A new species of extinct little owl from the Pleistocene of Mallorca (Balearic Islands)
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- Guerra, C., Bover, P. & Alcover, J.A. J Ornithol (2012) 153: 347. doi:10.1007/s10336-011-0749-3
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Athene vallgornerensis nov.sp. (Aves: Strigiformes: Strigidae) from the Early Pleistocene of the island of Mallorca (Balearic Islands, Western Mediterranean) is described. The material came from a fossil assemblage obtained in a collapsed gallery from Cova des Pas de Vallgornera (Llucmajor, south of Mallorca), the longest karstic system currently known in the Balearics. Associated remains include primitive representatives of the insular endemic fauna of Mallorca (Myotragus, Hypnomys, Nesiotites), as well as fossils of bats, birds (among them, Tyto balearica), lizards and toads. Although only two bones of Athene have been obtained, its highly distinctive tarsometatarsus—short, highly robust and significantly small—differentiates it from the remaining extant and extinct Athene species from the Palaearctic, justifying its description as a new species. At least four insular species of Athene are now known from the Mediterranean area, and two groups can be identified according to the shape of their tarsometatarsi.
KeywordsAthene vallgornerensis nov.sp.Balearic IslandsEarly PleistoceneTarsometatarsusFossil Strigiformes
Eine neue kleine, ausgestorbene Eulen-Art aus dem Pleistozän von der Insel Mallorca (Balearen)
In dieser Arbeit wird Athene vallgornerensis nov.sp. (Aves: Strigiformes: Strigidae) aus dem frühen Pleistozän von der Insel Mallorca (Balearen, westliches Mittelmeer) beschrieben. Das Material stammt von einer Fossilvergesellschaftung in einem zusammengefallenen Gang des Höhlensystems Cova des Pas de Vallgornera (Llucmajor, im Süden von Mallorca), dem ausgedehntesten bislang bekannten karstartigen Systems auf den Balearen. Weitere Funde in dieser fossilen Ansammlung konnten anderen primitiven Vertretern der endemischen Insel-Fauna zugeordnet werden (Myotragus, Hypnomys, Nesiotites), wie auch Überresten von Fledermäusen und Vögeln (darunter Tyto balearica), Eidechsen und Kröten. Obwohl nur zwei Knochen von Athene gefunden wurden, ermöglichen deren höchst eindeutiger kurzer, außergewöhnlich robuster und besonders kleiner Tarsometatarsus eine klare Unterscheidung von den anderen existierenden und ausgestorbenen Athene-Arten aus der Paläarktis und rechtfertigen deshalb die Beschreibung als neue Art. Damit sind jetzt mindestens vier Athene-Arten aus dem Mittelmeerraum bekannt, von denen zwei Gruppen anhand der Form ihrer Tarsometatarsi identifiziert werden können.
The presence of endemic Strigiformes is a characteristic trait of the Pleistocene fauna from the Mediterranean islands. Fossil endemic species have been described on Crete (Athene cretensis, Late Pleistocene, Weesie 1982), Corsica and Sardinia (Bubo insularis, Late Pleistocene, Mourer-Chauviré and Weesie 1986; Athene angelis, Middle and Late Pleistocene, Mourer-Chauviré et al. 1997), and Sicily (Athene trinacriae, Middle Pleistocene, Pavia and Mourer-Chauviré 2002; Tyto mourerchauvireae, Middle Pleistocene, Pavia 2004; Aegolius martae, early Middle Pleistocene, Pavia 2008). A high diversity of endemic insular species of Strigiformes is also a characteristic of other archipelagos (e.g. West Indies, Arredondo 1976) and periods (e.g. Gargano, Upper Pliocene, Ballmann 1973, 1976). On islands, in the absence of autochthonous Carnivora, birds frequently monopolise the predatory guilds (e.g. Alcover and McMinn 1994), and evolve to be adapted to the peculiar insular ecological conditions (e.g. Pavia and Mourer-Chauviré 2002; Louchart 2005), changing their body size and proportions.
Four species of Strigiformes have been recorded so far as fossils in Mallorcan Quaternary sites: (1) Tyto balearica, obtained in different Early and Middle Pleistocene sites (Mourer-Chauviré et al. 1980; Ballmann and Adrover 1970); (2) Tyto alba, recorded in Late Pleistocene and Holocene deposits (Mourer-Chauviré et al. 1977; McMinn and Alcover 1992); (3) Otusscops, recorded from the Middle and Late Pleistocene, and with doubt (as Otus cf. scops) from an Early Pleistocene site (Mourer-Chauviré in Alcover et al. 1981; Seguí et al. 1997); and (4) Athene noctua, recorded at the Late Pleistocene (Seguí et al. 1997). A fifth reported species, initially identified as Strix aluco (Ballmann and Adrover 1970), was later tentatively referred to Tyto balearica (see Mourer-Chauviré et al. 1980).
