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In the last decade, several new Cretaceous ichthyosaurs have been described and/or redescribed, challenging the traditional concept that, during the Cretaceous, ichthyosaurs were abundant but not diverse. Here, we redescribe the holotype and referred specimen of ' Platypterygius ' hauthali Huene (1927) from the Barremian of Argentinean Patagonia and compare its appendicular anatomy with that of a referred specimen from the Valanginian - Hauterivian of Chile. These specimens consist almost entirely of anterior appendicular elements, so we explore quantitatively the phylogenetic signal contained in the forefin of the ophthalmosaurids and include them in a new phylogenetic analysis. Our results support the revalidation of the genus Myobradypterygius Huene, 1927, for the reception of the materials previously assigned to ' Pl.' hauthali. Moreover, we found that forefin characters present a strong phylogenetic signal, highlighting the utility of these characters as a source of systematic information. • Redescription of the holotype and referred specimen of ' Platypterygius ' hauthali. • Revalidation of the genus Myobradypterygius. • We found strong phylogenetic signal in the ichthyosaurian forefin. [ABSTRACT FROM AUTHOR]

Abstract: Ichthyosaurs are widespread in Mesozoic marine sequences. The marginal marine to terrestrial strata of the Cretaceous Purbeck Limestone Group of Dorset are an unlikely source for the remains of such animals. A specimen in the collections of the Oxford University Museum of Natural History, acquired in the nineteenth century, is recorded as collected from these strata. Despite the suggestion that this specimen might represent a relict taxon of a much earlier lineage in the evolution of ichthyosaurs [Delair, J.B., 1969. The first record of the occurrence of ichthyosaurs in the Purbeck. Proceedings of the Dorset Natural History & Archaeological Society 90, 128–132], its age and source have not been questioned. A comprehensive investigation of the matrix, including a palynological study, confirms a Purbeck Limestone Group origin for the specimen. Reassessment of the preserved postcranial skeleton provides evidence that the specimen, though strictly indeterminate, is consistent with attribution to a juvenile of an ophthalmosaurid such as Brachypterygius. The ‘notched’ phalanx previously considered to be ‘primitive’ is an artefact of damage to the specimen, either as the slab broke away from the cliff or shore, or during collection and subsequent preparation. [Copyright &y& Elsevier]

One of the most significant morphological modifications in numerous tetrapod lineages in their secondary adaptation to life in open marine environment is the transformation of the limb into fins. The loss of perichondral bone has been pointed out as the mechanism through which this transformation was achieved. Advanced ichthyosaurs, including ophthalmosaurids, are characterized by the zeugopodium and autopodium not clearly differentiated, and bones dorsoventrally flattened and nodular. In the case of distal limb elements, particularly phalanges, two main arrangements can be recognized in dorsal and ventral views: one is characterized by spaced and quite rounded elements, whereas in the other phalanges tightly packed arrangement is observed, showing almost straight articular surfaces which result in polygonal outlines. Previously only distal limb elements of non-ophthalmosaurids, were described. In this study, we describe and interpret the microstructure of distal limb elements of six specimens of ichthyosaur, five ophthalmosaurids and one non-ophthalmosaurid. Our result shows persistence of abundant cartilage in articular and non-articular surfaces (with exception of the dorsal and ventral surfaces) independently of ontogenetic stage and shape. The coat layer of calcified cartilage is thicker in juvenile than adult specimens and this could be related to the bone remodeling. It is probable that the persistence of significant amount of cartilage in the joint surfaces of the distal limb elements of ichthyosaurs would be linked to more evenly distribute forces through the limb, the increase in the number of articulations and the increase maneuverability during swimming. • First report of distal limb elements microstructure and paleohistology in Ophthalmosaurids. • Presence of abundant cartilage in articular and non-articular surfaces of the phalanges independently of ontogenetic age and shape. • The loss of perichondral tissue is not related to the shape of the distal limb elements. [ABSTRACT FROM AUTHOR]