RESEARCH ARTICLE
A Galerella-like small mongoose from ca. 10 Ma of Kenya
2025 年 29 巻 p. 351-366
詳細
2025 年 29 巻 p. 351-366
Dentognathic fossil specimens of a Galerella-like small mongoose (Mammalia, Carnivora, Herpestidae) are described from the basal upper Miocene (ca. 10 Ma; Tortonian) Nakali Formation of central Kenya. They show comparable dental morphology to extant Herpestes, Xenogale, Galerella, and Urva: a better-developed parastylar shelf than the metastylar region on upper first molar (M1), an absence of the metastyle on M1, a trenchant and enlarged trigonid with a well-developed prevalid (mesial shearing blade) on lower first molar (m1), and much smaller m2 compared to m1. Compared with fossil “Herpestes”-like genera, the Nakali specimens are distinguished from them: they differ from Herpestides in being smaller and in having a much less developed cingulum on M1; from Leptoplesictis, Dunictis, and Forsythictis in having a less mesially-protruded paraconid (less mesiodistally-elongated prevalid) on m1; from Ugandictis and Kichechia in having a better-developed prevalid on m1, a much smaller m1 talonid, and much smaller m2 compared to m1. Taking the very small size into account, the Nakali specimens are more comparable to Galerella and very small species of Urva rather than to Herpestes, Xenogale, and larger species of Urva. The Nakali specimens are more comparable to very small Urva than to Galerella in the retention of small and single-rooted lower first premolar (p1). However, although extant Galerella generally lacks p1, several specimens of extant Galerella retain it. It is noteworthy that Galerella is an African genus, while Urva is an Asian genus. Here, we identified the Nakali specimens as cf. Galerella sp. because they are from Africa, but it should be noted that there is a possibility that they are of Urva or of unknown extinct lineage. This study highlights the problem of the taxonomic identification of fossil dentognathic specimens that were identified as “Herpestes.”
Mongooses or the Herpestidae are an extant family of the Carnivora (Mammalia) that includes 16 extant genera (Wozencraft, 2005; Patou et al., 2009; Egi et al., 2011; Nyakatura and Bininda-Emonds, 2012; Bininda-Emonds, 2013; Veron et al., 2022). All herpestid genera except one (Urva) are restricted to Africa and its nearby regions (Wozencraft, 2005; Patou et al., 2009; Bininda-Emonds, 2013; Veron et al., 2022). The genus Urva, which was formerly included in the genus Herpestes, is known from the southern part of Asia, and some species have been introduced to Europe, islands in the Pacific and the Caribbean, and North America (Wozencraft, 2005; Patou et al., 2009; Egi et al., 2011; Veron et al., 2022). All extant mongooses are small carnivores, weighing ca. 350 g–4.2 kg (Nowak, 1991; Kingdon, 1997). In Africa, mongoose fossils are recorded from the lower Miocene to Quaternary (Werdelin and Peigné, 2010). Peigné et al. (2005) described small herpestid specimens from the upper part of the upper Miocene (ca. 7–6 Ma; Vignaud et al., 2002) of Toros-Menalla (Chad) and identified them as an extant species Galerella sanguinea. If this identification is true, this record indicates that this extant species of mongoose has existed since ca. 7–6 Ma, which is a relatively long species duration (six to seven million years) among mammals (Peigné et al., 2005; Prothero, 2014; van den Hoek Ostende et al., 2023). However, this species identification was later disputed by Werdelin and Dehghani (2011).
Here, we describe five dentognathic herpestid fossil specimens discovered from the basal upper Miocene (ca. 10 Ma; Tortonian) Nakali Formation of central Kenya. The specimens are comparable to the dentognathic morphology of the small African herpestid Galerella. This study provides important data for the problem of taxonomic identification of “Herpestes”-like dentognathic fossil specimens.
The fossil specimens described here are stored in the Palaeontology Section, National Museums of Kenya, Nairobi, Kenya. The basic dental terminology mostly follows Bown and Kraus (1979) and Hershkovitz (1971). Comparative extant specimens were observed in The Mammals Collection at The Field Museum of Natural History, Chicago, IL, USA. Some comparisons were made using Animal Diversity Web (https://animaldiversity.org; University of Michigan, Ann Arbor, MI, USA).
The generic taxonomy of the extant Herpestidae is poorly resolved (Wozencraft, 1989, 1993, 2005; Egi et al., 2011; Bininda-Emonds, 2013; Taylor, 2013a; Van Rompaey and Colyn, 2013), and we mostly follow Patou et al. (2009) and Veron et al. (2022) with Nyakatura and Bininda-Emonds (2012) herein. As a result, the extant members of the family are classified in two subfamilies and 16 genera in this paper (Figure 1): the Herpestinae (= solitary mongooses) includes Atilax, Xenogale, Bdeogale, Cynictis, Paracynictis, Rhynchogale, Ichneumia, Galerella, Herpestes and Urva; and the Mungotinae (= social mongooses) includes Crossarchus, Dologale, Helogale, Liberiictis, Mungos and Suricata. It is noteworthy that species of Xenogale, Galerella, and Urva were previously included in the genus Herpestes. Under the current classification, extant Herpestes consists of a single species (Herpestes ichneumon), which is a large herpestid (Patou et al., 2009; Veron et al., 2022).
