Wessex Formation

Wessex Formation
Stratigraphic range: BerriasianBarremian, 145–125 Ma
The Undercliff - geograph.org.uk - 1378574.jpg
The Undercliff near Shalcombe, Isle of Wight
TypeGeological formation
Unit ofWealden Group
Sub-units
  • North West section - Yellow Sandstone, Pine raft, Hanover Point Sandstone, Rough Sandstone, Shippards Sandstone, Compton Grange Sandstone, Boundary Sandstone.
  • South East section - Sudmoor Point Sandstone, Chilton Chine Sandstone, Brighstone Sandstone, Grange Chine Sandstone, Grange Chine Black band, Ship Ledge Sandstone, Barnes Chine Sandstone, Chine Farm Sandstone, Hypsilophodon Bed
UnderliesVectis Formation
OverliesDurlston Formation
Thicknessup to 1000 m near Swanage
Lithology
Primarymudstone
Othersandstone, ironstone & conglomerate
Location
RegionSouthern England
Country UK
ExtentDorset, Isle of Wight, offshore Wessex Basin

The Wessex Formation is a fossil-rich English geological formation that dates from the Berriasian to Barremian stages (about 145–125 million years ago) of the Early Cretaceous. It forms part of the Wealden Group and underlies the younger Vectis Formation and overlies the Durlston Formation.[1] The dominant lithology of this unit is mudstone with some interbedded sandstones.

Fauna

Invertebrates

Invertebrates are commonly preserved in the Wessex Formation. Freshwater bivalves can be found including unionids such as Margaritifera, Nippononaia, and Unio. These bivalves are helpful in reconstructing what the freshwater paleoenvironment may have been like during the formation's deposition. Specimens of Viviparus, a genus of freshwater snail, have also been found. While compression fossils of insects are found in the overlying Vectis Formation, all insect fossils in the Wessex formation are found as inclusions in amber. Amber can be found present as a rare component in other plant debris beds in the Wessex formation both on the Isle of Wight and the Isle of Purbeck, however the only significant concentration and where all of the inclusions have been found is a lag channel in the L6 plant debris horizon just south-east of Chilton Chine. Only three species from the amber have been formally described, Cretamygale chasei a mygalomorph spider, and Dungeyella gavini[2] and Libanodiamesa simpsoni, both chironomid midges. Most of the other taxa in the table come from mentions in the paper describing the latter. However several images of some of the undescribed taxa have been released from various sources, including multiple chironomids, a therevid dipteran, and dryinid hymenopteran[3]

Color key
Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon
Notes
Uncertain or tentative taxa are in small text; crossed out taxa are discredited.
Invertebrates of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Note Images

Cretamygale

C. chasei[4]

Chilton Chine L6 Plant debris bed Single specimen Mygalomorph spider, has been described from a specimen found in amber. See article
Dungeyella D. gavini[5] Chilton Chine L6 Plant debris bed Multiple specimens a tiny buchonomyiine chironomid See article
Libanodiamesa L. simpsoni[6] Chilton Chine L6 Plant debris bed Single specimen Prodiamesinae chironomid, genus also known from the Lebanese amber
Chironomidae

Indeterminate

Chilton Chine L6 Plant debris bed 44% of all arthropod inclusions Uncertain how many taxa represented, likely at least two. At least one is a tanypodian with a wingspan twice that of Dungeyella.
Therevidae Indeterminate Chilton Chine L6 Plant debris bed At least one specimen At least one specimen figured Wealden Therevid.jpg
Diptera Indeterminate Chilton Chine L6 Plant debris bed Multiple specimens Uncertain how many taxa represented
Dryinidae Indeterminate Chilton Chine L6 Plant debris bed At least one specimen At least one specimen figured, presumably male due to presence of wings Wealden Dryinid.jpg
Hymenoptera

Indeterminate

Chilton Chine L6 Plant debris bed Multiple specimens Uncertain how many taxa represented
Blattodea

Indeterminate

Chilton Chine L6 Plant debris bed Single specimen
Coleoptera

Indeterminate

Chilton Chine L6 Plant debris bed Single specimen
Curculionoidea?

Indeterminate

Represented by a boring in a gymnospermous seed.[7]

Cartilaginous fishes

Cartilaginous fishes of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Note Images

Hybodus

H. basanus

Ergetenodus?

