Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT
Cranial Morphology of the Carboniferous-Permian Tetrapod Brachydectes newberryi (Lepospondyli, Lysorophia): New Data from µCT
复制标题
石炭纪-二叠纪四足动物 Brachydectes newberryi（Lepospondyli、Lysorophia）的颅骨形态：来自 µCT 的新数据
作者：
Jason D. Pardo;Jason S. Anderson
Lysorophians是一群早期的四足动物，具有非常细长的躯干，退化的四肢和高度退化的头骨。自首次发现这一类群以来，一些现代的利桑菲亚目（特别是有尾目和裸腹目）与利桑菲亚目在外观上的相似性已被确认，有时也成为利桑菲亚起源假说的基础。利用X射线微计算机断层扫描（μCT）研究了一个部分生长系列的溶鞘纲纽氏短肢介（Brachydectes newberryi）的头骨形态，重点是脑颅。我们的研究揭示了Brachydectes和brachystelechid recumbirostrans的braincase之间的相似性，证实了以前的工作表明这些类群之间的密切关系。我们还描述了形态的epipterygoid，镫骨，方在这个分类群的第一次。相反的建议，一些工人，我们没有发现预期的lissampibian synapomorphies的头骨形态在Brachydectes newberryi的证据，而是承认一些派生的braincase和suspensorium的特征。以前被认为指示分类多样性的形态学内Lysorophia可能反映个体发育，而不是分类变异。lysorophians的高度分歧的形态代表了一个完善的形态和功能的趋势内reumbirostrans，并类似于许多现代的fossorial爬行动物中观察到的形态。
Lysorophians are a group of early tetrapods with extremely elongate trunks, reduced limbs, and highly reduced skulls. Since the first discovery of this group, general similarities in outward appearance between lysorophians and some modern lissamphibian orders (specifically Urodela and Gymnophiona) have been recognized, and sometimes been the basis for hypotheses of lissamphibian origins. We studied the morphology of the skull, with particular emphasis on the neurocranium, of a partial growth series of the lysorophian Brachydectes newberryi using x-ray micro-computed tomography (μCT). Our study reveals similarities between the braincase of Brachydectes and brachystelechid recumbirostrans, corroborating prior work suggesting a close relationship between these taxa. We also describe the morphology of the epipterygoid, stapes, and quadrate in this taxon for the first time. Contra the proposals of some workers, we find no evidence of expected lissamphibian synapomorphies in the skull morphology in Brachydectes newberryi, and instead recognize a number of derived amniote characteristics within the braincase and suspensorium. Morphology previously considered indicative of taxonomic diversity within Lysorophia may reflect ontogenetic rather than taxonomic variation. The highly divergent morphology of lysorophians represents a refinement of morphological and functional trends within recumbirostrans, and is analogous to morphology observed in many modern fossorial reptiles.