The species taxonomy of extant Galerella is complicated. According to Wozencraft (2005), the genus Galerella includes four extant species: Galerella sanguinea, Galerella pulverulenta, Galerella flavescens, and Galerella ochracea. Among these extant four species, G. sanguinea is the most widely distributed in Sub-Saharan Africa except for around South Africa and the tropical rainforest regions surrounding Gabon (Hoffman and Taylor, 2013). Galerella pulverulenta is distributed in South Africa and nearby regions (Cavallini, 2013). The distributions of these two species (G. sanguinea and G. pulverulenta) are basically separated with small overlapping areas (Cavallini, 2013; Hoffman and Taylor, 2013). Galerella flavescens is distributed near the western coasts of Angola and Namibia, and G. ochracea is distributed in Somalia and nearby regions (Taylor, 2013b, c). The distributions of these latter two species (G. flavescens and G. ochracea) completely overlap with that of G. sanguinea (Hoffman and Taylor, 2013; Taylor, 2013b, c), and they are sometimes regarded as invalid species or synonyms of G. sanguinea (Taylor, 1975; Wozencraft, 1989, 1993; Cavallini, 1992; Peigné et al., 2005). Also, Galerella nigrata, which was synonymized with G. flavescens by Wozencraft (2005), may be conspecific with G. sanguinea according to Rapson et al. (2012). Therefore, our comparison with extant species of Galerella is focused on the two species, G. sanguinea and G. pulverulenta, as in the case of Peigné et al. (2005).
The generic and specific statuses of fossil “Herpestes”-like genera/species are also complicated (Petter, 1987; Werdelin and Peigné, 2010; Morales and Pickford, 2021). We follow the classification of “Herpestes”-like fossil taxa presented in Table 1.
| Galerella Gray, 1865 |
| Galerella debilis (Petter, 1973) |
| = Herpestes debilis Petter, 1973 |
| Galerella palaeoserengetensis (Dietrich, 1942) |
| = Mungos palaeoserengetensis Dietrich, 1942 |
| = Herpestes palaeoserengetensis (Dietrich, 1942) |
| (including Herpestes primitivus Petter, 1973) |
| Herpestes Illiger, 1811 |
| Herpestes mesotes Ewer, 1956 |
| Herpestes abdelalii Geraads, 1997 |
| Herpestes transvaalensis (Broom, 1937) |
| = Crossarchus transvaalensis Broom, 1937 |
| Herpestes alaylaii Haile-Selassie and Howell, 2009 |
| Urva Hodgson, 1837 |
| Urva fanchangensis Jiangzuo et al., 2025 |
| Leptoplesictis Forsyth Major, 1903 |
| Leptoplesictis filholi (Gaillard, 1899) |
| = Herpestes filholi Gaillard, 1899 |
| (including Leptoplesictis minor Forsyth Major, 1903) |
| Leptoplesictis peignei Grohé et al., 2020 |
| = Dunictis peignei (Grohé et al., 2020) |
| Dunictis Morales and Pickford, 2021 |
| Dunictis rangwai (Schmidt-Kittler, 1987) |
| = Leptoplesictis rangwai Schmidt-Kittler, 1987 |
| Dunictis? mbitensis (Schmidt-Kittler, 1987) |
| = Leptoplesictis mbitensis Schmidt-Kittler, 1987 |
| Dunictis senutae (Morales et al., 2008) |
| = Leptoplesictis senutae Morales et al., 2008 |
| Dunictis? namibiensis (Morales et al., 2008) |
| = Leptoplesictis namibiensis Morales et al., 2008 |
| Forsythictis Morales and Pickford, 2021 |
| Forsythictis aurelianensis (Schlosser, 1888) |
| = Stenogale aurelianensis Schlosser, 1888 |
| = Herpestes aurelianensis (Schlosser, 1888) |
| = Leptoplesictis aurelianensis (Schlosser, 1888) |
| Forsythictis atavus (de Beaumont, 1973) |
| = Leptoplesictis atavus de Beaumont, 1973 |
| Forsythictis ibericus Morales and Pickford, 2021 |
| Kichechia Savage, 1965 |
| Kichechia zamanae Savage, 1965 |
| Kichechia savagei Adrian et al., 2018 |
| Ugandictis Morales et al., 2007 |
| Ugandictis napakensis Morales et al., 2007 |
Dental abbreviations.—I/i, upper/lower incisors. C/c, upper/lower canines. P/p, upper/lower premolars. M/m, upper/lower molars.
Institutional abbreviations.—FMNH, Field Museum of Natural History, Chicago, USA. FSL, Faculté des Sciences de la Terre, Université de Lyon (Roth, 1988). GSN, Geological Survey of Namibia, Windhoek, Namibia. KNM, National Museums of Kenya, Nairobi, Kenya. MNCN, Museo Nacional de Ciencias Naturales, Madrid, Spain. NHMUK, Natural History Museum (= formerly British Museum of Natural History), London, UK. SMF, Forschungsinstitut Senckenberg, Frankfurt am Main, Germany (Morlo, 1996). SNSB-BSPG, Bavarian State Collection of Paleontology and Historical Geology, Munich, Germany.
