MACHAIRODONTINAE Gill, 1872

Miller, Sophie A., Barrett, Paul Z., McLaughlin, Win N. F. & Hopkins, Samantha S. B., 2020, Endemism and migration in the Kochkor Basin? Identification and description of Adcrocuta eximia (Mammalia: Carnivora: Hyaenidae) and c. f. Paramachaerodus (Mammalia: Carnivora: Felidae) fossils at the Miocene locality of Ortok, Kyrgyzstan, Palaeontologia Electronica (a 45) 23 (3), pp. 1-21 : 11-13

Subfamily MACHAIRODONTINAE Gill, 1872

Genus c.f. PARAMACHAERODUS Pilgrim, 1913

Figures 6 and 7

*. 1913 Paramachaerodus Pilgrim, p. 291

1924 Paramachairodus Zdansky , p. 130

*. 1929 Pontosmilus Kretzoi , p. 1298

*. 1929 Protamphimachairodus Kretzoi , p. 1316

Type species. Felis ogygia Kaup, 1832 , by original designation.

Occurrence. Bahean-Baodean; Vallesian-Turolian; MN Zones 9-13; middle late Miocene, Eurasia.

Localities. Bulgaria, China, Germany, Greece, Iran, Spain ( Salesa, 2002; Salesa et al., 2010; Li and Spassov, 2017); UO-4605 Ortok, Kyrgyzstan.

Referred specimen. UOMNH F-70509.

Description

UOMNH F-70509 is associated portions of an adult left M1, 5.42 mm long (ant.-post.), and 8.11 mm wide (med.-lat.) at maximal preserved portions; the ventral tip of C1 with a crown height of 15.69 mm and cross-sectional dimensions of 4.35 mm wide by 8.17 mm long at maximal preserved portions; and the paracone of left P4, 11.43 mm tall, 5.63 mm wide, and 8.99 mm long at maximal preserved portions ( Figure 6 ). The majority of the M1 ( Figure 6 E-F) is preserved including a buccally directed parastyle, paracrista, centrocrista, and metacone, while the lingual portion of the tooth is not preserved. The tooth is greatly reduced relative to the remaining preserved dentition, while additionally lacking a prominent paracone or metacone. However, it can be inferred that the tooth would have been triple-rooted, with two preserved roots and one more supporting the area associated with the non-preserved protocone. The C1 ( Figure 6 A- C) is greatly medially-laterally compressed, preserved ratio of length to width 1.88, with an anterior keel and incipient coarse crenulations on the posterior edge, producing a serration density of 2.6 serrations per millimeter (5 denticles/ 1.90 mm). The paracone of P4 ( Figure 6 G-I) displays a near vertical buccal margin while a dorsal-lingually flared lingual margin as it extends towards the non-preserved protocone. The anterior and posterior edge display thin cristae, while the posterior edge is additionally modified into the anterior portion of the carnassial notch with vertical orientation. No apparent wear is visible on this cusp indicating that the tooth may have been newly erupted at the time of the individual’s death.

Comparisons

The hypercarnivorous morphology of the preserved dentition of UOMNH F-70509, with greatly reduced M1 and medially-laterally compressed canine with coarse denticles on its posterior edge, are diagnostic of the Felidae , specifically the Machairodontinae ( Gill, 1872). Saber-tooth morphology is not solely diagnostic of the machairodontine felids; for this time period, Miocene nimravids such as Barbourofelis are possible, but UOMNH F-70509 differs in its lack of labial and lingual grooves on the C1, relatively large M1, and inferred presence of protocone ( Bryant, 1991). Additionally, comparisons of serration density, which has been shown to have generic diagnostic utility ( Barrett, 2016), to machariodontine felids and Late Miocene nimravids reveals that UOMNH F-70509 falls within the range of saber-toothed felids (1.1–2.6 serrations per millimeter), while substantially outside that of Late Miocene nimravids (3.7–4.3 serrations per millimeter) (see Appendix 2).

