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Keywords:

  • jaw muscles;
  • comparative myology;
  • phylogenetics;
  • Lacertilia;
  • Teiidae

The trigeminal jaw adductor musculature of Tupinambis is described in detail and compared to that of other teiids and other scincomorph lizards. A hypothesis of the phylogenetic relationships of scincomorph lizards is put forward on the basis of shared derived characters of the jaw adductor musculature. Extensive parallel evolution is inferred in the jaw adductor musculature of teiids and of Varanus, a platynotan lizard. Teiids share only primitive characters of the jaw adductors with iguanids. It appears from this study that the jaw adductor musculature provides useful information on the phylogenetic relationships of lizards at the subfamilial and familial level within infraorders. Parallel evolution appears to have been extensive in the differentiation of jaw adductors in lizards of different infraorders.

Summary

Investigation of the trigeminal jaw adductor musculature of scincomorph lizards reveals a number of muscular characteristics, the primitive (plesiomorph) or derived (apomorph) status of which can be evaluated reasonably well. The main characteristics which prove useful in the discussion of phylogenetic relationships derive from the structure of the levator anguli oris muscle and the bodenaponeurosis, from the origin of various muscles along the mesial margin of the upper temporal fossa and from the structure of the posterior adductor. Further investigation of lizard jaw adductors may provide the basis for the evaluation of additional characters derived from the pseudotemporalis profundus muscle and from the internus dorsalis complex. On the other hand, the quadrate aponeurosis appears to be too variable to be useful in discussion of phylogenetic relationships at the familial level.

The muscular characters used in the present study allow subdivision of the Scincomorpha into two sister-groups, a teiid-lacertid assemblage and a cor-dylid-scincid assemblage. Within the teiid-lacertid assemblage, the Lacertidae are the sister-group of the Teiidae. The Cordylidae appear to be the sister-group of the Scincidae, but further investigation is necessary to resolve the phylogenetic status of the Scincidae.

Although the teiid-lacertid assemblage shares a number of derived characters with the genus Varanus and at least one derived feature with some agamids, it has to be admitted that features of the trigeminal jaw adductor musculature of lizards may not form a reliable basis for investigation of phylogenetic relationships across the boundaries of the infraorders of lizards. This is due to die possibility of extensive parallelism, as becomes evident in a comparison of the Teiidae with Varanus and other platynotan lizards. The trigeminal jaw adductor musculature proves to be a very useful indicator of phylogenetic relationships within the lizard infraorders, however.