Fig 1
Preparation of sectioned osteoderms: (left) dorsal view of osteoderm before removal; (right) dorsal view of a transversely sectioned specimen, showing pitting on dorsal surface (specimen has been cleaned of tissue). Scale bar with osteoderm is 1 cm.
Source publication
Age was estimated for wild Australian freshwater crocodiles from
skeletochronology of growth marks in postoccipital osteoderms. Growth marks
were distinct and counted reliably in unstained calcified thin sections
(60–80 µm) viewed by Nomarski interference microscopy. The
periodicity of growth marks was validated directly from crocodiles of known
ag...
Contexts in source publication
Context 1
... corpora lutea were detected by either cloacal examination or laparoscopy (Limpus 1984). Males were confirmed as adults by histological evidence of active spermatogenesis (Webb et al. 1983) or by the presence of mature gonads viewed by laparoscopy. All crocodiles were released after processing at the point of capture. A postoccipital osteoderm ( Fig. 1) was removed with a pocket knife from >95% of all crocodiles captured during field trips in 1992-95. Samples included all sex, maturity and size classes (12-129 cm SVL) of crocodiles in order to be representative of the overall population structure. To obtain an osteological chronology, a second osteoderm was taken from a crocodile ...
Context 2
... narrow lines (10-15 m wide) were highly birefringent and the zones appeared isotropic, i. e. lines were much brighter than zones. The birefringent line was unquestionably a region of compact bone, but visible separation of annuli from LAGs was not possible at´40at´40 magnification. Surface remodelling or pitting of the dorsal osteoderm surface (Fig. 1) was noted in both sexes but had limited effects on the legibility of ventral GMs. GMs were often retained circumferentially on the dorsal keel or lateral margins but were never as consistent as GMs deposited on the ventral region of the ...
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Citations
... However, for rare, endemic or migrating, and endangered species, likely, the only accurate alternative to estimate age (CMR studies) is even more problematic than sclerochronological studies, due to both financial and logistic limitations (Lindquist et al. 2012;Christie et al. 2019). Despite critics (Brooks et al. 1997;Litzgus & Brooks 1998;Eden et al. 2007), the sclerochronological method was confirmed to be an appropriate and useful sampling technique for obtaining life-history values (Castanet 1985;Tucker 1997;Germano & Bury 1998;Avens et al. 2010;Dubey et al. 2013). Since it does not suffer from the limitations of CMR, sclerochronology should be the prevalent method of age estimation, especially for rare and endemic species, which in many cases occur in lowincome countries (Lindquist et al. 2012). ...
Age and growth-related data are basic biological parameters, essential in population ecology, evolution, and conservation biology. There is a growing body of published information on reptile demography derived from sclerochronology, a technique based on counting the growth layers deposited in bones (skeletochronology) and other hard body structures. Since the data are not always easily available, we compiled the existing published data, described the current status of knowledge, synthetized the conclusions of disparate studies, and identified patterns of research and information gaps, prioritizing the needs for future research. Our database includes the results of 468 published studies covering 236 reptile species from 41 families. These represent less than 2% of the total number of known extant species. Turtles and crocodiles are proportionally better studied, while snakes are the least examined group. The distribution of the research does not reflect conservation needs; we found an important geographic bias, with an overrepresentation of Northern temperate species. Only 23% of the studies checked the assumption of periodicity of growth marks deposition, and the method was found to be reliable or adequate in 79% of the cases. Overall, the data obtained through sclerochronology can be considered robust, especially if validation methods are employed, since the general goal is to characterize population parameters, trends, and dynamics, rather than determining the exact age of any specimen in particular.
... This area shows a decrease in the density of osteocyte lacunae periosteally. This is the only region of compact bone that preserves lines of arrested growth (LAGs; Figure 3c,d), which represent the slowing or complete cessation of growth (de Ricqlès et al., 2021;Francillon-Vieillot et al., 1990;Huttenlocker et al., 2013;Tucker, 1997;Woodward et al., 2011). Although this region of the proximal rib sample preserves the most accurate growth data, the outer rim of the bone has been partially assimilated into the matrix (Figure 3c,e), including some of the outer LAGs. ...
