Tiny Iberomesornis

Figure 1. Iberomesornis revisited. One of the smallest of the enantiornithes birds has a long pedal digit 4.

Figure 1. Iberomesornis revisited. One of the smallest of the enantiornithes birds has a long pedal digit 4. Note the placement of the longest toe beneath the center of balance at the shoulder glenoid in this volant biped, a configuration convergent with pterosaurs.

Iberomesornis romerali (Sanz and Bonaparte 1992, LH-22 (Las Hoyas Collection), Barremian, Early Cretaceous, 125 mya) tiny bird (8.7 cm axial column) with short wings (20 cm wingspan), pygostyle.  The long coracoids indicated powerful flapping muscles. The combination of a long p4.4 and short p3.3 makes the foot unique. This tiny taxon continued the phylogenetic size reduction that coincided with improvements in the ability to fly, as indicated by the longer coracoids and caudal fusion.

The Enanitornithes, or opposite birds, are so-named because their scapula/coracoid joint tabbed the opposite way of living birds. No living birds are enantiornithes.

References
Sanz JL and Bonaparte JF 1992. A New Order of Birds (Class Aves) from the Lower Cretaceous of Spain. In JJ Becker (ed): Papers in Avian Paleontology Honoring Pierce Brodkorb. Natural History Museum of Los Angeles County Contributions in Science 36:38-49

wiki/Iberomesornis

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