Machairodus giganteus
Creators: name: Geraads, Denis
name: Spassov, Nikolaï
Publisher: name: Zenodo
Year: 2020
Subjects: Biodiversity
Taxonomy
Animalia
Chordata
Mammalia
Carnivora
Felidae
Machairodus
Machairodus giganteus

description: Machairodus giganteus (Wagner, 1848)
HOLOTYPE (by monotypy). — Proximal ulna from Pikermi, Greece (Wagner 1848: pl. 10, fig. 6).
DESCRIPTION
The skull HD-9196 is virtually complete (Fig. 1; Appendix 1), as it lacks only the palatal roof and most of the right canine. It is almost undistorted, except for a strong crushing of the naso-frontal area, along the sagittal plane; this crushing also slightly affected the braincase, which shows longitudinal breaks along the squamoso-parietal suture, on either side of the skull. The associated left mandibular ramus lacks only the crowns of the incisors and canine.
Skull
The skull is deep and narrow, but the distortion prevents a reliable estimate of the skull outline in lateral view. All that can be said is that the sagittal crest was slightly inclined ventro-caudally; even accounting for some distortion, it was at most horizontal, not rising caudally.
Premaxillae
The premaxillae project strongly in front of the canines; they narrow upwards but remain broader than in Panthera Oken, 1816. The naso-maxillary sutures are caudally convergent in their rostral part, but probably (cracks obscures their precise course) almost parallel in their caudal part.
Face
Crushing obscures the naso-frontal suture. There is no evidence that it was transverse, as in most machairodonts, although it may not have been as V-shaped as in Panthera. Overall, the muzzle is not large, with the anterior border of the orbit located just anterior to the paracone of P4, and the ante-orbital foramen just in front of this tooth. This moderate size of the muzzle is probably related to the rather small size of the canine. The palatal roof is missing, but its posterior broadening is much weaker than in Panthera, as the toothrows diverged much less posteriorly.
Dihedral angle
As in other machairodonts, the orbits are small, and they face distinctly less forward than in LCTF (Fig. 2), an observation also made by Casares-Hidalgo et al. (2019) on Homotherium serum (Cope, 1893) and Smilodon Lund, 1842. Several parameters (the first of which is probably absolute size) are certainly involved in this orbital orientation, but we may observe that the orbits are less frontally oriented in cheetahs than in tigers, suggesting a possible connection with habitat (although Casares-Hidalgo et al. 2019 rejected it). In contrast to LCTF, the post-orbital processes are thick and laterally expanded, the skull being much broader at this level than across the muzzle. The skull narrows strongly but gradually behind this level, with a strong constriction anterior to the braincase. The ventral postorbital processes are rather large but rounded and not very prominent. The zygomatic arches are less expanded laterally and shorter antero-posteriorly than in Panthera, but with a similar antero-posterior curve. The area of insertion of the masseter muscle is not distinct, suggesting that this muscle was not strong. The glenoid fossa is located much more anteriorly than in Panthera, but its shape and concavity are very similar, with salient postglenoid processes mostly developed medially and a ridge-like anterior rim that is, however, of uniform height, unlike the laterally much taller crest of Panthera. It additionally differs from Panthera in that the root of the zygomatic arch is slightly stretched ventrally, so that the fossa is slightly more ventrally located (it is, e.g., more ventral than the base of the pterygoids, but this is also because the pterygoid blades are less expanded). Still, the glenoid fossae remain at about the same vertical level as the base of the occipital condyles, far above the alveolar line.
Cranial base
The basioccipital is similar to that of LCTF and the relief (anterior rugosities for longus capitis, posterior depressions for the rectus capitis anticus) is only slightly better marked.
The cranial base, like the skull as a whole, is more lengthened than in LCTF. The auditory bulla reaches farther anteriorly, and connects the base of the zygomatic root through a thick bridge forming the ventral wall of the external auditory meatus. Because of this, the foramen lacerum anterior is restricted in size, at the antero-medial end of the tympanic bulla. The condylar foramen opens in a fossa confluent with the foramen lacerum posterior, but well behind it.
The auditory bulla is almost invisible in lateral view, because it is wholly covered by a thick flange of bone, including the mastoid process anteriorly and the jugular process posteriorly: these two processes are located much farther apart than in LCTF. The mastoid process is very large; it forms a triangular protuberance, expanded anteriorly, laterally, and ventrally beneath the auditory bulla. The jugular process is shorter and more posteriorly directed than in LCTF. There is no remnant of the alisphenoid canal.
