The Judith River Formation is a fossil-bearing geologic formation in Montana, and is part of the Montana 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 MontanaSullivan, R.M. and Lucas, S. G. (2006). "The Kirtlandian land-vertebrate "age"–faunal composition, temporal position and biostratigraphic correlation in the nonmarine Upper Cretaceous of western North America." Pp. 7-29 in Lucas, S. G. and Sullivan, R.M. (eds.), Late Cretaceous vertebrates from the Western Interior. New Mexico Museum of Natural History and Science Bulletin 35. 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.
Lithology The Judith River Formation is composed of mudstone, siltstone and sandstone. Coal beds, bentonite and coquinas are also observed.
Relationship with other units The Judith River Formation conformably overlies the Claggett Formation and Pakowki Formation. It is overlain by the Bearpaw Formation. It is equivalent to the Belly River Formation in the southern Canadian Rockies foothills, the Lea Park Formation in central Alberta and the Wapiti Formation in the northwestern plains.
Sub-divisions
The Judith River Formation is divided into four members, the Parkman Sandstone Member, the McClelland Ferry Member, the Coal Ridge member, and the Woodhawk Member. 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.
Fauna
Faunal list follows a review published by Ashok Sahni in 1972 unless otherwise noted.Sahni, A. (1972). "The vertebrate fauna of the Judith River Formation, Montana." Bulletin of the AMNH, v. 147 article 6: 321-415.
Amphibians 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 sirenLisserpetonL. bairdiA scapherpetonid salamanderNezperciusN. dodsoniClambank HollowA frog known from a partial illium.OpisthotritonO. kayiA possible lungless salamanderProdesmodonP. copeiA lungless salamanderScapherpetonS. tectumA scapherpetonid salamander
Fish Bony fish Bony fishes of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesArotusA. hieroglyphusA holostean.BelonostomusBelonostomus longirostrisAn aspidorhynchiform.CyclurusC. fragosusA bowfin.LepisosteusL. occidentalisScalesA gar.?Paralbula?P. sp.A bonefish.PriscosturionP. longipinnisMcClelland Ferry Upper Campanian A sturgeon.PsammorhynchusP. longipinnisMcClelland FerryUpper CampanianPreoccupied name, renamed Priscosturion.PolyodontidaeIndeterminate A paddlefish. Known remains exceeded size of Chinese paddlefish, total length would exceed .
Cartilaginous fish Cartilaginous fishes of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesMyledaphusM. bipartitusA stingray.CretalamnaC. spMontana An Otodontid sharkCarchariasCarcharias sp.A sand tiger sharkSqualicoraxS.kaupiAn Anacoracid shark
Plesiosaurs Plesiosaurs of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesPlesiosauriaPlesiosauria indet. Pterosaurs Pterosaurs of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes Images?Quetzalcoatlus Hidden Valley Quarry PterosauriaindetJDM QuarryMcClelland Ferry
Choristoderes Choristoderes of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesChampsosaurusC. sp.
Crocodylomorphs Crocodylomorphs of the Judith River Formation Genus Species Location Stratigraphic position Abundance Notes ImagesBrachychampsaB. montana An alligatorid.LeidyosuchusL. canadensis An alligatoroid.DeinosuchusD. hatcheriTwo giant dorsal vertebrae and a number of osteoderms.An enormous eusuchian.
Lizards 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 Ankylosaurs Ankylosaurs reported from the Judith River Formation Genus Species Location Member Material Notes ImagesEdmontoniaE. longicepsIsolated teeth A nodosaurid.ZuulZ. crurivastatormiddle Coal RidgeCranial and postcranial skeletal remains and soft tissue, type specimenAn ankylosaurid.
