Wednesday, August 18, 2010
Jianshi--Earliest Extra-African Hominin, Further Evidence of Late Occurring Lufengpithecus or Fossil Orangutan?
Liu et al. (2010) have recently published a study of three supposedly hominin teeth from the Longgudong cave site in Jianshi county, Hubei. The teeth augment the sample of 4 hominin-like teeth collected in and around Jianshi in the 1970s that were initially attributed to an australopithecine (Gao 1975). The assessment by Liu et al. (2010) supplements the report in the 2004 monograph on Jianshi (Zheng 2004) published as the first in a series commissioned as part of the State Key Project of the 9th Five Year Plan – Origin of Early Humans and Environmental Background. The 2004 monograph is a comprehensive study of the geology, stratigraphy and paleontology of the fossil bearing site. In it the three hominin-like teeth, collected in 2000, were assigned to the Javanese genus and species Meganthropus paleojavanicus, based primarily on metric criteria.
The Jianshi site is further distinguished by the presence of a relatively large number of Gigantopithecus blacki teeth (28 in toto) and an extensive and diagnostic mammalian fauna. Study of the micro- and macro-mammalian fossils indicates a biochronological age slightly younger than the Longgupo site at Wushan, Chongqing (former Sichuan) or the Gigantopithecus cave site at Liucheng, Guangxi. Paleomagnetic research, however, suggests that the hominin-like material falls below the Reunion Normal Polarity Event or in excess of 2.15 mya. As such the Jianshi specimens would represent the earliest record of an extra-African human presence in all of Eurasia.
I recently reposted an essay written over a decade ago, derived from my 1994 Dissertation, which suggested that the original Jianshi molars could be favorably compared to fossil orangutan teeth previously collected in South China and Java. I have also written extensively on the Longgupo mandibular fragment and shown how it is compatible with an attribution to Lufengpithecus. Russ Ciochon, who along with Huang Wanpo, et al. (1995), originally described the Longgupo specimen as an early hominin, has since backtracked and conceded its non-hominin nature (Ciochon 2009). Given the possibility that the new Jianshi specimens may be mimicking a hominin morphotype I think it is essential to compare the new specimens not only to other hominins known from Africa, Europe and Asia, as has been done by Liu et al. (2010), but with other hominoids, including Lufengpithecus, known from southern China and Southeast Asia. In this regard Schwartz et al. (1994, 1995) published a study of hominoid dental remains from a variety of Pleistocene age sites in Vietnam. These included teeth ascribed to Gigantopithecus, Homo and Pongo. Amongst these teeth are some attributed to a new species, Pongo hooijeri, described as,
“Description and Diagnosis: Larger than most subspecies of fossil and living Pongo pygmaeus (see figs. 9-11), but differs from all known populations of P. pygmaeus in lacking significant crenulation on the occlusal surfaces of the molars and upper premolars, and on the basins of the lower premolars. Incisors are not known. Molar cusp disposition similar to that of P. pygmaeus, but the cusps themselves are puffier and more rounded occlusally as well as on their external slopes. The occlusal surfaces are thus more poorly defined, and the occlusal basins are more constricted. Discussion: The characters of the molars listed above distinguish these teeth very markedly from those of Pongo pygmaeus, and give them a very distinctive "gestalt." While it does appear that this new form belongs in the same general clade as the extant orangutan, it is by no means clear on the basis of current evidence that the two are very closely related. Pending better material, we feel a conservative interpretation is most appropriate, and have thus allocated this dentally distinctive primate to its own species of Pongo. It may well turn out, however, that the relationship between the two species is more distant than this implies, and it is possible that a separate generic designation for hooijeri will ultimately be warranted.”Unfortunately only the holotype specimen, a lower M2, is figured. In its overall appearance it looks remarkably similar to M2’s from Lufeng and is analogous in features to the M1 from Longgupo. Its description and analysis is also consistent with previously known Lufengpithecus.
The two recently described molars from Jianshi, one upper and one lower, are extremely well worn and lack most diagnostic surface features. They, as well as the original set of four molars described from Jianshi, are relatively large but fall within the upper range of variation of the Lufeng sample of hominoid molars. In this regard the Longgupo specimen falls within the lower range of variation. Therefore in terms of dental metrics there is no reason to dismiss the Jianshi and Longgupo remains as potentially members of a single highly dimorphic species such as seen in Lufengpithecus.
