The Charmouth Mudstone Formation is a geological formation in England, dating to the Early Jurassic (Sinemurian–Pliensbachian). It forms part of the lower Lias Group. It is most prominently exposed at its type locality in cliff section between Lyme Regis and Charmouth (alongside the underlying Blue Lias) but onshore it extends northwards to Market Weighton, Yorkshire, and in the subsurface of the East Midlands Shelf and Wessex Basin. The formation is notable for its fossils, including those of ammonites and marine reptiles and rare dinosaur remains. The formation played a prominent role in the history of early paleontology, with its Lyme Regis-Charmouth exposure being frequented by fossil collectors including Mary Anning.
Stratigraphy
Shales With Beef Member The Shales With Beef Member is around 28–30 metres thick in the Lyme Regis-Charmouth region and predominantly consists of thinly bedded medium to dark grey mudstone, blocky calcareous pale-weathering mudstone and brown-grey organic-rich mudstones with frequent bedding parallel veins of fibrous calcite ("beef"), that are usually less than 10 centimetres thick. Several beds of nodular and tabular limestone are also present. It is the lowest unit of the formation and directly overlies the Blue Lias Formation, with the boundary being marked by a prominent bioturbated horizon. Notable persistent marker beds within the member include the laminated calcareous siltstone "Fish Bed", "Table Ledge", which consists of lens beds of limestones with mud content with nests of rhynchonellid brachiopods, the Devonshire Head and the Spittles limestones and the Birchi Nodules (which are septarian concretions) The upper boundary with the Black Ven Marl Member is marked by the prominent laterally persistent limestone Birchi Tabular Bed.
Black Ven Marl Member The Black Ven Marl Member is around 43 metres thick consists of thinly bedded dark mudstones, with several laterally persistent cementstone horizons, notable horizons include the Lower and Upper Cement beds and the Stellare nodules.
Belemnite Marl Member The Belemnite Marl Member is around 20 to 27 metres thick, and consists of interbedded pale and dark grey calcareous mudstone, with numerous belemnites, hence the name. The top of the member is marked by the Belemnite Stone Bed
Green Ammonite Member The Green Ammonite Member is up to 31 metres thick predominantly consists of medium grey mudstones, with 3 limestone horizons, Lower Limestone; Red Band, and Upper Limestone, it is conformably overlain by the Dyrham Formation in some areas, but in the Charmouth area there is an erosive unconformable boundary with the much younger Early Cretaceous (Albian) aged Gault clays.
Paleobiota
Ammonites Ammonites of the Charmouth Mudstone FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagesApoderoceras A. cf. dunrobinense, A. subtriangulareArniocerasA. semicostatumSemicostatum ZoneAsterocerasA. obtusumObtusum zoneCaenisitesCymbitesEchiocerasE. raricostatumRaricostatum ZoneEoderoceras E. bispinigerumGemmellarocerasG. cf. peregrinumBelemnite MarlsOxynoticerasO. williamsiPhricodocerasP. taylori, P. lamellosumBelemnite MarlsPromicrocerasP. planicostaObtusum ZoneRadstockicerasR. complicatumTragophyllocerasT. ibex, T. loscombiGreen Ammonite MemberUptoniaU. bronni Xipheroceras