Other abbreviations.—1976 XXII, a collection of the Petersbuch 2 locality, Germany (Stored in SNSB-BSPG; Roth, 1988). BAR, a prefix of the specimen numbers used by Morales and Pickford (2008); Morales and Pickford (2008) did not mention the repository of the specimens of BAR. CMF-M, a prefix of the specimen numbers used by Savage (1965) (stored in NHMUK; Schmidt-Kittler, 1987). GT, the Grillental fossil locality, Sperrgebiet, Namibia (Morales and Pickford, 2021). MM, fossils from Mae Moh, Thailand (Grohé et al., 2020). MO, the Moruorot fossil locality, Kenya. NA, the Nakali Fossil locality, Kenya. NAP, the Napak fossil locality, Uganda (The specimens will be stored in Uganda Museum in Kampala; Schmidt-Kittler, 1987). RU, the Rusinga fossil locality, Kenya. TM, Fossils from the upper Miocene Toros-Menalla, Chad (Peigné et al., 2005). UMP, specimens stored in the Uganda Museum, Kampala, Uganda (Morales et al., 2007). VxC, the Vieux-Collonges locality (Roth, 1988).
The specimens described here were recovered from the “Upper Member” of the Nakali Formation at the Nakali locality (NA) (approx. 01°12′N and 36°23′E), about 40 km west of Maralal, central Kenya (Kunimatsu et al., 2007). The age of the formation is well constrained to around 10.0–9.8 Ma (early Tortonian, early late Miocene) based on 40Ar–39Ar dating and stratigraphic and paleomagnetic analyses (Kunimatsu et al., 2007; Sakai et al., 2013; Tsubamoto et al., 2017). The Nakali Formation has yielded many vertebrate fossils including fish, crocodiles, chelonians, snakes, birds, and nearly 50 species of mammals (Kunimatsu et al., 2007; Tsubamoto et al., 2020, 2023; Handa et al., 2021). The fossil mammals of the formation include great apes including Nakalipithecus nakayamai, which is a candidate for the latest common ancestor of the extant African great apes and humans (Kunimatsu et al., 2007, 2016). The palaeoenvironment of the formation was relatively humid with woodlands and lakes, according to the isotopic and sedimentologic analyses (Uno et al., 2011; Sakai et al., 2013).
Class Mammalia Linnaeus, 1758
Order Carnivora Bowdich, 1821
Suborder Feliformia Kretzoi, 1945
Family Herpestidae Bonaparte, 1845
Subfamily Herpestinae Bonaparte, 1845
Genus cf. Galerella Gray, 1865
cf. Galerella sp.
cf. Galerella sp., Tsubamoto et al., 2020, p. 44, table 1.
Material.—KNM-NA 52885, a left mandibular fragment with p4–m2; KNM-NA 52891, a trigonid of right m1; KNM-NA 51583, left M1 lacking the tip of the parastyle; KNM-NA 57480, right M1; KNM-NA 72612, right M1.
Formation and locality.—“Upper Member” of the Nakali Formation; the Nakali locality (approx. 01°12′N and 36°23′E), central Kenya (Kunimatsu et al., 2007).
Age.—Early Tortonian (early late Miocene), ca. 10.0–9.8 Ma (Kunimatsu et al., 2007; Sakai et al., 2013; Tsubamoto et al., 2017).
Measurements.—Shown in Table 2.
| cf. Galerella sp. from Nakali | “G. sanguinea” from Toros-Menalla | extant G. sanguinea | extant G. pulverulenta | ||||||
|---|---|---|---|---|---|---|---|---|---|
| KNM‑NA 51583 | KNM‑NA 57480 | KNM‑NA 72612 | KNM‑NA 52885 | KNM‑NA 52891 | range* | range*,** | range** | ||
| M1 | L | 2.8 | 2.7 | 3.0 | — | — | 2.6–3.0 (n=2) | 2.3–3.3 (n=37) | 3.3–4.4 (n=24) |
| L-buc | — | 3.4 | 3.7 | — | — | 2.9–3.9 (n=2) | 3.0–4.8 (n=20) | — | |
| W | >5.9 | 5.4 | 5.8 | — | — | 5.2–6.0 (n=2) | 4.9–7.0 (n=144) | 5.9–7.5 (n=57) | |
| p4 | L | — | — | — | 5.3 | — | 5.0 (n=2) | 3.8–5.4 (n=143) | 5.0–6.0 (n=54) |
| W | — | — | — | 2.2 | — | >2.0 (n=1) | 1.8–2.8 (n=143) | 2.1–3.2 (n=54) | |
| m1 | L | — | — | — | 5.4 | — | 6.0 (n=1) | 4.4–6.2 (n=144) | 5.6–6.8 (n=54) |
| L-trd | — | — | — | 3.6 | 3.6 | 4.0 (n=1) | 3.4–3.9 (n=17) | — | |
| W-trd | — | — | — | 3.0 | 3.7 | >3.0 (n=1) | 2.6–3.6 (n=143) | 3.2–3.8 (n=54) | |
| W-tad | — | — | — | 2.2 | — | — | — | — | |
| m2 | L | — | — | — | 2.2 | — | 3.0, >3.1 (n=2) | 2.0–3.3 (n=32) | 2.5–3.8 (n=19) |
| W-trd | — | — | — | 1.7 | — | 2.1 (n=1) | 1.7–2.3 (n=33) | 2.0–2.6 (n=19) | |
| W-tad | — | — | — | 1.5 | — | — | — | — | |
| p2–m2 | L-alv | — | — | — | 20.7 | — | 20.3 (n=1) | 17.3–21.8 (n=104) | 20.1–23.9 (n=35) |
| mandible | T-p3 | — | — | — | 4.1 | — | 3.6 (n=1) | 2.7–3.8 (n=16) | — |
| T-m1 | — | — | — | 3.8 | — | 3.5 (n=1) | 2.6–3.8 (n=16) | — | |
| D-p2–3 | — | — | — | 6.7 | — | — | 4.8–6.6 (n=16) | — | |
| D-p3–4 | — | — | — | 6.9 | — | 6.1 (n=1) | 4.5–6.4 (n=16) | — | |
| D‑p4‑m1 | — | — | — | 8.0 | — | 7.2 (n=1) | 5.0–7.4 (n=16) | — | |
| D-m1–2 | — | — | — | 7.6 | — | 7.3 (n=1) | 5.2–7.3 (n=16) | — | |
| D‑m2dist | — | — | — | 7.4 | — | 7.0 (n=1) | 5.3–7.0 (n=16) | — | |
Description.—The present specimens consist of a mandibular fragment with p4–m2, an m1 trigonid, and three M1s. The tooth enamel is smooth.
