Were the synapsids primitively endotherms? A palaeohistological approach using phylogenetic eigenvector maps

Faure‐Brac, Mathieu G.; Cubo, Jorge

doi:10.1098/rstb.2019.0138

Cited by 26 publications

(29 citation statements)

References 71 publications

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“…The zones of stress observed here in Antarctic Lystrosaurus are marked by iterative reactivation of metabolic activity similar to those seen in torpor patterns of modern endotherms. This contributes additional support for a growing body of evidence that dicynodonts like Lystrosaurus were likely endothermic 27 – 30 .…”

Section: Discussionsupporting

confidence: 61%

Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica

Whitney

Sidor

2020

Commun Biol

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Antarctica has hosted a wide range of ecosystems over the past 500-million years. Early in the Mesozoic, the Antarctic portion of southern Pangaea had a more habitable climate, but its position within the polar circle imposed extreme photoperiod seasonality on its resident flora and fauna. It remains unclear to what degree physiological adaptations underpinned the ability of tetrapods to establish the terrestrial communities captured in the fossil record. Here we use regular and stressful growth marks preserved in the dentine of ever-growing tusks of the Early Triassic mammalian predecessor, Lystrosaurus, to test for adaptations specific to this polar inhabitant. We find evidence of prolonged stress indicative of torpor when compared to tusk samples from non-polar populations of Lystrosaurus. These preliminary findings are to our knowledge the oldest instance of torpor yet reported in the fossil record and demonstrate unexpected physiological flexibility in Lystrosaurus that may have contributed its survivorship through the Permo-Triassic mass extinction.

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Section: Discussionsupporting

confidence: 61%

Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica

Whitney

Sidor

2020

Commun Biol

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“…B 375: 20190130 canal sizes and densities that impact O 2 diffusive capacity, reflected an expansion of aerobic scope in some Triassic therapsids and contemporary archosauromorphs that may or may not have been coincident with changes in thermoregulatory abilities [30]. The present authors conclude that palaeohistology reveals independent acquisition of endotherm-like resting metabolic rates in at least three amniote lineages: Therapsida, Sauropterygia and Archosauromorpha [9]. Stable isotope biogeochemistry helps to catalogue the fossil record of thermometabolism as a test of these hypotheses.…”

Section: Thermometabolismmentioning

confidence: 63%

“…'Vertebrate palaeophysiology' will promote a better understanding of how organism-environment interactions have evolved in terms of energy budgets, predator-prey relationships and sensitivity to environmental change. The research areas covered by this theme issue include: phospho-calcic metabolism [2], acid-base homeostasis [3,4], thermometabolism [4][5][6][7][8][9], respiratory physiology [10], skeletal growth [11], palaeopathophysiology [12,13], genome size and metabolic rate [14], and a concluding historical perspective [15]. Sometimes, the two components ( physiological mechanism and palaeobiological inference) are proposed in separate papers (for instance, three contributions devoted to mechanisms of thermogenesis mechanisms [5][6][7] and three papers dealing with the thermometabolic inferences in extinct taxa [4,8,9]).…”

Section: Introductionmentioning

confidence: 99%

Vertebrate palaeophysiology

Cubo

Huttenlocker

2020

Phil. Trans. R. Soc. B

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Physiology is a functional branch of the biological sciences, searching for general rules by which explanatory hypotheses are tested using experimental procedures, whereas palaeontology is a historical science dealing with the study of unique events where conclusions are drawn from congruence among independent lines of evidence. Vertebrate palaeophysiology bridges these disciplines by using experimental data obtained from extant organisms to infer physiological traits of extinct ones and to reconstruct how they evolved. The goal of this theme issue is to understand functional innovations imprinted on modern vertebrate clades, and how to infer (or ‘retrodict’) physiological capacities in their ancient relatives a posteriori. As such, the present collection of papers deals with different aspects of a rapidly growing field to understand innovations in: phospho-calcic metabolism, acid–base homeostasis, thermometabolism, respiratory physiology, skeletal growth, palaeopathophysiology, genome size and metabolic rate, and it concludes with a historical perspective. Sometimes, the two components (physiological mechanism and palaeobiological inference) are proposed in separate papers. Other times, the two components are integrated in a single paper. In all cases, the approach was comparative, framed in a phylogenetic context, and included rigorous statistical methods that account for evolutionary patterns and processes. This article is part of the theme issue ‘Vertebrate palaeophysiology’.

