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FIG 3. A, C in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG 3. A, C, Photographs and B, D, CT segmentation of the holotype of Eomakhaira molossus, a partial skull of a senescent individual preserving the rostrum and the anterior portion of the mandible (SGOPV 3490) in left (A, B) and right (C, D) lateral views. In renderings of the CT segmentation, nasal in orange, facial process of the lacrimal in teal, palatine in blue, all other bones of the cranium (maxilla, jugal, frontal, etc.) in purple, teeth in yellow, and dentary in green. Anterior to left in A–B and to right in C–D. Scale = 30 mm.

FIG 2 in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG 2. Locations of the Cachapoal locality and the similar-aged (likely coeval) Tinguiririca locality in central Chile. Gray area in inset box represents outcrops of the Abanico Formation.

FIG 10. A in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG 10. A, Photograph and B, C, CT images of the right upper canine of the holotype of Eomakhaira molossus (SGOPV 3490). A, Lateral view, showing bluntness of canine apex and the absence of enamel, longitudinal ridges, and labial median canine sulcus. B, Transverse section of canine, slightly below alveolar border (actual point at alveolar border obscured by a crack), showing posterior keel. Anterior root of P1 (aP1) marked to show that the longitudinal ridge is not an artifact of postmortem damage. C, Transverse section of canine, at level of tooth row, showing presence of median labial keel and lingual median sulcus. Approximate location of sections in B, C denoted by arrows on A. Anterior to right in all images, and lingual to top in B, C. Abbreviations: aP1, anterior root of P1; mk, labial median keel; ms, lingual median sulcus; pr, posterior ridge. Scale = 10 mm (A); 5 mm (B, C).

FIG 12 in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG 12. Oblique lateral CT image slice of SGOPV 3490 along the postcanine tooth row, showing position of lower molars and depth of horizontal ramus. Note how worn surfaces of P3 and m1 closely match one another. Scale = 30 mm.

FIG. 17 in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG. 17. Results of parsimony phylogenetic analysis under implied weights with concavity constant k = 3, showing the single recovered most parsimonious tree (MPT). Eomakhaira molossus in bold. Numbers to lower left represent bootstrap values. Support values not given for Dasyuromorphia, as this node was constrained a priori (see text).

FIG. 15 in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG. 15. Lower right dentition of SGOPV 3490 in A, labial, B, occlusal, and C, lingual views. Colors of elements in this CT segmentation are the same as in figure 3. Anterior to right in A, B and to left in C. Scale = 30 mm.

FIG 20 in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG 20. Lower canines of non-thylacosmiline proborhyaenids. A–B, Proborhyaena gigantea (MACN-A 52-382) in A, labial and B, lingual views. C, Arminiheringia auceta (MACN-A 10970) in labial view. D, Paraborhyaena boliviana (UATF-V-000129; left canine, reversed) in labial view. The upper canines of Arminiheringia show a comparable morphology (see fig. S4B; apices of the upper canines are unknown for Proborhyaena and Paraborhyaena). Scale bars = 10 mm.

FIG. 21 in Eomakhaira molossus, A New Saber-Toothed Sparassodont (Metatheria: Thylacosmilinae) from the Early Oligocene (?Tinguirirican) Cachapoal Locality, Andean Main Range, Chile

FIG. 21. Temporal durations of major lineages of mammalian saber-toothed carnivores, with metatherian lineage in grey and placental lineages in black. A representative skull of each clade is depicted to the right; from top to bottom: Thylacosmilus atrox (Thylacosmilinae), Machaeroides eothen (Machaeroidinae), Hoplophoneus primaevus (Nimravidae), Barbourofelis fricki (Barbourofelidae) and Smilodon fatalis (Machairodontinae). Images of Machaeroides, Barbourofelis, and Smilodon modified from Antón (2013), Thylacosmilus from Riggs (1934), and Hoplophoneus from Scott and Jepsen (1936) and Bryant (1996). Tick mark on Thylacosmilinae record represents the oldest occurrence of this clade (~20.2 Ma) prior to the discovery of Eomakhaira. Abbreviations: Plio., Pliocene; Ple., Pleistocene.

