GEOGRÁFICO Lo abiótico
5. CONSIDERACIONES FINALES
5.5.1
Sivapithecus
Sivapithecus was a large-bodied hominoid known from an abundance of craniodental and postcranial elements assigned to three species (Brown et al., 2005; Begun, 2007; Bilsborough and Rae, 2007). The genus is the best known of the Miocene hominoids, with an abundance of craniodental and postcranial specimens recovered from the Siwalik Hills of India and Pakistan, dated between 7.5 and 12.7 Ma (Ward and Pilbeam, 1983; Kappelman et al., 1991; Ward, 1997b; Brown et al., 2005; Begun, 2007; Bilsborough and Rae, 2007).
S. indicus, which likely includes 12 Myr-old unassigned specimens from the Middle Chinji Formation of Pakistan, is known from craniodental specimens dated from 10 to 12.5 Ma (Raza et al., 1983; Rose, 1984; Kappelman et al., 1991; Kelley, 2002; Begun, 2007). S. indicus is the oldest, smallest, and craniodentally most primitive species of Sivapithecus (Begun, 2007). S. parvada is the largest species, up to twice the size of the other Sivapithecus, and is known from craniodental specimens from the Nagri formation, Pakistan, dated to 10 Ma (Kelley, 2002; Begun, 2007; Bilsborough and Rae, 2007). S. sivalensis, the best known species, is dated from 8.5 to 9.5 Ma (Pilbeam, 1982; Kelley, 2002; Begun, 2007). S. sivalensis is represented cranially by a partial skull (GSP 15000), similar in size to female Pongo and exhibiting a number of
derived pongine characters including supraorbital costae, a narrow interorbital distance, tall and narrow orbits, the absence of a frontoethmoidal sinus, and an extremely airorhynchous or dorsally deflected face (Pilbeam, 1982; Ward and Kimbel, 1983; Ward and Brown, 1986; Ward, 1997b; Kelley, 2002; Begun, 2007; Bilsborough and Rae, 2007). However, S. sivalensis exhibits thicker occlusal molar enamel than Pongo and exhibits digastric fossae, markings for the anterior digastric muscles, when the absence of these fossae are considered an autapomorphy of Pongo among the extant hominids (Brown et al., 2005; Begun, 2007; Bilsborough and Rae, 2007). S.
sivalensis lacks the prominent crenulations of the molar enamel exhibited by Pongo (Brown et
al., 2005; Begun, 2007; Bilsborough and Rae, 2007). Humeri from S. indicus and S. sivalensis are more similar to primitive Early Miocene arboreal quadrupeds than they are to those of the extant suspensory orthograde hominids (Pilbeam, 1996; 1997; 2002; Rose, 1997; Madar et al., 2002; Begun, 2007). The morphology and size of the humerus in S. parvada is suggestive of a terrestrial quadruped that does not have a living hominoid analogue (Begun, 2007).
Specimens: The subnasal anatomy of S. sivalensis is represented by the holotype (GSI D-1), a hard palate from the Siwaliks of Pakistan (Kelley, 2002), a maxillary fragment (GSI D-196) from Haritalyangar, India (Kelley, 2002), and a partial cranium (GSP 15000) from the Potwar Plateau, Pakistan (Pilbeam, 1982; Ward, 1997b; Kelley, 2002; Brown et al., 2005; Begun, 2007; Bilsborough and Rae, 2007).
The subnasal anatomy is also represented by a lower face and hard palate (GSP 16075) not yet assigned to a species—but likely belonging to S. indicus—from the Chinji Formation, Pakistan (Kelley, 2002; Begun, 2007).
