Bartonian in the context of Archaeoceti

The Mokattam Formation is a Middle Eocene-aged geological formation in northern Egypt. Consisting of nummulitic marine limestone outcropping across the Mokattam Hills, it has been extensively quarried from Ancient Egypt to the present day, and represents the source material for most of the famous archeological sites of Greater Cairo, most notably the Giza pyramid complex, the Great Sphinx, and much of Historic Cairo.

The age of the formation is thought to span from the late Lutetian to the Bartonian, depending on the member (Building Stone or Giushi). However, some authors treat the Giushi Member as its own geologic formation, which would restrict the Mokattam to just the Lutetian.

The Lutetian is, in the geologic timescale, a stage or age in the Eocene. It spans the time between 48.07 and 41.03 Ma. The Lutetian is preceded by the Ypresian and is followed by the Bartonian. Together with the Bartonian it is sometimes referred to as the Middle Eocene Subepoch.

The Priabonian is, in the ICS's geologic timescale, the latest age or the upper stage of the Eocene Epoch or Series. It spans the time between 37.71 and 33.9 Ma. The Priabonian is preceded by the Bartonian and is followed by the Rupelian, the lowest stage of the Oligocene.

Priabona, an extinct dipteran of Pipunculidae family, is named after Priabonian, the age of deposits from which this insect is known.

The La Meseta Formation is a sedimentary sequence deposited during much of the Paleogene on Seymour Island off the coast of the Antarctic Peninsula. It is noted for its fossils, which include both marine organisms and the only terrestrial vertebrate fossils from the Cenozoic of Antarctica.

In some treatments, the La Meseta Formation is restricted to just the older Thanetian to Lutetian-aged strata, with the younger Bartonian to Rupelian strata treated as the overlying Submeseta Formation. However, other papers instead treat the Submeseta Formation as an allomember of the La Meseta Formation.

Nimravidae is an extinct family of carnivorans, sometimes known as false saber-toothed cats, whose fossils are found in North America, Africa, and Eurasia. Not considered to belong to the true cats (family Felidae), the nimravids are generally considered closely related and classified as a distinct family in the suborder Feliformia. Fossils have been dated from the Middle Eocene through the Late Miocene epochs (Bartonian through Messinian stages, 41.03–7 million years ago), spanning about 34.03 million years.

The barbourofelines, classified as a subfamily of the Nimravidae since 1991, were reassigned to their own distinct family in 2004. However, since 2020, the majority of experts consider barbourofelines as nimravids again.

Perucetus is an extinct genus of an early whale from Peru that lived during the Bartonian age of the middle Eocene. Perucetus is the largest Eocene whale, with length estimates varying from 15–16 meters (49–52 ft) to 17–20 meters (56–66 ft). It was initially claimed to have rivaled or exceeded the modern blue whale in weight, partly due to the incredibly thick and dense bones this animal possessed, coupled with its already great size, but subsequent studies argued that it was significantly lighter. The ecology of Perucetus also remains largely mysterious. Based on the fossils, it was likely a slow-moving inhabitant of shallow waters. Its diet can only be speculated, but one suggestion proposes that it may have fed on benthic animals like crustaceans and molluscs living on the ocean floor. Only a single species is currently known, P. colossus.