Namibiana Hedges, Adalsteinsson, & Branch

Adalsteinsson, Solny A., Branch, William R., Trape, Sébastien, Vitt, Laurie J. & Hedges, S. Blair, 2009, Molecular phylogeny, classification, and biogeography of snakes of the Family Leptotyphlopidae (Reptilia, Squamata), Zootaxa 2244, pp. 1-50 : 33-34

Genus Namibiana Hedges, Adalsteinsson, & Branch , New Genus

Type species. Leptotyphlops occidentalis FitzSimons, 1962: 239 .

Diagnosis. Species of Namibiana have 14 midbody scale rows, 10–12 midtail scale rows, 241–387 middorsal scale rows, 12–41 subcaudals, 1–2 supralabials, anterior supralabial absent or small scale present, 192–322 mm maximum adult total length, a body shape of 45–142 (total length/width), a relative tail length of 4.1–10.8 %, a tail shape of 3.8–7.8, no striped pattern, and usually a brown dorsum and pale brown venter (Table 2). Members of Namibiana can be distinguished from the other genus in the Tribe Leptotyphlopini (Leptotyphlops) by having a semilunate (rather than heart-shaped or subtriangular) cloacal shield (except N. gracilior ), a higher number (on average) of middorsal scales (241–387 versus 171–322), and a more attenuate body shape (ratio of total length divided by width at midbody, 45–142 versus 36–106). Namibiana occidentalis , reaching a total length of 322 mm (Bauer 1988), is the largest member of the Leptotyphlopinae . Only one species was included in the molecular phylogenetic analyses ( Figs. 3–4).

Content. Five species ( Table 1; Fig. 10).

Distribution. The genus is distributed in Southwest Africa, including South Africa, Namibia, and Angola ( Fig. 11).

Etymology. The generic name is a feminine noun derived from the name (Namib) given to that region of southwest Africa by the indigenous people (the Nama), used in allusion to the distribution of species in this genus.

Remarks. This genus comprises the former rostratus Group of " Leptotyphlops , " most recently defined by Broadley and Wallach (2007). See "Remarks" above under the Subfamily Leptotyphlopinae and Tribe Leptotyphlopini regarding diagnostic characters used for species groups.

Timetree of leptotyphlopid snakes. The results of time estimation analyses using the two rttm values, 159.9 Ma and 102.3 Ma, were similar, with point estimates for most nodes varying by less than two percent. For this reason, we averaged the times and credibility bounds, using the two rttm values, for each node. Additionally, corresponding time estimates from both data sets were similar, with most varying by <5%, and therefore they were averaged as well. Only the time tree from the mitochondrial RNA-gene data set is shown ( Fig. 12), but many divergence time estimates in Table 3 represent the average of divergence times estimated from that data set and the RNA+nuclear gene data set (denoted by bold node numbers).

Leptotyphlopidae diverged from Typhlopidae in the early Cretaceous (~139 Ma; 165–119 Ma, Bayesian credibility interval). A slightly older divergence (151.9 Ma; 163–137 Ma) was found in a recent study ( Vidal et al. 2009) using nine nuclear genes and a larger number (eight versus two here) of calibration points. The two subfamilies, Epictinae and Leptotyphlopinae , diverged from one another 92 Ma (113–75 Ma). In both subfamilies, divergences among the tribes occurred in the Late Cretaceous (100–67 Ma) whereas divergences among the subtribes and genera occurred in the Paleogene (67–23 Ma).

Divergences among morphologically distinct and previously recognized species were as recent as 3.8 Ma ( Myriopholis boueti and M. rouxestevae ), and 3.1 Ma ( Tetracheilostoma breuili and T. carlae ). Divergence times among individuals from the same population (e.g., in Epictia columbi , Mitophis asbolepis , M. leptepileptus , and Tetracheilostoma breuili ), and among populations of some species (e.g., Guinea bicolor and two populations of Epictia goudotii ) were so low (<1 Ma) as to be not measurable with precision. In contrast, divergences among other populations were deeper: Epictia goudotii (16.3–9.2 Ma), Leptotyphlops conjunctus (28.4–18.1 Ma), Leptotyphlops nigricans (14.1–7.4 Ma), Leptotyphlops scutifrons (23.1–8.1 Ma), Leptotyphlops sylvicolus (17.5 Ma), and Namibiana occidentalis (6.5 Ma). Using the divergence of T. breuili and T. carlae (3.1 Ma) for comparison, as many as 18 unrecognized species are present in our limited genetic data set alone. However, determining the actual number of species present, and assigning names, will necessarily require study of specimens from type localities and other relevant material.

The separate analyses that excluded the 94 Ma fossil calibration resulted in time estimates (as above, averaging estimates from the mitochondrial RNA gene data set and the RNA + nuclear gene data set), for the two key nodes, that were entirely in the Cretaceous and similar to those that included that calibration point. As described above in the Methods, estimates were obtained using three alternate calibrations for the typhlopid/ leptotyphlopid divergence: 163, 158, and 137 Ma. The resulting time estimates for the divergence of Epictinae and Leptotyphlopinae were 106.8 Ma (124–92 Ma), 104.3 Ma (121–90 Ma), and 92.9 Ma (108–81 Ma), respectively. The time estimates for the divergence of Epictini and Rhinoleptini were 88.2 Ma (105–74 Ma), 86.4 Ma (103–73 Ma), and 77.7 Ma (92–66 Ma), respectively. These were similar, but slightly older than, estimates we obtained for those two nodes using the 94 Ma calibration: 92 Ma (113–75 Ma) and 78 Ma (98– 63 Ma), respectively ( Table 3).