# Aguja Formation

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. 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 ago but also as recently as 68.5 million years ago. 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.

#### Ornithischians

Ornithischians of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes |
| Agujaceratops | A. mariscalensis | Texas | Lower Alto Shale | | Formerly considered a species of Chasmosaurus |
| Agujaceratops | A. mavericus | West Texas | Middle Alto Shale | | A chasmosaurine. |
| Angulomastacator | A. daviesi | Texas | Middle Alto Shale | A left maxilla. | A lambeosaurine. |
| Ankylosauridae | Indeterminate | Texas | Lower Alto Shale | Osteoderms, vertebrae & limb elements. | Remains of an ankylosaurid, possibly represents Euoplocephalus sp. |
| Aquilarhinus | A. palimentus | Texas | Middle Abajo Shale | Partial skeleton | Formerly referred to Kritosaurus and Gryposaurus. |
| Ceratopsidae genus & species indeterminate | Indeterminate | West Texas | Middle Abajo Shale | Ilia, sacral vertebra & sacral ribs. | May represent Agujaceratops, but undiagnostic. |
| Chasmosaurus | C. mariscalensis | Texas | | [Twelve] disarticulated skull (sic), postcrania, juvenile." | 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. |
| Edmontonia | E. sp | Texas | Lower Alto Shale | Osteoderm (TVP 45866-2) & skull (AMNH 3076). | A nodosaurid. |
| cf. Euoplocephalus | E. sp | Texas | Lower Alto Shale | Osteoderms, sacrum & vertebra (TL-05-14). | An ankylosaurid. |
| aff. Kritosaurus | K. navajovius | Texas | Upper Alto Shale | Two dentary teeth | Tooth crown morphology matches with Kritosaurus |
| Malefica | M. deckerti | Texas | Middle Alto Shale | A partial left maxilla. | Formerly referred to Kritosaurus. |
| Nodosauridae genus & species indeterminate | Indeterminate | West Texas | Middle Abajo Shale | Isolated & associated osteoderms. | Very similar to osteoderms of Invictarx. |
| Panoplosaurus | P. mirus | Texas | Lower Alto Shale | Osteoderm (TMM 45605-4). | A nodosaurid. |
| Saurolophinae | Indeterminate | Texas | Alto Shale | Various cranial and appendicular elements | Material from several localities previously referred to Kritosaurus but do not have its diagnostic features. |
| Saurolophinae | Indeterminate | Texas | Alto Shale | Various manual elements and vertebrae representing two individuals | Included in phylogenetic analyses as the "Big Bend OTU", most recently considered a kritosaurin |
| Stegoceras | S. sp. | West Texas | Middle Alto Shale | Frontal | A pachycephalosaur, represents a new unnamed species |
| Texacephale | T. langstoni | Texas | Lower Alto Shale | Two frontoparietal domes. | A pachycephalosaur. |
| Yehuecauhceratops | Y. mudei | Coahuila | | | A 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 |
| Avialae incertae sedis | | West Texas | Middle Abajo Shale | 4 teeth (TMM 45947-349, 350, 351). | A bird. |
| Chirostenotes | C. sp. | Texas | | Femur & manual ungual. | A caenagnathid |
| Dromaeosauridae genus & species indeterminate | Indeterminate | West Texas | Middle Abajo Shale | Pedal phalanges (TMM 45909-2, TMM 44066-4). | A dromaeosaur. |
| cf. Dromaeosaurus | Indeterminate | Texas | | | |
| Leptorhynchos | L. gaddisi | Texas | Lower Alto Shale | Dentaries, caudal vertebra & limb elements. | A caenagnathid |
| Ornithomimidae | New genus & species | West Texas | Middle Abajo Shale | Vertebrae, ischium & limb elements. | An unnamed species referred to informally as the 'Aguja ornithomimid'. |
| cf. Paronychodon | | West Texas | Middle Abajo Shale | 2 incomplete teeth (TMM 45947-362). | A maniraptoran. |
| Richardoestesia | R. cf. gilmorei | Texas | Low Upper Shale | Fragment of a small tooth. | A coelurosaur. |
| Richardoestesia | R. isosceles | Big Bend National Park, Texas | Low Upper Shale | Teeth. | A coelurosaur. |
| Saurornitholestes | S. cf. langstoni | Texas | Lower Alto Shale & Middle Abajo Shale | Teeth. | A dromaeosaur, Teeth can belong to different taxa. |
| Saurornitholestes | S. langstoni | Coahuila | | Teeth | A dromaeosaur, Teeth can belong to different taxa. |
| Saurornitholestes | Saurornitholestes sp. | Coahuila | | Teeth | A dromaeosaur, Teeth can belong to different taxa. |
| Theropoda incertae sedis | Morphotype A | West Texas | Alto Shale | 8 teeth. | Unserrated, recurved teeth. |
| Theropoda incertae sedis | Morphotype B | West Texas | Alto Shale | 5 tooth crowns. | Bi-serrated teeth. |
| Theropoda incertae sedis | Morphotype C | West Texas | Alto Shale | 7 teeth. | Finely serrated, distal plication only. |
| Theropoda incertae sedis | Morphotype D | West Texas | Alto Shale | 5 teeth. | Short, coarsely serrated distal plication. |
| Theropoda incertae sedis | Morphotype E | West Texas | Alto Shale | A tooth. | Strongly recurved, serrated distal plication. |
| Theropoda incertae sedis | Morphotype F | West Texas | Alto Shale | 2 tooth fragments. | Medium size, finely serrated plications. |
| cf. Troodon | Indeterminate | Texas | | | |
| Tyrannosauridae | Indeterminate | West Texas | Lower Alto Shale & Middle Abajo Shale | Isolated teeth & a handful of non-dental specimens. | Postcranial remains suggest a relatively small & gracile tyrannosaurid, considered a member of the Teratophoneini |