Little owls (genus Athene) seem to speciate particularly rapidly under genetic isolation on islands, as documented by the presence of at least three different fossil species of the genus on several Mediterranean islands. Currently, the European Little Owl Athene noctua, the sole western Palaearctic species of the genus, occurs over the whole of Europe except for northern areas, Corsica and the Balearic Islands.
A complete right tarsometatarsus and a pedal phalanx curated at the Vertebrate Collection of the Mediterranean Institute for Advanced Studies (Acronym: IMEDEA), under accession numbers IMEDEA-91958 and IMEDEA-91897, respectively, have been studied.
A direct comparison with all the small- and middle-sized living Strigidae from the western Palaearctic has been carried out. The material has also been compared with the Pleistocene species of Athene. Measurements follow the criteria of Campbell and Bocheński (2010). Corresponding bone measurements from Weesie (1982), Mourer-Chauviré et al. (1997) and Pavia and Mourer-Chauviré (2002) have been used in the comparisons. Anatomical nomenclature follows Livezey and Zusi (2006).
Class Aves Linnaeus, 1758
Order Strigiformes Wagler, 1830
Family Strigidae Leach, 1819
Genus Athene Boie, 1822
Athene vallgornerensis nov.sp.
The specific name vallgornerensis derives from the locality name, Cova des Pas de Vallgornera.
Cova des Pas de Vallgornera, Llucmajor, Mallorca, Balearic Islands.
The fossil assemblage is attributed to MN17 (i.e. Early Pleistocene according to the Gibbard et al.2010 update of the Quaternary base).
Only known from its type locality.
Species of Athene of small size with a tarsometatarsus shape and general aspect similar to Athene noctua, but characteristically shorter and more robust. It presents a well-developed cotyla lateralis with a narrow lateral extension and a well-developed crista medialis hypotarsi that is caudally oriented. In proximal view, a deep sulcus hypotarsi slightly laterally oriented. Remarkably massive trochlea metatarsi.
Major differences between IMEDEA-91958 and the four species of the same genus compared (A. noctua, A. cretensis, A. angelis and A. trinacriae, representing all the living and extinct western Palaearctic species of Athene) are mainly in terms of size and proportions. Additionally, in lateral view, the lateral extension of the cotyla lateralis is wider in A. angelis, and A. cretensis while in A. noctua and in IMEDEA-91958 it is narrower. The crista medialis hypotarsi is more developed in A. trinacriae and A. angelis and it is more caudally oriented in A. angelis and A. vallgornerensis. The proximal end of the tarsometatarsus is more robust in A. cretensis than in the remaining species, A. vallgornerensis included. The trochlea metatarsi are, in relation to the length of the bone, larger in A. vallgornerensis than in A. noctua and A. cretensis.
Description and comparison
IMEDEA-91958 and Athene share the following combination of diagnostic traits. In proximal view, the sulcus hypotarsi is relatively deep and the cotyla lateralis is relatively long and craniocaudally oriented. Both have a second foramen vasculare distale, apparently exclusive to Athene and some specimens of Otus scops. Athene and IMEDEA-91958, present a wider and more prominent lateral part of the trochlea metatarsi III than its medial part. In lateral view, the crista medialis hypotarsi merges gradually into the shaft of the tarsometatarsus. Nevertheless, it differs considerably in size and proportions from all the extant and extinct western Palaearctic Athene species, indicating that it definitively belongs to a different taxonomic entity. The phalanx ungualis of IMEDEA-91897 displays features identical to Athene noctua, but it is larger and more robust.
The two bones obtained in Cova des Pas de Vallgornera differ markedly from the corresponding bones of all the living small- and medium-sized European Strigidae (see Figs. 2 and 3). IMEDEA-91958 is a short and robust tarsometatarsus. Surnia, Aegolius and Glaucidium have a characteristic extremely short and robust tarsometatarsus, but very different from that of IMEDEA-91958. They present a more open sulcus hypotarsi than in the fossil specimen, mainly due to a lateral extension of the cotyla lateralis that laterally limits the sulcus. These three genera have a single foramen vasculare distale, while the fossil specimen (like Athene and some Otus) has a second clearly separated foramen, distally aligned with the first. The fossil also differs from Aegolius, Surnia and Glaucidium in the shape of the lateral extension of the cotyla lateralis; in the first two genera, this extension ends wider than in Athene. In Glaucidium, this extension is very short.
A characteristic feature of the tarsometatarsus of Otus is the equally-sized rims of the trochlea metatarsi III (Olson 1982). IMEDEA-91958 presents the lateral rim of the trochlea metatarsi III wider and more prominent than its medial part. The sulcus hypotarsi is more closed in Otus than in the fossil specimen. In lateral view, the crista medialis hypotarsi merges into the shaft of the tarsometatarsus more abruptly than in the fossil. The tarsometatarsi of Asio and Strix differ from IMEDEA-91958 in their greater length and robustness, and their sulci hypotarsorum are more open. The tarsometatarsi of the species of these genera display a deeply excavated cranial surface, while in the fossil specimen it is flat, as in Athene noctua.
