El Mers Group

The El Mers Group is a geological group in the Middle Atlas of Morocco. It is subdivided into three formations named the El Mers I, II, and III Formations, respectively. It is a marine deposit primarily consisting of marl, with gypsum present in the upper part of unit 3. It is the lateral equivalent of the terrestrial Guettioua Sandstone. Dinosaur remains are among the fossils that have been recovered from the group, most notably those of sauropods and the unusual thyreophorans Adratiklit, Thyreosaurus, and Spicomellus. This formation records a series of coastal to shallow marine settings of Middle Jurassic (with an age of Bajocian-Bathonian for El Mers 1 and a Bathonian-Callovian? for El Mers II-III), based on detailed stratigraphical biomarkers such as ammonites or Foranimifera.^[1]

El Mers Group
Stratigraphic range: Bajocian-Callovian ~168–161 Ma PreꞒ Ꞓ O S D C P T J K Pg N
El Mers I Formation at Thaghzout river canyon El Mers II along the El Mers river El Mers II along the El Mers river El Mers III Dinosaur Bearing beds
Type	Group
Sub-units	El Mers Formations 1–3
Underlies	Unconformity with Barremian or Plio-Pleistocene sediments
Overlies	Ich Timellaline–Bou Akrabene Formation
Thickness	Over 500 m (1,600 ft)
Lithology
Primary	Marl, gypsum (only in unit 3)
Other	Sandstone, limestone
Location
Coordinates	33.5°N 4.3°W / 33.5; -4.3
Approximate paleocoordinates	28.3°N 2.0°W / 28.3; -2.0
Region	Boulemane and Azilal Provinces
Country	Morocco
Extent	Middle Atlas
El Mers Group (Morocco)

Paleoenvironment

A Modern analogue for El Mers Group is found in the coastal sequences of Coorong, South Australia.

The El Mers formations are composed primarily of marls with intermittent layers of limestone and sandstone, characterized by abundant organic matter and benthic fauna.^[2] It is delineated into five distinct members, each exhibiting diverse lithological characteristics. The three members comprise a combination of layers of marls, sandstones, and limestones, marked by various unique fossils and organic materials. Sedimentary discontinuities reveal deltaic sequences that exhibit varying sedimentary structures and lithological compositions, reflecting dynamic depositional environments ranging from subtidal to continental. The facies associations within the El Mers Group are organized into elementary and mesosequences, delineating the transition from prodelta to deltaic plain environments. These sequences capture the evolution of tidal regimes and depositional dynamics.^[3][4]

During the Bajocian-Bathonian transition the local faices paint a picture of a dynamic paleoenvironment, where the interplay between land and sea was pronounced.^[1] This setting oscillated between a proximal continental shelf, marked by significant terrestrial input, and episodic marine incursions that suggest fluctuating sea levels.^[1] The lower parts of the section hint at shallow, sometimes oxygen-deprived, stagnant waters, much like modern lagoon or restricted bays where circulation is limited. Upwards there are signs of marine influence growing stronger, particularly at the base of "Interval C", where a notable sea-level rise seems to have occurred, akin to what we might see on today's outer continental shelves, like those in the North Sea, where marine life diversity peaks, specially Bivalves and Ammonites. However, this marine dominance is not consistent, reverting back to a more coastal, land-influenced environment towards the top, similar to modern deltaic regions where riverine and marine waters mix, such as the Louisiana coast or the Coorong National Park. The environment would have experienced variable salinity, much like estuaries where fresh and marine waters blend, affecting the types of biota that could thrive.^[1]

The shifts in facies and microfauna evolution in the area revelated intriguing patterns, from the establishment of initial supratidal environments characterized by charophytic marls and ostracod limestones followed by a resurgence of marine conditions, evident from the reappearance of coastal facies and the diversification of ostracod faunas, indicating a significant transgressive phase during the Upper Bathonian–Lower Callovian period. While in the Central High Atlas marine influences ceased by the Upper Bajocian–Lower Bathonian giving way to continental red layers, in the Middle Atlas marine influences persisted until the Upper Bathonian–Lower Callovian boundary, indicating a diachronic filling of the Atlas gulfs towards the Tethyan domain from west to east.^[5]

Fossils

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.