#### Sauropods

Indeterminate titanosaurid remains are known from the Upper Aguja Formation of Mexico.
Sauropods of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes | Images |
| Titanosauridae | Indeterminate | Chihuahua | | Four partial posterior caudal vertebrae & dorsal or sacrocaudal vertebra | A relatively massive titanosaurid. | |

#### Crocodylomorphs

Crocodylomorphs of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes |
| Crocodilia | Indeterminate | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Teeth. | A crocodilian. |
| Deinosuchus | D. riograndensis | Texas, Chihuahua, and Coahuila | Upper Shale | Multiple partial skulls & skeletons accounting for nearly the entire skeleton minus the tail. | A giant alligatoroid. |
| Deinosuchus | cf. D. sp. | West Texas | Middle Abajo Shale | Cervical osteoderm (TMM 44068-2). | An alligatoroid. |
| Goniopholididae | New genus & species | West Texas | Middle Abajo Shale | Partial skull & skeleton along with isolated osteoderms & teeth. | May pertain to Denazinosuchus or a related taxon. |
| Phobosuchus | P. riograndensis | Texas, Chihuahua, and Coahuila | | | Reclassified as a Deinosuchus species |

#### Turtles

Testudines of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes |
| Adocus | A. sp. | Big Bend National Park, Texas. | Upper Shale | Shell fragments. | An adocid. |
| Baenidae | | Big Bend National Park, Texas. | Upper Shale | Shell fragments. | 2 morphotypes present (A & B). |
| Basilemys | B. sp. | Big Bend National Park, Texas. | Upper Shale & Lower Shale | Shell fragments, partial plastron & leg scutes. | A nanhsiungchelyid. |
| Bothremydidae genus & species indeterminate | Indeterminate | West Texas | Lower Shale | Isolated peripheral bones (TMM 44068-1, 42452-8); costal bones (TMM 44064-6). | A bothremydid, compatible with Chupacabrachelys. |
| Chupacabrachelys | C. complexus | Big Bend, Texas. | Base of the Upper Shale | A complete skull, and a nearly complete skeleton. | A bothremydid. |
| cf. Denazinemys | cf. D. sp. | West Texas | Lower Shale | Shell elements. | A baenid. |
| cf. Helopanoplia | | Big Bend National Park, Texas. | Upper Shale | Shell fragments. | A softshell turtle. |
| cf. Hoplochelys | | Big Bend National Park, Texas. | Upper Shale | Shell fragments. | A kinosternoid. |
| Terlinguachelys | T. fischbecki | Big Bend National Park, Texas | Rattlesnake Mountain Sandstone | A large, incomplete specimen. | A protostegid. |
| Testudines indeterminate | Morphotype 1 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A shell fragment. | |
| Testudines indeterminate | Morphotype 2 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A shell fragment. | |
| Testudines indeterminate | Morphotype 3 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A shell fragment. | |
| Testudines indeterminate | Morphotype 4 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A shell fragment. | |
| Trionychidae | Gen. et. sp. indet. | Big Bend National Park, Texas. | Upper Shale & Lower Shale | Costal bone (TMM 44068-4) & shell fragments. | A softshell turtle. |

