Jasinoski Sandra C, Abdala Fernando
Evolutionary Studies Institute, University of the Witwatersrand, Private Bag 3, WITS 2050, Johannesburg, South Africa.
Anat Rec (Hoboken). 2017 Feb;300(2):353-381. doi: 10.1002/ar.23473. Epub 2016 Oct 3.
Ontogenetic changes in the skull and mandible of thirty-one specimens of Galesaurus planiceps, a basal non-mammaliaform cynodont from the Early Triassic of South Africa, are documented. The qualitative survey indicated eight changes in the craniomandibular apparatus occurred during growth, dividing the sample into three ontogenetic stages: juvenile, subadult, and adult. Changes in the temporal region, zygomatic arch, occiput, and mandible occurred during the transition from the subadult to adult stage at a basal skull length of 90 mm. At least four morphological and allometric differences divided the adult specimens into two morphs, indicating the presence of sexual dimorphism in Galesaurus. Differences include extensive lateral flaring of the zygomatic arches in the "male" morph resulting in a more anterior orientation of the orbits, and a narrower snout in the "female". This is the first record of sexual dimorphism in a basal cynodont, and the first time it is quantitatively documented in a non-mammaliaform cynodont. An ontogenetic comparison between Galesaurus and the more derived basal cynodont Thrinaxodon revealed differences in the timing and extent of sagittal crest development. In Galesaurus, the posterior sagittal crest, located behind the parietal foramen, developed relatively later in ontogeny, and the anterior sagittal crest rarely formed suggesting the anterior fibres of the temporalis were less developed than in Thrinaxodon. In contrast, craniomandibular features related to the masseters became more developed during the ontogeny of Galesaurus. The development of the adductor musculature appears to be one of the main factors influencing skull growth in these basal non-mammaliaform cynodonts. Anat Rec, 300:353-381, 2017. © 2016 Wiley Periodicals, Inc.
记录了南非早三叠世一种基干非哺乳形犬齿兽类——扁头盖氏兽（Galesaurus planiceps）31个标本的头骨和下颌骨的个体发育变化。定性调查表明，颅下颌器官在生长过程中发生了8种变化，将样本分为三个个体发育阶段：幼年、亚成年和成年。在基底头骨长度达到90毫米时，从亚成年到成年阶段的过渡过程中，颞区、颧弓、枕部和下颌骨发生了变化。至少有四种形态和异速生长差异将成年标本分为两种形态，表明盖氏兽存在两性异形。差异包括“雄性”形态的颧弓广泛向外扩张，导致眼眶更靠前，以及“雌性”的吻部更窄。这是基干犬齿兽类中两性异形的首次记录，也是首次在非哺乳形犬齿兽类中进行定量记录。盖氏兽与更进化的基干犬齿兽类三棱齿兽（Thrinaxodon）之间的个体发育比较揭示了矢状嵴发育的时间和程度上的差异。在盖氏兽中，位于顶孔后方的后矢状嵴在个体发育中相对较晚发育，前矢状嵴很少形成，这表明颞肌的前部纤维比三棱齿兽发育得更差。相比之下，与咬肌相关的颅下颌特征在盖氏兽的个体发育过程中变得更加发达。内收肌的发育似乎是影响这些基干非哺乳形犬齿兽类头骨生长的主要因素之一。《解剖学记录》，300:353 - 381，2017年。©2016威利期刊公司。
