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above the orbits. Compared with H. erectus the parietals are expanded, the occipital is more rounded, and the frontal bone is broader. H. heidelbergensis is the earliest hominin to have a brain as large as that of some anatomically modern Homo, and its postcranial skeleton suggests that its robust long bones and large lower limb joints were well suited to long-distance travel. Researchers who see the African part of this hypodigm as distinctive refer it to a separate species, Homo rhodesiensis. Those who see the European component of the H. heidelbergensis hypodigm (e.g., Sima de los Huesos) as already showing signs of H. neanderthalensis autapomorphies would sink it into the latter taxon.

Those who support Homo ergaster Groves and Mazák 1975 as a separate species point to features that are more primitive than H. erectus (e.g., mandibular premolar root and crown morphology) and those that are less derived than H. erectus (e.g., vault and cranial base morphology) (Wood, 1991). However, many researchers are unconvinced there are sufficient consistent differences between the hypodigms of H. ergaster and H. erectus (Spoor et al., 2007) to justify the former being a separate species. The taxon Homo antecessor Bermúdez de Castro et al. 1997 was introduced for hominins recovered from the Gran Dolina site at Atapuerca, Spain. The researchers who found the remains claim the combination of a modern human-like facial morphology with large and relatively primitive tooth crowns and roots is not seen in H. heidelbergensis (see below), and they see H. antecessor and not H. heidelbergensis as the likely recent common ancestor of H. neanderthalensis and H. sapiens.

The most recent taxon to be added to the genus Homo is H. floresiensis Brown et al. 2004. It is only known from Liang Bua, a cave in Flores, and its temporal range is ca. 74–17 ka. The initial discovery and type specimen is LB1, an associated partial adult skeleton, but a second associated skeleton and close to 100 separate fossils representing up to 10 individuals have subsequently been recovered. This hominin displays a unique combination of early Homo-like cranial and dental morphology, a hitherto unknown suite of pelvic and femoral features, a small brain (ca. 417 cm3), a small body mass (25–30 kg), and small stature (1 m). When it was first described researchers interpreted it as an H. erectus, or H. erectus-like, taxon that had undergone endemic dwarfing, but more recently researchers have suggested it could be a dwarfed Homo habilis-like transitional grade taxon (Brown and Moeda, 2009; Morwood and Jungers, 2009).

Transitional Hominins

For the purposes of this review, H. habilis and Homo rudolfensis are retained within Homo, but they are treated separately from the premod-

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