New Hominin calvaria discovery from Grenzbank Layer of Sangiran Dome (Java, Indonesia): The last archaic Homo erectus lived in Java

Sangiran Dome in Central Java, Indonesia, is the most significant hominin site in Island Southeast Asia. Up to now, there are more than a hundred of Homo erectus individuals recovered from the site, and the most recent finding is an unpublished posterior part of Bjg 1602 skullcap, discovered by a local people in 2016 from the surface of Kali (River) Bojong, out of stratigraphical context. But, based on the hard concretion well attached on the fossil, consists of coarse conglomeratic sand and pisoid-limestones – defined for the first time by G.H.R. von Koenigswald as the grenzbank layer – this skullcap is interpreted originally from this layer. Stratigraphically, the layer is situated between the black clay of Pucangan Formation of Lower Pleistocene and the fluvio-volcanic sands of Kabuh Formation of Middle Pleistocene. Thus, this layer was deposited on the Sangiran site some 0.9–0.8 ma, which is the minimal age of the skull respectively. This paper aims to identify the possibly position of the specimen and its context to the Homo erectus evolution in Java. The specimen was analysed by applying the morphological and metrical descriptions of the external characters. Then, a comparative study to other African (n = 5), Asian (n = 7), and Javan Homo erectus (n = 23) was conducted by using univariate and bivariate statistical analysis, in order to place the specimen into evolutionary perspective. The result shows that Bjg 1602 skullcap is very closed in morphology and size to the robust Sangiran 4 skullcap (firstly known as Pithecanthropus robustus), which is one of the robust Homo erectus members from the Early Pleistocene between 1.6 to 1.2 ma. Thus, it could be concluded that the specimen of Bjg 1602 represents the last survival of robust Homo erectus in Java during the early of Middle Pleistocene, some 0.9 ma.