Homo tsaichangensis

and Gigantopithecus

Mark A. S. McMenamin

Meanma Press

2015

Published January 28, 2015

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Meanma Press South Hadley, Massachusetts, USA ©2015 by Mark A. S. McMenamin All rights reserved. McMenamin, Mark A. S. Homo tsaichangensis and Gigantopithecus/Mark A. S. McMenamin ISBN 1-893882-19-5 ISBN13 978-1-893882-19-5 Printed in the United States of America

c 10 9 8 7 6 5

DOI: 10.13140/2.1.3463.7121

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INTRODUCTION

EVER SINCE Ralph von Koenigswald (von Koenigswald 1931, 1935, 1952), Pierre

Teilhard de Chardin (Teilhard 1926) and other Western scientists entered Asia in the

early decades of the 20th Century to search for paleontological data bearing on human

origins, Asia has been seen as rich in promise for this compelling area of paleontological

research. Recent new discoveries in the region are beginning to greatly increase our

understanding of Pleistocene higher primate evolution in East Asia.

An archaic human mandible ("Penghu Man" or Penghu 1, here named Homo

tsaichangensis n. sp.) dredged from the Penghu Channel off the west coast of Taiwan

shows intriguing similarities to a newly reported jaw fragment from Tegal, central Java,

here assigned to Gigantopithecus cf. G. blacki. These Pleistocene creatures may have

inhabited similar environments as part of what is referred to here as the Tegal-Penghu

Biogeographic Province. In addition to the primates, this province hosted the

proboscidean Stegodon and the hyaenid Crocuta. Morphological similarity between the

mandibular dentition of H. tsaichangensis n. sp. and Gigantopithecus blacki von

Koenigswald, 1935 suggest shared dietary preferences; indeed, the increased size of teeth

in H. tsaichangensis n. sp. contrasts sharply with the typical evolutionary trend of

"dentognathic reduction" (Chang et al. 2015) in successive species within the genus

Homo. The similarities represent an unusual case of convergent evolution between the

genus Homo and an unrelated group of primates.

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MAJOR RANGE EXTENSION FOR GIGANTOPITHECUS

On December 1, 2014, The Jakarta Post reported the discovery of a Gigantopithecus jaw

fragment from the Semedo excavation site, Semedo Village, Kedungbanteng District,

Tegal regency, central Java (Maryono 2014). The jaw fragment was found in association

with the fossil remains of a dwarf proboscidean belonging to the genus Stegodon. Fossils

of the pongid genus Gigantopithecus, the largest known primate of all time, were

previously known to occur only in China, India, and Vietnam. Gigantopithecus has

therefore experienced a major range extension with discovery of the Java specimen. This

new specimen is referred to here as Gigantopithecus cf. G. blacki.

ANCIENT HOMO FROM TAIWAN

On January 27, 2015, Chang et al. (2015) described the fossil of an archaic Homo

mandible that had been dredged from the Penghu Channel off the west coast of Taiwan.

The specimen was recovered from the seafloor by fishermen at a depth of approximately

90 meters, at a site about 25 kilometers from the coastline. The fossil was sold to a local

antique shop. A fossil collector named Kun-Yu Tsai later purchased the fossil. Mr. Tsai

donated the specimen to the National Museum of Natural Sciences in Taichung soon after

he recognized the importance of the discovery.

Although in their description of the fossil Chang et al. (2015) declined to give the

creature a new species name, it is true that important ancient higher primate species have

been established on far less extensive fossil material. For example, Gigantopithecus

blacki von Koenigswald, 1935 was named from isolated teeth (von Koenigswald 1935,

1952). It seems evident that the new Taiwan fossil, referred to as "Penghu Man" or

Penghu 1, represents a distinctive new hominoid species. It is here named Homo

tsaichangensis n. sp. to honor both the fossil collector who donated the fossil to the

museum in Taichung and the senior author of the initial scientific report on the find

(Figure 1).

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Figure 1. Homo tsaichangensis n. sp. Lateral view of right side of mandible. Note the

position of the mental foramen. The dashed line indicates the reconstructed shape of the

coronoid process. Width of fossil 12.5 cm.

CONVERGENT EVOLUTION AND HIGHER PRIMATES

Primarily due to similarities in dentition (Frayer 1973), Gigantopithecus was once

thought to be a closely related to the genera Australopithecus and Homo. The competing

view, expressed by David Pilbeam (1970), maintains that Gigantopithecus in fact

represents a giant pongid (i.e., orangutan relative). This latter view has prevailed. The

characteristic lingual groove on the pongid molar is the critical trait that ends the

controversy (Coichon 1988). Pilbeam (1970, p. 517) considered "it likely that the

'man-like' resemblances of the [Gigantopithecus] mandible are parallelisms." Taking this

a step further, even greater dental similarities may be observed when Gigantopithecus

and Homo tsaichangensis n. sp. are compared. This constitutes a case of convergent

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evolution that reflects similarities in dietary preferences between the two species.

Consider that the ratios of the maximum value of C1/M1 (width measured along the

predominant zahnreihe for each tooth in question) are similar between female G. blacki

and H. tsaichangensis n. sp., with values of C1/M1 = 0.875 and C1/M1 = 0.789,

respectively.

The major range extension of Gigantopithecus across the Sunda Shelf into Java,

and the range extension of an archaic species of Homo westward into Taiwan, confirms

the observation that a huge paleogeographic province (Teilhard 1930) extended from

Java, across the Sunda Shelf and up the southeastern Asian coast into Taiwan during

Pleistocene episodes of lowered sea level. This province, here called the Tegal-Penghu

Biogeographic Province (Figure 2), was populated by Stegodon and other distinctive

Pleistocene mammals. The province also hosted a diverse group of higher primates

including Gigantopithecus, Homo erectus and Homo tsaichangensis n. sp. The

Tegal-Penghu Biogeographic Province may be co-extensive with the biogeographic range

occupied by the Stegodon-Ailuropoda faunal assemblage (Zeitoun et al. 2005).

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Figure 2. The Tegal-Penghu Biogeographic Province. The irregular line shows the

modern coastline. The smooth line indicates the Pleistocene shoreline during low sea

level. The dotted line shows the approximate extent of the province.

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Based on its presumed co-occurrence with the hyaenid Crocuta crocuta ultima (an index

taxon known to have lived 500,000-250,000 years ago based on its occurrence at

Zhoukoudian locality 1 in northern China; Teilhard and Young 1929; Teilhard 1934; Pei

1934; Kahlke and Chow 1961; Chang et al. 2015) and the likelihood that the H.

tsaichangensis n. sp. mandible was deposited during a period of low sea level that

occurred 240,000-280,000 years ago, we may infer that H. tsaichangensis n. sp. lived

approximately 250,000 years ago and was thus contemporary with Gigantopithecus.

Gigantopithecus is known to have had a diet rich in bamboo, and this plant may also have

constituted part of the diet of H. tsaichangensis n. sp. In accordance with this inference,

Chang et al. (2015, p. 7-8) note that H. tsaichangensis n. sp. might have evolved "from a

gracile-jawed local H. erectus population, but this is contrary to the general trend of

dentognathic reduction in Pleistocene Homo." Thus, the dietary requirements of H.

tsaichangensis n. sp. probably explain the unexpected reversal in the evolutionary trend

of dentognathic reduction.

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SYSTEMATIC PALEONTOLOGY

Class Mammalia

Order Primates

Family Hominidae

Tribe Hominini

Subtribe Hominina

Genus Homo

Homo tsaichangensis n. sp.

(Fig. 1)

Synonymy:

"Penghu 1 mandible", Chang et al., 2015

Type specimen. Catalog Number F051911 [Access Number NMNS006655], National

Museum of Natural Science, Taichung, Taiwan.

Diagnosis. Large teeth (anterior row) with long incisors and premolars. Ramus and

corpus mandibulae relatively low in height. Corpus mandibulae robustly thick and

relatively low. Incisal part of jaw is wide; condyle very small. Chin absent; only a single

mental foramen. Root morphology of M2 unique, developing an extra root between the

lingual projections of the distal and mesial roots. M3 absent.

Remarks. This species is known from a right mandible that preserves both the symphysis

and five teeth (C1, P3, P4, M1, M2). The lack of M3 appears to be a species characteristic

in H. tsaichangensis n. sp. The coronoid process is broken. The dashed line in Fig. 1

shows a reconstruction of the coronoid process. Even with the end of the coronoid

process broken off, it seems clear that the H. tsaichangensis n. sp. coronoid process was

upright, much more like the coronoid process of H. neanderthalensis (Gibraltar) than like

the coronoid process of H. erectus (Zhoukoudian) that curves forward at its tip.

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The jaw ramus in Homo tsaichangensis n. sp. slants back posteriorly at a greater incline

(30°) than is typical for either Homo erectus (Zhoukoudian; 15°) or Homo

neanderthalensis (Gibraltar; 20°). Although Homo tsaichangensis n. sp. might be

compared to Hexian (H. erectus) from China's Anhui Province, I agree with Chang et al.

(2015) that it is unlikely that H. erectus was the sole species (albeit with clinal variation)

of the genus Homo in the Tegal-Penghu Biogeographic Province.

Homo tsaichangensis n. sp. has a considerably more prognathous aspect than

either Homo erectus (Zhoukoudian) or Homo neanderthalensis (Gibraltar), and is more

closely comparable to both male and female specimens of Gigantopithecus blacki in this

regard. H. tsaichangensis n. sp. shares with H. neanderthalensis (Gibraltar) a downward

expansion of the lower edge of the jaw directly underneath the molars and premolars. In

H. tsaichangensis n. sp., however, the point of greatest expansion (i.e., where the lower

jaw is locally greatest in height) is between P3 and M1, whereas in H. neanderthalensis

(Gibraltar) this point is closer to the M1-M2 junction.

Interestingly, the mental foramen in H. neanderthalensis (Gibraltar) is just

slightly posterior of the premolar-molar junction, whereas in H. tsaichangensis n. sp. the

mental foramen is located just beneath the junction of the two premolars, in accord with

the more prognathous character of the H. tsaichangensis n. sp. jaw. Significantly, H.

tsaichangensis n. sp. shares this feature (placement of the mental foramen) in common

with male Gigantopithecus blacki, where the mental foramen is directly beneath (or just

slightly anterior to) the junction between the two premolars. In contrast, female

Gigantopithecus blacki develops the mental foramen directly underneath P4. Thus we see

a progression as follows in the placement of the mental foramen in these chinless or

weak-chin mandibles going from the most anterior placement to the most posterior

placement:

G. blacki male anterior to P3-P4 junction

H. tsaichangensis n. sp. P3-P4 junction

G. blacki female P4

H. neanderthalensis (Gibraltar, Zafarraya) just posterior to P4-M1 junction

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Therefore, Homo tsaichangensis n. sp. with regard to this character falls intermediate

between male and female Gigantopithecus blacki, a relationship that clearly indicates that

H. tsaichangensis n. sp. belongs to a new and previously undescribed species of Homo,

one that is homoplasic with respect to Gigantopithecus.

Distribution and age. Pleistocene, approximately 250,000 years old. Stratigraphic

position unknown, as a marine dredge recovered the only known specimen. The

depositional environment may have been an estuarine, fluvial or lacustrine environment.

Etymology. The new species is named for Kun-Yu Tsai and Dr. Chun-Hsiang Chang.

ACKNOWLEDGEMENTS

I wish to thank S. Wheatley for assistance with this research.

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