Osteology

13 Chiappe L.M.

Walker C.A. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). 14 Chiappe L.M. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of northwestern Argentina. 15 Ji S.-A.

Atterholt J.A.

O’Connor J.K.

Lamanna M.

Harris J.

Li D.-Q.

You H.-L.

Dodson P. A new, three-dimensionally preserved enantiornithian (Aves: Ornithothoraces) from Gansu Province, northwestern China. 16 Sanz J.L.

Buscalioni A.D. A new bird from the Early Cretaceous of Las Hoyas, Spain, and the early radiation of birds. 17 Novas F.E.

Agnolín F.L.

Scanferla C.A. New enantiornithine bird (Aves, Ornithothoraces) from the Late Cretaceous of NW Argentina. The distal end of the right femur is jointed with a fully articulated tibiotarsus, fibula, and pes ( Figures 1 B and 1C). The femur is obscured by dense soft tissue. A separate, poorly preserved element contacts the lateral surface of the knee (possibly the distal ends of the ulna-radius). The tibiotarsus seems to bear a circular proximal articular surface that is expanded relative to the shaft, as in many enantiornithines []. The tibiotarsal shaft has an oval cross-section with the long axis oriented mediolaterally. The distal end of the tibiotarsus is expanded so that the articular surface formed by the condyles is much wider than the shaft. The medial condyle is wider than the lateral condyle, a condition typical of enantiornithines and other basal pygostylians []. The medial surface of the medial condyle appears somewhat excavated ( Figure 1 B). The articular surface extends onto the caudal surface of the tibiotarsus. The fibula is mediolaterally compressed and approximately three-quarters of the length of the tibiotarsus.

18 Chiappe L.M. Enantiornithine (Aves) tarsometatarsi and the avian affinities of the Late Cretaceous Avisauridae. 19 Atterholt J.

Hutchison J.H.

O’Connor J.K. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. 13 Chiappe L.M.

Walker C.A. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). 13 Chiappe L.M.

Walker C.A. Skeletal morphology and systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). 19 Atterholt J.

Hutchison J.H.

O’Connor J.K. The most complete enantiornithine from North America and a phylogenetic analysis of the Avisauridae. 20 O’Connor J.K.

Li D.-Q.

Lamanna M.

Wang M.

Harris J.D.

Atterholt J.A.

You H.-L. A new Early Cretaceous enantiornithine (Aves: Ornithothoraces) from northwestern China with elaborate tail ornamentation. 4 Xing L.-D.

O’Connor J.K.

McKellar R.C.

Chiappe L.M.

Tseng K.-W.

Li G.

Bai M. A mid-Cretaceous enantiornithine (Aves) hatchling preserved in Burmese amber with unusual plumage. 14 Chiappe L.M. Enantiornithine (Aves) tarsometatarsi from the Cretaceous Lecho Formation of northwestern Argentina. 21 Chiappe L.M.

Calvo J.O. Neuquenornis volans, a new Late Cretaceous bird (Enantiornithes: Avisauridae) from Patagonia, Argentina. The proximal tarsometatarsus appears fully fused ( Figures 1 B and 1C). The proximal ends of the metatarsals are expanded relative to their shafts, which remain unfused to one another—a condition typical even in adult enantiornithines. The dorsal surface of metatarsal III is convex, similar to the condition in avisaurid enantiornithines []. Typical of enantiornithines, metatarsal IV is narrower than metatarsals II and III []. Metatarsal III is the longest; metatarsals II and IV are subequal, extending to just above the trochlea of metatarsal III. The trochlea of metatarsal II is the widest, a proportion common among enantiornithines []. This trochlea is also slightly plantarly displaced relative to the coplanar trochleae III and IV. In plantar view, the medial condyle of the trochlea has greater plantar projection, and metatarsal III displays a slight depression just proximal to the trochlea. The trochlea of metatarsal IV appears reduced to a single condyle as in other enantiornithines []. Metatarsal I is approximately 20% of the length of metatarsal II, proximally tapered, and mediolaterally compressed. Similar to HPG-15-1 [], the shaft of metatarsal I articulates with the medial surface of metatarsal II, somewhat extending onto the plantar surface such that the lateral surface of the shaft of metatarsal I is deeply concave. The distal articular surface of metatarsal I projects plantarly, nearly perpendicular to the longitudinal axis of the shaft (J-shaped in medial view), a condition similar to some other enantiornithines []. The hallux was fully reversed in the anisodactyl condition.