GLGY 305 FINAL

Importance of the vertebral column

the vertebral column is a primitive character of all vertebrates and something we all inherited from a common ancestor

What was a Pikaia? And why is it important?

Small marine animal 505 mya
had a notochord and a head, no vertebretal column (evolution of the notochord was the first step to the evolution of all vertebrates)
one of the oldest known ancestors of all cephalochordates

vertebrata

animals with a jointed spinal column and were the first animals to develop a vertebral column but had no jaw (called jawless fish)
ex. modern hagfish and lamphreys

Gnathostomes

animals with jaws likely evolved from pre-existing support structures in the gills
have jaws and vertebral column
early ones have skeletons made of cartilage (ex. sharks)

Osteichthyes

fish with bony skeletons
two categories: ray finned fish and lobe-finned fish

Sarcopterygii

lobe-finned fishes
limbs became fleshy and limb-like

Tikaalik

an extinct lobed-finned fish that represents the next stage in vertebrate evolution
sometimes called fishapod (fish with feet)
has weight bearing elbows, simple wrist bones, rays that resemble feet, gills and lungs
was pre-adapted to transition to the land but did not

Tetrapoda

four-limbed vertebrates
lived on land but needed water to reproduce
one of the first was the ichthyostega
modern ones have lost gills but still have lungs
primitive ones like amphibians still require water in order to reproduce

example of homologous structures

lobe finned fish and primitive tetrapod
similar limbs
a similar feature found in two different animals thought to be from the same ancestor

Amniota

higher vertebrates (reptiles, birds and mammals) possessing an amnion during development
allows egg to become fully terrestrial
a calcified or leathery shell, yolk for nutrition, and waste-management system all evolved at the same time
humans and other mammals are amniotes but instead retain the fertilized egg internally

two groups of amniotes

synapsids - develop single pair of openings behind the eyes (temporal fenestrae) ex. mammals
diapsids - develop two pairs or openings behind the eyes (temporal fenestrae) ex. crocodiles

Clade

a monophyletic group, meaning it is group of organisms that includes common ancestor and all its descendants

synapsids that are misidentified as dinsoaurs

Dimentrodon and woolly mammoths
both before the time of the dinosaurs

are dinosaurs diapsids or synapsids?

diapsids which are group with birds and crocodiles

Diapsids can be split into two clades based on skeleton what are they?

1. Lepidosaurmorphs have short, non overlapping vertebrae in the neck (snakes, lizards, marine reptiles)
2. Archosauromorphs have longer vertebrae in the neck which overlap to provide support for longer necks (crocodiles, birds and dinosaurs)

Archosauria

substrate of the archosauromorphs that have additional openings in front of the eyes called antorbital fenestrae

Ornithodira

clade that includes dinosauria and pterosauria
have upright stance
pterosauria have an elongated IV digit to support wing whereas non avian dinosaurs do not

Dinosauromorphs

earliest most primitive non dinosaurs
were small and lightly built and most likely bipedal
suggests all dinosaurs started as bipedal and evolved into a quadrupedal stance
dinosauromorphs also exhibit digitigrade posture - standing on the balls of the feet allowing for a longer stride

Dinosauria

subsets of dinsauromorphs with some very minor modifications of some bones
1. elongate deltopectoral crest on humerus (powerful forearms)
2. perforated acetabulum (cup shaped opening on either side of the hips where the head of the femur inserts)
also large muscle attachment scars on their skulls \= powerful bite

first appearance of dinosauromorphs

244 - 242 Ma

did dinosaurs and dinosauromorphs coexist?

yes but by late triassic dinosauromorphs went extinct

Where is it suggested that dinosaurs originated?