The mandible (KNM-NA 52885; Figures 2, 3A) is relatively robust, and its ventral border is concave below p2–p3 and is convex below p4–m1. The mandible bears roots of p1–p3 and an alveolus for the canine. The p1 is single rooted. Both p2 and p3 have two roots. The p1 root is much smaller than the anterior root of p2, implying that p1 was very small. Based on the arrangement of the canine alveolus, p1 root, and anterior root of p2, there are no diastemata mesial and distal to p1. The alveolus for the canine is large, implying the presence of a large canine. There are two mental foramina: the anterior one is below p1, and the posterior one is below the mesial root of p3. The mandibular symphysis originates below p2. On the lingual side, there is a mandibular foramen at the posterior margin of the preserved mandible. The anterior margin of the masseter fossa extends to below the distal part of m2 in lateral (buccal) view.
The p4 (KNM-NA 52885; Figures 2, 3A) is mesiodistally elongated and has a large and probably tall protoconid, although the protoconid is broken away from its base. There is a small and low paraconid (mesial accessory cuspid) at the mesial base of the crown. The metaconid is also low, and it is larger than the paraconid, being located at the distobuccal base of the protoconid. The ‘talonid’ (or distal cingulid in Peigné et al., 2005) is small with a very small and shallow ‘talonid basin.’ There is no distinct cingulum (except for the ‘distal cingulid’ or ‘talonid’).
The m1 (KNM-NA 52885 and 52891; Figures 2, 3) is a carnassial tooth and has a trenchant and enlarged trigonid. The prevalid (mesial shearing blade, the buccal surface of the protoconid-paraconid) is large and diagonally oriented to the tooth row. The trigonid is approximately a right triangle (the angle protoconid-metaconid-paraconid is approximately a right angle) in occlusal view, with the paraconid relatively protruded mesially. The protoconid is the tallest cusp. The paraconid is smaller than the protoconid and is larger than the metaconid. The metaconid is located lingual to the protoconid. The talonid is much smaller and lower than the trigonid. There is a hypoconid, hypoconulid, and entoconid, all of which are small. The hypoconulid is smaller than the hypoconid and larger than the entoconid. The cristid obliqua is mesiodistally oriented and connects to the distal base of the protoconid. The talonid basin is shallow and open lingually.
The m2 (KNM-NA 52885; Figures 2, 3A) is much smaller than m1. Although the mesial portion of the trigonid is broken away, at least the protoconid and metaconid exist. The trigonid is likely slightly larger and taller than the talonid. The talonid basin is shallow and closed lingually. The talonid is somewhat pointed distally.
M1 (KNM-NA 51583, 57480, and 72612; Figure 4) is buccolingually much wider than mesiodistally long. In occlusal view, it is an obtuse triangle (the angle parastyle-metacone-protocone is a obtuse angle) and asymmetrical: the parastylar shelf is large and much better developed and more buccally protruding than the metastylar region. The parastyle does not form a blade or cone but is a blunt swelling. The metastyle is absent. The trigon cusps consist of the paracone, metacone, and protocone, without conules. The paracone is larger than the metacone. It is separated from the metacone with a notch between them. The preparacrista extends buccally, connecting to the parastyle. The postparacrista extends distally, connecting to the premetacrista. The premetacrista extends mesially. The postmetacrista is weak and extends distally, disappearing at the distal margin of the crown. The protocone is crescentic and larger than the paracone. It is located more distally than the paracone. The preprotocrista extends mesiobuccally, connecting to the mesial base of the paracone. The postprotocrista is weaker than the preprotocrista and extends distobuccally, merging to the lingual part of the distal cingulum. The trigon basin is open distally. A very slight swelling or very weak cingulum is observed around the mesial, lingual, and distal base of the protocone. The lingual part of the distal cingulum connects to the distolingual base of the metacone. There are three roots: the one under the protocone is the largest and is mesiodistally shorter than buccolingually wide, and the other two are under the paracone-parastyle region and the metacone, respectively. The root under the paracone-parastyle region is somewhat larger than that under the metacone.
The present mammalian fossil specimens from Nakali are assigned to the Carnivora in having a carnassial m1. They are assigned to the Herpestidae in having the following characteristics among the Carnivora: small body size; a diagonally oriented prevalid with the relatively developed talonid on m1; and M1 with a transversely long and triangular shaped crown, a stylar shelf, a metacone and paracone subequal in size, a well-developed protocone, a strong preprotocrista, a very weak or no lingual cingulum, and an absence of the paraconule and metaconule. They are generally distinguished from the Viverridae by their much smaller size and in having the following M1 characteristics: a transversely longer shaped crown, presence of the stylar shelf, much better-developed parastylar region than the metastylar region, and absence of conules in the trigon (e.g. Egi et al., 2011). They are distinguished from the small viverrid Poiana and the prionodontid Prionodon in having a smaller p1, a less mesially protruded paraconid on m1, and a more mesiodistally shorten premolar dentition on the mandible, and in lacking diastemata between p1 and p2 and between p2 and p3.