Hadrosaurs Hadrosaurs reported from the Judith River Formation Genus Species Location Member Material Notes ImagesBrachylophosaurusB. canadensismiddle McClelland FerryA hadrosaurid which was one of the more common dinosaurs in the area.CorythosaurusC. sp.middle Coal Ridgetwo partial skeletonsA lambeosaurine hadrosauridProbrachylophosaurusP. bergeilower McClelland FerryA brachylophosaurin hadrosaur
Marginocephalians Ceratopsians Ceratopsians reported from the Judith River Formation Genus Species Location Member Material Notes ImagesAlbertaceratopsA. nesmoiRyan and Evans, 2005Reclassified as Medusaceratops lokiiAvaceratopsA. lammersiRyan and Evans, 2005lower McClelland Ferry"[Two] partial skulls, skeleton, juvenile,""Table 23.1," in Weishampel, et al. (2004). Page 495. type specimenA ceratopsid. Possibly dubious.Chasmosaurinaegen. et sp. nov.A mostly complete skullMOR 11940, An unnamed Chasmosaur housed at the Museum of the Rockies.FurcatoceratopsF. elucidansFergus County, MontanaUpper Coal RidgeNearly complete subadult skeleton.A ceratopsidJudiceratopsJ. tigrislower McClelland FerryA ceratopsidLokiceratopsL. rangiformisKennedy Couleelower McClelland FerryDisarticulated, associated skeleton including most of the skull and fragmentary postcraniaA ceratopsidMedusaceratopsM. lokiiRyan, Michael J.; Russell, Anthony P., and Hartman, Scott. (2010). "A New Chasmosaurine Ceratopsid from the Judith River Formation, Montana", In: Michael J. Ryan, Brenda J. Chinnery-Allgeier, and David A. Eberth (eds), New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium, Indiana University Press, 656 pp. .lower McClelland FerryBonebedA ceratopsidMercuriceratopsM. geminiRyan, Michael J.; Evans, David C.; Currie, Phillip J.; Loewen, Mark A. (2014). "A New chasmosaurine from northern Laramidia expands frill disparity in ceratopsid dinosaurs". Naturwissenschaften. doi:10.1007/s00114-014-1183-1lower Coal Ridge"one apomorphic squamosal"A ceratopsidSpiclypeusS. shipporumMcClelland FerryPartial skull, vertebrae, ribs, humerus, ilium, femur, tibia, and fibula.A ceratopsid
Pachycephalosaurs Pachycephalosaurs reported from the Judith River Formation Genus Species Location Member Material Notes ImagesColepiocephaleC. lambeiKennedy Couleelower McClelland Ferry"nearly complete frontoparietal dome"A pachycephalosaurid closely related to Stegoceras.HanssuesiaH. sternbergiA pachycephalosaurid. Also present in the Dinosaur Park and Oldman Formations. Possible synonym of Stegoceras.
Theropods Dromaeosaurs Dromeosaurs reported from the Judith River Formation Genus Species Location Stratigraphic position Material Notes ImagesDromaeosaurusD. albertensisOx Hill Quarry, Careless Creek Quarry, Hidden Valley Quarry & Blackbird Ridge Quarry.lower McClelland FerryTeethA dromaeosaurid, also found in the Dinosaur Park FormationSaurornitholestesS. langstoniCareless Creek, Emily's Ankle, Top Cat, Hidden Valley & Blackbird Ridge quarries.Lower McClelland FerryNumerous teethA dromaeosaurid
Troodonts Troodonts reported from the Judith River Formation Genus Species Location Stratigraphic position Material Notes ImagesTroodonT. formosusAntelope Head, Careless Creek, Emily's Ankle, Top Cat, Hidden Valley, Blackbird Ridge & Jensen Ranch quarries.28 teethTeeth of a Small theropod distinct from those of tyrannosaurids
Tyrannosaurs Tyrannosaurs reported from the Judith River Formation Genus Species Location Stratigraphic position Material Notes ImagesDaspletosaurusD. torosusCoal RidgeMaxillaA large tyrannosaurid.D. wilsoniJack's B2lower Coal RidgePartial 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 D. sp.Coal RidgeMaltese, Anthony E. "DIFFICULT EXCAVATION AND PREPARATION OF A LARGE DASPLETOSAURUS SPECIMEN." Methods in Preparation: 63.Partial skeletonMaltese, Anthony E. "DIFFICULT EXCAVATION AND PREPARATION OF A LARGE DASPLETOSAURUS SPECIMEN." Methods in Preparation: 63.While initially referred to D. torosus Maltese, Anthony E. "DIFFICULT EXCAVATION AND PREPARATION OF A LARGE DASPLETOSAURUS SPECIMEN." Methods in Preparation: 63., it is more recently classified as Daspletosaurus sp. as it contains some characters in common with other named species of the genus as well as its own unique features. Furthermore, most of the skull is not preserved and is therefore missing many crucial features required for a specific classification GorgosaurusG. libratusPostorbitalA large tyrannosaurid, also found in the Dinosaur Park Formation and possibly the Two Medicine Formation.?TyrannosaurusT. sp. Fergus CountyA LacrimalFound alongside a specimen of Deinosuchus, but may not be from the Judith River Formation
Other theropods
Theropods reported from the Judith River Formation Genus Species Location Stratigraphic position Material Notes ImagesHesperornisH. altusPartial tibiotarsusOne of the only known freshwater occurrences of a hesperornithid.Fox, R.C. (1974). "A middle Campanian, nonmarine occurrence of the Cretaceous toothed bird Hesperornis Marsh." Canadian Journal of Earth Sciences, 11: 1335-1338. Ornithomimosauria indet.IndeterminateCoal Ridge MemberA left and right dentaryA large ornithomimosaur with potential affinities to the DeinocheiridaeRichardoestesiaR. gilmoreiCareless Creek, Emily's Ankle, Hidden Valley & Blackbird Ridge quarries.12 teethA coelurosaur
Dubious Taxa Many early American dinosaur discoveries were made in the Judith River Formation, and most of the early taxa are considered nomina dubia today.