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The Kaiparowits Formation is a sedimentaryrock formation found in the Kaiparowits Plateau in Grand Staircase–Escalante National Monument, in the southern part of Utah in the western United States. It is over 2800 feet (850 m) thick, and is Campanian in age. This Upper Cretaceous formation was formed from alluvialfloodplains of large rivers in coastal southern Laramidia; sandstonebeds are the deposit of rivers, and mudstone beds represent floodplain deposits. It is fossiliferous, with most specimens from the lower half of the formation, but exploration is only comparatively recent, with most work being done since 1982. It has been estimated that less than 10% of the Kaiparowits formation has been explored for fossils. The Natural History Museum of Utah has conducted most fieldwork.
Age
Traditionally, the Kaiparowits Formation has been considered to be roughly equivalent in age to the northern Dinosaur Park Formation. This, combined with the differences in fauna between the two formations, has led some scientists, most notably Scott Sampson, to conclude that there was some barrier separating northern and southern Laramidia at this time. However, preliminary re-calibration of late Cretaceous formation correlations suggests that the upper part of the Kaiparowits, where many of the unique species are found, is actually younger than the Dinosaur Park, and that some Kaiparowits species may simply be the descendants of Dinosaur Park species. However, new dates reveal that this is simply an artifact of inaccurate Ar-Ar dating, and both formations had similar ages.
According to new Uranium-Lead stratigraphic data, the fossil-bearing portion of the Kaiparowits Formation dates from about 77.24 to 75.02 million years ago, with the volcaniclastic Upper Valley Member estimated to date from 73.8 to 72.8 million years ago.
Biostratigraphy
The timeline below follows the re-calibrated timeline of Fowler (2017), showing species from the Kaiparowits Formation in green, and related species from Alberta in blue.
The Kaiparowits Formation is a muddy bed that was deposited between about 77.3 to 72.8 million years ago, in the area where the Grand Staircase–Escalante National Monument of Utah is today. It is extremely fossil rich, with thousands of plants and animal fossils being preserved in amongst its sandstone and mudstone deposits. Based on plants remains including multiple vines, leaves, and branches, It was assumed by paleontologists Scott Sampson and his colleagues that Utah in the Campanian was a dense jungle bordering the Western Interior Seaway. The jungle theory would also support why almost all the animals in the Kaiparowits Formation were new species, and why the deposits were so plentiful. Without the need for herbivores to migrate to find food, and theropods to migrate after herbivores, a whole ecosystem could evolve secluded from interbreeding. The theory also supported why the dinosaurs adorned such features like the 15 horns of Kosmoceratops, they were for sexual selection.
Paleofauna
A Kosmoceratops disturbed from its rest by a wandering Talos in Laramidia
Trace fossils are also known from the Kaiparowits, including an excellently preserved hadrosaur skin impression known from a recent analysis by Herrero and Farke.
A partial left mandible, a disarticulated forelimb consisting of a fused scapulocoracoid, humerus, radius, ulna, metacarpals, manual phalanx and an ungual, a scapula, coracoid, cervical vertebrae, caudal vertebrae, dorsal centra vertebrae, sacral vertebrae, chevrons, a complete cervical half ring, dorsal ribs, a partial tail club, numerous osteoderms and teeth.
An indeterminate ankylosaurid known from various partial specimens.
Right side of an articulated partial skull, including the ventral lacrimal, jugal, epijugal, quadratojugal, postorbital, maxilla, squamosal, and rostrolateral parietal in the region of the supratemporal fenestra.
Might be a distinct taxon based on its episquamosal and squamosal morphology.
An almost complete skull, a disarticulated adult skull, an isolated squamosal, a syncervical, fragmentary dorsal vertebrae, associated left forelimb and fragmentary right forelimb.
A centrosaurine ceratopsid with rounded horns above its eyes.
[Two] partially complete skulls, a partial postorbital consisting of the nearly complete supraorbital horncore, an isolated rostrum, premaxilla, nasal fragment, jugal, squamosal and parietal, an associated post cranium, and two immature specimens consisting of partial postorbitals with complete supraorbital horncores.
A chasmosaurine ceratopsid known from adult and juvenile specimens.
Ornithopods
Hadrosaurs reported from the Kaiparowits Formation
A mostly complete skull, a partial subadult skull, a partial skull roof and partial braincase, a partially articulated skeleton consisting of a portion of the skull and lower jaws, most of the dorsal, sacral, and caudal vertebral series, fragmentary ribs, scapulae, coracoid, humerus, and the entire pelvis, and a partial skeleton consisting of dorsal, sacral, and caudal vertebral series, a number of ribs, scapula, humerus, radius, ulna, and a complete pelvis.
[Eight] isolated partial skulls, a partial skeleton consisting of mostly the pelvic region, fragmentary associated elements, and a juvenile specimen consisting of a partial skull and articulated skeleton.
Originally identified as P. cyrtocristatus, then believed to be a new species, then tentatively referred back to P. cyrtocristatus.
Fragmentary distal left radius, complete left carpus including the semilunate and radiale, and left manus with complete digit I and III, complete digit II, fragmentary distal metatarsals and pedal phalanges, and articulated distal portion of pedal digit II.
Cervical vertebrae, thoracic vertebrae, pygostyle, phalanges, a complete humerus, femur, tarsometatarsus, a partial scapula, coracoid, furcula, tibiotarsus, and fragments of the sternum, radius, ulna, carpometacarpus, and manual phalanges.
A lacrimal, jugal, frontal, squamosal, otoccipital and proötic, otoccipital, basisphenoid, quadrates, jugal, maxilla, dentary, articular, cervical vertebra, scapula, coracoid, humerus, ulna, femur and a subadult specimen consisting of a maxilla, lacrimals, postorbitals, squamosal, quadratojugal, quadrate, frontals, parietals, braincase, ectopterygoids, epipterygoid, pterygoids, angulars, surangulars, prearticular, articular, atlas, postaxial cervical vertebrae, cervical ribs, dorsal vertebrae, dorsal ribs, sacral vertebrae, caudal vertebrae, chevrons, portions of ilia, pubes, ischia, complete femur, tibia, fibula, pedal phalanx, and ungual.
A tyrannosaurinetyrannosaurid known from immature specimens. It was the largest carnivore in the area, as well as the most common tyrannosaur in the area.
An isolated frontal, isolated caudal vertebra, a proximal tibia, fragmentary metatarsals, pedal phalanges, and pedal unguals, in addition to fragmentary cranial remains, including the basioccipital, fused parietals, portions of both squamosals, and isolated teeth.
Multiple adult specimens consisting of femora, tibiae, fibula, a complete astragalus and calcaneum, two metatarsal III, complete pedal PIII-1 and PIII-2, pedal phalanxes, pedal unguals, caudal vertebrae, isolated fused parietals, a partial dentary, an isolated humerus, an isolated lacrimal, an isolated jugal and a juvenile specimen consisting of fused parietals, a partial unfused frontal, and partial dentary.
