Aim To integrate ecological fitting, the oscillation hypothesis and the taxon pulse hypothesis into a coherent null model for the evolution of complex host–parasite associations. Location Global. Methods This paper reviews and synthesizes literature that focuses on phylogenetic analyses and reciprocal mapping of a model system of hosts and their parasites to determine patterns of host–parasite associations and geographical distributions through time.

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A macroevolutionary mosaic: episodic host-switching, geographical colonization and diversification in complex host-parasite systems

The evolution of Metriorhynchoidea (mesoeucrocodylia, thalattosuchia): an integrated approach using geometric morphometrics, analysis of disparity, and biomechanics

Reptiles constitute a primarily terrestrial assemblage, but several groups returned to the marine environment after the first appearance of reptiles in the late Palaeozoic era1 Successful diversification of the chelonioid sea turtles, particularly during the Cretaceous period, was perhaps one of the most important events in the history of turtles (and marine reptiles)2,3,4 The fossil record of chelonioids before the Late Cretaceous has been poorly documented Here I report the discovery of an exceptionally well-preserved skeleton of the oldest known chelonioid, from the Early Cretaceous stage (about 110 million years before the present)5,6,7 of eastern Brazil This specimen represents a new taxon, extending the history of chelonioids by 10 million years, and it sheds new light on the early evolution of the group The limb of the specimen is a relatively primitive paddle, which still possesses movable digits as in freshwater turtles However, the skull is specialized in the manner of later chelonioids, with large interorbital foramina that are indicative of huge lachrymal salt glands surrounding the eyes8,9 This discovery supports the idea that the establishment of the salt-excreting system, and the occupation of a marine habitat, may have preceded the formation of rigid paddles in the history of chelonioids

Oldest known sea turtle

Mass extinctions have played many evolutionary roles, involving differential survivorship or selectivity of taxa and traits, the disruption or preservation of evolutionary trends and ecosystem organization, and the promotion of taxonomic and morphological diversifications— often along unexpected trajectories—after the destruction or marginalization of once-dominant clades. The fossil record suggests that survivorship during mass extinctions is not strictly random, but it often fails to coincide with factors promoting survival during times of low extinction intensity. Although of very serious concern, present-day extinctions have not yet achieved the intensities seen in the Big Five mass extinctions of the geologic past, which each removed >50% of the subset of relatively abundant marine invertebrate genera. The best comparisons for predictive purposes therefore will involve factors such as differential extinction intensities among regions, clades, and functional groups, rules governing postextinction biotic interchanges and evolutionary dynamics, and analyses of the factors that cause taxa and evolutionary trends to continue unabated, to suffer setbacks but resume along the same trajectory, to survive only to fall into a marginal role or disappear (‘‘dead clade walking’’), or to undergo a burst of diversification. These issues need to be addressed in a spatially explicit framework, because the fossil record suggests regional differences in postextinction diversification dynamics and biotic interchanges. Postextinction diversifications lag far behind the initial taxonomic and morphological impoverishment and homogenization; they do not simply reoccupy vacated adaptive peaks, but explore opportunities as opened and constrained by intrinsic biotic factors and the ecological and evolutionary context of the radiation.

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Lessons from the past: Evolutionary impacts of mass extinctions

The poorly-known, long bodied, limb-reduced marine lizard Adriosaurus suessi Seeley, 1881, is reassessed. Adriosaurus and a number of other marine lizards are known from Upper Cretaceous (Upper Cenomanian-Lower Turonian) marine carbonate rocks exposed along the Dalmatian coast of the Adriatic Sea, from Komen, Slovenia, to Hvar Island, Croatia. A revised vertebral count reveals 10 cervical, 29 dorsal, and at least 65 caudal vertebrae. The projections previously interpreted as hypapophyses are instead transverse processes. Openings on the anterior part of the skull, previously described as external nares, are probably internal nares. Important features not noted previously include accessory articulations on all presacral vertebrae, pachyostosis of dorsal vertebrae and ribs, and the presence of two pygal vertebrae. Phylogenetic analysis of 258 osteological characters and all the major squamate lineages suggests that Adriosaurus and dolichosaurs are successive sister-taxa to snakes. This is consistent with their long-bodied, limb-reduced morphology being intermediate between typical marine squamates (e.g., mosasaurs) and primitive marine snakes (pachyophiids). The analysis further reveals that up to five successive outgroups to living snakes (pachyophiids, Adriosaurus, dolichosaurs, Aphanizocnemus, and mosasauroids) are all marine, suggesting a marine (or at least, semi-aquatic) phase in snake origins. These phylogenetic results are robust whether multistate characters are ordered or unordered, thus refuting recent suggestions that snakes cluster with amphisbaenians and dibamids (rather than aquatic lizards) if multistate characters are left unordered. Also, the recent suggestion that Pachyrhachis shares synapomorphies with advanced snakes (macrostomatans) is shown to be poorly supported, because the reinterpretations of the relevant skull elements are unlikely and, even if accepted, the character states proposed to unite Pachyrhachis and advanced snakes are also present in more basal snakes and/or the nearest lizard outgroups, and are consequently primitive for snakes.

Adriosaurus and the affinities of mosasaurs, dolichosaurs, and snakes

M.A. Taylor, Foreword. Ichthyosauria: J.M. Callaway, Introduction. P.M. Sander, The paleobiogeography of Shastasaurus. J.M. Callaway, A New Look at Mixosaurus. C. McGowan, A Transitional Ichthyosaur Fauna. R. Motani, Temporal and Spatial Distribution of Tooth Implantation in Ichthyosaurs. Sauropterygia: O.C. Rieppel, Introduction. O.C. Rieppel and H. Hagdorn, Paleobiology of Middle Triassic Sauropterygia in Central and Western Europe. G.W. Storrs, Morphologic and Taxonomic Clarification of the Genus Plesiosaurus. K. Carpenter, Comparative Cranial Anatomy of Two North American Cretaceous Plesiosaurs. Testudines: E.L. Nicholls, Introduction. R. Hirayama, Distribution and Diversity of Cretaceous Chelonoids. D.K. Elliott, G.V. Irby, and J.H. Hutchison, Desmatochelys Iowa, a Marine Turtle from the Upper Cretaceous. R.T.J. Moody, The Paleogeography of Marine and Coastal Turtles of the North Atlantic and Trans-Saharan Regions. Mosasauridae: G.L. Bell, Jr., Introduction. G.L. Bell, Jr., Phylogenetic Revision of North American and Adriatic Mosasauridea. A. Sheldon, Ecological Implications of Mosasaur Bone Microstructure. Crocodylia: S. Hua and E. Buffetaut, Introduction. R.K. Denton, Jr., J.L. Dobie, and D.C. Parris, The Marine Crocodile, Hyposaurus, in North America. Faunas, Behavior, and Evolution: J.A. Massare, Introduction. S.G. Lucas, Marine Reptiles and Mesozoic Biochronology. Z. Gasparini and M. Fernandez, Tithonian Marine Reptiles of the Eastern Pacific. R. Collin and C.M. Janis, Morphological Constraints on Tetropod Feeding Mechanisms: Why Were There No Suspenion-Feeding Marine Reptiles? R.L. Carroll, Mesozoic Marine Reptiles as Models of Long Term, Large-Scale Evolutionary Phenomena. Subject Index.

J. M. Calloway

Papers

Ancient marine reptiles