Disentangling isolated dental remains of Asian Pleistocene hominins and pongines.

Tanya M Smith,Anthony J Olejniczak,Adeline Le Cabec,Alexandra Houssaye,John De Vos,Friedemann Schrenk,Ottmar Kullmer,Paul Tafforeau,Alistair Robert Evans

doi:10.1371/journal.pone.0204737

Abstract

Scholars have debated the taxonomic identity of isolated primate teeth from the Asian Pleistocene for over a century, which is complicated by morphological and metric convergence between orangutan (Pongo) and hominin (Homo) molariform teeth. Like Homo erectus, Pongo once showed considerable dental variation and a wide distribution throughout mainland and insular Asia. In order to clarify the utility of isolated dental remains to document the presence of hominins during Asian prehistory, we examined enamel thickness, enamel-dentine junction shape, and crown development in 33 molars from G. H. R. von Koenigswald's Chinese Apothecary collection (11 Sinanthropus officinalis [= Homo erectus], 21 “Hemanthropus peii,” and 1 “Hemanthropus peii” or Pongo) and 7 molars from Sangiran dome (either Homo erectus or Pongo). All fossil teeth were imaged with non-destructive conventional and/or synchrotron micro-computed tomography. These were compared to H. erectus teeth from Zhoukoudian, Sangiran and Trinil, and a large comparative sample of fossil Pongo, recent Pongo, and recent human teeth. We find that Homo and Pongo molars overlap substantially in relative enamel thickness; molar enamel-dentine junction shape is more distinctive, with Pongo showing relatively shorter dentine horns and wider crowns than Homo. Long-period line periodicity values are significantly greater in Pongo than in H. erectus, leading to longer crown formation times in the former. Most of the sample originally assigned to S. officinalis and H. erectus shows greater affinity to Pongo than to the hominin comparative sample. Moreover, enamel thickness, enamel-dentine junction shape, and a long-period line periodicity value in the “Hemanthropus peii” sample are indistinguishable from fossil Pongo. These results underscore the need for additional recovery and study of associated dentitions prior to erecting new taxa from isolated teeth.

Highlights

Fossil remains attributed to Homo erectus have been recovered from numerous localities in mainland Asia and island Southeast Asia driven, in part, by intense scholarly interest during the last century in a potential Asian origin for the genus Homo
We examined two-dimensional (2D) relative enamel thickness, enamel-dentine junction shape, and crown development in 33 molars from von Koenigswald’s Chinese Apothecary (CA) collection (11 Sinanthropus officinalis [= Homo erectus], 21 “Hemanthropus peii,” 1 “Hemanthropus peii” or Pongo) and 7 teeth from Sangiran dome housed at the Senckenberg Research Institute (Frankfurt, Germany) (Table 1)
The type specimen of "Hemanthropus peii" (CA 673) has a maxillary molar relative enamel thickness (RET) value of 13.1, which is similar to the fossil Pongo mean (13.8)

Summary

Introduction

Fossil remains attributed to Homo erectus have been recovered from numerous localities in mainland Asia and island Southeast Asia driven, in part, by intense scholarly interest during the last century in a potential Asian origin for the genus Homo. Von Koenigswald [14] originally reported that this taxon was “difficult to define” and distinguished several isolated molar teeth from orangutans solely on the lack of “fine wrinkles” and resulting “better defined cusps,” promising a more detailed description that was never published. Both orangutans and humans show marked intraspecific variation in the expression of crenulations and the underlying cuspal morphology [7, 26]. Crenulations are compromised by wear, making this a tenuous morphological feature on which to erect a new genus and species

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Conclusion