Bio 324 Lecture+25+Fall+2024+rev

Lecture Overview

  • Title: Origin and Diversification of the Diapsida, cont.

Diapsida

  • Petrolacosaurus: among the earliest known diapsids.

  • Characteristics of basal diapsids:

    • Small, agile, and insectivorous.

    • Possessed temporal fenestrae, which reduced skull weight while enhancing jaw strength.

    • Adaptations facilitated ecological diversification into various niches.

Lizard Diversity

  • Diverse in body forms and prey preferences:

    • Small lizards: primarily insectivores.

    • Larger lizards: can be herbivorous or carnivorous.

Snake Diversity

  • Characteristics of extant snakes: all are limbless.

  • Size Variation:

    • Range from 4 inches to 30 feet.

    • Generalized terrestrial snakes: elongated with long tails.

    • Vipers: stout with long fangs that inject proteolytic venom.

    • Arboreal snakes: slimly built.

    • Fossorial snakes: have shiny scales that reduce friction.

    • Marine snakes: possess flattened tails.

Archosauromorpha

  • Definition: comprises Archosauria (crocodylians + birds) and Testudines.

  • Evolutionary split: diverged from Lepidosauromorpha approximately 255 million years ago.

  • Diagnostic challenges due to complexities in lineage.

Testudines: Phylogenetic Position

  • Positioned basally to Archosauria.

  • Key groups:

    • Archosauria: includes Birds (Aves) and Crocodylians (Crocodylia).

    • Sauropsida: contains Turtles (Testudinia) and Lepidosauromorpha (Lizards and snakes).

    • Amniota: includes Tuatara (Rhynchocephalia), Prototheria (Platypus and echidnas), Synapsida, and various mammals.

Testudinate Synapomorphies

  • Key features:

    • Trunk and limb girdles enclosed in a bony shell.

    • Carapace formed by the expansion of ribs.

    • Plastron comprises dermal bone.

    • Exteriors feature beta keratin forming horny scutes.

    • Skull is secondarily lacking post-orbital fenestrae (anapsid condition).

Testudinate Diversity

  • Cryptodire (hidden-necked):

    • Can retract head into shell by bending neck into a vertical S-shape.

    • Approximately 260 species inhabiting freshwater, marine, and terrestrial environments; found on all continents except Antarctica.

  • Pleurodire (side-necked):

    • Retract head by bending neck laterally/horizontally.

    • Consists of about 100 species; restricted to southern hemisphere, primarily in freshwater.

Archosauria

  • Groups included: Crocodylia and Dinosauria (modern birds).

  • Archosaur Synapomorphies:

    • Eggs have a hard calcium carbonate shell.

    • Nests constructed from vegetation.

    • Some species exhibit parental care.

    • Features of skull: Antorbital and mandibular fenestrae, with a noted secondary loss in crocodilians.

Closing

  • End of lecture summary.