Dinosaur Exam 3

Which clades are reptiles?

Aves, Ichthyosauria, Mosasauroidea, Non-avian saurischian = therapod or sauropod, ornithischia, pseudosuchia, pterosauria, sauropterygia

Which organisms are dinosaurs?

ornithischians, Non-avian saurischian = theropod or sauropod, aves

early split in dinosaurs

Ornithischians, saurischians

Saurischians are from and include

from dinosaurs, include non avian saurischians (theropod or sauropod), and aves

Which organsims are archosaurs

pseudosuchia, pterosauria, ornithischia, non-avian saurischian = theropod or sauropod, aves

which organisms are marine reptiles

ichthyosauria, sauropterygia, mosasauroidea,

which are not reptiles?

lissamphibia, Non-mammalian synapsid(dimetrodon), mammalia(synapsids),

Archosaurs

Group that includes the most recent common ancestor of living birds or crocodilians. Spits into 2 clades, pseudosuchia(crocs), and aves(birds and their extinct relatives such as non-avian dinos and pterosaurs

Dinosaurs

Which organisms are marine reptiles?

Ichthyosauria, mosasauroidea, sauropterygia

Mosasaur

• shorter faces

• small flippers

• large tail that bends down like ichthyopterigians

• True lizards, squamates that went back to living in the ocean.

Mosasaurs have: what are they?

• shorter faces

• small flippers

• large tail that bends down like ichthyopterigians

• True lizards, squamates that went back to living in the ocean.

Ichthyopterygian(ichthyosaur on tree): Pointy mouth, really large eyes, Small neck, small flipper, larger tail

• Tail-driven swimmers

• tail is downturned in the skeleton

Ichthyosaurus

Ichthyopterygians(ichthyosaurs on tree) have:, how do they swim?

Pointy mouth, really large eyes, Small neck, small flipper, larger tail

• Tail-driven swimmers

• tail is downturned in the skeleton

Sauropterygian: long neck, large flippers, short tails.

Sauropterygian have:, how do they swim?

long necks, large flippers, short tails.

• flipper driven swimmers

Make a tree out of:

• Aves

• Lissamphibia

• Ichthyosauria

• Mammalia

• Mosasauroidea

• Non-avian saurischian

• Non-mammalian synapsid

• Ornithischia

• Pseudosuchia

• Pterosauria

• Sauropterygia

Tree split 1:

synapsids and saurians (not on tree). 1) non-mammalian synapsids → mammalia. everything after is a saurian.

Non - mammalian synapsid (Dimetrodon)

Euriapasid group on tree and how to identify

ichthyosaur and sauropterygians, one opening high on the skull behind the eye socket

Ornithurae

Dinosauria (node or branch?)

(node) Ornithischians, non-avian saurischians, aves

ornithodira (node or branch?)

Pterosauria, ornithischians, non-avian saurischians, aves

Aves (definition)

Covers modern birds and early fossil groups.

Aves early split

Early split: Paleognathae and neognathae

Aves synapomorphies

1. Toothless beak

2. Syrinx (internal)

3. Air sacs penetrate humerus.

Paleognathae: Early split:

Tinamidae and Ratitae

Aves - Paleognathae (tinamidae)

Aves - Paleognathae (tinamidae)

Aves - paleognathae - Ratitae

Aves - paleognathae - ratitae

Neognathae major spilt

Galloanserae, neoaves

Neognathae synapomorphies and other identifiers for the test

• hinge between beak and rest of skull

• means (new jaw)

• identifiers for the test:

• large prominent sternum, fused wrist hand bones, long wading legs, flat broad duck-like bill, 4-toes foot

Aves - neognathae - galloanserae - anseriformes (waterfowl, ducks, geese, etc)

Aves, neognathae, galloanserae, Anseriformes (gamefowl - chicken, turnkeys, quail, grouse, etc)

Timing of bird evolution source 1:

1. Fossil record - looking for early bird fossils to understand where they came from

• This is direct evidence

• Oldest fossils for aves are from near end of cretaceous

• Many resemble living shorebirds (small birds, long beaks, short legs)

• Massive increase in diversity early in Cenozoic

• Led to “transitional shorebird” model of modern bird origins

• Modern bird lineages evolved from shorebirds

• Radiation following extinction of toothed birds and pterosaurs at end of Cretaceous

Timing of bird evolution source 2:

1. Molecular data

• Amount of difference in the DNA of 2 species is a function of how long ago they diverged

• amount of difference in the DNA of two species is a function

  of how long ago they diverged - The more different their dna is, the more in the past they diverged

• These methods support much older divergences between modern bird lineages deep within Cretaceous

Aves - neognathae

• hinge between beak and rest of skull

• means (new jaw)

• identifiers for the test:

• large prominent sternum, fused wrist hand bones, long wading legs, flat broad duck-like bill, 4-toes foot

