Northern alligator lizard (Gerrhonotus coeruleus) inner ear

The skull and vertebrae of a northern alligator lizard (Gerrhonotus coeruleus, NHM 1964.1829, from Walsh et al., 2009) were scanned at 18µm resolution from a spirit-preserved whole specimen. 

Hearing sensitivity in reptiles increases with the length of the hearing organ and the cochlear duct that houses it. Species that produce vocalisations for intra- and interspecific communication are generally presumed to be capable of hearing the sounds they produce, but few reptiles other than crocodiles, alligators and geckos are capable of vocalising. 

The inner ear labyrinth of the northern alligator lizard shown here has a short, conical cochlear duct. Not surprisingly, this species has not been observed to vocalise. 

Although the hearing sensitivity of this species has not been tested, the closely related Gerrhonotus multicarinatus has a relatively narrow hearing range of 600-3000Hz.

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