... Among ectothermic reptiles (e.g., crocodylians), the slowing and/or cessation of skeletal growth can reflect the animal's inability to adjust to seasonal stress (e.g., changes in temperature, precipitation, sunlight exposure), either directly and/or indirectly (e.g., influencing physiology, food resources; Rootes et al., 1991;Köhler et al., 2012;Werning, 2013;Rainwater et al., 2021). Because of the relationship between skeletal growth and seasonal variation, LAGs, or LAG 'packets' (group of associated LAGs) are hypothesized to represent a yearly cessation of growth (Tucker, 1997;Werning, 2013;Woodward et al., 2013). Therefore, because of the relationship between skeletal growth and seasonal variation, LAG or LAG 'packet' counts can be used as a proxy for absolute age (Griffin et al., 2020;Woodward et al., 2013). ...
... (1) endosteal resorption of the primary tissue in the inner cortex can result in the loss of LAG data, thus eliminating records of early growth Tucker, 1997;Woodward et al., 2011); (2) the incorporation of the outer bone cortex into the matrix seen in the proximal sample (Figure 3c,e) may have resulted in the loss of LAG data; ...
Maximum individual body size in pseudosuchian archosaurs is not well constrained in the fossil record, but it may be influenced by a variety of factors including basal metabolic rate, evolutionary relationships, and environmental conditions. Body size varies among the Aetosauria in which estimated total length ranges between 1 m (e.g., Coahomasuchus kahleorum ) and 5 m (e.g., Desmatosuchus spurensis ). A new, very large specimen of the aetosaurian Typothorax coccinarum from Petrified Forest National Park in northeastern Arizona is nearly twice the size of all other known specimens of Typothorax and is the largest aetosaur specimen currently known worldwide. The specimen lacks co‐ossified neurocentral sutures in the trunk vertebrae which may suggest that the individual had not yet reached skeletal maturity, yet smaller specimens of T. coccinarum exhibit partially or fully co‐ossified neurocentral sutures in the same region. If body size correlates with skeletal maturity in aetosaurs, this discrepancy warns that timing of neurocentral suture co‐ossification in aetosaurs may not be a reliable indicator of ontogenetic stage. Osteohistological observations of a trunk rib demonstrate that although PEFO 42506 shows a large body size, the specimen did not deposit an external fundamental system despite depositing as many as 19 growth lines, further indicating that it had not yet reached skeletal maturity. Thus, at least within Aetosauria, neurocentral suture co‐ossification and skeletal maturity may correlate, whereas body size can be incongruent in comparison. Furthermore, this specimen indicates that non‐desmatosuchin aetosaurs could exhibit large body sizes and suggests that some aetosaurs may have experienced indeterminate growth.
... Seidel (1979) was one of the first to suggest that the highly vascularized osteoderms of alligators may serve as mineral storage and nearly four decades later, Dacke et al. (2015) provided some evidence that the osteoderm density of females with ripe ovarian follicles was greater compared to those that had recently laid or contained eggs. This finding corroborated the observations of Hutton (1986) and Tucker (1997) that osteoderms of crocodiles undergo considerable remodelling during breeding and may represent an important source of calcium during oogenesis. Similarly, Curry Rogers et al. (2011) proposed that osteoderms may have provided an important reservoir of minerals in titanosaurs. ...
The functional significance of osteoderms—bony elements embedded in the dermis—remains a topic of much debate. Although many hypotheses have been put forward in the past, the idea that osteoderms can serve as calcium reservoirs has received little experimental attention thus far. In this study, we use micro-computed tomography to investigate inter-and intrasexual variation in osteoderm density in the viviparous lizard Ouroborus cataphractus and conduct histochemical analyses to unravel the potential mechanism involved in mineral resorption from the osteoderms. Our results show that females have denser, more compact osteoderms than males of similar body sizes, regardless of the season during which they were collected and their reproductive state. Furthermore, a histochemical study demonstrates the presence of mononucleated TRAP-positive cells in the vascular canals of the osteoderms. Based on the findings of this study, we suggest that the mineral storage hypothesis merits further attention as a candidate explanation for osteoderm evolution.
