The mixosaurid ichthyosaur Contectopalatus from the Middle Triassic of the German Basin

The skull of the mixosaurid species Contectopalatus atavus (Quenstedt, 1851-52) is the most bizarre of any known ichthyosaur. It possesses a very high sagittal crest formed by the nasal, frontal and parietal bones which grows higher during ontogeny. This skull structure - found to a lesser extent in the other mixosaurid genera Mixosaurus and Phalarodon - is a synapomorphy of the family Mixosauridae. It is here interpreted as correlated with a unique arrangement of the jaw adductor musculature among tetrapods, with the internal jaw adductors extending over most of the skull roof up to the external narial opening. This reconstruction would increase the biting force considerably and the hypothesis is supported by peculiarities of the dentition and jaws of Contectopalatus. Contectopalatus probably reached a length of about 5 meters. It is therefore the largest known mixosaurid and one of the largest Triassic ichthyosaurs. The general text-book picture of mixosaurs as small, rather unspecialized, primitive ichthyosaurs is incorrect. Mixosaurs were a highly specialized, uniquely adapted and very diverse ichthyosaur family, some members of which rank among the marine top predators of their time.     

The phylogenetic relationships within the Chamaeleonidae, with comments on some aspects of cladistic analysis

The phylogenetic relationships of the African mainland species of the genus Rhampholeon (formerly referred to the genus Brookesia ) with respect to Brookesia superciliaris, Bradypodion pumilus , and the genus Chamaeleo are analysed. Rhampholeon constitutes a genus well separated from Brookesia and may itself be subdivided in two subgroups on the basis of characters derived from the nasal and parietal complexes. A final section investigates problems of cladistic analysis, viz. the relationship of parsimony to character weighting, and pattern versus process as complementary perspectives of character analysis and coding.     

The structure of the skull and jaw adductor musculature in the Gekkota, with comments on the phylogenetic relationships of the Xantusiidae (Reptilia: Lacertilia)

The skull and trigeminal jaw adductor musculature of the lizard families Gekkonidae, Pygopodidae and Xantusiidae are described. The external jaw adductor shows a different structure in the Gekkonidae and Pygopodidae than is observed in other lizards, approached only by the Xantusiidae and Feyliniidae. Paedomorphosis seems to be involved in the differentiation of the jaw adductor musculature in the Gekkonidae. The Gekkonidae and Pygopodidae may be hypothesized to form a monophyletic group, the Gekkota, on the basis of numerous synapomorphies. Within the Gekkota, the Pygopodidae are the sister-group of the Gekkonidae and retain some plesiomorphous features which are absent in the latter. The Xantusiidae share few synapomorphies with the Gekkota on the one hand, and some with scincomorph lizards on the other, especially with the Lacertidae.     

The skull and jaw musculature as guides to the ancestry of salamanders

The fossil record provides no evidence supporting a unique common ancestry for frogs, salamanders and apodans. The ancestors of the modern orders may have diverged from one another as recently as 250 million years ago, or as long ago as 400 million years according to current theories of various authors. In order to evaluate the evolutionary patterns of the modern orders it is necessary to determine whether their last common ancestor was a rhipidistian fish, a very primitive amphibian, a labyrimhodom or a ‘lissamphibian’. The broad cranial similarities of frogs and salamanders, especially the dominance of the braincase as a supporting element, can be associated with the small size of the skull in their immediate ancestors. Hynobiids show the most primitive cranial pattern known among the living salamander families and “provide a model for determining the nature of the ancestors of the entire order. Features expected in ancestral salamanders include: (1) Emargination of the cheek; (2) Movable suspensorium formed by the quadrate, squamosal and pterygoid; (3) Occipital condyle posterior to jaw articulation; (4) Distinct prootic and opisthotic; (5) Absence ol otic notch; (6) Stapes forming a structural link between braincase and cheek. In the otic region, cheek and jaw suspension, the primitive salamander pattern (resembles most closely the microsaurs among known Paleozoic amphibians, and shows no significant features in common with either ancestral frogs or the majority of labyrinth odonts. The basic pattern of the adductor jaw musculature is consistent within both frogs and salamanders, but major differences are evident between the two groups. The dominance of the adductor mandibulae externus in salamanders can be associated with the open cheek in all members of that order, and the small size of this muscle in frogs can be associated with the large otic notch. The spread of different muscles over the otic capsule, the longus head ol the adductor mandibulae posterior in frogs and the superficial head of the adductor mandibulae internus in salamanders, indicates that fenestration of the skull posterodorsal to the orbit occurred separately in the ancestors of the two groups. Reconstruction of the probable pattern of the jaw musculature in Paleozoic amphibians indicates that frogs and salamanders might have evolved from a condition hypothesized for primitive labyrinthodonts, but the presence of a large otic notch in dissorophids suggests specialization toward the anuran, not the urodele condition. The presence of either an einarginated cheek or an embayment of the lateral surface of the dentary and the absence of an otic notch in microsaurs indicate a salamander-like distribution of die adductor jaw muscles. The ancestors of frogs and salamanders probably diverged from one another in the early Carboniferous, Frogs later evolved from small labyrinthodonts and salamanders from microsaurs. Features considered typical of lissamphibians evolved separately in the two groups in the late Permian andTriassic.