Hydrosaurus microlophus
Creators: name: Denzer, Wolfgang
name: Campbell, Patrick D.
name: Manthey, Ulrich
name: Glässer-Trobisch, Andrea
name: Koch, André
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Reptilia
Squamata
Agamidae
Hydrosaurus
Hydrosaurus microlophus

description: Hydrosaurus microlophus (Bleeker, 1860)
Chresonymy:
Istiurus microlophus (Bleeker 1860a: 80, 1860b: 85)
Istiurus amboinensis (part) (Bleeker 1860b: 85)
Lophura amboinensis (part) (Boulenger 1885: 402; Casto de Elera 1895: 417; de Rooij 1915: 128)
Lophura amboinensis var. celebensis (Weber 1890: 160, 167)
Hydrosaurus amboinensis (part) (Wermuth,1967: 64)
Type: Holotype NHMUK 1863.12.4.35, juvenile, collected by P. Bleeker, 1855.
Type locality: Makassar (= Ujung Pandang), Southwest Sulawesi, Indonesia (Figure 8).
Description of holotype: See above.
Diagnosis: Large species exceeding 1000 mm in total length; largest specimen, SMF 35996, SVL = 325mm, TL = 745mm (TL/SVL = 2.29), tip of the tail missing; complete specimen, MZB Lac 5870, SVL 131 mm, TL 315 mm (TL/SVL = 2.4) [Remark: The MVZ database gives 370 mm as tail length]. Head black; sometimes with yellowish colour around the eyes, the same on the lower half of the neck and in front of the shoulders as well as in the gular region; nuchal region black; a group of enlarged conical or pyramidal scales on either side of the neck; nuchal and dorsal crests continuous; in males, the sides of the body are dirty yellow with three groups of enlarged conical or pyramidal scales, often forming a triangular shape, between fore and hindlimbs that decrease in size ventrally to form transverse bands, the largest scales being black in colour; adult females are black with yellow enlarged scales; some females (presumably subadults or non-reproducing specimens) and juveniles typically grey with the groups of enlarged scales being whitish in colour; yellow ventrally, limbs on the upper side black and on the underside yellow (grey in subadults and juveniles); scales under fourth and fifth toes initially flat or singly keeled; tail black with some irregular yellow markings; sail dirty yellow to light brown with black stripes.
Allocation of adult museum specimens to Hydrosaurus microlophus. The preserved type material is only represented by a single specimen each. In the case of H. celebensis we located additional adult voucher specimens that match the holotype of this species (see Appendix 1). However, we were not able to locate any juvenile specimens that can be assigned unambiguously to H. celebensis.
However, in the case of H. microlophus the holotype is a juvenile and corresponding adult specimens present in museum collections had to be inferred as belonging to this species following morphological comparison. The main diagnostic characters for assignment of adult specimens to H. microlophus is the presence of groups of enlarged, strongly keeled scales dorsolaterally and the highly variable number of enlarged scales on the sides of the neck (≥ 3 up to eleven) as well as their shape and arrangement.
The Senckenberg collection holds three specimens (SMF 35996-98) from Sulawesi without precise locality or collector details. These specimens were received in 1930 from the Zoological Society Frankfurt and determined under the curatorship of Robert Mertens as H. amboinensis microlophus. All three specimens agree well with the characters outlined as specific for the H. microlophus type (i.e., enlarged dorsal scales in groups, ventral scales equal or larger than dorsal scales, 10/11 supra- and infralabials, respectively). Therefore, we consider the Senckenberg material adult representatives of H. microlophus (see also below for a comparison of live specimens). Two of these specimens lack parts of their tails but one has a nearly complete tail (SVL = 325mm, TL = 745mm, with only the tip of the tail missing according to G. Köhler [SMF, pers. comm.], TL/SVL = 2.3). Currently the specimens, although kept in the same jar, are not individually numbered. For clarity we consider the nearly complete specimen as SMF 35996, the specimen measuring SVL = 295mm, TL = 90mm as SMF 35997 and the one measuring SVL = 333mm, TL = 220 mm as SMF 35998. Gaulke (1989) examined these specimens and concluded that they were conspecific with H. (cf.) pustulatus unaware that the Philippine populations of Hydrosaurus constituted a species complex (Siler et al. 2014). A comparison with the juvenile type shows that the enlarged dorsal scales have a much more pronounced keel in adults and that these may exhibit a conical or near pyramidal shape. In the juvenile holotype the enlarged dorsal scales are white while they appear to be brown (SMF 35997), dark brown or black (SMF 35996 and SMF 35998) in the preserved adults. This is in contrast to the black and yellow speckled dorsal colouration in H. celebensis. Additionally, the enlarged dorsal scales in H. celebensis are typically light coloured or even white. A comparison between the type specimen of H. celebensis and an adult H. microlophus specimen (SMF 35996) is shown in Figure 5.