... lines of arrested growth and annuli), which are formed annually (e.g. Hutton 1986;Tucker 1997;Erickson and Brochu 1999;Erickson et al. 2003). The potential of any bony structure to be used for skeletochronological analysis is inversely proportional to the degree of internal bone resorption that occurs. ...
After the extinction of rebbachisaurids during the Cenomanian–Turonian interval, titanosaurs were the only group of sauropods to face the K–Pg event. This same global pattern also holds for the end-Cretaceous (Campanian–Maastrichtian) titanosaur record in South America, where their remains can be found from southern Argentina to Ecuador, with more frequent findings in Argentina and Brazil. In this chapter, we review these fossil findings and the main aspects of the taxonomy, systematics, and paleogeographic implications of this record and briefly discuss the importance of these occurrences for the understanding of titanosaur evolution. The diversity and abundance of end-Cretaceous titanosaur taxa in South America represent about 25% of the known Titanosauria species in the world, which makes them the most common group of large terrestrial herbivores of that time. Cretaceous titanosaurs from South America also vary highly in morphology and size, comprising small to large-sized taxa, for example. Their record mainly consists of appendicular and axial remains, including rare skull material, but also comprises eggs, nests, footprints, and coprolites. In South America, by the end of the Late Cretaceous, titanosaurs were generally represented by more derived titanosaurians that are mainly taxonomically assigned to more derived species within Aeolosaurini and Saltasaurinae.
... According to Castanet et al. (1993), the deposition of LAGs occurs annually in crocodylians, regardless of food, temperature, or photoperiod. Tucker (1997) suggested that the appearance of LAGs is associated with winter periods (food shortages and decreased metabolism). In this study, specimens that were in the first, second, and third years of life did not present evident lines and specimens that were in the fourth and sixth years of life presented underestimated numbers of growth marks regarding age. ...
Bone histology is an important tool for the interpretation of life patterns in animals of the past and extant fauna. The crocodylians have been studied as important inferential models for morphophysiological characteristics. We aimed to characterize the osteohistology of captive Caiman latirostris, identifying its microanatomy related to growth rates, ontogeny, and environmental conditions. We analyzed five pairs of humeri (proximal elements of the appendicular skeleton) and ribs (axial skeleton) of females' caiman. Ribs showed, in general, woven-fibered tissues, with low vascularization and parallel-fibered bone and many resorption and erosion cavities. It presented lines of arrested growth (LAGs) in three individuals, without skeletochronological compatibility. Humeri showed a gradient of woven-fibered to parallel-fibered and lamellar-zonal bone as the individuals aging. We observed compacted coarse cancellous bone (CCCB) and a higher number of LAGs in older specimens. Ribs remodel faster than humerus, showing an intra-individual histovariability. The humeri indicated an evident growth pattern with different ontogeny stages and growth rates in different ages. Fast-growing tissues are uncommon in crocodylians, but basal metabolism and optimal growth conditions can lead to this. Bone histology of C. latirostris shows patterns that can be used as inferen-tial models for extant and extinct groups, but we encourage further studies for a better understanding, under different environmental conditions, such as temperature and food availability.
... Among crocodylians, for which the use of ODs in skeletochronology has been more intensively studied, the emerging consensus is that the age estimates from the elements should be viewed with caution (Klein, Scheyer & Tütken, 2009). Although cyclical growth marks may be Lizard osteoderms present, age estimation is complicated by remodelling (e.g. by reproductive-aged females or pathological calcium deficiencies) and/or close spacing of annual bone deposits (Tucker, 1997;Klein et al., 2009). ...