#### Lepidosaurs

Lepidosaurs of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes |
| Anguidae | Gen. et. sp. indet. | Texas. | | Isolated osteoderms & partial right frontal. | An anguid. |
| Apsgnathus | A. triptodon | Brewster County, Texas. | | Jaw elements. | A scincomorph. |
| Catactegenys | C. solaster | Brewster County, Texas. | | Jaw elements & teeth. | A night lizard. |
| Dryadissector | D. shilleri | West Texas. | Middle Abajo Shale | Numerous isolated teeth. | A varanoid. |
| Mosasauridae | Indeterminate | Ten Bits Ranch. | Rattlesnake Mountain sandstone member. | 1 partial vertebra. | A mosasaur. |
| Odaxosaurus | O. piger | Brewster County, Texas. | | Jaw elements. | An anguid. |
| cf. Parasaniwa | cf. P. wyomingensis | Texas. | | Jaw fragments. | A platynotan. |
| Platynota | Gen. et. sp. indet. | Texas. | | Dorsal vertebra (TMM 43057-332). | A platynotan. |
| ?Scincidae | Gen. et. sp. indet. | Brewster County, Texas. | | Jaw elements. | A possible skink. |
| cf. Scincomorpha | Gen. et. sp. indet. | Brewster County, Texas. | | Jaw elements. | A scincomorph. |
| Serpentes | Gen. et. sp. indet. | Texas. | | Partial left dentary & right maxilla. | A snake. |
| cf. Xenosauridae | | Texas. | | Osteoderms & maxillae. | A knob-scaled lizard. |

