Cretaceogekko burmae, Arnold, Nicholas & Poinar, George, 2008

Arnold, Nicholas & Poinar, George, 2008, A 100 million year old gecko with sophisticated adhesive toe pads, preserved in amber from Myanmar, Zootaxa 1847, pp. 62-68 : 62-65

Cretaceogekko burmae n. gen. and n. sp.

( Figs 1–5 )

Material ( Figs 1–5 ). Holotype: left crus and foot preserved in Cretaceous amber from Myanmar; specimen deposited in the Poinar collection (accession # B-V-4) maintained at Oregon State University, Corvallis, Oregon, U.S.A.

Type locality and horizon. The specimen was obtained from an amber mine excavated in the Hukawng Valley in 2001, The mine, now known as the Noije Bum 2001 Summit Site, is located southwest of Maingkhwan in the state of Kachin (26º20´N, 96º36´E). Palynomorphs from the amber beds where the fossil originated have been assigned to the Upper Albian of the late Lower Cretaceous, 97–110 million years ago ( Cruickshank and Ko 2003). However, since the amber is secondarily deposited, its age could be older. Nuclear magnetic resonance ( NMR) spectra and the presence of araucaroid wood fibers in the amber samples from this site indicate an araucarian (probably Agathis ) tree source for the amber ( Poinar et al. 2007).

Diagnosis. A gecko with characteristic digital proportions of many climbing species, with toes II–IV subequal but toe III longest; broad basal pads present on the underside of the digits that gradually expand and then narrow, before giving rise to narrow, long and clawed distal sections on toes II–V that originate right from the pad tips; pads on toes I–IV with respectively about 10, 17, 19 and 18 transverse lamellae extending across the width of the toes; surface of crus with small scales in transverse rows, ventral surface with larger ones also in transverse rows that may contain around 12 scales and run obliquely distally towards trailing edge of crus. Tail with larger scales below than above but with no apparent enlarged laterally expanded subcaudal series.

Description. Basal part of tail, left hind foot and lower crus, and isolated partial right foot, embedded in a block of amber (maximum dimensions 9.8mm by 9.7mm by 4.7mm). The block also contains a large nabid hemipteran (damsel bug) and was probably prepared with the intention of displaying this, inadvertently cutting away additional parts of the gecko, as the tail and leg appear in section on the block surface.

The specimen suffered some decay before preservation, especially the separated remnants of the right foot, and the distal part of the tail, which is almost interrupted; elsewhere the tail surface is collapsed and wrinkled. Terminal sections of some toes are also decayed; here numbers II–IV are transluscent and ‘ghostly’ and the distal section of toe V is partly obscured by contact with the tail.

Dimensions. Tail section 4.7mm long and 1.2mm wide at base; crus plus foot to inflection behind knee 3.1mm long; crus to base of toe V 1.3mm long; foot to base of toe V 1.8mm long.

Tail. Dorsal surface of basal part of tail covered with small, slightly imbricate, rounded, quite convex scales that show some variation in size and are arranged in irregular transverse rows Scale size increases lateroventrally and ventral scales in the most basal area are larger and less convex than those dorsally, although again arranged in transverse rows. This is also true more distally, beyond the level of the hind limb, where the scales are larger still, being about 3–4 times the diameter of the dorsal scales on the tail base. They are weakly convex and their posterior edges imbricate, the free borders being rounded. Distally, scales may be staggered in each transverse row, producing a tessellated pattern. No laterally expanded medial series of enlarged subcaudal scales is apparent.

Crus. Dorsum of crus with small rounded scales similar to those on tail base, in transverse rows that slope distally towards trailing edge of limb; scales on underside larger, about twice as broad, and only slightly imbricate distally, in transverse rows that again slope slightly distally towards trailing edge of limb where they are smaller; about 12 of these enlarged scales visible in each row at mid-crus.

Foot. Basal area of foot covered above with small scales similar to those on dorsum of crus; those below on ‘heel’ only about half as big as those above, but scales on distal sole markedly larger. Toes all relatively short with toe III longest; broad basally with a long differentiated distal section in toes II–V that is narrow and laterally compressed at least towards the tip. Broad basal sections of toes III–IV quite similar in length, with those of toes V and especially I markedly shorter. At least toes III and IV are inflected in the vertical plane, with the much of the distal part of the pads directed downwards, and their tips and the narrow distal sections of the toes upwards; the narrow distal section of toe II is also inflected upwards.

Broad basal sections of toes covered above by small scales about the same size as those on dorsum of crus, lower parts form a flattened pad similar in structure to the adhesive toe pads of many living geckos; on toes II–IV these gradually increase in width distally and then gradually narrow for the last third or so of their length. Pads are covered below by simple straight transverse lamellae that extend to base of toes; approximate numbers on toes as follows: toe I – 10, toe II – 17, toe III – 19, toe IV – 18. Lamellae appear to bear clumped adhesive setae ( Fig. 4 ).

Distal laterally compressed sections of toes II to IV originate right at end of padded basal section and are covered by homogenious small scales; claws small. In at least dorsal view ( Fig. 5 ), toes I–IV give impression of being webbed between their bases.

Figures

FIGURE 1. Holotype of Cretaceogekko burmae; ventral view of section of basal tail (above) and left hind leg (lower right); what appear to be toes I – III of the isolated right foot are visible in dorsal view distal to the tail section (upper left).

FIGURES 2, 3. Ventral views of left crus and foot of Cretaceogekko burmae with different illumination.

FIGURE 4. Ventral view of toes I – IV (toe I at upper right). What appear to be clumped adhesive setae are visible on the more distal lamellae of toes II and III.

FIGURE 5. Dorsal view of left foot of Cretaceogekko burmae (toe I on left).