László Kordos

European Miocene Hominids and the Origin of the African Ape and Human Clade

In 1871, Darwin famously opined, “In each great region of the world the living mammals are closely related to the extinct species of the same region. It is therefore probable that Africa was formerly inhabited by extinct apes closely allied to the gorilla and chimpanzee; and as these two species are now mans nearest allies, it is somewhat more probable that our early progenitors lived on the African continent than elsewhere.” 1 Although this quote is frequently recalled today, Darwins next line is rarely acknowledged: “But it is useless to speculate on this subject, for an ape nearly as large as a man, namely the Dryopithecus of Lartet, which was closely allied to the anthropomorphous Hylobates, existed in Europe during the Upper Miocene period; and since so remote a period the earth has certainly undergone many great revolutions, and there has been ample time for migration on the largest scale.” 1

Evolution of locomotion in Anthropoidea: the semicircular canal evidence

Our understanding of locomotor evolution in anthropoid primates has been limited to those taxa for which good postcranial fossil material and appropriate modern analogues are available. We report the results of an analysis of semicircular canal size variation in 16 fossil anthropoid species dating from the Late Eocene to the Late Miocene, and use these data to reconstruct evolutionary changes in locomotor adaptations in anthropoid primates over the last 35 Ma. Phylogenetically informed regression analyses of semicircular canal size reveal three important aspects of anthropoid locomotor evolution: (i) the earliest anthropoid primates engaged in relatively slow locomotor behaviours, suggesting that this was the basal anthropoid pattern; (ii) platyrrhines from the Miocene of South America were relatively agile compared with earlier anthropoids; and (iii) while the last common ancestor of cercopithecoids and hominoids likely was relatively slow like earlier stem catarrhines, the results suggest that the basal crown catarrhine may have been a relatively agile animal. The latter scenario would indicate that hominoids of the later Miocene secondarily derived their relatively slow locomotor repertoires.

The Evolution of Thought: Cranial evidence of the evolution of intelligence in fossil apes

Fossil endocasts, natural or artificial casts of the inside of a cranial vault, provide the most direct evidence of the evolution of the brain. Among fossil hominoids, the vast majority of endocasts come from PlioPleistocene hominids, and these have been described in detail, (Conroy, Vannier & Tobias 1990; Dart 1925; Falk 1980a,b, 1983a,b, 1987, 1990; Falk & Conroy 1983; Holloway 1974a, 1982, 1983a, 1984, 1995; Holloway & De la Coste-Lareymondie 1982; Martin 1983, 1990; Martin & Harvey 1985; Schepers 1946, 1950; Tobias 1967, 1971a,b, 1975, 1978, 1983, 1991, 1995). Fossil great ape endocasts are extremely rare and are thus far undescribed. Therefore, beyond extrapolation from an outgroup, little is known of the primitive condition from which modern great ape and human brains could have evolved. Six specimens of the primitive Oligocene catarrhine Aegyptopithecus zeuxis from about 33–33.5 Ma are described (Radinsky 1973, 1974, 1977; Rasmussen 2002; Simons 1993). Among hominoids, only four specimens are sufficiently complete to estimate brain size: one for Proconsul nyanzae, an early Miocene (c. 18 Ma) primitive or stem1 hominoid that predates the emergence of the great ape and human clade, and three for the great apes Dryopithecus brancoi and Oreopithecus bambolii from between about 10 to 6 Ma (Begun 2002; Falk 1983a; Harrison 1989; Kordos 1990; Kordos & Begun 1997, 1998, 2001a; Walker et al. 1983). The only fossil hominoid for which the endocast has yet been described is Proconsul. Proconsul is said to be more encephalized than monkeys of similar size, and close to living great apes (Walker et al. 1983), though this conclusion is revisited here. Most authorities have also concluded that the endocast of Proconsul is morphologically more primitive than that of any living hominoid (Falk 1983a; Radinsky 1974). Between the primitive endocast of the early catarrhine Aegyptopithecus and the stem hominoid Proconsul there is about a 15 Ma gap. There is another 8 Ma gap from Proconsul to the late Miocene great ape Dryopithecus brancoi (Kordos & Begun 1997, 2001a). Oreopithecus and Sahelanthropus, a newly described hominid from Chad, both between 6 and 7 Ma in age, fill the gap between Dryopithecus and the earliest australopithecine for which brain and body size data are available, Australopithecus afarensis (Brunet et al. 2002; Harrison & Rook 1997). Oreopithecus appears unique in brain size (see below) while Sahelanthropus, like Dryopithecus, appears to have a great-ape-sized brain relative to its body mass (see below and Brunet et al. 2002). A. afarensis, from 3.6–2.9 Ma, shows a level of encephalization comparable to or slightly above that seen in living great apes and Dryopithecus and clearly above that seen in Proconsul, Oreopithecus, and most other anthropoids (see below and Jerison 1973, 1975; Kappelman 1996; Martin 1983, 1990; Pilbeam & Gould 1974; White 2002). In this chapter we review the available fossil evidence and assess its relevance to a reconstruction of the evolution of the brain in great apes.

