# Milk River Formation

The Milk River Formation is a sandstone-dominated stratigraphic unit of the Western Canada Sedimentary Basin in southern Alberta, Canada. It was deposited in near-shore to coastal environments during Late Cretaceous (late Santonian to early Campanian) time. Based on uranium-lead dating, palynology and stratigraphic relationships, deposition occurred between ~84.1 and 83.6 Ma.
The sandstones of the Virgelle Member in the centre of the formation are well-exposed at Writing-on-Stone Provincial Park in southwestern Alberta, where they bear petroglyphs carved into them by First Nations people.
The formation is fossiliferous and has yielded an extensive vertebrate fauna (see Tables below), as well as fossil ammonites. In some areas it hosts shallow natural gas reservoirs.

## Stratigraphy and lithology

The Milk River Formation is an eastward-thinning wedge of clastic sediments that was deposited along the western margin of the Western Interior Seaway during Late Cretaceous (late Santonian to early Campanian) time. It is age-equivalent to the marine shales of the Lea Park Formation in southeastern Alberta, and to the Eagle and Telegraph Creek Formations of north-central Montana.
In Alberta it is subdivided into the following three members:
* Telegraph Creek Member, at the base, consists primarily of mudstones and shales deposited in offshore marine settings. It has produced the ammonite index fossil Desmoscaphites bassleri, which indicates an age of ~84. Ma.
* Virgelle Member, the central member, is a sequence of massive, cliff-forming, yellow to white sandstones that were deposited in shoreface and tidal channel environments. It can be seen at Writing-on-Stone Provincial Park.
* Deadhorse Coulee Member, at the top, consists of predominantly nonmarine shales, siltstones, sandstones, and coal beds that were deposited in rivers, floodplains and swamps. Most of the vertebrate fossils have come from this member.

## Vertebrates

(references: Brinkman 2003; Gao and Fox 1995; Hilton and Grande 2006; Larson 2008; Sullivan 2003; University of Alberta webpage)

### Cartilaginous fishes

Remains of an indeterminate lamnid genus and species are present.
Cartilaginous fishes reported from the Milk River Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Lonchidion | Indeterminate | | | | Hybodontoidea |
| Myledaphus | M. bipartitus | | | | Rhinobatoidei |

### Bony fishes

Remains of Acipenseridae, Amiidae, Esocidae, indeterminate genera and species.
Bony fishes reported from the Milk River Formation :
| Genus | Species | Notes | Images |
| Belonostomus | Indeterminate | Aspidorhynchidae | Belonostomus Lepisosteus |
| Lepisosteus | L. occidentalis | Lepisosteidae | Belonostomus Lepisosteus |
| Palaeolabrus | Indeterminate | Lepisosteidae | Belonostomus Lepisosteus |

### Amphibians

Amphibians reported from the Milk River Formation :
| Genus | Species | Notes | Images |
| Albanerpeton | A. galaktion | Albanerpetontidae | Albanerpeton |
| Albanerpeton | A. nexuosus | Albanerpetontidae | Albanerpeton |
| Opisthotriton | Indeterminate | Batrachosauroididae | Albanerpeton |

### Squamates

Indeterminate Anguidae and Xenosauridae genera and species.
Squamates reported from the Milk River Formation :
| Genus | Species | Notes |
| Aocnodromeus | A. corrugatus | Scincidae |
| Chamops | Indeterminate | Teiidae |
| Coniophis | cf. C. precedens | Aniliidae |
| Cnephasaurus | C. locustivorus | Iguanidae |
| Glyptogenys | G. ornata | Teiidae |
| Parasaniwa? | Indeterminate | Necrosauridae |
| Penemabuya | P. antecessor | Scincidae |
| Sphenosiagon | S. simplex | Teiidae |

### Turtles

Indeterminate Solemydidae and Trionychidae genera and species.
Turtles reported from the Milk River Formation :
| Genus | Species | Notes |
| Adocus | Indeterminate | Adocidae |
| Basilemys | Indeterminate | Nanhsiungchelyidae |
| ?Boremys | Indeterminate | Baenidae |
| ?Compsemys | Indeterminate | Family indeterminant |
| Neurankylus | N. lithographicus | Baenidae |
| Plesiobaena | Indeterminate | Baenidae |

### Crocodilians

Crocodilians reported from the Milk River Formation :
| Genus | Species | Location | Stratigraphic position | Material | Notes |
| Gilchristosuchus | G. palatinus | | | | |

