Can vertebral remains differentiate more than one species of Australian Cretaceous ichthyosaur?

Vakil, Vikram; Webb, Gregory E.; Cook, Alex G.

doi:10.1080/03115518.2020.1853809

Cited by 3 publications

(5 citation statements)

References 33 publications

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“…The following equations were used (after Welles, 1952;Brown, 1981): Owing to incompleteness of specimens and differences in neck length for different taxa, normalised positions (relative to total number) of ver- tebrae within the key three body regions (cervical, dorsal, and caudal) (cf. Vakil et al, 2020) were plotted against VLIs for all specimens to compare any trends along the length of the vertebral column. Vertebrae were initially assigned to body region based on their morphology, with cervicals bearing rib facets wholly on the centrum, pectorals and sacrals partly on the centrum and neural arch, dorsals wholly on the neural arch, and caudals either on the neural arch or side of the centrum in addition to the presence of chevron facets on their ventral surfaces (e.g., Taylor et al, 1993;Druckenmiller, 2002;Noè et al, 2017).…”

Section: Methodsmentioning

confidence: 99%

“…Two methods were used to normalise CL, CW, and CH data so as to address heteroscedasticity and highlight ontogenetic changes in morphology. Firstly, vertebral dimensions (CX) were centred and normalised individually for CW, CH, and CL prior to analysis using the following formula (Vakil et al, 2020):…”

Section: Methodsmentioning

confidence: 99%

“…Principal Components Analysis for anterior cervicals of Australian xenopsarian specimens (including polycotylid QM F12719) and non-Australian elasmosaurids using SD-normalised data (cf. Vakil et al, 2020…”

Section: Appendix Figurementioning

confidence: 99%

“…This could help inform estimates of diversity amongst these commonly headless fossils and provide additional support for possible relationships among different species of Australian and non-Australian elasmosaurids (e.g., styxosaurines, aristonectines), which also commonly lack preserved skulls. This style of morphometric analysis could also be extended to other fossil assemblages lacking diagnostic cranial remains (see Vakil et al, 2020, for the application of this technique to ichthyosaurs).…”

Section: Introductionmentioning

confidence: 99%

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Taxonomic utility of Early Cretaceous Australian plesiosaurian vertebrae

Vakil

Webb

Cook

2021

Palaeontol Electron

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Despite their broad occurrence in Australian basins, lower-level taxonomy of Australian Early Cretaceous plesiosaurs is hindered by the scarcity of skulls and other diagnostic elements. This paper presents a morphological and morphometric analysis of the vertebrae of Australian plesiosaurs and a comparison with selected non-Australian elasmosaurids (basal elasmosaurs, styxosaurines, aristonectines). Biometric analysis involved measurements that include centrum height (CH), centrum width (CW), centrum length (CL), width of zygapophyses, and others. Principal component analysis (PCA) and multivariate analysis of variance (MANOVA) were carried out on CH, CW, and CL. Morphometric ratios [Vertebral Length Index (VLI), Height Index (HI), and Breadth Index (BI)] were plotted along the length of the vertebral column and on bivariate graphs where the analysis is independent of vertebral position and correct sequencing. Direct comparison of homologous groups of vertebrae (especially anterior cervicals) easily distinguished an Australian polycotylid from all elasmosaurids in all plots. Most Australian elasmosaurid specimens plotted near basal 'Cimoliasaurus'grade elasmosaurs, where they clustered as a group relatively distinct from, but overlapping coeval non-Australian forms. However, one specimen plotted consistently with the non-Australian styxosaurines and Opallionectes andamookaensis plotted with the aristonectines. Although it is not possible to distinguish phylogenetic relationships from morphological convergence in the plotted positions, the analyses provide potential hypotheses to be tested with additional data. Hence, vertebrae have some taxonomic value for potential assignment of Australian plesiosaurs, even in the absence of skulls or other diagnostic material.

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Section: Methodsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Appendix Figurementioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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Taxonomic utility of Early Cretaceous Australian plesiosaurian vertebrae

Vakil

Webb

Cook

2021

Palaeontol Electron

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“…From the most complete vertebrae (SABAP-BO-22.0002, SABAP-BO-22.0003), the diameter of the centra can be calculated (assuming the centrum to be circular), but, without the complete bone, this measure can only be approximated to be the centrum width/height. A high ratio between CH and CL in the anterior tailstock (≥ 3.0) is a character that had been reported among selected ophthalmosaurids and sometimes even used to discriminate ophthalmosaurid taxa (McGowan and Motani 2003;Massare et al 2006;Maxwell 2010;Paparella et al 2017;Serafini et al 2020;Vakil et al 2021); however it is not considered diagnostic above species level. The ichthyosaur vertebrae from Castagneto di Pavullo are higher than they are long (CH/CL 2.9 for SABAP-BO-22.0002; Table 2); however, due to the lack of positional information for the preserved vertebrae within the column, the ratio has no diagnostic value.…”

Section: Taxonomymentioning

confidence: 99%

Not Entirely Ichthyosaur: A Mysterious Lamniform and Ichthyopterygian-Fall Association From the Abyssal Upper Cretaceous of the Northern Apennines (Italy)

SERAFINI,

AMALFITANO,

DANISE

et al. 2023

Palaios

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Axial remains of a large ichthyosaur and a medium-sized anacoracid shark from the deep-water sediments of the Cenomanian of the Northern Apennines (Northern Italy) are described in detail. The specimens were found closely associated (less than 0.3 m apart), and offer an invaluable window into the taphonomy and dead-fall stages of pelagic vertebrates in a Mesozoic abyssal plain. The anacoracid shark remains, initially misinterpreted as an ichthyosaur, consist of eight articulated vertebrae embedded in a block of dark arenaceous matrix, and represent the first occurrence of an articulated shark from the Northern Apennines. The ichthyosaur remains consist of seven discoidal vertebrae and several unidentified fragments. Due to the absence of diagnostic skeletal elements, both specimens are assigned only at higher taxonomic levels. The two fossils, which come from the same outcrop and possibly from the same stratigraphic horizon, share a common taphonomic history, in terms of both their preservation and diagenesis. Mineralogy of the matrices of both is dominated by manganese micro-nodules, consistent with the deposition of polymetallic nodules in bathyal-abyssal settings. Biostratinomic processes that impacted the two specimens also provide insight on the development of Mesozoic marine vertebrate-falls in the deep-sea. Localized pyrite framboids inside the bone spongiosa are possible evidence of the sulfophilic stage (microbially mediated sulfur mobilization during lipid decay) in the ichthyosaur fall. Burrows assigned to Taenidium on the surface of the shark block, interpreted as worm-like feeding burrows or arthropod locomotion and feeding trails, might represent evidence of the enrichment opportunistic stage. Although intriguing, we have no evidence to support the hypothesis that this peculiar association of two pelagic predators is due to ecological interaction between the two animals.

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