Fossil sea urchins from the Middle Eocene of Barton

the spectacular fossil gastropods and the teeth of sharks – found at the type locality of the Middle Eocene Bartonian in Christchurch Bay (Hampshire and Dorset) – overshadow the other fauna and flora found there. However, among the ‘Cinderella’ groups are the echinoids (sea urchins). Several kinds, both ‘irregular’ and ‘regular’, can be found, some preserved with superb detail.

Fig. 1. Sketch maps to show the location of Barton-on-Sea (modified after Lewis & Donovan, 2008).

The coastal holiday resorts of Christchurch Bay, near the New Forest, include Highcliffe to the west, Milford-on-Sea to the east, and the well-known Barton Cliffs of Barton-on-Sea between the two (Fig. 1). All lie within the Hampshire Basin of southern England. This coastal stretch is famous for its extensive range of well-preserved Eocene fossils found in the sea cliffs and on the foreshore. The most fossiliferous area is sometimes referred to simply as ‘Barton’, and the clays and sands in which the fossils are found as the ‘Barton Beds’.

Of particular interest to fossil collectors, students and holiday-makers alike are the abundant fossil molluscs and the teeth of sharks. However, there are other fossils too, including plants, microfossils, a wide variety of other invertebrates such as bryozoans, brachiopods, corals, crabs, echinoderms (brittle-stars, starfish and sea urchins) and worms, and vertebrates including fishes, reptiles and rare mammals (see Hooker, 1986). Trace fossils can also be seen in the clay sequences. In fact, some of the clays allow considerable fine detail of the fossils to be preserved, including colour banding in gastropods and ‘mother-of-pearl’ in rare nautilus cephalopods.

Ernest St John Burton, a local collector and amateur palaeontologist, recognised various levels within the coastal cliff section and his notation is still used to identify where fossils are found in the cliffs (Burton, 1929). These are A1-A3 (lowest) to L (highest). Burton (1933) also recorded some 400 fossil species throughout the Barton Beds and further taxa have been added to this number ever since. Simplified guide books to the stratigraphy have also been written, including that by Dennis Curry in one of the early series of field guides to specific areas of the country, published by the Geologists’ Association (Curry, 1958). For more detailed information about the area and extensive bibliography, see the splendid online website by West (2010).

Fig. 2. a. Indeterminate cidarid, sometimes referred to ‘Cidaris websteriana’; b. Porosoma? sp. test fragment; and c-h. Porosoma? sp. spines.

Several stretches of the cliffs are protected by blocks of limestone from Purbeck and from the Mendip Hills (see Lewis et al, 2003; Lewis & Donovan, 2008; see also Deposits, Issue 14 Carboniferous fossils protecting our Eocene coastline: Barton on Sea by David Lewis and Stephen Donovan). Strong points at various locations along the cliffs have ensured a build-up of beach material, further protecting the cliffs. Together, these have slowed the erosion of the cliffs by the sea so that new falls of fresh material onto the beach are less frequent than in the past. The increase in the accumulation of beach material has also covered up the clay ledges of the foreshore, which were an easily accessible source of fossils that did not require digging into the cliffs themselves. However, occasional storms do still uncover parts of these ledges, from time to time.

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