Foraminifera

Genus	Species	Stratigraphic position	Material	Notes	Images
Bullopora[5]	B. tuberculata	SW part of the Skoura syncline	Tests/Shells	A benthic foraminiferan of the family Polymorphinidae
Pfenderella[5]	P. cf. arabica	SW part of the Skoura syncline	Tests/Shells	A benthic foraminiferan of the family Pfenderininae
Praekurnubia[5]	P. crusei	SW part of the Skoura syncline	Tests/Shells	A benthic foraminiferan of the family Pfenderinidae; a genus found in the Tethys between Bajocian and Oxfordian-aged layers
Pseudocyclammina[5]	P. maynci	SW part of the Skoura syncline	Tests/Shells	A benthic foraminiferan of the family Hauraniidae

Dinoflajellates

Genus	Species	Stratigraphic position	Material	Notes	Images
Aldorfia[1]	A. aldorfensis	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Cribroperidinium[1]	C. crispum C. venustum	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Ctenidodinium[1]	C. combazii C. continuum C. cornigerum	FD section, Skoura Syncline	Cysts	A Dinoflajellate, incertae sedis
Dichadogonyaulax[1]	D. sellwoodii	FD section, Skoura Syncline	Cysts	A Dinoflajellate, incertae sedis
Korystocysta[1]	K. gochtii K. pachyderma	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Meiourogonyaulax[1]	M. caytonensis M. reticulata M. valensii	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Nannoceratopsis[1]	N. deflandrei	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Nannoceratopsiaceae
Pareodinia[1]	P. ceratophora	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Pareodiniaceae
Rhynchodiniopsis[1]	R. cladophora	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Trichodinium[1]	T. scarburghense	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Tubotuberella[1]	T. dangeardii	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Wanaea[1]	W. acollaris W. indotata W. verrucosa	FD section, Skoura Syncline	Cysts	A Dinoflajellate of the family Gonyaulacaceae
Willeidinum[1]	W. spp.	FD section, Skoura Syncline	Cysts	A Dinoflajellate, incertae sedis

Brachiopoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Formosarhynchia[4]	F. (Rhynchonella?) dumortieri	El Mers	Isolated shells	A branchipod of the family Rhynchonellidae	Example of specimen of the genus (from Spain)

Ostracoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Cytherella[5]	C. index	Ait Hammou	Valves	A freshwater/brackish ostracod of the family Cytherellidae
Fastigatocythere[5]	F. aff. brentonensis	Ait Hammou	Valves	A freshwater/brackish ostracod of the family Progonocytheridae
Kinkelinella[5]	K. aff. triangula	Ait Hammou	Valves	A freshwater ostracod of the family Progonocytheridae
Metacypris[5]	M. spp.	Ait Hammou	Valves	A freshwater ostracod of the family Limnocytheridae. Local members of the genus genus would not be confined to limnic environments, but would be euryhaline or brackish, since they disappear when faunal diversity is at its maximum.
Procytheridea[5]	P. ihopyensis	Ait Hammou	Valves	A freshwater ostracod of the family Schulerideidae

Xiphosura

Genus	Species	Stratigraphic position	Material	Notes	Images
Selenichnites[6]	S. tesiltus S. isp.	Skoura Syncline Taferdouste	Isolated crescent-shaped trace fossils	Traces of xiphosurans, representing the second occurrence of this ichnogenus in Morocco	Extant Horseshoe crab (in New York state)