Hybodus fraasi (fossil).jpg

Hybodus

Indeterminate 1

Yaverland bed 38, L9

Indeterminate 2

Yaverland bed 38, L9

Indeterminate 3

Yaverland bed 38, L9

Lonchiodon

L. breve

Yaverland bed 38

L. striatum

Yaverland bed 38, L9

51.43% of total chondrichthyan taxa in L9

Indeterminate 1

Yaverland bed 38, L9

Indeterminate 2

Yaverland bed 38, L9

35.86% of total chondrichthyan taxa in Yaverland bed 38

Indeterminate 3

Yaverland bed 38, L9

Hylaeobatis

H. problematica

Palaeoscyllium

Indeterminate

Parvodus

P. heterodon

Protospinax

Indeterminate

Vectiselachos

V. ornatus

Ray-finned fish

Ray-finned fishes of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Notes Images

Belonostomus

Indeterminate

Caturus

Indeterminate

Caturus NT.jpg

Coelodus

Indeterminate

Coccolepis

Indeterminate

Lepidotes

Indeterminate

Ocloedus

Indeterminate

Pachythrissops

Indeterminate

Pycnodontiformes

Indeterminate

Scheenstia

Indeterminate

Scheenstia maximus.jpg

Lissamphibians

Amphibians of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Notes Images
Wesserpeton[8] W.evansae L2 and Yaverland 38 Albanerpetontid amphibian

Anura[9]

Indeterminate

Multiple 1: Yaverland 38 2: L2 and Yaverland 38 3: L2 and Yaverland 38 4: Yaverland 38 5: Yaverland 38 At least 5 distinct taxa distinguished by characters in their ilium
Urodela Indeterminate Multiple 1: L2, L14 and Yaverland 33 and 38 2: L9 and Yaverland 38 3: unnamed bed in Compton bay and Yaverland 38 At least 3 distinct taxa distinguished by their atlas vertebrae

Squamates

Squamates of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Notes Images
Meyasaurus Indeterminate Yaverland Yaverland bed 38 Teeth and a partial lower jaw Genus also known from Spain
Anguimorpha[9]

indeterminate

Multiple plant debris beds 1st taxon L14 and L2, 2nd L2 and Yaverland bed 38, 3rd Yaverland bed 38 At least 3 distinct taxa represented by isolated teeth, maxilla and lower jaw fragments
Scincomorpha[9]

indeterminate

Multiple plant debris beds 1: L14 and Yaverland 38 2: Yaverland 38, 3: L2 and Yaverland 38 4,5: Yaverland bed 38 6:L2, L14 and Yaverland 38 7,8,9: Yaverland 38 10: L2, L14 and Yaverland 38 At least 10 distinct taxa represented by isolated teeth, maxilla and lower jaw fragments, some of which are paramacellodids based on the common occurrence of osteoderms typical of this clade.

Turtles

Turtles of the Wessex Formation
Genus Species Location Stratigraphic Position Material Notes Images

Helochelydra

H. nopcsai

Shell and skull material

Helochelydra skull.png

Trionyx

Indeterminate

Shell fragments

Housed at the Dinosaur Farm Museum, Isle of Wight

Plesiochelys

Indeterminate

Shell

Housed at the Dinosaur Isle Museum, Isle of Wight

Pleurosternon Indeterminate

Brodiechelys

B. brodiei

Crurotarsans

Crurotarsans of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Notes Images

Anteophthalmosuchus[10]

A. hooleyi

Disputed, either uppermost Wessex or lowermost Vectis

Anteophthalmosuchus.png

A. epikrator[11] Hanover Point Mostly complete skull and partial dentaries and associated postcranial material
Bernissartia Indeterminate 40 Isolated teeth

Bernissartia BW.jpg

Hulkepholis

H. willetti

Koumpiodontosuchus[12]

K. aprosdokiti[12]

Koumpiodontosuchus.jpg

Theriosuchus

Indeterminate

Vectisuchus V. leptognathus Barnes High Just below base of Vectis formation "Partial semi-articulated skeleton"

Plesiosaurs

Plesiosaurs of the Wessex Formation
Genus Species Location Stratigraphic Position Abundance Notes Images

Elasmosauridae[13]

Indeterminate

Compton Bay

Vertebra

Plesiosauroidea[13]

Indeterminate

Tie pits, atherfield

Propodial

Leptocleididae?

Mammals

Mammals of the Wessex Formation
Genus Species Location Stratigraphic Position Material Notes Images

Eobaatar

E.clemensi[14]

Multiple debris beds L9, Yaverland bed 38 and CL3

Teeth

?Gobiconodon Indeterminate Yaverland Yaverland bed 38 Teeth GobiconodonDB15.jpg

Loxaulax

L.valdensis

Teeth

Yaverlestes[15]

Y.gassoni

Multiple debris beds Mandible from Yaverland bed 38, isolated teeth from L2, L9 and L14

Mandible Fragment and isolated teeth

Yaverlestes.png

Dryolestidae[9]

Indeterminate

Multiple debris beds Yaverland bed 38 and L9 Two lower molars, likely belonging to the same taxon, distinct from other dryolestid teeth so likely to be a new genus and species.
Eutriconodonta Indeterminate Yaverland Yaverland bed 38 Lower left molariform

Zatheria[9]

Indeterminate

Premolars

Eutheria?

