Braincase anatomy of Almadasuchus figarii (Archosauria, Crocodylomorpha) and a review of the cranial pneumaticity in the origins of Crocodylomorpha
Braincase anatomy of Almadasuchus figarii (Archosauria, Crocodylomorpha) and a review of the cranial pneumaticity in the origins of Crocodylomorpha
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Almadasuchus Figarii（始龙目，鳄形目）的脑壳解剖以及鳄形目起源中颅骨气动性的回顾
DOI：
10.1111/joa.13171
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发表时间：
2020
影响因子：
2.4
通讯作者：
Clark, James Matthew
中科院分区：
文献类型：
--
作者：
Leardi, Juan Martín;Pol, Diego;Clark, James Matthew
Almadasuchus figariii是一种基底鳄形动物，发现于阿根廷丘布特的Cañadón Calcáreo组（牛津阶-提东阶）的上侏罗纪地层。这分类群的代表是头盖骨的遗骸，包括部分的吻部和腭部的遗骸;一个保存良好的头盖骨的后部区域;和分离的头盖骨后的遗骸。利用高分辨率计算机显微断层扫描对唯一的单型Almadasuchus标本的头骨进行了重新研究。Almadasuchus的头骨与鳄鱼形目的近亲共享一种近形条件（即，hallopodids），其中方骨缝合到侧蝶骨并且耳枕骨后外侧地接触方骨，重组几个颅神经（例如迷走神经孔）的出口和颅骨枕部表面上血管（例如颈内动脉）的入口。管型是管状的，如以前在海鳄类中报道的，但有一个明显的后台阶，和其他基底鳄形类中强烈突出的絮状隐窝。在内部，Almadasuchus的头骨是严重的骨化，不同的空气腔侵入的骨骼悬骨和braincase，无论是在其背侧或腹侧的部分。Almadasuchus有一个大的基枕骨凹，这是由腔，挖掘基枕骨和后表面的基蝶骨，不像其他鳄鱼dylomorphes是连接到基蝶骨化。在耳囊的外侧，一个被耳枕和蝶基包围的气腔被认为是菱形隐窝。Almadasuchus的方体高度扁平化，是完全中空的，而脑壳的背侧扁平化是由乳突和面窦以及蝶侧腔（三叉神经憩室）形成的。为了更好地理解现存鳄形类中气动特征的起源，我们研究了鳄形类基底成员的颅侧对称性，发现：（a）前耳侧对称性可能是整个分支的一种突触形态;（B）基蝶骨侧对称性（颈动脉前、颈动脉后和吻侧隐窝）是基底鳄形类的衍生特征;（c）方骨化是在该组历史后期获得的;菱形窦是偶蹄类和鳄形类共有的衍生特征。海洋thallatosuchians表现出减少的braincase和这种减少考虑到两个系统发育的分支提出的位置进行评估。
Almadasuchus figariiis a basal crocodylomorph recovered from the Upper Jurassic levels of the Cañadón Calcáreo Formation (Oxfordian–Tithonian) of Chubut, Argentina. This taxon is represented by cranial remains, which consist of partial snout and palatal remains; an excellently preserved posterior region of the skull; and isolated postcranial remains. The skull of the only specimen of the monotypicAlmadasuchuswas restudied using high‐resolution computed micro tomography.Almadasuchushas an apomorphic condition in its skull shared with the closest relatives of crocodyliforms (i.e. hallopodids) where the quadrates are sutured to the laterosphenoids and the otoccipital contacts the quadrate posterolaterally, reorganizing the exit of several cranial nerves (e.g. vagus foramen) and the entry of blood vessels (e.g. internal carotids) on the occipital surface of the skull. The endocast is tubular, as previously reported in thalattosuchians, but has a marked posterior step, and a strongly projected floccular recess as in other basal crocodylomorphs. Internally, the skull ofAlmadasuchusis heavily pneumatized, where different air cavities invade the bones of the suspensorium and braincase, both on its dorsal or ventral parts.Almadasuchushas a large basioccipital recess, which is formed by cavities that excavate the basioccipital and the posterior surface of the basisphenoid, and unlike other crocodylomorphs is connected with the basisphenoid pneumatizations. Ventral to the otic capsule, a pneumatic cavity surrounded by the otoccipital and basisphenoid is identified as the rhomboidal recess. The quadrate ofAlmadasuchusis highly pneumatized, being completely hollow, and the dorsal pneumatizations of the braincase are formed by the mastoid and facial antra, and a laterosphenoid cavity (trigeminal diverticulum). To better understand the origins of pneumatic features in living crocodylomorphs we studied cranial pneumaticity in the basal members of Crocodylomorpha and found that: (a) prootic pneumaticity may be a synapomorphy for the whole clade; (b) basisphenoid pneumaticity (pre‐, postcarotid and rostral recesses) is a derived feature among basal crocodylomorphs; (c) quadrate pneumatization is acquired later in the history of the group; and (d) the rhomboidal sinus is a shared derived trait of hallopodids and crocodyliforms. The marine thallatosuchians exhibit a reduction of the pneumaticity of the braincase and this reduction is evaluated considering the two phylogenetic positions proposed for the clade.
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