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“…The observation that most of the cortex in the Lystrosaurus bones is comprised of primary, rapidly forming fibrolamellar bone, which is highly vascularized indicates rapid growth rates and does not reflect an osteoporotic lifestyle response comprised of secondary bone as proposed by Ray, Chinsamy & Bandyopadhyay (2005). Recent research using isotopes (Rey et al, 2017), primary osteon density (or primary osteon area) and phylogenetic eigenvector maps (Olivier et al, 2017;Faure-Brac & Cubo, 2020), and growth marks in dentine (Whitney & Sidor, 2020) have proposed that Lystrosaurus was endothermic. Rey et al (2017) and Faure-Brac & Cubo (2020) suggest that all Neotherapsida (the clade that includes anomodonts and theriodonts) had an endothermic metabolism.…”

Section: Discussionmentioning

confidence: 99%

“…Recent research using isotopes (Rey et al, 2017), primary osteon density (or primary osteon area) and phylogenetic eigenvector maps (Olivier et al, 2017;Faure-Brac & Cubo, 2020), and growth marks in dentine (Whitney & Sidor, 2020) have proposed that Lystrosaurus was endothermic. Rey et al (2017) and Faure-Brac & Cubo (2020) suggest that all Neotherapsida (the clade that includes anomodonts and theriodonts) had an endothermic metabolism. However, it is important to state what kind of endothermy may have been present as there is a whole spectrum of metabolic states from poikilothermic ectothermy in extant reptiles to homeothermic endothermy in extant mammals and birds.…”

Section: Discussionmentioning

confidence: 99%

The paleobiology and paleoecology of South African Lystrosaurus

Botha‐Brink

2020

PeerJ

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Lystrosaurus was one of the few tetrapods to survive the end-Permian mass extinction (EPME), the most catastrophic biotic crisis in Phanerozoic history. The significant increased abundance of this genus during the post-extinction Early Triassic recovery period has made Lystrosaurus an iconic survivor taxon globally and ideal for studying changes in growth dynamics during a mass extinction. There is potential evidence of a Lilliput effect in Lystrosaurus in South Africa as the two Triassic species that became highly abundant after the EPME are relatively smaller than the two Permian species. In order to test this hypothesis a detailed examination of the body size and life history of Permo-Triassic Lystrosaurus is required. In this study, the basal skull length and growth patterns of the four South African Lystrosaurus species from the Karoo Basin, L. maccaigi, L. curvatus, L. murrayi and L. declivis, were examined using cranial measurements and bone histology. The basal skull length measurements show that the Triassic species are smaller than the Permian species and supports previous studies. The osteohistology examination of all four species reveal rapidly forming fibrolamellar bone tissues during early to mid-ontogeny. Growth marks are common in L. maccaigi and L. curvatus, but rare and inconsistent in the purely Triassic L. murrayi and L. declivis. The inconsistency of the growth marks in these latter two taxa suggests the presence of developmental plasticity. This feature may have been advantageous in allowing these species to alter their growth patterns in response to environmental cues in the post-extinction Early Triassic climate. An overall transition to slower forming parallel-fibered bone is observed in the largest individuals of L. maccaigi, but absent from the limb bones of the other species. The absence of such bone tissue or outer circumferential lamellae in L. curvatus, L. murrayi and L. declivis indicates that even the largest collected specimens do not represent fully grown individuals. Although L. murrayi and L. declivis are smaller in size, the lack of a growth asymptote in the largest specimens indicates that adult individuals would have been notably larger and may have been similar in size to large L. maccaigi and L. curvatus when fully grown. Thus, the previously described Lilliput effect, recognized by some authors in the Karoo fossil record (such as the therocephalian Moschorhinus kitchingi), may be a product of high juvenile excess mortality in the Triassic rather than a strict “dwarfing” of Lystrosaurus species. The lifestyle of Lystrosaurus was also re-examined. Although previous studies have proposed an aquatic lifestyle for the genus, the similar morphology and bone microanatomy to several other large terrestrial Permo-Triassic dicynodonts supports a fully terrestrial mode of life.

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Were the synapsids primitively endotherms? A palaeohistological approach using phylogenetic eigenvector maps

Cited by 26 publications

References 71 publications

Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica

Evidence of torpor in the tusks of Lystrosaurus from the Early Triassic of Antarctica

Vertebrate palaeophysiology

The paleobiology and paleoecology of South African Lystrosaurus

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