Biogeographical affinities of Jurassic and Cretaceous continental vertebrate assemblages from SE Asia
Over the last 25 years, rich vertebrate assemblages have been discovered in three distinct formations of the Late Jurassic and Early Cretaceous of Thailand. This work aims to compare the taxonomic assemblages of SE Asia within their palaeogeographical context in Asia. Occurrences of 477 taxa in 94 Regional Faunal Assemblages (RFA) have provided the raw material for producing a dissimilarity matrix based on the Raup & Crick index. These distances have been investigated statistically to infer relationships between the diverse faunal assemblages in space and time. Our results show that the Thai formations are more similar to each other than to any other formations, suggesting a strong provincialism. The relationship of SE Asian RFAs with other Asian RFAs is more influenced by the presence of freshwater or near-shore taxa than by strictly terrestrial ones. Our analysis shows that the faunal interchange between RFAs was rather low from the Late Jurassic to the end of the Early Cretaceous. However, faunal dispersals dramatically decreased during the mid-Early Cretaceous in Asia. The faunas show an overall stronger provincialism during the mid-Early Cretaceous, indicating the role of possible geographical barriers. This event is characterized by the absence of ornithischian dinosaurs in the Sao Khua Formation although they are present in the under- and overlying formations. Taxonomic diversity and exchanges between faunal assemblages recovered rapidly as early as the Aptian in Asia, but the fauna of SE Asia still retained a strong biogeographical signature.