Hesperornithiformes

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Hesperornithiformes Furbinger 1888, amended Martin & Tate 1976

These enigmatic diving seabirds from the Upper Cretaceous are among the most aberrant birds, and indeed vertebrates to have ever lived, in multiple ways. Hesperornithiformes display an autapomorphic form of cranial kinesis which Gingerich (1976) referred to as "maxillokinesis" in which the maxillae are capable of sliding cranio-caudally over subnarial bars formed by the premaxillae and nasals. Martin & Tate (1976) reviewed the taxonomy and amended the diagnosis of Hesperornithiformes, but their assessment included plesiomorphic characters in the analysis, (e.g. mandibular symphysis not fused), and thus Galton & Martin's (2002) diagnosis of the order is offered herein, with the following characters synapomorphic of Hesperornithiformes:

a)Cranial elements caudal to the fronto-parietal suture, fused.

b)Pterygoids broad, short, with well developed articulation with the palatines, which are exceptionally narrow and elongate.

c)Pneumaticity of quadrate lacking or highly reduced.

d)Intramandibular articulation located between angular and splenial

e)Thoracic series heterocoelous

f)Long-bones apneumatic, apomorphic condition related to ecological constraints.

g)Cnemial crest isoceles in shape, composed of exclusively of the patella.

h)Patella perforated by a foramen for insertion tendon of M. ambiens.

i)Tarsometatarsus displays a craniolateral ridge extending to trochlea IV (lateral trochlea).

j)Lateral trochlea as large as trochlea III (middle trochlea).

k)Pedal digit IV longest

JGK