Lyme Regis Philpot Museum

Dorset, United Kingdom

Lyme Regis Philpot Museum

Dorset, United Kingdom
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Andrew C.,The Fossil Workshop | Howe P.,Lyme Regis Philpot Museum | Paul C.R.C.,Lyme Regis Philpot Museum | Paul C.R.C.,University of Bristol | Donovan S.K.,NCB Naturalis
Proceedings of the Geologists' Association | Year: 2011

Over 40 ammonites, mostly Promicroceras, with epifaunal worm tubes are described from the Lower Jurassic, Charmouth Mudstone Formation (Lias Group) of Dorset. Serpulids that were overgrown by the ammonites or responded to the ammonites' growth attached to juvenile, living ammonites. Some epifaunal serpulids attached post-mortem, indicating oxygenated bottom water, which was rare in the lower Charmouth Mudstone Formation. Other serpulids do not conform to either pre- or post-mortem growth predictions and require individual assessment. The commonest pattern of growth for serpulids on live juvenile ammonites was attachment in the umbilical seam, with later growth onto, and finally around, the venter. Reconstructing this pattern shows that serpulids kept their aperture at 6 o'clock with respect to the orientation of the living ammonite (105-115° behind the ammonite aperture) throughout life. Reorientation of growth lines in serpulid worms just before the aperture suggests some worm tubes were fully grown. The 6 o'clock position of the aperture enabled feeding currents generated by the worms to parallel currents generated by swimming ammonites, thus maximizing food gathering and confirming that ammonites swam backwards. The mid-ventral position enabled the worm to deploy its branchia on both sides of the ammonite. Growth on ammonites was beneficial to the worms, but parasitic to the ammonites. Promicroceras with epifaunal worm tubes died at smaller sizes than unencumbered examples and size at death correlates inversely to extra weight of worm tubes. Uniformitarian comparisons suggest fossil serpulid worms grew in one season and that Promicroceras reached full size in two or three years. © 2010 The Geologists' Association.

Thin, radiating, darker bands occur on pyritic internal moulds of the Early Jurassic ammonites Oxynoticeras and Cheltonia from Bishop's Cleeve, Gloucestershire. They closely resemble true colour patterns preserved in Early Jurassic Calliphylloceras from Kutch, India, and false colour patterns reported in Carboniferous and Triassic ammonoids. Up to five dark bands occur within the body chamber, suggesting that they do not represent serially repeated anatomical structures, but the same feature repeatedly formed during growth. Dark bands are interpreted as traces of black bands deposited on the inside of the shell at the aperture during pauses in growth. The angles between dark bands and between septa correlate strongly in Cheltonia, suggesting that pauses in growth coincided with septal secretion during the chamber formation cycle. There are, however, no other indications that growth was episodic in either genus. © The Palaeontological Association.

Paul C.R.C.,Lyme Regis Philpot Museum
Proceedings of the Yorkshire Geological Society | Year: 2014

Ammonites that preserve evidence of their soft anatomy or gut contents are exceedingly rare. An example of the Toarcian ammonite, Dactylioceras, with tightly packed fish scales in the supposed position of the stomach, plus further scales and three articulated fish vertebrae in the approximate position of the crop, is described. The body-chamber is largely filled with fine sedimentary rock, but shows several thin areas now lined with diagenetic calcite where the sediment was unable to penetrate. These are interpreted as the positions of ammonite soft tissue because they line parts of the body-chamber, which is consistent with the idea that the stomach and crop remained intact long enough for their contents to be preserved in place. Inquilinism is thought unlikely as an explanation because the fish remains are largely disarticulated and packed together in the rear of the body-chamber, but the fish debris could represent food of an animal that sheltered within the dead ammonite shell. Equally, passive fill of the body-chamber with sediment containing fish scales seems unlikely due to the local concentration at the rear of the body-chamber. Possibly this Dactylioceras ate fish either as a predator or scavenger. © 2014 Yorkshire Geological Society.

Andrew C.,Lyme Regis Philpot Museum | Howe P.,Lyme Regis Philpot Museum | Paul C.,Lyme Regis Philpot Museum
Proceedings of the Geologists' Association | Year: 2015

A small polished slab of 'Marston Marble', Lower Jurassic, from Marston Magna, Somerset, UK, contains several ammonite specimens with pieces of shell missing from the body chamber immediately in front of the last suture. The damage is visible in sagittal sections, yet its position and extent are almost identical to damage reported from several Lower Jurassic ammonite genera from the Dorset coast and elsewhere, and attributed to the trace fossil Bicrescomanducator rolli. A second cut, but unpolished slab of 'Marston Marble' shows two more ventrally damaged ammonites, one in sagittal section. The damage is interpreted as the result of predation, by a teuthoid cephalopod and affected two prey species. This is the first time ventral bite marks have been reported from sectioned ammonites.Some ammonites, but not bitten examples, have their body chambers largely filled with diagenetic calcite and were buried with the body inside. Often the calcite does not fill the full width of the body chamber, creating a false geopetal structure. As these are variously orientated with respect to bedding, the ammonites were possibly reworked before final burial. The polished slab derived from a septarian concretion. As the septarian cracks opened some ammonites were pulled apart. During shrinkage the sediment maintained a tight grip on fossils. © 2014 The Geologists' Association.

Andrew C.,Lyme Regis Philpot Museum | Howe P.,Lyme Regis Philpot Museum | Paul C.R.C.,Lyme Regis Philpot Museum | Paul C.R.C.,University of Bristol
Proceedings of the Yorkshire Geological Society | Year: 2012

New, well-preserved examples of the linguliform brachiopod Discinisca holdeni are reported from the Belemnite Marl and Green Ammonite members of the Lower Jurassic Charmouth Mudstone Formation, near Golden Cap, Dorset. Five specimens are attached to ammonites; two are attached to Tragophylloceras numismale and one plus another two possible specimens to Polymorphites evolutus. Three specimens are attached to a rhynchonellid brachiopod Scalpellirhynchia scalpellum? In addition, Discinisca infraoolithica is described attached to the ammonite Dactylioceras cf. athleticum from the Alum Shale Member of the Whitby Mudstone Formation of Yorkshire. An example of D. infraoolithica attached to the bivalve Dacryomya reveals previously unreported fine curved ridges on the pedicle valve. Discinisca spp. probably attached to the ammonite shells post mortem, but might have been attached to the rhynchonellid and bivalve when the latter were alive.

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