Sauropterygia Sauropterygia of the Charmouth Mudstone FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagesArchaeonectrusA. rostratusCharmouthArnioceras semicostatum-Echioceras raricostatum ammonoid zoneBMNH 38525 (holotype skeleton)A marine sauropterygian, member of the family RhomaleosauridaeAttenborosaurusA. conybeariBlack Ven Water, Charmouth Northwest corner of Black Ven WaterAsteroceras obtusum, Arnioceras semicostatum-Echioceras raricostatum ammonoid zonesHolotype skeleton (now destroyed) BMNH 40140, partial skeleton and skullA marine sauropterygian, early member of the family Pliosauridae. It was first identified as Plesiosaurus conybeari.PlesiosaurusP. dolichodeirusLyme RegisEchioceras raricostatum ammonoid zoneHolotype (BMNH 22656) Numerous specimens referredA marine sauropterygian, type member of the family Plesiosauroidea inside Plesiosauria.?P. sp.Eastern point of Wear Cliffs, below Golden CapProdactylioceras davoei ammonoid zoneBRSMG Ce17972a-o, articulated juvenile partial postcranial skeletonA juvenile specimen that resembles those assigned to the genus Plesiosaurus.ThaumatodraconT. wiedenrothiBetween Lyme Regis and CharmouthBlack VenNLMH 106.058, "a partial skeleton comprising a complete cranium, mandible, articulated cervical series, and indeterminate fragmentary remains"A rhomaleosaurid
Ichthyosauria Ichthyosauria of the Charmouth Mudstone FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagesIchthyosaurusI. anningaeCharmouthStonebarrow Marls MemberDONMG:1983.98 Subadult specimenAn ichthyosaurid ichthyosaurI. sp.West of Westhay Water, StonebarrowStonebarrow Marls MemberNHMUK R15907, partial skeletonConsidered to belong to I. communis by Bennett et al. 2012, considered indeterminate within Ichthyosaurus by Lomax and Massare 2015LeptonectesL. mooreiSeatown Belemnite Marls MemberBMNH R14370 partial anterior skeleton with most complete skullA leptonectid ichthyosaurL. soleiSeatownAcanthopleuroceras valdani Subzone, Tragophylloceras ibex Zone, lower PliensbachianNMW 91.296.2.2 "a large, isolated and incomplete forefin"TemnodontosaurusT. platyodonXiphodraconX. goldencapensisGolden CapGreen Ammonite Member, Davoei Zone, Maculatum Subzone, lower PliensbachianROM VP52596 "almost complete skull and skeleton, missing one hindfin and the posterior part of the tail"A leptonectid ichthyosaur
Thalattosuchia Thalattosuchia of the Charmouth Mudstone FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagesThalattosuchia Indeterminate Stonebarrow beach, Charmouth Conesby Quarry, Scunthorpe Black Ven Mudstone Member NHMUK PV R 36710, incomplete snout NHMUK PV R 9731, axis and four post-axial cervical vertebrae. Two incomplete axial ribs, the lef fourth cervical rib, and two cervical rib fragments NHMUK PV R 36 711, dorsal vertebra from the caudal end of the dorsal series, and the neural arch of another dorsal vertebra, both held together by matrix Early Thalattosaurian specimens that can't be referred to any concrete genus. Includes a possible early diverging metriorhynchoid TurnersuchusT. hingleyae1 kilometer west of the Charmouth Heritage Coast CentreBelemnite Marl MemberLRM 2021/45, a partial skeleton including cranial material, cervical, dorsal, and caudal vertebrae, ribs, right pectoral girdle, partial limb bones, and an osteodermAn early diverging thalattosuchian.
Pterosauria Pterosauria of the Charmouth Mudstone FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagesDimorphodonD. macronyxCharmouth Lyme RegisBlack Ven Marl MemberTail Fragments Tibia Femur Humerus Phalanax Metacarps Semi-Complete SkeletonsA basal pterosaur and the type member of the family Dimorphodontidae. DimorphodontidaeIndeterminateCharmouth, Black Ven Lyme RegisBlack Ven Marl MemberOUM J.53070 NHMUK PV R1595, wing phalangesA basal dimorphodontid pterosaur. Known as "Charmouth dimorphodontid" it shares resemblance with the genus Dimorphodon. IndeterminateNear Seatown Lower Pliensbachian memberAssociated remains of the rostrum and mandiblesA basal dimorphodontid pterosaur. The relatively deep rostrum and extreme size dimorphism in the dentition show clear similarities to Dimorphodon, also from the Lias of Dorset. The distinctive dentition, in which the first four pairs of rostral teeth and two pairs of mandibular teeth are relatively large and fang-like, while the remaining teeth are remarkably small and short.