South America
Possible this is the only place where they have been preserved this old

what lead to the great diversity of the dinosaurs

variability in dinosaurs, ecological variability, changes over time and ongoing natural selection

Morphospecies

group of individual that have some reliable characters distinguishing them from all other species

issues with defining morphospecies in the fossil record

unknown if observed variation is due to individual variation, sexual dimorphism, ontogenetic change or an incomplete fossil record

how to identify gender in the fossil record

genitals are not preserved
need to look for egg in body cavity and medullary bone
however absence of these does not automatically make a dinosaur male

how to identify age in fossil record

concentric growth rings called lines of arrested growth (LAGs) are found in bones and teeth can be counted to estimate age
lack of fusion in the skull bones suggests young
spongy (youth) vs more solid (adult) bones

three major groups of dinosaurs

1. therapods (mostly meat eating)
2. Sauropodomorphs (long necked dinosaurs)
3. Ornithischians (everything else)

what were the historical subdivisions within dinosauria

saurischians (includes therapods and sauropodomorphs) and ornithichians
pubis can move in two ways...
1. down and slightly forward - lizard-hipped (saurischians)
2. pubis points backwards - bird-hipped (ornithischians)

what category do birds fall into?

Birds are living theropod dinosaurs

characters of saurischians

Elongate vertebrae in the neck
distinctly large hand
loss of finger V
thumb (digit 1) falls across the palm
not well defined

Characters of Ornithischians

Predentary bone
toothless and roughened tip of snout
A narrow bone (called the palpebral) that crosses the outside of the eye socket
jaw joint set below upper tooth row
cheek teeth with low, subtriangular crowns
at least 5 sacral vertebrae
ossified (turned to bone) tendons above the sacral region
And many more meaning well defined

what was the big reorganization in 2017

Baron et al re-analyzed the morphologic characters and proposed a new cladogram which grouped therapods and ornithischians into a new group called ornithoscelida
this suggests that the hips are not a diagnostic character

three main parts of the herbivorous mammal skull

the cropping section (blade like teeth called incisors bite off chunks of food)
the diastema (toothless gap for food manipulation by the tongue)
the cheek teeth (molars, a place for grinding down food into a paste)

adaptations for chewing in mammals

1. An expansion of the coronoid process for jaw muscle attachment
2. Closely-packed teeth with flat grinding surfaces
3. Teeth occlude (fit together tightly top to bottom) for efficient grinding
4. An inset tooth row to support cheeks
5. Jaw joint is above the tooth row, allowing all the upper and lower teeth to make contact at the same time (like water pump pliers)

how do carnivores break down their food?

they do not chew food
large chunks of food are easily digested by the stomach acid
they have simple single chambered stomachs, short digestive tracts and typically slim torsos

how do herbivores and omnivores break down food?

plants are harder to digest
usually begins with chewing and is assisted by a digestive enzyme in their saliva that helps to break down carbohydrates
herbivores have larger barrel shaped guts that accommodate long digestive tracts to enhance the break down of plant matter

whats something some non chewers do to help digest food?

some animals will swallow stones to help mechanically process their food
these are called gastroliths
also used as ballast (weight to provide stability)
seen in crocodiles, birds, alligators, seals and sea lions etc

were therapods good or bad chewers

bad chewers:
teeth spaced out or no teeth at all
tooth row not inset
wide gap
point serrated teeth
dominant tooth function
slim torsos

did therapods hold onto prey

dinos held onto prey if they were smaller than them
dinos had a slashing technique (wait for them to bleed out) if they were smaller than the prey

were sauropodomorphs bad or good chewers

bad chewers:
Teeth spaced out
Tooth row not inset
Leaf, spatula and peg-shaped teeth with few grinding surfaces
Dominant tooth function: puncturing vegetation
Barrel-shaped guts for fermentation
gastroliths

were the ornithschians good or bad chewers?

ok, good and great chewers depending on the dino
same skull as herbivore mammals but instead of incisors at the cropping section they have a beak (rhampotheca)

what did dinos eat?

direct:
based on fossil poop (coprolites) they ate plants and arthropod legs
based on gut contents (cololites) they ate seeds of cycads anf other plants
indirect ways of finding out what they ate is by looking at teeth marks on bones, finding out the herbivores and carnivores in that area at the time and doing comparative anatomy

Some key features of the sauropodomorphs

small head
at least ten vertebrae that form a long neck
more vertebrae in front and behind the sacrum
enormous thumb with large claw
long femur

how long did the sauropodomorpha live for?

