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| Galegeeska revoilii (Hüet, 1881) in Heritage, Rayaleh, Awaleh & Rathbun, 2020. DOI: 10.7717/peerj.9652 |
Abstract
The Somali Sengi or Somali Elephant-shrew (‘Elephantulus’ revoilii, Macroscelidea, Mammalia) has been considered a “lost species” and is primarily known from about 39 museum specimens, with no new vouchered occurrence records since the early 1970s. The scientific literature contains no data concerning living Somali Sengi individuals and the species’ current Data Deficient conservation status is attributable to an absence of modern information. Almost everything that has been published about the species is derived from anatomical examinations of historic specimens, gleaned from museum collection notes, or inferred from the known habits and ecology of other sengi taxa. Here we report new evidence that the Somali Sengi is currently extant. These data include voucher specimens, georeferenced occurrence localities, body measurements, habitat parameters, and DNA sequences. While the species is historically documented as endemic to Somalia, these new records are from the neighboring Republic of Djibouti and thus expand the Somali Sengi’s known range in the Horn of Africa. Furthermore, Djiboutian locality data near international borders suggests that the Somali Sengi is also a current inhabitant of both Somalia and Ethiopia. Criteria that inform conservation status assessments (e.g., suitable habitat contiguity and occurrence in wildlife protected areas) can be positively characterized in Djibouti and therefore bode well for the survival of the Somali Sengi species. New data also inform previously undocumented substrate and sheltering affiliations. DNA analyses indicate that the Somali Sengi is a descendant of the Macroscelidini lineage and therefore reveal that the species’ referral to the genus Elephantulus is incompatible with sengi phylogeny. This taxonomic issue is resolved by recognizing a new genus replacement and recombinant binomial that redesignates the Somali Sengi as Galegeeska revoilii (gen. nov., nov. comb.). An analysis of ancestral biogeography suggests that the Somali Sengi has inhabited the Horn of Africa for more than 5.4 million years—and the recognition of the species’ phylogenetic ancestry appends the already remarkable biogeographic story of the Macroscelidini tribe.
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| Figure 1: Somali Sengi photograph at the Assamo locality in Djibouti. As is observed in other sengi species, Somali Sengis have some variation in pelage colors. These differences seem to correspond to the color variation of substrates between occurrence localities. At the Assamo site, in the extreme southeastern corner of Djibouti, sengi habitats are comprised of rocks with more rusty coloration than elsewhere in the country. Compared to other Djiboutian sites, sengis from Assamo have dorsal pelage hairs with more pronounced reds. CAS MAM 32728 photograph by Steven Heritage. |
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| Figure 4: Somali Sengi habitat photographs from four localities in Djibouti. The Somali Sengi has been hypothesized as a rupicolous (petrophilic) species based on the collection coordinates of historic museum specimens which generally occur within the montane ecosystems of northern Somalia. However, whether or not the species is an obligate rock-dweller has not been documented. In Djibouti, all evidence of Somali Sengis are from habitats with rocky substrates and relatively sparse vegetation where the predominant sheltering potential is among boulders. A rupicolous characterization of the Somali Sengi is valid, at least in Djibouti. (A) Arta Region, Djalelo Protected Area, Hansane Hill (east side). (B) Tadjoura Region, Goda Mountain, Day Forest Village (south hill). (C) Ali Sabieh Region, Assamo Decan Camp (south ridge base). (D) Arta Region, Arta Town, Oú Est Mon Camarade Hill (south side). See Table 1 for site coordinates and altitudes. Photographs by Galen Rathbun and Steven Heritage. |
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| Figure 5: Vouchered occurrence localities of the Somali Sengi. World museum collections preserve Somali Sengi individuals from 15 referenceable sites in northern Somalia (n = 35 specimens). The exact site of the holotype specimen (from 1881) is unknown, but Georges Révoil’s documented expedition route in the northern Majeerteen territory indicates that the specimen is from a location to the east of all other records. A minimum convex polygon estimated from these northern Somalia localities is about 88,500 sq km. Inclusion of the new localities from Djibouti increases this area to about 106,000 sq km (polygon in red). See methods for information concerning the Bud Bud site in the eastern branch of Somalia. Base map from Mapswire.com (CC-BY 4.0). |
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| Figure 7: Phylogenetic position of the Somali Sengi. Results from Bayesian phylogenetic analyses of combined nuclear (IRBP, VWF) and mitochondrial (12S, 16S, COX1, CYTB) loci. Clade credibility (=posterior probability) values at tree nodes indicate statistical support for lineage splits given analysis settings. Branch lengths are time-scaled estimates in millions of years (Ma, mega-annum). The Somali Sengi (revoilii) group is unambiguously recovered as a descendant of tribe Macroscelidini and sister to the Petrodromus-Petrosaltator clade. CAS MAM 32728 photograph by Steven Heritage. |
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| Figure 8: Ancestral biogeography model for tribe Macroscelidini. Subset results (Macroscelidini) from the Bayesian ancestral state reconstruction analysis of sengi biogeography. Continuous variable modeling was used to estimate geocoordinates at each lineage split using the time-scaled phylogenetic result and centroid estimates for species ranges. The spatiotemporal estimate for the common ancestor of tribe Macroscelidini is in Central Africa during the late Oligocene (25.5 Ma, 22.2–29.3 HPD). The arrival of the Somali Sengi in the Horn of Africa must postdate the diversification from its sister clade (early Miocene, 20.6 Ma, 16.8–24.6 HPD) and predate the common ancestor of the four revoilii individuals sampled in this study (latest Miocene, 5.4 Ma, 3.1–7.3 HPD). Colors for smoothed distribution polygons were chosen for graphical contrast where species ranges overlap but range colors are otherwise arbitrary. Base map from Mapswire.com (CC-BY 4.0). |
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| Figure 2: Somali Sengi photograph at the Day Forest locality in Djibouti. One extant sengi species (Petrosaltator rozeti) occurs in the Maghreb region but the other nineteen species have ranges restricted to latitudes south of the Sahara (i.e., south of ~13° N). New Somali Sengi records from Djibouti are the northernmost occurrence data for any sub-Saharan macroscelidean taxon and this photographed individual (uncollected) from the Day Forest site documents the northern extent of the Somali Sengi’s known geographic range. This animal was observed sunning itself near a wood pile within the Day Forest Village. Photograph by Houssein Rayaleh. |
Galegeeska Heritage & Rayaleh 2020, new genus
Type species: Galegeeska revoilii (Hüet, 1881).
