West, Ian M. 2013. Fossils of the Portland Group, Upper Jurassic: Geology of the Wessex Coast (including the Dorset and East Devon UNESCO World Heritage Coast - Jurassic Coast. Internet field guide. http://www.southampton.ac.uk/~imw/portfoss.htm. Version: 26th August 2014.
Fossils of the Portland Group, Upper Jurassic

Ian West,
Romsey, Hampshire
Faculty of Natural and Environmental Sciences,
Southampton University,
Webpage hosted by courtesy of iSolutions, Southampton University

|Home and Contents |Portland, Isle of, - General |Portland - Portland Bill |Portland Quarries |Portland - Withies Croft Quarry |Portland - Chesil Beach |Portland - Portland Harbour |Portland - Bibliography |Liassic Fossils |Kimmeridge - Fossils

|..... For more webpages go to: List of Webpages

(You can download this educational site to SurfOffline or similar software to keep an offline copy, but note that updating of the live version takes place periodically. SurfOffline)

A wide-bodied giant ammonite of Titanites type in the Portland Roach, Isle of Portland Dorset

Ammonites of the Portland Group

An ammonite, Titanites sp., from the Shrimp Bed of Blacker's Hole, west of Anvil Point, Swanage, Dorset, collected by Ian West

Titanites shell buried in carbonate sand during the Late Jurassic - reconstruction

The giant ammonite of the Portland Stone is a perisphinctid of the genus Titanites. It is not clear whether this specimen is Titanites anguiformis Wimbledon and Cope, 1978 or Titanites giganteus (Sowerby). By its stratigraphical position it should be the former. The ammonite is not complete; the outer whorl is missing and an indentation marks its former position. The inner whorls are not properly preserved. This particular example, now a garden ornament, comes not from Portland where such giant ammonites are common, but from the Shrimp Bed of the Portland Freestone near Blackers Hole (just east of it on the cliff top) in the Isle of Purbeck; it was found by me in about 1953 (and proved a heavy load on my back cycling back to Bournemouth). Some septal sutures are present.

Giant ammonite, probably Titantites anguiformis Wimbledon from the Portland Freestone at St. Aldhelm's Head Quarry, Isle of Purbeck, Dorset


An ammonites of Titanites genus, fractured on the late Jurassic sea floor, Isle of Portland, Dorset, 5th July 2014


The shells of the ammonites was originally aragonite, lustrous, that like of a modern nautilus shell, and probably coloured. This was lost in solution after burial, probably when the Portland Stone was uplifted above sea-level at the end of the Jurassic or in the early Cretaceous (i.e. Purbeck or Wealden times). A specimen of Titanites above is peculiar in two respects. It does not showing the cavity between the interior fill and the surrounding rock, after the dissolution phase. Of more interest is the fact that this was fractured on the sea-floor, prior to cementation. This feature is common in some other giant ammonites, the Coroniceras bucklandi ammonites in the Lower Jurassic, Blue Lias of Lyme Regis.

Titanites anguiformis is the characteristic giant ammonite of the Portland Freestone Formation. Titanites giganteus, at one time thought to be the common Portland Stone giant ammonite, actually occurs lower down, in the Basal Shell Bed of Portland in equivalent strata (Wimbledon and Cope, 1978).

T. anguiformis has been described by Wimbledon and Cope, (1978) gave a diagnosis as follows:

"Very large, up to 900mm diameter, evolute, round-whorled. Umbilical diameter 48-58 percent. whorl height 19-26 percent, and whorl thickness 21-30 percent of total diameter. At umbilical diameter of 120, 36 ribs; at 140, 34-44; at 170, 38-49; 200, 40-56; 230, 43-56; 260, 44-63; 290, 47-62; 320, 50-65; 350, 52-71; 380, 53-74. Outer whorl with 70 to over 90 ribs, frequent simple ribs with tendency to fading of ribs on body chamber. Growth lines frequently the only ornament towards aperture. Body chamber 340-360 degrees. Holotype - BMC 2956 - from the Roach, top of Portland Stone, Portland (probably from Kingsbarrow Quarry complex)."

Amongst other places, particularly on Portland, Titanites anguiformis has also been found at the base of the Shrimp Bed in Swanworth Quarry, Worth Matravers, Dorset. This is at approximately the same horizon as the specimen shown here.

