If the distinguished reader confesses much familiarity with the history of paleoanthropology, he or she might recognize the name “Trinil.” This site, now thought to date to around 1 Ma, was the type locality for the famous Java Man described by Eugene Dubois as Pithecanthropus erectus in 1894. Fossils of other animals collected by Dubois at Trinil have, perhaps understandably, received less popular attention. However, they include the oldest record of primates from island Southeast Asia, a langur Trachypithecus auratus and macaque Macaca fascicularis. Now, writing in PLOS One, Thomas Ingiccio and colleagues have reanalyzed another specimen of Dubois’s collection from Trinil and report it to represent the earliest evidence of a fossil ape from the whole of Southeast Asia.
Hay is occasionally made of the fragmentary nature of the hominin fossil record (famous remarks about billiard tables come to mind). I’ve always thought that point somewhat overstated, at least in relation to the fossil record of many mammalian groups, and nowhere is that clearer than in comparison with the nigh-nonexistent fossil record for the direct ancestry of most of the other living apes (orangutans being the only exception). So it’s a nice coup for ape paleontology to grab one from such a famous hominin site.
The specimen, Trinil 5703, is a partial left femur assigned by Dubois to the genus Semnopithecus. Currently restricted to the Hanuman langurs, this genus was once used as much more broadly to refer to Asian colobines generally. Semnopithecus sensu stricto do not occur anywhere particularly close to Java today, so this designation was prima facie due for revision. Ingiccio et al. gave the bone a second look by comparing it to a set of similarly sized carnivorans and primates known to occur in the Middle Pleistocene of Java. Visual inspection of the apparent length of the shaft and the proportion and position of the neck established the femur to be that of a primate and not of a carnivoran. The authors then used a set of detailed comparisons and morphometric tests to determine between the possible primate groups. All of the tests, as you can read about in detail in the paper, pointed to affinities with the family of gibbons and siamangs, the Hylobatidae.
Hylobatids are known from Late Miocene (Yuanmopithecus dental material) and Early Pleistocene sites in China, but only from teeth and jaws. Trinil 5703 therefore represents both the earliest member of the group to occur in Southeast Asia and adds an important piece of postcranial anatomy to the gibbon fossil record. It also suggests a relatively closed rainforest environment for Trinil in the Early/Middle Pleistocene when Homo erectus was there in occupation.
It is an irony that Dubois missed on the gibbon affinities of the femur in the first place, as an early gibbon on Java could have bolstered his own belief that humans, including Pithecanthropus, evolved from a gibbon-like ancestor in Southeast Asia. This is what motivated his often-misunderstood statement in the 1930s that Java Man represented a “giant-gibbon.” We can perhaps imagine Homo erectus feeling a similar kinship watching these charismatic little apes in the Pleistocene of Java. At least if they weren’t trying to eat them.
The paper is open access, so feel free to read all about it yourself in PLOS: