The Wayan Formation is a geological

formation Formation may refer to: Linguistics * Back-formation, the process of creating a new lexeme by removing or affixes * Word formation, the creation of a new word by adding affixes Mathematics and science * Cave formation or speleothem, a secondary ...

in Idaho whose strata date back to the latest

Early Cretaceous The Early Cretaceous (geochronological name) or the Lower Cretaceous ( chronostratigraphic name), is the earlier or lower of the two major divisions of the Cretaceous. It is usually considered to stretch from 145 Ma to 100.5 Ma. Geology Pr ...

and the earliest

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', ...

. Dinosaur, other reptile, mammal, and micro and macro-floral remains are among the fossils that have been recovered from the formation. The lack of extensive outcrops, limited geographic extent, and extreme structural deformation have limited paleontological explorations of the Wayan.

Geology and age

The Wayan occurs in the Caribou Mountains of eastern Idaho. Sediments are dominantly

floodplain A floodplain or flood plain or bottomlands is an area of land adjacent to a river which stretches from the banks of its channel to the base of the enclosing valley walls, and which experiences flooding during periods of high discharge.Goudi ...

mudstones (many having undergone extensive

pedogenic Soil formation, also known as pedogenesis, is the process of soil genesis as regulated by the effects of place, environment, and history. Biogeochemical processes act to both create and destroy order (anisotropy) within soils. These alterations l ...

processes) with some

fluvial In geography and geology, fluvial processes are associated with rivers and streams and the deposits and landforms created by them. When the stream or rivers are associated with glaciers, ice sheets, or ice caps, the term glaciofluvial or fluv ...

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

s and minor conglomerates,

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms wh ...

s, and

tuff Tuff is a type of rock made of volcanic ash ejected from a vent during a volcanic eruption. Following ejection and deposition, the ash is lithified into a solid rock. Rock that contains greater than 75% ash is considered tuff, while rock ...

s. Carbonate nodules in pedogenic mudstones suggest a semi-arid, seasonal climate during deposition. Radiometric U-Pb dates from detrital zircons indicate a latest

Albian The Albian is both an age of the geologic timescale and a stage in the stratigraphic column. It is the youngest or uppermost subdivision of the Early/Lower Cretaceous Epoch/ Series. Its approximate time range is 113.0 ± 1.0 Ma to 100.5 ± ...

to early to middle Cenomanian age. Detrital zircon U-Pb dating within one stratigraphic meter of an '' Oryctodromeus'' locality yielded an age of 99.1 +1.5/-1.3 Ma showing proximity to the

/ Cenomanian stage boundary.Krumenacker, L. J., 2010. Chronostratigraphy and paleontology of the mid-Cretaceous Wayan Formation of eastern Idaho, with a description of the first ''Oryctodromeus'' specimens from Idaho. BYU MS thesis." The Wayan is equivalent to the upper

Cedar Mountain Formation The Cedar Mountain Formation is the name given to a distinctive sedimentary geologic formation in eastern Utah, spanning most of the early and mid-Cretaceous. The formation was named for Cedar Mountain in northern Emery County, Utah, where Willia ...

of Utah, the Aspen Shale of Wyoming, and the Vaughn member of the Blackleaf Formation of Montana. Wayan Outcrop

Fauna and flora

The vertebrate fauna is dominated by the small basal ornithopod '' Oryctodromeus'', which dominates the vertebrate assemblage and is known from several partial skeletons. An

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

, a ''

Tenontosaurus ''Tenontosaurus'' ( ; ) is a genus of medium- to large-sized ornithopod dinosaur. It was a relatively medium sized ornithopod, reaching in length and in body mass. It had an unusually long, broad tail, which like its back was stiffened with a ...

''-like

iguanodontid Iguanodontidae is a family of iguanodontians belonging to Styracosterna, a derived clade within Ankylopollexia. Characterized by their elongated maxillae, they were herbivorous and typically large in size. This family exhibited locomotive dyna ...

, a

hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which incl ...

, dromaeosaurs, a

tyrannosauroid Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent ...

, a possible neovenatorid allosauroid, a giant

oviraptorosaur Oviraptorosaurs ("egg thief lizards") are a group of feathered maniraptoran dinosaurs from the Cretaceous Period of what are now Asia and North America. They are distinct for their characteristically short, beaked, parrot-like skulls, with or w ...

(represented by eggshell of the oogenus ''

Macroelongatoolithus ''Macroelongatoolithus'' is an oogenus of large theropod dinosaur eggs, representing the eggs of giant caenagnathid oviraptorosaurs. They are known from Asia and from North America. Historically, several oospecies have been assigned to ''Macro ...

carleylei''), indeterminate small

theropods Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

, possible

neoceratopsians Ceratopsia or Ceratopia ( or ; Greek: "horned faces") is a group of herbivorous, beaked dinosaurs that thrived in what are now North America, Europe, and Asia, during the Cretaceous Period, although ancestral forms lived earlier, in the Jurassi ...

, large and small crocodilians, turtles, a variety of small mammals, and semionotid fish are known from very fragmentary remains.Krumenacker, L. J., Scofield, G., Simon, J., Varricchio, D., and Wilson, G. P., 2014a. Outcrop envy: Paleontology and taphonomy of the Wayan Formation, the Cenomanian foredeep deposits of Idaho. Mid-Mesozoic: The age of dinosaurs in transition. Abstracts, Pp 63-64. Oryctodromeus family Wayan

Fossil plants are rare, but petrified conifer wood, and foliage from angiosperms, conifers and ferns has been reported.

