ESCI 2020 L4 - TETRAPODS

What are the characters uniting modern life, making it monophyletic?

→Cell membranes composed of lipids

→ Possession of RNA and DNA

→ Genetic code all keyed to exact same amino acids

→ Cells that function using the same metabolic pathways.

What is the oldest fossil to exhibit characters of Chordata?

Pikaia gracilens

What group represents the breakthrough to fully terrestrial life?

Amniota → amnion allowed reproduction away from water.

2 Primitive Chrodates alive today

Amphioxus

Urochordate Ciona (Sea Squirt)

What key chordata features did Pikaia have?

Pharyngeal gills

Notochord

Nerve chord

Example of chordata from class.

→ Pikaia

→ Amphioxus

What are the characters of Chordata?

→ Pharyngeal gills

→ Notochord

→ Nerve Cord

Cephalochordates add

→ Segmentation of body wall

→ Separation of upper and lower nerve and blood vessel branches

→ Many newly evolved hormone + enzyme systems.

Cephalochordate example

→ Amphioxus

Vertebrata diagnostic characteristics

→ mineralized internal skeleton divided into discrete segments

→ differentiation of cranial nerves

→ development of eyes and other features

Gnathostomata

Vertebrates with true jaws

Osteichthyes refers to

→ osteo - bone

→ ichthys - fish

→ boney fish.

Osteichthyes led to a major split, what are the two branches?

→ Actinopterygii

→ Sarcopterygii

Which branch of Osteichthyes has fleshy bases to the fins where they attach to the body?

Sarcopterygii

→ sarco- flesh

→ the lobe finned fishes.

Which branch of Osteichthyes leads to modern fishes?

Actinopterygii

Osteichthyes branch leading to tetrapods?

Sarcopterygii

There are homologous features linking lobe-finned fishes & Tetrapods, what are they?

• Shoulder girdle & 3 Primary limb bones

How are Modern Tetrapoda defined?

→ clade including salamanders, mammals, and all the descendants of their most recent common ancestor.

What are Modern Tetrapoda diagnosed by?

→ the appearance of limbs with distinctive arrangement of one bone + primary limb bones.

T/F: All tetrapods have the same basic structure

True

→ Vertebral Column

→ Limbs attached to the vertebral column by groups of bones called girdles

→ Head composed of skull and mandible

→ Tail

In tetrapods, limbs are attached to the_____ _______ by groups of bones called ________

→ vertebral column

→ girdles

Amniota defined as the monophyletic group including ___, ____ and all the descendents of their most comon ancestor. Characterized by the invention of the _____, a membrane for the embryo allowing gas exhange and water retention.

Birds, mammals, amnion

T/F Amnion enabled vertebrates to become fully terrestrial.

True

Groups of amniotes

Anapsids - no post-orbital temporal fenestra

Synapsids - Single temporal fenestra

Disapsids - 2 temporal fenestrae

______ - mammal like reptiles, eg. ______ and the mammals

Synapsida, Dimetrodon

Diapsida defined as monophyletic group including ____,_____ and all the descendants of their most recent common ancestor

Birds, lizards

What organisms belong to lepidosauromorpha?

Lepido- scaly

Sauros - Lizard

Morpho - Shape

snakes, lizards, tuatara, and extinct lizard like diapsids, including marine mosasaurs.

Mososaurs vs Ichthyosaurs

Mososaurs → Part of Lepidosauromorpha → Palate + teeth fused to jaw bone

Ichthyosaurs → marine replites → parallel evolution with dolphins

Archosauria

Teeth in sockets, anorbital fenestra

How are the 3 major amniote skull groups distinguished?

Number / positon of temporal openings

Which amniote lineage leads to mammals?

Synapsida

Turtle problem

• lack temporal openings but genetic evidence places them within diapsida

How does the pelvis differ in Saurischia vs Ornithischia?

Saurischia - pubis anteriorly directed and slightly downward

Ornithischia - at least part of pubis posteriorly

When does true Dinosauria appear first?

Late Upper Triassic of South America

→ spreads and takes over Dinosauromorpha by end of Triassic

When did early dinosauromorpha appear? True Dinosauria?

Middle and Early Late Triassic

Late Triassic

Archaeopteryx

• both bird and dinosaur features, helped establish dinosaur-bird relationship

Who showed Archaeopteryx was also a dinosaur?

John Ostrum

Dinosauria defined as

Triceratops and Passer(sparrow) and all members of the clade descended from the most recent common ancestor.

Dinosauria Diagnosed by

1. elongate deltopectoral crest on humerus

2. perforate acetabulum (hip socket with hole)

3. Fibula contacts <30% of astragulus (ankle) (tibia supports weight)

4. Epipophyses (bony projections) on cervical (neck) vertebrae

5. Asymmetrical 4th trochanter (projection for muscle attachment) on femur.

Unlike earlier Tetrapods, dinosaurs had a ______ _____ posture, leg joints that limtied movement to a ______ _______

Fully erect

Single plane

2 Clades of Dinosauria

Saurischia - lizard hip (pubis directed anteriorly (forward))

Ornithischia - bird hip (pubis atleast partly posteriorly (backward))

What evolves with Archosaurs?

• teeth in sockets, elongated nostril, vertebral featurs

• antorbital fenestra, loss of teeth on palate

• variety of specializations for flight

• perforate acetabulum

Main lineage from Chordata to Dinosauria?

Chordata

→ Vertebrata

→ Gnathostomata

→ Osteichthyes

→ Sarcopterygii

→ Tetrapoda

→ Amniota

→ Diapsida

→ Archosauria

→ Ornithodira

→ Dinosauria

T/F: Feathers were once thought of as a diagnostic character for birds, but now seem to be a diagnostic character for Dinosauria, therefore feathers did noe evolve specifically for flight

True

Why do feathers NOT appear to have originally evolved for flight?

feathers occured in dinosaurs that don’t fly

→ likely for insulation and display, flight evolved later

What are the 5 Sequential Stages for Feather Evolution?

1. Simple, Hollow cylindrical filaments (hair-like)

2. Tufts of Elongate multiple filaments

3. Filament tufts align in a single plane while also developing barbs and barbules

4. Closed vane with interlocking barbs and barbules, providing a rigid structure (“contour” feather)

5. Vane becomes asymmetrical (ex. a flight feather)