Vertebrate Zoology BI 322 Exam 3 Review - Avemetatarsalians, Dinosaurs, and Avian Biology

Vocabulary practice flashcards covering archosaur evolution, pterosaurs, dinosaur lineages, skeletal morphology, feather anatomy, flight aerodynamics, and avian physiology for Exam 3 review.

Avemetatarsalia

The archosaurian lineage ("bird feet") characterized by a functional decoupling of the fore- and hindlimbs and a mesotarsal ankle joint; first appeared in the Middle Triassic and is roughly synonymous with Ornithodira.

Restricted mesotarsal joint

An ankle joint structure characteristic of avemetatarsalians (such as †Lesothosaurus) where the astragalus and calcaneus are fixed proximal tarsal bones, and the hinge joint passes between the proximal and distal tarsals.

Crocodyloid joint

An ankle joint morphology found in crocodylomorphs in which the ankle hinge flexes between the astragalus (on the proximal side) and the calcaneus (on the distal side).

Cheiropatagium

The principal wing membrane of a pterosaur, spanning from the body to the vastly elongated fourth digit (wing finger).

Propatagium

The anterior flight membrane that spans along the leading edge of the wing between the shoulder and the wrist in pterosaurs and birds.

Cruropatagium

The flight membrane in pterosaurs located posteriorly between the hindlimbs and the tail.

Pteroid bone

A unique, forward-pointing wrist bone in pterosaurs that supported the propatagium along the leading edge of the wing.

Pycnofibers

Hair-like fuzzy integumentary filaments covering the bodies of pterosaurs, providing thermal insulation.

Perforated acetabulum

An open hip socket formed where the ilium, ischium, and pubis meet; the key diagnostic synapomorphy shared by all dinosaurs.

Ornithischia

The "bird-hipped" dinosaur lineage in which the pubis angles posteroventrally parallel to the ischium; first appeared in the Early Jurassic and reached peak diversity in the Late Cretaceous.

Saurischia

The "lizard-hipped" dinosaur lineage in which the pubis primitively points anteroventrally; this clade includes sauropodomorphs and theropods (from which birds evolved).

Thyreophora

The "shield-bearing" clade of armored ornithischian dinosaurs (including stegosaurs and ankylosaurs) characterized by keeled osteoderms.

Marginocephalia

The ornithischian clade defined by a shelf of bone projecting over the back of the skull, including dome-headed pachycephalosaurs and horned/frilled ceratopsians.

Tooth battery

A specialized arrangement of tightly packed, interlocking replacement teeth that continuously wear down to form a broad grinding occlusal surface, found in hadrosaurs.

Sauropodomorpha

A saurischian clade of enormous quadrupedal herbivores featuring long necks, small heads, pneumatic vertebrae, long tails, and continuously replaced non-chewing teeth.

Ziphodont teeth

Blade-like, laterally compressed, serrated teeth adapted for slicing flesh, typical of carnivorous theropod dinosaurs.

Furcula

The wishbone of theropods and birds, formed by the midline fusion of the clavicles; it acts as an elastic spring storing mechanical energy during the downstroke and releasing it on the upstroke.

Maniraptora

A diverse coelurosaurian theropod clade ("hand robbers") that includes dromaeosaurs and birds, characterized by elongated forelimbs, flexible wrists, and derived pennaceous plumage.

Archaeopteryx

A transitional Late Jurassic ($~150\,\text{Ma}$) avialan from Germany with modern asymmetrical flight feathers alongside ancestral reptilian traits including teeth, clawed wing digits, and a long bony tail.

Enantiornithes

The dominant, diverse clade of Mesozoic avialans known as "opposite birds" because the articular facets between their scapula and coracoid are reversed relative to modern birds.

Hesperornis

A flightless, toothed, foot-propelled diving ornithuran bird from the Late Cretaceous of North America that possessed vestigial wings.

Asteriornis

A Late Cretaceous ($~66.8\,\text{Ma}$) European avialan nicknamed the "wonder chicken," belonging to Galloanserae and representing one of the oldest known crown-group birds.

Exaptation

An evolutionary process where a trait originally selected for one function is co-opted for a completely new or additional function (e.g., feathers for insulation co-opted for flight).

Calamus

The hollow, bare basal portion of a feather's central shaft (quill) that anchors into the skin follicle.

Rachis

The solid, extended central axis of a feather above the calamus, supporting the vanes.

Barbules

Microscopic projections branching off the barbs of a feather, bearing tiny hooklets that interlock with adjacent barbules to create a unified vane surface.

Primaries

Contour flight feathers anchored to the hand (carpometacarpus and digits) that generate forward thrust during flapping flight.

