Conserved exopodite morphology in three-dimensionally preserved trilobites from the Walcott-Rust Quarry (Mohawkian, Ordovician) of New York, USA

IF 1.7 3区 农林科学 Q2 ENTOMOLOGY
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Abstract

Trilobites were extremely abundant and diverse euarthropods from the Paleozoic Era, but our understanding of their non-biomineralized ventral morphology is restricted to localities with exceptional fossil preservation. The Ordovician-aged Walcott-Rust Quarry in New York State preserves exceptional trilobite fossils as calcite casts in three-dimensions with little to no deformation, providing a valuable view of their ventral morphology. Appendages of the two most abundant trilobites, Ceraurus pleurexanthemus and Flexicalymene senaria, have been known for over 150 years but the original preparation of the specimens as thin sections has led to significant disagreement about their anatomy. Ceraruus pleurexanthemus is more abundant in the thin section collections (157 specimens) and features nearly complete appendages including a subtriangular protopodite with stud-like gnathobases along the medial edge and long endites ventrally. The exopodite consists of a long proximal article bearing dumbbell-shaped lamellae (in cross section) and a shorter distal article, closely resembling that of the cheirurid Anacheirurus adserai from the Lower Ordovician Fezouata Shale biota of Morocco. The appendages of F. senaria (37 specimens) are less well preserved. The exopodite bears up to 40 dumbbell shaped lamellae (in cross section) and is proportionally longer relative to the endopodite of C. pleurexanthemus. The close morphological similarity observed between the exopodites of C. pleurexanthemus and A. adersai, despite originating from paleogeographically distant latitudes and temporally separated by over ca. 20 million years, shows that the proposed “Cambrian type” exopodite persisted through the majority of the Ordovician. The morphology of the endopodites between C. pleurexanthemus and A. adersai is more variable when compared to the organization of the exopodites, may reflect selective pressures from locomotion and feeding between these species.

美国纽约沃尔科特-拉斯特采石场(莫霍肯,奥陶纪)三维保存的三叶虫中保存的外胚层形态
三叶虫是古生代数量极其丰富、种类极其繁多的类地行星,但我们对其非生物矿化腹面形态的了解仅限于化石保存特别完好的地方。纽约州奥陶纪时期的沃尔科特-拉斯特采石场(Walcott-Rust Quarry)以几乎没有变形的三维方解石铸件形式保存了特殊的三叶虫化石,为我们了解它们的腹部形态提供了宝贵的视角。150 多年前,人们就已经知道两种最丰富的三叶虫--Ceraurus pleurexanthemus 和 Flexicalymene senaria--的附肢,但由于最初将标本制作成薄片,人们对它们的解剖结构存在很大分歧。Ceraruus pleurexanthemus 在薄片标本中的数量较多(157 个标本),其特征是几乎完整的附肢,包括一个近三角形的原脚节,内侧边缘有螺柱状的钩喙,腹侧有长的内齿。外脚节由一个长的近端节和一个较短的远端节组成,近端节带有哑铃状薄片(横截面),与摩洛哥下奥陶世费祖阿塔页岩生物群中的螯足类 Anacheirurus adserai 非常相似。F. senaria(37 个标本)的附肢保存较差。外节上有多达 40 个哑铃状薄片(横截面),与 C. pleurexanthemus 的内节相比,外节的比例长度更长。尽管 C. pleurexanthemus 和 A. adersai 的外脚节起源于古地理上遥远的纬度地区,而且在时间上相隔约 2000 万年,但它们的外脚节在形态上却非常相似。这表明所提出的 "寒武纪类型 "外蜕皮一直持续到奥陶纪的大部分时期。C. pleurexanthemus 和 A. adersai 之间的内足器形态与外足器的组织相比变化更大,这可能反映了这些物种之间运动和取食的选择性压力。
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来源期刊
CiteScore
3.50
自引率
10.00%
发文量
54
审稿时长
60 days
期刊介绍: Arthropod Structure & Development is a Journal of Arthropod Structural Biology, Development, and Functional Morphology; it considers manuscripts that deal with micro- and neuroanatomy, development, biomechanics, organogenesis in particular under comparative and evolutionary aspects but not merely taxonomic papers. The aim of the journal is to publish papers in the areas of functional and comparative anatomy and development, with an emphasis on the role of cellular organization in organ function. The journal will also publish papers on organogenisis, embryonic and postembryonic development, and organ or tissue regeneration and repair. Manuscripts dealing with comparative and evolutionary aspects of microanatomy and development are encouraged.
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