There just haven’t been enough squamates around here lately (well, apart from the anguids). Because I have guilt, here is a good photo of a beautiful animal: a Plumed basilisk Basiliscus plumifrons. Thanks to their striking appearance, basilisks are often featured in books and on TV, but people only ever say the same two things about them: (1) that they have striking display structures like those so obvious here, and (2) that they can run (bipedally) across the surface of water. Yeah yeah, I’ve heard all that before – tell me something new, puh-lease!
I have to admit that I can’t: all the books all say the same stuff. Namely: basilisks are large green iguanians from Central and South America (they’ve also been introduced to Florida for some reason); they’re arboreal, frequenting vegetation around ponds, streams and rivers; they can run bipedally; and rectangular toe fringes allow them to run across the surface of the water for a short distance (see Glasheen & McMahon 1991, 1992). Laurie Vitt proposed (in Pianka & Vitt 2003) that the toe fringes that allow ‘water walking’ are exaptations. Their initial evolution presumably occurred because they’re advantageous amongst arboreal species, and they’ve since been co-opted by a group that – like quite a few other arboreal lizard groups – has learnt to drop into water when menaced by predators [image below from wikipedia. Photo at top courtesy Tina Whitlock].
Of the four species (Common basilisk B. basiliscus, Red-headed basilisk B. galeritus, Plumed basilisk and Striped basilisk B. vittatus), B. plumifrons is thought closest to B. basiliscus. I won’t even begin to discuss the affinities of basilisks within Iguania, as I don’t have time (see Frost et al. 2001), but they’ve generally been regarded as part of Corytophanidae, a group that includes various arboreal iguanians and may or may not be closely allied to (or part of) the clade that includes anoles. Incidentally, a group of entirely extinct iguanians from the Eocene and Oligocene of Europe and Oligocene of North America – the messelosaurines – are apparently part of Corytophanidae too (see Rossmann 1999a, b, 2005), though I’d like to see more testing of this hypothesis. Rossmann (1999a) proposed that corytophanids originated in Europe, and ended up in South America following dispersal to North America.
As for the crests… the posterior cranial crest is supported by a sheet-like bony parietal crest, and I’d like to know if there’s any bone supporting the dorsal and caudal crests. Does anyone know?
Thank you Tina, again.
Refs – –
Frost, D. R., Etheridge, R., Janies, D. & Titus, T. A. 2001. Total evidence, sequence alignment, evolution of polychrotid lizards, and a reclassification of the Iguania (Squamata: Iguania). American Museum Novitates 3343, 1-38.
Glasheen, J. W. & McMahon, T. A. 1992. A hydrodynamic model of locomotion in the basilisk lizard. Nature 380, 340-342.
– . & McMahon, T. A. 1992. An analysis of aquatic bipedalism in basilisk lizards. American Zoologist 32, 144.
Pianka, E. R. & Vitt, L. J. 2003. Lizards: Windows the Evolution of Diversity. University of California Press, Berkeley.
Rossmann, T. 1999a. Messelosaurine lacertilians (Squamata: Iguanoides) from the Palaeogene of France and North America. Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 1999, 577-592.
– . 1999b. “Crotaphytus” oligocenicus (Holman, 1972), (Squamata: Iguanoidea) from the Oligocene of Saskatchewan, reinterpretation and some paleobiogeographical implications. Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 1999, 186-192.
– . 2005. Nachtrag zur Osteologie und Palaobiologie von Geiseltaliellus longicaudus Kuhn (Lacertilia, Iguanoidea) aus dem Mittleren Eozän (MP 11) der Grube Messel, nahe Darmstadt. Courier Forschungsinstitut Senckenberg 255, 225-236.