An evolutionary and developmental perspective on the loss of regionalization in the limbs of derived ichthyosaurs

  title={An evolutionary and developmental perspective on the loss of regionalization in the limbs of derived ichthyosaurs},
  author={Erin E. Maxwell and Torsten M. Scheyer and Donald A Fowler},
  journal={Geological Magazine},
  pages={29 - 40}
Abstract Ichthyosaurs, a lineage of extinct Mesozoic marine reptiles, have garnered attention in both the palaeontological and developmental literature for the unique limb morphology seen in derived genera. These morphologies include an increase in the number of phalanges per digit (hyperphalangy) and in the number of digits (hyperdactyly), but most interestingly also a shift in element identity. Elements distal to the stylopodium acquire characteristics of mesopodial elements, such as a… 

Skeletal microstructure of Stenopterygius quadriscissus (Reptilia, Ichthyosauria) from the Posidonienschiefer (Posidonia Shale, Lower Jurassic) of Germany

Ichthyosaurians (Ichthyosauria) are a major clade of secondarily aquatic marine tetrapods that occupied several major predatory niches during the Mesozoic Era. Multiple lines of evidence including

Ontogeny of the Braincase in Stenopterygius (Reptilia, Ichthyosauria) from the Lower Jurassic of Germany

The morphology of the braincase elements of Stenopterygius over ontogeny is described and compared with that of other known ichthyosaur braincases and variability in relative braincase ossification between embryos within a single gravid female is observed.

A New Look at Ichthyosaur Long Bone Microanatomy and Histology: Implications for Their Adaptation to an Aquatic Life

The occurrence of two types of remodelling patterns along the diaphysis, characterized by bone mass decrease and increase respectively is described for the first time and raises questions about the definition of the osseous microanatomical specializations bone mass increase and osteoporosis, notably based on the processes involved.

Catutosaurus gaspariniae, gen. et sp. nov. (Ichthyosauria, Thunnosauria) of the Upper Jurassic of Patagonia and the Evolution of the Ophthalmosaurids

ABSTRACT Thunnosaurian ichthyosaurs were one of the most successful lineages of Mesozoic tetrapods in terms of adaptation to a pelagic lifestyle. Among them, the ophthalmosaurids are of particular

How the pterosaur got its wings

  • Masayoshi Tokita
  • Biology
    Biological reviews of the Cambridge Philosophical Society
  • 2015
Developmental data now accumulating for extant vertebrate taxa could be helpful in understanding the cellular and molecular mechanisms of body‐plan evolution in extinct vertebrates as well as extant vertebrates with unique morphology whose embryonic materials are hard to obtain.

A New Specimen of Ichthyosaurus conybeari (Reptilia, Ichthyosauria) from Watchet, Somerset, England, U.K., and a Reexamination of the Species

A revised diagnosis recognizes new morphological characters that distinguish the species: slender maxilla with a long, delicate premaxillary process; narrow postorbital; humerus with an anteriorly offset dorsal process that has a well-defined lip extending slightly into the shaft.

A revision of the Early Jurassic ichthyosaur Hauffiopteryx (Reptilia: Ichthyosauria), and description of a new species from southwestern Germany

It is concluded that Hauffiopteryx represents a valid genus, defined by a set of synapomorphies from both the skull and postcranium, and recovered as sister taxon to Stenopterygius + Ophthalmosauridae.

Hindfins of Ichthyosaurus: effects of large sample size on ‘distinct’ morphological characters

In Ichthyosaurus, the hindfin is taxonomically useful at the genus level, but species cannot be identified unequivocally from a well-preserved hindfin, although certain morphologies are more common in certain species than others.

New perspectives on ancient marine reptiles

  • B. KearG. Budd
  • Environmental Science, Geography
    Geological Magazine
  • 2013
Amniotes first invaded saline lagoons and coastal seaways towards the end of the Palaeozoic (Early Permian, ~ 280 Ma: Piñeiro et al. 2012), but by the dawn of the Mesozoic (Early–Middle Triassic, ~



Unraveling the influences of soft-tissue flipper development on skeletal variation using an extinct taxon.

  • E. Maxwell
  • Environmental Science, Biology
    Journal of experimental zoology. Part B, Molecular and developmental evolution
  • 2012
The results suggest that while the flipper structure and processes resulting in hyperphalangy may increase observed variation in phalangeal counts, these factors are unlikely to be causing high levels of qualitative variation in ichthyosaurs.

Homeotic effects, somitogenesis and the evolution of vertebral numbers in recent and fossil amniotes

It is shown that the mammalian (synapsid) and reptilian lineages show early in their evolutionary histories clear divergences in axial developmental plasticity, in terms of both regionalization and meristic change, with basal synapsids sharing the conserved axial configuration of crown mammals, and basal reptiles demonstrating the plasticity of extant taxa.

Patterns of ossification in the manus of the harbor porpoise (Phocoena phocoena): Hyperphalangy and delta‐shaped bones

  • S. D. Dawson
  • Biology, Environmental Science
    Journal of morphology
  • 2003
Examination of the ontogenetic pattern of ossification of the manus of the harbor porpoise finds delta‐shaped bones in the cetacean manus display a consistent orientation and the process by which they are formed may be similar to that in extinct marine reptiles.


The evolution of forefins within the Ichthyopterygia is re-evaluated based on the largest set of data available up to present, including recently reported Early Triassic forms, and it is concluded that StenopteryGius, and all other ichthyoperygians belonging to the clade that survived into the Jurassic, lack digit I of the forelimb.

Perspectives on hyperphalangy: patterns and processes

Factors of the limb‐patterning pathways located in the interdigital mesoderm, including bone morphogenetic proteins (BMPs), BMP antagonists, fibroblast growth factors (FGFs), growth/differentiation factor‐5 (GDF‐5), Wnt‐14 and ck‐erg, are implicated in maintenance of the flipper limb, secondary AER formation, digit elongation and additional joint induction leading to hyperphalangy.

Limb ossification patterns of the ichthyosaur Stenopterygius, and a discussion of the proximal tarsal row of ichthyosaurs and other neodiapsid reptiles

Abstract Limb ossification patterns for the Lower Jurassic (Toarcian) ichthyosaur, Stenopterygius , are described. It is found that limb ossification follows a continuous proximal to distal sequence

Ontogenetic and stratigraphic influence on observed phenotypic integration in the limb skeleton of a fossil tetrapod

Examining limb integration in the Lower Jurassic ichthyosaur Stenopterygius quadriscissus concludes that if samples are pooled, the resulting pattern of integration may not reflect any one subsample but will be a composite created through the superposition of several variables.

Modified perichondral ossification and the evolution of paddle-like limbs in ichthyosaurs and plesiosaurs

Evolution of paddle-like limbs in ichthyosaurs and plesiosaurs is correlated with loss of perichondral bone from the shafts of long bones, and Evolutionary changes to the ossification of perICHondral tissues appear to affect the sequence of limb Ossification as long bones lose perichONDral bone.

Adaptive evolution of 5'HoxD genes in the origin and diversification of the cetacean flipper.

The authors' results strongly implicate 5'HoxD genes in the modulation of digit number, web forming, and the high morphological diversity of the cetacean manus.