Island birds that were victim of anthropic extinctions were often more specialist species, having evolved their most distinctive features in isolation. Here we studied a fossil cranium of the ‘giant’ extinct scops owl Otus murivorus from Rodrigues Island (Mascarene Islands, southwestern Indian Ocean), to determine any potential unique characters. The fossil and extant strigids were imaged through x-ray microtomography, providing 3D views of external and internal (endocast, inner ear) cranial structures. Geometric morphometrics and analyses of traditional measurements yielded new information about the Rodrigues owl’s evolution and ecology. Otus murivorus exhibits a 2-tier “lag behind” phenomenon for cranium and brain evolution, both being proportionately small relative to increased body size. It also had a much more developed olfactory bulb than congeners, indicating an unexpectedly developed olfactory sense, suggesting a partial food scavenging habit. In addition, O. murivorus had the eyes placed more laterally than O. sunia, the species from which it was derived, probably a side effect of a small brain; rather terrestrial habits; probably relatively fearless behavior; and a less vertical posture (head less upright) than other owls (this in part an allometric effect of size increase). These evolutionary features, added to gigantism and wing reduction, make the extinct Rodrigues owl’s evolution remarkable, and with multiple causes.

This dataset comprises fossil cranium FLMR617 of the extinct owl Otus murivorus from Rodrigues Island, and ten crania of extant species of owls (Strigidae), as follows:

Otus scops male (UCBL-FSL-SKT 246.2), O. sunia (MNHN-LAC 2000.329), O. senegalensis (MNHN-LAC 1997.476), Megascops asio naevius (UCBL-FSL-SKL 1856-540), Bubo scandiacus male (UCBL-FSL-SKL 2626), B. bubo male (UCBL-FSL-SKL, no number, from Ariège), B. cinerascens (UCBL-FSL-SKL 453, FSL), B. zeylonensis male (MNHN-LAC 1986-05), Athene noctua glaux (UCBL-FSL-SKL 568-379), A. cunicularia (UCBL-FSL-SKL 656-436).

Institutions abbreviations: FLMR, François Leguat Museum, Rodrigues, Republic of Mauritius; MNHN-LAC, Laboratoire d’Anatomie Comparée, collection of bird skeletons, Muséum National d’Histoire Naturelle, Paris, France; UCBL-FSL-SKL, collection de la Faculté des Sciences de Lyon de l’Université Claude Bernard Lyon 1 (Villeurbanne, France), category extant bird skulls; UCBL-FSL-SKT, collection de la Faculté des Sciences de Lyon de l’Université Claude Bernard Lyon 1 (Villeurbanne, France), category extant bird skeletons.

All 11 specimens were imaged through x-ray microtomography at ENS de Lyon (GE Phoenix Nanotom 180 device (platform US8/UMS3444 SFR BioSciences), in order to obtain 3D reconstructions of cranium, endocast and inner ear, as well as virtual sections of cranium. Details anout the parameters of all 11 scans are given with the data itself for every taxon (see Usage Notes).

For each of the 11 species, two files are compised here: (i) a .pca file (text file that comprises all the technical parameters of x-ray microtomography) ; (ii) a .raw file that is the scan volume. The .pca file names comprise the species name. The .raw file names comprise the species name, the number of slices in each of the 3 planes, the mention "8 bit", and the voxel size at the initial stage of microtomography in micrometers (e.g., "45.8mic"). The 22 files are therefore as follows (in alphabetical order):

Athene cunicularia: a_cunicularia_cranium_.pca ; A_cunicularia_840-621-1077-8bit-45.8mic.raw

Athene noctua: A_noctua_cranium_.pca ; A_noctua_860-539-1050-8bit-48mic.raw

Bubo bubo: B_bubo skull.pca ; B_bubo_1142-776-1122_8bit_64mic.raw

Bubo cinerascens: B_cinerascens skull.pca ; B_cinerascens_966-701-1120_8bit_64mic.raw

Bubo scandiacus: B_scandiacus skull.pca ; B_scandiacus_1142-848-1137_8bit_60mic.raw

Bubo zeylonensis: B_zeylonensis skull.pca ; B_zeylonensis_1142-833-1127_8bit_64mic.raw

Megascops asio: m_asio_cranium_.pca ; M_asio_834-633-1065_46mic.raw

Otus murivorus: o_murivorus_cranium_.pca ; O_murivorus_1113-786-1050-8bit-36mic.raw

Otus scops: o_scops_cranium_.pca ; O_scops_882-666-1067-8bit-36mic.raw

Otus_senegalensis: O_senegalensis_cranium.pca ; O_senegalensis_840-685-1047-8bit-38mic.raw

Otus_sunia: o_sunia_cranium_.pca ; O_sunia 831-636-1030_8bit_40mic.raw