A giant Late Triassic ichthyosaur from the UK and a reinterpretation of the Aust Cliff ‘dinosaurian’ bones

Lomax, Dean R.; Massare, Judy A.; Gallois, R.W.

doi:10.1371/journal.pone.0194742

Cited by 20 publications

(49 citation statements)

References 35 publications

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“…Unfortunately, the latest Triassic record of ichthyosaurs is poor; the high Rhaetian skeletal completeness identified by Cleary et al 38 is attributable to representation by Leptonectes tenuirostris, which is known from highly complete specimens in the Early Jurassic 39 . However, Rhaetian ichthyosaurs are present and demonstrate a high diversity of taxa and ecology, but incompleteness and uncertain taxonomic affinities has limited their inclusion in analyses 40,41 . This suggests extensive turnover throughout the later part of the Triassic, but a more rapid extinction at the Triassic-Jurassic boundary; the selectivity of this extinction in ichthyosaurs has yet to be tested.…”

Section: Discussionmentioning

confidence: 99%

Early high rates and disparity in the evolution of ichthyosaurs

Moon

Stubbs

2020

Commun Biol

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How clades diversify early in their history is integral to understanding the origins of biodiversity and ecosystem recovery following mass extinctions. Moreover, diversification can represent evolutionary opportunities and pressures following ecosystem changes. Ichthyosaurs, Mesozoic marine reptiles, appeared after the end-Permian mass extinction and provide opportunities to assess clade diversification in a changed world. Using recent cladistic data, skull length data, and the most complete phylogenetic trees to date for the group, we present a combined disparity, morphospace, and evolutionary rates analysis that reveals the tempo and mode of ichthyosaur morphological evolution through 160 million years. Ichthyosaur evolution shows an archetypal early burst trend, driven by ecological opportunity in Triassic seas, and an evolutionary bottleneck leading to a long-term reduction in evolutionary rates and disparity. This is represented consistently across all analytical methods by a Triassic peak in ichthyosaur disparity and evolutionary rates, and morphospace separation between Triassic and post-Triassic taxa.

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Section: Discussionmentioning

confidence: 99%

Early high rates and disparity in the evolution of ichthyosaurs

Moon

Stubbs

2020

Commun Biol

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“…Some of the earliest forms were ‘lizard-like’ in appearance, although later forms evolved fish-shaped bodies (Motani, 2009). Species ranged in size from small-bodied forms less than one m long to giants over 20 m in length (Motani, 2005; Nicholls & Manabe, 2004; Lomax et al, 2018). Numerous Lower Jurassic ichthyosaurs have been found in the UK, the majority being from the Lyme Regis–Charmouth area in west Dorset (Milner & Walsh, 2010), the village of Street and surrounding areas in Somerset (Delair, 1969), sites around the coastal town of Whitby, Yorkshire (Benton & Taylor, 1984) and Barrow-upon-Soar, Leicestershire (Martin, Frey & Riess, 1986).…”

Section: Introductionmentioning

confidence: 99%

Descriptive anatomy of the largest known specimen ofProtoichthyosaurus prostaxalis(Reptilia: Ichthyosauria) including computed tomography and digital reconstruction of a three-dimensional skull

Lomax

Porro

Larkin

2019

PeerJ

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Ichthyosaur fossils are abundant in Lower Jurassic sediments with nine genera found in the UK. In this paper, we describe the partial skeleton of a large ichthyosaur from the Lower Jurassic (lower Sinemurian) of Warwickshire, England, which was conserved and rearticulated to form the centrepiece of a new permanent gallery at the Thinktank, Birmingham Science Museum in 2015. The unusual three-dimensional preservation of the specimen permitted computed tomography (CT) scanning of individual braincase elements as well as the entire reassembled skull. This represents one of the first times that medical imaging and three-dimensional reconstruction methods have been applied to a large skull of a marine reptile. Data from these scans provide new anatomical information, such as the presence of branching vascular canals within the premaxilla and dentary, and an undescribed dorsal (quadrate) wing of the pterygoid hidden within matrix. Scanning also revealed areas of the skull that had been modelled in wood, clay and other materials after the specimen’s initial discovery, highlighting the utility of applying advanced imaging techniques to historical specimens. Additionally, the CT data served as the basis for a new three-dimensional reconstruction of the skull, in which minor damage was repaired and the preserved bones digitally rearticulated. Thus, for the first time a digital reconstruction of the skull and mandible of a large marine reptile skull is available. Museum records show the specimen was originally identified as an example of Ichthyosaurus communis but we identify this specimen as Protoichthyosaurus prostaxalis. The specimen features a skull nearly twice as long as any previously described specimen of P. prostaxalis, representing an individual with an estimated total body length between 3.2 and 4 m.

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“…They include dinosaurs (Camelotia borealis, Megalosaurus? cambrensis and Thecodontosaurus antiquus (Storrs, 1999) but see Lomax et al, 2018) and some small and putative cynodont and mammal material (Boyd Dawkins, 1864). Significantly, these sediments also contain possible phytosaurs (Storrs, 1999) and potentially the earliest representative of the semi-aquatic choristoderes (Pachystropheus rhaeticus) that may have inhabited coastal or estuarine environments (Storrs and Gower, 1993).…”

Section: Track Interpretations and Possible Track Makersmentioning

confidence: 99%

The first tetrapod track recorded from the Rhaetian in the British Isles

Larkin

Duffin

Dey

et al. 2020

Proceedings of the Geologists' Association

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Terrestrial vertebrate trace fossils are relatively abundant in mid-to-late Triassic and early Jurassic deposits in the British Isles but to date none at all have been recorded from the Rhaetian, the final stage of the Triassic. This represents a persistent gap in the terrestrial ichnological record. We present the first Rhaetian track to be recognised in the British Isles, found at Aust Cliff on the south bank of the Severn Estuary near Bristol in SW England. This locality is well known for disarticulated remains of Rhaetian fossil reptiles including some terrestrial species but in 2006 a track (TECMAG0161) was found for the fist time. Although the specimen was found ex-situ the palynological data from the surrounding matrix confirms a Rhaetian age. The track was examined with CT scanning and photogrammetry. We tentatively assign the track to the ichnogenus Procolophonichnium based on size and digit proportions. The isolated nature of the specimen offers little concrete information about the track maker but such tracks have previously been attributed to parareptiles or therapsid trackmakers. The specimen adds a datapoint to an otherwise ichnologically empty period of time in the British Isles. The track also provides solid evidence for a [locally] terrestrial environment in a sequence that is otherwise considered predominantly marine or estuarine. This discovery suggests that there may be more such tetrapod tracks of Rhaetian age preserved, at least at Aust, and further searching will hopefully lead to the current minimal dataset being expanded.

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A giant Late Triassic ichthyosaur from the UK and a reinterpretation of the Aust Cliff ‘dinosaurian’ bones

Cited by 20 publications

References 35 publications

Early high rates and disparity in the evolution of ichthyosaurs

Early high rates and disparity in the evolution of ichthyosaurs

Descriptive anatomy of the largest known specimen ofProtoichthyosaurus prostaxalis(Reptilia: Ichthyosauria) including computed tomography and digital reconstruction of a three-dimensional skull

The first tetrapod track recorded from the Rhaetian in the British Isles

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