Secondaries

Contour flight feathers anchored along the ulna of the forearm that primarily generate aerodynamic lift.

Covert feathers

Small contour feathers that overlap the bases of primary and secondary flight feathers to smooth airflow across the wing surface.

Alula

A group of feathers attached to the first digit (thumb) that creates a leading-edge slot to increase air velocity over the wing and delay aerodynamic stalling at high angles of attack.

Angle of attack

The angle formed between the chord plane of an avian wing and the plane of the oncoming air stream.

Trabeculae

Internal strut-like bony cross-braces that reinforce the hollow cavities of pneumatic bird bones while maintaining low weight.

Uncinate processes

Posterior bony projections on avian ribs that overlap successive ribs, strengthening the thoracic cage against flight stresses.

Keel (Carina)

A prominent ventral blade-like extension of the sternum in birds that serves as the major attachment site for flight muscles.

Pectoralis muscle

The large superficial chest muscle attached to the sternal keel that powers the forceful downstroke of the avian wing.

Supracoracoideus muscle

The deep flight muscle lying beneath the pectoralis that powers the wing upstroke (recovery stroke) via a tendon routed through the triosseal foramen.

Triosseal foramen

A canal formed by the junction of the scapula, coracoid, and furcula through which the supracoracoideus tendon passes to act as a pulley elevating the wing.

High-aspect-ratio wings

Long, narrow wings with a high length-to-width ratio (such as in albatrosses), minimizing induced drag and used for dynamic soaring over open oceans.

Elliptical wings

Short, rounded wings that provide high maneuverability and rapid takeoffs in dense or complex forest habitats.

Dynamic soaring

A flight mode that exploits horizontal wind velocity gradients over the ocean, allowing birds to gain altitude and maintain flight speed with minimal flapping.

Static soaring

A flight mode where birds circle within rising columns of warm air (thermals) or upward winds over hills to gain altitude without flapping.

Anisodactyly

The classic perching foot arrangement in birds, possessing three forward-facing toes (digits 2, 3, and 4) and one backward-facing toe (digit 1, the hallux).

Zygodactyly

An avian foot morphology where two toes face forward (digits 2 and 3) and two face backward (digits 1 and 4), characteristic of climbing birds such as woodpeckers and parrots.

Didactyly

A specialized two-toed foot condition (retaining only digits 3 and 4) unique to ostriches, adapted for cursorial running.

Craniofacial hinge

A flexible transverse bending zone between the braincase and the facial bones that allows the upper bill to flex upward during jaw opening.

Rhynchokinesis

A specialized cranial kinesis where the tip of the upper bill can flex upward independently while the remainder of the beak remains closed (seen in probing shorebirds like godwits).

Crop

An expanded, muscular outpocketing of the esophagus used for temporary food storage, softening, and later regurgitation to offspring.

Proventriculus

The anterior glandular chamber of the avian stomach that secretes digestive enzymes and hydrochloric acid onto ingested food.

Gizzard (Ventriculus)

The thick-walled, muscular posterior compartment of the avian stomach that mechanically pulverizes food, often aided by ingested stones (gastroliths).

Tetrachromatic vision

Avian color perception mediated by four distinct cone photoreceptors, enabling birds to detect light wavelengths in the deep-blue and ultraviolet spectrum.

Asymmetrical external auditory meatuses

A vertical and horizontal asymmetry between the left and right ear openings in owls, allowing precise three-dimensional sound localization.

Compass orientation

A navigation mechanism where birds fly along a fixed heading using compass cues (sun, stars, or magnetic field) without the ability to correct course if displaced.

True navigation

An advanced navigation ability shown by experienced adult migrants that allows them to recognize geographical displacement and recalculate their heading toward their destination.

ZW sex-determination system

The genetic sex-determination system of birds where females are heterogametic ($ZW$) and males are homogametic ($ZZ$).

Palaeognathae

The basal clade of modern birds ("old jaw") comprising ratites (ostriches, emus, rheas, kiwis) and tinamous, characterized by an ancestral palate anatomy and mostly flightless forms without a keeled sternum.

Passeriformes

The perching birds (songbirds), an order encompassing over $6{,}500$ species (more than half of all extant birds), characterized by specialized perching feet, syrinx musculature, and vocal learning.

Phorusrhacidae

An extinct Cenozoic family of flightless apex predatory birds ("terror birds") from the Americas, characterized by massive bodies and hooked beaks.

Argentavis magnificens

An extinct giant teratorn from the Miocene of South America, representing one of the largest flying birds known, with an estimated wingspan of approximately $6\text{ to }7\,\text{m}$.