Aenigmachannidae, a new family of snakehead fishes (Teleostei: Channoidei) from subterranean waters of South India

Ralf Britz,V K Anoop,Lukas Rüber,Brett Clark,Siby Philip,Neelesh Dahanukar,Rajeev Raghavan

doi:10.1038/s41598-020-73129-6

Abstract

Pronounced organism-wide morphological stasis in evolution has resulted in taxa with unusually high numbers of primitive characters. These ‘living fossils’ hold a prominent role for our understanding of the diversification of the group in question. Here we provide the first detailed osteological analysis of Aenigmachanna gollum based on high-resolution nano-CT scans and one cleared and stained specimen of this recently described snakehead fish from subterranean waters of Kerala in South India. In addition to a number of derived and unique features, Aenigmachanna has several characters that exhibit putatively primitive conditions not encountered in the family Channidae. Our morphological analysis provides evidence for the phylogenetic position of Aenigmachanna as the sister group to Channidae. Molecular analyses further emphasize the uniqueness of Aenigmachanna and indicate that it is a separate lineage of snakeheads, estimated to have split from its sister group at least 34 or 109 million years ago depending on the fossil calibration employed. This may indicate that Aenigmachanna is a Gondwanan lineage, which has survived break-up of the supercontinent, with India separating from Africa at around 120 mya. The surprising morphological disparity of Aenigmachanna from members of the Channidae lead us to erect a new family of snakehead fishes, Aenigmachannidae, sister group to Channidae, to accommodate these unique snakehead fishes.

Highlights

Pronounced organism-wide morphological stasis in evolution has resulted in taxa with unusually high numbers of primitive characters
Among the seemingly endless diversity of animal life on our planet, a few extant species hold a unique position for our understanding of the evolution of the group to which they belong. Such taxa have previously been characterized with the term ‘living fossil’ starting with D arwin[1] or have been referred to as ‘basal taxa’[2]. They exhibit a striking level of morphological stasis as evidenced by a surprisingly large number of primitive characters compared to their extant sister group, and often represent lineages with only few extant representatives and a restricted distribution
Aenigmachanna gollum from subterranean waters in the Western Ghats area of Peninsular India is another recent discovery that fits the characterisation of ‘basal taxon’[2]