Rheosaurus, 2020

Vásquez-Restrepo, Juan D., Ibáñez, Roberto, Sánchez-Pacheco, Santiago J. & Daza, Juan M., 2020, Phylogeny, taxonomy and distribution of the Neotropical lizard genus Echinosaura (Squamata: Gymnophthalmidae), with the recognition of two new genera in Cercosaurinae, Zoological Journal of the Linnean Society 189, pp. 287-314 : 300

RHEOSAURUS VÁSQUEZ-RESTREPO ET AL. , GEN. NOV.

Type species: Echinosaura sulcarostrum Donnelly et al., 2006 .

LSID: urn:lsid:zoobank.org:act:A7C758C4-CD77-4CCF-BF4B-79C1D1A1C854

Content: One species: Rheosaurus sulcarostrum ( Donnelly et al., 2006) comb. nov.

Diagnosis: Phenotypic characteristics of Rheosaurus include: (1) dorsal scales heterogeneous, with large or polygonal, longitudinally keeled scales intermixed with small irregular scales; (2) dorsal surface of the head with large, symmetrical scales; (3) internasal divided; (4) frontonasals three; (5) prefrontals paired; (6) frontal single; (7) frontoparietals paired; (8) interparietal well defined; (9) parietals paired; (10) rostral and mental striated; (11) three rows of scales between rostral and frontal scales; (12) postmental absent; (13) large chin shields in three pairs; (14) lower eyelid developed, with a palpebral disc divided into several, unpigmented scales; (15) ventral scales squared, not imbricated; (16) limbs pentadactyl, digits clawed; (17) femoral pores present in males (weakly developed) and absent in females.

Rheosaurus differs from all other cercosaurines, including Echinosaura s.s. and its sister-group, in having striated rostral and mental scales and three rows of scales between rostral and frontal scales, and in lacking a postmental scale. It also differs from other cercosaurines, except Centrosaura , Echinosaura s.s., Gelanesaurus , Neusticurus and Potamites , in having heterogeneous dorsal scalation. For comparisons among related or similar genera see Figure 9 and Table 5.

Etymology: Rheosaurus (gender masculine) is derived from the Greek ρέω, rheo (flow or stream) and σαύρα, saura (lizard), in reference to the riparian habit of this lizard.

Geographic distribution: Pantepui bioregion of the Guiana Shield, from the vicinity of the Baramita area in north-western Guyana (100 m a.s.l.) to the Wokomung massif in west-central Guyana ( Donnelly et al., 2006; Cole et al., 2013).

Remarks: Donnelly et al. (2006) tentatively allocated sulcarostrum to Echinosaura and emphasized that this generic assignment reflected convenience rather than an understanding of the phylogenetic relationships of this species. They also anticipated that its disjunct distribution with respect to other Echinosaura and the differences in external head morphology, may reflect an independent phylogenetic history.