Reeve's Bonebed is a geological formation in Presidio County, Texas

Texas

Texas is the second largest U.S. state by both area and population, and the largest state by area in the contiguous United States.The name, based on the Caddo word "Tejas" meaning "friends" or "allies", was applied by the Spanish to the Caddo themselves and to the region of their settlement in...

, with the coordinates of 29.9° N, 104.2° W. It consists of fossiliferous sedimentary rock

Sedimentary rock

Sedimentary rock are types of rock that are formed by the deposition of material at the Earth's surface and within bodies of water. Sedimentation is the collective name for processes that cause mineral and/or organic particles to settle and accumulate or minerals to precipitate from a solution....

 dating from the late Eocene

Eocene

The Eocene Epoch, lasting from about 56 to 34 million years ago , is a major division of the geologic timescale and the second epoch of the Paleogene Period in the Cenozoic Era. The Eocene spans the time from the end of the Palaeocene Epoch to the beginning of the Oligocene Epoch. The start of the...

 and early Oligocene

Oligocene

The Oligocene is a geologic epoch of the Paleogene Period and extends from about 34 million to 23 million years before the present . As with other older geologic periods, the rock beds that define the period are well identified but the exact dates of the start and end of the period are slightly...

. It is well known for its vertebrate fossils, hence the name "bone bed". A few invertebrate

Invertebrate

An invertebrate is an animal without a backbone. The group includes 97% of all animal species – all animals except those in the chordate subphylum Vertebrata .Invertebrates form a paraphyletic group...

 fossils are also present.

Ecology

The University of Texas has a large collection of fossils from Reeve's Bonebed which represent numerous different taxonomic groups. In the following table, the number of specimens of each taxon in the university collection from the bonebed is indicated in the abundance column:

Mammals

Order	Family	Genus/Species	Abundance (?/870)	Notes
Cetartiodactyla Cetartiodactyla Cetartiodactyla is the clade in which whales and even-toed ungulates have currently been placed. The term was coined by merging the name for the two orders, Cetacea and Artiodactyla, into a single word. The term Cetartiodactyla reflects the idea that whales evolved within the artiodactyls...	Merycoidodontidae	Merycoidodon Merycoidodon Merycoidodon is an extinct genus of terrestrial herbivore of the family Merycoidodontidae, subfamily Merycoidodontinae ,...	91: midly common
		Bathygenys Bathygenys Bathygenys is an extinct genus of terrestrial herbivore of the family Merycoidodontidae , endemic to North America during the Late Eocene-Early Oligocene subepochs existing for approximately ....	709: extremely common	hundreds of endocasts (see below)
	Leptomerycidae	Hendryomeryx defordi	2: extremely rare
		Leptomeryx Leptomeryx Leptomeryx is an extinct genus of ruminant of the family Leptomerycidae, endemic to North America during the Eocene through Oligocene 38—24.8 Mya, existing for approximately .-Taxonomy:...	10: rare
	Oromerycidae Oromerycidae Oromerycidae is a small extinct family of artiodactyls closely related to living camels, known from the middle to late Eocene of western North America....	Eotylopus reedi	1: extremely rare
	Agriochoeridae	Agriochoerus Agriochoerus Agriochoerus is an extinct genus of terrestrial herbivore of the family Agriochoeridae, endemic to North America. Agriochoerus and other agriochoerids possessed claws, which is rare within Artiodactyla....	15: average abundance
	Protoceratidae Protoceratidae Protoceratidae is an extinct family of herbivorous North American artiodactyls that lived during the Eocene through Pliocene at around 46.2—4.9 Ma., existing for approximately .-Taxonomy:...	Leptotragulus Leptotragulus Leptotragulus is a small extinct genus of Artiodactyla, of the family Protoceratidae, endemic to North America from the Eocene epoch 40.2—33.9 Ma, existing for approximately .-Taxonomy:...	1: extremely rare
		Heteromeryx Heteromeryx Heteromeryx is an extinct genus of Artiodactyla, of the family Protoceratidae, endemic to North America from the Eocene epoch 40.2—33.9 Ma, existing for approximately .-Taxonomy:...  defordi	2: extremely rare
Rodentia	Eutypomyidae Eutypomyidae Eutypomyidae is a family of extinct rodents from North America and Eurasia thought to be related to modern beavers....	Eutypomys inexpectatus	13: average abundance
	Ischyromyidae	Pseudotomus johanniculi	1: extremely rare	holotype
		Leptotomus	1: extremely rare
	Cylindrodontidae	Ardynomys	1: extremely rare
		Cylindrodon fontis	3: extremely rare
Perissodactyla	Tapiridae	Colodon	4: rare
	Equidae Equidae Equidae is the taxonomic family of horses and related animals, including the extant horses, donkeys, and zebras, and many other species known only from fossils. All extant species are in the genus Equus...	Mesohippus Mesohippus Mesohippus is an extinct genus of early horse. It lived some 40 to 30 million years ago from the late Eocene to the mid-Oligocene...	11: average abundance
	Hyracodontidae Hyracodontidae Hyracodontidae is an extinct family of rhinoceroses endemic to North America, Europe, and Asia during the Eocene through early Miocene living from 55.8—20 mya, existing for approximately .They are typified as having long limbs and having no horns...	Hyracodon Hyracodon Hyracodon is an extinct genus of mammal.It was a lightly built, pony-like mammal of about 1.5 m long. Hyracodons skull was large in comparison to the rest of the body...  primus	1: extremely rare
	Brontotheriidae Brontotheriidae Brontotheriidae, also called Titanotheriidae, is a family of extinct mammals belonging to the order Perissodactyla, the order that includes horses, rhinoceroses, and tapirs. Superficially they looked rather like rhinos, although they were not true rhinos and are probably most closely related to...	Menodus Menodus Menodus giganteus is a species of brontothere. The best known specimen is a mounted skeleton in the Field Museum of Natural History.According to one source , M. giganteus is merged into the genus Megacerops....  bakeri	1: extremely rare
Carnivora Carnivora The diverse order Carnivora |Latin]] carō "flesh", + vorāre "to devour") includes over 260 species of placental mammals. Its members are formally referred to as carnivorans, while the word "carnivore" can refer to any meat-eating animal...	Miacoidea Miacoidea Miacoidea is paraphyletic superfamily that had been traditionally divided into two families of carnivores: Miacidae and Viverravidae. Miacoids were primitive carnivores which lived during the Paleocene and Eocene Epoch about 33-65 million years ago...	Miacis cognitus Miacis cognitus Miacis cognitus is the only species of the diverse genus Miacis that is regarded as belonging to the crown-group Carnivora, within the Caniformia. The type specimen or holotype was discovered in Reeve's bonebed, western Texas, in the Chambers Tuff Formation in 1986. The University of Texas holds...	1: extremely rare	holotype Holotype A holotype is a single physical example of an organism, known to have been used when the species was formally described. It is either the single such physical example or one of several such, but explicitly designated as the holotype...
Creodonta Creodonta The creodonts are an extinct order of mammals that lived from the Paleocene to the Miocene epochs. They shared a common ancestor with the Carnivora....	Hyaenodontidae Hyaenodontidae Hyaenodontidae is a family of the extinct order Creodonta, which contains several dozen genera.The Hyaenodontids were important mammalian predators that arose during the late Paleocene and persisted well into the Miocene...	Hyaenodon Hyaenodon Hyaenodon is an extinct genus of Hyaenodonts, a group of carnivorous creodonts of the family Hyaenodontidae endemic to all continents except South America, Australia and Antarctica, living from 42—15.9 mya, existing for approximately .-Morphology:Some species of this genus were amongst the largest...	2: extremely rare

Other taxa

Additional fossils to which a genus cannot be assigned include:

• gastropods (snails)

• testudinata (turtles)

• Pholidosteids (Placoderms, armored fish)

Oreodont braincasts

Reeve's Bonebed is known for the recovery of casts of the brain cavity (endocast

Endocast

An endocast is the internal cast of a hollow object, often specifically used for an endocasts of the cranial vault. Endocasts can be man-made for examining the properties of a hollow, inaccessible space, or occur naturally through fossilisation....

) of oreodonts. When an animal dies and the soft tissues decay, sediments fill the orifices of the bones including the brain case inside the skull

Skull

The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...

. If the bone subsequently falls apart, a cast of the inside of the skull may remain intact. Hundreds of brain casts, mainly from Bathygenys

Bathygenys

Bathygenys is an extinct genus of terrestrial herbivore of the family Merycoidodontidae , endemic to North America during the Late Eocene-Early Oligocene subepochs existing for approximately ....

, were recovered from Reeve's Bonebed. These casts have been used to gauge the size of the brain of these animals, as well as the size of the various brain lobes. The physical arrangement of the brain can give clues about the life of the living animal, such as how important smell was to it, as used in CT scans of Tyrannosaurus

Tyrannosaurus

Tyrannosaurus meaning "tyrant," and sauros meaning "lizard") is a genus of coelurosaurian theropod dinosaur. The species Tyrannosaurus rex , commonly abbreviated to T. rex, is a fixture in popular culture. It lived throughout what is now western North America, with a much wider range than other...

. Studies involving more than 150 of these endocasts have been performed from the Reeve's Bonebed samples.