Vertebrate fauna

* Cf. Semionotidae *

Eutriconodont Eutriconodonta is an order of early mammals. Eutriconodonts existed in Asia, Africa, Europe, North and South America during the Jurassic and the Cretaceous periods. The order was named by Kermack ''et al.'' in 1973 as a replacement name for the ...

mammal known from a tooth *

Multituberculate Multituberculata (commonly known as multituberculates, named for the multiple tubercles of their teeth) is an extinct order of rodent-like mammals with a fossil record spanning over 130 million years. They first appeared in the Middle Jurassic, ...

mammals known from teeth *

Metatherian Metatheria is a mammalian clade that includes all mammals more closely related to marsupials than to placentals. First proposed by Thomas Henry Huxley in 1880, it is a more inclusive group than the marsupials; it contains all marsupials as we ...

mammal known from tooth * Chelonia known from shell fragments.Dorr, J. A., 1985, Newfound Early Cretaceous dinosaurs and other fossils in southeastern Idaho and westernmost Wyoming. Contributions from the Museum of Paleontology, University of Michigan 27(3): 73-85. * Crocodylians known from teeth and partial skulls. * '' Oryctodromeus'' sp. known from numerous partial skeletons * Indeterminate ''

''-like iguanodontid known from teeth *

Hadrosaurid Hadrosaurids (), or duck-billed dinosaurs, are members of the ornithischian family Hadrosauridae. This group is known as the duck-billed dinosaurs for the flat duck-bill appearance of the bones in their snouts. The ornithopod family, which incl ...

known from teeth *

Ornithopoda Ornithopoda () is a clade of ornithischian dinosaurs, called ornithopods (), that started out as small, bipedal running grazers and grew in size and numbers until they became one of the most successful groups of herbivores in the Cretaceous wor ...

indet.known from isolated skeletal elements *

Ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

, probably

nodosaurid Nodosauridae is a family of ankylosaurian dinosaurs, from the Late Jurassic to the Late Cretaceous period in what is now North America, South America, Europe, and Asia. Description Nodosaurids, like their close relatives the ankylosaurids, w ...

known from partial skeleton and isolated elements.Weishampel, David B; et al. (2004). "Dinosaur distribution (Early Cretaceous, North America)." In: Weishampel, David B.; Dodson, Peter; and Osmólska, Halszka (eds.): The Dinosauria, 2nd, Berkeley: University of California Press. Pp. 553-556. . * Neoceratopsia indet. known from associated elements * Dromaeosaurs known from isolated teeth *

Tyrannosauroid Tyrannosauroidea (meaning 'tyrant lizard forms') is a superfamily (or clade) of coelurosaurian theropod dinosaurs that includes the family Tyrannosauridae as well as more basal relatives. Tyrannosauroids lived on the Laurasian supercontinent ...

known from an isolated tooth * Tyrannosauroid similar to ''Moros'' and ''

Suskityrannus ''Suskityrannus'' (meaning "coyote tyrant", ''suski'' meaning "coyote" in Zuni) is a genus of small tyrannosauroid theropod from the Late Cretaceous in southern Laramidia. It contains a single species, ''Suskityrannus hazelae,'' believed to h ...

'', known from the proximal half of a femur * Possible neovenatorid allosauroid known from an isolated juvenile vertebra * Unknown small theropods known from isolated bones and teeth * Giant

known from eggs and abundant eggshell of ''

carleylei''.Simon, J. D. 2014. Giant dinosaur (theropod) eggs of the oogenus Macroelongatoolithus (Elongatoolithidae) from southeastern Idaho: Taxonomic, paleobiogeographic, and reproductive implications (MS), Montana State University. * Large ''

Allosaurus ''Allosaurus'' () is a genus of large carnosaurian theropod dinosaur that lived 155 to 145 million years ago during the Late Jurassic epoch ( Kimmeridgian to late Tithonian). The name "''Allosaurus''" means "different lizard" alludi ...

''-size theropod, possibly piscivorous, known from isolated teeth

Macroflora

* ''

Gleichenia ''Gleichenia'' is a genus of ferns. Its closest relative is the genus '' Stromatopteris'', restricted to New Caledonia. Species include: * '' Gleichenia abscida'' Rodway * '' Gleichenia alpina'' R.Br. * ''Gleichenia cryptocarpa'' * ''Gleichenia ...

'' * ''Anemia'' *

Angiospermae Flowering plants are plants that bear flowers and fruits, and form the clade Angiospermae (), commonly called angiosperms. They include all forbs (flowering plants without a woody stem), grasses and grass-like plants, a vast majority of broad- ...

unidet. * Coniferae unidet. Wayan foliage

Taphonomy

Taphonomic Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efrem ...

modes of the Wayan are distinct. Fossiliferous 'pods' of '' Oryctodromeus'' skeletons and skeletal elements, sometimes with more than one individual represented, are the most common occurrence of vertebrate skeletal remains. Degrees of association and articulation range from fully articulated individuals to articulated strings of vertebrae and articulate limbs associated with other elements. These '' Oryctodromeus'' remains exhibit no appreciable pre-burial taphonomic modifications such as weathering, abrasion, breakage, or tooth marks. This combination of observations suggests the possibility of burial of these animals within unrecognized burrows. Excluding eggshell, almost all other vertebrate remains known from the Wayan occur as isolated teeth and partial to complete bones found in high energy

lag and possible debris flow deposits. These remains exhibit a more typical range of

taphonomic Taphonomy is the study of how organisms decay and become fossilized or preserved in the paleontological record. The term ''taphonomy'' (from Greek , 'burial' and , 'law') was introduced to paleontology in 1940 by Soviet scientist Ivan Efrem ...

modification with varying degrees of abrasion and breakage typical of skeletal remains preserved in

deposits. The overall fossil assemblage of the Wayan and patterns of preservation suggest that surface processes on the Wayan floodplains were less conducive to preservation, with preservation typically occurring subsurface and in

channels.

References

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