Seven Rock Point (?) (Jurassic of the United Kingdom)

Also known as Lyme Regis

Where: England, United Kingdom (50.7° N, 2.9° W: paleocoordinates 37.2° N, 3.0° E)

• coordinate estimated from map

• local area-level geographic resolution

When: Arietites bucklandi ammonoid zone, Lias Group, Sinemurian (199.3 - 190.8 Ma)

• "...the nature of the Liassic sediment and its fossil biota enables the provenance of the specimen to be constrained to the Sinemurain stage of probably the Lyme Regis area..."

•"The large size of the ammonites suggests they may belong to the Arietites bucklandi zone of the lowermost Sinemurian. However, the partial remains are not conlusive and further preparation is neccessary for specific identification of the ammonites. Arietitid ammonites are restricted to the Sinemurian, enabling the age of BRSUG 26539 to be constrained to this time period".

• group-level stratigraphic resolution

Environment/lithology: gray, blue limestone

• Chondrites represents dysaerobic to anaerobic consition, whereas the presence of Thalassionoides suggests higher levels of oxygenation (Ekdale & Mason 1988)... the presence of trace fossils and the disarticulated nature of the plesiosaur bones suggests that the palaeoenvironment was of a soft-ground substrate on the continental shelf above the storm-wave base
• BRSUG 26539 is embedded in a 200mm thick bed of blue/grey lower Lias lomestone. This massive limestone lacks lamination and is well cemented. The sediment is highly bioturbated by branched and unbranched burrows of Chondrites, no bigger than 5mm in length and infilled with a light-grey limestone. These trace fossils are uniformly developed throughout the limestone bed, but are locally absent where the sediment has been bioturbated by large Thalassionoides burrows characterised by an increase in the concentration of fossil fragments, including a fish vertebra and tooth. Pentacrinus fragments and shelly debris. These crustacean burrows are coarsely branched structures up to 150 mm in length.

Size class: macrofossils

Collected by Savage in the 1970s

Collection methods: surface (in situ), mechanical, acetic,

• BRSUG, University of Bristol Geology Museum, Bristol, England, United Kingdom

•The specimen was prepared using a combination of acid and mechanical methods. Each block was repeatedly submerged in dilute acetic acid (7.5%) and consolidated with dilute paraloid in acetone between treatments (for further details see Lindsay 1987). Breakages were repaired using a concentrated solution of paraloid in acetone. A hand-held pneumatic engraver was used to remove matrix from localised areas of coarser sediment that proved more resistant to the acid treatment. Wherever possible, acid was used to expose new areas of bone in order to avoid the risk of accidental drill contact.

Primary reference: P. J. Hopley. 2000. A new plesiosauroid specimen from the Sinemurian, Lower Jurassic, of southern England. Proceedings of the Dorset Archaeological and Natural History Society 122:129-138 [R. Benson/R. Benson]more details

Purpose of describing collection: taxonomic analysis

PaleoDB collection 138246: authorized by Roger Benson, entered by Roger Benson on 08.01.2013

Creative Commons license: CC BY (attribution)

Taxonomic list

Show authors, comments, and common names
unclassified
  -
Thalassionoides sp.
Crinoidea
 Isocrinida - Pentacrinitidae
Pentacrinus sp.
Pentacrinus sp. Miller 1821 Sea lily
Pentacrinus fragments
Pisces
  -
"Pisces indet." = Osteichthyes
"Pisces indet." = Osteichthyes Huxley 1880 bony fish
fish vertebrae and a tooth
Reptilia
 Plesiosauria -
aff. Plesiosaurus dolichodeirus
aff. Plesiosaurus dolichodeirus Conybeare 1824 plesiosaur
BRSUG 26539, partial postcranial skeleton
Cephalopoda
 Ammonitida -
"Arietites ? bucklandi" = Ammonites bucklandi
"Arietites ? bucklandi" = Ammonites bucklandi Sowerby 1816 ammonite
arietitid ammonites ranging in size from 100-300 mm
 Ichnofossils -
Chondrites sp.
Chondrites sp. von Sternberg 1833