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Comment on "Pierolapithecus catalaunicus, a New Middle Miocene Great Ape from Spain"

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Science  08 Apr 2005:
Vol. 308, Issue 5719, pp. 203
DOI: 10.1126/science.1108139

The recent report of Pierolapithecus catalaunicus by Moyà-Solà et al. (1) provides important new information on great ape origins. We congratulate the authors on their spectacular discovery and excellent analysis and propose some alternative phylogenetic and functional interpretations based on the data they present.

Moyà-Solà et al. conclude that Pierolapithecus is a new genus that represents the sister taxon to the great ape and human clade. From their descriptions and photographs, we were able to code 96 characters for Pierolapithecus into our database of living and fossil hominoid morphology (2, 3). Our published data matrix was modified for this analysis by dropping poorly known taxa and adding missing characters based on more recent discoveries. The results are consistent with the consensus phylogeny in (2) for previously known taxa but suggest that Pierolapithecus is most parsimoniously interpreted as a stem hominine (basal member of the African ape and human clade) rather than a stem hominid (great ape and human clade) (Fig. 1). The average consistency index (CI) for the nine characters supporting Pierolapithecus as a basal hominine (Table 1) is 0.89. Support for the hypothesis that Pierolapithecus is a stem hominid (1) requires six additional steps, and the seven characters supporting this hypothesis have a lower average consistency index of 0.74.

Fig. 1.

Cladogram representing the single most parsimonious phylogenetic hypothesis retrieved by adding 96 characters known for Pierolapithecus to a morphological data matrix modified from (2). Support for Pierolapithecus as a hominine is strong, but support for its being a sister clade to Dryopithecus is less so. We conclude that Pierolapithecus is near the base of the hominine clade.

Table 1.

Characters supporting the position of Pierolapithecus in Fig. 1.

Pierolapithecus as the sister clade to Dryopithecus
   low radial lunate/scaphoid angle
   narrow I1
   rounded supraorbital region
Pierolapithecus as a hominine (These are characters at the hominine node that includes Pierolapithecus, although most of them are not actually known to us for Pierolapithecus.)
   concavoconvex centrale facet on capitate
   biconvex alveolar premaxilla
   broad nasal aperture base
   horizontal frontal squama
   broad temporal fossa
   long neurocranium
   fused articular and tympanic temporal
   lacrimal fossa visible
   small articular tubercle
Crown hominids (with Pierolapithecus as a hominine) (These are characters at the hominid node that includes Pierolapithecus as a hominine, although most of them are not actually known to us for Pierolapithecus.)
   capitate head intermediate breadth
   no I2 cingulum
   P3 mesiodistal beak present
   high P4 talonid
   large maxillary sinus
   high maxillary sinus floor
   long neurocranium
   maxillary sinus anterior to the canine alveolus
   deep alveolar process
   high zygomatic root
   labiolingually large lower incisors

Although it is most parsimonious to consider Pierolapithecus a hominine, an additional argument in favor of this hypothesis is the effect on the support for a crown hominid clade. Most hypotheses, including those in previous analyses cited here (13), include both Dryopithecus and Sivapithecus in a crown hominid clade. However, when Pierolapithecus is interpreted as a stem hominid, as in (1), support for the crown hominid clade that includes Dryopithecus and Sivapithecus falls from 11 characters (average CI = 0.86) to only 2 characters (average CI = 0.75) (Table 1). In other words, the most prudent hypothesis interpreting Pierolapithecus as a hominine is also more consistent with most previous analyses of relations among fossil and extant hominids. We also found some support for the hypothesis that Pierolapithecus is the sister taxon to Dryopithecus, but the average CI is only 0.66 for the three characters placing Pierolapithecus on the Dryopithecus clade. We interpret these results as strong evidence that Pierolapithecus is a basal hominine, although its position as a member of the Dryopithecus clade is only weakly supported. As a hominine, the morphology of Pierolapithecus reinforces the hypothesis that a number of postcranial similarities of orangutans and African apes may be homoplasies (4).

Moyà-Solà et al. (1) conclude that Pierolapithecus was less suspensory than are extant apes and that suspensory adaptations in late Miocene and living apes are largely homoplasious. This interpretation is based on the shorter fingers and more dorsally oriented metacarpophalangeal joints of Pierolapithecus compared with Dryopithecus and extant great apes, and less dorsally placed vertebral transverse processes. Although these morphologies differ from those seen in extant apes, they do not preclude suspensory behavior. The fundamentally reorganized hominoid-like torso and wrist seen in Pierolapithecus is associated with both climbing and suspension in extant hominoids (5, 6). Although admittedly not identical to those of extant apes, the Pierolapithecus vertebrae and ribs resemble those of hylobatids, and so do not suggest limited suspensory behavior (5). The proximal and intermediate phalanges of Pierolapithecus are curved and bear strong attachments for the flexor tendon sheaths, also consistent with climbing and suspension. The incomplete preservation of the hand phalanges makes it difficult to be certain from which digital ray the specimens in figure 4 come (1). If they are not from ray 3, the comparison to ray 3 of Dryopithecus, the longest and most curved, may be misleading and could at least partly account for the shorter length and lower curvature.

We agree that the postcrania overall suggest that Pierolapithecus had a unique positional repertoire. We think, however, that the evidence suggests that this repertoire included climbing and suspension and a limited amount of palmigrady. Changes seen in later hominoids may represent further specialization for forelimb-dominated below-branch arboreality coupled with large body size and abandonment of palmigrady. We commend Moyà-Solà et al. on this astonishing discovery and look forward to further analysis of this important fossil.

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