Jean-Michel Mazin

Evolution and palaeobiology of pterosaurs

The first scientific description of a pterosaur was published in 1784 by Cosimo Alessandro Collini, a former secretary of Voltaire and at that time curator of the natural history cabinet of Karl Theodor, Elector of Palatinate and Bavaria. The specimen came from one of the main sources of such fossils, the Late Jurassic lithographic limestones of northern Bavaria, and Collini, after much deliberation, interpreted it as the skeleton of an unknown marine creature (Collini 1784). In 1801, Georges Cuvier, on the basis of Collini’s description and figure, identified the mysterious animal as a flying reptile (Cuvier 1801), for which he later coined the name ‘Ptero-Dactyle’ (Cuvier 1809). Cuvier’s basically correct interpretation of the ‘winged finger’ marked the beginning of the study of pterosaurs as an extinct group of flying reptiles. In the two centuries which have elapsed since those first efforts to understand what have been considered bizarre fossils, the study of pterosaurs has developed enormously. Some of the basic questions about them have long been solved: pterosaurs were neither birds, nor bats, as was suggested by various authors of the early nineteenth century, but a peculiar group of vertebrates which acquired the ability to fly in an original way, using a membrane attached to a single finger of the hand. From the few fossils from the Bavarian lithographic limestones known to Cuvier and his contemporaries, the number of pterosaur specimens has increased enormously, starting with the Early Jurassic specimens from Lyme Regis found by Mary Anning in the 1820s

Ontogenetic evolution of bone structurein Late Cretaceous Plesiosauria from New Zealand

Abstract Histological observations of homologous bones (vertebrae, ribs, humerus, phalanges) among conspecific juvenileand adult Upper Cretaceous plesiosaurs from New Zealand (elasmosaurs and pliosaurs) demonstrates a unique “ontogenetic trajectory” of skeletal histogenesis in these animals. While juveniles demonstrate a “pachyosteosclerotic” condition of the skeleton, adults have a very light “osteoporotic-like” bone structure. Until now, one or the other of these histological specializations was known among aquatic tetrapods, adapted along contrasting pathways to this environment, either by ballasting (pachyosteosclerosis; e.g. sirenians) or by lightening (osteoporotic-like adaptation: e.g. modern cetaceans) of the skeleton. The successive occurrence of these constrasting conditions during ontogenesis of a single organism had never been reported, as far as we know, but could well be an ontogenetic characteristic of Plesiosaurs sensu lato . The significance of these findings are discussed in various phylogenetical, functional and paleoecological contexts. The ontogenetic trajectory of the plesiosaur skeleton is interpreted within the general framework of developmental heterochrony. Specifically, it suggests that juvenile plesiosaurs kept a conservative (plesiomorphic) ecology for sauropterygians, as poorly mobile, lagoon or shore dwellers while, in contrast, the adults would shift towards much more active locomotory behaviors in the open sea.

Regulation of body temperature by some Mesozoic marine reptiles.

Warm-Blooded Reptiles? Existing reptiles are not thought to be endothermic, but what about extinct species? Three large extinct swimming reptiles, the ichthyosaurs, plesiosaurs, and mosasaurs, were active predators in the Mesozoic oceans. Bernard et al. (p. 1379; see the Perspective by Motani) investigated their metabolism by analyzing the oxygen isotopes in their teeth, compared with fish in deposits from a variety of ocean environments. The data imply that the ichthyosaurs and plesiosaurs, which were both pursuit predators, probably controlled their own temperature. The data for the mosasaurs, which are thought to have hunted by ambush, are more equivocal. Fast-swimming plesiosaurs, ichthyosaurs, and mesosaurs may have been able to thermoregulate. What the body temperature and thermoregulation processes of extinct vertebrates were are central questions for understanding their ecology and evolution. The thermophysiologic status of the great marine reptiles is still unknown, even though some studies have suggested that thermoregulation may have contributed to their exceptional evolutionary success as apex predators of Mesozoic aquatic ecosystems. We tested the thermal status of ichthyosaurs, plesiosaurs, and mosasaurs by comparing the oxygen isotope compositions of their tooth phosphate to those of coexisting fish. Data distribution reveals that these large marine reptiles were able to maintain a constant and high body temperature in oceanic environments ranging from tropical to cold temperate. Their estimated body temperatures, in the range from 35° ± 2°C to 39° ± 2°C, suggest high metabolic rates required for predation and fast swimming over large distances offshore.

Ichnological evidence for quadrupedal locomotion in pterodactyloid pterosaurs: trackways from the Late Jurassic of Crayssac (southwestern France)

Abstract More than 30 well-preserved pterosaurian trackways have been excavated from the site of Crayssac (Lower Tithonian, southwestern France), along with hundreds of isolated imprints. The general pattern of pterosaurian trackways is described and corresponds to the morphology of the ichnogenus Pteraichnus Stokes 1957. A crocodilian origin for Pteraichnus is rejected. The morphology of the pes and manus prints is described and discussed, and exhibits a great dynamic variability. The three manus digit prints are confirmed as the marks of digits I–III, but the high angle of divarication may reflect strong digit abduction as well as a backward folding of the digit III. The manus gait-width is as much as 3 × the pes gait-width. The narrowest manus trackways corresponds to low-velocity walking in a semi-erect stance, whereas the widest manus trackways corresponds to higher velocity walking (perhaps even running), with a subhorizontal body.

