Co-ossified vertebrae of mosasaurs and cetaceans: implications for the mode of locomotion of extinct marine reptiles

Mulder, Eric W.A.

doi:10.1666/0094-8373(2001)027<0724:covoma>2.0.co;2

Cited by 21 publications

(13 citation statements)

References 9 publications

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“…Comparable ligamentous ossifications reinforce the backbone at structurally weak points in extant cetaceans (e.g. Kompanje 1999), and have previously been documented from the sacral region of plioplatecarpine mosasaurs (Mulder 2001).…”

Section: Description and Interpretationsmentioning

confidence: 77%

A fishy mosasaur: the axial skeleton of Plotosaurus (Reptilia, Squamata) reassessed

Lindgren

Jagt

Caldwell

2007

LET

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The concept of convergence, that is, how unrelated animals independently evolve similar morphological traits, is a fundamental aspect of evolution. Hitherto, the Mesozoic ichthyosaurs were regarded as the sole obligate marine reptiles that achieved a fully streamlined body and a semilunate tail fluke. However, analyses of vertebral centrum morphometrics and process orientation have revealed that a subsequent clade of secondarily aquatic reptiles, the mosasaurs (here exemplified by the advanced, midMaastrichtian mosasaurine Plotosaurus ), had developed a deep, fusiform body and a probable pursuit-predatory behaviour by the time of their sudden extinction at the Cretaceous-Paleogene boundary. Stringent physical constraints and selection pressures, imposed by the surrounding water, probably were responsible for this spectacular example of large-scale evolutionary convergence. ᮀ Displacement unit, hypocercal, Mosasauridae, Plotosaurus , propulsive surface, tail fin, tail stock .

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Section: Description and Interpretationsmentioning

confidence: 77%

A fishy mosasaur: the axial skeleton of Plotosaurus (Reptilia, Squamata) reassessed

Lindgren

Jagt

Caldwell

2007

LET

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“…Because vertebral pathologies that cause fusion occur at low frequencies within species and are easily recognizable because of the deformation they cause (e.g. Gill & Fisk, 1966;Rothschild, 1987;Rothschild & Berman, 1991;Kompanje, 1995Kompanje, , 1999Mulder, 2001;Félix, Haase & Aguirre, 2007), these species-or subspecies-specific occurrences of fusion that occur in all or most individuals of a population are likely morphological adaptations.…”

Section: Introductionmentioning

confidence: 99%

Evolution and function of anterior cervical vertebral fusion in tetrapods

VanBuren

Evans

2016

Biol Rev

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The evolution of vertebral fusion is a poorly understood phenomenon that results in the loss of mobility between sequential vertebrae. Non-pathological fusion of the anterior cervical vertebrae has evolved independently in numerous extant and extinct mammals and reptiles, suggesting that the formation of a 'syncervical' is an adaptation that arose to confer biomechanical advantage(s) in these lineages. We review syncervical anatomy and evolution in a broad phylogenetic context for the first time and provide a comprehensive summary of proposed adaptive hypotheses. The syncervical generally consists of two vertebrae (e.g. hornbills, porcupines, dolphins) but can include fusion of seven cervical vertebrae in some cetaceans. Based on the ecologies of taxa with this trait, cervical fusion most often occurs in fossorial and pelagic taxa. In fossorial taxa, the syncervical likely increases the out-lever force during head-lift digging. In cetaceans and ricochetal rodents, the syncervical may stabilize the head and neck during locomotion, although considerable variation exists in its composition without apparent variability in locomotion. Alternatively, the highly reduced cervical vertebral centra may require fusion to prevent mechanical failure of the vertebrae. In birds, the syncervical of hornbills may have evolved in response to their unique casque-butting behaviour, or due to increased head mass. The general correlation between ecological traits and the presence of a syncervical in extant taxa allows more accurate interpretation of extinct animals that also exhibit this unique trait. For example, syncervicals evolved independently in several groups of marine reptiles and may have functioned to stabilize the head at the craniocervical joint during pelagic locomotion, as in cetaceans. Overall, the origin and function of fused cervical vertebrae is poorly understood, emphasizing the need for future comparative biomechanical studies interpreted in an evolutionary context.

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“…This pattern is strikingly similar to that observed amongst Cretaceous mosasaurine marine lizards, in which ankyloses in the caudal peak region seemingly formed as a result of mechanical stresses from undulatory swimming 31,32 . Other conditions, including infectious spondylitis and ligamentous ossifications, also cause ankylosis of the caudal vertebrae in many aquatic tetrapods [33][34][35][36][37][38][39] . Pointedly, though, we detected no traces of avascular necrosis in any of our Besano Formation ichthyosaurs, which is consistent with previous reports on other Triassic taxa 21 , and could indicate a preference for shallower water habitats and/or limited diving capabilities in the species that we examined.…”

Section: Discussionmentioning

confidence: 99%

Skeletal pathologies track body plan evolution in ichthyosaurs

Pardo-Pérez

Kear

Maxwell

2020

Sci Rep

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changing predator-prey interactions during the Mesozoic Marine Revolution (MMR) profoundly altered the trajectory of marine tetrapod evolution. Here, we assess potential signatures of this landmark transition through the fossil record of skeletal pathologies in ichthyosaurs-iconic marine reptiles that developed increasingly 'fish-like' body plans over time. We surveyed a stratigraphically constrained sample of 200 Middle Triassic ichthyosaur specimens and compared the type, distribution and prevalence of pathologies with an approximately equivalent assemblage of Early Jurassic age. Overall, skeletal pathologies were equally prevalent in these groups, and most often manifested in species >4 m long. However, pathological bones were found to be concentrated in the hind limbs and tail of Triassic ichthyosaurs, whereas the jaws, forelimbs, and ribcage were preferentially affected in Jurassic taxa. We posit that the occurrence of ankylosed zygapophyses in the caudal peak of triassic ichthyosaurs could represent a functional by-product of their primitive 'eel-like' swimming. Conversely, increased instances of broken ribs in Jurassic ichthyosaurs may infer ramming or tail strike behaviours that characterise morphologically 'fish-like' marine tetrapods, such as modern toothed whales. Different categories of skeletal pathologies thus evidently reflect structural modifications in the ichthyosaur body plan, and indirectly coincide with ecological turnover during the MMR.

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Co-ossified vertebrae of mosasaurs and cetaceans: implications for the mode of locomotion of extinct marine reptiles

Cited by 21 publications

References 9 publications

A fishy mosasaur: the axial skeleton of Plotosaurus (Reptilia, Squamata) reassessed

A fishy mosasaur: the axial skeleton of Plotosaurus (Reptilia, Squamata) reassessed

Evolution and function of anterior cervical vertebral fusion in tetrapods

Skeletal pathologies track body plan evolution in ichthyosaurs

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