Polycotylus latipinnis Cope (Plesiosauria, Polycotylidae), a Nearly Complete Skeleton from the Niobrara Formation (Early Campanian) of Southwestern South Dakota
Polycotylus latipinnis Cope (Plesiosauria, Polycotylidae), a Nearly Complete Skeleton from the Niobrara Formation (Early Campanian) of Southwestern South Dakota
复制标题
Polycotylus latipinnis Cope（蛇颈龙目，Polycotylidae），来自南达科他州西南部 Niobrara 组（早期坎帕尼亚）的近乎完整的骨骼
DOI：
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发表时间：
2016
影响因子：
1.4
通讯作者：
James E. Martin
中科院分区：
文献类型：
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作者：
B. Schumacher;James E. Martin
摘要
宽鳍复孔虫的一个几乎完整的骨架（SDSM 23020）来自Niobrara组上部（早期坎帕尼亚）产于南达科他州（美国）极大地改进了这以前很少被了解的分类群的信息。标本SDSM 23020和YPM 1125（副模式P. latipinnis）表现出许多区别多叶虫的颅后特征，特别是骶前椎骨计数，V形面的性质，独特的伊利亚，以及高度衍生的桨状骨，包括五个上足骨化和多指骨。多叶类的脊椎骨和趾骨数量较多，但伴随着异常的短缩;因此，相对的身体和肢体比例可能与较少衍生的多叶类相似，脊椎骨和趾骨更少，更长。完整的头骨，来自于多子目，具有短的颞窗，细长的额骨，非常细长的副蝶骨，突出的文化状突起，以及下颌联合内的角骨和脾骨的非常长的延伸。分支系统学分析表明，Polycotylus巢坚定地在衍生Polycotylidae作为一个潜在的姐妹分类群Dolichorhynchops osborni和Trinacromerum，尽管“原始”的骶前脊椎计数。未来的改进，在现有的数据，特别是更好的信息基础polycotylids，和完善的字符选择，以消除同质性可以显着改变树的结构，显示不同的亚群内Polycotylidae。北美的多子虫具有细长的颞窗、细长的足和相对较长的椎骨，仅限于赛诺曼晚期和图伦早期的出现，而在这些方面明显缩短的多子虫仅限于图伦晚期的出现。在多子纲中，Iceland的形态变化很大，除了分类学上的用途外，可能部分归因于性二型性。
ABSTRACT
A nearly complete skeleton of Polycotylus latipinnis (SDSM 23020) from the upper Niobrara Formation (early Campanian) of South Dakota (U.S.A) greatly improves information for this formerly poorly known taxon. Specimens SDSM 23020 and YPM 1125 (paratype P. latipinnis) exhibit numerous postcranial characters that distinguish Polycotylus, in particular presacral vertebral count, nature of chevron facets, unique ilia, and highly derived paddles including five epipodial ossifications and increased hyperphalangy. Greater vertebral and phalangeal counts of Polycotylus are accompanied by exceptional foreshortening; thus, the relative body and limb proportions are likely similar to less derived polycotylids, with fewer, more elongate vertebrae and phalanges. The complete skull, derived among polycotylids, has short temporal fenestrae, elongate frontals, exceptionally slender parasphenoid with prominent cultriform process, and exceptionally long extensions of the angulars and splenials within the mandibular symphysis. Cladistic analysis indicates that Polycotylus nests firmly within derived Polycotylidae as a potential sister taxon to Dolichorhynchops osborni and Trinacromerum, despite a ‘primitive’ presacral vertebral count. Future improvements in available data, in particular better information regarding basal polycotylids, and refinement of character selection to nullify homoplasy could significantly alter the tree structure to show distinct subgroups within Polycotylidae. North American polycotylids with elongate temporal fenestrae, elongate podials, and relatively long vertebrae are confined to occurrences of late Cenomanian and earliest Turonian age, whereas polycotylids distinctly foreshortened in these respects are restricted to post-Turonian occurrences. Ilium morphology is highly variable among polycotylids and, in addition to taxonomic utility, may be in part attributable to sexual dimorphism.