Wednesday 30 May 2012

The enigmatic Carboniferous Arthropod Camptophyllia.

The Carboniferous Arthropod Camptophyllia is known from coal measure deposits in northern England. It is always preserved as a dorsal exoskeleton about 25 mm in length, made up of 10 segments, each segment being split into five plates; three apparently dorsal and two apparently lateral. Since its discovery in the 1920s it has been assigned to a number of different Arthropod groups, but none with any degree of confidence.

Line drawing of Camptophyllia. Gill (1924).

In a paper published in the journal Palaeontologica Electronica in April 2012, Russell Garwood of the Manchester X-ray Imaging Facility at the School of Materials at The University of Manchester and Mark Sutton of the Department of Earth Science and Engineering at Imperial College London present the results of a high-resolution X-ray micro-tomography study of Camptophyllia, which attempted to gain a better insight into the structure and affinities of the animal.

Examples of Camptophyllia from museum and private collections. (1) 44 mm specimen from the Tyne Coalfield, Natural History Museum, London. (2) 28 mm specimen from Crawcrook, near
Ryton-On-Tyne, Durham, Natural History Museum, London. (3) Counterpoint to (2), 30 mm. (4) 39 mm specimen from the Tyne Coalfield, Natural History Museum, London. (5) 42 mm specimen from Crock Hey, private collection of Stephen Livesley. (6) 35 mm Specimen from Crock Hey, private collection of Sean Sale. (7) 18 mm specimen from Coseley Colliery, Natural History Museum. (8) 13 mm specimen from Coseley Colliery, Natural History Museum, London. (9) 20 mm specimen from Coseley Colliery, Natural History Museum, London. (10) 20 mm specimen from Coseley Colliery, Natural History Museum, London. Garwood & Sutton (2012).

Garwood and Sutton carried out high-resolution X-ray micro-tomography studies of six specimens from the Natural History Museum in London and from the private collections of Stephen Livesley and Sean Sale. These were not, however able to resolve any features of the underside of Camptophyllia on any specimen. They concluded that this was unlikely to be a coincidence, and that therefore the undersides had not been preserved for a common reason. Arthropods shed their outer shells periodically as they grow, making it possible that the Camptophyllia specimens are in fact shed carapaces. However no known Arthropod sheds its dorsal carapace intact in this fashion without any other part of the exoskeleton, making this scenario unlikely. For this reason Garwood and Sutton favor the alternative possibility, that the dorsal shell of Camptophyllia was significantly mineralized, but that the underside was not; a pattern found in several Arthropod groups. Unfortunately this in no way helps to resolve the problem of Camptophyllia's taxonomic position.

Garwood and Sutton have placed two animations made from high-resolution X-ray micro-tomographs of specimens online. (Animation 1. Animation 2.).

Even thought they were unable to resolve the taxonomic position of Camptophyllia Garwood and Sutton were able to make some deductions from their study. A heavily mineralized dorsal skeleton, combined with soft underparts, is often associated with an ability to roll up into a ball for defensive reasons, something which would seem to be possible from Camptophyllia's bodyplan. None of the preserved specimens show any sign of eyes or similar structures, suggesting that Camptophyllia lived in an environment where vision was not a useful sense. The fossils have previously been identified as coming from shallow lacustrine (lake) environment, which could quite possibly have been murky or cloudy. In addition Camptophyllia has a 'snowshoe' shape, which is often associated with animals that live on soft sediments, and need to avoid sinking in such.

See also An Eocene False Scorpion from Baltic amberTwo new species of True Bug from the Mesozoic of ChinaAn Assassin Bug from the Palaeocene of Spitsbergen IslandA fossil termite from the Late Oligocene of northern Ethiopia and Preserved Trilobite digestive tracts from the Middle Cambrian of Utah.

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