### Mammals

Mammals of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes | Images |
| Alphadon | A. perexiguus | Brewster County, Texas | Upper Shale | | A metatherian. | |
| Paleomolops | P. langstoni | Brewster County, Texas | Upper Shale | | A 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.
Bony fish of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes |
| Acanthomorpha indet. | family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | An acanthomorph. |
| Acanthopterygii indet. | order indet. family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | An acanthopterygian. |
| Acanthopterygii indet. | Acanthopterygian fin spine morph 1 | Lowerverse, west Texas | Lower Shale | Fin spines | An acanthopterygian. |
| Acanthopterygii indet. | Acanthopterygian fin spine morph 2 | Lowerverse, west Texas | Lower Shale | Fin spines | An acanthopterygian. |
| Acanthopterygii indet. | Acanthopterygian fin spine morph 3 | Lowerverse, west Texas | Lower Shale | Fin spines | An acanthopterygian. |
| Acanthopterygii indet. | Acanthopterygian fin spine morph 4 | Lowerverse, west Texas | Lower Shale | Fin spines | An acanthopterygian. |
| Acanthopterygii indet. | Euacanthopterygian fin spine morph 1 | Lowerverse, west Texas | Lower Shale | Fin spines | An acanthopterygian. |
| Acanthopterygii indet. | Euacanthopterygian fin spine morph 2 | Lowerverse, west Texas | Lower Shale | Fin spines | An acanthopterygian. |
| Albula | A. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Over 390 complete and fragmentary teeth. | A bonefish. |
| Albula | A. sp. | Lowerverse, west Texas | Lower Shale | Over 390 complete and fragmentary teeth. | A bonefish. |
| Amiidae indet. | genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | An amiid. |
| ?Anomoeodus | ?A. sp. | Lowerverse, west Texas | Lower Shale | Isolated tooth crown | A pycnodont. Likely transported out of a marine habitat. |
| Atractosteus | A. sp. | Lowerverse, west Texas | Lower Shale | Teeth, jaw fragments, vertebral centra, scales. | A gar. |
| Clupeiformes indet. | family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | A clupeiform. |
| cf. Cyclurus | cf. C. sp. | Lowerverse, west Texas | Lower Shale | 5 fragmentary tooth plates with teeth. | An amiid. |
| Ellimmichthyiformes indet. | family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | An ellimmichthyiform. |
| Elopiformes indet. | family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra | An elopiform. |
| ?Enchodus | ?E. sp. | Ten Bits ranch, west Texas. | Rattlesnake Mountain sandstone member. | 2 abraded teeth. | An aulopiform. |
| ?Enchodus | ?E. sp. | Lowerverse, west Texas | Lower Shale | 4 isolated teeth. | An aulopiform. |
| Eotexachara | E. malateres | Lowerverse, west Texas | Lower Shale | Dentaries. | A characiform. |
| ?Gonorynchiformes indet. | family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Cranial bone, vertebral centrum, basibranchial. | A gonorynchiform. |
| Hiodontidae indet. | genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | A hiodontiform. |
| Lepidotes | ?L. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Approximately 109 complete and fragmentary teeth. | A lepidotid. |
| cf. Melvius | cf. M. sp. | Lowerverse, west Texas | Lower Shale | Vertebrae, 13 isolated teeth. | An amiid. |
| Micropycnodon | M. sp. | Lowerverse, west Texas | Lower Shale | 4 isolated teeth | A pycnodont. Likely transported out of a marine habitat. |
| Osteichthyes indet. | Indeterminate species A | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 11 complete teeth. | A bony fish. |
| Osteichthyes indet. | Indeterminate species B | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 8 complete and fragmentary teeth. | A bony fish. |
| Osteichthyes indet. | Indeterminate species C | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 1 complete tooth. | A bony fish. |
| Osteichthyes indet. | Indeterminate species D | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 1 complete and 1 partial tooth. | A bony fish. |
| Osteichthyes indet. | Indeterminate | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Approximately 475 complete and fragmentary teleost centra. | A bony fish. |
| Osteichthyes indet. | Tooth morph 1 | Lowerverse, west Texas | Lower Shale | Teeth | A bony fish. |
| Osteichthyes indet. | Tooth morph 2 | Lowerverse, west Texas | Lower Shale | Teeth | A bony fish. |
| Osteichthyes indet. | Centrum morph 1 | Lowerverse, west Texas | Lower Shale | Vertebral centra. | A bony fish. |
| Osteichthyes indet. | Centrum morph 2 | Lowerverse, west Texas | Lower Shale | Vertebral centra. | A bony fish. |
| Osteichthyes indet. | Centrum morph 3 | Lowerverse, west Texas | Lower Shale | Vertebral centra. | A bony fish. |
| Osteichthyes indet. | Centrum morph 4 | Lowerverse, west Texas | Lower Shale | Vertebral centra. | A bony fish. |
| Ostariophysi indet. | order indet. family indet. genus et sp. indet. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | An ostariophysian. |
| Paralbula | P. cf. casei | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Approximately 900 complete and fragmentary teeth and tooth caps. | A bonefish. Lowerverse specimens likely transported out of a marine habitat. |
| Paralbula | P. cf. casei | Lowerverse, west Texas | Lower Shale | Approximately 900 complete and fragmentary teeth and tooth caps. | A bonefish. Lowerverse specimens likely transported out of a marine habitat. |
| Primuluchara | P. laramidensis | Lowerverse, west Texas | Lower Shale | Dentaries. | A characiform. |
| Stephanodus | ?S. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 21 whole and fragmentary specimens. | A pycnodont. |
| ?Wilsonichthys | ?W. sp. | Lowerverse, west Texas | Lower Shale | Vertebral centra. | An osteoglossiform. |

