Here, we provide the results of the first osteological study on the subterranean snakehead fish Aenigmachanna obtained from high resolution nano-CT scans. Snakehead fishes have parental care and either primitively guard a nest of floating eggs at the water surface or, as a more derived condition, are mouthbrooders 30. Some species have become highly invasive outside of their native range and two species are now established in the United States 28, 29. They are obligatory air breathers that swallow air into their suprabranchial organ, in which gas exchange takes place allowing them to survive in oxygen-deprived waters and even on land 27. Snakehead fishes are freshwater predators of medium to large size distributed in West and Central Africa and large parts of Asia 26. A total of ten freshwater fish species have been described from this unusual habitat since the mid-1900s: three species of the blind, pigment-less catfish genus Horaglanis 16, 17, 18, the enigmatic catfish Kryptoglanis 19, three highly elongate, whip-like species of the swamp eel genus Monopterus 20, 21, 22, the miniature, dorsal- and pelvic-finless eel loach Pangio bhujia 23 and the recently discovered Gollum snakehead Aenigmachanna gollum 24 as well as its sister species A. Some of the strangest relic lineages among the vertebrates of the Western Ghats are freshwater fishes from subterranean waters in the laterite areas at the foothills along the coast. Especially among vertebrates there are a number of such relic lineages in the Western Ghats, often with unclear phylogenetic relationships, such as the cyprinid Lepidopygopsis 13 and the catfish Kryptoglanis 14, or with remote biogeographical connections, such as the burrowing frog Nasikabatrachus 15. Its high levels of endemism 6, 7, 8 are not only the result of recent radiations 9, but also of the presence of a number of ancient lineages 10, 11, 12. The area where Aenigmachanna was collected is part of the Western Ghats – Sri Lanka Hotspot, one of the most significant global biodiversity hotspots 4, 5, 6. One of the most recent vertebrate examples is the eel Protanguilla palau 3, which combines many primitive morphological characters otherwise only known from Cretaceous fossil eels.Īs we show here, 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. ![]() Widely known examples of ‘living fossils’ or ‘basal taxa’ among vertebrates are the coelacanth Latimeria, the lungfish Neoceratodus, the tuatara Sphenodon or the platypus Ornithorhynchus. 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. Such taxa have previously been characterized with the term ‘living fossil’ starting with Darwin 1 or have been referred to as ‘basal taxa’ 2. 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.Īmong 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. 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. 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. ![]() Our morphological analysis provides evidence for the phylogenetic position of Aenigmachanna as the sister group to Channidae. 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. 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. These ‘living fossils’ hold a prominent role for our understanding of the diversification of the group in question. Pronounced organism-wide morphological stasis in evolution has resulted in taxa with unusually high numbers of primitive characters.
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