Sunday, June 19, 2016

[Paleontology • 2016] Wahlisaurus massarae • A New Leptonectid Ichthyosaur from the Lower Jurassic (Hettangian) of Nottinghamshire, England, UK, and the Taxonomic Usefulness of the Ichthyosaurian Coracoid

Wahlisaurus massarae 
 Lomax. 2016

Thousands of ichthyosaurs have been discovered from the rich Lower Jurassic deposits of the UK, with the majority collected from along the Lyme Regis-Charmouth area of the Dorset coast. Here, I describe a new leptonectid ichthyosaur, Wahlisaurus massarae gen. et sp. nov., based on a partial skull and an incomplete skeleton collected from the Lower Jurassic (Hettangian) of Nottinghamshire, England. Wahlisaurus can be referred to the Leptonectidae through the possession of an extremely slender and delicate snout, and a mandible shorter than the snout which produces an overbite. This referral is supported by a phylogenetic analysis. The new taxon is distinguished from other ichthyosaurs through a unique combination of characters and autapomorphies of the pectoral girdle including the presence of both a scapular-coracoid foramen and a large and roughly ovoid coracoid foramen. A coracoid foramen has only previously been reported in the Triassic ichthyosaur Cymbospondylus. The peculiar coracoid morphology further highlights the taxonomic utility of coracoids in ichthyosaurs. The aforementioned features demonstrate that W. massarae cannot be referred to any currently recognized leptonectid. Wahlisaurus is the ninth Lower Jurassic ichthyosaur genus to be recognized worldwide, and the fifth documented in the Lower Lias Group.

Keywords: ichthyosaur, Wahlisaurus massarae, Nottinghamshire, leptonectid, Lower Jurassic, Hettangian

Systematic palaeontology

Order Ichthyosauria de Blainville, 1835
Minorder Parvipelvia Motani, 1999b
Suborder Neoichthyosauria Sander, 2000

Family Leptonectidae Maisch, 1998
Genus Wahlisaurus gen. nov.

Type species. Wahlisaurus massarae sp. nov.

 Derivation of name. In honour of William (Bill) Wahl for his contribution to the study of Mesozoic marine reptiles and for introducing the author to the study of the group.

Wahlisaurus massarae sp. nov.
Holotype. LEICT G454.1951.5, a partial skull and an associated incomplete skeleton comprising the pectoral girdle, humeri, pelvic elements, partial hind fins, vertebrae and ribs. Only known specimen.

Derivation of name. In honour of Professor Judy Massare for her significant contribution to the study of Mesozoic marine reptiles, especially ichthyosaurs, and for introducing the author to the study of the group.

Diagnosis. Small-bodied leptonectid ichthyosaur with the following autapomorphies: coracoid with a large, ovoid foramen, a coracoid foramen is present in Cymbospondylus but it is much smaller in this genus (Merriam 1908; Sander 1989); presence of both a coracoid foramen and scapular-coracoid foramen (fenestra coracoscapularis), the latter formed by articulation of the coracoid and scapula; a coracoid with a posterior notch that is much more developed than the anterior notch. Three other features may be autapomorphies: humerus deltopectoral crest prominent and 2.5 times greater than the dorsal process; dorsoventral width of the humerus is greater than the anteroposterior width, which results in a D-shape in proximal view; and slender, long, needle-like teeth with marginally recurved crowns and large, bulbous infolded roots.


Figure 2. Basioccipital, rostrum and dentition of LEICT G454.1951.5, Wahlisaurus massarae gen. et sp. nov. 
A, basioccipital in posterior view; note the extensive extracondylar area, fragment of the left stapes and portion of basisphenoid. B, ventral view of mandible and snout with anterior portion of dentary rotated (in dorsal view) and positioned adjacent (dashed line indicates point of fit); note the slenderness of the rostrum and the presence of an overbite. C, close-up of the large, long and robust teeth and some of the needle-like teeth positioned under the maxilla. D, close-up of three dentary teeth; note the ‘waisted’ morphology, recurved crown and infolded root.
 Abbreviations: bas, basisphenoid; den, dentary; mx, maxilla (right maxilla); pmx, premaxilla; sta, stapes.   Scale bars: A = 5 cm; B = 10 cm; C = 3 cm.

Figure 1. Map of Nottinghamshire including the location of Normanton Hills (indicated by a star), near Normanton on Soar, the discovery site of LEICT: G454.1951.5 (holotype of Wahlisaurus massarae gen. et sp. nov.). The additional localitie have yielded other ichthyosaur specimens from the county. Reproduced from Lomax & Gibson (2015).

Wahlisaurus massarae gen. et sp. nov. is a new leptonectid ichthyosaur from the Lower Jurassic (lower Hettangian) of Nottinghamshire, England. It possesses a unique combination of characters that distinguish it from all other ichthyosaurs, including autapomorphic characters of the pectoral girdle such as a large, ovoid coracoid foramen and the combined presence of a coracoid foramen and scapular-coracoid foramen. These features further highlight the taxonomic utility of pectoral girdle elements in ichthyosaurs.

The recognition of Wahlisaurus massarae as a leptonectid adds to the currently valid taxa that form the family Leptonectidae (Maisch, 1998) Leptonectes (L. tenuirostrisLsolei and L. moorei), Excalibosaurus costini and Eurhinosaurus longirostris and unequivocally adds an additional region for the geographical occurrence of leptonectids. Presently, leptonectids are confidently identified from the following locations: Leptonectes tenuirostris from Dorset, Somerset, Leicestershire, Warwickshire (England: McGowan 1996; Smith & Radley 2007), Dusslingen (Germany: Maisch 1999) and Unter Hauenstein (Switzerland: Maisch & Reisdorf 2006); Leptonectes moorei from Dorset (England: McGowan & Milner 1999); Leptonectes solei from Dorset (England: McGowan 1993); Excalibosaurus costini from Somerset (England: McGowan 2003); and Eurhinosaurus longirostris from Yorkshire (England: McGowan 1994a), Holzmaden and surrounding areas (Germany: McGowan 1979), Staffelegg (Switzerland: Reisdorf et al. 2011), Dudelange (Luxembourg), Noirefontaine and Marcoux (France: Fischer et al. 2011b). Including Wahlisaurus, a total of nine ichthyosaur genera are recognized from the Lower Jurassic. The discovery of a new ichthyosaur from the well-studied British Lower Jurassic demonstrates that new taxa may yet be found through detailed re-examination of museum collections as well as new discoveries.

Dean R. Lomax. 2016. A New Leptonectid Ichthyosaur from the Lower Jurassic (Hettangian) of Nottinghamshire, England, UK, and the Taxonomic Usefulness of the Ichthyosaurian Coracoid. Journal of Systematic Palaeontology. DOI: 10.1080/14772019.2016.1183149  

New 200 million-year-old British species of marine reptile discovered via @physorg_com