The Aguja Formation is a geological formation in North America, exposed in Texas, United States and Chihuahua and Coahuila in Mexico, whose strata date back to the Late Cretaceous. 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 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, more primitive than an unnamed chasmosaurine from the De-na-zin Member of the Kirtland Formation, 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
Reptiles 2 fragmentary caudal vertebrae of indeterminate reptiles are known from the Rattlesnake Mountain sandstone member. Montellano-Ballesteros (2003) and Rivera-Sylva et al. (2006) reported indeterminate titanosaur fossils of Mexico as specimens from the upper portion of the Aguja Formation, but D'Emic et al. (2010) questioned the titanosaurian identity of the fossils reported by Montellano-Ballesteros (2003), and Rivera-Sylva and Carpenter (2014) suggested that all of the purported Aguja Formation titanosaur fossils are actually recovered from the lower portion of the Maastrichtian-aged Javelina Formation.
Ornithischians Ornithischians of the Aguja Formation Genus Species Location Member Material Notes ImagesAgujaceratopsA. mariscalensisTexasLower Alto ShaleFormerly considered a species of ChasmosaurusA. mavericusWest TexasMiddle Alto ShaleA chasmosaurine.AngulomastacatorA. daviesiTexasMiddle Alto ShaleA left maxilla.A lambeosaurine.AnkylosauridaeIndeterminateTexasLower Alto ShaleOsteoderms, vertebrae & limb elements.Remains of an ankylosaurid, possibly represents Euoplocephalus sp.AquilarhinusListed as ?Gryposaurus sp. in "Dinosaur distribution (Late Cretaceous; North America; Texas)." Weishampel, et al. (2004). Page 582.A. palimentusTexasMiddle Abajo ShalePartial skeletonFormerly referred to Kritosaurus and Gryposaurus.Ceratopsidae genus & species indeterminateIndeterminateWest TexasMiddle Abajo ShaleIlia, sacral vertebra & sacral ribs.May represent Agujaceratops, but undiagnostic.Chasmosaurus"Dinosaur distribution (Texas and Chihuahua)." Weishampel, et al. (2004). Page 582 and 588.C. mariscalensis Texas [Twelve] disarticulated skull (sic), postcrania, juvenile.""Table 23.1," in Weishampel, et al. (2004). Page 496.Considered by paleontologists Lucas, Sullivan, and Hunt to be distinct enough from the Chasmosaurus type species, C. belli to warrant being split off to a new genus, Agujaceratops.EdmontoniaE. spListed as Edmontonia cf. rugosidens in "Dinosaur distribution (Late Cretaceous; North America; Texas).", Weishampel et al., 2004, p.582TexasLower Alto ShaleOsteoderm (TVP 45866-2) & skull (AMNH 3076).A nodosaurid.cf. EuoplocephalusE. spTexasLower Alto ShaleOsteoderms, sacrum & vertebra (TL-05-14).An ankylosaurid.aff. KritosaurusK. navajoviusTexasUpper Alto ShaleTwo dentary teethTooth crown morphology matches with KritosaurusMaleficaM. deckertiTexasMiddle Alto ShaleA partial left maxilla.Formerly referred to Kritosaurus.Nodosauridae genus & species indeterminateIndeterminateWest TexasMiddle Abajo ShaleIsolated & associated osteoderms.Very similar to osteoderms of Invictarx.PanoplosaurusP. mirusTexasLower Alto Shale Osteoderm (TMM 45605-4).A nodosaurid.SaurolophinaeIndeterminateTexasAlto ShaleVarious cranial and appendicular elementsMaterial from several localities previously referred to Kritosaurus but do not have its diagnostic features.SaurolophinaeIndeterminateTexasAlto ShaleVarious manual elements and vertebrae representing two individualsIncluded in phylogenetic analyses as the "Big Bend OTU", most recently considered a kritosaurinStegocerasS. sp.West TexasMiddle Alto ShaleFrontalA pachycephalosaur, represents a new unnamed speciesTexacephaleT. langstoniTexasLower Alto ShaleTwo frontoparietal domes.A pachycephalosaur.YehuecauhceratopsY. mudeiCoahuilaA centrosaurine.
