Postcranial anatomy of Haldanodon exspectatus (Mammalia, Docodonta) from the Late Jurassic (Kimmeridgian) of Portugal and its bearing for mammalian evolution

The postcranium of the Late Jurassic docodont Haldanodon exspectatus Kuhne & Krusat, 1972 is represented by a partial skeleton and isolated bones of other individuals from the Late Jurassic (Kimmeridgian) of the Guimarota coal mine in Portugal. Haldanodon exhibits adaptations for a fossorial lifestyle such as stout and short limb bones and humeri with greatly expanded distal joints and strong deltopectoral crests. Short first and second phalanges and moderately curved and laterally compressed terminal phalanges with lateral grooves suggest that Haldanodon was a scratch-digger. The dorso-ventrally elongated, triangular scapula has a convex transverse profile with strongly laterally reflected anterior and posterior scapula margins, enclosing a deep trough-like 'infraspinous fossa'. A supraspinous fossa is not developed. The saddle-shaped glenoid facet is mainly formed by the coracoid and orientated antero-ventrally indicating a sprawling gait. No epiphyses were detected and the wide size range of humerus and femur possibly indicate a lifelong growth. Haldanodon is more derived than Morganucodon by complete reduction of the procoracoid, absence of the procoracoid foramen, and a peg-like coracoid. It shares with monotremes a postscapular fossa that is absent in Morganucodon. A PAUP analysis based on 280 cranio-dental and postcranial characters corroborated the position of Haldanodon above morganucodontids and below Hadrocodium. (c) 2005 The Linnean Society of London, Zoological Journal of the Linnean Society, 2005.