Microanatomy and growth of the mesosaurs Stereosternum tumidum and Brazilosaurus sanpauloensis (Reptilia, Parareptilia)
Microanatomy and growth of the mesosaurs Stereosternum tumidum and Brazilosaurus sanpauloensis (Reptilia, Parareptilia)
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DOI：
10.5194/fr-22-91-2019
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发表时间：
2019-10-22
期刊：
影响因子：
1.4
通讯作者：
Froebisch, Joerg
中科院分区：
文献类型：
--
作者：
Klein, Nicole;Verriere, Antoine;Froebisch, Joerg
对10个胸骨标本和1个巴西龙个体的2根背侧肋骨的椎骨、肋骨、血弓、肱骨和股骨进行了组织学和显微解剖研究。所有个体的体长都达到了50厘米(相当于已知最大体长的65%)或更长。所有的骨样都是高度骨硬化性的，这是由于髓腔的减少和骨内骨髓区的填充。钙化的软骨--如果有的话--仅在中干髓质区局部出现，在长骨的非中干部分和向肋骨中远端方向分别有较多的钙化软骨。初级骨组织由高度组织化的平行纤维组织和/或板层组织组成，在大多数样本中，这些组织相对较少地血运或甚至无血供。如果有的话，血管管主要是纵向的，有些是径向的。出现简单的血管管和初级骨小管。后者中的一些是二次改变的，即加宽的。骨膜皮质的重塑仅见于少数散在的侵蚀腔和次生骨。组织有规律地由停滞生长(LAG)线分层，通常表现为两条或多条休止线，表明对外源和内源因素的强烈依赖。由于骨膜重塑的抑制，生长记录是完整的，没有丢失内周期。粗胸藻个体的个体大小与生长记号数量的相关性很差，这可能是发育可塑性的结果。巴西龙的肋骨皮质有高度组织化的无血管板层组织和大量规则沉积的休止线。与立体胸骨相比，巴西龙肋骨的髓质区明显较大。然而，在这两个分类群中都有很强的骨硬化，这表明它们对水的适应程度很高。根据骨膜和骨内膜的分布，立体胸骨、巴西龙和中龙的肋骨可以清楚地相互区分。此外，与立体胸龙和中龙相比，巴西龙的生长模式(即休止线的间距)也不同。
Histology and microanatomy of vertebrae, ribs, haemal arch, and humeri and femora of 10 individuals of Stereosternum and two dorsal ribs of 1 individual of Brazilosaurus were studied. All individuals had achieved a body length of 50 cm (equal to 65% of the maximum known body length) or larger. All sampled bones are highly osteosclerotic due to the reduction of medullary cavities and the filling of medullary regions by endosteal bone. Calcified cartilage occurs - if at all - only locally in small clusters in the medullary regions of midshaft and in higher amounts only in non-midshaft sections of long bones and towards the medio-distal rib shaft, respectively. The primary bone tissue consists of highly organized parallel-fibred tissue and/or lamellar tissue, which is in most samples relatively lightly vascularized or even avascular. If present, vascular canals are mainly longitudinally oriented; some show a radial orientation. Simple vascular canals as well as primary osteons occur. Some of the latter are secondarily altered, i.e. widened. Remodelling of the periosteal cortex is only documented by few scattered erosion cavities and secondary osteons. The tissue is regularly stratified by lines of arrested growth (LAGs), which usually appear as double or multiple rest lines, indicating strong dependence on exogenous and endogenous factors. Because of the inhibition of periosteal remodelling the growth record is complete and no inner cycles are lost. Individuals of Stereosternum show a poor correlation of body size and number of growth marks, which might be the result of developmental plasticity. Brazilosaurus shows a highly organized, avascular lamellar tissue and a high number of regularly deposited rest lines throughout the cortex of the ribs. The medullary region in the ribs of Brazilosaurus is distinctly larger when compared to ribs of Stereosternum. However, strong osteosclerosis is obvious in both taxa, pointing to a high degree of aquatic adaption. Ribs of Stereosternum, Brazilosaurus, and Mesosaurus are clearly distinguishable from each other by the distribution of the periosteal and endosteal territory. Furthermore, Brazilosaurus differs in its growth pattern (i.e. spacing of rest lines) when compared to Stereosternum and Mesosaurus.