The mystery of the velvet worms migrationOnce again a fossil trapped in 105 million year old Burmese

The mystery of the velvet worms migrationOnce again a fossil trapped in 105 million year old Burmese amber has answered a riddle that puzzled ecologists and palaeontologists for decades and provided clear proof for one of the two main contending hypotheses that had been in contention. The question relates to the distribution of organisms worldwide both now and going back through deep time, a discipline known as biogeography. Already back in the early 20th century the distribution of fossils at varying times in geological history was one of the prime pieces of evidence thrown up by Alfred Wegener in his theory of continental drift (now evolved into the current plate tectonic paradigm).He identified amongst others the supercontinent of Gondwana (Africa, Antarctica, India, Australia and South America), that has aeons of separate evolution from Laurussia (from which it separated in the early Jurassic as Pangaea rifted and drifted apart) and a distinctive biome. The Wallace line in Indonesia today is one of its modern remnant expressions, the zone where deep sea cuts Eurasia off from Australia’s Gondwanan fauna. One of biogeography’s main jobs is to trace through the fossil record the radiations of new species, their dispersals and eventual extinctions, tracing the lineages through geological time, sometimes to an extinct dead end, at others to a living relative.The velvet worm provided them with a puzzle. They are odd organisms, not quite an arthropod (the insects), nor quite a tardigrade (see http://bit.ly/2elgovr for more on these fascinating critters). Current versions are a few cm in length and often brightly coloured with sets of legs each carrying a claw that trap animals in their gooey sticky slime in order to eat them. They are only found on land these days, and most species live in ex Gondwanan territory. A few however are found in Africa and Asia, once part of Laurussia, so the question is how did they get there: Did they radiate out from a common Pangaean source a long long time ago or hitch a ride on the Indian Subcontinent, now crashing slowly into Asia.Enter the fossil in the photo, and the answer to the puzzle. Since India collided some 55 million years ago, and the fossil weighs in at over a hundred, the original radiation must have been before the separation of Pangaea. The species is similar to the group of velvet worms still living in South East Asia today, as is the sole Indian species, implying that they might have died out in that part of Gondwana as it drifted northwards alone, and then re invaded southwards after the collision, turning the other contending hypothesis on its head.How’s that for an expression of the living methods of science, squeezed elegantly from one bit of fossil tree sap and an unfortunately trapped creature.LozImage credit: Ivo de Sena Oliveirahttp://bit.ly/2dysmNAOriginal paper, paywall access: http://bit.ly/2dmCPOq -- source link

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