Among extant herpestid genera, the Nakali fossil specimens are comparable to Herpestes, Xenogale, Galerella, and Urva (Herpestinae), all of which were previously included in the genus Herpestes in having the following characteristics (Figures 5, 6, 7; e.g. Petter, 1969; Taylor, 1975; Cavallini, 1992; Peigné et al., 2005): a better-developed and more buccally protruding parastylar shelf than the metastylar region without the metastyle on M1, p1 that is absent or very reduced, a very weakly developed paraconid (mesial accessory cuspid) on p4, a trenchant and enlarged trigonid with a well-developed prevalid on m1, an m1 metaconid that is located at the mesiodistally nearly same level as the protoconid, and much smaller (reduced) m2 compared to m1. The Nakali specimens are distinguished from mungotine and other herpestine genera in having a more mesially protruded m1 paraconid and more reduced m2 compared to m1. They further differ from the Mungotinae in having a more buccally protruded parastylar region compared to the metastylar region on M1 and a less developed m1 hypoconid. They are characterized by their small size, are comparable in size to Galerella and very small species of Urva, and are much smaller than Herpestes, Xenogale, and medium-to-large-sized species of Urva (including a fossil species Urva fanchangensis) (Figures 5, 6, 7; Tables 2, 3; Egi et al., 2011; Do Linh San et al., 2022; Jiangzuo et al., 2025). The Nakali specimens, Galerella, and very small Urva share the following characteristics with one another: an m1 metaconid that is located at the mesiodistally same level as the protoconid; and two mental foramina, one is below p1 and the other is below the mesial root of p3 (Figures 5A–C, E; 6A–C, E). Therefore, the Nakali specimens are most comparable to Galerella and very small Urva (such as Urva auropunctata and Urva javanica) (Table 3; Egi et al., 2011).
| Genus | Species | m1 length (in mm) | m1 width (in mm) | Geographic distribution | Geologic age | References |
|---|---|---|---|---|---|---|
| cf. Galerellasp. from Nakali | 5.4 | 3.0–3.7 | Kenya | Tortonian (early late Miocene) (ca. 10 Ma) | This study | |
| “G. sanguinea” from Toros-Menalla | 6.0 | >3.0 | Chad | Messinian (late late Miocene) (ca. 7–6 Ma) | Peigné et al. (2005) | |
| Galerella | G. sanguinea | 4.4–6.2 | 2.6–3.6 | Africa | Recent | Table 2 |
| G. pulverulenta | 5.6–6.8 | 3.2–3.8 | southern Africa | Recent | Table 2 | |
| G. debilis | 4.0 | — | Tanzania | Pleistocene | Petter (1973) | |
| G. palaeoserengetensis | 7.0–7.6 | 4.0–4.1 | Tanzania | Pliocene | Petter (1987) | |
| G. sp. from Laetoli | 5.9 | 3.5 | Tanzania | Pliocene | Werdelin and Dehghani (2011) | |
| Urva | U. auropunctata | 5.0–6.2 | 2.8–3.8 | Asia | Recent | ogirinal messurements |
| U. edwardsii | 6.7–6.9 | 3.6 | Asia | Recent | ogirinal messurements | |
| U. fanchangensis | — | — | China | Pleistocene (ca. 1.2–1.0 Ma) | Jiangzuo et al. (2025) | |
| U. sp. from Gwebin | — | — | Myanmar | late Pliocene | Egi et al. (2011) | |
| “Herpestes” spp. from Siwaliks | — | — | Pakistan | late Miocene (ca. 9.5–7.0 Ma) | Barry (1983) | |
| Herpestes | H. ichneumon | 9.1 | 4.7 | Africa | Recent | ogirinal messurements |
| H. mesotes | 8.7–8.8 | 5.4 | South Africa | Pleistocene | Ewer (1956) | |
| H. transvaalensis | 7.5 | — | South Africa | Pleistocene | Peigné et al. (2005) | |
| H. abdelalii | 6.7–7.5 | 3.8–4.1 | Morocco | Plio-Pleistocene (ca. 2.5 Ma) | Geraads (1997) | |
| H. alaylaii | 6.3–7.4 | 3.7–3.8 | Ethiopia | Messinian (late late Miocene) (ca. 5.8–5.5 Ma) | Haile-Selassie and Howell (2009) | |
| H. sp. A from Langebaanweg | 6.4–6.8 | 3.3–3.6 | South Africa | earliest Pliocene (ca. 5.2–5.0 Ma) | Hendey (1974) | |
| H. sp. B from Langebaanweg | 4.2–4.3 | 2.3–2.4 | South Africa | earliest Pliocene (ca. 5.2–5.0 Ma) | Hendey (1974) | |
| H. sp. from Lemudong’o | 4.5 | — | Kenya | Messinian (late late Miocene) (ca. 6.1–6.0 Ma) | Howell and García (2007) | |
| H. sp. from Toros-Menalla | 7.6 | 4.2 | Chad | Messinian (late late Miocene) (ca. 7–6 Ma) | Peigné et al. (2008) | |
| H. sp. from Kipsaraman | 6.5 | 3.4 | Kenya | middle Miocene (ca. 14.5 Ma) | Morales and Pickford (2008) | |
| Xenogale | X. naso | 8.9 | 5.3 | Africa | Recent | ogirinal messurements |
