Going Deeper Into Modern and Fossil Crocodilian Tooth Microanatomy: What Can Be Inferred of Palaeoenvironment and Taphonomy From Histochemical Analyses?

Abstract

Teeth provide information about the evolutionary pathway of an organism, its biology and habitat. This is the case even of fossilized teeth, since they have perdurable biomineralized structures, as biological apatite. The material that has been selected for this study comprises teeth from modern crocodilian individuals and extinct Cretaceous crocodylomorphs from Lo Hueco site. Microanatomy, histochemistry and crystallographic nature of enamel, dentine and cementum have been characterized by Polarized Light Microscopy, SEM-EDS, Confocal Raman Spectroscopy and SR-µXRD. A focus has been made on dentine lamination. In the fossil sample short-period incremental lines show alternate presence of dentinal tubules that has not been described previously either in living or fossil archosaur. This could be related to influence of environmental circadian rhythms in the abundance, size and/or activity of cells depositing dentine in the day-night cycle. Regarding histochemical and crystallographic compositions, the major and mostly unique phase is HA, but in the case of fossil teeth, a secondary phase identified as hematite appears locally between discontinuities of the material. Incremental lines would not be related to variation in chemical composition and furthermore do not present different HA crystallographic nature (different directions of HA or different crystallite sizes) either. Only small intensity oscillations are observed in the fossil sample by SR-µXRD which are compatible with the alternating abundance of dentinal tubules. Crystallinity differences between modern and fossil material, as crystallite size and presence of CO32- groups could be explained by postdepositional processes.

Ontogenetic and interelemental study of appendicular bones of Caiman latirostris Daudin, 1802 sheds light on osteohistological variability in crocodylians

“…The vascular canals sometimes anastomose to form reticular, circumferential, or radial organizations. Similar types of vascularization patterns have also been reported for other crocodylians ( A. mississippiensis , Klein et al, 2009; Lee, 2004; Rainwater et al, 2021; Werning, 2013; Woodward et al, 2014; Caiman yacare , Andrade et al, 2018; and Crocodylus niloticus , Audije‐Gil et al, 2023; Chinsamy, 1991). Some of these earlier studies also reported a concentric arrangement of the LVCs in other reptiles (e.g., Botha & Botha, 2019; Navarro et al, 2023; Pellegrini et al, 2021; Pereyra, 2022; Werning, 2013).…”

“…Below, we highlight the distinctive osteohistology at different stages of ontogeny: bone tissues formed during embryonic growth, histological variation among the hatchlings, juvenile to adult growth, the variation in growth among mature individuals. Audije-Gil et al, 2023;de Buffrenil & Castanet, 2000;Castanet & Baez, 1991;Horner et al, 2001;Hugi & Sánchez-Villagra, 2012;Lee, 2004;amphibians, Bruce & Castanet, 2006;and mammals, Chinsamy & Hurum, 2006;Garrone et al, 2019;Nacarino-Meneses & Köhler, 2018;Woolley, et al, 2021), and among crocodylians was described in humerus of specimens of Crocodylus niloticus (Audije-Gil et al, 2023), in tibia and femora of A. mississippiensis (Horner et al, 2001;Lee, 2004).…”

“…Foote (1911) and Enlow and Brown (1956) were among the first to describe the histology of long bones and osteoderms of living crocodylians, and since then, numerous studies have been carried out on both, extant (e.g., Audije‐Gil et al, 2023; de Buffrénil, 1982; Chinsamy, 1991, 1993a, 1993b; Cubo et al, 2012; Erickson & Brochu, 1999; Hutton, 1986; Klein et al, 2009; Lee, 2004; Mascarenhas‐Junior et al, 2021; Rainwater et al, 2021; Tucker, 1997; Tumarkin‐Deratzian, 2007; Werning, 2013; Woodward et al, 2011, 2014), and extinct taxa of this group (e.g., Andrade & Sayão, 2014; Company & Pereda‐Suberbiola, 2017; Erickson & Brochu, 1999; Padian et al, 2004; Pellegrini et al, 2021; Sayão et al, 2016). It is noteworthy that, although studies on bone microstructure of Crocodylia are becoming more numerous, the diversity of species studied remains scarce.…”

“…In this regard, although much research has focused on the Alligatoridae clade (e.g., especially on Alligator mississippiensis Daudin, 1801; Klein et al, 2009; Lee, 2004; Tumarkin‐Deratzian, 2007; Woodward et al, 2011, 2014), few studies have been done on Caimaninae (Andrade et al, 2018; Mascarenhas‐Junior et al, 2021), and so far, only the study by Mascarenhas‐Junior et al (2021) focuses on the histology of humerus and rib of juveniles C. latirostris from Brazil. Also, although the osteohistology of living crocodiles has been reasonably well published, most of the works analyze either an ontogenetic series of a single bone element or numerous postcranial bones from single juvenile or subadult specimens of a particular species (e.g., Audije‐Gil et al, 2023; Chinsamy, 1991, 1993a, 1993b; Lee, 2004; Woodward et al, 2014), and currently there are no studies that have analyzed the overall osteohistological changes that occur in the skeleton during growth (see below).…”

Synchrotron X-ray Studies of the Structural and Functional Hierarchies in Mineralised Human Dental Enamel: A State-of-the-Art Review

“…In this regard, in this second part of the review, the main focus is to give an overview of the use of synchrotron X-ray applications in human dental research (for animal species, numerous studies have been carried out on a variety of species and fossils [ 256 , 257 , 258 , 259 , 260 , 261 , 262 , 263 , 264 , 265 , 266 , 267 , 268 , 269 , 270 , 271 , 272 , 273 , 274 , 275 , 276 , 277 , 278 , 279 ], as well as studies on biofilms [ 280 , 281 , 282 , 283 ]). This review was performed by searching several platforms, including ScienceDirect, Web of Science, and SciFinder.…”