New binomial combination. The genus is currently monotypic.
Species Synonyms: Elephantulus revoilii, Elephantulus revoili,
Macroscelides revoilii
Holotype: The type specimen, MNHN ZM-MO-1881-11, is located at the National Museum of Natural History in Paris, France. See Data S5 for hypodigm voucher specimens.
Distribution: The documented geographic range includes Somalia and Djibouti. The species may also occur in other Horn of Africa countries.
Diagnosis and description: See Corbet & Hanks (1968), Hüet (1881), and elsewhere in this manuscript for full details. In brief, the Somali Sengi can be distinguished from all other macroscelidean species by a combination of traits including: the presence of a pale eye ring with a dark post-ocular mark, hair on the lower portion of the rhinarium, a tufted tail, and second upper incisors that are subequal in size to adjacent upper incisors.
Etymology: In the Somali language, the word geeska ([gey·skah], /'gāskä/) means corner or horn—as in Geeska Afrika (=Horn of Africa). This root is chosen to indicate that the species has a broader geographic range than was previously recognized. From the Ancient Greek, galê translates to weasel (Beekes, 2009) and has been widely used as a general descriptor for small mammal taxa (e.g., Galeopterus, Petrogale, Microgale). In Somali, gal (variants: gala, galay, gale) can refer to one who enters or inhabits. A direct translation of Galegeeska is “weasel of the horn”, but a Somali speaker’s interpretation could be “inhabitant of the horn”. The root gale is also chosen to honor Galen B. Rathbun (1944–2019), who devoted more than four decades of scientific inquiry to sengi biology and who hiked the Djiboutian hillsides in search of this species.
The genus-level taxonomic hierarchy for extant sengis is as follows:
Class: Mammalia Linnaeus, 1758
Supercohort: Afrotheria Stanhope et al., 1998
Order: Macroscelidea Butler, 1956
Family: Macroscelididae Bonaparte, 1838
Subfamily: Rhynchocyoninae Gill, 1872
Genus: Rhynchocyon Peters, 1847
Subfamily: Macroscelidinae Bonaparte, 1838
Tribe: Elephantulini Dumbacher, Carlen & Rathbun, 2016
Genus: Elephantulus Thomas & Schwann, 1906
Tribe: Macroscelidini Bonaparte, 1838
Genus: Macroscelides A. Smith, 1829
Genus: Petrodromus Peters, 1846
Genus: Petrosaltator Dumbacher, Carlen & Rathbun, 2016
Genus: Galegeeska Heritage & Rayaleh, 2020, new genus
Conclusion:
These new records confirm the Somali Sengi as an extant taxon and reveal a broader geographic distribution than was previously documented. Further, the species’ conservation status can now be reconsidered using modern evidence which we have discussed as positively informing assessment criteria. New data also characterizes habitat use (including substrate and sheltering affiliations)—a species attribute that has been hypothesized but never formally reported. DNA from voucher specimens have yielded a robust phylogenetic estimate that newly identifies the Somali Sengi as a descendant of the Macroscelidini lineage. The former taxonomic referral to the genus Elephantulus (and tribe Elephantulini) has been revised and the Somali Sengi species-group is now recognized as Galegeeska revoilii. Future fieldwork in the Horn of Africa should aim to further document extent of occurrence, to monitor population trends, and to study the behavioral ecology and life history of the species.
Steven Heritage, Houssein Rayaleh, Djama G. Awaleh and Galen B. Rathbun. 2020. New Records of A Lost Species and A Geographic Range Expansion for Sengis in the Horn of Africa. PeerJ. 8:e9652. DOI: 10.7717/peerj.9652
