Mesosaurid Swim Traces

Silva, Rafael C. da; Sedor, Fernando Antonio

doi:10.3389/fevo.2017.00022

Cited by 6 publications

(5 citation statements)

References 34 publications

(68 reference statements)

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“…Based on the large size (compare to Rossmann [ 10 , 14 ]), the absence of the suture which divides the procoracoid and metacoracoid in juveniles [ 30 ] and the presence of a well-ossified tarsus [ 31 ], the specimen is considered an adult [ 24 ]. This supports the view that lateral undulations of the trunk were not the key factor of locomotion in mesosaurs [ 2 , 24 , 32 – 35 ]. Possibly, their slow-paced swimming technique required only minor trunk flexibility or they mainly utilized the posterior portion of the vertebral column, using mostly the tail-driven propulsion, in a sub-carangiform (sub-anguilliform, axial subundulatory) fashion [ 2 , 24 , 32 , 34 , 35 ].…”

Section: Discussionsupporting

confidence: 86%

“…This supports the view that lateral undulations of the trunk were not the key factor of locomotion in mesosaurs [ 2 , 24 , 32 – 35 ]. Possibly, their slow-paced swimming technique required only minor trunk flexibility or they mainly utilized the posterior portion of the vertebral column, using mostly the tail-driven propulsion, in a sub-carangiform (sub-anguilliform, axial subundulatory) fashion [ 2 , 24 , 32 , 34 , 35 ]. This agrees with the speculation as to feeding habits of mesosaurs, which were shown to prey mostly on small, slow-moving pygocephalomorph crustaceans and occasionally scavenged on mesosaurid corpses [ 9 , 34 , 36 , 37 ].…”

Section: Discussionsupporting

confidence: 86%

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The oldest record of aquatic amniote congenital scoliosis

et al. 2017

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We report the first occurrence of congenital scoliosis in an early Permian aquatic parareptile, Stereosternum tumidum from Paraná state, Brazil. The spine malformation is caused by a congenital hemivertebra. These observations give insight into the biomechanical aspects of underwater locomotion in an axial skeleton-compromised aquatic amniote. This is the oldest record of a hemivertebra in an aquatic animal.

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Section: Discussionsupporting

confidence: 86%

Section: Discussionsupporting

confidence: 86%

The oldest record of aquatic amniote congenital scoliosis

et al. 2017

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“…Mesosaurs are swimming reptiles, and the degree of involvement of the limbs in locomotion is still debated. Some authors support the idea of mainly tail-driven mesosaurs ( Braun & Reif, 1985 ; Villamil et al, 2016 ) while others suggested a potentially larger role of limbs in propulsion ( Da Silva & Sedor, 2017 ; MacDougall et al, 2020 ). Yet, the ontogenetic limb reduction we expose seems incompatible with the conception that limbs were crucial for locomotion.…”

Section: Discussionmentioning

confidence: 97%

“…1 ). This peculiar appearance has resulted in conflicting hypotheses about their ecology, from amphibious ( Núñez Demarco et al, 2018 ) to fully marine ( Modesto, 1999 ; Modesto, 2010 ; Canoville & Laurin, 2010 ), from undulatory ( Braun & Reif, 1985 ; Villamil et al, 2016 ) to partially limb-propelled swimmers ( Da Silva & Sedor, 2017 ; MacDougall et al, 2020 ).…”

Section: Introductionmentioning

confidence: 99%

Ontogenetic, dietary, and environmental shifts in Mesosauridae

Verrière

Fröbisch

2022

PeerJ

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Mesosaurs are the first secondarily aquatic amniotes and one of the most enigmatic clades of reptiles from the early Permian. They have long puzzled paleontologists with their unique morphologies: possessing an elongated skull with thin needle-like teeth, a long neck, large webbed hindlimbs, banana-shaped pachyosteosclerotic ribs, and a long tail. Here, we look at a large dataset of morphometric measurements from 270 mesosaur specimens in collections around the world. These measurements characterize skull, tooth, and limb proportions and their variation with size. This data presents evidence of surprising ontogenetic changes in these animals as well as new insights into their taxonomy. Our results support the recent hypothesis that Mesosaurus tenuidens is the only valid species within Mesosauridae and suggest that “ Stereosternum tumidum ” and “ Brazilosaurus sanpauloensis ” represent immature stages or incomplete specimens of Mesosaurus by showing that all three species occupy an incomplete portion of the overall size range of mesosaurs. Under the single-species hypothesis, we highlight a number of ontogenetic trends: (1) a reduction in skull length accompanied by an elongation of the snout within the skull, (2) an elongation of teeth, (3) a reduction in hind limb length, and (4) a reduction in manus length. Concurrent with these changes, we hypothesize that mesosaurs went through a progressive ecological shift during their growth, with juveniles being more common in shallow water deposits, whereas large adults are more frequent in pelagic sediments. These parallel changes suggest that mesosaurs underwent a diet and lifestyle transition during ontogeny, from an active predatory lifestyle as juveniles to a more filter-feeding diet as adults. We propose that this change in lifestyle and environments may have been driven by the pursuit of different food sources, but a better understanding of the Irati Sea fauna will be necessary to obtain a more definitive answer to the question of young mesosaur diet.