Teeth of enigmatic neoselachian sharks and an ornithischian dinosaur from the uppermost Triassic of Lons-le-Saunier (Jura, France)

KurzfassungVon einer neuen rhätischen Fundstelle bei Lons-le-Saunier (Jura, Frankreich) werden Zähne von Haien und einem Dinosaurier der Ordnung Ornithischia beschrieben. Die stratigraphische Einordnung der Fundstelle basiert auf palynologischen Daten. Die Struktur des Enameloides vonSynechodus rhaeticus wird beschrieben; sie unterscheidet sich deutlich von jener der Neoselachier, wodurch die systematische Zuordnung dieser Art erschwert wird. ‘Hybodus’minor wird zu den Synechodontiformes gestellt. Ornithischier sind aus der neuen Fundstelle durch einen Zahn nachgewiesen. Die Befunde von Lons-le-Saunier deuten auf einen Faunenwechsel im marinen Bereich während der Rhät-Transgression hin, wobei besonders die Neoselachier sowie die durophagen Actinopterygier, letztere überwiegend mit der ArtSargodon tomicus, deutlich häufiger werden.AbstractShark teeth and an ornithischian dinosaur tooth are described from a new palynologically dated Rhaetian locality at Lons-le-Saunier (Jura, France). The structure of the enameloid of the teeth ofSynechodus rhaeticus has been studied, but this appears quite different from the usual pattern seen in neoselachian sharks, making the precise relationships of this species difficult to determine. On the other hand,‘Hybodus’ minor, which has long be thought to be a hybodont shark, is included among the Synechodontiformes. The find of the tooth of an ornithischian dinosaur is also reported. Study of the Lonsle-Saunier site seems to indicate a change in the marine faunas during the Rhaetian transgression, preferentially affecting the neoselachian sharks, which increase in abundance, and thedurophasous bony fishes, which become dominated bySareodon tomicus.

The systematic problem of tetrapod ichnotaxa: the case study of Pteraichnus Stokes, 1957 (Pterosauria, Pterodactyloidea)

Abstract This paper deals with the systematics of tetrapod ichnotaxa based on footprints. Beyond the consideration of the nomenclatural rules for ichnotaxa in the ICZN, this paper tries to determine how to establish an ichnotaxonomy that reflects the identity of the track-maker (the organism that has made the track) and how to include this ichnotaxonomy in the skeleton-based taxonomy. This leads to the establishment of several criteria, e.g. ichnospecies should be defined on the print morphology and the relative position of the prints (including the variability due to the track-maker’s dynamics), two ichnospecies should represent different species, the ichnospecies and ichnogenus levels are sufficient to discriminate the ichnotaxa and link them to the skeleton-based taxonomy. These ichnotaxonomical criteria are applied to a revision of the ichnogenus Pteraichnus Stokes 1957 (Pterosauria, Pterodactyloidea). Only the type species Pteraichnus saltwashensis is considered as valid, the pterosaurian origin of Purbeckopus is questioned and Agadirichnus is highlighted because it could be a senior synonym of Pteraichnus. The result of this drastic revision underlines the importance of the proposed ichnotaxonomical principles to avoid the unfounded proliferation of tetrapod ichnotaxa.

A new neoselachian shark from the Upper Triassic of Grozon (Jura, France)

Two successive assemblages of vertebrate microremains have been found at Grozon (Jura, northeastern France). Palynological analysis confirms a Norian age for the first one and a Rhaetian age for the second. A new species of neoselachian shark, Grozonodon candaui, is erected from isolated teeth of Norian age, based on their enameloid ultrastructure. Distinctive parallel-fibred enameloid is recognized among teeth previously assigned to Hybodus minor, which therefore represents another early neoselachian shark. These structural characteristics confirm the close relationship of hybodont and neoselachian sharks.

Le gisement de Crayssac (Tithonien inférieur, Quercy, Lot, France) : découverte de pistes de dinosaures en place et premier bilan ichnologique

The Tithonian limestones of Crayssac (Lot, Quercy, Southwestern France) correspond to a large littoral mud-flat with sedimentation in the inter- to supratidal area where continental and marine influences alternate. Vertebrate and invertebrate ichnites are abundant, among which pterosaurian and dinosaurian prints are the most common.

First record of a pterosaur landing trackway

The terrestrial progression of pterosaurs, the flying reptiles of the Mesozoic Era, has been debated for over two centuries. The recent discovery of quadrupedal pterodactyloid pterosaur tracks from Late Jurassic sediments near Crayssac, France, shows that the hindlimbs moved parasagittally, as in mammals, birds and other dinosaurs, and the hypertrophied forelimbs could make tracks both close to the body wall and far outside it. Their manus tracks are unique in form, position and kinematics, which would be expected because the forelimbs were used for flight. Here, we report the first record of a pterosaur landing track, which differs substantially from typical walking trackways. The individual landed on both hind feet in parallel fashion, dragged its toes slightly as it left the track, landed again almost immediately and placed the hindfeet parallel again, then placed its forelimbs on the ground, took another short step with both hindlimbs and adjusted its forelimbs, and then began to walk off normally. The trackway shows that pterosaurs stalled to land, a reflection of their highly developed capacity for flight control and manoeuverability.

Speciation along rifting continental margins: a new Nothosaur from the Negev (Israël)

Abstract Middle Triassic Muschelkalk deposits in the Negev (Israel) yielded two endemic species of the sauropterygian reptile genus Nothosaurus, one of which is new. These two species of nothosaurs from the Nahal Ramon Basin provide evidence for cladogenesis in a newly opened habitat with resource partitioning between the daughter species. The two Nahal Ramon species are sister-taxa, and jointly they form the sister-clade of Nothosaurus mirabilis from the Germanic Muschelkalk. Cladistic analysis of nothosaur interrelationships supports the hypothesis of a Burgundy Gate, linking the Germanic Basin with the developing Neotethys during late Anisian and Ladinian times.