关键词: 元谋古猿; 禄丰古猿; 形态测量; 三维分析; 欧氏距离矩阵分析(EDMA)

Abstract: 1 Introduction
Among the four Miocene hominoid sites of Kaiyuan, Lufeng, Yuanmou and Baoshan in Yunnan Province of China, Lufeng and Yuanmou are the richest fossil sites.Yuanmou hominoid was found in 1986. The exvacation and collection in the past years have accumulated a big fossil collection including cranium, maxilla, mandibles and more than 1000 isolated teeth.In the past decade, some colleagues described the morphology of bone and teeth of Yuanmou hominoid. However, till now, the studies of Yuanmou hominoid fossils are not enough in both depth and breadth.The research methods are also limited. Many key problems concerning with fossil traits, variations, the relationship with other Miocene hominoids, phylogenetic status in evolution and the possible role in early hominid origins are not clear. Although the studies of geological dating and paleoenvironment for Yuanmou site are still in progress, it is usually thought that the living period for Yuanmou hominoid are closer to that of Lufengpithecus, indicating that in both geographical distribution and living time, Yuanmou hominoid and Lufengpithecus are very similar.The studies of fossil specimens also reveal that the morphological patterns of Yuanmou and Lufeng are very close.From this point, the further studies of Yuanmou hominoid fossils will be important in the relationship of fossil morphology and evolution, and for the study of the role of Asian Miocene hominoids in hominoid evolution.In recent years, EDMA(Euclidean Distance Matrix Analysis) has been gradually used to the fossil studies, especially the 2D and 3D studies of dental traits.The present authors also used this method doing 2D morphometric study of Yuanmou lower molars. In present study, 3D morphometric measurements and EDMA statistical analyses will be used to the lower molars of Yuanmou hominoid, Lufengpithecus, extant great ape and humans.
2 Material and methods
72 Yuanmou hominoid teeth with no wear were chosen in present study for landmark measurements. Lufengpithecus specimens include 10 lower molars. 6 of them are kept in the Provincial Institute of Archaeology, and 4 of them are casts housed in the Peabody Museum of Harward University. Other comparative specimens are the lower molars of chimpanzee, gorilla, orangutan and humans housed in Natural History Museum of Smithsonian Institution, Cleveland Museum of Natural History, and Filed Museum of Natural History respectively. Table 1 lists the information of the specimens.
In present study, 13 landmarks were used for 3D measurements.Among them, 11 are located on the occlusal surface which are 5 cusp tips and 6 intercusp fissure termini landmarks used by Ungar (1994)on hominoid lower first molar found in Lukeino of Kenya.The authors designed two cervical landmarks.
meatconid(med)
distal groove(dgrv)
entoconid(en)
buccal distal groove(bdgrv)
hypoconulid(hylid)
buccal mesial groove(bmgrv)
hypoconid(hy)
central
fovea(cefo)
proconid(pr)
lingual cerval(lcer)
anterior fovea(anfo)
buccal cerval(bcer)
lingual groove(lgv)
Metconid, entoconid and protoconis were set as measuring plane(X, Y, Z), and metaconid as origin point.MicroScribe-3D system developed by Immersion Human Interface Corporation was used to measure the 13 landmarks for each tooth.3 measurements were taken for each landmark and averaged. The data were analyzed with EDMA programme(version 1.0)coded by Tim Cole.The significant level is 0.1.
3 Results and discussion
The 3D morphometric comparisons of Yuanmou hominoid with Lufengpithecus, extant great ape and humans can provide the following information:
(1)The similaritiies of lower molars between Yuanmou hominoid and Lufengpithecus
Among the samples studied here, the 3D morphometric traits of Yuanmou and Lufeng resemble mostly each other.Among the 78 distances composed by 13 landmarks, only 5 distances have significant differences between Yuanmou and Lufeng.These differences are mainly located in cusp and fissure landmarks.Among the five significant differences, except metc-lcer distance which is Yuanmou is bigger than Lufeng, all other distances are bigger in Lufeng than Yuanmou.Compared with orangutan and other extant great apes, the lower molars of Yuanmou hominoid and Lufengpithecus have lower crowns.
