Triassic Dicynodont reptiles

Camp, Charles L.; Welles, Sumner

doi:10.1080/11035895809447242

Cited by 20 publications

(31 citation statements)

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“…Full-size DOI: 10.7717/peerj.10408/ fig-11 A semi-aquatic lifestyle for Lystrosaurus was first proposed by Broom (1902) and Broom (1903) and later supported by several studies (Watson, 1912;Watson, 1913;Brink, 1951;Camp, 1956;Cluver, 1971;Hotton, 1986;Kemp, 1982;Kitching, 1968) based on various cranial and postcranial morphological features. These studies were later refuted by King (1991) and King & Cluver (1991) who proposed that the morphological characteristics used to infer an aquatic lifestyle could equally represent a fossorial or burrowing ecology.…”

Section: Discussionmentioning

confidence: 95%

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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Section: Discussionmentioning

confidence: 95%

The paleobiology and paleoecology of South African Lystrosaurus

Botha‐Brink

2020

PeerJ

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“…2 ) . That pattern of sex dimorphism is matched in dicynodont reptiles (Toerien 1953;Camp & Welles 1956) and is rivalled in a variety of living mammals (pigs, peccaries, chevrotains, muskdeer and Chinese water-deer) where males have large tusks and females have smaller tusks or lack them entirely. The size and orientation of heterodontosaurid tusks would have precluded their use in feeding, and they were most probably employed as weapons, rather like the tusks of peccaries and chevrotains.…”

Section: A Circannual Life Cyclementioning

confidence: 97%

Aestivation among ornithopod dinosaurs of the African Trias

Thulborn

1978

LET

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LETHAIA Thulborn, Richard A. 1978 07 15: Aestivation among ornithopod dinosaurs of the AfricanTrias. Lc,thuiu. Vol. 1 I , pp. 185-198. Oslo. ISSN 0024-1 164.Dental and circumstantial evidence supports the theory that ornithopod dinosaurs of the African Red Beds responded to seasonal changes in their environment by resorting to aestivation (dry season dormancy). One group of ornithopods. the heterodontosaurids. apparently suppressed tooth replacement to permit efficient grinding of their plant food and probably replaced their entire cheek dentitions while aestivating. The sympatric fabrosaurid ornithopods had a simple open-and-shut jaw action and replaced their teeth continuously in standard reptilian fashion. Seasonal dormancy must have imposed major constraints on the lives of fabrosaurids and heterodontosaurids. and these constraints are summarized in the model o f a circannual life cycle. Richurd A . Thulborn, Depurtmmt of Zoology, University (f Quccn.slund. St Lwicr. Qitwnslund 4067.

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“…The only therapsid species that have been demonstrated to have been sexually dimorphic are amongst the Dicynodontia (e.g. Placerias [ 39 ], Pelanomodon [ 22 ], Aulacephalodon [ 33 ], Diictodon [ 34 ], Cistecephalus [ 36 ], Lystrosaurus [ 35 ] and maybe Digalodon [ 37 ]). Dicynodont are know to have had a cornified beak and many species have rugose nasal and/or supraorbital bosses and ridges that are consistent with the presence of a keratinized covering or projecting nasal horns [ 69 ] that are likely to have been sexually dimorphic and involved in intraspecific combat [ 20 – 22 , 39 , 78 , 34 , 36 ].…”

Section: Discussionmentioning

confidence: 99%

“…Geist [ 38 ] hypothesized much the same behaviour for some dicynodonts. Though less widely acknowledged, this hypothesis has been proposed for some sexually dimorphic dicynodonts, such as Diictodon , Pelanomodon or Placerias [ 22 , 34 , 39 ]. Also, the enlarged canines of the basal anomodont Tiarajudens eccentricus have been interpreted as a possibly sexually dimorphic structure for intraspecific combat or intimidation [ 9 ].…”

Section: Introductionmentioning

confidence: 99%

Cranial Bosses of Choerosaurus dejageri (Therapsida, Therocephalia): Earliest Evidence of Cranial Display Structures in Eutheriodonts

et al. 2016

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Choerosaurus dejageri, a non-mammalian eutheriodont therapsid from the South African late Permian (~259 Ma), has conspicuous hemispheric cranial bosses on the maxilla and the mandible. These bosses, the earliest of this nature in a eutheriodont, potentially make C. dejageri a key species for understanding the evolutionary origins of sexually selective behaviours (intraspecific competition, ritualized sexual and intimidation displays) associated with cranial outgrowths at the root of the clade that eventually led to extant mammals. Comparison with the tapinocephalid dinocephalian Moschops capensis, a therapsid in which head butting is strongly supported, shows that the delicate structure of the cranial bosses and the gracile structure of the skull of Choerosaurus would be more suitable for display and low energy combat than vigorous head butting. Thus, despite the fact that Choerosaurus is represented by only one skull (which makes it impossible to address the question of sexual dimorphism), its cranial bosses are better interpreted as structures involved in intraspecific selection, i.e. low-energy fighting or display. Display structures, such as enlarged canines and cranial bosses, are widespread among basal therapsid clades and are also present in the putative basal therapsid Tetraceratops insignis. This suggests that sexual selection may have played a more important role in the distant origin and evolution of mammals earlier than previously thought. Sexual selection may explain the subsequent independent evolution of cranial outgrowths and pachyostosis in different therapsid lineages (Biarmosuchia, Dinocephalia, Gorgonopsia and Dicynodontia).

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Triassic Dicynodont reptiles

Cited by 20 publications

References 0 publications

The paleobiology and paleoecology of South African Lystrosaurus

The paleobiology and paleoecology of South African Lystrosaurus

Aestivation among ornithopod dinosaurs of the African Trias

Cranial Bosses of Choerosaurus dejageri (Therapsida, Therocephalia): Earliest Evidence of Cranial Display Structures in Eutheriodonts

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