Mollusca

Genus	Species	Stratigraphic position	Material	Notes	Images
Cadomites[5]	C. bremeri C. cf. bremeri	East Skoura syncline	Isolated shells	An ammonite of the family Stephanoceratidae and indicator of the Bathonian age	Example of specimens (from France)
Cercomya[4]	C. undulata	El Mers	Isolated shells	A marine clam of the family Laternulidae
Choffatia[7]	C. cf. urinacensis	East Skoura syncline	Isolated shells	An ammonite of the family Perisphinctidae and indicator of the Callovian age
Corbula[4]	C. pectinata	Aït Kermouss	Isolated shells	A marine clam of the family Corbulidae
Clydoniceras[7][8]	C. discus	Tamguert n'Tarit Tizi n'Juillerh	Isolated shells	An ammonite of the family Clydoniceratidae
Eomiodon[4]	E. angulatus	El Mers	Isolated Shells	A marine clam of the family Neomiodontidae
Isognomon[4]	I. (Mythiloperna) murchisoni	El Mers	Isolated shells	A marine oyster of the family Malleidae	Example of extant member of the genus (from Cape Verde)
Lima[4]	L. (Plagiostoma) subcardiformis	Aït Kermouss	Isolated shells	A marine file clam of the family Limidae	Example of extant member of the genus (from Puerto Rico)
Lopha[4]	L. costata	Aït Kermouss	Isolated shells	A marine oyster of the family Ostreidae	Example of extant member of the genus (from Micronesia)
Modiolus[4][8]	M. imbricatus M. cf. bipartitus	Aït Kermouss El Mers Tamguert n'Tarit	Isolated shells	A marine mussel of the family Mytilidae	Example of extant member of the genus (from Norway)
Morphoceras[7]	M. macrescens	East Skoura syncline	Isolated shells	An ammonite of the family Morphoceratidae and indicator of the Bathonian age
Mytilus[4]	M. (Falcimytilus) tumidus	Aït Kermouss	Isolated shells	A marine mussel of the family Mytilidae	Example of extant member of the genus (from an unknown location)
Nucula[4]	N. (Paleonucula) waltoni	El Mers	Isolated shells	A marine nut clam of the family Nuculanidae	Example of extant member of the genus (from Massachusetts)
Oraniceras[7]	O. sp.	East Skoura syncline	Isolated shells	An ammonite of the family Parkinsoniidae and indicator of the Bathonian age
Orionoides[4]	O. cf. pseudorion	East Skoura syncline	Isolated shells	An ammonite of the family Perisphinctidae
Ostrea[4][7][8]	O. sandalina O. (Liostrea) hebridica	Aït Kermouss El Mers Tamguert n'Tarit	Isolated shells	A marine oyster of the family Ostreidae	Example of extant member of the genus (from an unknown location)
Paracenoceras[4]	P. sp.	Aït Kermouss	Isolated shells	A Nautilidan of the family Paracenoceratidae	Example of specimen (from an unknown location)
Parkinsonia[5]	P. sp.	Skoura syncline	Isolated shells	An ammonite of the family Parkinsoniidae and indicator of the Bajocian age for the lower portions of the Group	Example of specimen (from England)
Protocardia[7][8]	P. tikechkachensis	El Mers Tamguert n'Tarit	Isolated shells	A marine cockle of the family Cardiidae

Echinoderms

Genus	Species	Stratigraphic position	Material	Notes	Images
Acrosalenia[4]	A. spinosa	El Mers Ich Timellaline	Isolated Individuals	An Echinoidean of the family Acrosaleniidae
Hemicidaris[4]	H. jauberti H. cf. icaunensis	Ich Timellaline	Isolated Individuals	An Echinoidean of the family Hemicidaridae	Example of specimen of the genus (from Switzerland)

Fishes

Genus	Species	Stratigraphic position	Material	Notes	Images
Lepidotes[9]	L. spp.	Ait Hammou Djmila Oued El Mers Tizi n'Juillerh	Cranial material, isolated teeth and scales	A marine/brackish bony fish of the family Lepidotidae	Example of specimen of the genus (from an unknown location)
Scheenstia[9]	S. cf. mantelli	Oued El Mers	Partial specimen wirth cranial material	A marine/brackish bony fish of the family Lepidotidae	Reconstruction

