The Aguja Formation is a geological formation in North America, exposed in

Texas Texas (, ; Spanish: ''Texas'', ''Tejas'') is a state in the South Central region of the United States. At 268,596 square miles (695,662 km2), and with more than 29.1 million residents in 2020, it is the second-largest U.S. state by ...

, United States and Chihuahua and Coahuila in Mexico, whose strata date back to the

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 remains are among the fossils that have been recovered from the formation.Weishampel et al., 2004, "Dinosaur distribution (Late Cretaceous, North America).", pp.574-588 Fossil palms have also been unearthed here.

Age

The ages of the Aguja Formation and its primary fossil-bearing unit, the Upper Shale, are not well understood. Due to the presence of the ammonite ''Baculites mclearni'', which only occurs from 80.67 - 80.21 Ma, in the underlying Rattlesnake Mountain Sandstone and the Terlingua Creek Sandstone, it is likely that the Upper Shale was younger than 80.2 Ma. A radiometric date of 76.9 Ma was recovered in the Upper Shale, making it likely the formation wasn't younger than 76.9 Ma. The contact with the overlying Javelina Formation has been estimated at about 70 Ma agoWoodward, H. N. (2005). Bone histology of the sauropod dinosaur Alamosaurus sanjuanensis from the Javelina Formation, Big Bend National Park, Texas. but also as recently as 68.5 million years ago.Sankey, J. (2010). Faunal composition and significance of high–diversity, mixed bonebeds containing ''Agujaceratops mariscalensis'' and other dinosaurs, Aguja Formation (Upper Cretaceous), Big Bend, Texas. In New Perspectives on Horned Dinosaurs: The Royal Tyrrell Museum Ceratopsian Symposium (pp. 520-537). This is unlikely, however, due to the presence of ''

Bravoceratops ''Bravoceratops'' is a genus of large chasmosaurine ceratopsid dinosaur that lived approximately 70 million years ago, and is known from the Late Cretaceous Javelina Formation in what is now Texas, United States. Discovery and naming ''Bravoc ...

,'' more primitive than an unnamed

chasmosaurine Chasmosaurinae is a subfamily of ceratopsid dinosaurs. They were one of the most successful groups of herbivores of their time. Chasmosaurines appeared in the early Campanian, and became extinct, along with all other non- avian dinosaurs, durin ...

from the De-na-zin Member of the

Kirtland Formation The Kirtland Formation (originally the Kirtland Shale) is a sedimentary geological formation. Description The Kirtland Formation is the product of alluvial muds and overbank sand deposits from the many channels draining the coastal plain th ...

, in the lowermost section of the formation. The age of the Basal Sandstone is constrained by the presence of ''

Scaphites hippocrepis ''Scaphites'' is a genus of heteromorph ammonites belonging to the Scaphitidae family. They were a widespread genus that thrived during the Late Cretaceous period. Morphology ''Scaphites'' generally have a chambered, boat-shaped shell. The ini ...

'' III in the overlying Pen Formation which has been dated as old as 81.53 Ma.

Vertebrate paleofauna

Hadrosaur bone in the Aguja Formation by Nick Longrich

Reptiles

2 fragmentary caudal vertebrae of indeterminate reptiles are known from the Rattlesnake Mountain sandstone member.

Pseudosuchians

Ornithischians

Theropods

Indeterminate ornithomimid remains are known from the Upper Aguja Formation.Sullivan, 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
" New Mexico Museum of Natural History and Science, Bulletin 35:7-29. Indeterminate tyrannosaurid fossils are known from the Upper Aguja Formation of Texas and Mexico.

Lepidosaurs

Turtles

Bony Fish

Approximately 75 whole and broken fragments of coprolites are known from the Rattlesnake Mountain sandstone member, presumably from bony fish.

Cartilaginous fish

Invertebrates

Ammonites

References

Bibliography

* * Longrich, N.R., Sankey, J., and Tanke, D. (2010) ''Texacephale langstoni'', a new genus of pachycephalosaurid (Dinosauria: Ornithischia) from the upper Campanian Aguja Formation, southern Texas, USA. Cretaceous Research. . * Sullivan, 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
" New Mexico Museum of Natural History and Science, Bulletin 35:7-29. * Spencer G. Lucas, Robert M. Sullivan and Adrian P. Hunt: ''Re-evaluation of ''Pentaceratops'' and ''Chasmosaurus'' (Ornithischia: Ceratopsidae) in the Upper Cretaceous of the Western Interior.'' In: New Mexico Museum of Natural History and Science Bulletin 35 (2006), S. 367-37
PDF
* * {{Portal bar, Earth sciences, Paleontology, Dinosaurs, Cretaceous Geologic formations of Texas Cretaceous geology of Texas Geologic formations of Mexico Cretaceous Mexico Campanian Stage Sandstone formations Conglomerate formations Shale formations Deltaic deposits Lacustrine deposits Tidal deposits Paleontology in Mexico Paleontology in Texas Formations Formations

Age