Osteoderms are mineralised structures consisting mainly of calcium phosphate and collagen. They form directly within the skin, with or without physical contact with the skeleton. Osteoderms, in some form, may be primitive for tetrapods as a whole, and are found in representatives of most major living lineages including turtles, crocodilians, lizards, armadillos, and some frogs, as well as extinct taxa ranging from early tetrapods to dinosaurs. However, their distribution in time and space raises questions about their evolution and homology in individual groups. Among lizards and their relatives, osteoderms may be completely absent; present only on the head or dorsum; or present all over the body in one of several arrangements, including non-overlapping mineralised clusters, a continuous covering of overlapping plates, or as spicular mineralisations that thicken with age. This diversity makes lizards an excellent focal group in which to study osteoderm structure, function, development and evolution. In the past, the focus of researchers was primarily on the histological structure and/or the gross anatomy of individual osteoderms in a limited sample of taxa. Those studies demonstrated that lizard osteoderms are sometimes two-layered structures, with a vitreous, avascular layer just below the epidermis and a deeper internal layer with abundant collagen within the deep dermis. However, there is considerable variation on this model, in terms of the arrangement of collagen fibres, presence of extra tissues, and/or a cancellous bone core bordered by cortices. Moreover, there is a lack of consensus on the contribution, if any, of osteoblasts in osteoderm development, despite research describing patterns of resorption and replacement that would suggest both osteoclast and osteoblast involvement. Key to this is information on development, but our understanding of the genetic and skeletogenic processes involved in osteoderm development and patterning remains minimal. The most common proposition for the presence of osteoderms is that they provide a protective armour. However, the large morphological and distributional diversity in lizard osteoderms raises the possibility that they may have other roles such as biomechanical reinforcement in response to ecological or functional constraints. If lizard osteoderms are primarily for defence, whether against predators or conspecifics, then this ‘bony armour’ might be predicted to have different structural and/or mechanical properties compared to other hard tissues (generally intended for support and locomotion). The cellular and biomineralisation mechanisms by which osteoderms are formed could also be different from those of other hard tissues, as reflected in their material composition and nanostructure. Material properties, especially the combination of malleability and resistance to impact, are of interest to the biomimetics and bioinspired material communities in the development of protective clothing and body armour. Currently, the literature on osteoderms is patchy and is distributed across a wide range of journals. Herein we present a synthesis of current knowledge on lizard osteoderm evolution and distribution, micro- and macrostructure, development, and function, with a view to stimulating further work.
... The required reliable information, however, might not always be available for taxa about which only very little is known and is simply inaccessible for extinct species. Concomitant with this latter circumstance is that the vast majority of studies that actually took external control data into account are based on microtomized sections only (but see [45]). For all of the numerous previous skeletochronological studies, it is impossible to (a) add such a frame of reference a posteriori, and (b) to conduct a comparison of the two approaches, given that this already needs to be considered at the stage of tissue sampling. ...
Histology-based skeletochronology is a widely used approach to determine the age of an individual, and is based on the assumption that temporal cessations or decelerations of bone growth lead to incremental growth marks (GM), reflecting annual cycles. We studied the reliability of histology-based skeletochronology in a variety of extant tetrapods by comparing two different approaches: petrographic ground sections versus stained microtomized sections. Each bone was cut into two corresponding halves at its growth centre in order to apply both approaches to one and the same sample. None of the samples unequivocally revealed the actual age of the specimens, but truly concerning is the fact that the majority of samples even led to conflicting age estimates between the two approaches. Although the microtomized sections tended to yield more GM and thus indicated an older age than the ground sections, the contrary also occurred. Such a pronounced ambiguity in skeletochronological data strongly challenges the value of the respective age determinations for both extant and extinct animals. We conclude that much more research on the fundamental methodological side of skeletochronology-especially regarding the general nature and microscopic recognition of GM-is required.
... In the neontological literature, an individual is often considered to have reached adulthood at reproductive maturity, regardless of whether maximum size has been reached or any other anatomical indicator of maturity has been attained (e.g. Dunham, Miles & Reznick, 1988;Tucker, 1997;Roulin, 2004;Natusch & Lyons, 2012;Bjorndal et al., 2013). This sense is occasionally used in the palaeontological literature as well (e.g. ...
... Although long bones are by far the most common elements sampled histologically, the histology of vertebrae and osteodermsand rarely, other dermal skeletal elementsis also used across many saurians to determine ontogenetic stage, notably among crocodile-line archosaurs and squamates. As in long bones, growth marks in osteoderm histology have been correlated with annual interruptions of growth (Hutton, 1986;Tucker, 1997) and are therefore useful in assessing absolute ontogenetic age (e.g. Erickson & Brochu, 1999;Parker, Stocker & Irmis, 2008;Scheyer, Klein & Sander, 2010;Scheyer, Desojo & Cerda, 2014;Hill, 2011;Cerda et al., 2013Cerda et al., , 2015Lacerda et al., 2016). ...
