Cenomanian

The Cenomanian is, in the ICS' geological timescale, the oldest or earliest age of the Late Cretaceous epoch or the lowest stage of the Upper Cretaceous series.[2] An age is a unit of geochronology; it is a unit of time; the stage is a unit in the stratigraphic column deposited during the corresponding age. Both age and stage bear the same name.

System/ Period	Series/ Epoch	Stage/ Age	Age (Ma)
Paleogene	Paleocene	Danian	younger
Cretaceous	Upper/ Late	Maastrichtian	66.0	72.1
		Campanian	72.1	83.6
		Santonian	83.6	86.3
		Coniacian	86.3	89.8
		Turonian	89.8	93.9
		Cenomanian	93.9	100.5
	Lower/ Early	Albian	100.5	~113.0
		Aptian	~113.0	~125.0
		Barremian	~125.0	~129.4
		Hauterivian	~129.4	~132.9
		Valanginian	~132.9	~139.8
		Berriasian	~139.8	~145.0
Jurassic	Upper/ Late	Tithonian	older
Subdivision of the Cretaceous system according to the ICS, as of 2017.[1]

As a unit of geologic time measure, the Cenomanian age spans the time between[3] 100.5 ± 0.9 and 93.9 ± 0.8 million years ago (Mya). In the geologic timescale, it is preceded by the Albian and is followed by the Turonian. The Upper Cenomanian starts around at 95 Mya.

The Cenomanian is coeval with the Woodbinian of the regional timescale of the Gulf of Mexico and the early part of the Eaglefordian of the regional timescale of the East Coast of the United States.

At the end of the Cenomanian, an anoxic event took place, called the Cenomanian-Turonian boundary event or the "Bonarelli event", that is associated with a minor extinction event for marine species.

Stratigraphic definitions

The Cenomanian was introduced in scientific literature by French palaeontologist Alcide d'Orbigny in 1847. Its name comes from the New Latin name of the French city of Le Mans (département Sarthe), Cenomanum.

The base of the Cenomanian stage (which is also the base of the Upper Cretaceous series) is placed at the first appearance of foram species Rotalipora globotruncanoides in the stratigraphic record. An official reference profile for the base of the Cenomanian (a GSSP) is located in an outcrop at the western flank of Mont Risou, near the village of Rosans in the French Alps (département Hautes-Alpes, coordinates: 44°23'33"N, 5°30'43"E). The base is, in the reference profile, located 36 meters below the top of the Marnes Bleues Formation.[4]

The top of the Cenomanian (the base of the Turonian) is at the first appearance of ammonite species Watinoceras devonense.

Important index fossils for the Cenomanian are the ammonites Calycoceras naviculare, Acanthoceras rhotomagense, and Mantelliceras mantelli.

Sequence stratigraphy and palaeoclimatology

The late Cenomanian represents the highest mean sea level observed in the Phanerozoic eon, the past 600 million years (about 150 meters above present-day sea levels). A corollary is that the highlands were at all time lows, so the landscape on Earth was one of warm broad shallow seas inundating low-lying land areas on the precursors to today's continents. What few lands rose above the waves were made of old mountains and hills, upland plateaus, all much weathered. Tectonic mountain building was minimal and most continents were isolated by large stretches of water. Without highlands to break winds, the climate would have been windy and waves large, adding to the weathering and fast rate of sediment deposition.

Palaeontology

The crown group Crocodylia, the true crocodiles, first appear during the Cenomanian.[5]

Belemnites

Belemnites of the Cenomanian
Taxa	Presence	Location	Description	Images
Hibolites

Bony fish

Bony fish of the Albian
Taxa	Presence	Location	Description	Images
Cladocyclus		Akfabou Formation, Morocco; Upper Plattenkalk; Italy	An ichthyodectid osteoglossomorph.
Eubiodectes			A member of Pachycormiformes.

Ankylosauria

Ankylosaurs of the Cenomanian
Taxa	Presence	Location	Description	Images
Acanthopholis	Albian or Aptian to Cenomanian	Upper Greensand Group, Cambridgeshire, England	A nodosaurid with an armor of oval plates set almost horizontally into the skin, with spikes protruding from the neck and shoulder area, along the spine, its size has been estimated to be in the range of 3.0 to 5.5 m (10 to 18 ft) long and about 380 kg (840 lb) in weight.	Acanthopholis
Animantarx	Cenomanian to Turonian	Cedar Mountain Formation, Utah, USA	thought of as a nodosaurid ankylosaur, although its precise relationships within that family are uncertain
Nodosaurus		Wyoming, Kansas, USA	A nodosaurid ankylosaur about 4 to 6 m (13 to 20 ft) long with bony dermal plates covering the top of its body, it may have had spikes along its side, as well. It had four short legs, five-toed feet, a short neck, and a long, stiff, clubless tail.
Silvisaurus	Late Albian to early Cenomanian	Dakota Formation, Kansas, USA	A genus of nodosaurid known from a nearly complete skull
Stegopelta	Late Albian to early Cenomanian	Frontier Formation, Wyoming, USA	A poorly known genus of nodosaurid
Tsagantegia		Baynshiree Svita Formation, Dzun-Bayan, Mongolia	An ankylosaurid known from the remains of its skull
Zhejiangosaurus		Chaochuan Formation, Zhejiang, China	Ankylosaurid
Zhongyuansaurus		Ruyang, Henan, China	Ankylosaurid

