Department of Vertebrate Paleontology, American Museum of Natural History, New York, NY, USA.
NOAA/Southeast Fisheries Science Center/NMFS/Mississippi Laboratories, Pascagoula, MS, USA.
J Anat. 2018 Jul;233(1):15-32. doi: 10.1111/joa.12823. Epub 2018 May 14.
Dalatiid sharks are members of a family of predominantly small, midwater meso- and bathypelagic chondrichthyans. The family is notable for both its number of monotypic genera and high morphological disparity. Three of the seven dalatiid genera are known only from holotype specimens (Mollisquama parini) or from only a handful of specimens (Euprotomicroides zantedeschia, Heteroscymnoides marleyi), with the only detailed anatomical work consistent across all taxa being studies of dentition. Here, we present detailed anatomical description of the second-ever specimen of Mollisquama (Mollisquama sp.) covering chondrocranial, jaw, dental, and muscular anatomy, derived from a phase-contrast synchrotron microtomographic scan. Mollisquama sp. is unique among dalatiids in possessing a deep carinal process, extending ventrally from the bar between the subethmoid region and basal angle in squaloid sharks, containing a large fenestra infiltrated by the suborbitalis muscle. Mollisquama sp. also exhibits additional possibly diagnostic features, including a planar configuration of the labial cartilages and the absence of labial folds; a pad-like orbital process on the palatoquadrate; and the origination of the suborbitalis muscle solely on the carina, rather than the intraorbital wall. Character optimization of anatomical data onto a phylogeny of dalatiid sharks suggests Mollisquama sp. to be among the most specialized in the family, expanding the existing dalatiid morphospace. However, the functional significance of such transformations remains unclear. Synchrotron-derived data, which do not require chemical pretreatment of specimens, may elucidate soft-tissue functional correlates in future studies of undersampled taxa, such as dalatiids.
长尾鲨科是一群主要生活在中层和深海区的小型软骨鱼类。该科以其单型属的数量和高度的形态差异而闻名。在七个长尾鲨属中，有三个属仅知其模式标本（Mollisquama parini）或仅知少数几个标本（Euprotomicroides zantedeschia、Heteroscymnoides marleyi），而唯一在所有分类单元中进行的详细解剖学研究是对牙齿的研究。在这里，我们展示了第二个 Mollisquama （Mollisquama sp.）标本的详细解剖描述，涵盖了软骨颅、颌、牙齿和肌肉解剖学，该标本源自相位对比同步辐射微断层扫描。Mollisquama sp. 在长尾鲨科中是独一无二的，它具有一个深的脊状突起，从位于软鼻区和基角之间的杆状结构向腹侧延伸，其中包含一个被眶下肌渗透的大窗孔。Mollisquama sp. 还表现出其他可能的诊断特征，包括唇软骨的平面构型和唇褶的缺失；在方骨上有一个垫状的眶突；以及眶下肌仅起源于脊状突起，而不是眶内壁。对解剖学数据进行特征优化并构建长尾鲨科的系统发育树表明，Mollisquama sp. 是该科中最特化的物种之一，扩大了现有的长尾鲨科形态空间。然而，这些形态变化的功能意义尚不清楚。同步加速器衍生的数据不需要对标本进行化学预处理，这可能会在未来对采样不足的分类单元（如长尾鲨科）的研究中阐明软组织的功能相关性。
