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Tribolonotus annectens ZWEIFEL, 1966

IUCN Red List - Tribolonotus annectens - Data Deficient, DD

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Higher TaxaScincidae, Egerniinae (Tiliquini), Scincoidea, Sauria, Squamata (lizards)
Common NamesE: Zweifel's Helmet Skink 
SynonymTribolonotus annectens ZWEIFEL 1966
Tribolonotus annectens — MYS 1988: 147
Tribolonotus annectens — ADLER, AUSTIN & DUDLEY 1995 
DistributionNew Britain, Bismarck Archipelago

Type locality: Mount Sinewit on Gazelle Peninsula (between 1000 and 1200 m), New Britain  
TypesHolotype: BPBM 1001 (Bernice P. Bishop Museum) 
DiagnosisDiagnosis: This new species is most closely related to the three species found in the Solomon Islands. Tribolonotus blanchardi is readily distinguished from T. annectens in having only one row of enlarged vertebral scales, whereas annectens has two. Tribolonotus schmidti resembles annectens in having two rows of enlarged dorsals, but in schmidti the rows commence on the nape directly posterior to the enlarged shields of the head, whereas in annectens the two juxtaposed rows of enlarged dorsal scales originate well back on the nape, just anterior to the insertions of the forelegs. Tribolonotus ponceleti and T. annectens are similar in the number and dis position of the enlarged vertebral scale rows but differ in other characters of scutellation. Ventral scales number 40 in T. annectens; 44 to 54 (mean 48.6) in 45 specimens of T. ponceleti. In both species there is a prominent row of enlarged scales paralleling the much larger vertebrals, but where at midbody in ponceleti there is one of these smaller scales for each verte bral, annectens has only one for every two vertebrals. There are two primary temporal scales in ponceleti and three in annectens. A sublabial scale in annectens lies between the first infralabial and the gulars and is wholly separated from the margin of the lip. The corresponding scale in ponceleti borders partly on the lip and is, therefore, the second infralabial (Zweifel 1966).

Comparisons: Tribolonotus annectens resembles T. blanchardi in the longi tudinal number of enlarged dorsal scales, number of gular and ventral rows, and number of lamellae under the fourth toe (table 1). The presence of only a single row of enlarged dorsals (fig. 3A) sets blanchardi apart from annectens and from all other species of Tribolonotus. Probably blanchardi is a smaller lizard than annectens^ for the largest of five specimens meäsures only 38 mm. from snout to vent, whereas the only specimen of annectens is 49 mm. in length. Tribolonotus schmidti resembles T. annectens in having two rows of en larged vertebrals (fig. 3B) and in the number of ventral and gular scale rows, but diflfers significantly in other respects. The most obvious difference is that the rows of enlarged vertebrals in schmidti commence well forward on the nape, even touching the enlarged parietal scale, whereas in an nectens the nape is largely covered by granular or spinose scales, and the vertebral rows begin only shortly anterior to the forelimbs. Lateral to the enlarged vertebral scales of schmidti is a wavy or scalloped row of spiny scales, quite different from the series of large, separated, spiny scales seen in this region of annectens. A difference in size between the two species also is evident. Among 35 specimens of schmidti, the six largest (all males) measure approximately 41 mm. from snout to vent, whereas the only specimen of annectens is 8 mm. longer. The number of subdigital lamellae probably is fewer in schmidti (table 1).
Tribolonotus annectens is clearly most closely related to T. ponceletl An important difference is in the nature of the row of large scales paral leling the enlarged vertebrals. In ponceleti there is one enlarged scale for each pair of vertebrals in the middorsal region, whereas these scales are only half as numerous in annectens (fig. 2A, B). Other differences in scutellation also are present. Both enlarged vertebrals and ventral and gular scales are less numerous in annectens than in ponceleti, and the number of subdigital lamellae on the fourth toe falls at the lower limit observed in ponceleti (table 1). In ponceleti there are two primary temporal scales (fig. IB), but in annectens a third temporal is present (fig. lA). This character is invariable in my series of 45 ponceleti, but two of five blanchardi have the large primary temporal divided by a horizontal suture, rather than a diagonal one as in annectens. The first infralabial of annectens is elongate and completely excludes the sublabial below it from the margin of the lip (fig. lA). The first infralabial of ponceleti is also long and thin, but it is relatively shorter than that of annectens. As a result, the posterior dorsal edge of the scale of ponceleti homologous with the sublabial of annectens lies on the free margin of the lip (fig. IB), and the scale is to be regarded as the second infralabial rather than as a sublabial. Therefore, the second infralabial of annectens is homologous with the third of ponceleti, and so on. In only one of 45 specimens of ponceleti is this second infralabial ex cluded from the lip, and in that instance just barely (both sides of the specimen are symmetrical in this respect). Another specimen has the second and third infralabials fused on both sides of the head.
The Tribolonotus species of New Guinea, T. novaeguineae and T. gracilis, are distinct from the other species in a number of ways, including larger size (greater than 90 mm. from snout to vent) and the number and nature of the enlarged dorsal scales. In the Papuan forms there are four rows of enlarged scales, each scale rising in a prominent, hooked fashion in contrast to the somewhat flattened, keeled morphology of the homolo gous scales in the other four species. 
  • Adler,G.H.; Austin,C.C. & Dudley,R. 1995. Dispersal and speciation of skinks among archipelagos in the tropical Pacific Ocean. Evolutionary Ecology 9: 529-541 - get paper here
  • Austin, Christopher C.; Eric N. Rittmeyer, Stephen J. Richards, George R. Zug 2010. Phylogeny, historical biogeography and body size evolution in Pacific Island Crocodile skinks Tribolonotus (Squamata; Scincidae). Molecular Phylogenetics and Evolution 57 (1): 227-236 - get paper here
  • Mys, Benoit 1988. The zoogeography of the scincid lizards from North Papua New Guinea (Reptilia: Scincidae). I. The distribution of the species. Bull. Inst. Roy. Sci. Nat. Belgique (Biologie) 58: 127-183
  • Zweifel, Richard G. 1966. A New Lizard of the Genus Tribolonotus (Scincidae) from New Britain. American Museum Novitates 2264: 1-12. - get paper here
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