Glaucidium Boie, 1826

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 : 708-712

Genus Glaucidium Boie, 1826

Type species: Strix passerina Linnaeus, 1758 (G. R. Gray, 1840), type by subsequent designation; Recent, Sweden.

Taxonomic remarks.—The species of Glaucidium differ from those of Aegolius Kaup, 1829 , which are approximately the same size as the North American species of Glaucidium , by having tarsometatarsus with (1) shaft, in anterior view, bowing markedly mediad distal to medial edge of Cotyla medialis (bows only slightly mediad, close to medial edge of Cotyla medialis in Aegolius ), which gives a greater curvature to Sulcus extensorius and positions Crista medialis hypotarsi, in posterior view, more centrally on shaft than in Aegolius ; (2) shaft with anterior face distal and lateral to Sulcus extensorius shallowly to moderately excavated, with anterolateral corner of shaft a low, rounded ridge (moderately to deeply excavated, with anterolateral corner of shaft a high, narrow ridge in Aegolius ); (3) shaft, in posterior view, more deeply and broadly excavated proximally between Cristae hypotarsi; (4) shaft with proximal half of Fac. medialis narrow anteroposteriorly, in medial view (broad, in medial view, in Aegolius ); (5) Sulcus extensorius proximally forms a shallow groove in the anterolateral side of Eminentia intercotylaris (Sulcus extensorius lies just lateral to anterolateral edge of Eminentia intercotylaris in Aegolius ); (6) Tuberositas m. tibialis anticus lies proximal, but close, to mid−length of shaft, with Sulcus extensorius extending only slightly distad past it (Tuberositas m. tibialis anticus lies closer to proximal end of shaft, with Sulcus extensorius extending farther distad than the tuberosity in Aegolius ); (7) Crista medialis hypotarsi much less robust than in Aegolius ; (8) Trochlea metatarsi III with anterolateral corner bulging laterad significantly (anterolateral corner not bulging significantly laterad in Aegolius ); (9) Trochlea metatarsi II with “wing” curving moderately mediad, in distal view (curving more mediad in Aegolius ); and (10) Trochlea metatarsal IV with “wing” directed posteriad (directed posteromediad in Aegolius , resulting in a larger gap between tips of Trochleae metatarsi II and IV). These distinguishing characters can be observed by

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comparing the specimens of G. californicum and A. acadicus in Figs. 1 and 2.

The nine non−North American species of Glaucidium and Taenioglaux examined agreed fairly closely with all characters of the North American species of Glaucidium noted above. These two genera are in the tribe Surniini of the subfamily Surniinae , whereas Aegolius is in the tribe Aegoliini of the same subfamily (del Hoyo et al. 1999; König and Weick 2008). This distinction appears to be well supported by the many osteological differences noted between the two groups.

The mandible of Glaucidium differs from that of Aegolius by having (1) Proc. retroarticularis short, less flattened dorsoventrally, in lateral view; (2) dorsolateral rim of Fac. artic. quadratica medialis not prominently overhanging ventrolateral portion of Fac. artic. quadratica medialis; and (3) Fac. artic. quadratica lateralis broader and more rounded, in dorsal view.

The coracoid of Glaucidium differs from that of Aegolius by having (1) Proc. acrocoracoideus narrow and produced anteriad, in ventral view (very broad and blunt anteriorly, in ventral view, in Aegolius ); (2) Proc. procoracoideus, in medial view, extending ventromediad at low angle to long axis of shaft (extends more ventrad than mediad at steep angle to long axis of shaft in Aegolius ); (3) Proc. procoracoideus, in proximal view, extending more mediad than ventrad, with ventral tip close to shaft, in ventral view (Proc. procoracoideus, in proximal view, extending more ventrad than mediad, with ventral tip farther from shaft, in ventral view, in Aegolius ); (4) Cotyla scapularis of Proc. procoracoideus well rounded medially (forms a prominent corner medially on Proc. procoracoideus in Aegolius ); (5) Fac. artic. humeralis narrow for length, especially toward sternal end, in dorsal view (broad throughout, especially near Proc. acrocoracoideus, in Aegolius ); (6) Fac. artic. sternalis with sternal rim steeply curving, or deeply concave, in ventral view (sternal rim gently curving, or slightly concave, in ventral view, in Aegolius ); (7) Fac. artic. sternalis with dorsal surface moderately long mediolaterally and long anteroposteriorly (dorsal surface long mediolaterally and short anteroposteriorly in Aegolius ); and (8) Fac. artic. sternalis with lateral end of articular rim appearing slightly twisted dorsad, in sternal view (Fac. artic. sternalis with gentle curvature for length in Aegolius ).

