Inner tooth morphology of Homo erectus from Zhoukoudian. New evidence from an old collection housed at Uppsala University, Sweden

Abstract

Locality 1, in the Lower Cave of the Zhoukoudian cave complex, China, is one of the most important Middle Pleistocene paleoanthropological and archaeological sites worldwide, with the remains of c. 45 Homo erectus individuals, 98 mammalian taxa, and thousands of lithic tools recovered. Most of the material collected before World War II was lost. However, besides two postcranial elements rediscovered in China in 1951, four human permanent teeth from the 'Dragon Bone Hill,' collected by O. Zdansky between 1921 and 1923, were at the time brought to the Paleontological Institute of Uppsala University, Sweden, where they are still stored. This small sample consists of an upper canine (PMU 25719), an upper third molar (PMU M3550), a lower third premolar crown (PMU M3549), and a lower fourth premolar (PMU M3887). Some researchers have noted the existence of morpho-dimensional differences between the Zhoukoudian and the H. erectus dental assemblage from Sangiran, Java. However, compared to its chrono-geographical distribution, the Early to Middle Pleistocene dental material currently forming the Chinese-Indonesian H. erectus hypodigm is quantitatively meager and still poorly characterized for the extent of its endostructural variation. We used micro-focus X-ray tomography techniques of virtual imaging coupled with geometric morphometrics for comparatively investigating the endostructural conformation (tissue proportions, enamel thickness distribution, enamel-dentine junction morphology, pulp cavity shape) of the four specimens stored in Uppsala, all previously reported for their outer features. The results suggest the existence of time-related differences between continental and insular Southeast Asian dental assemblages, the Middle Pleistocene Chinese teeth apparently retaining an inner signature closer to the likely primitive condition represented by the Early Pleistocene remains from Java, while the Indonesian stock evolved toward tooth structural simplification.

Comparative observations on the premolar root and pulp canal configurations of Middle Pleistocene Homo in China

“…Single‐rooted lower premolars are also frequently reported for the Middle Pleistocene hominins from Eurasia, including specimens from Zhoukoudian (Weidenreich, ; Xing et al, ; Zanolli, Pan, et al, ) and Chenjiawo (this study), the P 4 of Penghu 1 (Chang et al, ), Qesem Cave (Hershkovitz et al, ), Atapuerca Sima de los Huesos (Martinón‐Torres et al, 2012), and Visogliano (Zanolli et al, ).…”

“…Compared with early members of H. erectus s.l . (e.g., specimens from Dmanisi, East Africa, and Sangiran), upper premolars from Zhoukoudian and Yiyuan have less complex root and canal structures, whereas the lower premolars are closer to the early Homo condition (Martinón‐Torres et al, ; Xing et al, ; Zanolli, Pan, et al, ). On the other hand, Hexian H. erectus differs from northern Chinese H. erectus and European Middle Pleistocene hominins by showing primitive affinities (three‐rooted upper premolar, robust mandible and premolar roots) with the Early Pleistocene specimens from Africa ( H. ergaster ) and Java ( H. erectus ; Liu et al, ; Xing et al, ).…”

“…Except for PMU M 3887 housed at Uppsala University (which was scanned using X‐ray microtomography (μCT) at the Multidisciplinary Laboratory of the ICTP, Trieste (Tuniz et al, ; Zanolli, Pan, et al, )), all other Chinese specimens (fossil and recent humans) were scanned using a 225 kV‐μXCT scanner at the Institute of Vertebrate Paleontology and Paleoanthropology (IVPP, Chinese Academy of Sciences); micro‐CT data or STL mesh of the Neanderthals were downloaded from the NESPOS Database ([dataset] NESPOS database 2018); data for South African modern human specimens were produced on an X‐Tek (Metris) XT H225L industrial XCT system at the South African Nuclear Energy Corporation (Necsa; Hoffman & de Beer, ); European modern human specimens were acquired using a Phoenix Nanotom 180 scanner from the FERMAT Federation from the Inter‐university Material Research and Engineering Centre (CIRIMAT, UMR 5085 CNRS). Isometric voxel size ranged from 40 to 70 μm.…”

“…To date, root and pulp canal structure has been reported for a number of archaic Homo in East Asia (Chang et al, ; Liu et al, , ; Xing et al, , ; Zanolli et al, ); previous investigations (Liu et al, ; Xing et al, ) have revealed a general trend toward root number reduction, but a retention of primitive traits is still represented in particular cases like Hexian H. erectus (Liu et al, ; Xing et al, ) and Penghu 1 mandible (Chang et al, ). However, the root and pulp canal structure of Chinese Middle Pleistocene hominins has not been sufficiently recorded (especially late Middle Pleistocene specimens that are generally assigned to archaic H. sapiens ).…”

A distinguishing feature of Pongo upper molars and its implications for the taxonomic identification of isolated hominid teeth from the Pleistocene of Asia

“…Unless they are the result of dental tissue mineralization, which occurs later in morphogenesis, cusps (including small cuspules, conules, and tubercles) and crests develop as folds of the inner enamel epithelium (Butler, ). Thus, the study of the EDJ not only allows to more clearly determine topological relationships among dental structures (compared to the OES where these relationships may be masked by enamel deposition), but also represents an important means to distinguish between hominid taxa, even at the infraspecific level (e.g., Hanegraef et al, ; Macchiarelli et al, ; Macchiarelli, Bayle, Bondioli, Mazurier, & Zanolli, ; Macchiarelli, Bondioli, & Mazurier, ; Ortiz et al, ; Skinner et al, ; Skinner, Gunz, Wood, Boesch, & Hublin, ; Zanolli et al, , , ).…”