Capitellum, Hedges & Conn, 2012
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publication ID |
https://doi.org/ 10.11646/zootaxa.3288.1.1 |
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persistent identifier |
https://treatment.plazi.org/id/39191A7F-0730-FFC7-2DA9-EB627DAEF9F3 |
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treatment provided by |
Felipe |
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scientific name |
Capitellum |
| status |
gen. nov. |
Genus Capitellum gen. nov.
Antillean Small-headed Skinks
Type species. Mabuya metallica Bocourt, 1879:400 .
Diagnosis. Species in this genus are characterized by (1) frontoparietals, two, (2) supraciliaries, 5–6, (3) supraoculars, four, (4) prefrontal contact, absent, (5) parietal contact, present (except in C. parvicruzae sp. nov.), (6) rows of nuchals, one, (7) dorsals + ventrals, 125–128, (8) total digital lamellae, 167–190, (9) a dark middorsal stripe, absent, (10) dark dorsolateral stripes, absent, (11) a dark lateral stripe, present, and (12) dark ventral striping, absent. Maximum body sizes among species in this genus range from 68–78 mm SVL ( Table 2). They are smallheaded (head length 15–16% SVL; head length in mabuyines is typically 17–21% SVL).
This genus differs from others in having a combination of small hands, small feet, short heads, and lacking dark dorsolateral stripes. It differs from Alinea , Copeoglossum , Mabuya , Notomabuya , Panopa , Psychosaura , and Varzea in having fewer total digital lamellae (<191). It differs from Manciola in having more total lamellae (> 166), fewer dorsals + ventrals (125–128 versus 136–141), and five or six (versus four) supraciliaries. From Exila , Notomabuya , and Panopa , it differs in having two frontoparietals (versus one fused frontoparietal in those other genera). In having four supraoculars, Capitellum is separated from two genera with three supraoculars: Aspronema separates this genus from Copeoglossum . It differs from Alinea by having fewer finger-IV + toe-IV lamellae (24– 26 versus 28–36), having dark lateral stripes (present as a trace in only one species of Alinea , A. berengerae ), and lacking ventral striping. It is distinguished from Manciola , Maracaiba , and Marisora by its 5–6 supraciliaries (versus four in nearly all Marisora ). It shares with Brasiliscincus small hands and feet but differs in lacking dark dorsolateral stripes (present in most Brasiliscincus ), having dark (versus pale) palms and soles, and having more dorsals + ventrals (125–128 versus 113–124). From Orosaura , it is distinguished by lacking a dark dorsolateral stripe. Eyelid window size (length 2.21–2.42% SVL) is also relatively large for the genus, where most other species fall within the range 1.5–2.0% SVL. However, we did not score that character in all individuals and species.
Content. Three species are placed in this genus: Capitellum mariagalantae sp. nov., C. metallicum , and C. parvicruzae sp. nov. ( Table 1).
Distribution. The genus is distributed on the islands of Martinique and Marie-Galante ( Guadeloupe) in the Lesser Antilles and on St. Croix in the U.S. Virgin Islands ( Figs. 1 View FIGURE 1 , 8A View FIGURE 8 , 10G View FIGURE 10 , and 11B–C View FIGURE 11 ).
Etymology. The generic name ( Capitellum ) is a neuter singular noun (Latin) meaning "small head," in reference to the relatively small heads of the three included species.
Remarks. Each species is represented by a single adult specimen collected 135–190 years ago. They occur on islands where the mongoose was introduced in the late 19th century, likely explaining their subsequent disappearance. We have gleaned some critical information on morphology from fetuses and accounts of lost specimens. Molecular data are unavailable. Nonetheless, the shared set of morphological characters argue that they are close relatives and warrant placement in a single group, distinct from other genera. They have a gracile form and unusually small heads, which suggests that they had (or have, if they still exist) terrestrial (ground-dwelling) and possibly cryptozoic (subterranean-dwelling) habits similar to species of Brasiliscincus ( Vrcibradic & Rocha 2002a). They also have a similar, tubular body shape, as opposed to the dorsoventrally flattened body shape typical of most mabuyines.
Although only one adult specimen exists for each species, there are several clues that suggest that they probably have small maximum body sizes. First, all three adults are relatively small (68–78 mm SVL). Secondly, one of the species ( Capitellum mariagalantae sp. nov.) has developing young. Thirdly, they all have a relatively small number (30) of midbody scale rows, a trait correlated with body size: 71% of species of mabuyines with 30 or fewer midbody scale rows are <80 mm maximum SVL , whereas 78% of species with 32 or more midbody scale rows are> 80 mm maximum SVL. Although they are scored as being variable in contact between parietals, all three are similar in being at the contact/no contact boundary, with C. parvicruzae sp. nov. having no contact.
The closest relative to Capitellum appears to be Brasiliscincus (South America), and therefore an independent overwater dispersal from an ancestor of Brasiliscincus probably led to Capitellum . The fact that each of the three species occurs on a non-adjacent island could be explained by separate dispersal events from the mainland (least likely), or an initial dispersal to the Lesser Antilles (perhaps Martinique) followed by secondary dispersals to Marie-Galante and St. Croix, or to Marie-Galante and then from there to St. Croix. Because these skinks apparently were decimated by the mongoose before extensive herpetological collections were made in the 20th century, it is possible that the genus was even more widely distributed on Caribbean islands, with one or more extinctions and extirpations occurring before any specimens were collected. Ancient DNA methods may prove useful in addressing the relationships of Capitellum .
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