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BRITISH CHALK VERTEBRATES

 

 

Lamna appendiculata;  Booth Museum

 

Chondrichthyes
(Cartilaginous Fish)

     
Introduction    

A very diverse vertebrate fauna is recorded from the British Chalk.  However, the amateur collector is unlikely to ever encounter anything more than fragmentary material.  The spectacular whole and articulated specimens seen in major museum collections were mostly collected over a century ago when working quarries were numerous and hand-worked. 

The scarcity of articulated material reflects the nature of Chalk sedimentation.  Chalk ooze accumulated very slowly so that animal remains on the seafloor were exposed to prolonged scavenging and breakdown prior to burial.  Once finally entrained within the sediment, intense burrowing (bioturbation) further disturbed any potential fossils.  Those exceptional examples of whole and articulated skeletons may represent rapid seafloor burial of live or very recently dead individuals.  This burial would need to have been to a suitable depth to place remains out of the range of bioturbators (and therefore beyond the influence of oxygen).  Exceptionally preserved Chalk vertebrates, therefore, may record instances of mass sediment flow / slumping on the seafloor.  The sedimentary structures which typically record such gravity flows cannot be readily recognised in the chalk because of its homogeneity.  Thus, exceptional preservation in the Chalk may offer a unique proxy for mass sediment flows.  Further, as such sedimentary movements require a slope and a trigger, this may also be a workable proxy for palaeotopography (the relief of the ancient seafloor) and perhaps tectonic activity (modern gravity flows are often triggered by local earth movements). 

Poor locality records for Museum material is an obstacle to research but a broad regional pattern may at least be discernable.  Limited stratigraphic constraint may be overcome by micro- and nannofossil analysis; micro- and nannofossils extracted from the associated matrix can indicate with some accuracy the horizon which a specimen was collected from.