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

Fallen Diving Bird Baptornis advenus Time: 80 Ma ago Location: Kansas, USA Habitat: Smokey Hill Chalk Member, Niobrara Formation. Deep waters of a warm inland sea dominated by ammonites and a diversity of small to gigantic fish. Size: WS 36cm (1.2ft); BL ~70cm (2.3ft); TL unknown Features: Marine. Head long & slender w/ very slim, toothed snout ending in a moderately long bill. Neck long & slender. Body long & barrel-shaped. Wings small & vestigial. Legs long, but w/ short tarsus & small feet. Biology: The smallest hesperornithean species in this environment, probably foraged for smaller prey and possibly in shallower water than relatives. Anatomy of the toe joints implies the feet were likely webbed, rather than lobed. Alex’s Near Western Bird Parahesperornis alexi Time: 80 Ma ago Location: Kansas, USA Habitat: Smokey Hill Chalk Member, Niobrara Formation Size: WS unknown; BL 1.1m (3.6ft); TL unknown Features: Similar to, but more primitive than, Hesperornis. Toe anatomy consistant with lobed rather than webbed feet. Biology: Only known hesperornithean remains to preserve skin & feather impressions. Like grebes, tarsus was covered at the front w/ broad scutes near the feet (26 scutes in all). Closer to the body, the tarsus was covered in very long, plumulaceous feathers, the tips of which reached almost to the foot. Thick-footed Western Bird Hesperornis crassipes Time: 80 Ma ago Location: Kansas, USA Habitat: Smokey Hill Chalk Member, Niobrara Formation Size: WS unknown; BL 1.1m (3.6ft); TL unknown Features: Marine, similar to H. regalis in anatomy. Differ in distinct tarsus w/ larger muscle attachmentssites at the ankle, & shallower attachment sites on the breastbone. Biology: Lived alongside related species, probably exploited different ecological niche. The differences in tarsal anatomy may indicate a different foot-propelled diving stroke. Regal Western Bird Hesperornis regalis Time: 80-78 Ma ago Location: Kansas, USA Habitat: Smokey Hill Chalk Member, Niobrara Formation Size: WS ~46cm (1.5ft); BL 1.7m (5.5ft); TL unknown Features: Head small with long, thin jaws tipped w/ compound beak. Numerous teeth in jaws behind beak. Beak restricted to predentary on lower jaw, extensive in upper jaw, covering long premaxilla & continuing slightly above teeth. Beak slightly hooked. Lower jaw teeth set in grooves. Lower teeth locked into pits in premaxilla when jaws were closed. Body short & round w/ arched back. Wings very small, probably vestigial & hidden beneath body feathers. Upper legs attached to torso & likely affixed to body wall by soft tissue. Tarsi & feet emerged laterally from hip/tail area. Toes long, w/ fourth/inner toe longest. Toes probably lobed. Tail broad & flat, possibly somewhat beaver-like. Biology: Known from numerous remains incl. nearly complete skeletons. Like many large, deep-sea diving birds, they may have been counter-shaded for camouflage. While diving, necks were probably locked into place by ligaments in a tight curve with the head adjacent to the torso, to avoid torsion during quick underwater turning. Given the degree to which the hind limbs were permanently splayed & incorporated into the streamlined body wall similar to loons, these were probably extremely awkward on land, unable to walk, instead pushing along on the belly w/ a dragging motion similar to seals (Martin & al. 2012). 168

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