Judith River Formation

Fossil bearing geologic formation in Montana, part of the Judith River Group

The Judith River Formation is a fossil bearing geologic formation in Montana, and is part of the Judith River Group. It dates to the Late Cretaceous, between 79 and 75.3 million years ago, corresponding to the "Judithian" land vertebrate age. It was laid down during the same time period as portions of the Two Medicine Formation of Montana and the Oldman Formation of Alberta. It is an historically important formation, explored by early American paleontologists such as Edward Drinker Cope, who named several dinosaurs from scrappy remains found here on his 1876 expedition (such as Monoclonius). Modern work has found nearly complete skeletons of the hadrosaurid Brachylophosaurus.

The Judith River Formation is composed of mudstone, siltstone and sandstone. The McClelland Ferry Member (78.7 76.3 Ma) is believed to be equivalent to the Oldman Formation, with the Coal Ridge Member (76.3 75.3 Ma) equivalent to the Dinosaur Park Formation.

There are three potential species of discoglossid frogs. Hip bones, possibly representing a North American member of the European spadefoot toad family are also known from the formation. Amphibians of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesHabrosaurusH. dilatusA siren. LisserpetonL. bairdiA scapherpetonid salamander. OpisthotritonO. kayiA possible lungless salamander. ProdesmodonP. copeiA lungless salamander. ScapherpetonS. tectumA scapherpetonid salamander.

Bony fishes of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesBelonostomusBelonostomus longirostrisAn aspidorhynchiform. CyclurusC. fragosusA bowfin. LepisosteusL. occidentalisScalesA gar.?Paralbula?P. sp. A bonefish. PriscosturionP. longipinnisMcClelland Ferry Upper CampanianPolyodontidaeIndeterminate A paddlefish. Known remains exceeded size of Chinese paddlefish, total length would exceed .

Cartilaginous fishes of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesMyledaphusM. bipartitusA stingray.

Choristoderes of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesChampsosaurusC. sp.

Crocodilians of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesBrachychampsaB. montana An alligatorid. LeidyosuchusL. canadensis An alligatorid. DeinosuchusD. hatcheriTeeth

Lizards of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesChamopsC. segnis A whiptail. ExostinusE. lancensisA knob scaled lizard. LeptochamopsL. denticulatusA whiptail. ParadermaP. bogertiA parasaniwid. ParasaniwaP. wyomingensisA parasaniwid.

Ornithischians reported from the Judith River Formation Genus Species Location Member Material Notes ImagesAlbertaceratopsA. nesmoiReclassified as Medusaceratops lokiiAvaceratopsA. lammersilower McClelland Ferry"[Two] partial skulls, skeleton, juvenile," type specimenA ceratopsidBrachylophosaurusB. canadensismiddle McClelland FerryA hadrosaurid which was one of the more common dinosaurs in the area. CeratopsC. montanus"occipital condyle, paired horn cores," type specimenA dubious ceratopsidCorythosaurusC. sp. middle Coal Ridgetwo partial skeletonsA lambeosaurine hadrosauridDicloniusD. calamarius"Teeth. "Nomen dubiumD. pentagonius"Fragmentary dentary with teeth,"FurcatoceratopsF. elucidansFergus County, Montana. Upper Coal RidgeJ. tigrisMedusaceratopsM. lokiilower McClelland FerryBonebedlower Coal Ridge"one apomorphic squamosal"lower Coal Ridge"[Five] skulls, [one] complete. "A dubious hadrosauridTrachodonT. mirabilisIsolated teeth, type specimenPartial skull, vertebrae, ribs, humerus, ilium, femur, tibia, and fibula. A ceratopsidZuulZ. crurivastatormiddle Coal RidgeCranial and postcranial skeletal remains and soft tissue, type specimenAn ankylosaurid

Theropods reported from the Judith River Formation Genus Species Location Stratigraphic position Material Notes ImagesAublysodonA. lateralis"Isolated teeth," type specimenJunior synonym of Deinodon horridusDaspletosaurusD. torosusCoal Ridge Member and two partial skeletons A large tyrannosaurid. D. wilsoniJack’s B2Partial skull, cervical, sacral, and caudal vertebrae, and a rib, chevron, and first metatarsalOriginally considered to be a transitional species between D. torosus and D. horneri, though the validity of this claim has been questioned DeinodonD. falculusTeethIsolated tyrannosaur teeth classified in the dubious genus DeinodonD. hazenianusTeethJunior synonym of Deinodon horridusTeethPossible relative of SaurornitholestesD. laevifrons"Tooth. "A possible troodontid or juvenile tyrannosauridParonychodonP. lacustrisTeeth, type specimenAn indeterminate maniraptoran, also found in the Dinosaur Park, Milk River, and Kirtland FormationsRichardoestesiaR. gilmoreiCareless Creek, Emily's Ankle, Hidden Valley & Blackbird Ridge quarries. Z. abradens"Teeth," type specimenA dromaeosaurid

Turtles of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesAdocusA. sp. BasilemysB. sp. A Mesoamerican river turtle.