160 million years (entire time all dinosaurs were on earth)

What did the sauropodomorphs eat and how?

they were herbivores
long necks allowed them to eat tall plants
bad chewers with small mouths so they would have been constantly eating
claw may have helping with ripping food into smaller pieces

what features kept the sauropoda light?

pneumatic bone in the vertebrae
skull was small and delicately built full of large openings

two groups of sauropoda?

Diplodocoidea
Macronaria

key features of diplodocoidea

sub rectangular snout
fully retracted external nares above the eyes
peg like teeth along front of the jaw forming tooth comb

key features of macronaria

nares as large or larger than orbit
nares move towards top of skull
shortening and elevation of skull, indicating more powerful biting force

what were early scientists explanations of nostrils on the top of the skull for sauropoda?

hypothesized saurapoda used their nostrils like a snorkel and were aquatic due to how heavy they were
idea fell apart when they found water pressure too high for breathing, robust features suggest life on land

Where are the sauropoda found?

in a variety of environments from swamps to lakes to coastal areas and terrestrial areas (discovered this in the 80s to 90s)

why did the sauropoda most likely not have trunks like elephants?

1) mobile trunk compensates for short neck (saurapoda have long neck)
2) facial nerve in diplodocus is relatively small compared to elephants
3) comparative anatomy with crocodiles and turtles tell us possibly where the nasal cavity was

What is the nuchal ligament?

elastic rope of connective tissue that ran down back to support the head so the muscles didn't have to work as hard

where were the nostrils of the sauropoda most likely?

abundance of foramina and blood vessels suggests the fleshy nostrils were closer to the mouth than the eyes

What does sauropoda posture tell us about how far above the ground they could eat?

had long necks but they were near horizontal so they could only feed with 2-3m above the ground (most not all)
could not reach the tallest trees but still had access to more food just by standing in one spot
some sauropoda like brachiosaurus had long forelimbs allowing them to raise head 13 m above the ground and 8 m above the heart

what is the possible mechanism to allow sauropoda to lift head 8m above heart?

the cervicle ribs flex while the dinosaurs walked compressing of the ribs may have put pressure on the vertebral artery helping to pump blood up the neck
therefore long neck \= more muscle \= more pump
prevent them from fainting (but if any higher they would faint)

what stopped the sauropoda from having a tripod stance causing them to faint?

the shape of their pelvis

what helped the sauropoda breathe through their long necks?

pneumatic bone with an air sac system to increase efficiency of breathing and oxygen exchange
unidirectional breathing

why could sauropods get big?

a light skeleton
small heads because they didn't chew
unidirectional respiration
could have long necks but still have an efficient metabolism

what did the ornithischians eat? and what features helped them?

herbivorous and consumed large amounts of tough plant matter predentary supported beak for cropping vegetation ribs flare widely and backward pointing pubis may have accommodated a large gut

what did primitive ornithischians look like?

bipedal
looked similar to most primitive dinosaurs but had a jaw joint lower than teeth row (chewing)

What main clade is within ornithischians?

genasauria (a group defined by having cheeks)

what are the two divisions within genasauria?

thyreophora
cerapoda (marginocephalia and ornithopoda)

what is distinguishing about the thyreophorns?

genasaurs with dermal armor-bony plates embedded in the skin, along the back surface of the body (osteoderms)

what is distinguishing about the cerapoda?

genasaurs with a pronounced diastema

two divisions of cerapoda?

marginocephalia
ornithopoda

what is distinguishing about the marginocephalians?

united by having a shelf of bone extending over the back of the skull (frill)

what is distinguishing about the ornithopoda?

duckbilled dinos like iguanodon and other excellent chewers

what is the rhamphotheca (beak) made out of?

keratin

importance of the hadrosaur

originally believed to have a duck shaped bill instead of a beak and lived a semi aquatic lifestyle
turns out that there was a beak used for gripping ripping and breaking vegetation (evidence from coprolites and stomach contents proves this)

what were primitive thyreophora like?

all were bipedal but quickly evolved into much larger quadrupedal dinosaurs

how good were the thyreophora at chewing?

okay chewers
had beak
inset tooth row
however: teeth were small simple and triangular, lack regular grinding surfaces and do not fit together well
also coronoid process is small

what did thyreophora eat?

heads were close to ground so ate ferns and cycads less than 1 m off of the ground

what are the two groups within thyreophora?

stegosauria
anklyosauria

when did stegosauria live?