FIG. 16 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 16. Borhyaena tuberata MPM-PV 3625 from Puesto Estancia La Costa, Santa Cruz, Argentina; Santa Cruz Formation; Santacrucian, Early Miocene. Ventral view of A, the caudal cranium, with B, key; and MACN-A 5922 (C). Abbreviations: AL, alisphenoid; bjs, basijugular sulcus; BO, basioccipital; BS, basisphenoid; cc, carotid canal; cod, occipital condyle; cs, carotid sulcus; eam, external acoustic meatus; ewal, alisphenoid epitympanic wing; EX, exoccipital; ffc, fossula fenestrae cochleae; gf, glenoid fossa; hfc, caudal hypoglossal foramen; hfr, rostral hypoglossal foramen; ips, inferior petrosal sinus; ji, jugular incisure; pcp, paracondylar process; PE, petrosal; pf, piriform fenestra; pgf, postglenoid foramen; ptp, posttympanic process; SQ, squamosal. Unusually, in this specimen the caudal aperture of the inferior petrosal sinus is completely ringed by basioccipital bone. More often, the aperture opens in the basicapsular fissure, between the petrosal and basioccipital, in advance of the jugular foramen. Because the roof of the tympanic cavity is incompletely prepared, actual boundaries of the piriform fenestra are unknown. Asterisk (*) indicates groove for medial contact of petrosal. Arrow indicates the direction to or the position of features hidden by other structures.

FIG. 9 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 9. Thylacosmilus atrox, paratype, FMNH P14344, in A, oblique ventral and B, lateroventral views, with C, general key. Note that in A the detached bulla is in its original position. Abbreviations: AL, alisphenoid; bjs, basijugular sulcus; BO, basioccipital; BS, basisphenoid; cc, carotid canal; cod, occipital condyle; eam, external acoustic meatus;?EC,?ectotympanic; ewal, alisphenoid epitympanic wing; ewsq, squamosal epitympanic wing; EX, exoccipital; ffc, fossula fenestrae cochleae; fmg, foramen magnum; fo, foramen ovale; for, foramen rotundum; FR, frontal; fv, fenestra vestibuli; hfc, caudal hypoglossal foramen; hfr, rostral hypoglossal foramen; ips, inferior petrosal sinus; lps, lateral paratympanic space (= epitympanic sinus); PE, petrosal; pf, piriform fenestra; pgc, postglenoid canal;?sat,?sulcus for the auditory tube; sfn, septum for facial nerve; sjf, secondary jugular foramen; sof, sphenoorbital fissure; SQ, squamosal. Dashed line on left bulla marks suture track, the accuracy of which is undetermined. Asterisk (*) indicates unprepared area, within which the primary jugular foramen is located. The canal conducting the internal jugular and cranial nerves through the left bulla to the secondary jugular foramen on the latter's outer wall can be seen in B (broken during removal of right bulla, no longer identifiable on basicranium). Crosshatching indicates damage due to erosion or bullar removal. Arrow indicates the direction to or the position of features hidden by other structures.

FIG. 12 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 12. Thylacosmilus atrox, paratype, FMNH P14344. Digital reconstruction of the fragmentary left ectotympanic based on micro-CT data in A, rostral, B, lateral, and C, medial views. D, horizontal section of the left middle ear in dorsal view, showing fragments of ectotympanic (asterisk, *). Abbreviations: BO, basioccipital; cac, caudal crus;?chtym, groove for chorda tympani nerve (CNVII); ctpsq, caudal tympanic process of squamosal; cty, crista tympani; eam, external acoustic meatus; EC, ectotympanic; jfis, jugular fissure;?gma, groove for rostral process of malleus; lps, lateral paratympanic space (= epitympanic sinus); pgc, postglenoid canal; roc, rostral crus; rtpsq, rostral tympanic process of squamosal; SQ, squamosal; stp, styliform process (= anterolateral process of ectotympanic); tpex, tympanic process of exoccipital.

