Tomonori Tanaka, Kentaro Chiba, Tadahiro Ikeda, Michael J. Ryan
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Here we describe a new, early‐branching neoceratopsian, <jats:italic>Sasayamagnomus saegusai</jats:italic> gen. et sp. nov., from the Albian Ohyamashimo Formation in southwestern Japan, representing the easternmost fossil record of ceratopsians in Asia. <jats:italic>Sasayamagnomus</jats:italic> exhibits three diagnostic features in the jugal, squamosal and coracoid, respectively, and also has a unique combination of characters in the lacrimal. Our phylogenetic analysis indicates that <jats:italic>Sasayamagnomus</jats:italic> forms a clade with <jats:italic>Aquilops americanus</jats:italic>, one of the earliest neoceratopsians from North America, followed by the sister taxon <jats:italic>Auroraceratops rugosus</jats:italic> from China. The present time‐calibrated phylogenetic tree indicates that the immigration of neoceratopsians from Asia to North America occurred during the latest Aptian or early Albian, refining the previously suggested timeframe. 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引用次数: 0
摘要
在晚侏罗世到晚白垩世期间,食草恐龙支系角龙(Ceratopsia)在北半球兴盛一时。以前的古生物地理学研究表明,它们最初的分化发生在亚洲,新角龙的早期分支在巴里米亚到白垩纪的某个时期将其地理范围扩展到了北美洲。然而,它们从亚洲扩散到北美洲的具体时间和方式仍然未知。在这里,我们描述了一个新的、早期分支的新角龙--Sasayamagnomus saegusai gen.Sasayamagnomus的颈骨、鳞骨和冠状骨分别具有三个诊断特征,泪骨也具有独特的特征组合。我们的系统发育分析表明,Sasayamagnomus 与北美最早的新角龙之一 Aquilops americanus 形成一个支系,其次是中国的姊妹类 Auroraceratops rugosus。目前的时间校准系统发生树表明,新角龙类从亚洲向北美洲的移民发生在最晚的始新世或白垩纪早期,从而完善了之前提出的时间框架。这与北美下白垩统零星的新角龙化石记录以及白令陆桥的初步形成相吻合。此外,全球变暖(这使得北极地区的森林得以大面积发展)和白令陆桥的出现同时发生在安息-阿尔卑斯时期,这可能在促进新角龙类从亚洲向北美洲移民的过程中起到了至关重要的作用。
A new neoceratopsian (Ornithischia, Ceratopsia) from the Lower Cretaceous Ohyamashimo Formation (Albian), southwestern Japan
The herbivorous dinosaur clade Ceratopsia flourished in the northern hemisphere during the Late Jurassic to Late Cretaceous. Previous palaeobiogeographic studies have suggested that their initial diversification occurred in Asia, with early‐branching neoceratopsians extending their geographical range to North America sometime during the Barremian to Albian. However, the specific timing and mode of their dispersal from Asia to North America remains unknown. Here we describe a new, early‐branching neoceratopsian, Sasayamagnomus saegusai gen. et sp. nov., from the Albian Ohyamashimo Formation in southwestern Japan, representing the easternmost fossil record of ceratopsians in Asia. Sasayamagnomus exhibits three diagnostic features in the jugal, squamosal and coracoid, respectively, and also has a unique combination of characters in the lacrimal. Our phylogenetic analysis indicates that Sasayamagnomus forms a clade with Aquilops americanus, one of the earliest neoceratopsians from North America, followed by the sister taxon Auroraceratops rugosus from China. The present time‐calibrated phylogenetic tree indicates that the immigration of neoceratopsians from Asia to North America occurred during the latest Aptian or early Albian, refining the previously suggested timeframe. This aligns with fragmentary neoceratopsian fossil records from the Lower Cretaceous of North America and the initial formation of the Bering land bridge. Furthermore, the simultaneous occurrence of global warming (which enabled the development of extensive forests in the Arctic region) and the emergence of the Bering land bridge during the Aptian–Albian, probably played a crucial role in facilitating the immigration of neoceratopsians from Asia to North America.
期刊介绍:
Papers in Palaeontology is the successor to Special Papers in Palaeontology and a journal of the Palaeontological Association (www.palass.org). The journal is devoted to the publication of papers that document the diversity of past life and its distribution in time and space.
Papers in Palaeontology is devoted to the publication of papers that document the diversity of past life and its distribution in time and space. As a sister publication to Palaeontology its focus is on descriptive research, including the descriptions of new taxa, systematic revisions of higher taxa, detailed biostratigraphical and biogeographical documentation, and descriptions of floras and faunas from specific localities or regions. Most contributions are expected to be less than 30 pp long but longer contributions will be considered if the material merits it, including single topic parts.
The journal publishes a wide variety of papers on palaeontological topics covering:
palaeozoology,
palaeobotany,
systematic studies,
palaeoecology,
micropalaeontology,
palaeobiogeography,
functional morphology,
stratigraphy,
taxonomy,
taphonomy,
palaeoenvironmental reconstruction,
palaeoclimate analysis,
biomineralization studies.