... Although osteoderms generally seem to preserve a reliable record of growth marks, those deposited during earlier ontogenetic stages may be destroyed, either by increased sculpturing on the dorsal surface of the osteoderm eroding dorsal growth marks (Hutton, 1986) or by secondary remodelling, which occurs during ontogeny. Remodelling has been reported as especially extensive in mature crocodylian females (Hutton, 1986;Tucker, 1997), so the degree of osteoderm remodelling may be useful in determining sex if the sample size is large enough. The osteoderms of Alligator mississippiensis ossify much later than the rest of the skeleton, and not simultaneously (Vickaryous & Hall, 2008), suggesting that speciesor clade-specific timing and pattern of osteoderm development may influence skeletochronological inferenceswe advise caution in interpreting these records uncritically for most clades. ...
Morphology forms the most fundamental level of data in vertebrate palaeontology because it is through interpretations of morphology that taxa are identified, creating the basis for broad evolutionary and palaeobiological hypotheses. Assessing maturity is one of the most basic aspects of morphological interpretation and provides the means to study the evolution of ontogenetic changes, population structure and palaeoecology, life‐history strategies, and heterochrony along evolutionary lineages that would otherwise be lost to time. Saurian reptiles (the least‐inclusive clade containing Lepidosauria and Archosauria) have remained an incredibly diverse, numerous, and disparate clade through their ~260‐million‐year history. Because of the great disparity in this group, assessing maturity of saurian reptiles is difficult, fraught with methodological and terminological ambiguity. We compiled a novel database of literature, assembling >900 individual instances of saurian maturity assessment, to examine critically how saurian maturity has been diagnosed. We review the often inexact and inconsistent terminology used in saurian maturity assessment (e.g. ‘juvenile’, ‘mature’) and provide routes for better clarity and cross‐study coherence. We describe the various methods that have been used to assess maturity in every major saurian group, integrating data from both extant and extinct taxa to give a full account of the current state of the field and providing method‐specific pitfalls, best practices, and fruitful directions for future research. We recommend that a new standard subsection, ‘Ontogenetic Assessment’, be added to the Systematic Palaeontology portions of descriptive studies to provide explicit ontogenetic diagnoses with clear criteria. Because the utility of different ontogenetic criteria is highly subclade dependent among saurians, even for widely used methods (e.g. neurocentral suture fusion), we recommend that phylogenetic context, preferably in the form of a phylogenetic bracket, be used to justify the use of a maturity assessment method. Different methods should be used in conjunction as independent lines of evidence when assessing maturity, instead of an ontogenetic diagnosis resting entirely on a single criterion, which is common in the literature. Critically, there is a need for data from extant taxa with well‐represented growth series to be integrated with the fossil record to ground maturity assessments of extinct taxa in well‐constrained, empirically tested methods.
... Our main goal in examining the bone histology of Acaenasuchus is to assess its skeletal maturity, given that some previous authors have explicitly hypothesized that this material represented juvenile specimens of the stagonlepidid aetosaur Desmatosuchus (Heckert and Lucas, 2002a). We selected osteoderms (Fig. 8) for our analysis because: (1) they are the most plentiful element in the known hypodigm; and (2) previous studies demonstrate that osteoderms from both extant and extinct pseudosuchian archosaurs record valuable skeletochronological data (e.g., Hutton, 1986;Games, 1990;Woodward and Moore, 1992;Tucker, 1997;Erickson and Brochu, 1999;Cerda and Desojo, 2011;Cerda et al., 2013Cerda et al., , 2018Taborda et al., 2013;Scheyer et al., 2014). This previous work also showed that longitudinal sections through the dorsal eminence (or equivalent) provide one of the most complete records of growth (Hutton, 1986;Tucker 1997;Cerda and Desojo, 2011;Taborda et al., 2013;Cerda et al., 2018), so we followed this strategy in our work (Fig. 8A-D) in sampling one paramedian osteoderm (UCMP 175103) and one lateral osteoderm (UCMP 175114). ...