Pterosaurs

ornithodira, Pterosauria

ornithodira major split

pterosauria and dinosauromorpha

Pterosauria synapomorphies

• elongated 4th digit

• pteroid bone

• bony sternum

earliest flying vertebrates

pterosauria

what helps pterosaurs with powered flight?

pteroid bone and bony sternum

flight surface of pterosaurs

Skin supported primarily by a single digit (4th)

How did flight evolve in this group? Pterosauria

1. Trees-Down (Arboreal) Hypothesis

• Pterosaur ancestors lived in trees and glided down

• Flight evolved from gliding, gradually developing powered flight

• Similar to how some suggest bird flight evolved

2. Ground-Up (Cursorial) Hypothesis

• Ancestors were fast ground runners

• They developed flight from running and leaping

• Flapping evolved to generate lift from the ground

How did pterosaurs achieve flight?

• membrane supported by pteroid bone and it extended from hand to neck

• wing membrane extended from tip of 4th finger to hindlimb

• Bones were hollow and pneumatized (air-filled) for lightweight flight

How did pterosaurs achieve flight vs flight evolution in birds, bats?

Pterosaurs

• Wing supported by one massively elongated fourth finger

• Membrane stretched from that finger to the body and possibly hind limb

• Had a propatagium (forward membrane) for extra lift

• Membrane contained actinofibrils — stiffening internal fibers unique to pterosaurs

• Origin: unknown/debated — no transitional fossils

🐦 Birds

• Flight evolved from feathered theropod dinosaurs

• Feathers first evolved for insulation/display, then co-opted for flight

• Wings are modified forelimbs with fused hand bones (carpometacarpus)

• Best supported by the trees-down gliding hypothesis but still debated

• Excellent transitional fossil record (Archaeopteryx, Microraptor, etc.)

🦇 Bats

• Wing membrane stretches across four elongated fingers (2nd–5th)

• Membrane also connects to the hind limbs and tail in many species

• Origin also has poor transitional fossil record — earliest bats already fully formed fliers

• Hypothesized to have evolved from small arboreal (tree-dwelling) mammals

• Trees-down hypothesis most widely accepted for bats

crucial distinction between pterosaurs, birds, and bats:

• Pterosaurs → one finger

• Birds → feathers on whole forelimb

• Bats → four fingers

What are the novel anatomical features associated with flight in pterosaurs

• The massively elongated fourth digit is the single most defining feature

• No other flying vertebrate uses a single finger to support the entire wing

• The other three fingers remained short and clawed, used for walking/climbing

• Unique internal stiffening fibers within the wing membrane

• Made the membrane active and controllable rather than passive

• Pteroid bone: A completely unique bone found only in pterosaurs

• Elongated Metacarpals: The hand/palm bones were greatly elongated compared to other reptiles, Created a long rigid base for the wing finger to attach to

early pterosaur commonalities:

Pterosaur in late - Jurassic, Long neck, very short tail, long metacarpals, notarium (part of dorsal vertebrae, blade formed by fusion of dorsal neural spines)

archisauriform, euparkeria

• antorbital fenestra (opening in front of the eye socket)

• Serrated teeth

• deep, robust and elongated skull shape

• elongated tail

Archosauriformes, archisauria, pseudosuchia

pseudosuchians

• most have osteroderms (not necessarily a synapomorphy for the group

archosauriformes major split

euparkeria, archosauria

euparkeria splits with and from

archosauria, archosauriformes

archosauria split

pseudosuchia, ornithodira

pseudosuchia split with and from

ornithodira, from archosauria

archosauria split with and from

euparkaria, from archosauriphormes

pseudosuchian

crocodylomorpha, pseudosuchia, archosauria

• Cone shaped teeth - all teeth are conical

• Paired carpals to radius and ulna

• Radius paired to radiale (carpal)

• Ulna paired to ulnare (carpal)

put crocoodylomorpha, crocodyliformes, and crocodylia on a phylo tree and name who their common ancestor is

common ancestor is pseudosuchia

Crocodylomorpha synapomorphies

cone shaped teeth

• Paired carpals to radius and ulna

• Radius paired to radiale (carpal)

• Ulna paired to ulnare (carpal)

early ones were

• Lightly built

• Long legged

• Erect or semi-erect posture

• Gracile bodied

external nares near the tip of snout

Crocodyliformes synap

2. Secondary Palate

• Bony secondary palate formed by the palatine and pterygoid bones

• Allows breathing while the mouth is submerged/full

• More developed than in basal crocodylomorphs

Reduced Antorbital Fenestra

• The antorbital fenestra (defining archosauriform feature) is greatly reduced or closed

• This is a key distinguishing feature from earlier archosauriforms

4. Elongated Skull

• Skull becomes notably longer and flatter relative to basal crocodylomorphs

external nares moves back and up

weird ass bipedal pseudosuchia

crocodylia synap

nares fully retracted to the tip of the skull near the eyes. dorsally positioned, works with the fully developed secondary palate. can breathe even when entire body is submerged

