# 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.

## Paleoenvironment

The El Mers formations are composed primarily of marls with intermittent layers of limestone and sandstone, characterized by abundant organic matter and benthic fauna. 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.
During the Bajocian-Bathonian transition the local faices paint a picture of a dynamic paleoenvironment, where the interplay between land and sea was pronounced. This setting oscillated between a proximal continental shelf, marked by significant terrestrial input, and episodic marine incursions that suggest fluctuating sea levels. 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.
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.

## 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 |
| Bullopora | B. tuberculata | SW part of the Skoura syncline | Tests/Shells | A benthic foraminiferan of the family Polymorphinidae |
| Pfenderella | P. cf. arabica | SW part of the Skoura syncline | Tests/Shells | A benthic foraminiferan of the family Pfenderininae |
| Praekurnubia | 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 | P. maynci | SW part of the Skoura syncline | Tests/Shells | A benthic foraminiferan of the family Hauraniidae |

### Dinoflajellates

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

### Brachiopoda

| Genus | Species | Stratigraphic position | Material | Notes | Images |
| Formosarhynchia | 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 |
| Cytherella | C. index | Ait Hammou | Valves | A freshwater/brackish ostracod of the family Cytherellidae |
| Fastigatocythere | F. aff. brentonensis | Ait Hammou | Valves | A freshwater/brackish ostracod of the family Progonocytheridae |
| Kinkelinella | K. aff. triangula | Ait Hammou | Valves | A freshwater ostracod of the family Progonocytheridae |
| Metacypris | 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 | P. ihopyensis | Ait Hammou | Valves | A freshwater ostracod of the family Schulerideidae |

### Xiphosura

| Genus | Species | Stratigraphic position | Material | Notes | Images |
| Selenichnites | 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 | 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 | C. undulata | El Mers | Isolated shells | A marine clam of the family Laternulidae | |
| Choffatia | C. cf. urinacensis | East Skoura syncline | Isolated shells | An ammonite of the family Perisphinctidae and indicator of the Callovian age | |
| Corbula | C. pectinata | Aït Kermouss | Isolated shells | A marine clam of the family Corbulidae | |
| Clydoniceras | C. discus | Tamguert n'Tarit Tizi n'Juillerh | Isolated shells | An ammonite of the family Clydoniceratidae | |
| Eomiodon | E. angulatus | El Mers | Isolated Shells | A marine clam of the family Neomiodontidae | |
| Isognomon | 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 | 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 | L. costata | Aït Kermouss | Isolated shells | A marine oyster of the family Ostreidae | Example of extant member of the genus (from Micronesia) |
| Modiolus | 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 | M. macrescens | East Skoura syncline | Isolated shells | An ammonite of the family Morphoceratidae and indicator of the Bathonian age | |
| Mytilus | 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 | 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 | O. sp. | East Skoura syncline | Isolated shells | An ammonite of the family Parkinsoniidae and indicator of the Bathonian age | |
| Orionoides | O. cf. pseudorion | East Skoura syncline | Isolated shells | An ammonite of the family Perisphinctidae | |
| Ostrea | 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 | P. sp. | Aït Kermouss | Isolated shells | A Nautilidan of the family Paracenoceratidae | Example of specimen (from an unknown location) |
| Parkinsonia | 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 | 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 | A. spinosa | El Mers Ich Timellaline | Isolated Individuals | An Echinoidean of the family Acrosaleniidae | |
| Hemicidaris | 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 | 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 | 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 | 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 |
| Hatcherichnus | H. ispp. | Inzar O'Founass | Footprints | Indeterminate Crocodrylomorph Tracks |
| "Megalosaurus" | "M." mersensis | Botane Tizi n'Juillerh | Isolated teeth and vertebra | A marine crocodylomorph of the family Teleosauridae. Mistaken as Theropod remains in the past. |
| Steneosaurus? | 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 |
| Carmelopodus | cf.C. isp. | Tassmante O'Moche | Footprints | Theropod tracks of uncertain affinity, suggested to come from Ceratosauria members |
| Grallator? | G.? isp. | Ifri N'Tfrane | Footprints | Theropod Tracks, referred usually to small-medium sized Genera |
| Hispanosauropus? | H.? isp. | Ifri N'Tfrane | Footprints | Theropod tracks of uncertain affinity, different from Megalosauripus in the larger metatarsophalangeal region |
| Megalosauripus | 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 | 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. |
| Theropodipedia | 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" |

#### Sauropoda

| Genus | Species | Stratigraphic position | Material | Notes |
| Breviparopus | 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. |
| Cetiosaurus | "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 |
| Sauropoda | Indeterminate | Aït Tamjout Boulahfa 1 km east of Taguelft | Isolated and articulated bones | Indeterminate or undescribed sauropod remains |
| Sauropodina | 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. |

#### Ornithischia

| Genus | Species | Stratigraphic position | Material | Notes |
| Adratiklit | 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 | Indeterminate | Boulahfa | USMBA 001, a partial left femur | The oldest known cerapodan dinosaur |
| Ornithopodichnus? | O.? ispp. | Ifri N'Tfrane | Footprints | Ornithichian tracks, referred to short-toed forms such as Gilmoreosaurus |
| Spicomellus | S. afer | Boulahfa | NHMUK PV R37412, a partial rib bearing four co-ossified spines | An early ankylosaurian |
| Thyreosaurus | 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 | H. lusitanica | SW part of the Skoura syncline | Calcareous imprints | A dasycladacean algae of the family Dasycladaceae | |
| Sarfiatella | 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 | 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 | A. australis | FD section, Skoura Syncline | Pollen | Affinities with Araucariaceae inside Coniferae. | Example of extant Araucaria cones |
| Callialasporites | C. dampieri C. segmentatus C. turbatus C. spp. | FD section, Skoura Syncline | Pollen | Affinities with Araucariaceae inside Coniferae. | Example of extant Araucaria cones |
| Classopollis | C. (Corollina) spp. | FD section, Skoura Syncline | Pollen | Affinities with Cheirolepidiaceae inside Coniferae. | |
| Cyathidites | 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 | D. spp. | FD section, Skoura Syncline | Spores | Affinities with the Selaginellaceae in the Lycopsida. | Modern Selaginella. Densoisporites probably come from a similar Plant |
| Lycopodiumsporites | 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 | 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) |