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Tribolonotus gracilis. JCM |
Skinks come in a
plethora of shapes and sizes, with about 1500 species they have invaded a huge
variety of habitats and evolved a great diversity of life styles. They are
found in almost all landscapes that support squamates and are perhaps the most
successful lineage of living reptiles – if the measure is by the number of
species. Among the most bizarre skinks are the South Pacific Crocodile Skinks
of the genus Tribolonotus. Currently
8 species are recognized and they inhabit northern
New Guinea and the Admiralty, Bismarck and Solomon Archipelagoes. They are semi-fossorial
lizards, often found under vegetation and in the vicinity of water. At least
two species are known to vocalize, and they demonstrate parental care. Hartdegen
et al. (2001) described defensive vocalizations and parental care in captive specimens.
They observed females curled around their egg and when eggs were gently handled
by the observer the female exhibited defensive open-mouth lunges. When eggs
were left uncovered by human observers they were reburied by the female. Hatchlings
stayed near their mother (within 2 cm) and on occasion they were observed resting
on the female's dorsum for two weeks after hatching. Their overall appearance
is distinctive; they have unusually heavily keeled or spinose scales and two
unique characters, abdominal glands and volar pores (pores on the plantar and palmer
surfaces).
Recently,
Austin et al. (2010) used molecular techniques and found evidence that Tribolonotus
originated on either Greater Bougainville Island or in New Guinea, and
subsequently dispersed to surrounding islands multiple times. Maximum body size
ranged from 40 mm in T. blanchardi (and
T. schmidti was a close second at 41
mm) to 125 mm in T. ponceleti. The
authors did not find a phylogenetic explanation for differences in body size,
and suggest that it evolved as the result of character displacement and
ecological factors.
Exactly what the
sister of Tribolonotus is remains a
point of contention. They have been considered lygosomine
skinks, allied with the genera Sphenomorphus,
Mabuya, and Egernia by various authors. However, Donnellan (1991) found Tribolonotus
gracilis, has 32 chromosomes, a similar karyotype, to Egerina but there were differences that did not allowed a firm conclusion.
Literature
Austin,
C. C., E. N. Rittmeyer, S. J. Richards and G. R. Zug.
2010. Phylogeny,
historical biogeography and body size evolution in Pacific Island Crocodile
skinks Tribolonotus (Squamata; Scincidae). Molecular Phylogenetics and Evolution, 57:227-236.
Donnellan,
S. C. 1991. Chromosomes of Australian lygosomine skinks (Lacertilia: Scincidae).Genetica 83:207-222.
Hartdegen,
R. W., M. J. Russell, B. Young, and R. D. Reams. 2001. Vocalization of the
Crocodile Skink, Tribolonotus gracilis
(De Rooy, 1909), and evidence of parental care. Current Herpetology 2001(2). On-line.
McCoy, M., 2006.
Reptiles of the Solomon Islands.
Pensoft Publishing, Sofia-Moscow.
Labels: body size, evolution, natural history, Tribolonotus