Squirrels are members of the family Sciuridae, a family that includes small or medium-size rodents. The squirrel family includes tree squirrels, ground squirrels, and flying squirrels. Squirrels are indigenous to the Americas, Eurasia, and Africa, and were introduced by humans to Australia. The earliest known fossilized squirrels date from the Eocene epoch, and among other living rodent families, the squirrels are most closely related to the mountain beaver and to the dormice.
Flying squirrels are a tribe of 50 species of squirrels in the family Sciuridae. Despite their name, they are not in fact capable of full flight in the same way as birds or bats, but they are able to glide from one tree to another with the aid of a patagium, a furred parachute-like skin membrane that stretches from wrist to ankle. Their long tails also provide stability as they glide. Anatomically they are very similar to other squirrels with a number of adaptations to suit their lifestyle; their limb bones are longer and their hand bones, foot bones, and distal vertebrae are shorter. Flying squirrels are able to steer and exert control over their glide path with their limbs and tail.
The Anomaluridae are a family of rodents found in central Africa. They are known as anomalures or scaly-tailed squirrels. The six extant species are classified into two genera.
The squirrel glider is a nocturnal gliding possum. The squirrel glider is one of the wrist-winged gliders of the genus Petaurus.
A dormouse is a rodent of the family Gliridae. Dormice are nocturnal animals found in Africa, Asia, and Europe. They are named for their long, dormant hibernation period of six months or longer.
Leptictidium is an extinct genus of small mammals that were likely bipedal. Comprising eight species, they resembled today's bilbies, bandicoots, and elephant shrews. They are especially interesting for their combination of characteristics typical of primitive eutherians with highly specialized adaptations, such as powerful hind legs and a long tail which aided in locomotion. They were omnivorous, their diet a combination of insects, lizards and small mammals. Lepticidium and other lepticids are not placentals, but are non-placentral eutherians, although closely related. They appeared in the Lower Eocene, a time of warm temperatures and high humidity, roughly fifty million years ago. Although they were widespread throughout Europe, they became extinct around thirty-five million years ago with no descendants, probably because they were adapted to live in forest ecosystems and were unable to adapt to the open plains of the Oligocene.
The Messel pit is a disused quarry near the village of Messel about 35 km (22 mi) southeast of Frankfurt am Main, Germany. Bituminous shale was mined there. Because of its abundance of well-preserved fossils dating from the middle of the Eocene, it has significant geological and scientific importance. Over 1000 species of plants and animals have been found at the site. After almost becoming a landfill, strong local resistance eventually stopped these plans and the Messel Pit was declared a UNESCO World Heritage Site on 9 December 1995. Significant scientific discoveries about the early evolution of mammals and birds are still being made at the Messel Pit, and the site has increasingly become a tourist site as well.
Plesiadapis is one of the oldest known primate-like mammal genera which existed about 58–55 million years ago in North America and Europe. Plesiadapis means "near-Adapis", which is a reference to the adapiform primate of the Eocene period, Adapis. Plesiadapis tricuspidens, the type specimen, is named after the three cusps present on its upper incisors.
Eomanis is the earliest known true pangolin from extinct family Eomanidae within suborder Eupholidota. It lived during the Eocene in Europe. Eomanis fossils found in the Messel Pit in Germany are very similar in size and anatomy to living pangolins of the genus Manis, indicating that pangolins have remained largely unchanged in morphology and behavior for 50 million years. However, unlike modern pangolins, its tail and legs did not bear scales. According to the stomach contents of the excellently preserved Messel specimens, Eomanis’ diet consisted of both insects and plants.
Chriacus is an extinct genus of placental mammals that lived in what is now North America during the Paleocene epoch and died out after the early Eocene. In life, members of the genus would have looked something like a kinkajou or binturong, though they were not closely related to any living mammal. Well preserved fossils allow clear information on what they looked like. They were about 1 metre (3.3 ft) long including a long, robust tail, which may or may not have been prehensile. Other features include a light build, weighing approximately 7 kg (15 lb), and many adaptations typical of animals that live in trees. These include walking on the soles of their five-toed feet, and having long, curved, compressed claws. The powerfully built limbs had flexible joints, especially the ankles, an adaptation that allows an animal to turn its hind feet behind it, like modern tree squirrels, in order to climb downward. They were probably omnivores, eating fruit, eggs, insects and small mammals.
