The first definite record of a Valanginian ichthyosaur and its implications on the evolution of post-Liassic Ichthyosauria

Abstract

A complete ichthyosaur rostrum, with 124 associated teeth, was recently discovered in LauxMontaux locality, department of Drôme, southeastern France. The associated belemnites and ammonites indicate a late Valanginian age (Neocomites peregrinus Zone, Olcostephanus nicklesi Subzone) for this fossil, which consequently represents the first diagnostic ichthyosaur ever reported from Valanginian strata. This specimen also represents the first occurrence of Aegirosaurus outside the Tithonian (Upper Jurassic) lithographic limestones of Bavaria (southern Germany). Tooth morphology and wear pattern suggest that Aegirosaurus belonged to the "Pierce II/ Generalist" feeding guild, which was hitherto not represented in post-Liassic ichthyosaurs. Most Late Jurassic ichthyosaurs actually crossed the Jurassic-Cretaceous boundary.

A new Barremian (Early Cretaceous) ichthyosaur from western Russia

“…They are very small: the largest tooth measures 19 mm in total height and the tooth length index (TLI, sensu McGowan, 1976) is 0.11, which is about half that of typical toothed post-Liassic ichthyosaurs such as Platypterygius or Brachypterygius, but slightly larger than those of Aegirosaurus Fischer et al, 2011). About half of the teeth are recurved.…”

“…However, most of the ichthyosaurs used in Massare's analysis were Early Jurassic in age, coming from the well-known Hettangian-Sinemurian and Toarcian anoxic shales from Europe. The incorporation of Late Jurassic to middle Cretaceous ichthyosaurs in that canvas proved to be problematic because of the appearance of intermediate or mosaic-like dental morphologies in taxa whose diet cannot be constrained by gastric contents or bromalites (Fischer et al, 2011). Furthermore, some ichthyosaurs, which were identified as belonging to the 'Grasp: smash' guild and supposedly fed on lightly armored cephalopods, were probably far more opportunistic than hypothesized by Massare: the preserved gut of a specimen of P. australis from the Albian of Australia contained the remains of birds, fishes, cephalopods, and small turtles .…”

Simbirskiasaurus and Pervushovisaurus reassessed: implications for the taxonomy and cranial osteology of Cretaceous platypterygiine ichthyosaurs

“…As in some other ichthyosaurs (e.g. Aegirosaurus; see Bardet & Fernández, 2000;Fischer et al, 2011a), there are multiple lateral foramina at the anterior extremity of the rostrum, which are not necessarily aligned with the fossa praemaxillaris. The dental groove is deep along the whole of its length (around 35 mm deep at the level of emergence of the nasal).…”

“…Although relatively larger than in Aegirosaurus leptospondylus (see Bardet & Fernandez, 2000), the shape and robustness of the teeth and the lack of specialized features suggest that Simbirskiasaurus birjukovi also occupied a 'generalist' feeding guild (see the scheme developed in Fischer et al, 2011a;Fischer et al, 2014b). Too few tooth apices are preserved to allow for the quantitative analysis of the wear pattern, but most crown apices are slightly polished and there is at least one broken-off tip with a polished broken surface; a very similar condition to that in the Aegirosaurus sp.…”

“…Fernández & Talevi, 2014) and the Cretaceous (e.g. Bardet, 1994;Fischer et al, 2011a); however, the taxonomie diversity of Cretaceous ichthyosaurs has recently increased, with the recognition of several new taxa in the Albian of North America (Maxwell & Caldwell, 2006b, 2006aDruckenmiller & Maxwell, 2010;Maxwell & Druckenmiller, 2011) and the Early Cretaceous of Eurasia and the Middle East (Fischer et al, 2011b(Fischer et al, , 2013(Fischer et al, , 2014a. Our knowledge of Cretaceous ichthyosaur diversity is still poor (Zammit, 2012), however, especially outside the better-known intervals of the latest Jurassic-earliest Cretaceous ('Volgian'; e.g.…”