Crocodylomorphs

Crocodylomorphs of the Maastrichtian
Taxa	Presence	Location	Description	Images
Aegisuchus Aegisuchus witmeri	95 Ma	Kem Kem Beds, Morocco	A genus of giant, flat-headed eusuchian crocodyliform within the family Aegyptosuchidae.	Aegisuchus Araripesuchus patagonicus Stomatosuchus
Aegyptosuchus Aegyptosuchus peyeri		Egypt	Aegyptosuchus was once considered to be a member of Stomatosuchidae, it is now understood to be a more derived neosuchian and placed within Eusuchia in its own family, Aegyptosuchidae.
Araripesuchus Araripesuchus buitreraensis Araripesuchus patagonicus Araripesuchus rattoides	125–66 Ma	Araripesuchus buitreraensis: Candeleros Formation, Patagonia, Argentina Araripesuchus patagonicus: Patagonia, Argentina Araripesuchus rattoides: Kem Kem Beds, Morocco	A long-lived, widespread, and diverse genus of basal notosuchians that appeared early in the Cretaceous and lasted until the end of it. Multiple species are from this genus, three of them having lived during the Cenomanian, and have been found from both South America and Africa.
Laganosuchus Laganosuchus thaumastos Laganosuchus maghrebensis		Niger; Morocco	A genus of rather large neosuchian crocodyliform. It was similar to its closely related Stomatosuchus.
Stomatosuchus Stomatosuchus inermis		Egypt	A genus of large neosuchian crocodyliform. Its flattened skull had a long, flat, lid-like snout, which was lined with small, conical teeth. The mandible may have been toothless and may have supported a pelican-like throat pouch. Aegyptosuchus

Ornithopoda

Ornithopods of the Cenomanian
Taxa	Presence	Location	Description	Images
Anabisetia		Cerro Lisandro Formation, Neuquén, Argentina	A small bipedal herbivore, almost 2 m (7 ft) long	Eolambia Muttaburrasaurus
Bihariosaurus		Bihor, Romania	An iguanodont similar to Camptosaurus
Eolambia	Albian-Cenomanian	Utah, USA	A basal hadrosaur
Fostoria		Australia	A new iguanodont
Muttaburrasaurus	Albian-Cenomanian	Australia	A large ornithopod that stood about 5 m high known from about 60% of its skeleton
Notohypsilophodon	Cenomanian-Turonian	Bajo Barreal Formation, Chubut, Argentina	A hypsilophodontid or other basal ornithopod, Notohypsilophodon would have been a bipedal herbivore. Its size has not been estimated.
Oryctodromeus		Blackleaf Formation, Montana, and Wayan Formation, Idaho, USA	A burrowing hypsilophodont
Protohadros		Flower Mound, Texas, USA	A primitive hadrosauroid, Protohadros reached 6 m (19.5 ft) in length and had many hadrosaur-like features.
Shuangmiaosaurus	Cenomanian-Turonian	China	A poorly known iguanodont
Talenkauen		Pari Aike Formation, Lake Viedma, Santa Cruz	A 4 metres (13 ft) long elasmarian

Plesiosauria

Plesiosaurs of the Cenomanian
Taxa	Presence	Location	Description	Images
Plesiopleurodon		Belle Fourche Shale, Wyoming, USA	A pliosaurid characterized by a moderately long symphysis bearing eight pairs of teeth that are nearly circular in cross-section and are smooth on the outer surface (except near the base), ribs of the neck vertebrae being singled-headed (double-headed in Jurassic pliosaurs), and a long slender interpectoral bar on the coracoid	Plesiopleurodon
Thalassomedon		Graneros Shale Formation, Colorado and Belle Fourche Formation, Montana	Thalassomedon is among the largest elasmosaurids, with a total length of 10.86 metres (35.6 ft) for the holotype.

Pterosauria

Pterosaurs of the Cenomanian
Taxa	Presence	Location	Description	Images
Anhanguera		Brazil	An ornithocheirid pterosaur
Lonchodraco	Albian-Turonian	Chalk Formation and Cambridge Greensand, England

Sauropoda

Sauropods of the Cenomanian
Taxa	Presence	Location	Description	Images
Andesaurus		Candeleros Formation, Argentina		Argentinosaurus Paralatitan Qiaowanlong
Argentinosaurus		Huincul Formation, Neuquén, Argentina
Diamantinasaurus		Winton Formation, Queensland, Australia
Paralititan		Bahariya Formation, Egypt
Puertasaurus		Pari Aike Formation, Patagonia, Argentina	Originally believed to be from Maastrichtian age.
Qiaowanlong		China
Sibirosaurus		Kiya River, Russia