Testudinata

Genus	Species	Stratigraphic position	Material	Notes	Images
Testudinata[7][8]	Indeterminate	Tamguert n'Tarit Tizi n'Juillerh	Very numerous debris: escutcheons, plates, vertebrae, ribs, long bones	Turtle remains of uncertain affinity

Crocodylomorpha

Genus	Species	Stratigraphic position	Material	Notes	Images
Hatcherichnus[10]	H. ispp.	Inzar O'Founass	Footprints	Indeterminate Crocodrylomorph Tracks
"Megalosaurus"[7][8]	"M." mersensis	Botane Tizi n'Juillerh	Isolated teeth and vertebra	A marine crocodylomorph of the family Teleosauridae. Mistaken as Theropod remains in the past.[11]
Steneosaurus?[7]	S.? spp.	Bou Iferaoun Botane Darak Djmila Oued Tamemecht Tamguert r'Tane Tirardine Tissenfelt	Isolated teeth, cranial and postcranial material, both isolated and semi-articulated	A marine crocodylomorph of the family Teleosauridae. The referral to the genus Steneosaurus should be taken with caution, as this genus was overlumped.

Dinosauria

Theropoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Carmelopodus[10]	cf.C. isp.	Tassmante O'Moche	Footprints	Theropod tracks of uncertain affinity, suggested to come from Ceratosauria members
Grallator?[10]	G.? isp.	Ifri N'Tfrane	Footprints	Theropod Tracks, referred usually to small-medium sized Genera
Hispanosauropus?[10]	H.? isp.	Ifri N'Tfrane	Footprints	Theropod tracks of uncertain affinity, different from Megalosauripus in the larger metatarsophalangeal region
Megalosauripus[12][10]	M. ispp. cf.M. ispp.	El Mers Tasra Tasra Westbank Tassmante O'Moche Oued Tamghilt	Footprints	Traces of theropods; members of the ichnofiber family Eubrontidae, incertae sedis within Theropoda
Averostra[7][12]	Indeterminate	Oued Botane	Isolated Teeth	Isolated teeth of unidentified or undescribed/studied theropods. Teeth associated with the Teleosaur "Megalosaurus" mersensis have recently been suggesting to come from indeterminate Averostrans. Other remains need revision.[13][14]
Theropodipedia[10][15][12]	Indeterminate	El Mers Inzar O'Founass Ifri N'Tfrane Laach O'Medda Oulad Ali Tasra Tasra Westbank Tassmante O'Moche	Footprints	Theropod tracks of uncertain affinity, suggested to come from "allosaurs or megalosaurs"[15]

Sauropoda

Genus	Species	Stratigraphic position	Material	Notes	Images
Breviparopus[12][10]	B. isp.	El Mers Oued Tamghilt	Footprints	Traces of sauropods typical of the ichnofamily Parabrontopodidae, incertae sedis within Sauropodomorpha. Includes traces with pes similar to Diplodocoidea.[12]
Cetiosaurus[7][16]	"C." mogrebiensis	Aîn ou N'Jourh Taghrout Tamguert r'Tane Tamguert n'Tarit Tich Niouine Oued Botane	Complete skeleton and referred co-types of partially complete and incomplete specimens	A eusauropod of the family Cetiosauridae, currently awaiting revision and likely not a member of the genus Cetiosaurus[17]
Sauropoda[18][19]	Indeterminate	Aït Tamjout Boulahfa 1 km east of Taguelft	Isolated and articulated bones	Indeterminate or undescribed sauropod remains
Sauropodina[10][15][20]	Indeterminate	El Mers Tasra Tasra Westbank Oulad Ali	Footprints	Sauropod tracks of uncertain affinity. There are both small and enormous sauropod tracks, including some among the largest known worldwide, with a pes track length of up to 130 cm.[10]

