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

Texas Texas ( , ; or ) is the most populous U.S. state, state in the South Central United States, South Central region of the United States. It borders Louisiana to the east, Arkansas to the northeast, Oklahoma to the north, New Mexico to the we ...

, United States and Chihuahua and

Coahuila Coahuila, formally Coahuila de Zaragoza, officially the Free and Sovereign State of Coahuila de Zaragoza, is one of the 31 states of Mexico. The largest city and State Capital is the city of Saltillo; the second largest is Torreón and the thi ...

in Mexico, whose strata date back to the

Late Cretaceous The Late Cretaceous (100.5–66 Ma) is the more recent 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 ''cre ...

. 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 Alto 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 Alto 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 ''Bravocer ...

,'' more primitive than an unnamed chasmosaurine from the De-na-zin Member of the

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

, in the lowermost section of the formation. The age of the La Basa Sandstone is constrained by the presence of '' Scaphites hippocrepis'' III in the overlying Pen Formation which has been dated as old as 81.53 Ma.

Paleofauna

Hadrosaur bone in the Aguja Formation by Nick Longrich

Reptiles

2 fragmentary caudal vertebrae of indeterminate

reptile Reptiles, as commonly defined, are a group of tetrapods with an ectothermic metabolism and Amniotic egg, amniotic development. Living traditional reptiles comprise four Order (biology), orders: Testudines, Crocodilia, Squamata, and Rhynchocepha ...

s are known from the Rattlesnake Mountain sandstone member.

Ornithischians

Theropods

Indeterminate ornithomimid remains are known from the Upper Aguja Formation. Indeterminate tyrannosaurid fossils are known from the Upper Aguja Formation of Texas and Mexico.

Sauropods

Indeterminate titanosaurid remains are known from the Upper Aguja Formation of Mexico.Montellano-Ballesteros, M. 2003.

"

Crocodylomorphs

Turtles

Lepidosaurs

Mammals

Bony fish

A diversity of bony fish, comprising both marine (Ten Bits/Rattlesnake Mountain locality) and freshwater (Lowerverse/Lower Shale locality) taxa, is known. Approximately 75 whole and broken fragments of

coprolite A coprolite (also known as a coprolith) is fossilized feces. Coprolites are classified as trace fossils as opposed to body fossils, as they give evidence for the animal's behaviour (in this case, diet) rather than morphology. The name ...

s are known from the Rattlesnake Mountain sandstone member, presumably from bony fish.

Cartilaginous fish

Invertebrates

Ammonites

Plants

References

Bibliography

* * {{Portal bar, Earth sciences, Paleontology, Dinosaurs Geologic formations of Texas Cretaceous geology of Texas Geologic formations of Mexico Cretaceous Mexico Campanian Stage Sandstone formations Conglomerate formations of the United States Shale formations Deltaic deposits Lacustrine deposits Tidal deposits Paleontology in Mexico Paleontology in Texas Formations Formations Conglomerate formations of Mexico

Age