FIG. 26 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 26. Features related to blood vessels in representative sparassodonts: A, Thylacosmilus atrox, external features (based on Thylacosmilus atrox, holotype, FMNH P14531); B–C, Lycopsis longirostrus, external and internal features (based on UCMP 38061 and Marshall, 1977b) Abbreviations: bsp, basilar plexus; cc, carotid canal; CNV3, mandibular branch of trigeminal (cranial) nerve; CNVII, facial (cranial) nerve; CNXII, hypoglossal (cranial) nerve; cars, cavernous sinus; csvs, cerebrospinal venous system; cv, condyloid vein; cvv, craniovertebral vein; cx, canal x (see fig. 6 and text); evfo, emissary vein of foramen ovale; fo, foramen ovale;?fsp, foramen spinosum; hf, hypoglossal foramen; iam, internal acoustic meatus; ica, internal carotid artery; ijv, internal jugular vein; ips, inferior petrosal sinus; jf, jugular foramen; mmv, middle meningeal vein; ophv, ophthalmic vein; ramx, ramus anastomoticus; sev, sphenoparietal emissary vein; sjf, secondary jugular foramen; smf, stylomastoid foramen; sphev, sphenoidal emissary vein (= vein of Vesalius); sphps, sphenoparietal sinus; sps, superior petrosal sinus; ss, sigmoid sinus. Only major channels are indicated. The position and relations of most of the large vessels leaving impressions on the basicranium, such as the internal carotid, sphenoparietal emissary vein, and inferior petrosal sinus are not controversial. However, other features, also evidently related to vasculature, have received less attention. As explained in the text, in addition to CNV3, in Thylacosmilus the foramen ovale may have transmitted a large vein to the extracranial pharyngeal plexus. In the absence of a functioning and intact stapedial system, the foramen here identified as the foramen spinosum (?fsp) may have given passage to an anastomotic ramus running from the maxillary artery to the meningeal system, although this task could have been performed by other vessels (e.g., the ophthalmic artery) that have left no mark. The large groove identified as the basijugular sulcus (bjs, see fig. 6), connecting the caudal aperture for the inferior petrosal sinus to the hypoglossal foramen/foramina in many sparassodonts, surely transported the sinus itself. However, instead of leaving for the internal jugular vein, the inferior petrosal sinus seems to have re-entered the endocranium through one or another of the hypoglossal foramina, only to immediately leave again through the foramen magnum, now as the (conjectured) craniovertebral vein (cvv). Asterisk (*) indicates the likely connection between the internal jugular vein and the craniovertebral vein. How drainage through the sinus in this scenario would have related to that through the internal jugular system is unclear. There is some indication that the internal jugular was relatively small in size, although how this affected endocranial drainage cannot be inferred from the material available. In all investigated sparassodonts the posttemporal foramen for the diploic artery and vein are missing. Thylacosmilus evidently lacked a transverse venous foramen, but one is present in Lycopsis and other taxa (see text).

FIG. 6 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 6. Thylacosmilus atrox, holotype, FMNH P14531. Basicranium in A, ventral view, with B, key. Shaded areas represent incompletely prepared or restored areas. Foraminal locations mostly indicated on specimen's better-preserved left side. Abbreviations: AL, alisphenoid; bjs, basijugular sulcus; BO, basioccipital; BS, basisphenoid; cc, carotid canal; cod, occipital condyle; ctpsq, caudal tympanic process of squamosal; cx, canal x (see text); eam, external acoustic meatus; EX, exoccipital; fo, foramen ovale; for, foramen rotundum;?fsp, foramen spinosum; gf, glenoid fossa; hfc, caudal hypoglossal foramen; ips, inferior petrosal sinus; otcr, orbitotemporal crest; pgf, postglenoid foramen; pgp, postglenoid process of squamosal; ptp, posttympanic process of the squamosal;?sat, sulcus for the auditory tube; smf, stylomastoid foramen; sof, sphenoorbital fissure; SQ, squamosal; st, sphenoidal tubercle; sjf, secondary jugular foramen; tpex, tympanic process of exocipital. Arrow indicates direction to or position of features hidden by other structures.

FIG. 21. Digital 3-D in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 21. Digital 3-D reconstructions of the left osseous labyrinth of selected sparassodonts, based on micro- CT data in A, D, G, lateral, B, E, H, ventral, and C, F, I, dorsal views. Thylacosmilus atrox, paratype, FMNH P14344 (A–C); Sipalocyon gracilis, AMNH VP 9254 (D–F), and Borhyaena tuberata, YPM PU 15120 (G–I; right petrosal inverted). Abbeviations: aam, anterior ampulla; asc, anterior semicircular canal; av, aqueductus vestibuli; cco, crus commune; chlc, cochlear canaliculus (= aqueductus cochlearis); co, cochlea; fc, fenestra cochleae; fv, fenestra vestibuli; lam, lateral ampulla; lsc, lateral semicircular canal; pam, posterior ampulla; psc, posterior semicircular canal.