Ornithischia

Genus	Species	Stratigraphic position	Material	Notes	Images
Adratiklit[21]	A. boulahfa	Boulahfa	NHMUK PV R37366 (A dorsal vertebra), three cervical vertebrae (NHMUK PV R37367; R37368), a dorsal vertebra (NHMUK PV R37365), and a left humerus (NHMUK PV R37007)	A dacentrurine stegosaur
Cerapoda[22]	Indeterminate	Boulahfa	USMBA 001, a partial left femur	The oldest known cerapodan dinosaur
Ornithopodichnus?[10]	O.? ispp.	Ifri N'Tfrane	Footprints	Ornithichian tracks, referred to short-toed forms such as Gilmoreosaurus
Spicomellus[23]	S. afer	Boulahfa	NHMUK PV R37412, a partial rib bearing four co-ossified spines	An early ankylosaurian
Thyreosaurus[24]	T. atlasicus	Boulahfa North	HIIUC-BN00, a partial postcranial skeleton that includes nine dorsal vertebrae and 21 dorsal rib remains, a limb bone (fibula?), and six dermal elements	A dacentrurine stegosaur with unusual recumbent osteoderms

Dasycladales

Genus	Species	Stratigraphic position	Material	Notes	Images
Heteroporella[5]	H. lusitanica	SW part of the Skoura syncline	Calcareous imprints	A dasycladacean algae of the family Dasycladaceae
Sarfiatella[5]	S. dubari	SW part of the Skoura syncline	Calcareous imprints	A dasycladacean algae, associated in adjacent regions with Aalenian–Bajocian faunas

Charophyta

Genus	Species	Stratigraphic position	Material	Notes	Images
Porochara[5]	P. hians	Ait Hammou	Oogonia	A characean algae of the family Porocharaceae; charophytes are abundant in lower levels, associated with freshwater ostracods	Example of modern characean algae

Plantae

Genus	Species	Stratigraphic position	Material	Notes	Images
Araucariacites[1]	A. australis	FD section, Skoura Syncline	Pollen	Affinities with Araucariaceae inside Coniferae.	Example of extant Araucaria cones
Callialasporites[1]	C. dampieri C. segmentatus C. turbatus C. spp.	FD section, Skoura Syncline	Pollen	Affinities with Araucariaceae inside Coniferae.
Classopollis[1]	C. (Corollina) spp.	FD section, Skoura Syncline	Pollen	Affinities with Cheirolepidiaceae inside Coniferae.
Cyathidites[1]	C. ssp.	FD section, Skoura Syncline	Spores	Affinities with the family Cyatheaceae inside Cyatheales. Arboreal Fern Spores	Modern Cyathea, Cyathidites come probably from similar genera
Densoisporites[1]	D. spp.	FD section, Skoura Syncline	Spores	Affinities with the Selaginellaceae in the Lycopsida.	Modern Selaginella. Densoisporites probably come from a similar Plant
Lycopodiumsporites[1]	L. austroclavatidites L. spp.	FD section, Skoura Syncline	Spores	Affinities with the family Lycopodiaceae in the Lycopodiopsida. Lycopod spores, related to herbaceous flora common in humid environments.	Modern Lycopodium. Lycopodiumsporites probably come from a similar plant
Protocupressinoxylon[25]	P. choubertii	Skoura syncline	Fossil wood	Conifer wood of the family Hirmeriellaceae, considered to be a potential synonym of the genus Brachyoxylon	Example of petrified wood trunk of the same genus (from an unknown location)

See also

• Tafraout Group (Toarcian–Aalenian)
• Azilal Formation (Toarcian-Aalenian)
• Guettioua Formation (Bathonian–?Callovian)
• Anoual Formation (Bathonian)
• Ksar Metlili Formation (Tithonian–?Berrasian)