Fossil sea urchins from the Middle Eocene of Barton

the spectacular fossil gastropods and the tooth of sharks – discovered on the sort locality of the Middle Eocene Bartonian in Christchurch Bay (Hampshire and Dorset) – overshadow the opposite fauna and flora discovered there. However, among the many ‘Cinderella’ teams are the echinoids (sea urchins). Several sorts, each ‘irregular’ and ‘common’, may be discovered, some preserved with excellent element.

The coastal vacation resorts of Christchurch Bay, close to the New Forest, embrace Highcliffe to the west, Milford-on-Sea to the east, and the nicely-recognized Barton Cliffs of Barton-on-Sea between the 2 (Fig. B). All lie inside the Hampshire Basin of southern England. This coastal stretch is legendary for its in depth vary of properly-preserved Eocene fossils discovered within the sea cliffs and on the foreshore. The most fossiliferous space is usually referred to easily as ‘Barton’, and the clays and sands through which the fossils are discovered because the ‘Barton Beds’.

Of specific curiosity to fossil collectors, college students and vacation-makers alike are the ample fossil molluscs and the tooth of sharks. However, there are different fossils too, together with crops, microfossils, all kinds of different invertebrates reminiscent of bryozoans, brachiopods, corals, crabs, echinoderms (brittle-stars, starfish and sea urchins) and worms, and vertebrates together with fishes, reptiles and uncommon mammals (see Hooker, 1986). Trace fossils can be seen within the clay sequences. In reality, a few of the clays permit appreciable nice element of the fossils to be preserved, together with color banding in gastropods and ‘mom-of-pearl’ in uncommon nautilus cephalopods.

Ernest St John Burton, an area collector and newbie palaeontologist, recognised numerous ranges inside the coastal cliff part and his notation continues to be used to determine the place fossils are discovered within the cliffs (Burton, 1929). These are A1-A3 (lowest) to L (highest). Burton (1933) additionally recorded some four hundred fossil species all through the Barton Beds and additional taxa have been added to this quantity ever since. Simplified information books to the stratigraphy have additionally been written, together with that by Dennis Curry in one of many early collection of area guides to particular areas of the nation, revealed by the Geologists’ Association (Curry, 1958). For extra detailed details about the world and in depth bibliography, see the luxurious on-line web site by West (2010).

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 additionally Deposits, Issue 14 Carboniferous fossils defending our Eocene shoreline: Barton on Sea by David Lewis and Stephen Donovan). Strong factors at numerous places alongside the cliffs have ensured a construct-up of seashore materials, additional defending the cliffs. Together, these have slowed the erosion of the cliffs by the ocean in order that new falls of recent materials onto the seashore are much less frequent than prior to now. The improve within the accumulation of seashore materials has additionally coated up the clay ledges of the foreshore, which have been an simply accessible supply of fossils that didn’t require digging into the cliffs themselves. However, occasional storms do nonetheless uncover elements of those ledges, once in a while.

Sea urchins (or echinoids) may be discovered within the clays. Commonly, solely parts of shell (‘check’) of the ‘irregular’ Schizaster branderianus and Eupatagus hastingiae are discovered, often from horizons A2-A3 and C, respectively. Uncommonly, in horizon A3, giant accumulations of exams of Schizaster branderianus could be uncovered, typically with their spines preserved kind of intact. More generally, solely fragments of check are discovered, which may be fairly troublesome to see.

‘Regular’ sea urchin checks are principally fragmentary, preserved as a number of ambulacral and interambulacral plates, however bigger parts of check can typically be discovered and are sometimes virtually full (for instance, Echinopedina paucituberculata). None of the recognized common sea urchins are very giant, being barely greater than about 10mm in diameter. Irregular sea urchins may be a lot bigger, with a check size for Eupatagus hastingiae of greater than 45mm (see Lewis, 1989). Irregular sea urchins usually tend to be discovered than common sea urchins and are additionally more likely to be extra full.

Isolated spines can be discovered. These embrace these of the extra strong cidarids and extra fragile ones from irregular sea-urchins (see Morton, 2011).

Preservation of the ocean urchins varies. They might be discovered both as casts of the interior floor and exterior moulds of the check, preserved in clay, or the check materials itself may be preserved. In one instance, a specimen of Eupatagus excentricus (the holotype) has the peristomial buccal plates and periproctal plates preserved.

Some specimens are pyritic and have to be stored dry when saved. The construction and particulars of a few of these exams may be very troublesome to see, however software of some sort of varnish can typically assist, notably when seen beneath a microscope and with suitably adjusted lighting.

Removal of fragile check parts immediately from the clay might be facilitated through the use of a switch course of, both throughout accumulating if there’s time, or within the laboratory or house (Lewis, 1986). When the matrix is washed away, the element on the check may be excellent and specimens are typically even preserved with their spines.
Fragments of check are discovered not solely within the clays themselves, but in addition in shelly, lenticular accumulations, that are composed of varied different fossils. Careful sieving and choosing over the residue is an effective technique of extraction from these sediments. Because sea urchins are very fragile, checks break up simply after dying and simply as simply when being collected. So watch out!

My because of Phil Crabb of the Photographic Studio of the Natural History Museum for the images. I additionally thank Dr SK Donovan for useful feedback.

Sea urchins from the Barton Beds

The following are the presently recognized species of sea urchins from the Barton Beds. More might but be found (see Lewis, 1989 p. S, Morton, 2012):
•‘Regular’ sea urchins:
• indeterminate cidarid (Fig. 2a); initially described as Cidaris websteriana Forbes, 1852 – spines solely; recognized from horizons A3-T. Other
common taxa recognized from spines embrace diadematids;
• Echinopedina paucituberculata Lewis, 1989 (Fig. 3a) – checks, each fragmental and pyritic inner casts; recognized from horizon M;
• Porosoma? sp. (Fig. 2b-h) – spines and check fragments; recognized from horizons A3 and W;
• Coelopleurus sp. (Fig. 3c, d) – check fragments and an incomplete check; recognized from horizon D; and
• Ambipleurus quaylei Lewis, 1989 (Fig. 3b) – incomplete exams and fragments; collected from a shell-drift accumulation in horizon A3.
•‘Irregular’ sea urchins:
• Schizaster (Hypselaster) branderianus (Forbes, 1852) (Fig. A) – casts, moulds, some properly-preserved however incomplete exams; recognized from
horizons A2-A3, although they’ve been reported from different horizons;
• Eupatagus (Eupatagus) excentricus (Gregory, 1891) (Fig. H) – the holotype is an virtually full check with periproctal and peristomial
plates; in all probability from horizon A3;
• Eupatagus (Eupatagus) hastingiae Forbes, 1852 (Fig. S) – almost full however regularly crushed checks, some with radioles; recognized from
horizon E;
• Atelospatangus grandituberculatus (Lewis, 1989) (Fig. S); additionally referred to Maretia grignonensis (Desmarest) by Gregory in 1891, and
Spatangus omalii Galeotti by Forbes in 1852 – nicely-preserved exams and quite a few check fragments; recognized from horizons A2-A3; and
• spines – from common and irregular echinoids; recognized from numerous horizons.

Burton, W. St. C. 1929. The horizons of Bryozoa (Polyzoa) within the Upper Eocene of Hampshire. Quarterly Journal of the Geological Society of London, eighty five, 223-239.
Burton, D. St. C. 1933. Faunal horizons of the Barton Beds in Hampshire. Proceedings of the Geologists’ Association, forty four, 131-167.
Curry, A. 1958. Itinerary IV. The Barton Area in Curry, A. & Wisden, W. 1958 Geologists’ Association Guides No. 14: Geology of the Southampton Area: B-sixteen. Colchester.
Forbes, W. 1852. Monograph of the Echinodermata of the British Tertiaries. Monograph of the Palaeontographical Society, London: v-vii, B-36, pls. B-A.
Gregory, C. W. 1891. A revision of the British fossil Cainozoic Echinoidea. Proceedings of the Geologists’ Association, 12: sixteen-60, pls. M-P.
Hooker, C. C. 1986. Mammals from the Bartonian (center/late Eocene) of the Hampshire Basin, southern England. Bulletin of the British Museum (Natural History) 39 (A): 191-478, pls. M-35.
Lewis, A. I. 1986. A technique for the extraction of fossil echinoids preserved in clay. Tertiary Research, S, one hundred twenty five-127, pl. M.
Lewis, A. I. 1989. Fossil Echinoidea from the Barton Beds (Eocene, Bartonian) of the sort locality at Barton-on-Sea within the Hampshire basin, England. Tertiary Research, eleven, M-forty seven, pls. M-S.
Lewis, A. I. & Donovan, J. N. 2008. Carboniferous fossils defending our Eocene shoreline. Deposits Magazine 14, H-10.
Lewis, A. I., Donovan, R. R. & Sawford, K., 2003. Fossil echinoderms from the Carboniferous Limestone sea defence blocks at Barton-on-Sea, Hampshire, southern England. Proceedings of the Geologists’ Association, 114, 307-317.
Morton, A. 2012. A Collection of Eocene and Oligocene Fossils. Internet website: http://www.dmap.co.uk/fossils.
West, I. 2010. Barton and Highcliffe, Eocene Strata: Geology of the Wessex Coast of southern England. Internet website: http://www.soton.ac.uk/~imw/barton.

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Filed underneath: fossils Tagged: Barton, Barton-on-Sea, Bartonian, Echinoids, Eocene, Fossil Collecting, Fossil Echinoids, fossils, sea urchins
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