Jurassic to Early Cretaceous

how did stegosaurus walk?

quadrupedal
super slow because weight is mostly distributed towards head

size of stegosauria brains?

tiny and long brain
1:1000 (brain:body ratio)
enlarged olfactory lobe

why did stegosaurus have spikes and plates?

possibly for defense
the end of the tail is equipped with pointed and splayed spikes (thagomizer) that were likely slashed from side to side
however the plates may have made stegosaurs look bigger and scarier especially from side view so most likely not for defence

proof of sexual dimorphism in stegosaurs

two distinct sizes and shapes of plates equal numbers of both sizes

females are more spikey males are more rounded

What were the spines and plates for, if not for defense?

thought to be for thermoregulation

features of the Ankylosauria

longer hindlimbs than forelimbs but still quadrupedal
large gut
encased in osteoderms along back tail neck throat and even cheeks and eyelids

when were the anklyosaurs around?

early Jurassic to Late Cretaceous

two main groups of anklyosauria

anklyosauridae
nodosauridae

What is distinguishing about the anklyosauridae?

Shorter, broader head/beak
Large, triangular plates attached to rear corners of skull
Well-armored, but fewer tall spikes along body.
Tail with a massive, bony club, sometimes with paired tail spikes or knobs
Tail first defense

what is distinguishing about the nodosauridae?

Longer, narrow snouts/beak
Well-muscled shoulders
Tall spikes at the shoulder
No tail club
Head first defense

what did the Anklyosauria eat?

narrow beak of nodosaurids suggests selective feeding (plucking fruits and foliage)
broad beak of ankylosaurids suggests they were less selective

what were anklyosauria like?

small brain to body ratio like stegosaurs
good at smelling (enlarged olfatory lobe/convoluted nasal passages)
incredibly slow moving

why were the anklyosaurs able to be slow moving?

had good defense mechanisms

two main groups of marginocephalians

pachycephalosauria
ceratopsia

what is distinguishing about the pachycephalosauria?

dome heads
Strong neck muscles
Vertebrae are uniquely linked with a tongue and groove articulation
spiny osteoderms on the snout

where were the pachycephalosauria found?

only found in northern hemisphere (asia and north america)
early to mostly late cretaceous

what are the difference in domes based on origin?

north american tends to have high domes
asian forms tend to have both high and flattened domes

what were Pachycephalosauria brains like?

although they had large domed skulls, they had very typical ornithischians brains
enlarged olfactory lobes
brain tilted towards back of the skull (bigger the dome more downwards it faced)

Evidence proving that head butting existed in pachycephalosauria

structure of dome is very dense and bone fibers are oriented perpendicular to the external surface of the dome, helps resist stresses from head butting
possibly the rotation of bones at the back of the skull minimized the potential for violent rotation or dislocation
the vertebrae uniquely linked with a tongue and groove articulation that made the spine rigid and limited lateral rotation

features on the pachycephalosaurs that were related to display

1. dome
2. canine teeth
3. knobby/spiny osteoderms on the snout/side of the face and marginocephalian shelf

the arrangemnents of pachycephalosauria bones depending on where they were found (NA or Asia)

NA:
mainly water-worn skull caps, isolated bones
lots of transport before burial
lived in/near the mountains
Asia:
complete skulls and articulated skeletons
buried close to where they died
lived in sahara-desert with ephemeral streams

what is distinguishing about the ceratopsia?

they all have a bone at the tip of the snout (rostral bone)
narrow skulls with a hooked beak
a skull that flares in the cheek region (jugal horns)
boney shelf that extends off the back of the head (frill)
thick hooves

where were the ceratopsia fossils found?

asia and north america

what is important about horns and ceratopsia?

had facial horns that consisted of bony core with a sheath of keratin
however primitive forms lack horns
in fossil records only boy core is preserved therefore they were a lot bigger than what we have found