Confused with a terror bird (Phorusrhacidae Ameghino) because of its gigantic size (Arredondo 1954, 1955, 1956, 1957a,b, 1958a,b, Koopman 1958), the extinct genus Ornimegalonyx was erected by Arredondo (1958a) on the basis of post-cranial elements from Cueva de Pío Domingo, Pinar del Río province, western Cuba. The material was collected from the floor of the cave on 2 January 1954 by members of the Sociedad Espeleológica de Cuba (SEC). Subsequently, Brodkorb (1961) realised that this taxon actually belonged to the family Strigidae due to the presence of an ossified supratendinal bridge in the tarsometatarsus. He designated a lectotype for the type species: Ornimegalonyx oteroi Arredondo, 1958a. Arredondo (1975) later summarised the taxonomic history of O. oteroi, including synonyms, new material and localities. He believed that a number of specimens that were larger or smaller than the type material (a single individual) represented new species (contra Brodkorb's opinion, see Arredondo 1975: 140). Apparently discarding the possibility of considerable intraspecific variation in so large a raptor (see also Kurochkin & Mayo 1973: 59), those specimens, mostly from western Cuba, were described as O. acevedoi, O. minor and O. gigas, respectively, with the result that four synchronic species in the genus were recognised as having occurred sympatrically in Cuba during the Quaternary (Arredondo 1982: 45–47).

In 1947, a decade prior to the description of Ornimegalonyx, A. Moreno of the Museo Felipe Poey, La Habana, sent to A. Wetmore, at the Smithsonian Institution, Washington DC (USNM), two fossil bones of a large bird from eastern Cuba for study (Arredondo & Olson 1994: 436). Wetmore (1959: 15) identified them as a giant barn owl, Tytonidae, but this was never published. Thirty-five years later, Arredondo & Olson (1994) reassessed the material (Fig. 1B–C)—a near-complete right femur (USNM 447022) and partial humerus (USNM 447023). They identified it with fossils of a large extinct strigid discovered in western Cuba, which was named Bubo osvaldoi Arredondo & Olson, 1994. Both east Cuban bones were included in the type series of B. osvaldoi because they ‘probably belong to the same species as represented by the bones from Pinar del Río [west Cuba], which cannot be referred to any known species of owl, living or fossil’ (Arredondo & Olson 1994: 436).

I have now had the opportunity to study fossil and living Strigiformes from the West Indies (Olson & Suárez 2008, Suárez & Olson 2015, 2020) for some years, and have collected and examined material pertaining to Ornimegalonyx in Cuba (see, for example, Alegre 2002, Suárez 2020), as well as the type material of Bubo osvaldoi including specimens at the Museo Nacional de Historia Natural de Cuba (MNHNCu), La Habana. After comparisons with living and extinct taxa, including Bubo, I have discovered that the type series of B. osvaldoi is a composite, comprising two different large strigid owls that are similar in size. The holotype of B. osvaldoi, a right tarsometatarsus (MNHNCu 75.27.1), and two topotypical paratypes (cited here with their original numbers), a femur (MNHNCu 75.27.3) and a shaft of tarsometatarsus (MNHNCu 75.27.2), are from western Cuba, assigning the name Bubo osvaldoi to that form. However, the two remaining USNM bones, from the eastern extreme of the archipelago, belong to a species that agrees with Ornimegalonyx and differs from Bubo Duméril, 1805, by the following qualitative characters (see Arredondo & Olson 1994: figs. 2A, 3A–D; Fig. 1): (1) humerus small, having (2) shaft (palmar and / or anconal aspect) thinner proximally (also unlike large extinct Tytonidae), with (3) marked curvature and (4) impression of brachialis anticus reduced; femur (anterior and / or posterior aspect) with (5) shaft wider at ends (less expanded in Bubo), (6) anterior intermuscular line crossing (transversal) completely the anterior face of the shaft, from proximal (more lateral) to distal (medial) margins of the bone, not parallel with borders of the shaft (parallel, or almost parallel in Bubo), (7) anterior face of the shaft very flat above condyles (more rounded or convex in Bubo; some characters, including this one, were incorrectly depicted in Arredondo & Olson 1994: fig. 3), (8) rotular groove extremely wide, with condyles placed far apart (closer together in Bubo), and (9) external condyle bent laterally (not, or less bent in Bubo).

Figure 1.

Left humeri (A–B, palmar view) and right femora (C–D, anterior view) of three large owls: (A) Bubo bubo (Linnaeus, 1758), large female (USNM 610384); (B) Ornimegalonyx ewingi sp. nov. (paratype, USNM 447023 [paratype of Bubo osvaldoi]); (C) O. ewingi sp. nov. (holotype, USNM 447022 [paratype of B. osvaldoi]); (D) B. osvaldoi (paratype, MNHNCu 75.27.3 [formerly MNHN 27.3]). Scale = 2 cm. Modified from Arredondo & Olson (1994: figs. 2 and 4) with permission of the Proceedings of the Biological Society of Washington.

TABLE 1

Measurements (mm) of the holotype femur of Ornimegalonyx ewingi sp. nov. (USNM 447022) compared to those of the type species of the genus, O. oteroi. Measurements by WS unless otherwise stated. Sequence: range (mean, sample size).

I was unable to detect any diagnostic character, or distinction, between the highly variable material of O. oteroi (with chronoclines at some localities; WS unpubl.) and specimens of the other three species described in the genus (see Arredondo 1982: 45–47). But all of the material agrees in intraspecific variation observed in skeletons of modern Strigidae. The most enigmatic of the extinct taxa is O. minor, of which the type material, two fragmentary proximal femora (Arredondo 1975: fig. 9; 1982: fig. 14), was unavailable to me until recently. These fossils were sent to B. Patterson at the Museum of Comparative Zoology (MCZ), Harvard Univ., MA, by O. Arredondo (see Arredondo 1975: 139). Thanks to S. L. Olson, this material and that of other Cuban taxa at MCZ, were sent on loan to USNM, were I examined it. No differences other than sexual were observed in O. minor, of which material named by Arredondo appears to represent the male (smaller sex) of O. oteroi. The holotype, a proximal right femur (SEC P-37), is the smaller of the two specimens, and Arredondo (1982: table 6) estimated its total length at 130 mm. The paratype, a proximal left femur (SEC P-38), is larger than the holotype, with a fractured trochanter. This fragment of bone is similar in size to other specimens previously identified by Arredondo (in some cases in my company) as O. oteroi; but its measurements (see Table 1) were not included in the original description of O. minor. If we take the above-mentioned estimated length of the holotype of O. minor as correct, which persuaded Arredondo to describe it as a new species, we have a strigid too large for the Ornimegalonyx material previously included within Bubo osvaldoi (see Table 1).

In conclusion, of the species previously referred to Ornimegalonyx only O. oteroi Arredondo, 1958a, is valid; the other three described by Arredondo (1982) are junior subjective synonyms. The much smaller species Bubo osvaldoi Arredondo & Olson, 1994, is represented solely by material from the type locality in Pinar del Río in western Cuba, whereas two other specimens from its type series, collected in eastern Cuba, are representative of a previously undescribed Ornimegalonyx, as diagnosed above. This is named below, in the following taxonomic arrangement: