Mammalia: Desmostylia).
Paleontological Research 19(3): 251-265. 4 tabs. 6 figs. DOI: 10.2517/2015PR007. July 1, 2015.
–ABSTRACT: A new specimen of Paleoparadoxia found from a marine lower Miocene deposit in the Chikubetsu area, Hokkaido, Japan, is described. The material consists of a distal part of the scapula, proximal end of the humerus from the right side, as well as a fragmentary rib, preserved in a float of calcareous fine sandstone. The specimen is referred to the order Desmostylia and subsequently to the genus Paleoparadoxia sp. The well preserved shoulder girdle of this specimen provides the first detailed morphology of this anatomical region in Paleoparadoxia. We compared the specimen with a wide range of desmostylid samples to reveal new diagnostic characters for the genus, such as the greater tubercle extending toward the proximal side above the head and the distinct lesser tubercle located on the medial side, projected medially. The lower Miocene Sankebetsu Formation outcrops in the area where the float was found, and the lithology and associated fossil fauna of the float indicate that it was derived from there. The fossil pollen assemblages and molluscs found in the formation indicate that it was deposited under cool to temperate conditions. The new specimen thus suggests that Paleoparadoxia had inhabited a cool environment in addition to warm areas, as suggested in previous studies. The published age estimate of the formation places the present specimen between 23.8±1.5 and 20.6±1.0 Ma. This represents the oldest record of the genus Paleoparadoxia, exceeding the previous record of ca. 19 Ma for a specimen found from the Chichibu Basin, and nearly matches the oldest record of Paleoparadoxiinae in the Northwestern Pacific. This indicates that the ages of the oldest occurrences of basal and derived paleoparadoxiines overlapped (i.e., Archaeoparadoxia from the Northeastern Pacific Region and Paleoparadoxia from the Northwestern Pacific, respectively). It is also likely that the geographic range of Paleoparadoxiinae had already expanded from the Northeast Pacific to the Northwest Pacific in the early stage of their evolution.
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Matsui, Kumiko
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2017 |
How can we reliably identify a taxon based on humeral morphology? Comparative morphology of desmostylian humeri.
PeerJ 5: e4011.
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Matsui, Kumiko; Sashida, Katsuo; Agematsu, Sachiko; Kohno, Naoki
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2017 |
Habitat preferences of the enigmatic Miocene tethythere[s] Desmostylus and Paleoparadoxia (Desmostylia; Mammalia) inferred from the depositional depth of fossil occurrences in the Northwestern Pacific realm.
Palaeogeogr. Palaeoclim. Palaeoecol. 471: 254-265. 7 tabs. 7 figs. http://dx.doi.org/10.1016/j.palaeo.2017.02.005. Published online Feb. 8, 2017; Apr. 1, 2017.
–ABSTRACT: Desmostylus and Paleoparadoxia are extinct marine mammals belonging to the order Desmostylia that existed in the period between the late Oligocene and middle Miocene. All occurrences of their fossils are limited to marine strata along the coasts of the North Pacific Ocean. Although these two genera have similar body form, their paleoecologies including habitat preferences are thought to be different because their cranial structures are distinctive as well as they have been known separately in different localities. We estimated the depositional depths of their fossil occurrences on the basis of the associated mollusks and benthic foraminiferal assemblages from 45 desmostylian localities. Only data on complete or partial skeletal specimens were considered in order to exclude cases of reworking and pre-burial drift of carcasses that would confound our inference.
Our results indicate that the depositional environment of Desmostylus specimens was restricted to the inner sublittoral zone shallower than 30 m in depth whereas that of Paleoparadoxia specimens ranged from the inner sublittoral (0–50 m) to upper bathyal zone (between 150 and 400 and 500 m). This finding indicates that Desmostylus lived in nearshore water while Paleoparadoxia foraged in a relatively deep, offshore water. The depositional segregation of these two genera most likely reflects their different habitat preferences.
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Matsui, Kumiko; Kimura, Yuri; Nagata, Mitsuhiro; Inose, Hiroaki; Ikeda, Kazuya; Beatty, Brian Lee; Obayashi, Hideyuki; Hirata, Takafumi; Otoh, Shigeru; Shinmura, Tatsuya; Agematsu, Sachiko; Sashida, Katsuo
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2018 |
A long-forgotten 'dinosaur' bone from a museum cabinet, uncovered to be a Japan's iconic extinct mammal, Paleoparadoxia (Desmostylia, Mammalia).
Royal Society Open Science 5: 172441. 1 tab. 7 figs. http://dx.doi.org/10.1098/rsos.17244. Supplementary material available at https://doi.org/10.6084/m9.figshare.c.4175684.
–ABSTRACT: Here, we report a new 'discovery' of a desmostylian fossil in the geological collection at a national university in Japan. This fossil was unearthed over 60 years ago and donated to the university. Owing to the original hand-written note kept with the fossil in combination with interview investigation, we were able to reach two equally possible fossil sites in the town of Tsuchiyu Onsen,Fukushima. Through the interviews, we learned that the fossil was discovered during construction of a debris flow barrier and that it was recognized as a 'dinosaur' bone among the locals and displayed in the Village Hall before/until the town experienced a fire disaster in 1954. As scientific findings, the fossil was identified to be a right femur of Paleoparadoxia (Desmostylia), which shows well-preserved muscle scars on the surface. The age was estimated to be 15.9 Ma or younger in zircon-dating. This study shows an excellent case that historical and scientific significances could be extracted from long-forgotten uncatalogued specimens as long as the original information is retained with the specimens.
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Matsui, Kumiko; Tsuihiji, Takanobu
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2019 |
The phylogeny of desmostylians revisited: proposal of new clades based on robust phylogenetic hypotheses.
PeerJ 7: e7430 https://doi.org/10.7717/peerj.7430. 4 figs. + 15 online supplemental files.. Published online Oct. 17, 2019.
–ABSTRACT: Background: Desmostylia is a clade of extinct aquatic mammals with no living members. Today, this clade is considered belonging to either Afrotheria or Perissodactyla. In the currently-accepted taxonomic scheme, Desmostylia includes two families, 10 to 12 genera, and 13–14 species. There have been relatively few phylogenetic analyses published on desmostylian interrelationship compared to other vertebrate taxa, and two main, alternative phylogenetic hypotheses have been proposed in previous studies. One major problem with those previous studies is that the numbers of characters and OTUs were small.
Methods: In this study, we analyzed the phylogenetic interrelationship of Desmostylia based on a new data matrix that includes larger numbers of characters and taxa than in any previous studies. The new data matrix was compiled mainly based on data matrices of previous studies and included three outgroups and 13 desmostylian ingroup taxa. Analyses were carried out using five kinds of parsimonious methods.
Results: Strict consensus trees of the most parsimonious topologies obtained in all analyses supported the monophyly of Desmostylidae and paraphyly of traditional Paleoparadoxiidae. Based on these results, we propose phylogenetic definitions of the clades Desmostylidae and Paleoparadoxiidae based on common ancestry.
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Matsui, Kumiko; Pyenson, Nicholas D.
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2023 |
New evidence for the antiquity of Desmostylus from the Skooner Gulch Formation of California.
_Royal Society Open Science_ 10: 221648. 1 tab. 4 figs. https://doi.org/10.1098/rsos.221648 + electronic suppl. material at https://doi.org//10.6084/m9.figshare.c.6673576.
–ABSTRACT: Desmostylus is an extinct marine mammal genus that belongs to Desmostylia, a clade of extinct herbivorous mammals. While desmostylian remains are widely reported from Paleogene and Neogene marine strata of the North Pacific Rim, occurrences of the genus Desmostylus are almost entirely limited to middle Miocene strata, with only a few early Miocene records from Japan. Here we report a Desmostylus tooth from the earliest Miocene (Aquitanian) Skooner Gulch Formation in northern California, USA. This specimen exhibits cuspules around the crown, a primitive trait of the subfamily Desmostylidae, as seen in more basal branching desmostylid taxa such as Cornwallius and Ounalashkastylus, but with a high tooth crown and thickened enamel. The specimen is also diagnostically different from all other desmostylid genera, such as Cornwallius, and Ounalashklastylus. The Aquitanian age of the Skooner Gulch Formation implies that the distinctive tooth morphology of Desmostylus has persisted, largelyunchanged, for more than 15 million years and that desmostylids possibly originated in western North America.
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Bibliography and Index of the Sirenia and Desmostylia 