| Leptoplesictis | L. filholi | 4.4–5.1 | 2.4–2.6 | Europe | middle Miocene (NM6–8) | Morales and Pickford (2021) |
| L. peignei | 5.9–7.1 | 2.7–3.6 | Thailand | late middle Miocene (ca. 13.4–13.2 Ma) | Grohé et al. (2020) | |
| Dunictis | D. rangwai | 4.9–5.1 | 2.6–2.7 | Kenya | early to earliest middle Miocene (ca. 20–15.5 Ma) | Schmidt-Kittler (1987), Morales and Pickford (2021) |
| D.? mbitensis | 5.1 | 2.5–2.7 | Kenya | early to earliest middle Miocene (ca. 20–15.5 Ma) | Schmidt-Kittler (1987), Morales and Pickford (2021) | |
| D. senutae | 5.5–6.0 | 2.8–3.0 | Namibia | early Miocene (ca. 21–19 Ma) | Morales et al. (2008), Morales and Pickford (2021) | |
| D.? namibiensis | 8.3 | 4.4 | Namibia | early Miocene (ca. 21–19 Ma) | Morales et al. (2008), Morales and Pickford (2021) | |
| Forsythictis | F. aurelianensis | 5.3–5.6 | 2.5 | Europe | late early Miocene (MN4) | Roth (1988), Morales and Pickford (2021) |
| F. atavus | 4.7–5.1 | 2.4–2.5 | Europe | latest early to earliest middle Miocene (MN5) | Roth (1988), Morales and Pickford (2021) | |
| F. ibericus | 5.6 | 2.8 | Europe | late early Miocene (MN4) | Morales and Pickford (2021) | |
| Kichechia | K. zamanae | 5.6–7.1 | 3.1–4.6 | Kenya & Uganda | early Miocene | Savage (1965), Adrian et al. (2018) |
| K. savagei | 5.6–6.3 | 3.3–3.8 | Kenya | early Miocene | Adrian et al. (2018) | |
| Ugandictis | U. napakensis | 6.0–6.7 | 3.4–3.7 | Uganda & Kenya | early Miocene | Savage (1965), Morales et al. (2007) |
Many fossil herpestid or herpestid-like genera are reported from the Neogene of Africa, Europe, and Asia (e.g. Savage, 1965; Petter, 1973, 1987; Schmidt-Kittler, 1987; Roth, 1988; Morlo, 1996; Morales et al., 2007, 2008; Morales and Pickford, 2008, 2021; Werdelin and Peigné, 2010; Grohé et al., 2020). Compared with the fossil “Herpestes”-like genera, the Nakali specimens are distinguished from Herpestides (Viverridae) in being smaller, in having a much less developed cingulum on M1, and in lacking a lingual swelling at the distolingual base of the p4 protoconid (Figures 5A, N; 7A, H–I; Schmidt-Kittler, 1987); from Ugandictis and Kichechia in having a much smaller and narrower m1 talonid compared to the m1 trigonid, and much smaller m2 compared to m1 (Figures 5O–Q, 7F; Schmidt-Kittler, 1987; Morales et al., 2007; Adrian et al., 2018); and further from Kichechia in having a better-developed prevalid on the m1 trigonid and a more buccally protruding parastylar shelf than the metastylar region on M1 (Figures, 5O, 7J; Schmidt-Kittler, 1987). Leptoplesictis is a fossil small “Herpestes”-like genus that was previously known from the lower to middle Miocene of Europe and Africa (e.g. Schmidt-Kittler, 1987; Roth, 1988; Werdelin and Peigné, 2010; Grohé et al., 2020). Grohé et al. (2020) described Leptoplesictis peignei from the middle Miocene of Thailand. Morales and Pickford (2021) erected two new genera, Dunictis and Forsythictis, and assigned some species of Leptoplesictis into those two genera (Table 1). The Nakali specimens are distinguished from the Leptoplesictis filholi, which is the type species of the genus, in having a much less mesially protruded m1 paraconid (m1 prevalid), a less developed p4 paraconid, and smaller p1 (Figure 5F; Morales and Pickford, 2021). They are distinguished from L. peignei in having a less mesially protruded m1 paraconid (= a less elongated prevalid on m1) and an m1 metaconid that is located at the mesiodistally same level as the protoconid (Figure 5I–J; Grohé et al., 2020). The m1 metaconid is somewhat distally shifted compared to the protoconid in L. peignei. The Nakali specimens are distinguished from Dunictis and Forsythictis in having a much less mesially protruded m1 paraconid (m1 prevalid) and a less developed p4 paraconid (Figure 5G–H, K–L; Schmidt-Kittler, 1987; Roth, 1988; Morales and Pickford, 2021). They further differ from Dunictis senutae, which is the type species of the genus, in having larger m1 metaconid and smaller p1 (Figure 5H; Morales and Pickford, 2021), and from Dunictis? mbitensis in lacking a lingual cuspid on p4 (Schmidt-Kittler, 1987). They further differ from Forsythictis atavus in having proportionally shorter and wider M1 (Figure 7G; Roth, 1988).