Pterosaurs

Pterosaurs of the Wessex Formation
Genus Species Location Stratigraphic Position Material Notes Images

Caulkicephalus

C. trimicrodon

Skull and rostrum fragments

An ornithocheirid

Caulkicephalus trimicrodon.jpg

Istiodactylus

I. latidens

Partial skeleton and skull, and referred mandible fragment

An istiodactylid

IstiodactylusDB3.jpg

Istiodactylidae

Indeterminate

Found throughout the sub basin

Teeth

Two other species, distinct from I.latidens

Coloborhynchus

Indeterminate

Rostrum fragment

An ornithocheirid

Coloborhynchus piscator jconway.jpg

Neoazhdarchia

Indeterminate

Humerus

Ctenochasmatidae

Indeterminate

Tooth, potentially a gnathosaurine

Dinosaurs

Ornithischians

Ornithischians reported from the Wessex Formation
Genus Species Synonyms Location Stratigraphic Position Material Notes Images

Hypsilophodon

H. foxii

Hypsilophodon bed Many partial skeletons

Hypsilophodon.jpg

Heterodontosauridae?

Indeterminate

Teeth Closely resemble the cheek teeth of the heterodontosaurid Tianyulong

Iguanodon

I. bernissartensis

Specimens classified as Iguanodon seelyi are referable to this species

Iguanodon new NT.jpg

Mantellisaurus

M. atherfieldensis

Dollodon bampingi, Proplanicoxa?[16]

Mantellisaurus atherfieldensis Steveoc.jpg

Polacanthus

P. foxii

Polacanthoides ponderosus?

Polacanthus foxii.jpg

Polacanthinae

Indeterminate

Distinct from P. foxii.[17]

Valdosaurus

V. canaliculatus

Multiple partial skeletons A dryosaurid

Valdosaurus.png

Sauropods

Sauropods reported from the Wessex Formation
Genus Species Location Stratigraphic Position Material Notes Images

Chondrosteosaurus

C. gigas

"Several cervical vertebrae."[18]

Eucamerotus

E. foxi

"Dorsal vertebra."[18]

Perhaps a somphospondylan?[19]

Iuticosaurus

I. valdensis

"Several caudal vertebrae."[18]

Oplosaurus

O. armatus

"Tooth."[20]

Ornithopsis

O. eucamerotus

"Ischia and pubis.",[18] regarded as an "undiagnostic titanosauriform of uncertain affinities."

O. hulkei

One dorsal vertebra.[21]

Undescribed Sauropod Indeterminate "Partial postcranial skeleton, including presacral vertebrae, anterior caudal vertebrae, girdle and limb elements" Currently in private collection and unavailable to researchers. Known informally as "the Barnes High sauropod" Possibly the same as Eucamerotus
Sauropoda Indeterminate One cervical vertebra and possible associated centrum Represents a large animal 20 metres or greater in length. Known informally as "Angloposeidon". Perhaps a somphospondylan?

Rebbachisauridae

Indeterminate

Scapula, radius and ulna, several cervical sacral and caudal vertebrae and isolated teeth from multiple individuals

Taxon has possible close affinities with Demandasaurus and Nigersaurus

Titanosauria

Indeterminate

Two isolated large middle caudal vertebra, one isolated large cervical vertebra

Theropods

Theropods reported from the Wessex Formation
Genus Species Location Stratigraphic Position Material Notes Images

Avialae

Indeterminate

Isolated teeth

Possibly an Enantiornithe and a Hesperornithid present

Aristosuchus

A. pusillus

"Sacrum and pubes."[22]

A compsognathid

Aristosuchus restoration.jpg

Baryonyx

Indeterminate

Isolated teeth, manus bones, vertebrae and skull material

A spinosaurid possibly synonymous with Suchosaurus cultridens

Baryonyx walkeri restoration.jpg

Calamosaurus

C. foxi

"Vertebrae."[23]

A compsognathid

Calamospondylus

C. oweni

"Vertebrae."[23]

A possible oviraptorosaur

Eotyrannus

E. lengi

"Partial skull and skeleton."[24]

A tyrannosauroid

Neovenator

N. salerii

"Partial skull and skeleton."[25]

A carcharodontosaurian

Neovenator.png

Ornithodesmus

O. cluniculus

A dubious species of dromaeosaurid, once misidentified as a pterosaur

Richardoestesia?

Indeterminate

Teeth

Dubious, uncertain referral on the genus level

Tetanurae Indeterminate Chilton Chine Partial pubes and femur[26] Distinct from Neovenator and Baryonyx. Currently in private collection.

Thecocoelurus

T. daviesi

"Cervical vertebrae."[27]

A theropod of uncertain classification, possibly an ornithomimosaur (this assignment has been questioned by both Mortimer and Naish).[28][29]

Undescribed coelurosaur Indeterminate Partial associated skeleton Apparently small. In private collection and undescribed.

Velociraptorinae

Indeterminate

Isolated teeth

May belong to a proceratosaurid.[30]

Yaverlandia

Y. bitholus

Yaverland Known from a "partial skull roof comprising both frontals and parts of the right postorbital and left orbitosphenoid". A second specimen is known but what elements are represented have not been published as of 2018.

A maniraptoran of uncertain classification, originally identified as an ornithischian.

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