BARBOUROFELIDAE TO

Morlo, Michael, Peigné, Stéphane & Nagel, Doris, 2004, A new species of Prosansanosmilus: implications for the systematic relationships of the family Barbourofelidae new rank (Carnivora, Mammalia), Zoological Journal of the Linnean Society 140 (1), pp. 43-61 : 54-56

RELATIONSHIPS OF BARBOUROFELIDAE TO NIMRAVIDAE

The most detailed analysis placing the Barbourofelidae as a subfamily in Nimravidae s.l. was made by Bryant (1991: table 1, appendix I). His cladistic analysis of almost all morphological characters regarded as diagnostic by previous authors supported the sistergroup relationship of Nimravinae to Barbourofelinae with 14 synapomorphies. However, nine of these are not exclusive to Nimravidae , but are also present in other carnivoran groups. Thus, these characters (skull catlike with shortened rostrum and mesocranium, short palate, cerebrum with continuous ectosylvian sulcus, distinct angle between the anterior and lateral surface of the mandible, loss or reduction of the anterior premolars and the posterior molars, incisors with reduced lingual cingula, C1/ significantly larger than C/1, C1/ eruption delayed, hourglass-shaped crenulations on C/1) do not contain phylogenetic information by themselves, but can be interpreted as synapomorphies only after the sister-group relationship has been established based on other, autapomorphic, characters. We therefore do not discuss these characters here, with the exception of the hourglass-shaped crenulations on C/1. Only five characters used by Bryant (1991) may indeed be unique to the Nimravidae (sensu Bryant, 1991) . To facilitate character analysis, we discuss dental (based on the cladistic analysis presented above), basicranial, and other characters (cranium and postcranium) separately for barbourofelidnimravid and barbourofelid-felid comparisons.

Among the dental features used by Bryant (1991), the moderately to extremely enlarged dC1/ is the only character known from both Nimravidae and Barbourofelidae , but not from other taxa. According to Bryant (1991: 69), the particular shape of the crenulations is unique for the Nimravidae s.l. However, this statement is refuted by illustrations of the crenulation shape on upper canines of felids like Nimravides (see Baskin, 1981: fig. 6B) or Machairodus (see Pons-Moya, 1989 -90: fig. 1; M. Morlo, unpubl. data) which display crenulations very similar to those in Nimravidae s.s. Our cladistic analysis supports the view that crenulations appeared independently in Nimravidae and Barbourofelidae . In our analysis of early species of nimravids, barbourofelids and felids, the relative size of dC1/ compared to C1/ is a character unknown in all taxa but Nimravus (see cladistic analysis), in which it is of moderate size. Within barbourofelids, an extremely large dC1/ is currently known only in Barbourofelis , the most apomorphic genus of the family. This character must therefore be considered as uninformative when comparing the Barbourofelidae to other carnivoran families. As with this character, previous comparisons between the Barbourofelidae and Nimravidae were mainly based on the most apomorphic (and stratigraphically latest) North American genus, Barbourofelis . However, comparison of the dentition of the most primitive barbourofelids (and especially P. eggeri as the most plesiomorphic European barbourofelid) with that of the most plesiomorphic nimravids, Eofelis and Nimravus (see Peigné, 2000, 2001, 2003) from the Oligocene of Quercy provides a very different interpretation (see cladistic analysis presented above; Fig. 4 ; Table 3). It reveals extremely poor support for a Nimravidae- Barbourofelidae sister-group relationship. Barbourofelidae differs from Nimravidae s.s. by the following dental characters (see also Table 3): vertical grooves present on upper canines (autapomorphy); P1/, P/1 and M/2 lost; M/1 with a relatively tall protoconid; an extremely reduced talonid which only forms a posterior bulge and is markedly more reduced than the relatively large metaconid. In addition, the lower premolars of the Barbourofelidae retain posterior accessory cusps (consistantly lacking in Nimravidae ) and, as in early felids, the upper carnassial has a parastyle and a more posteriorly located protocone (at least primitively).

