Necrobyas: a fossil owl known mostly from leg bones

Necrobyas is a genus of fossil owls described chiefly from isolated leg bones in western Europe. Its best-known material comes from the Quercy phosphate deposits of southwestern France, where old collections often lack precise locality and layer information. The short, robust tarsometatarsus preserves characters that can be compared with living owls, but skulls, soft tissues and securely associated food remains are scarce. Its assignment near the barn-owl family is common, though authors differ on the exact classification. The extinct bird catalogue includes Necrobyas as one of the uncertain branches in the early history of owls.

Quick facts

A name from Quercy’s phosphate deposits

Alphonse Milne-Edwards introduced Necrobyas harpax in 1892 from the phosphate-bearing deposits of Quercy in southwestern France. These deposits accumulated in karst fissures and cavities rather than in one continuous, easily read rock layer. Quercy collections consequently combine fossils from many localities and ages. A label that says “Quercy” may not identify the precise fissure or geological horizon.

The type material of N. harpax has itself required clarification. Milne-Edwards’s description was based on a tarsometatarsus and mentioned an ulna and humerus as additional elements. Later reviews disagreed over which museum bone matched the description. Mlíkovský’s 1998 reassessment treated the incomplete left tarsometatarsus MNHN QU-15696 as the holotype and the other bones as referred material. Earlier selections of QU-15695 or QU-15742 do not displace the name-bearing element fixed by the original description.

This distinction matters because the genus is diagnosed mainly from the tarsometatarsus. A newly found bone can be compared with a reference specimen, but not every owl bone from the same broad deposit automatically belongs to Necrobyas. Revisions also differ in how many species they accept, so the genus should not be presented as one uniform animal unchanged across all sites and millions of years.

The leg bone that carries the diagnosis

The tarsometatarsus of Necrobyas is relatively short and sturdy compared with the same bone in many living owls. Mourer-Chauviré’s 1987 monograph compared its structure with Strigidae, Tytoninae and Phodilinae. One feature of the lower leg is a long connection between the fibula and tibia, resembling the condition in living Tyto more than in many strigid owls. Other joint and muscle-attachment details distinguish the fossil form from modern groups.

Measurements assigned to the genus vary with species and identification. In one Quercy sample, mean tarsometatarsus lengths were about 33.6 millimetres for N. rossignoli, 37.1 for N. harpax and 41.2 for the larger N. edwardsi. Those means summarise specimens placed in named groups; they do not show that every individual fit a neat size class. The material is fragmentary, and fossils from different fissures may not be the same age.

Short, robust feet can suggest a strong perch grip or a different balance of limb functions from that of living barn owls. Such proposals are biomechanical interpretations. They do not reveal the force of a strike, preferred perch height or whether the bird hunted from a branch, the ground or both.

Why the species names changed

Historical lists include N. harpax, N. rossignoli, N. edwardsi, N. arvernensis and N. minimus. In Mourer-Chauviré’s revision, the small late Eocene N. rossignoli was treated as a synonym of the early Oligocene N. harpax. The larger N. edwardsi was joined with N. arvernensis, an owl originally described under Bubo from the early Miocene of Saint-Gérand-le-Puy. Mlíkovský later selected the tarsometatarsus MNHN Av. 2834b as the lectotype of N. arvernensis.

The small species N. minimus has been transferred to Prosybris, with synonymy proposed under P. antiqua. Not every catalogue adopts exactly the same combination, partly because species diagnoses rely on a limited and uneven record. When a fossil database lists more species than a modern revision, it may be retaining historical names rather than asserting that all are currently accepted.

A conservative description recognises small and larger owl material assigned to this lineage, while stating which revision is being followed. Calling every name a separate valid species would overstate the evidence. Treating every difference as meaningless would also ignore changes in size, age and anatomical diagnosis that motivated the revisions.

How securely does it belong with barn owls?

Necrobyas is often placed in Tytonidae or in an extinct subfamily, Necrobyinae, near the barn-owl branch. The tarsometatarsus shares characters with Tyto, but also differs in proportions and details. The exact placement of fossil owls has shifted as researchers have compared more specimens and revised the names attached to them.

The term “stem barn owl” is a useful cautious description when the analysis places a fossil outside the crown group of living barn owls. It signals a relationship without claiming that the animal had all of the specialised features of modern Tyto. The evidence does not establish a pale, heart-shaped facial disk, asymmetric ear openings, nocturnal activity or silent flight. Those features require skull and soft-tissue evidence that is missing or too incomplete.

Nor does an owl-like foot prove a detailed diet. No stomach contents or pellets have been securely assigned to Necrobyas. The taxon was almost certainly predatory in the broad sense expected of owls, but the prey size, habitat and hunting method remain uncertain. The nearby late Eocene and Oligocene deposits preserve diverse mammals and birds, yet the fissure record cannot turn their co-occurrence into a scene of one animal hunting another.

A reconstruction bounded by the fossils

A scientifically restrained reconstruction can show a small to medium-sized owl with short, sturdy lower legs. The precise body size depends on the species and specimen selected. Because the known fossils are mostly disarticulated, combining a skull, wing, legs and feathers into one individual can create a composite not documented by any single skeleton.

Feather colour, facial pattern, tufts, eye colour, call and exact perch behaviour are not preserved. A branch or woodland background is a plausible artistic choice, not proof of an arboreal lifestyle. Quercy deposits include multiple environments and time intervals; the place where a bone was finally buried does not by itself identify the bird’s daily habitat.

Necrobyas is most informative as evidence that Europe supported several distinct owl forms during the Paleogene. Its short leg bones add a concrete anatomical record, while the changing species list and broad age range show how much interpretation still rests on fragmentary fossils.