Oligosoma oliveri ( McCann, 1955 )

Jewell, Tony R., 2019, New Zealand forest-dwelling skinks of the Oligosoma oliveri (McCann) species-complex (Reptilia: Scincidae): reinstatement of O. pachysomaticum (Robb) and an assessment of historical distribution ranges, Zootaxa 4688 (3), pp. 382-398 : 391

Oligosoma oliveri ( McCann, 1955)

Figure 2

Synonomy

Leiolopisma oliveri McCann, 1955

Leiolopisma oliveri Robb, 1975

Cyclodina oliveri (in part) Hardy, 1977

Cyclodina oliveri (in part?) Wells & Wellington, 1985

Cyclodina oliveri (in part) Patterson & Daugherty, 1997

Cyclodina oliveri (in part) Chapple et al. 2008b

Oligosoma oliveri (in part) Chapple et al. 2009

Holotype: NMNZ RE153 , Poor Knights Islands , northern islet (= Tawhiti Rahi), 35°28 S 174°44 E, adult female. W. R. B. Oliver, February 1934.

Diagnosis. An Oligosoma with a squarish mid-body cross-section; opaque, divided palpebral disc; a prominent tear-drop mark beneath each eye; iris light brown to orange; mid-body scale rows 37–44; ventral scale rows 88–97; eye diameter <distance from the eye to mouth; adult SVL ≥ 90 mm; dorsal markings dominated by pale blotches or mottling; belly cream and markings form broad blotching. Distinguished from similar congeners (which share both the squarish body cross-section and the tear-drop subocular marking) as follows: alani (Robb) has a black iris, much larger dorsal blotches and is bulkier, up to 142 mm SVL; macgregori (Robb) has longitudinal streaks on the dorsum and a uniform belly; ornatum (Gray) is much smaller (SVL usually <80 mm), usually has a yellow belly and usually has a tapering pale dorso-lateral stripe; pachysomaticum has 32–36 mid-body scale rows, 72–88 ventral scale rows, dorsal and ventral patterns dominated by dark flecks, and a larger eye (diameter> distance from eye to mouth); roimata (Patterson, Hitchmough & Chapple) (sympatric) is much smaller at up to 65 mm SVL, has only 32–34 mid-body scale rows and 1 primary temporal scale (versus 2 in oliveri ); townsi usually has only 1 primary temporal scale and few ventral markings; and whitakeri has a dark-brown iris, yellow-orange venter and dorsal and ventral patterns of dark flecks.

Etymology. McCann named the species for Dr W.R.B. Oliver (1883–1957), former director of the Dominion Museum (now Museum of New Zealand /Te Papa Tongarewa) in Wellington, New Zealand. The established vernacular name ‘marbled skink’ should ideally remain with this taxon as it is strongly associated with the name oliveri and aptly describes the characteristic colour pattern of this species.

Distribution. Known only from the Poor Knights Islands off the east coast of Northland ( Figure 1 ) where it has been recorded from seven islets including Tawhiti Rahi I., Aorangi I., Motu Kapiti I., Archway I., Stack ‘A’, Stack ‘B’, and Stack ‘C’ ( Table 1 ; Chapple et al. 2008b).

Ecology. Lives primarily among leaf litter on the floor of coastal forest and scrub, utilizing a range of cover objects and sea bird burrows as retreat sites, and is crepuscular with peaks of activity after dusk and before dawn. Gravid females occasionally bask but the species is normally otherwise inactive by day. Co-exists in this habitat with two much smaller skinks, i.e. Oligosoma hardyi (Chapple, Patterson, Bell & Daugherty) (62 mm SVL) and O. roimata (65 mm SVL) ( Towns 1999; Whitaker 1968; van Winkle et al. 2018).

Biogeography. The Poor Knights Islands are the remnants of a ten million year old rhyolite volcano that has been separated from the mainland since the Pliocene, between 1–2 million years ago ( Hayward 1991). Members of the Oligosoma oliveri species-complex are vulnerable to extremes of temperature and hydration, experiencing high levels of cutaneous body water loss ( Towns 1999) and so are unlikely to be effective oversea rafters. This indicates that O. oliveri has likely been isolated on these islands for between 1–2 million years.

Phylogeny. Chapple et al. (2008a, b) present phylogenetic reconstructions based on analysis of the sequence differentiation observed among three mitochondrial genes (i.e. 600 base pairs of ND2, 850 base pairs of ND4, 700 base pairs of Cytochrome b). The calibration they employed indicated a split between Oligosoma oliveri and O. pachysomaticum of between 1.07–1.43 million years ago, which coincides with the estimated isolation of the Poor Knights Islands themselves (see ‘Biogeography’, above).

Remarks. The taxonomic definition is returned to its original concept, i.e. that of McCann (1955), who provides a full morphological description.

Figures

FIGURE 1. Map of upper North Island of New Zealand showing distribution records for extant populations of the four members of the Oligosoma oliveri species-complex. Bold outline = maximum expanse of land during the Otira Glaciation 18,000–20,000 years ago; thin outline = present extent of land; dotted line = former path of Waikato River; blue shading = suggested former distributional extent of O. townsi in this region; pink shading = suggested former distributional extent of O. pachysomaticum in this region.

FIGURE 2. Oligosoma oliveri (McCann) from Aorangi Island in the Poor Knights group, off the east coast of Northland (photo: D. van Winkle).