Observations on Triassic ichthyosaurs. Part IX. The first associated skeletal remains of Merriamosaurus n.g. (Ichthyosauria, Lower Triassic) and their bearing on the systematic position of the Omphalosauria

Maisch, Michael W.; Matzke, Andreas T.

doi:10.1127/njgpa/226/2002/59

Cited by 9 publications

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“…Furthermore, the dorsal vertebral centra of Cymbospondylus sp. from the Spathian of Spitzbergen 18 (originally identified as an ichthyopterygian taxon Merriamosaurus hulkei 44 , 45 , which is currently disputed) shows anteriorly truncated diapophysis 18 as in NSM PV 23854, although the height/length ratio of Spitzbergen Cymbospondylus centra is almost 2.0, unlike in NSM PV 23854, which has a height/length ratio of almost 1.0. In addition, the associated rib can be identified as a dorsal rib based on its curved shape 46 , 47 .…”

Section: Methodsmentioning

confidence: 99%

Early Triassic ichthyopterygian fossils from the Russian Far East

Nakajima

Shigeta

Houssaye³

et al. 2022

Sci Rep

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Ichthyopterygia is a major clade of reptiles that colonized the ocean after the end-Permian mass extinction, with the oldest fossil records found in early Spathian substage (late Olenekian, late Early Triassic) strata in the western USA. Here, we describe reptilian remains found in situ in the early Spathian Neocolumbites insignis ammonoid zone of South Primorye in the Russian Far East. Specimen NSM PV 23854 comprises fragmentary axial elements exhibiting a combination of morphological characteristics typical of Ichthyopterygia. The cylindrical centra suggest that the specimen represents a basal ichthyopterygian, and its size is comparable to that of Utatsusaurus. Specimen NSM PV 24995 is represented by a single limb bone, which is tentatively identified as an ichthyopterygian humerus. With a body length of approximately 5 m estimated from the humeral length, NSM PV 24995 represents one of the largest specimens of early Spathian marine reptiles known to date. Such size variation among the earliest ichthyopterygians might suggest an explosive diversification in size immediately after the end-Permian mass extinction. Both vertebrae and humerus specimens exhibit an extremely cancellous inner structure, suggesting a high degree of aquatic adaptation in ichthyopterygians, despite their short history of evolution in the ocean.

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Section: Methodsmentioning

confidence: 99%

Early Triassic ichthyopterygian fossils from the Russian Far East

Nakajima

Shigeta

Houssaye³

et al. 2022

Sci Rep

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Ichthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic–Jurassic boundary

Fischer

Cappetta

Vincent

et al. 2014

Naturwissenschaften

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Mesozoic marine reptiles went through a severe turnover near the end of the Triassic.Notably, an important extinction event affected ichthyosaurs, sweeping a large part of the group. This crisis is however obscured by an extremely poor fossil record and is regarded as protracted over the entire Norian-earliest Jurassic interval, for the lack of a more precise scenario. The iconic whale-sized shastasaurid ichthyosaurs are regarded as early victims of this turnover, disappearing by the middle Norian. Here we evaluate the pattern of this turnover among ichthyosaurs by analyzing the faunal record of two Rhaetian localities. One locality is Autun, eastern France; we re-discovered in this material the holotypes or partial 'type' series of Rachitrema pellati, Actiosaurus gaudryi, Ichthyosaurus rheticus, Ichthyosaurus carinatus, andPlesiosaurus bibractensis; a revised taxonomic scheme is proposed. The second assemblage comes from a new locality: Cuers, southeastern France. Both these assemblages provide several lines of evidence for the presence of shastasaurid-like ichthyosaurs in the Rhaetian of Europe. These occurrences suggest that both the demise of shastasaurids and the sudden radiation of neoichthyosaurians occurred within a short time window; this turnover appear more abrupt but also more complex than previously postulated and adds a new facet of the endTriassic mass extinction.

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Tooth histology, attachment, and replacement in the Ichthyopterygia reviewed in an evolutionary context

Maxwell

Lamoureux

2011

Paläontol. Z.

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Ichthyosaurs, an extinct group of Mesozoic marine diapsids, show a relatively small range of tooth crown morphologies. With few exceptions, members of the group bear a large number of conical teeth and show only minor heterodonty within a jaw. This uniformity in gross morphology masks a high degree of variation in both the quantity and arrangement of the mineralized tooth tissues. Here, we describe tooth tissue structure and distribution in derived ichthyosaurs. We synthesize these new observations with the historical literature, to map changes in the quantity and arrangement of tooth tissues. These changes affected tooth attachment, tooth replacement, plicidentine morphology, and the amount and distribution of cellular cementum. The amount of variation detected in features relating to ichthyosaurian dentition is not surprising given the geological longevity and morphological disparity of the group, but does emphasize the importance of extensive taxon sampling in studies of tooth histology and evolution. This study is important in that it incorporates morphological and histological information in a phylogenetic and developmental context, something that is rarely done for marine reptile dentitions.

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Observations on Triassic ichthyosaurs. Part IX. The first associated skeletal remains of Merriamosaurus n.g. (Ichthyosauria, Lower Triassic) and their bearing on the systematic position of the Omphalosauria

Cited by 9 publications

References 0 publications

Early Triassic ichthyopterygian fossils from the Russian Far East

Early Triassic ichthyopterygian fossils from the Russian Far East

Ichthyosaurs from the French Rhaetian indicate a severe turnover across the Triassic–Jurassic boundary

Tooth histology, attachment, and replacement in the Ichthyopterygia reviewed in an evolutionary context

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