The humerus of Glaucidium differs from that of Aegolius by having (1) Crista deltopectoralis projecting mostly dorsad (projects posteriad in Aegolius ); (2) Impressio m. coracobrachialis anterior broad, deep proximally and shallow distally, and very short (broad, deep, extending distad about length of Crista bicipitalis in Aegolius ); (3) Caput humeri rounded, in anterior view, not projecting much proximad (Caput humeri smaller, projecting prominently proximad in Aegolius ); (4) Crista bicipitalis with ventral edge short, moderately convex ventrad, in anterior view (long, only slightly convex ventrad, in anterior view, in Aegolius ); (5) Crista bicipitalis with large Fossa pneumotricipitalis (Fossa pneumotricipitalis of moderate size in Aegolius ); (6) Tuberculum ventrale positioned near midline ridge of shaft, in posterior view (positioned well ventral to midline ridge of shaft, in posterior view, in Aegolius ); (7) Incisura intercondylaris deep, in anterior view (shallow, in anterior view, in Aegolius ); (8) Sulcus humerotricipitalis deep, slightly undercutting dorsal side of Proc. flexorius (shallow, not undercutting Proc. flexorius in Aegolius ); and (9) Proc. flexorius narrow, projecting distad beyond distal end of Condylus ventralis (broad and not projecting distad beyond distal end of Condylus ventralis in Aegolius ).

The radius of Glaucidium differs from that of Aegolius by having (1) Tuberculum bicipitale radii with ventral edge curving, or concave dorsad, in anterior view, with distal end protruding more dramatically from shaft (ventral edge straight in Aegolius , in anterior view, with distal end protruding much less from shaft); (2) areas of attachment of the osseous arch to shaft minimal (well developed in Aegolius ).

The carpometacarpus of Glaucidium differs from that of Aegolius by having (1) Proc. pisiformis longer and more pointed; (2) Synos. metacarpalis distalis longer and Fac. artic. digiti minoris extending farther distad; (3) tuberosity for attachment of Lig. ulnocarpometacarpale ventrale on Os metacarpale minus a more prominent protuberance; (4) Fac. artic. ulnocarpalis wider anteroposteriorly, with posterodistal rim merging with Os metacarpale minus more abruptly, giving appearance of a “corner” to rim, in ventral view; and (5) Synos. metacarpalis proximalis, in dorsal view, ending distally in a narrow groove (ends distally in a broad groove in Aegolius , a consequence of the Os metacarpali minus bowing more posteriad distal to synostosis).

The femur of Glaucidium differs from that of Aegolius by having (1) attachment of M. iliotrochantericus anterior lying distal to, or overlapping slightly, that for M. ischiofemoralis (the two muscle scars overlap to a large degree in Aegolius ); (2) Condylus lateralis, in distal view, with posteromedial end bulging moderately and not projecting posteriad much beyond Crista fibularis (posteromedial end not bulging mediad in Aegolius , but projecting posteriad well beyond Crista fibularis); (3) Trochlea fibularis broad and shallow (narrow, deeper, and more V−shaped in Aegolius ); (4) Fac. medialis of Condylus medialis deeply excavated (slightly to moderately excavated in Aegolius ); and (5) Tuberculum m. gastrocnemius lateralis long, prominently raised, extending well proximad of Condylus lateralis (short, not prominently raised, and not extending as far proximad in Aegolius ).

The tibiotarsus of Glaucidium differs from that of Aegolius by having (1) Fac. artic. medialis protruding less mediad, with posteromedial rim more rounded in proximal view; (2) Incisura intercondylaris deeply undercut anteroproximally (not undercut in Aegolius ); (3) Spina fibulae first fuses to shaft distal to lateral attachment of Lig. transversum (first fuses to shaft proximal to lateral attachment of Lig. transversum in Aegolius ); and (4) lateral attachment of Lig. transversum less prominent, projecting more anteromediad than

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anteriad (lateral attachment a more distinct protuberance, projecting more anteriad than anteromediad in Aegolius ).

Geographic and stratigraphic range.—Worldwide; upper Pleistocene–Recent.