A B C D
Occipital
The occipital differs considerably from that of LCTF. The foramen magnum is broad, and the condyles are located far apart. Dorso-medially to each of them, the occipital is hollowed out by large, deep fossae, probably for nuchal muscles. At this level, the occipital is not wider than over the condyles, and it further narrows strongly dorsally, largely because the lambdoid crest, instead of expanding laterally, is stretched caudally, forming a roof over the occipital. As a whole, the occipital is triangular, rather than bell-shaped as in LCTF, but this may be partly due to the young ontogenic age of the specimen.
Upper teeth
The upper incisors are arranged in a gentle arch, well forward of the canines; they are large and high-crowned, I3 being distinctly larger than the others. They all have a mesial and a distal keel, best expressed in I3, which is almost caniniform. At least both keels of I3 and the lateral keel of I2 are serrated. Compared to other teeth, the canines are rather small (Table 1); because this tooth is sexually dimorphic in this group (e.g., Antón et al. 2004), this probably means that HD-9196 is a female. The compression is also moderate. Both keels are serrated, with a distinct curvature in lateral view, but the tooth is straight in front view. There is no wear facet for the lower canine, and the other teeth are at most slightly worn. There is almost no diastema between the canine and P3, whose anterior root probably contacts the canine within the bone. The main cusp of P3 is less than half of the tooth length, because there are a small mesio-lingual cingulum, a large anterior accessory cusp, almost in line with the main cusp, a smaller posterior one, and a strong posterior cingulum. The tooth is narrow, in spite of a lingual expansion at about two thirds of its length, quite long (it is the longest recorded machairodont P3), but shorter than in many LCTF.
The P4 is also among the longest recorded in Machairodus. The preparastyle is small, and in line with the other cusps. The parastyle and paracone bear strong anterior and posterior serrated keels. A ridge, inflated at its base, descends anterolingually from the apex of the paracone, and ends in a lingual root, but there is no distinct protocone. The paracone is much taller than long, and also much taller than P3, in contrast to LCTF, where they are of comparable height. The metastyle is much longer than the paracone. Slight wear affects the posterior half of the paracone and the metastyle. On the whole, all cusps together form a long, narrow, almost straight shearing blade. The M1 is about as reduced as in modern LCTF, but is wholly lingual to P4, so that it is not visible in lateral view.
Mandible
The mandible (Fig. 3) is long and slender, with a corpus that is almost straight and bucco-lingually thin. Its anterior border is more vertical than in P. uncia (Schreber, 1775) or Neofelis Gray, 1867 (the modern taxa that have the most vertical chins). There is an incipient mental flange below the canine; its base reaches slightly farther ventrally than the symphysis, but not more than the angular process. There is no conspicuous scar for the digastric muscle. A very large mental foramen is located close to the ventral border of the corpus, below the anterior root of p3. The masseteric fossa and the condyle do not differ significantly from those of Panthera, but the coronoid process is distinctly lower and shorter antero-posteriorly, i.e., more reduced than in all modern felids, in which it is highly variable.
Lower incisors
The missing lower incisors were certainly rather large, and wholly visible in lateral view, in front of the broken canine. The latter was small, and much shorter than p3. There is no p2, and the diastema is rather short. The lower premolars are similar to each other in their extremely tall, slender main cusp that is less lanceolate (‘fleur-de-lys’) than in LCTF with tall premolars, like in Acinonyx Brookes, 1828; in p4, this main cuspid is inclined backwards. The anterior and posterior accessory cuspids are also tall, especially in p4, and subequal in length. The posterior cingulum is poorly expressed in p3, thicker in p4, but still rather thin. Both p3 and p4 are serrated; if serration was present on m1 before wear, it would have been restricted to the cutting edges of the paraconid and protoconid. These cuspids are subequal in length at the base, but the cutting edge of the paraconid is short, because the mesial edge of this cuspid is inclined backwards, parallel to the main axis of the cuspids of p4. A barely distinct basal bulge is all that remains of the metaconid/talonid complex.
description: Published as part of Geraads, Denis & Spassov, Nikolaï, 2020, A skull of Machairodus Kaup, 1833 (Felidae, Mammalia) from the late Miocene of Hadjidimovo (Bulgaria), and its place in the evolution of the genus, pp. 123-137 in Geodiversitas 42 (9) on pages 124-128, DOI: 10.5252/geodiversitas2020v42a9, http://zenodo.org/record/3768743