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July 19, 2011

Fin loss in a spiny eel

Posted by John Jackson Jul 19, 2011

Vertebrates - mammals, birds, fish and amphibians - have broadly the same body plan with two pairs of limbs.  However, over time, some species and groups have lost one or both pairs of limbs.  Many others have reduced limbs.  Whales, snakes, caeclian amphibians and a range of fish are some of the examples.


Modern scientific research has a strong interest both in the patterns of development and in how and why these change as a result of genetic evolution - it does appear that different genes can be involved in limb reduction and loss in different groups. 


Drs Ralf Britz and Lukas Rüber (NHM Zoology) and colleagues from University College London and the South African Institute for Aquatic Biodiversity, Grahamstown reported the first case of pectoral fin loss in the Mastacembelidae (Teleostei: Synbranchiformes) with the discovery of a new species of spiny eel from Lake Tanganyika in the Journal of Zoology.


A previous evolutionary phylogeny of mastacembelids using comparisons of genetic differences between different species,  coauthored by Dr Rüber , had placed the new species Mastacembelus apectoralis sp. nov. within the Lake Tanganyikan species flock, having diverged from its sister species M. micropectus around 4.5 million years ago. M. micropectus also shows a reduction in the size of its pectoral fin and endoskeletal girdle, and has largely cartilaginous pectoral radials and a reduced number of pectoral-fin rays. This is in contrast to the bony skeletons of most fish species in this group


The loss of pectoral fins and reduction of associated girdle elements in M. apectoralis represent another independent occurrence of this evolutionary phenomenon within teleosts. The discovery of this species highlights the exceptional diversity of the biodiversity hotspot, Lake Tanganyika, the understanding of which is of critical importance with the pressures of pollution, overfishing and climate change threatening the speciose and evolutionarily significant diversity of this ancient lake.

Brown, K. J., Britz, R., Bills R., Rüber, L. & Day J. J. (2011). Pectoral fin loss in the Mastacembelidae: a new species from Lake Tanganyika. Journal of Zoology April 2011 doi:10.1111/j.1469-7998.2011.00804.x


Palaeontology Department Seminar


Thursday 21st July
Neil Chalmers Seminar Room, DC2, 16:00




Whale skeletons as ecological reefs in the shallow marine Eocene of Egypt .


Dr. Charles Underwood, Department of Earth and Planetary Sciences, Birkbeck College, Univerisity of London


The Late Eocene shallow marine sediments of Wadi Al-Hitan, Egypt are famous for their fossil whales. Many of the whale skeletons are present in shallow marine sandstones that also contain common teeth of sharks and rays. The assemblages of sharks and rays in the sandstones away from the whale skeletons are similar to those that would be expected in shallow marine sandy environments today, dominated by stingrays (Dasyatidae) and Lemon sharks (Negaprion). Teeth collected from amongst whale bones are different, with higher diversity faunas including taxa that are otherwise only common in deeper marine facies. These are sometimes associated with possible chemosymthetic bivalves (Lucinidae). It is therefore likely that the whale skeletons acted as reefs, giving cover to shark and ray species that were otherwise rare or absent in shallow water.