Subnasal anatomy: The premaxillae of S. sivalensis are very elongated and oriented nearly horizontally, similar to Pongo (Ward and Kimbel, 1983; Begun, 2007; Bilsborough and Rae, 2007). The premaxillae are convex only in the sagittal plane, as the premaxillae are flat in the transverse plane, similar to Pongo, but unlike other Middle and Late Miocene hominoids (Kelley, 2002; Begun, 2007). The premaxillae extensively “overlap” the palatine processes and transitions smoothly into the palatine processes, resulting in the absence of a pronounced “step- down” in the floor of the nasal cavity lateral to the nasal incisive fossae and a “smooth” nasal cavity floor (Kelley, 2002; Brown et al,. 2005; Begun, 2007; Bilsborough and Rae, 2007). The
nasal and oral incisive fossae are very narrow, almost slit-like to indistinct in appearance, and are connected by an “incisive canal” (Kelley, 2002; Brown et al., 2005; Bilsborough and Rae, 2007). The “incisive canal” is very long and narrow relative to all other Miocene hominoids, but similar
to Pongo (Kelley, 2002; Brown et al., 2005). The subnasal anatomy of S. sivalensis is
noteworthy for its synapomorphies with Pongo to the exclusion of all other genera of Miocene hominoids (Ward and Kimbel, 1983; McCollum et al., 1993; Begun, 2002; 2007).
The subnasal anatomy of the older S. indicus from the Chinji Formation is more primitive than that of S. sivalensis (Begun, 2007). The shape of the hard palate is similar to Pongo and S. sivalensis (Raza et al., 1983; Ward, 1997b; Kelley, 2002; Begun, 2007). The premaxillae are elongated, robust and oriented horizontally, relative to earlier Miocene hominoids but the premaxillae are short relative to S. sivalensis (Kelley, 2002; Begun, 2007). The premaxillae “overlap” the palatine processes and there is a smoother transition into the palatine processes than in other Miocene hominoids (Begun, 2007). However, the incisive fossae and the incisive foramina are not preserved and thus, a definite diagnosis of the presence of a Pongo-like “incisive canal” cannot be made (Begun, 2007). It is not surprising that the older S. indicus might exhibit a more primitive form of the subnasal anatomy than S. sivalensis.
5.5.2
Lufengpithecus
Lufengpithecus was a large-bodied sexually dimorphic Asian hominoid, known from thousands of craniodental specimens, including several crania from Lufeng, Yunnan province, China, dated from 8 to 9 Ma (Kelley, 2002; Brown et al., 2005; Begun, 2007; Bilsborough and Rae, 2007). Lufengpithecus is notable among hominoids in having a marked degree of sexual dimorphism – greater than that exhibited by extant hominoids (Kelley and Qinghua, 1991; Bilsborough and Rae, 2007). Three species of Lufengpithecus are recognized, distinguished by size and geography – each is known from a specific locale (Begun, 2007; Bilsborough and Rae, 2007). L. lufengensis from Shihuiba is the best known species and is represented by a number of partial crania, while L. keiyuanensis is known from Yuanmou (Harrison et al., 2002; Brown et al., 2005; Begun, 2007). L. lufengensis exhibits thick and crenulated molar enamel and a robust mandibular morphology and is considered to be closely affiliated with Pongo based on dental similarities, although unlike Pongo, L. lufengensis exhibits digastric fossae, markings for the
anterior digastric muscles (Ward, 1997b; Begun, 2007; Bilsborough and Rae, 2007). The postcrania of Lufengpithecus are suggestive of extant hominid suspensory behaviour, unlike Sivapithecus (Begun, 2007).
Specimens: The subnasal anatomy of L. lufengensis is represented by a fragmentary partial cranium (PA 644) from Shihuiba, Lufeng, China, and that of L. keiyuanensis from a juvenile partial cranium (YV0999) from Hudie Liangzi, Yuanmou Basin, China ( Kelley, 2002; Brown et al., 2005).
Subnasal anatomy: The premaxillae of L. lufengensis are relatively short and oriented vertically (Kelley, 2002; Brown et al., 2005; Begun, 2007). The premaxillae of the L. keiyuanensis juvenile (YV0999) are shorter than Pan at an equivalent stage of development (Brown et al., 2005). The posterior poles of the premaxillae are elevated above the palatine processes, resulting in a “step-down” in the floor of the nasal cavity, similar to Ankarapithecus, but unlike
Sivapithecus (Brown et al, 2005; Begun, 2007). The nasal and oral incisive fossae of L.
keiyuanensis are relatively deep and broad in diameter, but reduced in size relative to Early Miocene hominoids (Brown et al., 2005). Brown et al. (2005) suggest that the adult crania of L. lufengensis, though superoinferiorly crushed, may exhibit a similar morphological pattern of the subnasal anatomy as the juvenile L. keiyuanensis.