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“…Rather than being a primarily tail driven swimmer as has been previously suggested 30 , mesosaurs could have used a combination of limbs and tail during aquatic locomotion, regardless of whether they were autotomizing their tails. Swim traces ascribed to mesosaurs have shown that while the tail was used in aquatic propulsion, the hind limbs would have also been used as a source of propulsion 45 . Overall, this suggests that, regardless of whether they could drop their tails or not, the limbs of mesosaurs would have played a larger role in aquatic locomotion than has previously been considered, something that warrants further investigation.…”

Section: Discussionmentioning

confidence: 99%

Conflicting evidence for the use of caudal autotomy in mesosaurs

MacDougall

Verrière

LeBlanc

et al. 2020

Sci Rep

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The early Permian mesosaurs were the first amniotes to re-invade aquatic environments. One of their most controversial and puzzling features is their distinctive caudal anatomy, which has been suggested as a mechanism to facilitate caudal autotomy. Several researchers have described putative fracture planes in mesosaur caudal vertebrae -unossified regions in the middle of caudal vertebral centrathat in many extant squamates allow the tail to separate and the animal to escape predation. However, the reports of fracture planes in mesosaurs have never been closely investigated beyond preliminary descriptions, which has prompted scepticism. Here, using numerous vertebral series, histology, and X-ray computed tomography, we provide a detailed account of fracture planes in all three species of mesosaurs. Given the importance of the tail for propulsion in many other aquatic reptiles, the identification of fracture planes in mesosaurs has important implications for their aquatic locomotion. Despite mesosaurs apparently having the ability to autotomize their tail, it is unlikely that they actually made use of this behaviour due to a lack of predation pressure and no record of autotomized tails in articulated specimens. We suggest that the presence of fracture planes in mesosaurs is an evolutionary relic and could represent a synapomorphy for an as-yet undetermined terrestrial clade of Palaeozoic amniotes that includes the earliest radiation of secondarily aquatic tetrapods.As the first group of amniotes to return to an aquatic lifestyle, and a key line of evidence for the theory of continental drift 1 , mesosaurs have figured prominently in reconstructions of early amniote evolution. Mesosauridae is currently composed of three monotypic genera (Mesosaurus tenuidens Gervais, 1865 2 , Stereosternum tumidum Cope, 1886 3 , and Brazilosaurus sanpauloensis Shikama and Ozaki, 1966 4 ), all of which are only known from localities that would have been part of an inland Gondwanan sea during the early Permian. Despite debate regarding the exact placement of Mesosauridae among early reptiles, researchers generally agree that they represent one of the most basal reptile clades 5-9 .The anatomy of mesosaurs has also been debated extensively, and one of the more contentious aspects concerns whether or not they had the capacity for caudal autotomy. Caudal autotomy is the ability to drop a part of the tail in order to escape predation, an anti-predator behaviour that is prevalent in several clades of extant lepidosaurs 10,11 . In extant reptiles, caudal autotomy can occur between caudal vertebrae (intervertebral) or along planes of weakness along the caudal centrum that split a vertebra in two (intravertebral). The latter form of autotomy is the most common among extant reptiles and is the only traceable form of autotomy in the fossil record 12,13 . Regeneration of a cartilage cone posterior to the autotomized region may also occur following autotomy, however, several lineages of lepidosaurs do not regenerate their tails 11 .Several rese...

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Mesosaurid Swim Traces

Cited by 6 publications

References 34 publications

The oldest record of aquatic amniote congenital scoliosis

The oldest record of aquatic amniote congenital scoliosis

Ontogenetic, dietary, and environmental shifts in Mesosauridae

Conflicting evidence for the use of caudal autotomy in mesosaurs

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