Middle Miocene hominoid origins.

Ward et al. (1) ably show that samples of thickly enameled Middle Miocene hominoids that they attribute to a new genus, Equatorius, are distinct from Kenyapithecus. They fail to show, however, how Equatorius differs from Griphopithecus. In so doing, they may have missed the hominoid connection between Eurasia and Africa by 2 to 3 million years. The authors note the presence of a welldeveloped buccal cingulum on the type specimen of G. darwini, an M3 from Devı́nska Nová Ves, Slovakia, that they say distinguishes this taxon from Equatorius. Samples from Paşalar and Çandır in Turkey that have been assigned to G. alpani, however, show that M3 cingulum expression is variable in Griphopithecus; indeed, specimens from these samples are quite similar to M3 specimens of Equatorius. In addition, the upper molars of G. darwini lack well-defined lingual cingula. This is probably a shared derived character with other thickly enameled Middle Miocene hominoids, and distinguishes both Griphopithecus and the Maboko and Kipsaramon samples from Early Miocene forms. Nothing in the diagnosis of Equatorius excludes most of the specimens currently attributed to G. darwini or G. alpani; the portions of the diagnosis of Equatorius that can be compared to the current hypodigm of Griphopithecus could apply just as well to it. This is true even for the more apomorphic characters of Equatorius related to the inferior transverse torus, sublingual plane, and I2. What Ward et al. really provide is evidence for a link between Eurasian and African thickly enameled hominoids of 15.5 million years ago (Ma) in addition to the link they describe between ;14 Ma Kenyapithecus (sensu stricto) and the unnamed second taxon from Paşalar. This is most effectively communicated by recognizing two taxa— Griphopithecus for the samples from Devı́nska Nová Ves, Paşalar, Çandır, Kipsaramon, the Maboko Formation, Nachola, and the Tugen Hills, and Kenyapithecus for the samples from Fort Ternan and the Paşalar unnamed second taxon. Taxonomic issues aside, recognition of this more complex biogeographic pattern is significant: in both cases, the earlier-occurring taxon is Eurasian, not African. Both the unnamed taxon from Paşalar and a molar from Engelsweis, Germany, that cannot be distinguished from Griphopithecus predate their African counterparts by at least 1 million years (2–4). This pattern may result from an incomplete fossil record, but it more likely means that African Middle Miocene hominoids represent successive radiations of forms dispersing from Eurasia—a pattern thought to hold for many other mammals, including muroid rodents, the bovid Eotragus, gomphotheriids, amebelodontines, carnivores, and at least one suid (5–7). The confirmation of a taxonomic and phyletic distinction between Kenyapithecus and Griphopithecus, and the proposed link between Kenyapithecus and earlier hominoids from Paşalar, strengthen the Eurasian-origins hypothesis by providing yet another example of related hominoids that appear in Eurasia before they appear in Africa (8, 9).