(2)The lower molar morphologies of both Yuamou and Lufeng are more similar to those of apes than humans
Compared with the lower molars of human and extant great apes, both Yuanmou hominoid and Lufengpithecus show very significant differences with humans and closer to apes.Among the 78 land-mark distances compared, significant differences between both Yuanmou and Lufeng,, and humans are 66 and 46 respectively, while the number of significant differences between Yuanmou and orangutan, chimpanzee and gorillas are 30, 32 and 37 respectively.And the same number of differences for Lufeng are 14, 15 and 25 respectively.Viewing from another point, the differences of both Yuanmou and Lufeng with humans are very similar to those between great apes and humans.The number of land-mark distances with significant differences between the three great ape and humans are 57, 56 and 55, which are quite closer to those number between both Yuanmou and Lufeng, and humans.Among the differences each of Lufeng, orangutan, chimpanzee and gorillas with humans, 89.1% -95.7% of them are identical with those between Yuanmou and humans.Figures 2-figures 4 show that among the five lower molar cusps in human, hypoconid is the highest and the heights of meatconid, entoconid, hypoconulid and proconid are similar.In great apes, hypoconid and hypoconulid are much higher than other cusps.For the 6 intercusp fissure termini landmarks, the depths of anterior fovea, central fovea and lingual groove are similar in great apes, and all of them are significantly deeper than other three landmarks.In human, only anterior fovea and central fovea are deeper than other intercusp fissure termini landmarks with central fovea deeper than anterior fovea.The distances between two cervical landmarks and metaconid is smaller in apes than human indicating the lower crown.The pattern expressions for these traits in Yuanmou and Lufeng lower molars are the same as apes and differ from humans.These results indicate that compared with humans, both Yuanmou hominoid and Lufengpithecus share more dental patterns with extant apes, indicating Yuanmou hominoid, Lufengpithecus and extant great apes keep some primitive features.
(3)The differences between Yuanmou and each of the three great apes are similar
In present study, the analyses of 3D metric data of Yuanmou lower molars and those of the three great apes show that the differences between Yuanmou and each of the three great apes in 3D metric patterns of lower molars are very similar.The number of landmark distances with significant differences between Yuanmou and orangutan, chimpanzee and gorillas are 30, 32 and 37 respectively, which are quite closer.Among them, the fewest significant differences were found between Yuanmou and orangutans indicating there seems be further closer relationship between Yuanmou and orangutans.Among the landmark distances with significant differences between Yuanmou and each of the great apes, 11 distances are common shared.For the remained distances, no one can be served as the evidence to support further closer relationship between Yuanmou and any of the great apes.The similar results were also obtained from the comparisons between Lufengpithecus and the three great apes.The comparisons of each of the three great apes show that the number of landmark distances with significant differences are 32, 42 and 31 respectively, which are closer to those between Yuanmou and the three great apes.All these comparisons offer further support for the opinion of closeness between Yuanmou hominoid and great apes in dental traits.
(4)Compared with Yuanmou, fewer differences found between Lufengpithecus and other samples
We found one interesting phenomenon that is:when comparisons were made between both Yuanmou and Lufeng, and others, the number of landmark distances with significant differences between Lufeng and these samples are fewer than those between Yuanmou and the same samples.According to table 5, the landmark distance number between Yuanmou and orangutan, chimpanzee, gorilla and humans are 30, 32, 37 and 66, while the number for Lufeng with the same comparative samples are 14, 15, 25 and 46 respectively.The specimens of Lufengpithecus used in present study are only 10 may be the main reason for the phenomenon.
The Z values for the EDMA analyses between Yuanmou and all other samples in table 6 show that Z value between Yuanmou and Lufeng is the smallest (0.104), the following is that between Yuanmou and orangutans(0.105).The Z values between Yuanmou and other samples are much bigger than these two which further indicate Yuanmou and Lufeng have closer affinity and both of them have closer relationship with orangutans, and are far different form humans.
In the past years, some description and comparisons of Yuanmou hominoid fossilsindicate that the cranial and dental morphologies of Yuanmou fossils resemble those of Lufeng very much, and have obvious differences with the hominoid fossils found in some other parts of the world.Both Yuanmou and Lufeng crania have broad interorbital distance and broad face.But Yuanmou hominoids also show some different morphological features from Lufengpithecus.These feature include:the area between orbits does not depress.The lower third premolar(P3)only has one cusp.According to these findings, Zheng and Zhang proposed the hominoid fossils found in Yuanmou represent a new species within the genus Lufengpithecus.In present study, the comparisons of 3D morphometric patterns of Yuanmou hominoid lower molars with Lufengpithecus and other samples also indicate that Yuanmou hominoids are most close to Lufengpithecus.Contrary to this, the differences between Yuanmou hominoids and extant great apes and humans are much obvious.Compared with extant ape and humans, both Yuanmou hominoid and Lufengpithecus show very obvious differences from humans while similar to apes.The two kinds of hominoids found in China and extant apes share many morphometric differences with humans. In comparisons with chimpanzee, gorilla and orangutans respectively, the differences between Yuanmou hominoid and the three great apes are basically similar with more resemblance to orangutans.In previous studies of statistical analysis of metric data of Yuanmou hominoid teeth, and 2D EDMA study of the same Yuanmou sample as the present study also revealed the similar results.These findings indicate that the dental morphologies of Yuanmou hominoid and Lufengpithecus are very similar.At present, we are not quite clear the mechanism and evolution significance for these dental similarities.The authors propose that even though the lower molar crown morphometric traits are very similar between Yuanmou hominoid and Lufengpithecus from both 2D and 3D analyses, the exact significance of the similarities are still unclear.Also, there are still some differences in both cranial and dental traits between Yuan-mou and Lufeng fossils.So, some more evidences are needed for us to reliably set the phylogenetic relationship between Yuanmou hominoid and Lufengpithecus.

Key words: Yuanmou hominoid; Lufengpithecus; Morphometrics; 3D analysis; EDMA