Comparative bone histology of two thalattosaurians (Diapsida: Thalattosauria): Askeptosaurus italicus from the Alpine Triassic (Middle Triassic) and a Thalattosauroidea indet. from the Carnian of Oregon (Late Triassic).

IF 3 2区 地球科学 Q1 PALEONTOLOGY
Swiss Journal of Palaeontology Pub Date : 2023-01-01 Epub Date: 2023-08-16 DOI:10.1186/s13358-023-00277-3
N Klein, P M Sander, J Liu, P Druckenmiller, E T Metz, N P Kelley, T M Scheyer
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引用次数: 0

Abstract

Here, we present the first bone histological and microanatomical study of thalattosaurians, an enigmatic group among Triassic marine reptiles. Two taxa of thalattosaurians, the askeptosauroid Askeptosaurus italicus and one as yet undescribed thalattosauroid, are examined. Both taxa have a rather different microanatomy, tissue type, and growth pattern. Askeptosaurus italicus from the late Anisian middle Besano Formation of the southern Alpine Triassic shows very compact tissue in vertebrae, rib, a gastralium, and femora, and all bones are without medullary cavities. The tissue shows moderate to low vascularization, dominated by highly organized and very coarse parallel-fibred bone, resembling interwoven tissue. Vascularization is dominated by simple longitudinal vascular canals, except for the larger femur of Askeptosaurus, where simple vascular canals dominate in a radial arrangement. Growth marks stratify the cortex of femora. The vertebrae and humeri from the undescribed thalattosauroid from the late Carnian of Oregon have primary and secondary cancellous bone, resulting in an overall low bone compactness. Two dorsal vertebral centra show dominantly secondary trabeculae, whereas a caudal vertebral centrum shows much primary trabecular bone, globuli ossei, and cartilage, indicating an earlier ontogenetic stage of the specimens or paedomorphosis. The humeri of the thalattosauroid show large, simple vascular canals that are dominantly radially oriented in a scaffold of woven and loosely organized parallel-fibred tissue. Few of the simple vascular canals are thinly but only incompletely lined by parallel-fibered tissue. In the Oregon material, changes in growth rate are only indicated by changes in vascular organization but no distinct growth marks were identified. The compact bone of Askeptosaurus is best comparable to some pachypleurosaurs, whereas its combination of tissue and vascularity is similar to eosauropterygians in general, except for the coarse nature of its parallel-fibred tissue. The cancellous bone of the Oregon thalattosauroid resembles what is documented in ichthyosaurs and plesiosaurs. However, in contrast to these its tissue does not consist of fibro-lamellar bone type. Tissue types of both thalattosaurian taxa indicate rather different growth rates and growth patterns, associated with different life history strategies. The microanatomy reflects different life styles that fit to the different environments in which they had been found (intraplatform basin vs. open marine). Both thalattosaurian taxa differ from each other but in sum also from all other marine reptile taxa studied so far. Thalattosaurian bone histology documents once more that bone histology provides for certain groups (i.e., Triassic Diapsida) only a poor phylogenetic signal and is more influenced by exogenous factors. Differences in lifestyle, life history traits, and growth rate and pattern enabled all these Triassic marine reptiles to live contemporaneously in the same habitat managing to avoid substantial competition.

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两个丘脑龙类的比较骨骼组织学(Diapsida:Talattosauria):阿尔卑斯三叠纪(中三叠纪)的倾斜阿斯克托龙和独立的丘脑龙科。来自俄勒冈州卡尼阶(三叠纪晚期)。
在这里,我们首次对丘脑龙进行了骨骼组织学和显微解剖学研究,丘脑龙是三叠纪海洋爬行动物中的一个神秘群体。研究了丘脑龙类的两个分类群,斜口龙类Askeptosaurus italicus和一个尚未描述的丘脑龙类。这两个分类群都有相当不同的显微解剖、组织类型和生长模式。来自阿尔卑斯-三叠纪南部阿尼斯阶-中贝萨诺组晚期的斜体阿斯克普托龙在脊椎、肋骨、胃和股骨中显示出非常紧密的组织,所有骨头都没有髓腔。该组织显示中度至低度血管化,以高度组织化和非常粗糙的平行纤维骨为主,类似于交织的组织。血管形成主要由简单的纵向血管管支配,但阿斯克普龙较大的股骨除外,在那里,简单的血管管以放射状排列为主。生长标记使股骨皮质分层。俄勒冈州卡尼阶晚期未描述的丘脑龙类的脊椎和肱骨具有初级和次级松质骨,导致整体骨密度较低。两个背侧椎体主要显示次级小梁,而一个尾侧椎体显示许多初级小梁骨、球骨和软骨,表明标本的个体发育阶段或儿童形态发生较早。丘脑龙类的肱骨显示出大而简单的血管管,主要呈放射状排列,由编织和松散组织的平行纤维组织组成。很少有简单的血管管是薄的,但只是不完全由平行纤维组织排列。在俄勒冈州的材料中,生长速率的变化仅通过血管组织的变化来指示,但没有发现明显的生长标记。Askeptosaurus的致密骨骼最能与一些厚皮龙相媲美,而其组织和血管结构的组合与一般的始龙目相似,除了其平行纤维组织的粗糙性质。俄勒冈丘脑龙类的松质骨类似于鱼龙和蛇颈龙的记录。然而,与之相反,它的组织并不由纤维板层骨类型组成。两种丘脑龙分类群的组织类型表明,它们的生长速度和生长模式截然不同,与不同的生活史策略有关。微观解剖反映了不同的生活方式,这些生活方式适合于发现它们的不同环境(平台内盆地与开阔海洋)。这两个丘脑龙分类群彼此不同,但总的来说,也与迄今为止研究的所有其他海生爬行动物分类群不同。Thalattosaurian骨组织学再次证明,骨组织学为某些类群(即三叠纪硅藻目)提供了较差的系统发育信号,并且更多地受到外源因素的影响。生活方式、生活史特征、生长速度和模式的差异使所有这些三叠纪海洋爬行动物能够同时生活在同一栖息地,从而避免实质性的竞争。
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来源期刊
Swiss Journal of Palaeontology
Swiss Journal of Palaeontology Earth and Planetary Sciences-Paleontology
CiteScore
4.30
自引率
16.70%
发文量
17
审稿时长
4 weeks
期刊介绍: The Swiss Journal of Palaeontology publishes original research and review articles of interest to the international community in the fields of palaeontology, taxonomy and systematics, while recognising at the same time the importance of documenting high-quality palaeontological data in a regional context. Palaeobiology in combination with alpha taxonomy is a core topic of the journal. Submitted papers should have an appeal as wide as possible, directed towards an international readership. Contributions should not have been simultaneously submitted elsewhere, and the overlap of content between related articles should be minimal. Duplications of text and the use of previously published illustrations without adequate citation are unacceptable. If a manuscript has two or more authors, both or all have to sign to confirm they all were involved in the work and have agreed to its submission. The preferred manuscript language is UK English, but consistently used US English is also acceptable. We encourage the publication of proceedings of international meetings as well as special thematic issues. Short contributions and book reviews are also accepted. An international editorial team as well as guest editors guarantee that the thematic issues as well as all articles in regular issues are peer-reviewed and meet the highest standards.
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