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.
Theropods of the Aguja Formation Genus Species Location Member Material Notes ImagesAvialae incertae sedisWest TexasMiddle Abajo Shale4 teeth (TMM 45947-349, 350, 351).A bird.ChirostenotesC. sp.TexasFemur & manual ungual.A caenagnathidDromaeosauridae genus & species indeterminateIndeterminateWest TexasMiddle Abajo ShalePedal phalanges (TMM 45909-2, TMM 44066-4).A dromaeosaur.cf. DromaeosaurusListed as cf. Dromaeosaurus sp. in "Dinosaur distribution (Late Cretaceous; North America; Texas)." Weishampel, et al. (2004). Page 582.IndeterminateTexas"Dinosaur distribution (Late Cretaceous; North America; Texas)." Weishampel, et al. (2004). Page 582.LeptorhynchosL. gaddisiTexasLower Alto ShaleDentaries, caudal vertebra & limb elements.A caenagnathidOrnithomimidaeNew genus & speciesWest TexasMiddle Abajo ShaleVertebrae, ischium & limb elements.An unnamed species referred to informally as the 'Aguja ornithomimid'.cf. ParonychodonWest TexasMiddle Abajo Shale2 incomplete teeth (TMM 45947-362).A maniraptoran. Richardoestesia R. cf. gilmoreiTexasLow Upper ShaleFragment of a small tooth.A coelurosaur.R. isoscelesBig Bend National Park, TexasLow Upper ShaleTeeth.A coelurosaur.SaurornitholestesS. cf. langstoniTexasLower Alto Shale & Middle Abajo ShaleTeeth.A dromaeosaur.SaurornitholestinaeInderteminateCoahuila Teeth and Teeth fragment A dromaeosaur. Theropoda incertae sedisMorphotype AWest TexasAlto Shale8 teeth.Unserrated, recurved teeth.Morphotype BWest Texas5 tooth crowns.Bi-serrated teeth.Morphotype CWest Texas7 teeth.Finely serrated, distal plication only.Morphotype DWest Texas5 teeth.Short, coarsely serrated distal plication.Morphotype EWest TexasA tooth.Strongly recurved, serrated distal plication.Morphotype FWest Texas2 tooth fragments.Medium size, finely serrated plications.cf. TroodonListed as cf. Troodon sp. in "Dinosaur distribution (Late Cretaceous; North America; Texas)." Weishampel, et al. (2004). Page 582.IndeterminateTexasTyrannosauridaeIndeterminateWest TexasLower Alto Shale & Middle Abajo ShaleIsolated teeth & a handful of non-dental specimens.Postcranial remains suggest a relatively small & gracile tyrannosaurid, considered a member of the Teratophoneini
Crocodylomorphs Crocodylomorphs of the Aguja Formation Genus Species Location Member Material Notes ImagesCrocodiliaIndeterminateTen Bits Ranch, west Texas.Rattlesnake Mountain sandstone member.Teeth.A crocodilian.Deinosuchus"Aguja Formation (Upper Shale Member), Big Bend Region, Texas," in Sullivan and Lucas (2006). Page 16.D. riograndensisTexas, Chihuahua, and CoahuilaUpper ShaleMultiple partial skulls & skeletons accounting for nearly the entire skeleton minus the tail.A giant alligatoroid.cf. D. sp.West TexasMiddle Abajo ShaleCervical osteoderm (TMM 44068-2).An alligatoroid.GoniopholididaeNew genus & speciesWest TexasMiddle Abajo ShalePartial skull & skeleton along with isolated osteoderms & teeth.May pertain to Denazinosuchus or a related taxon.PhobosuchusP. riograndensisTexas, Chihuahua, and CoahuilaReclassified as a Deinosuchus species