Furthermore, the Nakali specimens are distinguished from the fossil species of Galerella and Herpestes by their size. They are larger than Galerella debilis and are smaller than Galerella palaeoserengetensis, Herpestes mesotes, Herpestes abdelalii, Herpestes transvaalensis, and Herpestes alaylaii (Tables 1, 3; Broom, 1937; Dietrich, 1942; Ewer, 1956; Petter, 1973, 1987; Geraads, 1997; Peigné et al., 2005).
The Nakali specimens appear to be referrable to Galerella rather than to Urva. The Nakali specimens are comparable in dental size to the extant Galerella without any significant differences as well as the positions of the two mental foramina on the mandible (Figures 5A–C; 6A–C; 7A–C). The dental morphologies and positions of the two mental foramina of Galerella and very small Urva are very similar to each other (Figures 5, 6, 7), so there is a difficulty in distinguishing these two genera based on the dentognathic material. Urva retains a single-rooted p1 (Figure 5C, E), whereas Galerella generally lacks p1 (Petter, 1969; Taylor, 1975; Cavallini, 1992). In this point, the Nakali specimens are more comparable to very small Urva than to Galerella, although the Nakali specimens appear to have smaller p1 than very small Urva (Figure 5A, E). However, several extant specimens of Galerella have a very small and single-rooted p1 (Peigné et al., 2005). Among the 45 extant adult specimens of extant G. sanguinea we examined at FMNH, five specimens (FMNH 38353, 27345, 177226, 177228, 196629) retained p1s that were smaller than those of very small species of Urva (Figures 5B, C; 6B, E). In addition, Urva is an Asian genus, whereas Galerella is an African genus. The Nakali specimens are from Kenya, which is within the distributional range of living Galerella (Taylor, 1975, 2013a, b, c; Cavallini, 1992, 2013; Wozencraft, 2005; Hoffman and Taylor, 2013). Therefore, the identification of the Nakali specimens as Galerella may be reasonable. The teeth of the Nakali specimens are generally as large as those of extant Galerella sanguinea and are slightly smaller than those of extant Galerella pulverulenta, although most of the dental measurements of the Nakali specimens and G. pulverulenta overlap with each other (Table 2; Taylor, 1975; Watson and Dippenaar, 1987; Petter, 1987; Cavallini, 1992, 2013; Peigné et al., 2005).
Nevertheless, a possibility that the Nakali specimens may be of Urva or perhaps of unknown extinct lineage cannot be excluded. The lineages of Urva and Galerella had already or likely occurred near the age of the Nakali Formation (ca. 10 Ma) according to molecular analyses (Figure 1; Bininda-Emonds et al., 1999; Patou et al., 2009; Nyakatura and Bininda-Emonds, 2012; Veron et al., 2022). The Urva lineage is considered to have migrated from Africa/Europe to Asia during the Miocene (e.g. Barry, 1983; Grohé et al., 2020; Veron et al., 2022). Therefore, the presence of the Urva lineage in ca. 10 Ma of Africa is not unrealistic. It should be noted that the Nakali specimens have possible autoapomorphic or diagnostic characters compared to Galerella and very small species of Urva: a more mesiodistally oriented M1 postprotocrista, p4 as long as m1, somewhat proportionally smaller m2 compared to m1, and somewhat more robust mandible (Figures 5, 6, 7; Table 2). The M1 postprotocrista of Galerella, very small Urva, and “Galerella sanguinea” from Toros-Menalla extends more diagonally (more buccally) from the tip of the protocone than that of the Nakali specimens do (Figures 4, 7). Nevertheless, among the Nakali specimens, KNM-NA 72612 (Figure 4C) has more diagonally (more buccally) oriented postprotocrista than KNM-NA 51583 (Figure 4A) and KNM-NA 57480 (Figure 4B), implying that this character reflects intraspecific variation, neither a critical taxonomic nor phyletic difference. The mesiodistal length of p4 of Galerella, very small Urva, and “Galerella sanguinea” from Toros-Menalla compared to the m1 length is likely slightly shorter than that of the Nakali specimens do (Table 2). Although the mandibular corpus of the Nakali specimen is generally somewhat more robust than that of Galerella, very small Urva, and “Galerella sanguinea” from Toros-Menalla (Figure 6A, B, D, E), it is as robust as that of FMNH 85978 (extant Galerella sanguinea) (Figure 6A, C). Some of these characters may indicate another possibility that the Nakali specimens are assigned to an unknown extinct (fossil) lineage within the Herpestinae, neither to Galerella nor to Urva.
In sum, we identified the Nakali specimens as cf. Galerella sp. because they are from Africa and are morphologically very comparable to Galerella. However, there is a possibility that they are of Urva or of an unknown extinct lineage.
