Describer

Chiappe, 1993

Time

Cretaceous Late Campanian Maastrichtian

Classification

Saurischia Theropoda Tetanurae Coelurosauria Maniraptora Avialae Ornithothoraces Enantiornithes

Fossilsite

Lecho Formation, Estancia El Brete, Department of Candelaria, Province of Salta, Argentina

Info

Diagnosis

Enantiomithine bird with short and broad tarsometatarsus possessing the following autapomorphies: distal end much broader than proximal end; broad, dorsoplantarly compressed, and pulleylike trochlea of metatarsal II; distal end of metatarsal III laterally curved; metatarsal IV equal in length to metatarsal III; prominent dorsal ridge between distal halves of metatarsals II and III.

Etymology

Yungavolucris from Latin volucris, meaning \\\"bird,\\\" and Yunga referring to the phytogeographic region in which El Brete is located; brevipedalis from Latin brevis, \\\"short,\\\" and pedalis referring to the foot.

Holotype

PVL-4053 nearly complete right tarsometatarsus, lacking the craniolateral border of the lateral cotyla and the cranial portion of the trochlea of metatarsal IV.

Referred specimens

Incomplete right tarsometatarsi PVL-4040 and PVL-4692, incomplete left tarsometatarsus PVL-4052, and specimen PVL-4268 represented by the distal trochleae of right metatarsals II and III. 4 NO. 3083

Description

The tarsometatarsus of Yungavolucris brevipedalis is short and stout. It is dorsoplantarly compressed, being generally convex dorsally and flat plantarly. Its distal end is much broader than its proximal end. Metatarsals II, III, and IV are firmly attached to each other, although they are fused only in their proximal portion. In the proximal end, the medial cotyla is well developed and suboval; the lateral cotyla is less defined and its articular surface is slightly convex medially. Both an intercondylar eminence and hypotarsus are absent.

Metatarsal II is the most robust ofthe three metatarsals, but not the longest. It is straight throughout its length. Dorsally, in its middle portion it exhibits a very pronounced ovate-shaped tubercle, with its long axis oriented proximodistally. This tubercle was tentatively interpreted as the area of attachment of the M. tibialis cranialis (Brett-Surman and Paul, 1985; Chiappe, 1992a). The distal halfof this metatarsal is fairly compressed dorsoplantarly, especially in its medial portion. In the lateral portion of the distal half, its contact with metatarsal III forms a prominent ridge.

The distal end of metatarsal II is very broad. The trochlea of this metatarsal is ample, dorsoplantarly compressed and pulleylike. Both rims of the trochlea are bulbous and are separated from each other by a broad central furrow. Just proximal to the medial rim of the trochlea, on the medial margin ofthe dorsal face, there is a dorsomedial projection. The degree of development and orientation ofthis projection varies among the different specimens. Metatarsals III and IV are bent laterally over their distal third, and they are much longer than metatarsal II. In the dorsal face ofthe metatarsal III, just distal to the proximal end, there is a slender and elongated ridge for muscle attachment. Distally, in spite of the lateral bending of the shaft, the trochlea of metatarsal III is in a vertical position.

The medial rim of this trochlea is larger and more bulbous than the lateral, and deep collateral ligamental fossae excavate both sides. Metatarsal IV is very small with respect to metatarsals III and II. It is more weakly attached to metatarsal III than this one is to metatarsal II. The trochlea is missing in all available specimens except in the holotype where only the plantar half is preserved. It is simple and laterally compressed.

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