A new reconstruction of RUD 77, a partial cranium of Dryopithecus brancoi from Rudabánya, Hungary.

A newly reconstructed cranium (RUD 77) of the Miocene fossil hominoid Dryopithecus, formerly Rudapithecus (Kretzoi [1969] Symp. Biol. Hung. 9:3-11; Begun and Kordos [1993] J. Hum. Evol. 25:271-286) is presented here. This specimen, from the late Miocene locality of Rudabánya, in northeastern Hungary, consists of portions of the neurocranium, face, and postcanine dentition. Newly recovered portions of the parietal, occipital, temporal, zygomatic, and premaxillary bones, which are described here for the first time, in association with previously described portions of this specimen (Kordos [1987] Ann. Hist. Nat. Mus. Natl. Hung. 79:77-88) make RUD 77 among the most complete and well preserved neurocrania of any Miocene hominoid. Detailed anatomical descriptions and measurements are provided here, along with comparisons to other relatively complete Miocene hominoid cranial remains, and to living hominoids. While a more complete phylogenetic analysis is in preparation based on the sample as a whole, it is suggested here that RUD 77 provides some additional evidence in support of a previous hypothesis that Dryopithecus is more closely related to the African apes and humans than is Sivapithecus.

New evidence for diet and niche partitioning in Rudapithecus and Anapithecus from Rudabánya, Hungary

Rudabánya is rare among Eurasian Miocene fossil primate localities in preserving both a hominid and pliopithecoid, and as such provides the unique opportunity to reconstruct the nature of sympatry and niche partitioning in these taxa. Rudapithecus and Anapithecus have similar locomotor and positional behavior and overlapping body mass ranges. While prior analyses of molar occlusal anatomy and microwear identify Rudapithecus as a soft-object frugivore, reconstructing the dietary behavior of Anapithecus has been more problematic. This taxon has been interpreted to be more folivorous by some, and more frugivorous by others. Here, we use high-resolution polynomial curve fitting (HR-PCF) to quantify and evaluate the mesiodistal and cervico-incisal curvatures of the incisor crowns of Rudapithecus and Anapithecus to identify diet-specific morphological variation in these taxa. Results are consistent with the interpretation that Anapithecus and Rudapithecus were primarily frugivorous and had diets that included similar resource types. However, Anapithecus may have consumed greater amounts of foliage, similar to extant mixed folivore-frugivores (i.e., Gorilla gorilla gorilla, Symphalangus syndactylus), while Rudapithecus generated elevated compressive loads in the incisor region consistent with a specialized role for the anterior dentition in food processing (i.e., removal of tough protective fruit pericarps). We interpret these findings in light of the paleoecology at Rudabánya and conclude that, if these taxa were indeed sympatric, Anapithecus may have used additional leaf consumption as a seasonal fallback resource to avoid direct competition with Rudapithecus. Conversely, Rudapithecus may have relied on less preferred and harder fruiting resources as a seasonal fallback resource during periods of fruit scarcity.