Kimmeridgian Jurassic Postcranial Mammal Fossils From Portugal

Mammalian postcranial bones from the Late Jurassic of Portugal and their implications for forelimb evolution

Author:

Thomas Martin

Abstract:

Isolated bones of forelimb and pelvic girdle (two humeri, five ulnae, and an ilium) recovered from the Late Jurassic (Kimmeridgian) Guimarota coal mine in western central Portugal are attributed to the docodont Haldanodon exspectatus, dryolestoids, and a ?paulchoffatiid multituberculate. The larger of the two humeri is assigned to the dryolestid Dryolestes leiriensis based on size and shape. It clearly exhibits an incipient trochlea at the distal joint, suggesting that this derived character was well established among Late Jurassic dryolestidans, including Henkelotherium. Plesiomorphic characters are the prominent spherical radial condyle and the weakly developed ulnar condyle. An incipient medial keel is present in distal aspect of the humerus trochlea. The shallow olecranon fossa of the humerus corresponds to the small anconeal process of the radius. The smaller humerus with damaged distal joint is 50% smaller and cannot be assigned to a specific dryolestoid taxon. It is in the size range of the smaller Guimarota dryolestoids Krebsotherium, Drescheratherium, and Henkelotherium. One ulna differs from the dryolestoid ulnar shape by the nearly semicircular articular surface for the ulnar condyle of the humerus, the asymmetric olecranon with medial overhang, as well as the prominent anconeal process and is tentatively attributed to a paulchoffatiid multituberculate.