Even if major differences in the dental pattern occur, the basicranial structure is more important for analyses of high rank relationships within the Carnivora . As a result some authors have paid particularly attention to that region to pinpoint the systematic position of Nimravidae s.l. Most of these contributions (e.g. Baskin, 1981; Neff, 1983; Hunt, 1987) conclude that the Nimravidae s.l. have a distinctive basicranial structure, but this conclusion has mainly been based on the Oligocene taxa ( Nimravidae s.s.). Two of the remaining five characters of Bryant (1991) belong to the auditory region: the anterior limb of the ectotympanic is long and more anteriorly articulated with the squamosal; a short septum, composed of the rostral and caudal entotympanics, lies anteromedial in the bulla. In our view, these studies have not provided strong evidence that Nimravidae s.s. and Barbourofelidae share a similar basicranial configuration. The anterior ectotympanic crus is long and applied against the squamosal in Barbourofelis , but somewhat more slender in Sansanosmilus palmidens (see Ginsburg, 1961: fig. 65, pl. 13, fig. 1) and thus more plesiomorphic than in the Nimravidae s.s. This supports an interpretation that the feature may have appeared in Barbourofelidae and Nimravidae s.s. separately. The presence of an unusually short septum (proseptum) made up of the rostral and caudal entotympanics in the anteromedial corner of the auditory bulla has so far only been demonstrated in Dinictis ( Hunt, 1987) . Given that all Nimravidae s.s. share a very similar configuration of the auditory bulla throughout their stratigraphic distribution ( Joeckel et al., 2002), inferring the presence of a similar septum in all Palaeogene nimravids is reasonable. However, the presence of a similarly placed and constructed proseptum in the bulla of the much later Barbourofelidae has not yet been demonstrated, though such a short septum may be present in some Barbourofelis specimens ( Baskin, 1981: UF 24432, fig. 2; Hunt, 1987: UF 55859, fig. 9). In additional North American specimens (but excluding UF 55859), Neff (1983: 306) identified a crista in the anteromedial corner of the bulla, which she identified as a septum; the dorsal edge is vertical, but the ventral edge “curves mediad to form a horizontal septum”. According to Neff (1983: 306), the dorsal part of the crista is similar to the anterior end of the entotympanic in Dinictis while “the horizontal orientation of the ventral part is unlike the condition in Dinictis ”. We observed the same low, horizontally orientated crest in Sansanosmilus palmidens (MNHN-Sa 472, Ginsburg, 1961: fig. 65; MNHN-Sa 3384, Fig. 6D ) from Sansan, which may indicate a relative uniformity of the barbourofelid bulla. It is important to note that it is not possible to separate an ectotympanic from an entotympanic portion on the surface of the ossified bulla in Barbourofelis and Sansanosmilus as is clearly the case in the Nimravidae s.s. As a result, the relationships, origin and composition of the proseptum of B. loveorum ( Hunt, 1987: fig 9; Fig. 6B herein) and S. palmidens (e.g. MNHN-Sa 472, MNHN-Sa 3384; Fig. 6D ) cannot be considered as identical to those of the proseptum described in Dinictis ( Hunt, 1987; Fig. 6A ), nor to those of any other auditory separation observable in mammals. Among the features listed in Bryant (1991), the presence of an external auditory meatus that is wider than the auditory notch may be the only basicranial character the Nimravidae and Barbourofelidae have in common ( Neff, 1983; Bryant, 1991). In contrast, the auditory bullae of Barbourofelis and Sansanosmilus present further basicranial differences to the Palaeogene taxa which were not included in Bryant’s analysis: a fully ossified bulla which invades the mastoid and a thinner wall of the entotympanic which is not composed of three distinct layers in Barbourofelidae as in some Nimravidae ( Neff, 1983) . Even if these barbourofelid characters may have been derived from the nimravid condition, as argued by Hunt (1987), this is not the case for the deep recessing of the auditory region, especially the petrosal, into the basicranium, resulting in a less dorsal placement in the Nimravidae .

