10.5061/DRYAD.SF85S
Lomax, Dean R.
University of Manchester
Massare, Judy A.
Department of Earth Sciences
Data from: Two new species of Ichthyosaurus from the lowermost Jurassic
(Hettangian) of Somerset, England
Dryad
dataset
2017
Ichthyosauria
Ichthyosaurus larkini
Ichthyosaurus somersetensis
Lower Jurassic
Hettangian
2017-09-27T00:00:00Z
2017-09-27T00:00:00Z
en
https://doi.org/10.1002/spp2.1065
268436 bytes
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CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
All specimens of Ichthyosaurus from the Lower Jurassic of Somerset were
previously identified as I. communis, an abundant and extremely variable
species. Here, two new species of Ichthyosaurus are recognized from
multiple specimens. The species are assigned to Ichthyosaurus on the basis
of the humerus, pectoral girdle and forefin morphologies. I. larkini sp.
nov. is distinguished by a broad jugal with a blunt anterior end that
extends as far forward as the middle of the external naris, separating the
maxilla and lacrimal; and a unique combination of other features. I.
somersetensis sp. nov. is distinguished by a jugal with a nearly straight
dorsal ramus that lacks a right-angle dorsal bend; a high, narrow,
crescentic postorbital that forms almost all of the posterior margin of
the orbit and separates the jugal dorsal ramus from the orbit; and an
ilium that is wide relative to its length, more oblong than rib-like. The
identifications are supported by a phylogenetic analysis which finds the
new species more closely related to each other than to other species of
the genus. We also identify a squamosal in both species, which confirms
that it is present in the genus. This study suggests that hindfin
morphology has some taxonomic utility, at least within the genus. The new
species increases the diversity of Ichthyosaurus to six species, three of
which are found in the Hettangian of Somerset.
Lomax & Massare APPENDIXAPPENDIX. Description of characters used
in the phylogenetic analysis. Characters are polarized using
Temnodontosaurus and Suevoleviathan as outgroups. All characters are
unordered. Lengths or widths of skeletal elements are evaluated as
‘approximately equal’ if the measurements are within 10% of each other.
Characters that are not referenced were developed as part of this
study.Lomax & Massare supplementary material 1SUPPLEMENTARY
INFORMATION 1Lomax & Massare supp material 1.docxLomax &
Massare supplementary material 2 (matrix)SUPPLEMENTARY INFORMATION 2 -
Nexus fileLomax & Massare supp material 2 (matrix).nexLomax
& Massare supplementary material 3SUPPLEMENTARY INFORMATION 3Lomax
& Massare Supp material 3.docx
Somerset