Abstract
A solid phylogenetic framework is the basis of biological studies, yet higher level relationships are still unresolved in some major vertebrate lineages. One such group is Crocodylia, where the branching pattern of three major families (Alligatoridae, Crocodylidae and Gavialidae) has been disputed over decades due to the uncertain relationship of two slender-snouted lineages, gavialines and tomistomines. Here, we report a bizarre crocodylian from the Bronze Age of China, which shows a mosaic of gavialine and tomistomine features across the skeleton, rendering support to their sister taxon relationship as molecular works have consistently postulated. Gavialine characters of the new Chinese crocodylian include a novel configuration of the pterygoid bulla, a vocal structure known in mature male Indian gharials. Extinct gavialines have repeatedly evolved potentially male-only acoustic apparatus of various shapes, illuminating the deep history of sexual selection on acoustic signalling in a slender-snouted group of crocodylians. Lastly, a cutmark analysis combined with accelerator mass spectrometry (AMS) radiocarbon dating of bone remains demonstrated that two individuals from Shang and Zhou dynasties in Guangdong, China, suffered head injuries and decapitation. Archaeological evidence together with historical accounts suggests the human-induced extinction of this unique crocodylian only a few hundred years ago.
Highlights
Extant crocodylians are large semi-aquatic predators represented by approximately 30 species in the tropics and subtropics [1]
Gavialoidea is a group of slender-snouted crocodylians including the living ecomorphological end-member, the Indian gharial (Gavialis gangeticus), which is characterized by a slender snout and short limbs [10,12]
The debate stems from the different phylogenetic positions of the Indian gharial in molecular and morphological trees—the Indian gharial is the extant sister taxon to the Malayan gharial (Tomistoma schlegelii) in molecular trees [18–22], whereas it is an outgroup to all other extant crocodylians in morphological trees [16,23–26], except few recent ones that are consistent with the molecular tree [17,27]
Summary
Extant crocodylians are large semi-aquatic predators represented by approximately 30 species in the tropics and subtropics [1]. Gavialoidea is a group of slender-snouted crocodylians including the living ecomorphological end-member, the Indian gharial (Gavialis gangeticus), which is characterized by a slender snout and short limbs [10,12] This group is of importance to understand the evolutionary process of snout shape and associated skeletal morphologies [7,13], the clade position and membership, and relationships among clade members are still disputed [14–17]. The new Chinese crocodylian superficially resembles tomistomines, it shows a wealth of gavialine features including a potentially sexually selected vocal structure, reducing the morphological gap between gavialines and tomistomines and providing insights into sexual selection on acoustic signalling in crocodylians It represents one of the most compelling examples of the human-mediated reptile extinction in the late Quaternary. Chop marks left on the skeletons of two Bronze-age specimens together with historical accounts suggest that the human–crocodylian conflict had lasted in southern China from the Bronze Age until a few hundred years ago when this unique species became extinct
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