Morphology of the nasal capsule of Heloderma suspectum with comments on the systematic position of helodermatids (Squamata: Helodermatidae)

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Abstract:

A serially sectioned embryonic head of Heloderma suspectum formed the basis for a three-dimensional reconstruction of the cartilaginous nasal capsule and its membrane bones. Further, the soft parts of the nasal capsule were analysed microscopically. The embryonic nasal capsule is described and compared to the morphological conditions in other lizards, especially the varanids, which many recent authors believe to be their closest relatives.

The results support the close affinities between the helodermatids and the varanids. Both groups have a well developed recessus lateralis in a cartilaginous capsule, entered by the nasal concha. Further, in both groups a fragmentation of the cartilago paraseptalis occurs in a comparable location and form. Heloderma has no double lacrimal duct, in contrast to previous accounts, but the two canaliculi at the origin of the duct fuse noteworthy far ahead (in other squamates they fuse in front of the bulbus oculi). In the varanids the two branches of the lacrimal duct remain separate and open separately.

Some unique features of Heloderma are presented as well, above all the presence of a second concha.

Keywords: Heloderma suspectum; Helodermatidae; Varanoidea; morphology; nasal capsule; systematics

Document Type: Research Article

DOI: http://dx.doi.org/10.1046/j.1463-6395.1999.00020.x

Affiliations: Lehrstuhl für Spezielle Zoologie, der Universität Tübingen, Auf der Morgenstelle 28, D-72076 Tübingen, Germany

Publication date: August 1, 1999

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