Bleeker (1860b) reported specimens from “Boni” as Istiurus (= Hydrosaurus) amboinensis. There is a dried specimen at Naturalis (ZMA 12611) that was previously housed in the collection of the Tropeninstituut Amsterdam, and subsequently transferred to the ZMA collection (now at Naturalis). Boni (or Bone State) was a former sultanate on the east coast of the southwestern arm of Sulawesi near Danau (=Lake) Tempe. The specimen has enlarged conical, near pyramidal scales on either side of the neck and two groups of similar scales on the back. As its dorsal scalation matches that of H. microlophus and the locality record falls within the range of this species it should be classified as such.
Intraspecific Variation: One variable character is the number of enlarged scales on either side of the neck. The enlarged scales along the neck are sometimes arranged in a single row and sometimes intermixed with slightly smaller ones forming a group (picture collection AGT). The number of enlarged scales varies from three to eleven. The lateral groups of enlarged body scales consist of 10 to 20 scales, with the anterior most group having the highest number of scales. Typically there are three groups of enlarged scales between the fore and hindlimbs. One specimen (picture collection AGT) contains a group of three enlarged scales between the midbody and the onset of the tail group.
Sexual dimorphism: Adult males of H. microlophus have a considerably higher dorsal sail and a typically more pronounced nasal crest than do females, although we also observed some females with a well-developed nasal crest. In addition, males and females show a clear sexual dimorphic colouration (dichromatism, see above). Thus, in female specimens the groups of enlarged scales are whitish/yellowish coloured on a dark grey to nearly black dorsal ground colour while male specimens typically show a dirty yellow dorsal colouration with the groups of enlarged scales being black or brown in colour.
Comparisons: H. microlophus differs from H. amboinensis by the possession of the following characters: grossly enlarged scales near the onset of the forelimbs; strongly enlarged conical or pyramidal scales in groups forming dorsolateral bands (all of these characters are either not or only slightly developed in H. amboinensis). Furthermore, H. microlophus differs from H. amboinensis in colouration (yellowish green in male H. amboinensis and green in females with black marbling in both sexes vs. dirty yellow dorsal colouration with the groups of enlarged scales being dark coloured in male H. microlophus, plus dark dorsal colouration with the groups of enlarged scales being whitish/yellowish in female H. microlophus together with the top of the head and neck being black and the throat being yellow in colour in both sexes) they also possess a nasal crest (absent in H. amboinensis, see Figure 6a). Most noticeably, the males of H. microlophus differ in their pattern from the males of H. celebensis the latter having complete or near complete black heads, limbs and tails. H. microlophus differs from H. weberi in general colouration and pattern, the latter being grey green. H. microlophus differs from H. celebensis and H. weberi by having groups of enlarged (black in males, white or yellow in females) conical and pyramidal scales on the dorsum. In every case the number of scales in the major groups of enlarged scales is larger than that in H. celebensis. In H. microlophus the nuchal and dorsal crests are continuous, while they are separated by considerably smaller scales on the neck in H. weberi.
Biology: H. microlophus appears to prefer open freshwater habitats mostly surrounded by high trees. We observed this species mainly on stony or rocky ground. In Bantimurung specimens were seen in a river with large boulders and low vegetation on the banks. Remarkably, this site was near the entrance of the Bantimurung National Park that is highly frequented by many visitors. Some specimens even occurred near a busy building site.
Near Bengo-Bengo six specimens (one male and five females) were observed on a tree. It appeared as if this assemblage had a harem structure with the single male being the dominant individual. According to locals and own observations, individuals living close to human settlements are often seen in trees during the dry season to escape the hunting dogs. In contrast, during the rainy season a more terrestrial behaviour is observed. Individuals or groups of sailfin lizards of different ages are mainly seen on riverbanks and flee into the river when disturbed. We observed several specimens of all age groups living together within a relatively small range especially in the dry season. The semiaquatic habitat was shared with Varanus togianus, a potential predator of juvenile Hydrosaurus.
Distribution: H. microlophus is endemic to Sulawesi. It appears to be restricted to Southwest Sulawesi, the bordering southern part of Central Sulawesi and possibly also inhabits parts of West Sulawesi (Figure 8). See also the Discussion below.
description: Published as part of Denzer, Wolfgang, Campbell, Patrick D., Manthey, Ulrich, Glässer-Trobisch, Andrea & Koch, André, 2020, Dragons in neglect: Taxonomic revision of the Sulawesi sailfin lizards of the genus Hydrosaurus Kaup, 1828 (Squamata, Agamidae), pp. 275-301 in Zootaxa 4747 (2) on pages 286-290, DOI: 10.11646/zootaxa.4747.2.3, http://zenodo.org/record/3694804