The true carnivores, represented by Miacis, remained small in size, perhaps to avoid competition with the larger surviving creodonts.
Insectivores from the Fowkes Formation are abundant and varied. Unfortunately, they are known almost exclusively from teeth. Fowkes insectivores include the hedge-hog-like Nyctitherium, Talpavus, and Scenopagus. Apatemys is an insectivore of uncertain affinities. The feeding habits of these early insectivores were probably similar to those of contemporary insectivore species (moles and shrews); however, there is some evidence to suggest many of these small creatures may have been semi-arboreal.
One of the most unusual of middle Eocene creatures is the giant Uintatherium. This was a large browsing animal, about the size of a rhinoceros. What was most unusual about Uintatherium was its skull which was large and strongly built. The large upper canines were apparently formidable defensive weapons. The skulls of the males bore six prominent bony protuberances which grew from the frontal region of the skull. The function of these structures is unknown. They may have been of use for defense.
During Bridgerian times, the rodents underwent an explosive adaptive radiation which ultimately may have led to the near extinction of the less well-adapted multituberculates. The diversity of Bridgerian rodents from Fossil Basin is impressive. Species of Leptotomus, Paramys, Thisbemys, Microparamys, Sciuravus, Mysops, and Pauromys demonstrate that a wide range of adaptations of environments was exploited by the rodents. This diversity in life habits has been a mark of rodent evolution from the middle Eocene to the present day.
The above descriptions of the known mammal fossils from the Fossil Butte area are intended to demonstrate the varied life forms that once existed in southwestern Wyoming. Further collecting will almost certainly expand the number of fossil mammal species from Fossil Basin and increase our knowledge of the succession of ancient environments which prevailed at different times in the Fossil Basin area.
TABLE 2. Mammals known from Fossil Basin
Faunal lists—Middle Paleocene: Torrejonian Class Mammalia Multituberculata Ptilodus Neoplagiaulax Ectypodus Insectivora Leptacodon Aphronorus Primates Torrejonia Pronothodectes Condylarthra Chriacus Tricentes Promioclaenus Litaletes Haplaletes Late Paleocene: Tiffanian Multituberculata Ptilodus? Primates Plesiadapis Condylarthra Thryptacodon Claenodon Litomylus Haplaletes Gidleyina Phenacodus Carnivora Didymictis Pantodonta Genus indeterminant. Early Eocene: Graybullian Primates Pelycodus Tillodontia Esthonyx Rodentia Paramys Creodonta Proviverra Carnivora Didymictis Vassacyon Condylarthra Pachyaena Haplomylus Hyopsodus Phenacodus Meniscotherium? Pantodonta Coryphodon Perissodactyla Hyracotherium Artiodactyla Diacodexis Early Eocene: Lysitean Insectivora Diacodon Primates Pelycodus Microsyops Tillodontia Esthonyx Rodentia Paramys Reithroparamys Creodonta Proviverra Carnivora Didymictis Vulpavus Condylarthra Pachyaena? Hyopsodus Phenacodus Meniscotherium? Pantodonta Coryphodon Perissodactyla Hyracotherium Heptodon Artiodactyla Protodichobune Early Eocene: Wasatchian (general) Chiroptera Icaronycteris Late Middle Eocene: Late Bridgerian Marsupialia Peratherium Insectivora Apatemys Nyctitherium Scenopagus Talpavus Primates Hemiacodon Omomys Notharctus Condylarthra Hyopsodus Rodentia Leptotomus Microparamys Mysops Paramys Pauromys Sciuravus Thisbemys Dinocerata Uintatherium Perissodactyla Orohippus Hyrachyus
PALEOECOLOGY AND TAPHONOMY
Paleoecology is the study of ancient biotic communities and their relationship to the abiotic environment. The conclusions of paleoecology are reached by studying in detail the fossils and sediments and whatever relationships exist between them. Its ultimate aim is to build a picture of the climate, flora, fauna, and topographic setting of an area. For this reason it borrows heavily from paleontology, paleobotany, sedimentology, and climatology.
From studying modern environments, it is observed that each has its own type of sediment. When certain sediments are found in the rock record, it is generally assumed that they represent environments similar to modern ones that produce similar deposits. For example, limestone is forming today in warm, shallow, well-lighted, well-aerated water. When limestone is found in a rock sequence, it is usually assumed that the same or similar environmental conditions occurred in that area in the past. Fossils can further refine the interpretation.