Dinosauria Dinosauria of the Charmouth Mudstone FormationGenusSpeciesLocationStratigraphic positionMaterialNotesImagesCoelophysidae"M." lydekkeriLyme Regis Black Ven Marl MemberNHMUK OR 41352, isolated toothIt was identified as Zanclodon(?) sp. b., M. lydekkeri and reassigned as M.(?) lydekkeri. It was found on mostly of recent works to be non diagnostic, probably a coelophysoid. Dornraptor D. normani Lower cliff face, Charmouth Black Ven Marl Member (Likely) NHMUK OR 39496, Partial hind limb GSM 109560, left femurAn Averostran theropod, possible Ceratosaur or Tetanuran. In 2024 was formally described, but referred to the older Blue Lias. A paper non quoted on the description relocated it on the Charmouth mudstone. NeotheropodaIndeterminateNear Lyme Regisobtusum Zone, obtusum subzoneNHMUK PV R36855, Left fibula, ~ 17 cm longPreviously misidentified as a referred specimen of the pterosaur Dimorphodon macronyx. Considered an early branching neotheropod, with a size range similar to Coelophysis bauri, representing an individual of approximately 10 kg.MassopodaIndeterminatelower cliff face, Charmouthobtusum Zone, obtusum subzoneGSM 109561 pedal ungualA sauropodomorph, possibly a member of Massopoda. While it was not associated with BMNH 39496 or GSM 109560 and was not assigned to "Merosaurus" it was classified as coming from an indeterminate theropod. Mortimer found closer resemblance with pedal unguals of basal massopods like Blikanasaurus and Jingshanosaurus.ScelidosaurusS. harrisoniiCharmouth, Black Ven Black Ven landslipBlack Ven Marl MemberNHMUK OR42068. Six osteoderms NHMUK OR42070. Phalanx. NHMUK OR42072. Large bone fragment – indet. NHMUK OR42074. Ulna (paired with NHMOR41323). NHMUK OR43062. Shaft of a large humerus, crushed proximal femur, fibula, fragmentary radius?, other large bone fragments NHMUK OR46011. Probable rib fragment – indet. BRSMG Ce12785. Partial skull and some disarticulated postcranial elements BRSMG Ce12787. Partly eroded femur and vertebra BRSMG Ce12788. cervical osteoderms. BRSMG Ce12789. Vertebra and bone fragments BRSMG Cf2781. nine middle-distal caudal vertebrae and some haemal arches with some organic (kerogenized) remains of the skin preserved. BRSMG LEGL 0004. Articulated skeleton BRSMG LEGL 0005. Articulated partial skeleton DORCM G.7542. Osteoderms DORCM G.10817. Osteoderms CAMSM X39256. Cranial: disarticulated skull and jaw elementsA basal thyreophoran, and the type member of the family Scelidosauridae. One of the best known armored dinosaurs of the lower Jurassic, also the most complete found to date, with specimens preserving even the skin and dermal armour.S. "sp. A"Belemnite Marls at SeatownBelemnite Marl Member, Uptonia jamesoni Zone DORCM G.7842. Three dorsal vertebrae in articulationCf. S. sp.Foot of Black Ven, CharmouthAsteroceras obtusum ammonoid zone, Black Ven Marl MemberNHMUK R6704, juvenile specimen NHMUK R12019. A posterior fragment of the occiput and an articulated series of six cervical vertebrae NHMUK R10103. Indeterminate bone fragments NHMUK OR28333. Two scapulae NHMUK OR32396. Radius NHMUK OR39516. Osteoderms. NHMUK OR39517. Caudal or?sacral vertebra, small distal caudal vertebra, small distal caudal NHMUK OR39518. Haemal arch (chevron). NHMUK OR39519. Two phalanges.
NHMUK OR39520. Ungual phalanx of ?pes.
NHMUK OR39521. Several bone fragments. NHMUK OR40503. Tibia (proximal end). NHMUK OR41322. Femur NHMUK OR41323. Radius NHMUK OR41324. Scapular blade NHMUK OR41325. Humerus NHMUK OR41326. Fibula NHMUK OR41327. Two caudal vertebrae NHMUK OR41328. Three metatarsals NHMUK OR41329. Osteoderm NHMUK OR41330. Ischium
Fish Numerous fish species are known from the Charmouth Mudstone and underlying Blue Lias, from such horizons as the "Fish Bed" of the Shales With Beef Member.