Eostrix

• E. mimica described in 1938 by Alexander Wetmore using hindlimb elements in Eocene strata in Wyoming.
• E. martinellii was described in 1972 from a left tarsometatarsus recovered from an escarpment above the southeastern bank of Cottonwood Creek in Fremont County, Wyoming by Jorge Martinelli on a field trip in 1970 under the auspices of the University of Kansas. The strata was a Lysite member of the Wind River Formation. Martinelli was studying paleontology at the University of Barcelona. Paleontologists Larry D. Martin and Craig Call Black from the University of Kansas Natural History Museum named it in his honour. The smaller of the two species, it was similar in size to the living long-eared owl. Differences in the trochleas of the lower end of the tarsometatarsus set it apart from living owls, namely a groove in the trochlea for digit 2, a deeper posterior groove in a relatively narrow trochlea for digit 3, and an unusually rounded trochlea for digit 4.
• E. vincenti described in 1980 by Colin Harrison from the early Eocene London Clay in England, known from pedal phalanx and proximal tarsometatarsus bones. Some scholars think E. vincenti resembles Necrobyas more than Eostrix.
• E. tsaganica described in 2011 by Evgeny Kurochkin and Gareth J. Dyke, found in Mongolia.
• E. gulottai described in 2016 by Gerald Mayr, found in the early Eocene Nanjemoy Formation in Virginia alongside a dozen other species of birds. This species is the smallest known fossil owl, with a distal width of 3.9 mm. The structure of its trochlea metatarsi II, a bone in the owl's foot, strongly indicates that it would have restricted the rotation of the second toe. Since a similar bone structure has been observed on birds with webbed feet, this detail has led to the conclusion that the E. gulottai also had webbed feet. Named for the finder of the holotype, Marco Gulotta.