Wahweap Formation
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The Wahweap Formation of the Grand Staircase–Escalante 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.
Age
The Wahweap formation is divided into four members, which are listed below with their respective ages:
- Last Chance Creek Member: 82.17-81.55 Ma
- Reynolds Point Member: 81.55-80.61 Ma
- Coyote Point Member: 80.61-79 Ma
- Pardner Canyon Member: 79-77.29 Ma
Paleobiota
Invertebrates
The Wahweap Formation shows a substantial amount of invertebrate activity ranging from fossilized insect burrows in petrified logs to various mollusks that characterize the shell beds. Large fossilized crabs 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.
Elasmobranchs
| Elasmobranchs of the Wahweap Formation | ||||||
|---|---|---|---|---|---|---|
| Taxon | Species | Locality | Member | Material | Notes | Images |
| Cantioscyllium | C. estesi | MNA Locality 705 MNA Locality 455-1 UMNH VP Locality 82 | MNA V10230-32, MNA V10384-85, MNA 10390, UMNH VP 18915-16, UMNH VP 18919; teeth | A nurse shark which inhabited freshwater. | Chiloscyllium griseum (grey bamboo shark)Hybodus hauffianus | |
| Chiloscyllium | C. missouriense | UMNH VP Locality 77 MNA Locality 455-1 | MNA V10386, UMNH VP 18880, UMNH VP 18882, UMMNH VP 18886, UMNH VP 18887, UMNH VP 18888; teeth | A bamboo shark which inhabited freshwater. One specimen is similar to Restesia americana. | ||
| Columbusia | C. deblieuxi | UMNH VP Locality 77 | UMNH VP 18877, UMNH VP 18879, UMNH VP 18836, UMNH VP 18876, UMNH VP 18878; teeth | A sclerorhynchid ray, closely related to Squatirhina. | ||
| Cristomylus | C. ciffelli | MNA Locality 456-1 UMNH VP Locality 77 UMNH VP Locality 82 | MNA V9531, MNA V9568, MNA V9600, UMNH VP 17393; symphysial teeth MNA V9502, MNA V9525, MNA V9569, MNA V9633, MNA V9635, MNA V9652, UMNH VP 17393, UMNH VP 17395, UMNH VP 17399, UMNH VP 17404; small teeth MNA V9593, MNA V9683, MNA V9686, UMNH VP 17401; large teeth | A small guitarfish, suited for handling hard-shelled prey. | ||
| Hybodus? | H. sp | MNA Locality 456-2 | MNA V10387; Tooth | A large hybodont shark reaching over 2 m (6.6 ft) in length. Normally a marine species but would enter freshwater environments | ||
| Lonchidion | L. sp. | UMNH VP Locality 82 | UMNH VP 18917; Tooth | Smaller than Lonchidon selachos. | ||
| Texatrygon | T. brycensis | UMNH VP Locality 77 UMNH VP Locality 82 | UMNH VP 18882-83; Rostral teeth UMNH VP 18836, UMNH VP 18885, UMNH VP 18889-94, UMNH VP 18920; Oral teeth UMNH VP 18918; denticle | A sawfish. |
Osteichthyes
| Osteichthyes of the Wahweap Formation | ||||||
|---|---|---|---|---|---|---|
| Taxon | Genus | Locality | Member | Material | Notes | Images |
| Lepidotes | Indeterminate | Teeth | A seminotiform fish, no extant relatives live today. | Albula vulpes (Bonefish) | ||
| Micropycnodon | M. sp. | MNA Locality 706-2 | MNA V10336; pharyngeal tooth | A pycnodontiform fish, adapted to crush its prey. | ||
| Paralbula | P. sp. | Teeth | A bonefish which is adapted to eating hard-shelled prey. | |||
| Polyodontidae | Indeterminate | MNA Locality 456-2 | MNA 10356; denticle | A paddlefish, very rare in the Wahweap Formation. |
Salamanders
| Lissamphibians of the Wahweap Formation | ||||||
|---|---|---|---|---|---|---|
| Taxon | Species | Locality | Member | Material | Notes | Images |
| Gen. nov. | sp. nov. | UMNH VP Locality 77 | UMNH VP 19209; trunk vertebra | Higher level relationships are uncertain. Similar to sirenids, but lacks sirenid synapomorphies. | ||
| Opisthotriton | O. sp. | UMNH VP Locality 130 | UMNH VP 19194-19198; atlantes UMNH VP 19199-19200; trunk vertebrae | A batrachosauroidid, a family of extinct aquatic salamanders. | ||
| Scapherpeton | S. sp. | UMNH VP Locality 77 | UMNH VP 19186; atlas | A scapherpetontid. |
Dinosaurs
Dinosaurs known from the Wahweap include at least 2 species of hadrosaur, at least two ceratopsians and at least one theropod.
