Preparing detailed morphological features of fossil brittle stars (Ophiuroidea, Echinodermata) for scanning electron microscopy using a combination of mechanical preparation techniques

Abstract

The comprehensive taxonomic study of fossil brittle stars (Echinodermata: Ophiuroidea) requires the plates of the disk and arms to be cleared of matrix as fully as possible to reveal significant characters, such as spine articulations, ornament and clear plate boundaries. However, this needs to be done delicately, as the plate surfaces and boundaries are fragile and easily obliterated when only using air abrasive techniques. Ophiuroid fossils are frequently over-prepared, which becomes apparent particularly when examined by scanning electron microscopy (SEM), hampering taxonomic studies. Preparation may be further complicated by the entanglement of the arms of multiple individuals. In order to facilitate detailed SEM analysis of recently available, undescribed fossil ophiuroid material from the Aptian, Lower Cretaceous, Atherfield Clay Formation of the Isle of Wight, Hampshire, UK a combination of careful mechanical preparation techniques was employed to great effect. Specimens were initially exposed using standard air abrasive techniques, but the final few millimetres of matrix were removed using pins. To get individual arm pieces exceptionally clear of matrix, they were removed from the blocks using a mini pedestalling technique and then further cleaned using an ultrasonic pen. This combination of techniques fully exposed all the elements required for full taxonomic study without causing severe damage to the plate surfaces and greatly improved the overall aesthetic of the specimens. These techniques could be more widely applied in fossil preparation.