The Postcranial Skeleton of Lanthanotus borneensis (Reptilia, Lacertilia)

The Postcranial Skeleton of Lanthanotus borneensis (Reptilia, Lacertilia) Olivier Rieppel Paläontologisches Institut und Museum der Universität, Künstlergasse 16, CH-8006 Zürich, Switzerland Abstract. The postcranial skeleton of Lanthanotus borneensis is described and compared to that of Heloderma and Varanus. In an evolutionary sense, Lathanotus is intermediate in structure between Heloderma showing relatively primitive and Varanus showing relatively advanced character states. This conclusion is well supported by the structure of the tarsus. Cladistically, Lanthanotus is the sister-taxon of Varanus, the two lineages together forming the sister-taxon of Heloderma, a conclusion based on the distribution of shared derived characters. Introduction Lanthanotus borneensis is still a poorly known lizard from the Sarawak region of Borneo. Until very recently it has been represented by few specimens only in museum collections, but by now a fair number has accumulated. The first specimens of Lanthanotus to be known have been classified with the Helodermatidae by BOULEN- GER (1885, 1899) and CAMP (1923). The status of Lanthanotus has been extensively reviewed by McDOWELL and BOGERT (1954) who concluded, in contrast to BOULEN- GER and CAMP, that "Lanthanotus is not a primitive pre-platynotan intermediate between the Helodermatidae and the Varanidae, but rather is an advanced and specialised platynotan lizard ... " (pg. 75). They concluded that Lanthanotus is related to the fossil Aigialosauridae and Dolichosauridae (c. f. also McDOWELL, 1972). More recently, RUSSELL (1967) pointed out that Lanthanotus is most closely related to the Saniwinae, an extinct subfamily of the Varanidae. A recent re-investigation of the head anatomy of Lanthanotus led me to the view (RIEPPEL, 1980) that Lanthanotus is certainly more primitive than the Saniwinae and cannot be classified with this group. The Aigialosauridae and the Dolichosauridae are probably more closely related to the varanoid lineage of platynotan lizards sensu NOPCSA (1903) than to Lanthanotus or Heloderma. In an evolutionary sense, Lanthanotus is intermediate in structure between Heloderma and Varanus. In a cladistic sense, Lanthanotus proved to be the sister-group of the Varanidae among extant Platynota.