The first known neonate<i>Ichthyosaurus communis</i>skeleton: a rediscovered specimen from the Lower Jurassic, UK

Lomax, Dean R.; Larkin, Nigel R.; Boomer, Ian; Dey, Steven; Copestake, Philip

doi:10.1080/08912963.2017.1382488

Cited by 6 publications

(4 citation statements)

References 18 publications

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“…Fossil embryos are well documented in Ichthyosauriformes 14 – 17 , 22 , 32 , 58 – 61 . However, cranial material has been described or depicted for only a few, most notably Platypterygius australis 32 .…”

Section: Discussionmentioning

confidence: 99%

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Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Miedema

Maxwell

2022

Sci Rep

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The availability of a large sample size from a range of ontogenetic stages makes Stenopterygius quadriscissus a good model to study ontogenetic variation in a fossil sauropsid. We qualitatively examined pre- and postnatal ontogenetic changes in the cranium of S. quadriscissus. The prenatal ossification sequence is similar to other diapsids, exhibiting delayed chondrocranial ossification compared to the dermatocranium. In the dermatocranium, the circumorbital area is more ossified earlier in development relative to other elements, especially those of the skull roof where ossification is comparatively weaker across prenatal stages. Perinatally all cranial elements are ossified, and many scarf and step joints are already closed. We propose four prenatal and three postnatal stages in S. quadriscissus on the basis of relative ossification, size and qualitative cranial characters pertaining to the jugal, parietal, frontal, pterygoid and surangular. These will provide a basis for determining ontogenetic stages in other ichthyosaurs. Moreover, our postnatal observations aid in refining ontogenetic characters for phylogenetic studies. Lastly, we observed that the antimeric sutures of the midline of the skull roof are open perinatally and that fusion of the midline only appears in the adult stage. We hypothesize that the loose connection of the midline functions as a fontanelle, limiting potential damage during birth.

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Section: Discussionmentioning

confidence: 99%

“…An absence of post-parturitional care is further supported by ontogenetic differences in diet 3 . Amongst other ichthyosaurian taxa, overall dermatocranial ossification is high in perinatal and neonatal individuals 15 , 17 , 32 , 58 .…”

Section: Discussionmentioning

confidence: 99%

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Miedema

Maxwell

2022

Sci Rep

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“…Ichthyosaurus is one of the most speciose genera of parvipelvian ichthyosaurs and is currently represented by six species; Ichthyosaurus communis, I. breviceps, I. conybeari, I. anningae, I. larkini and I. somersetensisall of which are distinguished predominantly by skull and humerus features (Massare and Lomax, 2017). Ichthyosaurus was the first genus of ichthyosaur to be recognised scientifically (De la Beche and Conybeare, 1821) and is the most common genus of Lower Jurassic ichthyosaur to be found in the UK (Lomax et al, 2017a). Well over a thousand specimens are present in various institutional collections across the world, particularly in the UK.…”

Section: Ichthyosaurus Communis De La Beche and Conybeare 1821mentioning

confidence: 99%

A revision of Temnodontosaurus crassimanus (Reptilia: Ichthyosauria) from the Lower Jurassic (Toarcian) of Whitby, Yorkshire, UK