One of the remaining five characters of Bryant (1991) uniting the Nimravidae and Barbourofelidae concerns the skull: the posteriorly converging lateral walls of the nasopharynx. This character occurs in the most specialized genera Hoplophoneus , Eusmilus , Barbourofelis , Nimravus , Dinictis and Sansanosmilus . It is uninformative in the cladistic analysis presented above and has to be confirmed in the earliest and/or most primitive members (nimravids: Eofelis, Dinaelurictis , Quercylurus , Dinaelurus ; barbourofelids: Ginsburgsmilus , Syrtosmilus , Afrosmilus , Prosansanosmilus ). The structure of the frontal sinus shows the plesiomorphic condition of Carnivora even in the highly evolved Barbourofelis morrisi , but extends over the brain cavity in the nimravids Hoplophoneus and Dinictis . Among barbourofelids, only B. fricki , as the most apomorphic taxon, shows such an extended frontal sinus (see Joeckel & Stavas, 1996). It can thus be stated, that the consecutive occurrence of converging lateral walls of the nasopharynx and an extended frontal sinus is not unique to Nimravidae s.l. and/or reflects an increasing specialization towards the sabretooth bauplan. In Barbourofelidae , the most apomorphic condition shows up in B. fricki - that is, not before the latest Miocene and about 30 Myr later than in the apomorphic Oligocene Nimravidae s.s. Because Sansansmilus and B. morrisi verify that the less apomorphic character states were also present in Barbourofelidae , we interpret both characters as symplesiomorphies rather than as synapomorphies.

Among the postcranial characters, some authors ( Bryant, 1991; Joeckel & Stavas, 1996; see Ginsburg, 1961: 162, fig. 68/5) have also noted the morphological similarity of the metacarpus in Nimravidae and Barbourofelidae . It must be understood, however, that the postcranial anatomy of nimravid and barbourofelid genera is far from well known, due to the poor fossil record. The manus (and thus the morphology of the metacarpus) plays an important role in grasping prey in all scimitar-toothed carnivorans and assists in avoiding canine breakage, as these teeth are highly vulnerable to lateral forces (e.g. Bohlin, 1940; Gonyea, 1976; Van Valkenburgh & Ruff, 1987; Van Valkenburgh & Hertel, 1993). Manus morphology is correlated both to use of the forepaw and to locomotion ( Ivaniuk et al., 2001), and thus has great functional influence. If the postcranial anatomy of nimravids is usually regarded as plesiomorphic within Carnivora ( Tedford, 1978; Bryant, 1991), the obvious similarities may be interpreted as symplesiomorphies based on similar functional necessities.

The previous discussion and cladistic analysis of dental characters of early barbourofelids, nimravids and felids show that there is little support for a sister-group relationship of the Barbourofelidae to the Nimravidae . As a result, we exclude the Barbourofelidae from Nimravidae . An alternative approach is to make the Barbourofelidae a subfamily of the Felidae ( Morales et al., 2001) ; this is discussed below.

Figures

Figure 4. One of eight most parsimonious trees obtained from the cladistic analysis. See text for discussion and Table 3 for character support.

Figure 6. Auditory region of Nimravidae, Barbourofelidae and Felidae. A, auditory region in juvenile Dinictis (UNSM 4051–81) from Nebraska (Hunt, 1987: fig. 5A). B, auditory bulla of Barbourofelis lovei (UF 55859) from Love bone bed, Florida (Hunt, 1987: fig. 9B). C, auditory bulla of Lynx rufus (UNSM 33–67) from Nebraska (Hunt, 1987: fig. 10B). D, auditory region of Sansanosmilus palmidens (MNHN Sa 3384) from Sansan, France. Abbreviations after Hunt (1987). E, ossified caudal entotympanic - Ea, anterior lamina, Ep, posterior lamina, Ev, vertical lamina; P, petrosal; PS, nimravid proseptum; Rs, septate lateral margin of rostral entotympanic; SB, septum bullae; SQ, squamosal; T, ectotympanic.