• synapomorphy – ball and socket joints between vertebrae

• Skull table (with orbits on either sid)

• Secondary palate

• Internal choana

  • Allows to breathe and eat at the same time

Crocodyliformes

archosauria

crocodiles up to birds, defined by crocodylians and birds,

• 4-chambered heart

• Acetabular crest

  • Braces femur in upright orientation

• Unidirectional airflow in lungs

• When they breathe, breathe in air into airsack and with breathe out they push the air from the airsack into their lungs

  • Incredibly efficient and lets them use more oxygen that they breathe in

  • Complex nests; protection of nest and young

breathing/walkign simultaneously (definitely)

2 major archorsauria lineages:

• Pseudosuchia: the crocodylian lineage 

• avemetatarsalia/ornithodira: the bird/dinosaur lineage

Semi-aquatic ambush predator vs. other niches

• one of the most energetically efficient strategies in nature

• sacrifice habitat breadth (stay on shores, shallow riverbanks), for concealment and prey diversity

• not burning a ton of calories

• Water acts as a camouflage, a speed multiplier, a disorienting medium for prey, and a prey-attracting resource

what is morphology

study of physical form, structure, and bone anatomy to understand biology, evolution, and classification

what are “living fossils”

• Living fossils mean they didn’t have to change a lot and have settled into a niche

the myth of the “living fossil”

• old assumption that crocodilians are primitive, unchanged “living fossils,” that they look like they did 200 million years ago

• myth: fossil crocodilians don’t deviate enough from the living forms to need special description

Why is the “living fossil” a myth?

• Morphologically, croc skulls from the Late Jurassic (150 Ma), Late Cretaceous (70 Ma), and modern day do look similar on the outside (slide 59), which is what gives the "living fossil" impression.

• But the fossil diversity of Crocodylia and Crocodyliformes was enormous — many groups occupied completely different ecological niches

• Modern semiaquatic ambush predators are actually the survivors of a much more diverse group, not a representative snapshot of croc evolution.

• The ancestral crocodylian was not "crocodile-shaped" — it was small (skull ≤ 10 cm), resembled an early alligatorid, and was not especially "crocodile-shaped" (slide 69). The typical big, flat-snouted, semiaquatic form evolved later.

molecular relationship in crocodylia

gavialis and tomistoma are sister taxa. DNA says they are close relatives despite looking very different morphologically

morphological/fossil relationship in crocodylia

fossils place gavialis as the outgroup(earliest branching lineage) with Borealosuchus and Planocraniidae as relatives of the other crocs.

Puts tomistoma groups with true crocodiles.

Gavialis and Tomistoma similarity 2 opinions

both have a long narrow snout and morphology based analyses treat this as convergent

Molecular data says this shape was inherited from a common ancestor

Three living croc families

Alligatoridae, Crocodylidae, and Gavialidae

ancestral crocodylian identifyers:

• small,

• resembled early alligatorid

• not especially crocodile-shaped

semiaquatic

• spends much of their time in the water but can also go on land

  • Sea lion

Aquatic

• Aquatic: spends all of their time in the water

  • Beluga whale

Secondarily aquatic:

descended from land-living ancestors, but lives in water

secondarily marine

descended from land-living ancestors, but lives in seawater

What are the challenges to becoming secondarily aquatic/marine?

1. Locomotion:

• limbs modified into flippers or paddles

• two general modes of locomotion in water:

  • tail driven: long powerful tail; short humerus/femur

  • flipper-driven – short tail; long humerus/femur

2. Sensory system

• modifications to work in water

  • Large eyes

  • Well developed ears

3. Breathing:

• no secondarily aquatic amniote has ever re-evolved gills

• nares usually shifted toward top of head

4. Reproduction

• Amniote eggs drown in water

• two strats: live birth or lay eggs on land

How did Sauropterygians overcome challenges of being secondarily marine/aquatic?  

(Marine)

Locomotion? Flipper driven

Respiration? nares shifted back

Senses? large eyes

Reproduction? live birth

early sauropterygian

groups of secondarily marine reptiles

euryapsids(dominant) = sauropterygia and icthyopterygia,

Euryapsida synapomorphies

• loss of infratemporal fenestra

Sauropterygia synap

broad, flat coracoid, ischium, pubis

• supported large muscles for moving flippers

long, robust femur and humerus

propel themselves with their front flippers and back flippers

Thalassomedon - sauropterygian

sauropterygian

plesiosaur - sauropterygia

euryapsida - loss of infratemporal fenestra

Ichthyopterygian synap

• downwardly-bent tail caused by wedge-shaped vertebrae in the middle of the caudal series

How did Ichthyopterygians overcome challenges of being secondarily marine/aquatic?  

(marine)

Locomotion? small humerus/ femur, robust tail

• tail driven swimmer

Respiration? nares shifted up

Senses? HUGE eyes

Reproduction? live birth

when did ichthyoptergynarians die out?

middle cretaceous