Navigation:Geological Time Periods/Phanerozoic Eon/Mesozoic Era/Cretaceous Period/Maastrichtian Stage

The Maastrichtian is the final stage of the Late Cretaceous period, covering the duration of time from 72 - 66 million years ago.

Flora & Paleoecology
Maastrichtian flora include Metasequoia, a species of 60 meter tall fast-growing redwood. The genus has one living species. The extant (not extinct) genus of coniferous tree Araucaria is also found in many Maastrichtian formations.

A detailed study of Alaskan rock formations dating to the Maastrichtian has revealed that the Maastrichtian arctic ecosystem had an average temperature of around 7-8 degrees Celsius, comparable to modern places like Stockholm or Helsinki. The study (link) also found that the climate was highly seasonal.

North America
North America has the most intensely studied Mesozoic rock formations and thus some very well-documented fossil ecosystems, some of which will be detailed below. During the Cretaceous, the Western Interior Seaway covered much of central North America and before the Maastrichtian this had divided North America in two; however, by the Maastrichtian the Western Interior Seaway had shrunk until it only reached up until about Canada's modern border.

The Western Interior Seaway formed two distinctive parts of the continent, Laramidia in the west and Appalachia to the east, with the sea in the middle. Little is known about Appalachia's ecology, but Larimidia had extensive coastal floodplains along the length of most of the north-western shore of the Interior Seaway, which are believed to have been the ideal location for ancient river-filled forests.

The fact that this region had lots of water and might have occasionally flooded provides ideal location for fossilization, and is the direct cause of two formations that are listed below - Hell Creek and the Lance Formation.

The more southern parts of Larimidia, home to the Ojo Alamo formation and animals like Alamosaurus and Quetzalocatlus, were arid and much drier than the north. Along the western part of the subcontinent the Rocky Mountains were beginning their formation, leading to dry highland with very bad fossilization environments. Very little is known about these dry highlands.

Hell Creek Formation (late Maastrichtian)
The Hell Creek formation contains fossils from the last one million years before the asteroid impact and is spread out across parts of Montana, North Dakota, South Dakota and Wyoming. Its environment would have consisted of riverine forest, floodplain and beaches, providing an ideal fossilization environment.

Fish

Acipenser - a genus of sturgeon, still living today.

Lepisosteus - a genus of gar (small, mostly freshwater fish group)

Coriops

Amphibians

Opisthotriton - A prehistoric salamander

Pterosaurs

Quetzalcoatlus? - single pterosaur neck vertebra, probably belonging to Quetzalocatlus.

Crocodylomorphs

Borealosuchus - 3-meter crocodile, found across North America during the Late Cretaceous and Paleocene

Brachychampsa - an alligator

Thoracosaurus

Turtles

Compsemys

Hoplochelys

Trionyx

Gamerabaena

Lizards

Obamadon - named after the US president, about 30 cm long, preyed on insects

Mammals

Mesodma

Alphadon

Didelphodon - one of the largest Mesozoic mammals, 50-100 cm long

Cimolodon

Ankylosaurid dinosaurs

Anyklosaurus

Ceratopsian dinosaurs

Triceratops - Tatankaceratops is most likely species of Triceratops

Torosaurus - A horned dinosaur similar to Triceratops

Leptoceratops - a small, basal ceratopsian

Ornithopod dinosaurs

Edmontosaurus

Thescelosaurus 

Pachycephalosaurid dinosaurs

Pachycephalosaurus  - probably includes Dracorex and Stygimoloch

Sphaerotholus - probably same genus as Prenocephale

Ornithomimosaurian dinosaurs

Struthiomimus - some species may have reached 4 meters

Oviraptorosaurid dinosaurs

Anzu - newly discovered species

Maniraptoran dinosaurs

Avisaurus

Archeroraptor - considered to be the sole dromaeosaur in Hell Creek

Brodavis 

Tyrannosaurids

Tyrannosaurus 

Horseshoe Canyon Formation (early Maastrichtian)
The Horseshoe Canyon Formation, located in southwestern Alberta, Canada, dates from the early Maastrichtian (about 72-67 million years ago). As the formation's history spans 5 million years, not all of the species lived at the same time. It is divided into 5 stratigraphic units, dating from different periods of the formation's history and allowing for very precise chronological dating for these animals.

UNIT 1 (73 - 71 mya)

Epichirostenotes 

Pachyrhinosaurus

Ornithomimus 

Edmontosaurus 

Anchiceratops

Pachycephalosaur (previously known as Sphaerotholus)

UNITS 2-3 (71 - 70 mya)

Ornithomimus 

Edmontosaurus

Edmontonia

Anodontosaurus

Parksosaurus 

Albertosaurus

UNIT 4 (70 - 68,5 mya)

Ornithomimus 

Anodontosaurus

Albertosaurus

Saurolophus

Hypacrosaurus 

Albertonykus 

Struthiomimus - only one species present, currenlty unnamed

Atrociraptor 

UNIT 5 (68,5 - 67 mya)

Albertonykus

Hypacrosaurus

Eotriceratops

Other dinosaurs known from this formation include Richardoestesia and Arrhinoceratops.

Lance Formation (mid to late Maastrichtian)
The Lance Formation is an exceptionally diverse formation that dates from 69 to 66 million years ago and is located in modern-day Wyoming. During the Maastrichtian the area had a subtropical climate with barely no cold season. The Lance Formation existed at the edge of the Western Interior Seaway which, from the Early Cretaceous to the Campanian, split North America into three parts; however, by the time of the Lance formation it had shrunk in size to an area covering Mexico, Texas, New Mexico, Colorado, Oklahoma, Nebraska, South Dakota and parts of Wyoming (Map)

The environment of the Lance formation is thought to be similar to that of Hell Creek, with floodplains and forests.

Non-avian Coelurosaurs

Pectinodon

Richardoestesia

Struthiomimus

Tyrannosaurus 

Avian Coelurosaurs (birds)

Ceramornis

Cimolopteryx

Graculavus

Lonchodytes

Palintropus

Potamoris

Ankylosaurids and nodosaurids

Ankylosaurus

Edmontonia

Other Ornithischians

Leptoceratops

Nedoceratops

Pachycephalosaurus 

Triceratops

Edmontosaurus

Thescelosaurus 

Madagascar
As it is today, the Madagascar of the Late Cretaceous was an island, having separated from the island of India earlier on it geologic history. Both would have been drifting northwards as during the Maastrichtian Madagascar was still around ten degrees latitude more to the south than it is today.

Madagascar's environment is believed to have been strongly seasonal and semi-arid towards the interior, though with floodplains and tidal flats along the shore. Majungasaurus and Beelzebufo were certainly inhabitants of these coastal habitats. Dinosaurs

Majungasaurus - lowly built abelisaurid theropod

Rapetosaurus - moderately large 15 meter sauropod

Rahonavis - A small dromaeosaur

Masiakasaurus - A small abelisaurid

Crocodylomorphs

Araripesuchus

Simosuchus

Mahajangasuchus

Amphibians

Beelzebufo - largest known frog, up to 40 cm