Herpetotherium is an extinct genus of metatherian mammal, belonging to the possibly paraphyletic family Herpetotheriidae. Native to North America from the Eocene to Early Miocene, fossils have been found in California, Oregon, Texas, Florida, Montana, Wyoming, Colorado, North and South Dakota, Nebraska, and Saskatchewan. The oldest species, H. knighti, is dated to around 50.3 mya, and the most recent, an unnamed species, may be as recent as 15.97 mya. A morphological analysis of marsupials and basal metatherians conducted in 2007 found Herpetotherium to be the sister group to extant marsupials. It is the youngest known metatherian from North America until the migration of the Virginia opossum from South America within the last 2 million years.
The Yorktown Formation is a mapped bedrock unit in the Coastal Plain of Maryland, Virginia, North Carolina and South Carolina. It is overconsolidated and highly fossiliferous.
The Salisbury Embayment was an arm of the Atlantic Ocean which covered what is now Delaware, southern and eastern Maryland, the Virginia Peninsula and parts of southern New Jersey during Paleogene and Neogene times, from about 65 million to 5 million years ago. Sea level throughout most of this period stood several hundred feet higher than at present, and deposition of sediments draining off the continent possibly caused the underlying rocks to sink down, creating the embayment. The shore of the embayment lay inland at the present-day Fall Line in the region. Throughout the Paleogene and Neogene times, sediment accumulated on the floor of the Salisbury Embayment during pulses of high sea level, forming the Paleocene Aquia and Brightseat Formations, the Eocene Pamunkey Group, and the Miocene Chesapeake Group. There are no deposits from the Oligocene epoch due to a drop in sea level, however, a 2- to 3- mile diameter meteorite or asteroid is thought to have left a 50-mile diameter crater upon impact in the southern Chesapeake Bay.
The Malargüe Group is a group of geologic formations of the Neuquén Basin of the Mendoza, Neuquén, Río Negro and La Pampa Provinces in northern Patagonia, Argentina. The formations of the Malargüe Group range in age between the middle Campanian to Deseadan, an Oligocene age of the SALMA classification, straddling the Cretaceous–Paleogene boundary, about 79 million to 30 million years in age. The group overlies the older Neuquén Group, separated by an unconformity dated to 79 Ma. The rocks of the Malargüe Group comprise both marine and continental deposits which are over 400 m (1312 ft) thick in total.
The Chesapeake Group is a geologic group in Maryland, Virginia, Delaware, and North Carolina. It preserves mainly marine fossils dating back to the Miocene and Pliocene epochs of the Neogene period. This group contains one of the best studied fossil record of Neogene oceans in the world. Professional Paleontologists and amateur fossil hunters alike collect from this group intensely. The Calvert Cliffs stretch the length of Calvert County, Maryland and provide the best continuous stretch of the Calvert, Choptank, and St. Marys Formations. Ward (1985) recommended including the Old Church Formation in this group.
The Belgrade Formation is a limestone geologic formation in North Carolina characterized by limestone coquina mixed with sand, and thinly laminated clays. It preserves fossils dating back to the Paleogene period.
The River Bend Formation is a limestone geologic formation in North Carolina. It preserves fossils dating back to the Paleogene period.
The Castle Hayne Limestone is a geologic formation in North Carolina. It consists of cobble to pebble sized clasts, usually rounded, coated with phosphate and glauconite in a limestone matrix. The Castle Hayne Limestone is known for containing fossils dating back to the Paleogene period. It preserves many of North Carolina's renowned Eocene fossils. It is named after the locality of Castle Hayne in New Hanover county, though the formation itself stretches over several counties.
The Potomac Group is a geologic group in Delaware, Maryland, New Jersey, and Virginia. It preserves fossils dating back to the Cretaceous period. An indeterminate tyrannosauroid and Priconodon crassus, a nodosaurid, are known from indeterminate sediments belonging to the Potomac Group. The Potomac Group was initially believed to have been Late Jurassic in age by Othniel Charles Marsh but later studies, such as Clark (1897), have found that the Potomac Group is in fact Early-Late Cretaceous (Aptian-Turonian) in age.
The St. Marys Formation is a geologic formation in Maryland and Virginia, United States. It preserves fossils dating back to the Miocene Epoch of the Neogene period. It is the youngest Miocene formation present in the Calvert Cliffs and is part of the Chesapeake Group.
The Choptank Formation is a geologic formation in Virginia and Maryland. It preserves fossils dating from the Miocene epoch of the Neogene period.
The Nanjemoy Formation is a geologic formation pertaining to both the Wilcox Group and the Pamunkey Group of the eastern United States, stretching across the states of Virginia, Maryland, and District of Columbia. The formation crops out east of the Appalachians and dates back to the Paleogene period. Specifically to the Ypresian stage of the Eocene epoch, about 55 to 50 Ma or Wasatchian in the NALMA classification, defined by the contemporaneous Wasatch Formation of the Pacific US coast.
The Piney Point Formation is a geologic formation in Virginia. It preserves fossils dating back to the Lutetian Stage of the Eocene Epoch of the Paleogene period.
The Ashley Formation is a geologic formation in South Carolina. It preserves fossils dating back to the Paleogene period.
The Chandler Bridge Formation is a geologic formation in South Carolina. It preserves fossils dating back to the Chattian of the Paleogene period, corresponding to the Arikareean in the NALMA classification. The formation overlies the Ashley Formation and is overlain by the Edisto Formation.
The Alum Bluff Group is a geologic group in the states of Georgia, Florida, and Alabama. It preserves fossils dating back to the Neogene period.
The White River Formation is a geologic formation of the Paleogene Period, in the northern Great Plains and central Rocky Mountains, within the United States.
The Yaquina Formation is a geologic formation in Oregon. It preserves fossils dating back to the Paleogene period.
The Jewett Sand Formation is a geologic formation in California, USA. It preserves fossils dating back to the Miocene Epoch of the Neogene period.
The Calvert Formation is a geologic formation in Maryland, Virginia, and Delaware. It preserves fossils dating back to the early to middle Miocene epoch of the Neogene period. It is one of the three formations which make up the Calvert Cliffs, all of which are part of the Chesapeake Group.