### Dinosaurs

Indeterminate Ankylosauridae, Aves, Ceratopsidae, Dromaeosauridae, Hadrosauridae, Nodosauridae, Ornithomimidae, Pachycephalosauridae, Protoceratopsidae, Thescelosauridae, and Tyrannosauridae genera and species.
| 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. |
Dinosaurs reported from the Milk River Formation :
| Genus | Species | Material | Notes | Images |
| Lithostrotia | Indeterminate | Caudal Centrum | An indeterminate Titanosaurian sauropod, the first from Canada. Cited to be similar to caudals referred to Alamosaurus. | |
| Acrotholus | A. audeti | Skull domes | A pachycephalosaur | Acrotholus Saurornitholestes |
| Brachyceratops | Indeterminate | | | Acrotholus Saurornitholestes |
| Continuoolithus | cf. C. canadensis | One eggshell fragment | Laid by a theropod. | Acrotholus Saurornitholestes |
| Gryphoceratops | G. morrisoni | Partial right dentary | A leptoceratopsid | Acrotholus Saurornitholestes |
| Kritosaurus | Indeterminate | | | Acrotholus Saurornitholestes |
| Palaeoscincus | Indeterminate | | | Acrotholus Saurornitholestes |
| cf. Paronychodon | cf. P. lacustris | | Theropoda incertae sedis | Acrotholus Saurornitholestes |
| Porituberoolithus | cf. P. warnerensis | One eggshell fragment | Laid by a theropod | Acrotholus Saurornitholestes |
| Prismatoolithus | Indeterminate | 6 isolated eggshell fragments | Laid by a theropod. | Acrotholus Saurornitholestes |
| cf. Richardoestesia | cf. R. gilmorei | | Maniraptora incertae sedis | Acrotholus Saurornitholestes |
| cf. Richardoestesia | cf. R. isosceles | | Maniraptora incertae sedis | Acrotholus Saurornitholestes |
| Saurornitholestes | S. langstoni | | Dromaeosauridae | Acrotholus Saurornitholestes |
| Spheroolithus | cf. S. choteauensis | 313 isolated eggshell fragments | Laid by an ornithopod. | Acrotholus Saurornitholestes |
| Triprismatoolithus | Indeterminate | 60 isolated eggshell fragments | Laid by a bird or theropod. | Acrotholus Saurornitholestes |

### Mammals
#### Other mammals

Other Mammals reported from the Milk River Formation :
| Genus | Species | Notes |
| Alticonodon | A. lindoei | Triconodontidae |
| Cimexomys | C. antiquus | Neoplagiaulacidae? |
| Cimexomys | C. magister | Neoplagiaulacidae? |
| Cimolodon | C. electus | Cimolodontidae |
| Cimolodon | C. similis | Cimolodontidae |
| Cimolomys | Indeterminate | Cimolomyidae |
| Ectypodus | cf. E. powelli | |
| Meniscoessus | M. ferox | Cimolomyidae |
| Mesodma | Mesodma senecta | |
| Mesodma | Indeterminate | |
| Mictodon | Mictodon simpsoni | Tinodontidae |
| Paracimexomys | P. magister | Family indeterminent |
| Paranyctoides | Paranyctoides maleficus | Nyctitheriidae |
| Picopsis | P. pattersoni | Picopsidae |
| Picopsis | Indeterminate | Picopsidae |
| Potamotelses | P. aquilensis | Potamotelsidae |
| Symmetrodontoides | S. canadensis | Spalacotheriidae |
| Viridomys | V. orbatus | Neoplagiaulacidae? |

#### Didelphomorphs

Didelphomorphs reported from the Milk River Formation :
| Genus | Species | Notes | Images |
| Albertatherium | A. primus | Peradectidae | Alphadon Didelphodon |
| Albertatherium | A. secundus | Peradectidae | Alphadon Didelphodon |
| Alphadon | A. halleyi | Peradectidae | Alphadon Didelphodon |
| Alphadon | Indeterminate | Peradectidae | Alphadon Didelphodon |
| Aquiladelphis | A. incus | Aquiladelphidae | Alphadon Didelphodon |
| Aquiladelphis | A. minor | Aquiladelphidae | Alphadon Didelphodon |
| Didelphodon | Indeterminate | Stagodontidae | Alphadon Didelphodon |
| Eodelphis | Indeterminate | Stagodontidae | Alphadon Didelphodon |
| Iqualadelphis | I. lactea | Pediomyidae | Alphadon Didelphodon |
| Pediomys | cf. P. clemensi | Pediomyidae | Alphadon Didelphodon |
| Pediomys | P. exiguus | Pediomyidae | Alphadon Didelphodon |
| Pediomys | P. florencae | Pediomyidae | Alphadon Didelphodon |
| Protalphadon | P. creber | Peradectidae | Alphadon Didelphodon |