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首页> 外文学位 >The Paleobiology of South African Therocephalian Therapsids (Amniota, Synapsida) and the Effects of the End-Permian Extinction on Size, Growth, and Bone Microstructure
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The Paleobiology of South African Therocephalian Therapsids (Amniota, Synapsida) and the Effects of the End-Permian Extinction on Size, Growth, and Bone Microstructure

机译：南非Therocephalian Therapsids（Amniota，Synapsida）的古生物学以及末端二叠纪灭绝对大小，生长和骨微结构的影响

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摘要

Despite their relative diversity in terrestrial Permian and Triassic rocks, the fossil record of therocephalian therapsids (Eutheriodontia) and their utility for understanding evolutionary patterns in the therapsid forerunners of mammals remains poorly understood. In this study, I investigate the extent to which body size reductions and shifts in growth patterns in Triassic therocephalians were influenced by the end-Permian mass extinction (ca. 252.3 Ma) (rather than the culmination of longer-term phylogenetic trends traceable to their Permian predecessors). Specifically, I examine whether body size reductions observed in earliest Triassic therocephalians (`Lilliput phenomena') were the product of within-lineage size reductions, differential extinctions, or rapid diversifications of new small-bodied clades. To address this question, I first review the global diversity and taxonomic composition of therocephalians from the Middle Permian through early-Middle Triassic (Chapter 1). I then present a paleobiological investigation of the Permo-Triassic therocephalian Moschorhinus as a case study on within-lineage patterns of growth and body size evolution during the end-Permian mass extinction (Chapter 2). Finally, I examine clade-wide (among-taxon) size patterns by evaluating the stratigraphic and phylogenetic components of body size evolution (Chapter 3) and the underlying influences of bone histology and growth (Chapter 4). To examine within-lineage patterns, I studied cranial sizes and limb bone histology in Permian and Triassic specimens of Moschorhinus, the largest therapsid predator found both before and after the end-Permian mass extinction. Triassic specimens were found to have significantly decreased basal skull lengths compared to Permian specimens. Histological analysis indicated that variations in body size were associated with differences in subadult growth rate and duration (traits that are highly variable in environmentally stressed extant reptile species). Small Triassic individuals tended to display limb bones with fewer growth marks and more richly vascularized bone tissues than similarly sized Permian individuals, with an abundance of radially-oriented vascular canals, corroborating the hypothesis that conditions of the earliest Triassic favored rapid growth to a minimum body size requirement in Moschorhinus and, consequently, shortened developmental times. Broader-scale `Lilliput-type' patterns were examined in a large sample of therocephalians and compared with that of their sister clade, Cynodontia, in both geologic and phylogenetic contexts. Using a museum collections-based approach, I evaluated temporal and phylogenetic distributions of body size in Permo-Triassic eutheriodonts by time series