| Dinosaurs of the Wahweap Formation | ||||||
|---|---|---|---|---|---|---|
| Taxon | Species | Locality | Member | Material | Notes | Images |
| Acristavus | A. gagslarsoni | "near the junction of Smokey Mountain Road and Right Hand Collet Canyon" | Upper part of Reynolds Point Member | UMNH VP 16607; "a partial articulated skull roof including lacrimals and entire braincase, and a single cervical vertebra" | A hadrosaurid closely related to Brachylophosaurus and Maiasaura. Also known from the Two Medicine Formation. | AcristavusAdelolophusBrachylophosaurusDiabloceratopsLythronaxMachairoceratops |
| Adelolophus | A. hutchisoni | UCMP V98173 | Lower part of Coyote Point Member | UCMP 152028; partial maxilla | A lambeosaurine hadrosaurid, possibly a parasaurolophin. | |
| Ankylosauridae | Indeterminate | Coyote Point Member | OMNH 21280 (in part), OMNH 21858, OMNH 24276; Teeth | |||
| Brachylophosaurus | Indeterminate | Death Ridge | Upper part of Coyote Point Member | UMNH VP 9548; "Partial limb bones and a partial maxilla" | Different from Acristavus. | |
| Centrosaurinae | Indeterminate | Nipple Butte | Upper part of Last Chance Creek Member | UMNH VP 16704; Partial skull | Originally referred to Diabloceratops, but is more derived, possibly a nasutoceratopsin. | |
| Centrosaurinae | Indeterminate | Pilot Knoll | Upper part of Last Chance Creek Member | UMNH VP 20600; "A partial braincase and a nearly complete parietosquamosal frill" | Also known as "Wahweap Centrosaurine A." Similar to Albertaceratops. | |
| Centrosaurinae | Indeterminate | Death Ridge | Upper part of Coyote Point Member | UMNH VP 9549; "Partial frill and some postcranial elements" | Also known as "Wahweap Centrosaurine C." Possibly has spikes similar to Styracosaurus. | |
| Diabloceratops | D. eatoni | 42Ka800V, south side of Last Chance Canyon | Middle part of Reynolds Point Member | UMNH VP 166999; "a skull preserving the entire left side of the skull and portions of the right side" | The older specimen from Nipple Butte may not belong to Diabloceratops. | |
| Lythronax | L. argestes | UMNH VP Locality 1501 | Lower part of Reynolds Point Member | UMNH VP 20200; partial skeleton | A tyrannosaurine | |
| Machairoceratops | M. cronusi | Star Seep | Coyote Point Member | UMNH VP 20550; partial skull | A centrosaurine closely related to Diabloceratops. Previously known as "Wahweap Centrosaurine B." | |
| Nodosauridae | Indeterminate | Last Chance Creek Member? Reynolds Point Member Coyote Point Member | OMNH 21280 (in part), OMNH 21992, OMNH 24278; Teeth UMNH VP 13981, UMNH VP 15664, UMNH VP 16408, UMNH VP 21207; osteoderms a cranium (lost) a partial skeleton | The skeleton was under excavation as of 2013. The cranium was only tentatively identified as a nodosaurid, but now can't be confirmed. | ||
| Pachycephalosauridae | Indeterminate | Clints Cove | Lower part of Reynolds Point Member | UMNH VP 11939; incomplete frontoparietal dome some isolated teeth | The dome doesn't preserve diagnostic features, so its affinity with other pachycephalosaurids is uncertain. | |
| Saurolophinae | Indeterminate | Reynolds Point Member | UMNH VP 21087; partial juvenile skeleton UMNH VP 13881; partial adult skeleton | Probably represents a new distinct taxon. |
Mammals
A fair number of mammals spanning the lower Campanian are known from the Wahweap as well, including at least 15 genera of multituberculates, cladotherians, marsupials, and placental insectivores.
Trace fossils
Trace fossils 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 maniraptoran dinosaur. The proximity indicates a case of probable active predation of the burrow inhabitants by the owners of the claw marks.