Despite the phalanx ungualis having few diagnostic traits, some differences between IMEDEA-91897 and the remaining western Palaearctic Strigidae can be observed (Fig. 3). In ventral view, in Aegolius and Surnia, the tuberculum flexorium is more prominent than in Athene and IMEDEA-91897. Otus has the tuberculum flexorium shallower than IMEDEA-91897 and the complete phalanx is very straight. The phalanx ungualis of Asio is remarkably straighter than in the fossil and in Athene. Additionally, in Asio and Strix, the distance between tuberculum flexorium and the body of the claw is proportionately much smaller than in the fossil and in Athene.
On the basis to their morphological characteristics, both Strigidae bones obtained from Cova des Pas de Vallgornera are attributed to Athene. The tarsometatarsus of Strigidae is a highly characteristic bone, and its richness in diagnostic features has made it a suitable bone to be used in taxonomical analysis. Within Athene, the tarsometatarsus IMEDEA-91958 differs from all living and extinct western Palaearctic species, representing a new species as described here.
Mesurements (in mm) of the tarsometatarsi of A. vallgornerensis nov.sp. and middle- and small-sized western Palaearctic strigids for comparison
Two subspecies of A. noctua have been described from the European Plio-Pleistocene: A. n. lunellensis (Middle Pleistocene, Mourer-Chauviré 1975) and A. n. veta (Late Pliocene–Early Pleistocene, Jánossy 1974). The measurements of the sole tarsometatarsus attributed to A. noctualunellensis by Mourer-Chauviré (1975) are remarkably greater than A. vallgornerensis. A. noctua veta was described based on a fragment of coracoid (Jánossy 1974) from Rebielice Krolewskie in Poland, but it was later synonymized to Aegolius funereus (Mlìkovský 1992).
Weesie (1999) obtained an Athene sp. left tarsometarsus of small size in Su Corbeddu Cave (Late Pleistocene, Sardinia), and suggested that it could represent a new undescribed insular form. Nevertheless, Pavia and Mourer-Chauviré (2002) considered that it could be assigned to A. noctua. Consequently, this material has been discarded for comparison. Alcover (1989) reported Athene cf. veta from the Late Pliocene–Early Pleistocene of Cova de Ca Na Reia, Eivissa, but it was not figured and the fossil has not been located.
The phalanx IMEDEA-91897 has a similar shape to Athene noctua, although it is larger (Fig. 3). No phalanges of the three insular species of Athene described are available for comparative purposes.
Although IMEDEA-91958 is the sole large bone recovered of Athene vallgornerensis, it differs considerably, in size or shape, from the remaining extant and extinct Athene species. Although the size differences between IMEDEA-91958 and A. angelis are remarkable, the great similarity of their shape suggests that they could have shared a common ancestor (Fig. 2). The Pleistocene fauna from Corsica–Sardinia and Mallorca–Menorca share some mammalian taxa (e.g. shrews derived from mainland Asoriculus, related glirids and the closely related bovids Nesogoral and Myotragus) and both islands are situated in the western Mediterranean Sea, suggesting that they were settled by closely related fauna. In contrast, the Pleistocene mammalian fauna from Sicily and Crete does not share taxa closely related to the Mallorcan one. The emerging insular Athene species distribution pattern, with A. vallgornerensis–A. angelis displaying the highest similarities, fits well with these data. The presence of Athene vallgornerensis in Mallorca improves the knowledge of the evolution of little owls on the Mediterranean islands, where two main types of insular little owls seem to have evolved, one displaying a short and robust tarsometatarsus (A. angelis and A. vallgornerensis nov.sp.) and the other with a slender and longer tarsometatarsus (A. cretensis and A. trinacriae). The relatively long legs of A. cretensis and A. trinacriae, associated with relatively shorter wings, have been interpreted elsewhere as indicative of a more terrestrial life-style than Athene noctua (Weesie 1982; Pavia and Mourer-Chauviré 2002; Louchart 2005). Long legs are also characteristic of A. cunicularia, the Burrowing Owl, a species displaying terrestrial habits, while A. angelis should have had a less terrestrial life-style, according to its body shape and proportions (Louchart 2005). The life-style of A. vallgornerensis remains unknown.
A. vallgornerensis nov.sp. represents the fifth species of Strigiformes reported as fossil material in Mallorca. This Early Pleistocene Mallorcan representative of the genus Athene is unknown from the late Pleistocene and Holocene sites, as also happens with Tyto balearica.
Thanks are due to the Balearic Federation of Speleology (FBE) for its help in the excavation of Cova des Pas de Vallgornera and for the permission to publish the topographic survey of Fig. 1c. Mrs. Xana Villa (Oxford) reviewed the English of the manuscript. Carmen Guerra has a FPI grant from the Ministerio de Ciencia e Innovación (MICINN, Spain). Pere Bover has a contract JAE-DOC (CSIC) of the program “Junta para la Ampliación de Estudios”. This paper is included in the Project CGL2010-17889 of the Dirección General de Investigación (Ministerio de Educación y Ciencia, Spain).