analysis, rank order correlations, and phylogenetic model fitting. Results supported significant size reductions in earliest Triassic eutheriodonts, but suggested a pattern that was underscored largely by Brownian processes and constructive selectivity (a more general tendency to evolve smaller body sizes as in background intervals). Geologically brief size reductions were likely accomplished by the ecological removal of large-bodied species without rapid originations of new small-bodied clades or shifts from long-term evolutionary patterns. Finally, a survey of growth patterns and histomorphology in limb bones of Karoo therocephalians indicated that long-term changes in bone tissue vascularization (and thus growth) correlated with evolutionary changes in body size (e.g., smaller-bodied descendants tended to have less vascularized bone tissues than their larger-bodied ancestors). Results support a synergistic model of size reductions for Triassic therocephalians, influenced both by within-lineage heterochronic shifts in survivor taxa (e.g., Moschorhinus) and cladistically inferred survival of small-bodied taxa with short growth durations (e.g., baurioids). These findings mirror the multi-causal Lilliput patterns described in marine faunas, but contrast with skeletochronologic studies that suggest slowed, prolonged shell secretion in marine benthos. Subjecting new histologic data to phylogenetic comparative methods, as in these therocephalians, will improve our understanding of the generality of growth and size shifts in Lilliput faunas and interplay between macroevolution and extinction during this and other major geologic transitions.
机译：尽管它们在陆生二叠纪和三叠纪岩石中具有相对多样性，但对热头颅类节肢动物（Eutheriodontia）的化石记录及其对了解哺乳动物的无节制先驱者进化模式的实用性仍知之甚少。在这项研究中，我调查了三叠纪有节肢动物灭绝（大约252.3 Ma）对三叠纪therocephalians体型缩小和生长方式变化的影响（而不是可追溯到其长期系统发育趋势的高潮）二叠纪的前身）。具体来说，我研究了最早出现在三叠纪的therocephalians中的体型缩小（“小人国现象”）是否是世系内尺寸减小，不同物种灭绝或新的小型身体进化迅速多样化的产物。为了解决这个问题，我首先回顾了从中二叠纪到中三叠世早期的头颅动物的全球多样性和分类学组成（第一章）。然后，我将对二叠纪-三叠纪的Therocephalian Moschorhinus进行古生物学研究，作为二叠纪末大灭绝期间生长和体型进化的谱系内模式的案例研究（第2章）。最后，我通过评估人体大小演变的地层学和系统发育成分（第3章）以及骨骼组织学和生长的潜在影响（第4章）来研究整个进化枝（分类单元）的大小模式。为了检查谱系内模式，我研究了二叠纪和三叠纪Moschorhinus标本的颅骨大小和四肢骨组织学，Moschorhinus是二叠纪大规模灭绝前后发现的最大的捕食者。与二叠纪标本相比，发现三叠纪标本的基底颅骨长度明显减少。组织学分析表明，体型大小的变化与亚成体的生长速度和持续时间的差异有关（在受环境胁迫的现存爬行动物中，这些特征变化很大）。与同等大小的二叠纪个体相比，小型三叠纪个体趋向于显示出四肢骨骼，其生长标记较少，血管化的骨组织更丰富，并且具有大量的径向血管，从而证实了三叠纪最早的条件有利于快速生长至最小体质的假说。 Moschorhinus的体型需求，因此缩短了发育时间。在地质学和系统发育的背景下，对大量的狼头虫样本进行了更广泛的“小人型”模式研究，并将其与其姐妹进化枝犬齿齿科进行了比较。使用基于博物馆收藏的方法，我通过时间序列分析，等级顺序相关性和系统发育模型拟合，评估了Permo-Triassic真牙动物的体大小的时间和系统发育分布。结果支持了最早的三叠纪真牙齿的显着减小，但表明这种模式在很大程度上由布朗过程和建设性的选择性所强调（更普遍的趋势是，在背景间隔中会逐渐变小）。从地质上简短地减小大小可能是通过生态去除大型物种而实现的，而没有新的小型身体进化枝的迅速起源或长期发展模式的转变。最后，一项对Karoo therocephalians肢体骨骼的生长方式和组织形态的调查表明，骨骼组织血管化的长期变化（以及由此而来的生长）与体型的进化变化相关（例如，体型较小的后代倾向于骨骼的血管化程度较低）组织比其大体祖先）。结果支持三叠纪therocephalians尺寸减小的协同模型，这受幸存者类群（例如Moschorhinus）的血统内异时性移位以及长生持续时间短的小体类群（例如鲍里奥利德）的共谋推断生存影响。这些发现反映了海洋动物群中描述的多因利利普特模式，但与骨骼年代学研究相反，后者表明海洋底栖动物的壳分泌缓慢，延长。将新的组织学数据进行系统发育比较方法（如这些狼头虫科动物），将有助于我们进一步了解小轮虫动物的生长和大小变化的普遍性，以及在此和其他主要地质转变过程中宏观进化与灭绝之间的相互作用。

著录项

  • 作者

    Huttenlocker, Adam Keith.;

  • 作者单位

    University of Washington.;

  • 授予单位 University of Washington.;
  • 学科 Paleontology.;Biology.;Histology.
  • 学位 Ph.D.
  • 年度 2013
  • 页码 432 p.
  • 总页数 432
  • 原文格式 PDF
  • 正文语种 eng
  • 中图分类
  • 关键词

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