ABSTRACT

Although Neogene crocodylians were well documented from Indo-Pakistan, few fossils were known from Southeast Asia, precluding the understanding of their evolutionary and biogeographic history. Here, we describe crocodylians from the Neogene Irrawaddy Formation of central Myanmar and evaluate their taxonomic status. Tebingan, SE of Magway (lower Upper Miocene) yields Gavialis and Crocodylus that differ from the previously known species of each genus, and the Gwebin area, SW of Bagan (Upper Pliocene) produces Crocodylus cf. palaeindicus. Taking into account the materials without provenance data, Neogene crocodylians from Myanmar include at least three gavialids and two Crocodylus that are characterized by different craniomandibular and postcranial features. The body length estimates for the gavialines from Tebingan and an unknown locality in central Myanmar are 7.5 m and 8.6 m, respectively, which exceed the maximum size limit of extant Gavialis gangeticus. Together with the previously reported large taxa, gavialids repeatedly evolved large body sizes in the Neogene of Asia. Gavialis from the Miocene of Myanmar is one of the oldest records of the genus, and its unraised orbital rim suggests that the “telescoped” eyes derived later during the genus evolution. Crocodylus cf. palaeindicus from the Pliocene of Myanmar indicates the species range was extended from western India to Myanmar during the Neogene. The absence of Crocodylus siamensis in the Neogene of India and central Myanmar implies the species originated east of central Myanmar.

摘要

尽管新近纪的鳄鱼从印度巴基斯坦得到了充分的文献记载，但化石在东南亚却鲜为人知，这排除了对其进化和生物地理历史的了解。在这里，我们描述了来自缅甸中部新近纪伊洛瓦底江群的鳄鱼，并评估了它们的生物分类地位。Tebingan，马圭省（降低上中新统）的SE产生Gavialis和鳄，从各属的先前已知的物种不同，并且Gwebin区域，蒲甘（上新世）的SW产生鳄比照 古生物学。考虑到没有来源数据的材料，来自缅甸的新近代鳄鱼包括至少三个加维亚利德和两个鳄鱼具有不同的颅颌和颅后特征。来自Tebingan和缅甸中部一个不知名地区的加维亚林的体长估计分别为7.5 m和8.6 m，超过了现存的Gavialis gangeticus的最大大小限制。gavialids与先前报道的大型分类单元一起，在亚洲新近生中反复进化出较大的体型。Gavialis从缅甸中新世是属最古老的记录之一，其unraised眶缘表明，“伸缩”眼睛属进化过程中衍生以后。湾鳄cf. 古生物来自缅甸上新世的数据表明，在新近纪期间，物种范围从印度西部扩展到了缅甸。印度新近纪和缅甸中部地区没有暹罗鳄，这说明该物种起源于缅甸中部东部。