Long bone histology indicates sympatric species of<i>Dimetrodon</i>(Lower Permian, Sphenacodontidae)

a b s t r a c tOphiacodontids have long been considered the basalmost synapsids, and to have retained a fairly aquatic, piscivorous lifestyle typical of stem-amniotes. A restudy of their bone histology and microanatomy shows that Clepsydrops collettii, a Late Carboniferous ophiacodontid, has a thin, compact cortex and lacks a medullary spongiosa, two features that suggest a truly terrestrial lifestyle. The Early Permian Ophiacodon uniformis has a thicker cortex with a few resorption cavities and bone trabeculae surrounding the free medullary cavity. An inference model yields a terrestrial lifestyle for both taxa, though O. uniformis may have been slightly more aquatic (possibly amphibious) than C. collettii. However, an optimization of inferred lifestyle of other early stegocephalians (based on bone microanatomy) suggests that the first amniotes were terrestrial. The potentially amphibious lifestyle of O. uniformis, though not supported by our inference model, would thus be secondary. Histological features of femoral cortices in these two taxa closely resemble those previously described in extant species of large varanids and teids. This similarity, along with other comparative elements, is discussed in reference to the possible growth patterns and life history traits of Clepsydrops and O. uniformis. Mots clés : Clepsydrops OphiacodonMicro-anatomie osseuse Histologie osseuse Inférence de mode de vie Patron de croissance Paléobiologie r é s u m é Les ophiacodontidés ont longtemps été considérés comme les synapsidés les plus basaux et on leur a longtemps attribué le mode de vie aquatique et le régime piscivore typique des premiers amniotes-souches. Cette étude de micro-anatomie et d'histologie osseuse montre que le fémur de Clepsydrops collettii, un taxon du Carbonifère supérieur, possède un cortex compact peu épais et est dépourvu de spongieuse médullaire, deux caractères indicatifs d'un mode de vie franchement terrestre. Ophiacodon uniformis, du Permien inférieur, a un cortex plus épais avec quelques lacunes de résorption, ainsi que des travées osseuses autour de la cavité médullaire. L'usage d'un modèle d'inférence conduit à attribuer un mode de vie terrestre à ces deux taxons, encore que O. uniformis ait pu être un peu plus aquatique (peut-être G Model No. of Pages 13 2 M. Laurin, V. de Buffrénil / C. R. Palevol xxx (2015) xxx-xxx amphibie) que C. collettii. Cependant, l'optimisation des inférences de mode de vie effectuées chez d'autres stégocéphales en référence à la micro-anatomie de leurs os suggère que les premiers amniotes étaient terrestres. D'éventuelles moeurs amphibies chez Ophiacodon (bien qu'elles ne soient pas confirmées par l'emploi de nos modèles d'inférence) seraient donc secondaires. Les caractères histologiques du fémur dans les deux taxons étudiés ici rappellent fortement ceux attribués dans la littérature aux grands varanidés et téidés. Cette similitude, ainsi que d'autres éléments comparatifs, est discutée en référence aux modèles de croissance et aux traits d'histoire de vie qui pourraie...

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“…(Huttenlocker and Rega, 2012) and Dimetrodon natalis (Shelton et al, 2013; see also Huttenlocker et al, 2010).…”

Section: Comparative Data On Bone Histologymentioning

confidence: 99%

Microstructural features of the femur in early ophiacodontids: A reappraisal of ancestral habitat use and lifestyle of amniotes

Laurin

Buffrénil

2016

Comptes Rendus Palevol

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“…The vascular canals are mainly small, longitudinal canals that may be simple or osteonal. Thin radial canals, arrayed from the inner to outer cortex, also perfuse the cortex, forming a sunburst or 'bicycle wheel' pattern as observed in limb bones of other carnivorous eupelycosaurs [29,36]. The canals exhibit a relatively low density (Vasc dens , 48-91 canals per mm 2 ).…”

Section: Description Of Histological Profiles In Sampled Femora (A) Mmentioning

confidence: 99%

Bone histology of varanopids (Synapsida) from Richards Spur, Oklahoma, sheds light on growth patterns and lifestyle in early terrestrial colonizers

Huttenlocker

Shelton²

2020

Phil. Trans. R. Soc. B

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Varanopids were a group of small to medium-sized synapsids whose fossil record spans the Carboniferous through middle Permian. Although their phylogenetic relationships have received some interest in recent years, little is known about other aspects of their palaeobiology, including their skeletal growth, allometry and habitat preference. Here, we describe varanopid long bone histology based on a sample of well-preserved femora from the lower Permian Richards Spur fissure fill locality, Comanche County, Oklahoma, USA. The sample includes five femora from at least two varanopid taxa— Mycterosaurus and the large varanodontine Varanops brevirostris —and four additional mycterosaurine femora not diagnosed to genus. Prior work on femoral bone compactness provided a baseline to make lifestyle inferences and evaluate whether varanopids were ancestrally terrestrial. Moreover, the large availability of specimens spanning different sizes made possible an assessment of size-related ontogenetic histovariability. All specimens revealed moderately dense cortical bone tissues composed of sparsely vascularized parallel-fibred and lamellar bone with radially arranged rows of longitudinal canals (mostly simple), and many preserved regularly spaced growth marks (annuli and lines of arrested growth) as in modern varanids. We show that bone histology has the potential to explain how ballast was shed and the skeleton lightened for terrestrial mobility in ancestral synapsids and their basal amniote kin, as well as how adjustments in postnatal growth influenced the evolution of larger body sizes in the terrestrial frontier. This article is part of the theme issue ‘Vertebrate palaeophysiology'.

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“…On one hand, more complete 2006; Klein and Sander 2008;Horner and Goodwin 2009;Scannella and Horner 2010;Knoll et al 2010;Padian 2013;Shelton et al 2013), because absolute size may not be a true measure of relative ontogeny (e.g., Johnson 1977;Andrews 1982;Galton 1982;Gibson and Hamilton 1984;Brinkman 1988;Bennett 1993;Sander and Klein 2005;). …”

Section: Prondvai E | 35mentioning

confidence: 99%

Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity

Prondvai¹,

Bodor²,

Ősi³

2014

Paleobiology

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Abstract.-With a single complete mandible and 56 mandibular symphyseal fragments of various sizes, the Late Cretaceous Hungarian azhdarchid material has been considered one of the most extensive monospecific pterosaur assemblages in the world. Representing a broad size range, these elements have been thought to demonstrate a developmental series of Bakonydraco galaczi. As such, they were ideal to test whether absolute size and/or morphology reliably indicate relative ontogenetic stages in this pterosaur. Forty-five specimens were selected for multivariate morphometrics and classified into four size classes. After acquiring the morphometric data set, we thin-sectioned eight symphyses representing all size groups and classified them into relative ontogenetic stages based on qualitative microstructural inspection prior to quantitative histological analyses. Microstructural characters suggestive of developmental state were then quantified for intra-and interindividual uni-and multivariate analyses to test the correspondence among the results of qualitative and quantitative analyses.In contrast to our expectations, histological features identified the smallest specimen as an adult and not an early juvenile. The substantial size difference between this specimen and other adults, along with its distinct microanatomical and histological features, implies the presence of at least two pterosaur taxa in this symphysis assemblage. This hypothesis is further supported by multivariate morphometrics, which separate the smallest symphyses from all other specimens that form one continuous group. Although the latter group also shows considerable size variability in corresponding ontogenetic stages, this suggests developmental plasticity rather than the presence of even more taxa, and indicates that symphysis size and morphology are poor indicators of skeletal maturity in these animals. Hence, bone histology is an important independent test of the assessment of ontogenetic stage using size and morphology. The Late Cretaceous (Santonian) vertebrate locality at Iharkút (Bakony Mountains) in western Hungary has provided numerous azhdarchid pterosaur remains, including elements from the axial and appendicular skeleton as well as from the skull. Nevertheless, the only diagnostic element known so far, on which the Hungarian medium-sized azhdarchid Bakonydraco galaczi was described, is a complete lower jaw ( si et al. β00ő). Besides this uniquely preserved, three-dimensional, edentulous mandible, 56 additional symphyseal fragments have been discovered over several years of excavation, making them the most frequently found pterosaur elements in the locality. Although these additional mandibular symphyses represent a great size range, their overall appearance is practically identical to the symphysis of the holotype mandible, and therefore they have been thought to represent the largest monospecific azhdarchid pterosaur assemblage to date ( si et al. β00ő, 2012). The abundance of these mandibular symphyses made it possible for us to condu...

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Long bone histology indicates sympatric species ofDimetrodon(Lower Permian, Sphenacodontidae)

Cited by 28 publications

References 46 publications

Microstructural features of the femur in early ophiacodontids: A reappraisal of ancestral habitat use and lifestyle of amniotes

Microstructural features of the femur in early ophiacodontids: A reappraisal of ancestral habitat use and lifestyle of amniotes

Bone histology of varanopids (Synapsida) from Richards Spur, Oklahoma, sheds light on growth patterns and lifestyle in early terrestrial colonizers

Does morphology reflect osteohistology-based ontogeny? A case study of Late Cretaceous pterosaur jaw symphyses from Hungary reveals hidden taxonomic diversity

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