... We selected osteoderms (Fig. 8) for our analysis because: (1) they are the most plentiful element in the known hypodigm; and (2) previous studies demonstrate that osteoderms from both extant and extinct pseudosuchian archosaurs record valuable skeletochronological data (e.g., Hutton, 1986;Games, 1990;Woodward and Moore, 1992;Tucker, 1997;Erickson and Brochu, 1999;Cerda and Desojo, 2011;Cerda et al., 2013Cerda et al., , 2018Taborda et al., 2013;Scheyer et al., 2014). This previous work also showed that longitudinal sections through the dorsal eminence (or equivalent) provide one of the most complete records of growth (Hutton, 1986;Tucker 1997;Cerda and Desojo, 2011;Taborda et al., 2013;Cerda et al., 2018), so we followed this strategy in our work (Fig. 8A-D) in sampling one paramedian osteoderm (UCMP 175103) and one lateral osteoderm (UCMP 175114). ...
Acaenasuchus geoffreyi is a diminutive armored archosaur from the Upper Triassic Chinle Formation of northern Arizona, U.S.A., with uncertain evolutionary relationships and skeletal maturity. Known only from osteoderms, the taxon has been considered a valid taxon of aetosaur, juvenile specimens synonymous with the aetosaur Desmatosuchus spurensis, or a non-aetosaurian pseudosuchian archosaur. Here, we describe new fossils of Acaenasuchus geoffreyi that represent cranial, vertebral, and appendicular elements as well as previously unknown variations in the dorsal carapace and ventral shield. The skull bones are ornamented with the same anastomosing complex of ridges and grooves found on the paramedian and lateral osteoderms, and the appendicular skeleton resembles that of Revueltosaurus callenderi, Euscolosuchus olseni, aetosaurs, and other armored archosaurs such as erpetosuchids. Histology of osteoderms from the hypodigm of Acaenasuchus geoffreyi shows multiple growth lines, laminar tissue, and low vascularity, evidence that the individuals were close to skeletal maturity and not young juveniles. A revised phylogenetic analysis of early archosaurs recovers Acaenasuchus geoffreyi and Euscolosuchus olseni as sister taxa and members of a new clade that is the sister taxon of Aetosauria. This new phylogeny depicts a broader distribution of osteoderm character states previously thought to only occur in aetosaurs, demonstrating the danger of using only armor character states in aetosaur taxonomy and phylogeny. Acaenasuchus geoffreyi is also a good example of how new fossils can stabilize 'wild card' taxa in phylogenetic analyses and contributes to our understanding of the evolution of the aetosaur carapace.
... Ayrıca kertenkelelerde bu yöntem kuyruğun gövdeye yakın omurlarından denenmiş ve sonuç femurlara benzer olarak tespit edilmiştir (Guarino 2010). Canlıların osteodermlerinin ve arka bacak kalıntısı gibi kesildiğinde canlının hayatını tehdit etmeyecek yapılarının yaş tayini için kullanılmasındaki temel amaç, canlıya zarar vermeden yaşların tespit edilmesidir ve bu yöntem sadece birkaç genus (Crocodylus; Gerrhonotus; Elgaria; Ophisaurus; Anguis) üzerinde denenmiştir (Tucker 1997, Bochaton vd. 2015. ...
... Daha önceden yaşları bilinen Crocodylus johnstoni örneklerinin postoccipital osteodermlerinde bu yöntem denenmiş ve bilinen yaşlara oldukça yakın sonuçlar elde edilmiştir. Önceki çalışmalarda söz konusu türde yapılan çalışmaların hatalı olmasının erken büyüme halkalarının görülememesinden kaynaklandığını, bunun da sebebinin kesim yönü (longitudinal yerine transversal) nedenli olduğunu ileri sürmüştür (Tucker 1997). Bu çalışmada A. fragilis kompleks için kuyruktaki osteodermler ve P. apodus için ise arka bacak kalıntısı kullanılmıştır. ...
... 2016. Ekstremitelerini kaybetmiş veya ekstremiteleri iskelet kronolojisi yönteminde kullanılamayacak kadar küçülmüş sürüngenlerde ise genellikle ektopterigoid kemiği, gövde omurları veya kuyruk omurları ve osteodermler kullanılmaktadır (Tucker 1997, Waye ve Gregory 1998, Guarino 2010, Bochaton vd. 2015. ...