FIG. 17. Monodelphis domestica AMNH M 133247 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 17. Monodelphis domestica AMNH M 133247. Ventral view of the caudal cranium. Abbreviations: AL, alisphenoid; at, aperture for auditory tube; BO, basioccipital; BS, basisphenoid; cc, carotid canal; ct, tympanic cavity; eam, external acoustic meatus; EC, ectotympanic; ewal, epitympanic wing of alisphenoid; EX, exoccipital; ffc, fossula fenestrae cochleae; fmg, foramen magnum; fo, foramen ovale; gf, glenoid fossa; hfc, caudal hypoglossal foramen; hfr, rostral hypoglossal foramen; ips, inferior petrosal sinus; jf, jugular foramen; mp, mastoid process of petrosal; pcp, paracondylar process; PE, petrosal; pf, piriform fenestra; pgf, postglenoid foramen; ptc, pterygoid canal; ptp, posttympanic process; rtpp, rostral tympanic process of petrosal; smef, suprameatal foramen; SQ, squamosal; tc, transverse canal; tpal, tympanic process of alisphenoid. Arrow indicates the direction to or the position of features hidden by other structures.

FIG. 4 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 4. Thylacosmilus atrox, paratype, FMNH P14344 (Río Santa María, Chiquimil, Catamarca, Argentina; Andalgalá Formation; Huayquerian, Late Miocene). Skull in A, dorsal and B, ventral views. Abbreviations: AL, alisphenoid; BO, basioccipital; C, upper canine; cc, carotid canal; cod, occipital condyle; cps, caudal paratympanic space; ctpsq, caudal tympanic process of squamosal; eam, external acoustic meatus; EX, exoccipital; fo, foramen ovale; for, foramen rotundum; FR, frontal; hfr, rostral hypoglossal foramen; ips, inferior petrosal sinus; lps, lateral paratympanic space (= epitympanic sinus); MX, maxilla; nc, nuchal crest; PA, parietal; rt, rami temporales; s, sagittal crest; sjf, secondary jugular foramen; sof, sphenoorbital fissure; SQ, squamosal; tl, temporal line; tpex, tympanic process of exoccipital. Arrow indicates direction to or position of features hidden by other structures.

FIG. 11. Thylacosmilus atrox MMP 1443-M. A in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 11. Thylacosmilus atrox MMP 1443-M. A, detail of the basicranium, with B, key. Abbreviations: AL, alisphenoid; bjs, basijugular sulcus; BO, basioccipital; BS, basisphenoid; cc, carotid canal; cod, occipital condyle; ctpsq, caudal tympanic process of squamosal; eam, external acoustic meatus; EX, exoccipital; fmg, foramen magnum; fo, foramen ovale;?fsp, foramen spinosum; gf, glenoid fossa; ips, inferior petrosal sinus; pgf, postglenoid foramen; ptp, posttympanic process of the squamosal; sjf, secondary jugular foramen; smf, stylomastoid foramen; SQ, squamosal; st, sphenoidal tubercle; tpex, tympanic process of exoccipital. Arrow indicates direction to or position of features hidden by other structures and shading indicates damage or reconstruction.

FIG. 1 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 1. Diversity of sparassodonts through time. Lines representing the diversity curve based on number of species (black blocks) as predicted by the fossil record (Lazarus taxa not included). Possible fossil record biases include hiatuses (time spans lacking known fossils), different taxon durations, and averaging of biochronological units. Other biases which may mask the real diversity pattern include inadequate or imprecise chronological ages for associations determined by radiometric dating, as well as differences in sampling effort across temporal units or geographical regions (Prevosti and Forasiepi, 2018). Dot cluster indicates the temporal span of Thylacosmilus atrox from the Late Miocene (Huayquerian) to Pliocene (Chapadmalalan). Scale: 1:1 species.

FIG. 5. Thylacosmilus atrox MMP 1443-M in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 5. Thylacosmilus atrox MMP 1443-M (Chapadmalal, Buenos Aires, Argentina; Chapadmalal Formation; Chapadmalalan, mid-Pliocene). Skull in A, lateral and B, dorsal views. Abbreviations: cod, occipital condyle; eam, external acoustic meatus; FR, frontal; MX, maxilla; NA, nasal; nc, nuchal crest; PA, parietal; rt, ramus temporalis; s, sagittal crest; SQ, squamosal; tl, temporal line.

FIG. 3 in Caudal Cranium Of Thylacosmilus Atrox (Mammalia, Metatheria, Sparassodonta), A South American Predaceous Sabertooth

FIG. 3. Thylacosmilus atrox, holotype, FMNH P14531 (Hualfin, Catamarca, Argentina; Corral Quemado Formation; Chapadmalalan, mid-Pliocene). Skull in lateral (A) and dorsal (B) views. Abbreviations: cod, occipital condyle; eam, external acoustic meatus; FR, frontal; MX, maxilla; NA, nasal; nc, nuchal crest; PA, parietal; rt, rami temporales; s, sagittal crest; SQ, squamosal; tl, temporal line.