Bone microstructure analyses in ontogenetic series of Mesosaurus tenuidens from the early Permian of Brazil.

IF 1.8 4区 医学 Q2 ANATOMY & MORPHOLOGY
Thiago Carlisbino, Brodsky Dantas Macedo de Farias, Fernando Antonio Sedor, Cesar Leandro Schultz
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Abstract

Osteohistological evidence is widely used to infer paleobiological traits of fossil vertebrates, such as ontogeny and growth rates. Mesosaurs, an enigmatic group of aquatic reptiles from the early Permian, are the most well-known Paleozoic amniotes from Africa and South America. Their fossils are abundant in South America, ranging from the central-west region of Brazil to the southernmost areas, as well as parts of Paraguay and Uruguay. In this contribution, we examined the bone microstructure of Mesosaurus tenuidens by analyzing thin sections of axial and appendicular elements of several specimens collected from various Brazilian sites. The microstructure of the bones showed minimal histological variability among elements, predominantly composed of parallel-fibered tissues, indicating slow growth rhythm, along with increased bone density attributed to pachyosteosclerosis. The cortical area consists of poorly vascularized parallel-fibered bone tissue, which was interrupted by multiple cyclical growth marks, some of them being supernumerary, suggesting a strong influence of seasonality. Moreover, the organization of growth marks suggests distinct life history trajectories among individuals collected from different outcrops, reflecting environmental heterogeneity throughout the basin. Internally, the endosteal domain exhibits greater vascularization compared to the cortices and frequently contained calcified cartilage. In the ontogenetic series, there was a progressive filling of the medullary region from small to large individuals. The presence of the External Fundamental System (a proxy indicating somatic maturity) was observed in femora and ribs, suggesting that determinate growth was already occurring in Permian mesosaurs and may not be an exclusive specialization of crown amniotes.

巴西二叠纪早期中龙(Mesosaurus tenuidens)个体发育系列的骨骼显微结构分析。
骨组织学证据被广泛用于推断脊椎动物化石的古生物特征,如本体和生长速度。中龙是二叠纪早期的一类神秘的水生爬行动物,是非洲和南美洲最著名的古生代羊膜动物。它们的化石在南美洲非常丰富,从巴西的中西部地区到最南端地区,以及巴拉圭和乌拉圭的部分地区都有。在这篇论文中,我们通过分析从巴西不同地点采集的几件标本的轴和附肢薄片,研究了tenuidens中龙的骨骼显微结构。骨骼的微观结构显示,不同元素之间的组织学差异极小,主要由平行纤维组织组成,表明生长节奏缓慢,同时骨密度增加,这归因于柏骨硬化。皮质区域由血管不发达的平行纤维骨组织组成,被多个周期性生长标记打断,其中一些是超常生长标记,这表明季节性影响很大。此外,生长痕迹的组织结构表明,从不同露头采集的个体具有不同的生活史轨迹,反映了整个盆地的环境异质性。在内部,与皮层相比,内骨层显示出更多的血管化,并经常含有钙化软骨。在个体发育系列中,髓质区从小到大逐渐充填。在股骨和肋骨中观察到了外部基本系统(表示躯体成熟的替代物)的存在,这表明二叠纪的中生代已经出现了确定性生长,这可能不是冠羊膜动物的专有特化。
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来源期刊
CiteScore
4.80
自引率
15.00%
发文量
266
审稿时长
4 months
期刊介绍: The Anatomical Record
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