Remarks on some fossil “Herpestes”There are many herpestid fossil specimens that were assigned to “Herpestes sp.” (Table 3; e.g. Hendey, 1974; Barry, 1983; Howell and García, 2007; Morales and Pickford, 2008; Peigné et al., 2008; Haile-Selassie and Howell, 2009; Werdelin and Peigné, 2010). The oldest fossil record of Herpestes sp. is from the middle Miocene (ca. 14.5 Ma) of Kipsaraman, Kenya (Morales and Pickford, 2008). The Nakali specimens differ from Herpestes sp. from Kipsaraman in being smaller and in lacking a lingual swelling at the distolingual base of the p4 protoconid (Figure 5M; Table 3). The dental (p4–m1) morphology of Herpestes sp. from Kipsaraman is comparable to that of Herpestides, which is assigned to the Viverridae based on the basicranial morphology (Hunt, 1991; Werdelin and Peigné, 2010), in the dental size and in having a lingual swelling at the distolingual base of the p4 protoconid (Figure 5M, N). Therefore, the generic identification of the Kipsaraman material (Figure 5M), which is from the middle Miocene, should be carefully reconsidered. On the basis of recent taxonomic revisions of the Herpestidae, Herpestes only comprises one extant species, H. ichneumon (Patou et al., 2009; Veron et al., 2022). H. ichneumon is a large herpestid in body size, which is roughly as large as extant Xenogale (Table 3; Figures 5R, S; 7K, L). All the fossil Herpestes species/specimens except for H. mesotes from Africa are much smaller than H. ichneumon in the m1 size (Table 3). Therefore, the generic identification of those species/specimens should be carefully treated. It should be noted that fossil species of Herpestes/Galerella and the fossil specimens of Herpestes/Galerella-like specimens from Langebaanweg, Lemudong’o, and Toros-Menalla as well as from Nakali generally retain a single-rooted p1, which is generally absent in extant Galerella and is generally present in extant Herpestes/Xenogale/Urva and fossil herpestid genera (Figure 5; Ewer, 1956; Petter, 1969, 1987; Hendey, 1974; Geraads, 1997; Peigné et al., 2005, 2008; Howell and García, 2007; Haile-Selassie and Howell, 2009). Therefore, the retention of p1 is likely plesiomorphic. Consequently, at least the specimens of the very small-sized “Herpestes sp.” such as those of Herpestes sp. B from Langebaanweg (earliest Pliocene, ca. 5.2–5.0 Ma) and Herpestes sp. from Lemudong’o (Messinian, ca. 6.1–6.0 Ma) (Table 3), both of which retain single-rooted p1, may be better assigned to Galerella, on the basis of their small size. “Herpestes” spp. from the upper Miocene part (ca. 9.5–7.0 Ma) of the Siwaliks of Pakistan described by Barry (1983) appear to be better assigned to Urva, which is the only extant Asian herpestid genus.
The dentognathic fossil specimens of a small herpestid (Mammalia, Carnivora) from the basal upper Miocene Nakali Formation (ca. 10 Ma) of Kenya (Figures 2, 3, 4) are morphologically most comparable to Galerella, which is an extant African genus, and to very small species of Urva, which is an extant Asian genus. They are here identified as cf. Galerella sp., although it should be noted that the specimens may be of Urva or of an unknown extinct lineage. Most records of the extinct herpestid or herpestid-like genera are from the lower to middle Miocene of Africa and Europe, and most of the fossil record of the extant herpestid genera are from the Messinian (upper part of the upper Miocene) to Plio-Pleistocene (e.g. Werdelin and Peigné, 2010; Egi et al., 2011; Grohé et al., 2020; Morales and Pickford, 2021). The only record of an extinct herpestid genus in Asia is from the middle Miocene (ca. 13.4–13.2 Ma) of Thailand (Grohé et al., 2020), and the oldest record of a probable extant herpestid genus (likely Urva) is from the upper Miocene (ca. 9.5 Ma; Tortonian) of Siwaliks, Pakistan (Barry, 1983). Therefore, the Tortonian (early late Miocene) is a time of the herpestid faunal transition in Africa and Asia: from extinct genera to extant genera. This study highlights the difficulty of taxonomic (generic and specific) identification of dentognathic fossil specimens identified as “Herpestes” and “Herpestes”-like, such as those of Leptoplesictis, Herpestides, Dunictis, Forsythictis, and Galerella. In addition, the Nakali Formation yields two more herpestid taxa that might belong to extant genera (Tsubamoto et al., 2020), implying that the Nakali fossil mammalian fauna is critical for discussing the evolution of extant herpestid genera as well as the early evolution of the African hominids during the Tortonian.
We are grateful to the National Commission for Science, Technology and Innovation (NACOSTI) of the Government of Kenya for giving research permission for us. We are also grateful to Mary Gikungu, Fredrick Kyalo Manthi, Emmanuel K. Ndiema, Sarah Wanjiku Kimani, Margaret Omoto, Mary Muungu, and Francis Ndiritu Muchemi (National Museums of Kenya, Nairobi, Kenya) and to Adam Ferguson, Anderson Feijó, and Lauren Johnson (Field Museum of Natural History, Chicago, USA) for facilitating access to specimens in their collections. Thanks are also due to the personnel of Japan Society for the Promotion of Science, Nairobi Research Station for their help during our stay in Kenya and to the support of the Domestic Research Program from Ryukoku University. We also thank Naoko Egi (National Museum of Nature and Science, Tsukuba, Japan) for her advice on the taxonomic identification of the specimens described here. This manuscript was improved by critical comments from Lars Werdelin (Swedish Museum of Natural History, Stockholm, Sweden) and two other anonymous reviewers. This research was supported by JSPS KAKENHI Grant Numbers 25257408, 16H02757 and 23H02562 (to M. Nakatsukasa) and Bilateral Programs Joint Research Project (JSPS-NACOSTI).
T. T. organized this study, analyzed data, and was primarily responsible for the taxonomic aspects. T. T. and Y. K. examined the specimens. Y. K. and M. N. conducted geological and paleontological field research and collected fossil specimens. All authors contributed to the writing of the paper.