Swaby

Lomax

2020

Historical Biology

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Temnodontosaurus is known from the Lower Jurassic (Hettangian -Toarcian) of England, Germany, France and Belgium and is the largest Jurassic ichthyosaur known from complete remains, with the total body length of the largest Temnodontosaurus exceeding 12 m. Six different species are presently identified: Temnodontosaurus platyodon (Conybeare, 1822), T. trigonodon (Theodori, 1843), T. crassimanus (Blake, 1876), T. eurycephalus McGowan 1974a, T. acutirostris (Owen, 1840), and T. azerguensis Martin et al. 2012. In the UK, Lower Jurassic ichthyosaurs have been collected extensively from many localities, primarily in Lyme Regis and Charmouth, Dorset; Street and Strawberry Bank, Somerset; and Whitby, North Yorkshire. The Yorkshire coast is of historic interest in being one of the earliest British localities to be exploited for fossil marine reptiles, and has produced many well-preserved specimens of plesiosaurs, ichthyosaurs and marine crocodilians. During the 19th century, the Yorkshire coast was extensively quarried for the manufacture of alum, which yielded many specimens of marine reptiles during its operation, including a large, partially-complete, threedimensionally preserved specimen (YORYM 497)the holotype of Temnodontosaurus crassimanus. While the holotype still remains on display at the Yorkshire Museum, it has remained largely understudied and the validity of the species has long been questioned. Through re-examination of YORYM 497, the study highlighted several morphological features of the postcranial skeleton and determined that T. crassimanus differs sufficiently from other species of Temnodontosaurus, specifically T. trigonodon, in possessing several distinct characteristics. These defining characters include a large, robust humerus that is proximodistally longer than the scapula (scapula length vs humerus length ratio: ~ 0.68); forefins which are significantly longer but less than twice the length of the hindfin (forefin length vs hindfin length ratio: ~ 1.51); and notching of the anterior facet of at least five leading edge elements (digit II) of both the fore-and hindfins. Several additional specimens, previously tentatively assigned to T. crassimanus, were located and examined, but none could confidently be assigned to the species. Furthermore, the species was incorporated into a phylogenetic analysis, and results confirm the temnodontosaurid affinities and close relationship with T. trigonodon. To understand further the relationship of T. crassimanus within Ichthyopterygia, a thorough taxonomic revision of the genus Temnodontosaurus and the associated species is greatly required, but this is beyond the scope of the present study. Additionally, this study further highlights the need for a complete re-examination of all the Yorkshire Lias ichthyosaur material, in order to understand better the variety and abundance of marine reptiles from the coastline during the Toarcian. This study has helped to lay the foundations for this future research to be undertaken. 11 DECLARATIONNo portion of the work refer...

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“…Juveniles, in particular, often lack an interlocking mosaic of fin elements (Johnson, 1977; but see Lomax et al . 2017). In spite of gaps between bones, the presence of facets on adjacent elements often indicates that bones were in contact or have the potential to be in contact if the gaps were eliminated by additional growth or re-articulation.…”

Section: Hindfin Development and Homologymentioning

confidence: 99%

Hindfins ofIchthyosaurus: effects of large sample size on ‘distinct’ morphological characters

Massare

Lomax

2018

Geol. Mag.

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The abundance of specimens of Ichthyosaurus provides an opportunity to assess morphological variation without the limits of a small sample size. This research evaluates the variation and taxonomic utility of hindfin morphology. Two seemingly distinct morphotypes of the mesopodium occur in the genus. Morphotype 1 has three elements in the third row: metatarsal two, distal tarsal three and distal tarsal four. This is the common morphology in Ichthyosaurus breviceps, I. conybeari and I. somersetensis. Morphotype 2 has four elements in the third row, owing to a bifurcation. This morphotype occurs in at least some specimens of each species, but it has several variations distinguished by the extent of contact of elements in the third row with the astragalus. Two specimens display a different morphotype in each fin, suggesting that the difference reflects individual variation. In Ichthyosaurus, the hindfin is taxonomically useful at the genus level, but species cannot be identified unequivocally from a well-preserved hindfin, although certain morphologies are more common in certain species than others. The large sample size filled in morphological gaps between what initially appeared to be taxonomically distinct characters. The full picture of variation would have been obscured with a small sample size. Furthermore, we have found several unusual morphologies which, in isolation, could have been mistaken for new taxa. Thus, one must be cautious when describing new species or genera on the basis of limited material, such as isolated fins and fragmentary specimens.

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The first known neonateIchthyosaurus communisskeleton: a rediscovered specimen from the Lower Jurassic, UK

Cited by 6 publications

References 18 publications

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

Ontogenetic variation in the skull of Stenopterygius quadriscissus with an emphasis on prenatal development

A revision of Temnodontosaurus crassimanus (Reptilia: Ichthyosauria) from the Lower Jurassic (Toarcian) of Whitby, Yorkshire, UK

Hindfins ofIchthyosaurus: effects of large sample size on ‘distinct’ morphological characters

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