A field guide to mesozoic birds and other winged dinosaurs
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A field guide to mesozoic birds and other winged dinosaurs

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19.07.2019 Views

IAA Vega Bird Vegavis iaai Time: 65.5 Ma ago Location: Vega Island, Antarctica Habitat: Sandwich Bluff Member, Lopez de Bertodano Formation Size: WS unknown; BL ~25cm (10in); TL unknown Features: Known from a fragmentary skeleton severely damaged during preparation out of the rock matrix. Wing incompletely known. Legs relatively long, w/ tibia as long or longer than humerus. Tarsus about ¼ or ½ length of ulna (based on known radius length). Biology: The relatively long legs may indicate a wading lifestyle similar to the related Paleogene period presbyornithids, broad-billed, stilt-legged ducks more advanced than V. iaai. Numerous subtle characteristics of the skeleton show that this species was a primitive member of the duck, goose, & swan lineage (Anatoidea), possibly similar to modern basal anatoids like screamers (Anhimidae) & the magpie-geese (Anseranatidae), which diverged from the duck lineage before the evolution of the characteristic broad, flat bill of anatids & presbyornithids. The bill of Vegavis may therefore have been narrow & slightly hooked, like primitive anseriformes, or may have begun to broaden. This would have determined their exact method of feeding, but like all basal anseriformes, V. iaai probably foraged for soft plant material either in the water &/or in marshy shores & wetlands. Like screamers & magpie-geese, their feet may have been partially webbed. Gregory’s Polar Bird Polarornis gregorii Time: 65.5 Ma ago Location: Vega Island, Antarctica Habitat: Sandwich Bluff Member, Lopez de Bertodano Formation Size: WS unknown; BL ~80cm (2.6ft); TL unknown Features: Known from a partial skeleton including partial skull, vertebrae & limb bones. Toothless bill long, narrow & triangular. Head long & squat. Neck long (nearly equal to torso length when fully extended). Legs probably long, w/ very short femur (less than half skull length) & large tibia w/ strong muscle attachments. Tibia probably long, but most of it unknown. Biology: Advanced features of the skull & legs show that these birds were probably members of the modern loon lineage (Gaviiformes). The walls of the bones were relatively thick compared to modern loons, indicating a flightless or near-flightless, diving lifestyle. The wings may therefore have been small compared to modern loons. Neogaeornis wetzeli, another early loon relative from Chile, may be a senior synonym of this species or an unnamed, apparently flying species from Antarctica that has yet to be described. 162

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