H. naledi crania, DH1, LES1, and DH3 are in the center row. All crania are oriented as near as possible to the Frankfort plane, delineated by the light gray lines in the background of the figure. Compared to other hominin genera, including Australopithecus and Paranthropus, fossil Homo is often recognized by cranial and dental features such as a more vertical face profile, a reduced postcanine dentition, larger endocranial volume, a higher frontal, and a true supraorbital torus. Au. africanus (Sts 5, top left) represents the ancestral hominin condition lacking these traits. The other crania in the top two rows vary substantially in these features. LB1 has a vertical face, reduced dentition, and high, rounded frontal, but has comparatively small endocranial volume. KNM-ER 1470 has a large volume, a high frontal, and a more vertical face profile, but also is inferred to have a large postcanine dentition and has no true supraorbital torus. MH1 (Au. sediba) has a small volume, but shares features with Homo that include the less sloping face profile, a supraorbital torus, and reduced postcanine dentition. O.H. 24 has a low, sloping frontal, and a concave facial profile, but a true supraorbital torus and reduced postcanine teeth. This variability among species that are interpreted as ‘primitive’ Homo, such as H. habilis and H. floresiensis, and Homo-like australopiths makes it difficult to delineate the genus Homo (Wood and Collard, 1999; Dembo et al., 2016). H. erectus is also highly variable. It includes several crania with endocranial volumes below 700 ml, including KNM-ER 42700 and D2282, but also many larger crania, here represented by Sangiran 17 and Zhoukoudian L2 (ZKD L2). Specimens attributed to H. erectus tend to share a series of traits first noted in Asian H. erectus samples, including a long, low cranial profile, thick cranial bone, sagittal keeling, prominent supraorbital, angular, and occipital tori, a sharply angled occiput, and a postbregmatic depression. The smallest H. erectus crania share most of these features, with a low cranial profile, angled occiput and postbregmatic depression visible here in D2282. But these features do vary substantially and are less evident in the immature KNM-ER 42700. The H. naledi crania are similar to KNM-ER 1470 in having a transversely flat clivus contour, but all are smaller, with a much smaller palate and with very different frontal morphology. Like O.H. 24 and KNM-ER 1813, the H. naledi crania have relatively thin cranial bone and a thin and projecting supraorbital torus. But H. naledi manifests a different clivus shape, a projecting nasal spine, a greater cranial height, sagittal keeling and an angular torus. The H. naledi crania bear little resemblance to LB1, differing in face profile, size, and their larger postcanine dentitions. Known African Homo specimens from the later Middle Pleistocene other than H. naledi, such as the Kabwe skull (pictured), contrast strongly with H. naledi in cranial size and morphology. The Omo 2 skull, one of the earliest known modern human crania at approximately 196,000 years (McDougall et al., 2005), is vastly larger and very different from any H. naledi specimen, despite being near the same geological age. In this figure, O.H. 24, KNM-ER 1470, LB1, KNM-ER 42700, ZKD L2, and Omo 2 are represented by casts. Images have been adjusted to a common scale by maximum cranial length, or by glabella-bregma length where maximum length is not available. Photos of Sangiran 17 and D2282 are courtesy of Milford Wolpoff.