Several species of late Miocene machairodontines are present in Asia. The features of UOMNH F-70509 preclude inclusion into the morederived “dirk-tooth” machairodontines, typically with clearly defined canine denticles (though Megantereon cultridens lacks denticles), minute M1, and near absent P4 protocone. Instead UOMNH F-70509 better fits with the features of “scimitar-toothed” machairodontines, specifically Paramachaerodus (Pilgrim, 1913). A recent review of this genus combines it with the genus Promegantereon (now a junior synonym of Paramachaerodus ) into a grade of like-forms ( Li and Spassov, 2017). This grade has Paramachaerodus ogygia ( Kaup, 1832) as its basal-most member, lacking crenulations on its canines, a sinusoidal buccal border of the P4, and an elongated M1 with “…two roots; [having] a buccolingually lengthened crown, with a slight ridge extending from the mesiobuccal to the lingual borders” ( Siliceo et al., 2014, p. 412). The more derived P. maximiliani ( Zdansky, 1924) on the other hand, possesses well-defined canine denticles, a straight buccal border to the P4, a reduced protocone on the P4, and a single rooted M1 ( Li and Spassov, 2017). Specimen UOMNH F-70509 possesses a combination of these features, as is true of several other recently reported Eurasian specimens ( Li and Spassov, 2017), but bears the most similarity to the above diagnostic features of Paramachaerodus ogygia . However, it does differ in the nascent denticles on the posterior edge of the canine and triple-rooted M1, though this latter feature may be a result of individual variation given that the third root is minute in dimensions.

Remarks

The earliest taxon is Paramachaerodus ogygia , which is known only from MN 9–11 of Europe ( Salesa et al., 2010). Subsequently, the taxon P. transasiaticus diverges with an occurrence in the latter half of MN 11 (Bahean, Asian Land Mammal Age) of China and Bulgaria, followed by P. orientalis in MN 12 of Iran and Europe ( Salesa et al., 2010; Qiu et al., 2013; Li and Spassov, 2017). Finally, the last occurring and most derived taxon, P. maximiliani , appears in the late Bahean to Baodean of China ( MN 11–13) and with a single occurrence in MN 13 of Spain ( Salesa et al., 2010). Preserved diagnostic characters place the Kyrgyz specimen closest to P. ogygia , though with certain features similar to that of P. transasiaticus , such as incipient crenulations on the canine. However, the age of the Kyrgyz specimen, approximately 6 Ma, is substantially younger than what is known for either of these above-mentioned taxa. One hypothesis is that the Kyrgyz specimen represents an endemic taxon that has evolved some additional saber-tooth characteristics during its unsampled time interval from a European originating, P. ogygia- like ancestor. An additional hypothesis is that it constitutes a new species splitting off from an ancestral Asian Paramachaerodus ancestor, also unsampled in Central Asia. However, we feel a new species designation would require additional fossil material to adequately assess this Kyrgyz saber-tooth cat.

Figures

FIGURE 6. Annotated views of UOMNH F-70509, cf. Paramachaerodus. A, distal tip of canine, labial view; B, distal tip of canine, posterior view, note incipient crenulations on posterior edge (arrows); C, distal tip of canine, lingual view; D, schematic representation of preserved post-canine elements, not to common scale, inferred missing anatomy modified from Li and Spassov (2017); E, occlusal view of preserved left M1; F, anterior view of preserved left M1; G, occlusal view of preserved P4 paracone; H, lingual view of preserved P4 paracone; I, labial view of preserved P4 paracone; Abbreviations: cc, centrocrista; cn, carnassial notch; mt, metacone; pc, paracrista; *prt, flared portion of paracone cusp leading to protocone; ps, parastyle. Scale bar A–C, and G–I, equals 15 mm, E–F, equals 6 mm.

FIGURE 7. Time-scaled phylogeny of the Paramachaerodus genus and UOMNH F-70509’s placement within it. The depicted tree is a strict consensus of two most-parsimonious trees of score 32. Note the location of UOMNH F-70509 as unresolved relative to “Promegantereon” ogygia at the base of the genus even though it occurs much later in the rock record. Time-scaling was performed in R, version 3.6.1 (R Core Team, 2019) with the Strap package (Bell and Lloyd, 2014) using the “basic” method. Taxa ages derive from Li and Spassov (2017). The outgroup taxon Proailurus lemanensis has an Oligocene occurrence, not shown for clarity, but its basal position in our analysed taxa is depicted with dotted lines.