Tackling the ‘teleost gap’

Teleosts are a staggeringly diverse and abundant group, accounting for 99% of the 30,000 living species of actinopterygians. The early evolution of the group, and the assemblage leading to it, is poorly understood, despite a wealth of three-dimensional fossils belonging to a number of taxonomically diverse and anatomically disparate groups (e.g. Arratia 2013, Giles et al. 2016). Re-evaluation of key representatives of these radiations will resolve questions of phylogenetic affinity and character evolution leading to the living teleost radiation. Time-calibrated molecular phylogenies suggest that the living teleost radiation originated around 225 million years ago, but the oldest fossil evidence is nearly 75 million years younger (Near et al. 2012, Giles et al. 2017). Revisiting stratigraphic periods in which teleost fossils are expected but not identified may inform the use of fossils to calibrate nodes in molecular phylogenies, with potential downstream effects for the ‘teleost gap’. Once a robust hypothesis of phylogenetic relationships has been established, macroevolutionary patterns relating to teleost success, including rates of speciation and diversification, hypotheses of dispersal, and selective extinction pressures, may be investigated.

SUPERVISORY TEAM

Dr Sam Giles, Earth Sciences, University of Oxford (samantha.giles@earth.ox.ac.uk) & Dr Zerina Johanson, Natural History Museum, London

METHODOLOGY

This project will use CT scanning to investigate the internal and external anatomy of key taxa leading to the living teleost radiation. These anatomical data will be used to revise our understanding of relationships on the teleost stem. Quantitative methods, including 3D geometric morphometrics and interrogation of database occurrences, will be used to investigate macroevolutionary patterns in the group.

TIMELINE

Year 1: Literature review, training, CT scanning and segmenting, database construction.

Year 2: Comparative anatomy, phylogenetic analysis, database construction.

Year 3: Data analysis, quantitative techniques.

Year 4: Data analysis and synthesis, completing thesis, writing manuscripts (although manuscripts will be written throughout project).

TRAINING & SKILLS

CT scanning & segmentation, comparative anatomy & description, systematics & phylogenetic techniques, database construction, geometric morphometrics, quantitative analysis.

REFERENCES & FURTHER READING

Arratia, G. (2013). Morphology, taxonomy, and phylogeny of Triassic pholidophorid fishes (Actinopterygii, Teleostei). Journal of Vertebrate Paleontology, 33(sup1), 1-138.

Friedman, M. (2015). The early evolution of ray‐finned fishes. Palaeontology, 58(2), 213-228.

Giles, S., Rogers, M., & Friedman, M. (2016). Bony labyrinth morphology in early neopterygian fishes (Actinopterygii: Neopterygii). Journal of Morphology.

Giles, S., Xu, G. H., Near, T. J., & Friedman, M. (2017). Early members of ‘living fossil’lineage imply later origin of modern ray-finned fishes. Nature, 549(7671), 265-268.

Near, T. J., Eytan, R. I., Dornburg, et al. (2012). Resolution of ray-finned fish phylogeny and timing of diversification. Proceedings of the National Academy of Sciences, 109(34), 13698-13703.

Sallan, L. C. (2014). Major issues in the origins of ray‐finned fish (Actinopterygii) biodiversity. Biological Reviews, 89(4), 950-971.