Asphaltoglaux cecileae, Campbell & Jr. & Bochenski, 2013

Campbell, Kenneth E., Jr. & Bochenski, Zbigniew M., 2013, Two new late Pleistocene miniature owls from Rancho La Brea, California, Acta Palaeontologica Polonica 58 (4), pp. 707-721 : 717-720

Asphaltoglaux cecileae sp. nov.

Figs. 2, 4 .

Etymology: Dedicated to our friend and colleague, Cécile Mourer− Chauviré, Université Claude Bernard, Lyon, France, in recognition of her many contributions to our understanding of avian evolution, especially the fossil owls of Europe, and for her long service and dedication to the Society of Avian Paleontology and Evolution.

Holotype: Complete right tarsometatarsus, LACM RLB K1180 ( Fig.2).

Type horizon: Pit 36, Los Angeles, California, USA.

http://dx.doi.org/10.4202/app.2011.0125

Type locality: Rancho La Brea asphalt deposits; upper Pleistocene.

Diagnosis.—As for genus.

Referred material.— The following specimens from Rancho La Brea are referred to Asphaltoglaux cecileae , but because they were not found in articulation or close association with the holotype it cannot be conclusively demonstrated that they represent that species. Therefore, we exclude them from the type series. Complete right coracoid, LACM RLB E9533 (Pit 16); complete left humerus, LACM RLB K9441 (Pit A); complete right femur, LACM RLB K9349 (Pit A). All specimens damaged by abrasion .

Description and comparison.—The coracoid of Asphaltoglaux ( Fig. 4 ) resembles that of Aegolius and differs from that of the similar−sized Glaucidium , by having those characters listed above that distinguish Aegolius from Glaucidium , except for character 1, which differs in Asphaltoglaux . The coracoid of Asphaltoglaux differs from that of Aegolius by having (1) Proc. acrocoracoideus long, narrow mediolaterally and sharply curved mediad, in ventral view (shorter, broad mediolaterally, and not curving mediad in Aegolius ); (2) Fac. artic. clavicularis well rounded, not a protruding corner of Proc. acrocoracoideus (Fac. artic. clavicularis a distinct, protruding corner of Proc. acrocoracoideus in Aegolius ); (3) Proc. acrocoracoideus with distal portion, in proximal view, as thick or thicker dorsoventrally as mediolaterally (expanded more mediolaterally than dorsoventrally in Aegolius ); (4) groove, or depression, between Fac. artic. humeralis and bicipital attachment (= neck of Howard 1980) shallow, in proximal view (deep in Aegolius ); (5) Fac. artic. sternalis with articular rim very long and slightly concave, in ventral view (shorter and more concave in ventral view in Aegolius ); (6) Fac. artic. sternalis medialis very wide, dorsoventrally, forming a deep shelf (much narrower dorsoventrally in Aegolius , forming a shallow shelf); (7) Fac. artic. sternalis lateralis with ventromedial portion largest at flattened medial end, or tip, of Angulus medialis (ventromedial portion largest lateral to pointed medial tip of Angulus medialis in Aegolius ); and (8) shaft very stout, with medial portion just proximal to Fac. artic. sternalis medialis quite rounded dorsally (shaft more slender, with medial portion just proximal to Fac. artic. sternalis medialis flattened or slightly concave in Aegolius ).

The humerus of Asphaltoglaux ( Fig. 4 ) resembles that of Aegolius and differs from that of the similar−sized Glaucidium , by having those characters listed above that distinguish Aegolius from Glaucidium , except for character 3 (see #1 following). The humerus of Asphaltoglaux differs from that of Aegolius by having (1) Caput humeri more rounded, extending farther proximodorsad proximal to Tuberculum dorsale than in Aegolius , in anterior and dorsal view; (2) Crus dorsale fossae, in ventral view, with distal end a pronounced ridge extending distad beyond distal end of Crista bicipitalis (distal portion not a pronounced ridge and not extending distad beyond distal end of Crista bicipitalis in Aegolius ); (3) Crus dorsale fossae, in ventral view, angled posteriad for much of length in nearly a straight line at about 45 ° to shaft (curving posteriad distally in Aegolius ); (4) Crista bicipitalis with distal end merging gradually with shaft, in anterior view (slightly damaged, but does not appear to affect character) (distal end merging more abruptly with shaft in Aegolius , in anterior view, because Crista bicipitalis extends farther ventrad distally); (5) Epicondylus ventralis rounded, relatively long proximodistally, in anterior view (more angular, shorter proximodistally, and projecting relatively farther ventrad, in anterior view, in Aegolius ). Numerous points of minor damage limit observable characters.

The femur of Asphaltoglaux ( Fig. 4 ) resembles that of Aegolius and differs from that of the similar−sized Glaucidium by having those characters listed above that distinguish Aegolius from Glaucidium . The femur of Asphaltoglaux differs from that of Aegolius by having (1) Caput femoris with Fovea lig. capitis open via broad groove to Collum femoris, in proximal view (can be notched, but still closed off from Collum femoris in Aegolius ); and (2) Caput femoris extending only slightly proximad to medial edge of Collum femoris, in posterior view (extending significantly proximad to medial edge of Collum femoris in Aegolius ). The proximal and distal ends are too damaged to identify additional definitive distinguishing characters. Nonetheless, the Condylus lateralis appears to be more rounded posteriorly and not to extend as far posteriad, in lateral view, in Asphaltoglaux than in Aegolius .