Wimbledon and Cope, (1978) further commented on this species:

"Very large evolute form with dense strong ribbing. The holotype is 665mm in diameter, has a whorl height of 155mm, whorl thickness of 170mm and an umbilical diameter of 340mm. It has 85 primary ribs on the last whorl... The holotype shows predominantly bifurcatre normal ribs to the brown coloured plain peristome. Paratype C 2927, on the other hand, shows a marked fading of the ribs at maturity with well-developed grown lines... Since this species of Titanites is much more finely-ribbed than other species of this genus, it is readily recognisable in the field. Thus field identification tends to be more reliable than with some other species or genera. Many specimens of the species have been seen in situ, but have proved impossible to extract."

Most of the giant ammonites from the Portland Stone are probably Titanites anguiformis, but do not necessarily assume this. See the paper of Wimbledon and Cope, (1978) and compare any specimen with the coarser-ribbed Titanites giganteus in addition. Large ammonites from the Portland Sands may be Glaucolithites or other genera, and probably not Titanites. Many Portland Stone Titanites can be seen in the fossil garden at the Portland Heights Hotel, on the summit of the Isle of Portland.


Go back to top

Bivalves and Some Other Fossils

The oyster Liostrea expansa, in a patch reef in the Portland Freestone of Inmosthay Quarry, Isle of Portland, Dorset, 29th March 2012

Internal moulds of Plicatula from the Roach of the Portland Freestone, Isle of Portland, Dorset

Some fossil bivalves and a gastropod from the Portland Group, Dorset

Procardia dissimilis, Portland Stone, Portland, Dorset

Perna (Isognomon), Isastraea oblonga and other from the Portland Stone, Upper Jurassic, Dorset

Camptonectes lamellosus bored by small Lithodomi molluscs, waste block of Portland Stone, Godnor Quarry, Freshwater Bay, Portland, Dorset

Natural casts of Lithodomi from a hardground in the Curf, Portland Stone, Grove Quarries, Portland, Dorset, after Damon (1884) A typical example of the Basal Shell Bed, Portland Stone, near Red Door, Portland, Dorset

A grey, argillaceous limestone with abundant bivalves, probably of Lima, at the base of the Basal Portland Shell Bed, near Red Door, Freshwater Bay, Isle of Portland, Dorset, April 2009

Molluscs of the Portland Group, Dorset, after Cox

For more information on Portland bivalves see Cox (1928), A synopsis of the Lamellibranchia and Gastropoda of the Portland Beds of England. Part 1 - Lamellibranchia.

Go back to top

|Home and Contents |

Go back to top

For other fossils see: Liassic Fossils,
Kimmeridge - Fossils.

Go back to top

Copyright © 2014 Ian West, Catherine West, Tonya Loades and Joanna Bentley. All rights reserved. This is a purely academic website and images and text may not be copied for publication or for use on other webpages or for any commercial activity. A reasonable number of images and some text may be used for non-commercial academic purposes, including field trip handouts, lectures, student projects, dissertations etc, providing source is acknowledged.

Disclaimer: Geological fieldwork involves some level of risk, which can be reduced by knowledge, experience and appropriate safety precautions. Persons undertaking field work should assess the risk, as far as possible, in accordance with weather, conditions on the day and the type of persons involved. In providing field guides on the Internet no person is advised here to undertake geological field work in any way that might involve them in unreasonable risk from cliffs, ledges, rocks, sea or other causes. Not all places need be visited and the descriptions and photographs here can be used as an alternative to visiting. Individuals and leaders should take appropriate safety precautions, and in bad conditions be prepared to cancell part or all of the field trip if necessary. Permission should be sought for entry into private land and no damage should take place. Attention should be paid to weather warnings, local warnings and danger signs. No liability for death, injury, damage to, or loss of property in connection with a field trip is accepted by providing these websites of geological information. Discussion of geological and geomorphological features, coast erosion, coastal retreat, storm surges etc are given here for academic and educational purposes only. They are not intended for assessment of risk to property or to life. No liability is accepted if this website is used beyond its academic purposes in attempting to determine measures of risk to life or property.

Go back to top

Dr Ian West, author of these webpages

Webpage - written and produced by:

Ian West, M.Sc. Ph.D. F.G.S.


at his private address, Romsey, Hampshire, kindly supported by Southampton University,and web-hosted by courtesy of iSolutions of Southampton University. The website does not necessarily represent the views of Southampton University. The website is written privately from home in Romsey, unfunded and with no staff other than the author, but generously and freely published by Southampton University. Field trips shown in photographs do not necessarily have any connection with Southampton University and may have been private or have been run by various organisations.