Palaeochiropteryx is an extinct genus of bat from the Middle Eocene of Europe and North America. It contains three very similar species – Palaeochiropteryx tupaiodon and Palaeochiropteryx spiegeli, both from the famous Messel Pit of Germany, as well as Palaeochiropteryx sambuceus from the Sheep Pass Formation. They are usually found complete and exceptionally preserved, even retaining the outlines of their fur, ears, and wing membranes.
Ailuravus is a genus of prehistoric rodents in the family Ischyromyidae.
Paroodectes is an extinct genus of placental mammals from clade Carnivoraformes, that lived in Europe during middle Eocene.
Heterohyus is an extinct genus of apatemyid from the early to late Eocene. A small, tree-dwelling creature with elongated fore- and middle fingers, in these regards it somewhat resembled a modern-day aye-aye.
Three skeletons have been found at the early Eocene site at Messel Pit, Germany
Macrocranion is a genus of extinct mammal from the Eocene epoch of Europe and North America. Exceptional fossils have has been found in the Messel Pit of Germany. Macrocranion species are often described as forest-floor predators, about the size of small squirrels but with longer limbs. The genus is represented at the Messel Pit site by two species, M. tupaidon and M. tenerum.
Pantolestidae is an extinct family of semi-aquatic, non-placental eutherian mammals. Forming the core of the equally extinct suborder Pantolesta, the pantolestids evolved as a series of increasingly otter-like forms, ranging from the Middle Paleocene Bessoecetor to the Late Eocene (Ergilian) Gobiopithecus and Kiinkerishella. They first appear in North America, whence they spread to Europe.
Buxolestes is an extinct genus of semi-aquatic, non-placental eutherian mammals belonging to the family Pantolestidae. Species in this genus were part of the first placental evolutionary radiation during the Middle Eocene and found in the Bracklesham Group and Wittering Formation of England, at the Messel Pit in Germany and in Bouxwiller, France.
Geiseltaliellus is an extinct genus of iguanian lizards that lived in what is now western Europe during the Eocene. It belongs to the family Corytophanidae, which includes modern casquehead lizards. Many fossils are known from Germany, France, and Belgium, with the most well preserved coming from the Messel pit lagerstätte in Messel, Germany. German paleontologist Oskar Kuhn named the genus in 1944 after the Geiseltal valley where the first specimens were found, designating the type species Geiseltaliellus longicaudus. Three new species — G. louisi, G. lamandini, and G. grisolli — were named in the 1990s and 2000s on the basis of more fragmentary remains from France and Belgium, although G. louisi has since been synonymized with G. longicaudus. In 2009 the Messel pit specimens were recognized as belonging to a species distinct from that of the G. longicaudus specimens in Geiseltalt and were collectively reclassified under a new name, G. maarius.
Peradectes is an extinct genus of small metatherian mammals known from the latest Cretaceous to Eocene of North and South America and Europe. The first discovered fossil of P. elegans, was one of 15 Peradectes specimens described in 1921 from the Mason pocket fossil beds in Colorado. The monophyly of the genus has been questioned.
Apatemys is a member of the family Apatemyidae, an extinct group of small and insectivorous placental mammals that lived in the Paleogene of North America, India, and Europe. While the number of genera and species is less agreed upon, it has been determined that two apatemyid genera, Apatemys and Sinclairella, existed sequentially during the Eocene in North America. The genus Apatemys, living as far back as 50.3 million years ago (mya), existed through part of the Wasatchian and persisted through the Duchesnean, and Sinclairella followed, existing from the Duchesnean through the Arikareean. Examinations of specimens belonging to the genus Apatemys suggest adaptations characteristic of arboreal mammals.
