禄丰古猿幼年下颌骨的研究

THE JUVENILE MANDIBLE OF LUFENGPITHECUS

本文记述了１９８０年在云南省禄丰县石灰坝村禄丰古猿地点发现的最晚中新世禄丰古猿（Ｌｕｆｅｎｇｐｉｔｈｅｃｕｓｌｕｆｅｎｇｅｎｓｉｓ）的幼年下颌骨ＰＡ８６９．作者将此标本与西瓦古猿的、南方古猿的和现生大猿的幼年下颌进行了对比，记述了禄丰古猿幼年下颌的若干特征．这些特征表明禄丰古猿幼年下颌体各部主要尺寸的比例关系与本种成年的十分相似．

A hominoid mandible of PA869 was collected from Lufeng. Yunnan Province during theexcavation of wi.nter season in 1980. The greater part of the left mandibular corpus behind thedml and the rami were broken off But the bulk of the right mandibular body was preservedbasically and the symphyscal part was beautifully preserved. All of the deciduous teeth, exceptthe tWo dm2 are kept in situ. And the crown of the embryo of right first molar had developedwell inside the mandibular body, and will emerge soon. The mandible is of about 3-3.5 yearsold, and belongs to a female individual. The distinctive characters of the juvenile mandible ofLnfengpithecus were observed and measured, and compared with Sivapithecus, Australopithecusand the living great apes. The results of these comparisons were as follows.At the frontal surface of the symphyseal region, the superior part is vertical, and the centralpart has the shape of sharp bulge, to be strongly sticking out. At the posterior surface of theSymphyscal region the planum alveolare is steeper, and it intersects the hasal plane of mandiblewith an angle of 65°. The angle is larger than that of the jUvenile mandible of Sivapithecusfrom Pakistan, GSP 11536, of Australopithecus from Kenya, KNM-ER 820 and KNM-ER1477A, and of the living great apes, except the Simia stayrus No.19, with an angle of 65° too.The superior transverse ton is weak.Compared with the length of mandibular corpus, the height of symphyseal region is muchlarger. Its symphyseal highness-length of body index (I100) is 73.5, and the same index of GSP 11536 is 73.3. Both indices are very similar. It indicatedthat all of the mandibular corpora of both infant Miocene hominoids are high and short. Butthe same indices of the juvenile extant great apes (No.389, No.19 and No.246), and that of theinfant Australopithecus (KNM-ER 820 and 1477A) are all small than that of Lufcng infant ape.The Lufeng juvenile jaw has the lateral prominence on the surface of lateral corpus, and thelateral prominence divides into two branches, an upper and a lower one. This feature of theLufeng juvenile is similar to the adult individual. In comparative specimen in this article, onlythe Simia satyrus, No.246 seemingly possess this feature. The whole lateral corpus of the Lufengkvenile mandible is specially high and thin. The thickness-height index of mandibular body ×100) is very small. Index I (at mental foramen) is 33.5, and index Ⅱ (at M1) is60.0; and the GSP 11536, Index Ⅰis 54.7, Index Ⅱ is 74.1. It indicates that the robustness ofthe jUvenile mandibulc body of Sivapithecus from Pakistan is larger than that of Lufcng infantmandible. The Thickness-height index of mandibular body(Ⅱ) of the juvenile Australopithecus,for example, KNM-ER 820 is 94.1, KNM-ER 1477A is 93.1, i.e. the juvenile mandibularrobustness of Australopithecus is largest among the fossil hominoids. There are double mentalforamina on the corpus of the Lufeng juvenile mandble. The vertical situation index of mentalforamen (×100 ) of the Lufeng mandiblehas a mid vaule between that of Australopithecus (KNM-ER 820) / Sivapithecus (GSP 11536)and that of the living great apes (No. 19, 246, 389).The above characters of the juvenile mandible of Lufengpithecus indicate that the proporhonal relations betwccn the lengths, the heights and the thicknesses of the frontal and posteriorparts of the corpora arc very similar to those of the adult mandible of same species.