Turtles Testudines of the Aguja Formation Genus Species Location Member Material Notes ImagesAdocusA. sp.Big Bend National Park, Texas.Upper ShaleShell fragments.An adocid.cf. AspideretoidesBig Bend National Park, TexasUpper ShaleA softshell turtleBaenidaeBig Bend National Park, Texas.Upper ShaleShell fragments.2 morphotypes present (A & B).BasilemysB. sp.Big Bend National Park, Texas.Upper Shale & Lower ShaleShell fragments, partial plastron & leg scutes.A nanhsiungchelyid.Bothremydidae genus & species indeterminateIndeterminateWest TexasLower ShaleIsolated peripheral bones (TMM 44068-1, 42452-8); costal bones (TMM 44064-6).A bothremydid, compatible with Chupacabrachelys.ChupacabrachelysC. complexusBig Bend, Texas.Base of the Upper ShaleA complete skull, and a nearly complete skeleton.A bothremydid.DenazinemysD. nodosaWest TexasLower ShaleShell elements.A baenid.cf. HelopanopliaBig Bend National Park, Texas.Upper ShaleShell fragments.A softshell turtle.cf. HoplochelysBig Bend National Park, Texas.Upper ShaleShell fragments.A kinosternoid.NeurankylusN. baueriWest TexasLower ShaleA baenidTerlinguachelysT. fischbeckiBig Bend National Park, TexasRattlesnake Mountain SandstoneA large, incomplete specimen.A protostegid.ThescelusT. rapiensWest TexasLower Shale A baenidTestudines indeterminateMorphotype 1Ten Bits Ranch, west Texas.Rattlesnake Mountain sandstone member.A shell fragment.Morphotype 2Ten Bits Ranch, west Texas.Rattlesnake Mountain sandstone member.A shell fragment.Morphotype 3Ten Bits Ranch, west Texas.Rattlesnake Mountain sandstone member.A shell fragment.Morphotype 4Ten Bits Ranch, west Texas.Rattlesnake Mountain sandstone member.A shell fragment.TrionychidaeGen. et. sp. indet.Big Bend National Park, Texas.Upper Shale & Lower ShaleCostal bone (TMM 44068-4) & shell fragments.A softshell turtle.
Lepidosaurs Lepidosaurs of the Aguja Formation Genus Species Location Member Material Notes ImagesAnguidaeGen. et. sp. indet.Texas.Isolated osteoderms & partial right frontal.An anguid.ApsgnathusA. triptodonBrewster County, Texas.Jaw elements.A scincomorph.CatactegenysC. solasterBrewster County, Texas.Jaw elements & teeth.A night lizard.DryadissectorD. shilleriWest Texas.Middle Abajo ShaleNumerous isolated teeth.A varanoid.MosasauridaeIndeterminateTen Bits Ranch.Rattlesnake Mountain sandstone member.1 partial vertebra.A mosasaur.OdaxosaurusO. pigerBrewster County, Texas.Jaw elements.An anguid.cf. Parasaniwacf. P. wyomingensisTexas.Jaw fragments.A platynotan.PlatynotaGen. et. sp. indet.Texas.Dorsal vertebra (TMM 43057-332).A platynotan.?ScincidaeGen. et. sp. indet.Brewster County, Texas.Jaw elements.A possible skink.cf. ScincomorphaGen. et. sp. indet.Brewster County, Texas.Jaw elements.A scincomorph.SerpentesGen. et. sp. indet.Texas.Partial left dentary & right maxilla.A snake.cf. XenosauridaeTexas.Osteoderms & maxillae.A knob-scaled lizard.
Mammals Mammals of the Aguja Formation Genus Species Location MemberMaterial Notes ImagesAlphadonA. perexiguusBrewster County, TexasUpper ShaleA metatherian.PaleomolopsP. langstoniBrewster County, TexasUpper ShaleA tribosphenidan; "cannot be confidently allied with either marsupials or eutherians".
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 coprolites are known from the Rattlesnake Mountain sandstone member, presumably from bony fish.