Wednesday, 9 January 2013

Mr Leeds’ Blood-Biting Super-Predator: Recognition, After a Hundred Years.


The report of a new ‘super-predator’ – a carnivore well-adapted to feeding on prey as large or even larger than itself – in the fossil record is not particularly rare as a news story.  However, this week’s publication in the Journal of Systematic Palaeontology, revealing the oldest known metriorhynchid (marine crocodile) super-predator, is surprising because it was recovered from the Middle Jurassic Oxford Clay.  Many hundreds of specimens of marine crocodiles are known from this ancient seabed sediment, and they have been recovered from an area of just under 50 square miles around Peterborough on a large-scale basis for almost 150 years, courtesy of collectors like Alfred Nicholson Leeds (1847-1917).  You might think that after so many years of fossil hunters searching through the Oxford Clay as it was exposed by excavators digging the clay for bricks, all the truly large animals from the ecosystem of that Middle Jurassic sea would have been found by now.  And yet in the 21st century it is still possible to find the fossilised remains of previously undiscovered genera – from bony fish over 2m long to crocodiles greater than 3m in length. 

It is worthwhile noting that the type specimen of this newly-described genus and species, excavated by Alfred Leeds between 1907 and 1909, was already regarded by Leeds as being something special, prior to his death in August 1917.  Leeds worked closely with Charles W. Andrews on the material for the lavishly-illustrated A Descriptive Catalogue of the Marine Reptiles of the Oxford Clay. It was published in two volumes - part one in 1910 dealing with the ichthyosaurs and plesiosaurs, and part two in 1913 dealing with the pliosaurs and crocodiles.  Although throughout his career he refused to formally publish or be a co-author, his anatomical opinion was clearly highly respected by Andrews and other scientists that published on Leeds’ collection.  In private correspondence, Leeds gently rebuked Bill Smellie for creating a new plesiosaur taxon Apractocleidus out of one of his specimens, pointing out – long before the true advent of palaeopathology - that in his opinion this was simply an old or diseased individual of the plesiosaur Cryptoclidus.  With the passing of time, Leeds’ opinion was proved correct.

After the first batch of Alfred’s collection was sold to the British Museum (now the Natural History Museum London), Leeds started a catalogue of his specimens, logging date of discovery, pit number and the depth at which they were found in the pit.  He also recorded their fate – whether sold to a museum or to the Bonn dealer St├╝rtz, a regular house-guest in the Leeds family home of Eyebury – and identified the specimens, where possible, down to species level.  As someone who had handled so many thousands of marine reptile bones, he was intimately familiar with their variations and could confidently attribute them to a given species – his understanding of anatomy perhaps reflecting his unfulfilled desire to study to become a medical doctor. 

The 670 mm long right lower jaw of the holotype of Tyrannoneustes lythrodectikos. Photograph courtesy of Mark Young
Leeds specimen 146 - registered as GLAHM V972, the metriorhynchid that forms the type specimen of this week’s new genus Tyrannoneustes lythrodectikos or ‘blood-biting tyrant swimmer’ – is a real oddity within his catalogue.  Although having a series of vertebrae, rib fragments and isolated teeth, the main component of this specimen is a prodigious right mandible, 670 mm long, yet still incomplete (see above).  Whereas Alfred Leeds throughout his handwritten catalogue confidently assigns specimens to particular species, and is also satisfied to leave an entry identified only to the level of ‘Metriorhynchus sp.’ where he feels it is not diagnostic beyond genus level, 146 has the unique record of ‘Metriorhynchus ?species’.  This type of annotation is distinct, occurring nowhere else in his catalogue.  In this regard, it looks very much as though he recognised that this fossil was different, but could not assign it to any of the known species. 

The journey that was begun around a hundred years ago by Alfred flagging up this specimen as not fitting within the recognised species of Metriorhynchus is completed with this week’s publication of the full description of the fossil as a new taxon in the Journal of Systematic Palaeontology.  In that spirit, we as authors recognised his contribution, and his first priority as a worker that correctly identified this animal as a taxonomic anomaly, by giving him a co-authorship when this paper was first submitted to the journal.  The reviewers – in my opinion, quite wrongly – disagreed with this, and insisted that we removed his name from the authorship.  The inclusion of posthumous authors on scientific works that have entirely separately been picked up and finished by other workers is far from without precedent, and it is a shame that the journal has not seen fit to let Alfred Leeds receive some small recognition for the huge contribution that he as a collector made to the science of vertebrate palaeontology.  Again, it is worth noting that this would not have been the traditional authorship recognition of a collector, whereby a collector is simply rewarded for discovery of a specimen through being included as an author on the scientific description: this would have been acknowledging his anatomical expertise, and his recognition of a new taxon.

Andrews’ second volume of A Descriptive Catalogue of the Marine Reptiles of the Oxford Clay came out in 1913, and amongst the crocodiles therein was his suite of new Metriorhynchus species based on Alfred Leeds’ specimens.  For decades afterwards he was recognised as the authority on these animals, the first serious revision only being undertaken  by Susan Adams-Tresman in the mid 1980s.  This week’s publication serves as a fitting opportunity to belatedly and publicly recognise that, even in the time of Charles Andrews, there was perhaps one man that knew and understood the variety of different marine crocodiles present in the Oxford Clay, better than he.

Guest post by Jeff Liston, Co-Author, Yunnan Key Laboratory for Palaeobiology, Yunnan University, Kunming, Yunnan Province, People’s Republic of China.