Wahweap Formation
Encyclopedia
The Wahweap Formation of the Grand Staircase-Escelante National Monument is a geological formation in southern Utah and northern Arizona, around the Lake Powell region, whose strata date back to the Late Cretaceous
(Campanian
stage). Dinosaur remains are among the fossils that have been recovered from the formation.
burrows in petrified logs
to various mollusks that characterize the shell beds. Large fossilized crab
s are common at most shell bed sites in the Wahweap, and over 1,900 gastropod specimens (of four likely genera) have been unearthed in the formation's siltstone
.
at least two different types of hadrosaur, two ceratopsians and at least one theropod.
Trace fossil
s are also relatively abundant in the Wahweap, and include vertebrate tracks as well as burrow activity. Tracks preserved in the capping sandstone indicate the presence of crocodylomorphs, which had been previously known in this area only from teeth elements, as well as ornithischian dinosaurs. At least one possible theropod track has been identified in this area as well.
In 2010 a unique trace fossil from the Wahweap was discovered that indicates a predator-prey relationship between dinosaurs and primitive mammals. The trace fossil includes at least two fossilized mammalian den complexes as well as associated digging grooves presumably caused by a maniraptora
n dinosaur. The proximity indicates a case of probable active predation of the burrow inhabitants by the owners of the claw marks.
A fair number of mammals spanning the lower Campanian are known from the Wahweap as well, including at least 15 genera of multituberculates, cladotheria
ns, marsupials, and placental insectivores.
In addition to terrestrial vertebrates, freshwater fish
fossils have been uncovered from the Wahweap which include bowfin
vertebrae, ray
teeth, and probable lungfish
burrows.
Late Cretaceous
The Late Cretaceous is the younger of two epochs into which the Cretaceous period is divided in the geologic timescale. Rock strata from this epoch form the Upper Cretaceous series...
(Campanian
Campanian
The Campanian is, in the ICS' geologic timescale, the fifth of six ages of the Late Cretaceous epoch . The Campanian spans the time from 83.5 ± 0.7 Ma to 70.6 ± 0.6 Ma ...
stage). Dinosaur remains are among the fossils that have been recovered from the formation.
Invertebrate Paleofauna
The Wahweap Formation shows a substantial amount of invertebrate activity ranging from fossilized insectInsect
Insects are a class of living creatures within the arthropods that have a chitinous exoskeleton, a three-part body , three pairs of jointed legs, compound eyes, and two antennae...
burrows in petrified logs
Petrified wood
Petrified wood is the name given to a special type of fossilized remains of terrestrial vegetation. It is the result of a tree having turned completely into stone by the process of permineralization...
to various mollusks that characterize the shell beds. Large fossilized crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s are common at most shell bed sites in the Wahweap, and over 1,900 gastropod specimens (of four likely genera) have been unearthed in the formation's siltstone
Siltstone
Siltstone is a sedimentary rock which has a grain size in the silt range, finer than sandstone and coarser than claystones.- Description :As its name implies, it is primarily composed of silt sized particles, defined as grains 1/16 - 1/256 mm or 4 to 8 on the Krumbein phi scale...
.
Vertebrate Paleofauna
Vertebrates known from the Wahweap include, AcristavusAcristavus
Acristavus is a genus of hadrosaurine hadrosaurid dinosaur. Fossils have been found from the Campanian Two Medicine Formation in Montana and Wahweap Formation in Utah. The type species A. gagslarsoni was named in 2011. Unlike nearly all hadrosaurids except Edmontosaurus, Acristavus lacked...
at least two different types of hadrosaur, two ceratopsians and at least one theropod.
Trace fossil
Trace fossil
Trace fossils, also called ichnofossils , are geological records of biological activity. Trace fossils may be impressions made on the substrate by an organism: for example, burrows, borings , urolites , footprints and feeding marks, and root cavities...
s are also relatively abundant in the Wahweap, and include vertebrate tracks as well as burrow activity. Tracks preserved in the capping sandstone indicate the presence of crocodylomorphs, which had been previously known in this area only from teeth elements, as well as ornithischian dinosaurs. At least one possible theropod track has been identified in this area as well.
In 2010 a unique trace fossil from the Wahweap was discovered that indicates a predator-prey relationship between dinosaurs and primitive mammals. The trace fossil includes at least two fossilized mammalian den complexes as well as associated digging grooves presumably caused by a maniraptora
Maniraptora
Maniraptora is a clade of coelurosaurian dinosaurs which includes the birds and the dinosaurs that were more closely related to them than to Ornithomimus velox. It contains the major subgroups Avialae, Deinonychosauria, Oviraptorosauria and Therizinosauria. Ornitholestes and the Alvarezsauroidea...
n dinosaur. The proximity indicates a case of probable active predation of the burrow inhabitants by the owners of the claw marks.
A fair number of mammals spanning the lower Campanian are known from the Wahweap as well, including at least 15 genera of multituberculates, cladotheria
Cladotheria
Cladotheria is a group of mammals that is defined as including the ancestor of Dryolestoidea, Peramuridae and Zatheria .-External links:* * -Further reading:Zofia Kielan-Jaworowska, Richard L...
ns, marsupials, and placental insectivores.
In addition to terrestrial vertebrates, freshwater fish
Freshwater fish
Freshwater fish are fish that spend some or all of their lives in freshwater, such as rivers and lakes, with a salinity of less than 0.05%. These environments differ from marine conditions in many ways, the most obvious being the difference in levels of salinity...
fossils have been uncovered from the Wahweap which include bowfin
Bowfin
The Bowfin, Amia calva, is the last surviving member of the order Amiiformes , and of the family Amiidae...
vertebrae, ray
Batoidea
Batoidea is a superorder of cartilaginous fish commonly known as rays and skates, containing more than 500 described species in thirteen families...
teeth, and probable lungfish
Lungfish
Lungfish are freshwater fish belonging to the Subclass Dipnoi. Lungfish are best known for retaining characteristics primitive within the Osteichthyes, including the ability to breathe air, and structures primitive within Sarcopterygii, including the presence of lobed fins with a well-developed...
burrows.