One of palaeontology‘s great themes of questioning is the rise of novelty: how new structures and functions arise in specific lineages. In this episode we speak with Neil Shubin, Professor of Organismal Biology at the University of Chicago, who has been studying novelty in the context of the vertebrate transition from water to land.
Neil studies the fossil record of early tetrapods, the first vertebrates with limbs, to understand what changes underpinned this great transition. The other half his lab uses molecular techniques on living organisms to see how changes to the development of appendages (and their underlying genetic architecture) effected the shift from a fin to a limb.
In this interview, we hear about his fieldwork in the Arctic and Antarctic, how palaeontologists decide where to look for key fossils, why development matters, and about his deep involvement in science communication.
Much of Neil’s fieldwork has seen him working at polar latitudes. His most recent fieldwork was in Antarctica. Pictured is Aztec mountain showing exposures of wind-weathered, fossiliferous Devonian rock above the snow layer. He has also worked on the Triassic of Greenland. Here, Neil’s team sits above a 1000-meter drop to the East Greenland Sea , the lunch break vistas accompanied by narwhals and polar bears on the ice below.Neil’s most famous find, Tiktaalik roseae, was in the Devonian rocks of Ellesmere Island, Nunavut, Canada.
The Tiktaalik quarry where Neil, Ted Daeschler and Farish Jenkins first discovered and described the original Tiktaalik specimen. Top Left: Extraction of the holotype of Tiktaalik roseae; Top Right: Skull of the specimen in situ; Bottom Left: The extracted specimen in its plaster jacket; Bottom Right: The prepared specimen.Scientific reconstruction of Tiktaalik roseae. Reconstruction of Tiktaalik roseae. Artwork by Flick Ford using colors and patterns of modern predatory fish living in shallow freshwater ecosystems. Phylogenetic analysis of early tetrapods puts Tiktaalik between the finned, fish like Eusthenopteron– which has no recognizable neck, for example, and Acanthostega, which has four recognizable limbs complete with individual digits. Details of the transition from fin-to-limb . The fins of most ray-finned fish, e.g. a zebrafish, have large amounts of fin webbing and many bones at the base. Lungfish are lobe-finned fishes and have just one bone at their base. Eusthenopteron has bones that compare to our upper arm and forearm and began to fill in the gaps between fin and limb. Acanthostega shares the same pattern of bones as Eusthenopteron but with the addition of fully-formed digits. The forelimb of Tiktaalik, showing a recognizable humerus, radius and ulna- all homologous with bones in tetrapods like dinosaurs or mammals.
A reconstruction of Tiktaalik with inset of front limb bones in life position.
The overall picture is that Tiktaalik sits between ‘fish’ and tetrapod.
UChicago grad student Justin Lemberg’s reconstruction of suction feeding and biting in gars- created by combining video recordings of live animals with specially contrast enhanced CT scans. The feeding mechanics of the gar are suggested as a good analogy for those of Tiktaalik.
Prof. Neil Shubin and a cast of the Tiktaalik holotype at its discovery site on Ellesmere Island, Nunavut, Canada.
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