Hyaenodonta, Van Valen, 1967

Morlo, Michael, Friscia, Anthony, Miller, Ellen R., Locke, Ellis & Nengo, Isaiah, 2021, Systematics and paleobiology of Carnivora and Hyaenodonta from the lower Miocene of Buluk, Kenya, Acta Palaeontologica Polonica 66 (2), pp. 465-484 : 469-471

Hyaenodonta indet. A (size of Leakitherium Savage, 1965 )

Fig. 3A, B , Table 2.

Material.—KNM­WS 12619, proximal left ulna fragment; KNM­WS 12584, distal left tibia; from Buluk, east of Lake Turkana, Kenya; lower section of the Buluk Member, Bakate Formation, uppermost lower Miocene.

Description.—KNM­WS 12619 ( Fig. 3A ) is a left proximal ulna fragment, with a maximum diameter of 25.8 mm, which is comparable in size to a large leopard (<100 kg) ( Stein and Hayssen 2013). The length of the olecranon cannot be determined due to breakage, but morphologically the olecranon appears to bend strongly posteriorly as indicated by the strong posteriorly running anterior olecranon ridge. This is reminiscent of specimens of H. sulzeri ( Ginsburg 1980: fig. 25).

KNM­WS 12584 ( Fig. 3B ) preserves the distal end of a left tibia, which, based on size alone, may belong to the same taxon as KNM­WS 12619. The morphology of the tibia is felid­like in being more similar to extant species of Panthera Oken, 1816 , than Amphicyon ( Argot 2010) , but as in H. sulzeri , the medial malleolus is strong and more symmetrical than in members of Carnivora (see Ginsburg 1980: fig. 34). Moreover, no felid of this size is known from the lower Miocene of Africa. We thus refer this specimen to Hyaenodonta and suggest that the ulnar and tibial fragments may belong to the same species.

Remarks.—The only leopard­sized hyaenodonts known from the lower Miocene of Kenya are Leakitherium hiwegi Savage, 1965 , and Isohyaenodon andrewsi Savage, 1965

Lewis and Morlo 2010). However, no postcranial material is included in the hypodigm of either of these taxa, and no corresponding dental remains are known from Buluk.

Hyaenodonta indet. B (size of Sectisodon occultus Morales and Pickford, 2017 )

Fig. 3C , Table 1.

Material.—KNM­WS 65730, right edentulous mandible fragment, with alveoli for m1 and m2, and roots of m3; from Buluk, east of Lake Turkana, Kenya; lower section of the Buluk Member, Bakate Formation, uppermost lower Miocene.

Description.—For its size, KNM­WS 65730 ( Fig. 3C ) is a fairly deep mandible. A tiny mental foramen is present below m1. Only the posterior alveolus of m1 is intact; the anterior one is broken anteriorly. However, what can be seen suggests that m1 was slightly shorter mesiodistally than m2. The alveoli for m3 suggest that the tooth was much larger than either m1 or m2. The m3 anterior alveolus is ovoid, points slightly lingually, and is wider than the posterior alveolus, suggesting that the m3 trigonid was larger than in m2.

