Mandibular Fossa Morphology in the Ngandong and Sambungmacan Fossil Hominids

Abstract

There has been debate in recent years concerning the significance of the mandibular fossa morphology in the Ngandong and Sambungmacan hominids. These fossils lack a postglenoid process and their squamotympanic fissure runs along the apex of the fossa for its entire length. This configuration differs from that seen in other fossil and modern humans, which have a prominent postglenoid process and a squamotympanic fissure that takes a more posterior course that does not lie in the apex of the fossa. Some recent studies have suggested that the Ngandong and Sambungmacan hominids are not unique in their expression of these characteristics, and that they can also be found in other fossil crania from Africa and Indonesia. The present study reexamines these morphologies in an effort to better understand their distribution in the hominid fossil record. The results confirm that the lack of a prominent postglenoid process in combination with a squamotympanic fissure that lies wholly in the apex of the mandibular fossa along its entire length is indeed autapomorphic for the Ngandong and Sambungmacan fossils. This finding, in conjunction with work on other nonmetric features in these hominids, suggests that at least two hominid morphs, possibly representing separate species, were present on Java during the Pleistocene. In addition, if this apparent autapomorphy is confirmed, then it is also unlikely that the Ngandong hominids contributed to the gene pool of modern humans. Anat Rec, 291:1212Rec, 291: -1220Rec, 291: , 2008 2008 Wiley-Liss, Inc.Key words: Homo erectus; Java; Sangiran; Sambungmacan; temporomandibular jointIn hominids, the mandibular fossa is located on the temporal bone on the lateralmost edge of the skull base. It forms the cranial portion of the temporomandibular joint, and is formed largely by the squamous portion of the temporal bone. The posterior wall of the mandibular fossa is made up of a combination of the anterior surface of the tympanic plate and an inferior projection of the squamous temporal, the postglenoid process or tubercle. The squamous temporal component of the posterior wall of the mandibular fossa, including the postglenoid process, is separated from the tympanic plate by the squamotympanic fissure (STF), also sometimes known as the Glaserian fissure.The potentially unique nature of the Ngandong mandibular fossa was first noted by Weidenreich (1951). His description is as follows (note that he is writing from the point of view of looking down upon the base of the calotte):''The deepest point of the [mandibular] fossa in modern man and in Sinanthropus is situated farther forward than in Solo man, and the floor of the fossa

<i>Homo erectus</i> calvaria from Ngawi (Java) and its evolutionary implications

“…The mandibular fossa depth of Ngawi 1 (11 mm) is closer to the figures for the Bapang-AG specimens (9-10 mm) but less than those of Ngandong (13-16 mm). Together with Sm 1 (personal observation; contra Durband, 2007Durband, , 2008 and Sm 4 (Baba et al, 2003), the mandibular fossa of Ngawi 1 is intermediate between the morphological variations seen in Ngandong and Bapang-AG.…”

“…[38] The mandibular fossa is unique in Ngandong (Weidenreich, 1951;Durband, 2002Durband, , 2008Baba et al, 2003) as well as Sm 3 Delson et al, 2001). In this group, the fossa is deep and anteroposteriorly short; the postglenoid process shows minimal or no development; the entire squamous portion of the fossa inclines posterosuperiorly so that its deepest part occurs along the squamotympanic fissure, whereas in the Bapang-AG, as well as other fossil and extant hominins, the squamous part of the temporal bone forms a concave fossa roof in front of the squamotympanic fissure (Figure 8).…”

“…It has been claimed that a few of the Ngandong specimens, Ng 7 and Ng 10, show more normal fossa configurations (Mowbray et al, 2002). Durband (2008) suggested that this is partly affected by taphonomic deformation, and noted that the fossa floor of Ng 7 is flat rather than concave. We found no evidence of deformation in our micro-CT scan of the right fossa of Ng 7 (Figure 8).…”

“…In this framework, some researchers emphasize morphological similarities among Ngawi, Sambungmacan, and Ngandong to erect the Ngandong/Sambungmacan/Ngawi group (or morph) and highlight its morphological distinction from the chronologically earlier Sangiran/Trinil group of Javanese H. erectus (Widianto and Zeitoun, 2003;Durband, 2008;Baab, 2010;Zeitoun et al, 2010;Grimaud-Hervé et al, 2012). Based on such recognition, some of them even propose species-level distinction between the two groups: the earlier H. erectus and later H. soloensis (Widianto and Zeitoun, 2003;Schwartz and Tattersall, 2005;Durband, 2008;Zeitoun et al, 2010).…”

Human evolution in Sunda and Sahul and the continuing contributions of Professor Colin Groves

“…Kaifu et al, 2008) as well as the evolution of several autapomorphic features of the cranial vault and base (Durband, 2002(Durband, , 2004(Durband, , 2008c. Features such as a divided foramen ovale located in a pit, the unique configuration of the mandibular fossa, and a 'teardrop' shaped foramen magnum caused by an opisthionic recess are some of the characters that have been shown to be autapomorphic in Ngandong, with most appearing in Sambungmacan and Ngawi (Durband 2004(Durband , 2008c. The faunal record of Java during this time period is indicative of relative isolation and endemism (de Vos et al, 1994;van den Bergh et al, 1996van den Bergh et al, , 1999van den Bergh et al, , 2001, which would be consistent with the interpretations of the patterns seen in the hominins.…”