Skeletons of the Little-Known Palawan Monitor, Varanus palawanensis (Squamata: Varanidae)
Varanus (Soterosaurus) monitors recently received increased scrutiny from herpetologists, resulting in identification of previously unrecognized morphologic and genetic diversity. These advances rendered Varanus salvator salvator as one of the most narrowly distributed monitors, because most populations are reassigned to existing or newly identified species. No diagnostic skeletal characters are known for those species. Two skeletonized specimens of the recently named Varanus palawanensis are in the collection of the U.S. National Museum of Natural History, but are labeled V. salvator. Here, I offer some observations on those skeletons, make comparisons with some other Varanus(Soterosaurus) monitors, and update the diagnosis of the species with some probable osteological autapomorphies. Varanus palawanensis differs from other Varanus (Soterosaurus) in possessing a unique combination of character states. The premaxilla extends to the level of the frontal, the frontal and parietal lack dermal sculpturing, the lacrimal anteroposteriorly narrow, the vidian canal entirely within the parabasisphenoid, and the anterostapedial process is tab-like. I contend that species should be holophyletic even in the face of taxonomic upheavals created by newly identified diversity.Abstract
Two specimens of Varanus palawanensis. (A) Skin (USNM R 216258) in dorsal view. (B) Skull and mandible in right lateral view (USNM R 287381). (C) Braincase (USNM R 287381) in right lateral view. Appendicular skeletal elements: sternum, clavicle, and interclavicle (USNM R 287381) in ventral view (D); right scapulocoracoid (E); and left pelvis in lateral views (USNM 216258) (F). a, angular; acet, acetabulum; apr, anterior iliac process; bpt, basipterygoid; c, coronoid; cl, clavicle; co, coracoid; d, dentary; e, epipterygoid; ec, ectopterygoid; f, frontal; fo, fenestra ovalus; gl, glenoid; icl, interclavicle; il, ilium; is, ischium; j, jugal; l, lacrimal; m, maxilla; obf, obturator foramen; oo, otooccipital; p, pubis; pm, premaxilla; pra, prearticular; prf, prefrontal; pro, prootic; pvc, posterior opening of the vidian canal; q, quadrate; sa, surangular; sc, scapula; sq, squamosal; st, sternum; thf, thyroid fenestra; 1pc, primary coracoid emargination; and 2pc, secondary coracoid emargination. Scale bars = 10 mm.
Comparative osteology and phylogenetics of selected Varanus. (A) Simplified Varanus (Soterosaurus) cladogram derived from data published by Welton (2012). Illustrated terminal groups are highlighted with asterisks (*). (B–C) Comparisons between the skull of some Varanus (Soterosaurus) and an outgroup (V. griseus). (B) Highlight of the relative dimensions of the skulls in (C), with the premaxilla (red), nasal (blue), and frontals (green) highlighted. Dotted lines show the posterior tip of the premaxilla, posterior tip of the nasal, and anterior tip of the frontal. Note that, among illustrated taxa, V. palawanensis is unusual in that the premaxillary and frontal morphology and that the entire snout is posteriorly shifted. A purple dotted line connects the illustrations in (C) with their corresponding photos in (B), and purple text is used to indicate the taxa from (A) illustrated in (B) and (C). Scale bars = 10 mm.
Skull of Varanus marmoratus marmoratus (USNM R 498916) in right lateral view. (A) Entire skull. (B) Detail of the braincase illustrating the hooklike anterostapedial process of the prootic crest. c, coronoid; cal, alar crest of the prootic; cpr, prootic crest (highlighting the anterostapedial process); d, dentary; f, frontal; l, lacrimal; m, maxilla; pm, premaxilla; pra, prearticular; prf, prefrontal; and sa, surangular. Scale bars = 10 mm.