Remarks.—Although KNM­WS 65730 is edentulous, the alveoli preserved clearly indicate that molar size increases posteriorly. We interpret these tooth positions to represent m1–m3 and note that the size gradient of m1<m2<m3 is a common pattern for African hyaenodonts but not for African carnivorans. Alternatively, the alveoli could represent p3– m1 of a carnivoran with m2 lacking. The only carnivorans lacking m2 known from the early Miocene of Africa are the barbourofelids Afrosmilus and Ginsburgsmilus , and the felids Diamantofelis and Namafelis . However, the mandibular corpus of barbourofelids tends to be curved ( Morlo et al. 2004) and less deep, and all of these barbourofelids and felids are much larger than KNM­WS 65730 with the exception of Namafelis minor , which is much smaller than the mandible from Buluk. Also, in N. minor p4 is longer relative to its width compared to KNM­WS 65730. Absolute and relative alveolar lengths of KNM­WS 65730 molars are close to those observed for the early Miocene hyaenodonts Sectisodon occultus Morales and Pickford, 2017 , from Napak ( Morales and Pickford 2017: text­fig. 3) and Buhakia moghraensis Morlo, Miller, and El­Barkooky, 2007 , from Moghra ( Morlo et al. 2007), while most other early and middle Miocene hyaenodonts, e.g., Dissopsalis Pilgrim, 1910 , have the m3 much larger than m2 (see Morales and Pickford 2017: text­fig. 3). We suggest that this specimen represents a hyaenodont with the m3 being much more trenchant than m2, but not much longer as in other hyaenodonts. However, due to lack of other comparable features, we refer the specimen only to Hyaenodonta . At present, KNM­WS 65730 is the only specimen representing a small­sized hyaenodont from Buluk.

Order Carnivora Bowdich, 1821

Family Amphicyonidae Trouessart, 1885

Subfamily Amphicyoninae Hunt, 1998

Genus Cynelos Jourdan, 1862

= Hecubides Savage, 1965

Type species: Cynelos lemanensis ( Pomel, 1846) , originally described as Amphicyon lemanensis . Early Miocene (MN 2) of Billy (Allier, France).

Diagnosis.—Emended after Peigné and Heizmann (2003), Werdelin and Peigné (2010), and Morlo et al. (2019): small to large sized amphicyonids with low, slender mandibles; diastemata between anterior premolars; premolars widest distally; p4 with strong postprotocuspid; the p4 is larger in relation to m1 and to m2 than in Amphicyon , the tip of the main cusp of p4 does not project posteriorly, and the p4 talonid is wider; m1 with low metaconid and tall hypoconid crest, entoconid crest distinct but low, talonid wider than trigonid; m2 mesiodistal length about two thirds the length of m1, m2 lacking the paraconid, with a long and wide talonid, protoconid lacking a distal crest; P4 with small protocone; M1 rectangular; M2 slightly more reduced than M1, with paracone slightly larger than metacone, and v­shaped hypocone crests in African species.

Cynelos differs from Afrocyon and African Amphicyon in having a diastema between p3 and p4 and further differs from Afrocyon in having a single­rooted m3. African Cynelos differs from Myacyon Sudre and Hartenberger, 1992 , in having a much longer m2 talonid and having a swelling at the posterobuccal corner of m2 (see Tsujikawa 2005: fig. B, D; discussion in Morales et al. 2016; Morlo et al. 2019).

Remarks.—In this contribution, we focus on the African occurrences of Cynelos . The composition of Cynelos has been discussed previously (e.g., Morlo et al. 2007, 2019; Morales et al. 2016; Adrian et al. 2018; Jiangzuo et al. 2018). We follow Adrian et al. (2018) and Morlo et al. (2007, 2019) in recognizing “ Hecubides ” Savage, 1965, as a junior synonym of Cynelos , and Myacyon , as a middle Miocene descendant of Cynelos , rather than referring small amphicyonid specimens to Hecubides and large ones to Myacyon (e.g., Morales et al. 2016). For a detailed discussion see Morlo et al. (2019).

Figures

Fig.3. Hyaenodonts Hyaenodonta indet.A, size of Leakitherium Savage, 1965 (A, B) and Hyaenodonta indet.B, size of Sectisodon Morales and Pickford, 2017 (C), from the lower Miocene of Buluk, Kenya. A. KNM­WS 12619, fragment of left ulna in anterior (A1) and lateral (A2) views, arrows point to very low anterior olecranon ridge. B. KNM­WS 12584, distal end of left tibia in anterior (B1), posterior (B2), and distal (B3) views. C. KNM­WS 65730, right edentulous jaw with broken alveoli of m1, alveoli of m2, and roots of m3 in buccal (C1) and occlusal (C2) views, notice length of molars increasing distally.