### Cartilaginous fish

Cartilaginous fish of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes |
| Brachyrhyzodus | B. wichitaensis | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 11 complete teeth. | |
| Cantioscyllium | C. aff. meyeri | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 1 anterior tooth and 5 lateral teeth. | A nurse shark. |
| Chiloscyllium | C. aff. greeni | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Approximately 90 abraded and fragmentary teeth. | A bamboo shark. |
| Chondrichthyes | | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 23 placoid scales and 69 dermal scales. | 4 morphotypes of placoid scales (A to D) present. |
| Columbusia | C. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 20 complete & fragmentary teeth. | A wobbegong. |
| Cretalamna | C. appendiculata | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 3 fragmentary teeth. | Reassigned to C. cf. C. sarcoportheta. |
| Cretalamna | C. cf. C. sarcoportheta | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 3 incomplete teeth & fragments of additional teeth. | Originally reported as C. appendiculata. |
| Cretorectolobus | C. olsoni | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | "20 complete and fragmentary teeth". | A carpet shark. |
| Hybodontidae genus & species indeterminate | Indeterminate | West Texas | Lower Shale | Fragment of a dorsal fin spine (TMM 42536-10). | A hybodont. |
| Hybodus | H. sp. | Ten Bits Ranch. | Rattlesnake Mountain sandstone member. | 2 specimens, one complete and one partial tooth. | A hybodont. |
| Igdabatis | I. indicus? | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A single incomplete tooth. | A myliobatid. |
| Ischyrhiza | I. cf. avonicola | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 5 complete and fragmentary rostral teeth. | A sawskate. |
| Ischyrhiza | I. mira | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 11 fragmentary rostral teeth and 230 whole and fragmentary oral teeth. | A sawskate. |
| Lonchidion | L. selachos | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 4 complete and 5 fragmentary teeth. | A hybodont. |
| Meristodon | M. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 2 teeth. | A hybodont. |
| Myliobatiformes | Incertae sedis | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 3 complete specimens. | |
| Protoplatyrhina | P. renae | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 70 complete and fragmentary teeth. | A hypsobatid. |
| Ptychotrygon | P. agujaensis | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Over 690 complete and fragmentary teeth. | A sawskate. |
| Ptychotrygon | P. triangularis | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Over 170 complete and fragmentary teeth. | A sawskate. |
| Ptychotrygon | P. aff. cuspidata | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 7 whole and fragmentary teeth. | A sawskate. |
| Ptychotrygon | P. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | One complete tooth (TMM 46018-71). | A sawskate. |
| Rhinobatos | R. casieri | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | "14 complete and fragmentary specimens". | A guitarfish. |
| Rhinobatos | R. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 18 complete & fragmentary specimens. | A guitarfish. |
| Rhombodus | R. levis | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Over 22 complete and fragmentary teeth. | A rajiforme. |
| Scapanorhynchus | S. texanus | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | Over 800 complete and fragmentary teeth. | A mitsukurinid. |
| Sclerorhynchidae | Morphotype 1 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | One fragmentary rostral spine (TMM 46018-59). | A sawskate. |
| Sclerorhynchidae | Morphotype 2 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | One fragmentary rostral spine (TMM 46018-60). | A sawskate. |
| Sclerorhynchidae | Morphotype 3 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 3 fragmentary rostral teeth. | A sawskate. |
| Sclerorhynchidae | Morphotype 4 | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 27 fragmentary rostral spines. | A sawskate. |
| Serratolamna | S. cf. S. caraibaea | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | About 34 teeth. | A mackerel shark. |
| Squalicorax | S. kaupi | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | "26 complete and fragmentary anterior and lateral teeth". | An anacoracid. |
| Squalicorax | S. aff. S. lindstromi | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 4 specimens. | An anacoracid. |
| Squalicorax | S. pristodontus | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 2 specimens. | An anacoracid. |
| Squalicorax | S. aff. S. yangaensis | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 4 complete & several fragmentary teeth. | An anacoracid. |
| Squatina | S. hassei | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A single complete specimen. | An angelshark. |
| Squatina | S. sp. | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | A complete tooth & 2 fragmentary teeth. | An angelshark. |
| Texatrygon | T. cf. T. copei | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 4 complete & fragmentary teeth. | A sawskate formerly reported as T. hooveri. |
| Texatrygon | T. hooveri | Ten Bits Ranch, west Texas. | Rattlesnake Mountain sandstone member. | 4 complete and fragmentary specimens. | Reassigned to T. cf. T. copei. |

### Invertebrates
#### Ammonites

Ammonites of the Aguja Formation :
| Genus | Species | Member |
| Baculites | B. mclearni | Rattlesnake Mountain Sandstone Terlingua Creek Sandstone |
| Hoplitoplacenticeras | H. plasticum | Rattlesnake Mountain Sandstone |
| Pachydiscus | P. paulsoni | Rattlesnake Mountain Sandstone |

### Plants

Plants of the Aguja Formation :
| Genus | Species | Location | Member | Material | Notes | Images |
| Sabal | S. bigbendense | Big Bend National Park, Texas. | Upper Shale | 4 seeds. | A palm. It has the largest seeds of any fossil Sabal. | |
| Sabal | S. bracknellense | Big Bend National Park, Texas. | Upper Shale | 5 seeds. | A palm. The seeds are indistinguishable from those of Eocene S. bracknellense, and so were assigned to that species. However, it is likely these Aguja palms would be found to represent distinct species if other parts of the plants were available for comparison. | |
| Color key Taxon Reclassified taxon Taxon falsely reported as present Dubious taxon or junior synonym Ichnotaxon Ootaxon Morphotaxon | Notes Uncertain or tentative taxa are in small text; crossed out taxa are discredited. |