Remarks.—Using the method for estimating body mass noted above, the body mass of Asphaltoglaux cecileae is estimated at 78.2 g based on the single referred femur. There is an unknown error associated with this estimate, which is probably an underestimate, because the specimen is crushed. The recorded body mass range for Aegolius acadicus is 54–124 g, whereas that for Aegolius funereus is 90–194 g ( König and Weick 2008). The tarsometatarsus of Asphaltoglaux cecileae is stouter, or more robust, than a specimen of slightly greater length of Aegolius acadicus ( Fig. 2), although because of the small size of the specimens the actual metric differences are small ( Table 2). If the three referred specimens, from two additional pits, are correctly assigned to species, then it can be postulated that the extinct species was overall a slightly heavier−bodied species than Aegolius acadicus . We also take the large size and robustness of the Crista medialis hypotarsi, and its Fac. plantaris, of Asphaltoglaux cecileae ( Fig. 5 ) to indicate a heavier−bodied bird than seen in Aegolius acadicus . Confirmation of this hypothesis can only come with more specimens.

As noted above, Aegolius funereus is, in general, a much heavier bird than Aegolius acadicus . However, the tarsometatarsus of Aegolius funereus is generally shorter than that of Aegolius acadicus , although more robust ( Fig. 5B , Table 2). On the other hand, the humerus of Aegolius funereus is longer than that of Aegolius acadicus ( Table 2). There are too few fossil specimens to draw any definitive conclusions, but

Tarsometatarsus total length based on the single humerus, femur, and tarsometatarsus available, the limb proportions of Asphaltoglaux cecileae appear to be more similar to those of Aegolius acadicus than those of Aegolius funereus . The more robust tarsometatarsus of Asphaltoglaux cecileae might be indicative of a feeding strategy more similar to that of Aegolius funereus than Aegolius acadicus , which could have provided niche separation between the extinct species and Aegolius acadicus .

In a note left with the coracoid herein referred to Asphaltoglaux cecileae dated 19 April 1932, Hildegarde Howard described this coracoid, LACM RLB E9533 from Pit 16, as too small for Speotyto (now included in Athene ) and too large for Aegolius (but see Table 2). She did not elaborate on any osteological characters. Nonetheless, the single specimen she referred to Aegolius acadicus ( Howard 1962: table 1) was said to have come from Pit 16, and this specimen, the above noted coracoid, was referred to in the original, pre−1960s Rancho La Brea catalogue as Cryptoglaux (now included in Aegolius ) acadica . Why the holotypic tarsometatarsus of Asphaltoglaux cecileae was not listed in Howard’s (1962) table is puzzling

http://dx.doi.org/10.4202/app.2011.0125

because it was also referred to in the original, pre−1960s Rancho La Brea catalogue as Cryptoglaux acadica .

There is little to be said about this new genus of miniature owls, given its representation by only four specimens. If its superficial osteological similarity to Aegolius reflects its taxonomic position, then it could be placed within the tribe Aegoliini , which currently comprises four species of Aegolius . All but one of these owls has a widespread geographic distribution, and all frequent extensive forests. If Asphaltoglaux preferred similar habitats, which is far from certain, the drier climate and reduction of forest cover in the southwestern United States ( Bochenski and Campbell 2006; Campbell and Bochenski 2010) at the end of the last glaciation could very well have resulted in its extinction.

Aegolius acadicus has been found in upper Pleistocene deposits at several localities in the southwestern United States and Mexico ( Brodkorb 1971), including the asphalt deposits at Carpinteria, California. Those specimens that we have been able to examine are as readily distinguished from Asphaltoglaux cecileae as are the modern comparative specimens. No specimens of Aegolius acadicus have been found at Rancho La Brea, although this species can be found in mountain forests around the Los Angeles Basin today.

Geographic and stratigraphic range.—Rancho La Brea, California USA; upper Pleistocene.

Figures

Fig. 4. Stereopairs of specimens from late Pleis− tocene, Rancho La Brea, California, USA re− ferred to miniature owls Asphaltoglaux cecileae sp. nov. (A, C, D) and Glaucidium kurochkini sp. nov. (B). A. Left humerus (RLB K9441) in anterior (A1) and posterior (A2) views. B. Right carpometacarpus (RLB K9404) in dorsal (B1) and ventral (B2) views. C. Right femur (RLB K9349) in anterior (C1) and posterior (C2) views. D. Right coracoid (RLB E9533) in ven− tral (D1) and dorsal (D2) views. See Fig. 3 for additional labeled osteological features. Abbre− viations: artic., articularis; Fac., Facies.

Fig. 5. Scatter plots illustrating the disproportionately large size of the Crista medialis hypotarsi of Asphaltoglaux cecileae sp. nov. A. Length versus width of Fac. plantaris of Crista medialis hypotarsi. B. Width of Crista medialis hypotarsi stem versus tarsometatarsus total length. All measurements in mm.