Liu et al. (2010) use a bevy of geometric morphometric techniques to tease apart shape discriminations to sort the Jianshi teeth relative to a variety of hominin samples. In a cursory comparison of the new Jianshi molars with homologous teeth in Schwartz et als study it appears that the sort of comparisons made by Liu et al. (2010) should also be done with non-hominin taxa from contiguous regions of East and Southeast Asia.
Additionally, the Mohui and Chuifeng Cave sites in the Bubing Basin of southern Guangxi have produced an abundant early Pleistocene fauna with, respectively, 16 and 92 teeth assigned to Gigantopithecus blacki. Another set (n=17) of smaller teeth from Mohui have been tentatively assigned to Hominoidea (gen. et sp. indet.)(Wang et al. 2007). These are said to include molars similar to those from the Longgupo mandibular fragment (Huang et al., 1995). Wang et al. go on to say that this Mohui sample does not strongly resemble Pongo remains found in Wuyun Cave and other sites in China. In addition Chuifeng Cave has produced "24 relatively large teeth, with high crowned molars and a simple occlusal pattern, (that) differ from the low crowned and wrinkled molars of Pongo, as well as the very large teeth of G. blacki. These teeth are provisionally assigned to Hominoidea gen. et sp. indet." (Wang 2009) Unfortunately neither the Mohui nor Chuifeng specimens are figured in the pertinent articles. Another similar molar specimen has been reported from Sanhe Cave in Chongzuo, Guangxi (Jin et al. 2009). Given the fact that non-hominin, non-pongine teeth that have been mistaken for specimens of Homo are now found widespread throughout southern China and northern Vietnam, the possibility must be entertained that the Jianshi teeth also represent a non-hominin taxon.
Zhao et al. (2009) describe and discuss a set of orangutan-like teeth from the early Late Pleistocene (~110 kya) site of Mulanshan, Guangxi. They review similar specimens collected from throughout southern China and from Chinese drugstores since the 1930s. They reach similar conclusions as have others, that there are two distinct morphs within the sample. Specimens that are morphologically similar, but larger than, extant and subfossil orangutans from Indonesia (see also Wang et al. 2009) and those that are less crenulated with smoother, less complex occlusal surfaces. These latter specimens are said to be similar to Lufengpithecus but on average somewhat larger. Zhao et al. go on to say that there are also specimens within the Lufeng and Yuanmou hypodigms of Lufengpithecus that are similar to the more crenualted specimens collected from Pleistocene sites in southern China and northern Vietnam. They conclude that "In the absence of the skull and postcranial bones, it is difficult to establish new genus or species based on Pleistocene orangutan-like isolated teeth."
Thus, there are a number of possibilities, none of which are, as of yet, conclusive.
1. All the specimens discussed above including the Jianshi molars are variants of one or more species or subspecies of orangutan.
2. The specimens can be divided between a Pleistocene descendant of Lufengpithecus, fossil forms of Pongo or a previously unidentified "mystery ape".
3. Some of the specimens can be allocated to an early form of hominin, the rest to Pongo or some other combination of the above.
Below are some visual comparisons of relevant specimens:
|Tham Hai Cave Upper RM1 or M2 (reversed)|
To the left is an upper right molar of Lufengpithecus hudienensis recovered from the Yuanmou Basin of Yunnan. The Yuanmou sites are dated between 7-8 mya. Note the similarity of the Yuanmou specimen's occlusal outline to the specimen of Homo erectus from Zhoukoudian (ZKD) shown below (specimens are not to scale).
|Occlusal views of UM1s a) Jianshi b) Australopithecus c) ZKD H. erectus d) Sangiran H.erectus e) modern Chinese|
|Right Lower M1 or M2 (TK 65/123), Right Lower M1 or M2 (Jianshi PA 1277), Longgupo Right Lower M1 (not to scale).|
|Original Jianshi lower molars compared to Pongo lower molar from Tham Khuyen Cave Vietnam (center). Note median placement of longitudinal fissure and alignment of transverse fissures in all specimens (not to scale).|
|Original Jianshi lower molars compared to Lufengpithecus hudienensis from Yuanmou Basin, Yunnan and a specimen from Mohui originally described as "hominid" (not to scale).|
Given the ambiguous nature of hominoid dentitions from the Mio-Plio-Pleistocene of East Asia the issues discussed above cannot be resolved until more diagnostic material is recovered.
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