Theropoda

Theropods of the Cenomanian
Taxa	Presence	Location	Description	Images
Alectrosaurus		Iren Dabasu Formation, Mongolia	A medium sized tyrannosauroid closely related to later Eutyrannosauria.	Australovenator Carcharodontosaurus Giganotosaurus Erliansaurus Mapusaurus Segnosaurus Spinosaurus Unenlagia
Australovenator		Winton Formation, Queensland, Australia	A megaraptoran.
Bahariasaurus		Bahariya Oasis, Egypt; Niger	A large theropod of dubious classification. May be synonymous with Deltadromeus.
Carcharodontosaurus		Kem Kem Formation, Eckhar Formation, Bahariya Formation, Morocco; Niger; Egypt	A large carcharodontosaurid. Original specimens destroyed in World War II, new remains uncovered in the 1990s. Two species known; C. saharicus and C. iguidensis. Contemporaneous with Rugops, Spinosaurus and Deltadromeus/Bahariasaurus.
Deltadromeus		Morocco	A ceratosaur or possible neovenatorid carnosaur, it may be synonymous with Bahariasaurus and contemporaneous with Spinosaurus, Rugops, and Carcharodontosaurus.
Enigmosaurus		Mongolia
Erliansaurus		Mongolia	A therizinosaurid
Erlikosaurus		Mongolia	A therizinosaurid
Giganotosaurus		Candeleros Formation, Argentina	A carcharodontosaurid, it is one of the largest theropods currently known.
Mapusaurus		Huincul Formation, Argentina	A carcharodontosaurid known from multiple specimens in a single bone bed
Moros intrepidus		Utah	A tyrannosauroid.
Nothronychus		Moreno Hill Formation, Zuni Basin, New Mexico; Tropic Shale, Utah, USA	A therizinosaur, two species are known: N. mckinleyi and N. graffmani.
Oxalaia		Brasil	A spinosaurid, the largest theropod thus far recovered from Brazil
Orkoraptor		Pari Aike Formation, Patagonia, Argentina; South America	A megaraptoran originally thought to have been from Maastrichtian deposits
Rugops		Niger	An abelisaurid, contemporaneous with Spinosaurus, Carcharodontosaurus, and Deltadromeus/Bahariasaurus.
Segnosaurus		Mongolia	A theropod belonging to the Therizinosauridae family.
Siamosaurus		Thailand
Siats	Cenomanian	Mussentuchit Member, Cedar Mountain Formation, Utah, USA	An 11- to 12-m neovenatorid carcharodontosaur known from juvenile remains, it is the youngest allosauroid known from North America.
Sigilmassasaurus		Tafilalt, Morocco	A spinosaurid known from fragmentary remains
Spinosaurus		Bahariya Oasis, Egypt; Tunisia; Morocco	A spinosaurid, it is currently considered one of the largest known theropods at an estimated 15 m (49 ft).
Unenlagia		Comahue, Argentina	A unenlagiine dromaeosaurid
unnamed enantiornithine bird[6]		Nammoura, Ouadi al Gabour, Lebanon
Xenotarsosaurus		Bajo Barreal Formation, Chubut Province, Argentina	An abelisaurid

References

1. Super User. "ICS - Chart/Time Scale". www.stratigraphy.org.
2. See for a detailed geologic timescale Gradstein et al. (2004)
3. International Commission on Stratigraphy. "International Stratigraphic Chart" (PDF). Archived from the original (PDF) on 2008-05-29. Retrieved 2008-06-17.
4. The GSSP for the Cenomanian was established by Kennedy et al. (2004)
5. Mateus, O., Callapez P. M., & Puértolas-Pascual E. (2017). The oldest Crocodylia? a new eusuchian from the Late Cretaceous (Cenomanian) of Portugal. Journal of Vertebrate Paleontology, Program and Abstracts. 2017, 160.
6. Vecchia, F. M. D.; Chiappe, L. M. (2002). "First avian skeleton from the Mesozoic of northern Gondwana". Journal of Vertebrate Paleontology. 22 (4): 856. doi:10.1671/0272-4634(2002)022[0856:FASFTM]2.0.CO;2.

Further reading

• Gradstein, F.M.; Ogg, J.G. & Smith, A.G.; 2004: A Geologic Time Scale 2004, Cambridge University Press.
• Kennedy, W.J.; Gale, A.S.; Lees, J.A. & Caron, M.; 2004: The Global Boundary Stratotype Section and Point (GSSP) for the base of the Cenomanian Stage, Mont Risou, Hautes-Alpes, France, Episodes 27, pp. 21–32.

External links

• GeoWhen Database - Cenomanian
• Late Cretaceous timescale, at the website of the subcommission for stratigraphic information of the ICS
• Stratigraphic chart of the Lower Cretaceous (including the Cenomanian), at the website of Norges Network of offshore records of geology and stratigraphy
• Cenomanian Microfossils: 20+ images of Foraminifera