History of Life final

Cambrian

• Continental Movements:

• Continents clustered near equator; shallow seas widespread.

• Laurentia, Siberia, Gondwana shifting apart.

• Climate:

• Warm, stable; rising sea levels; high oxygen allows larger body plans.

• Organisms Alive:

• Trilobites, Anomalocaris, Hallucigenia, Wiwaxia.

• Burgess Shale fauna.

• Early chordates like Pikaia.

• Explosion of predators + new sensory structures (including eyes).

• Evolutionary “Firsts”:

• First shelled organisms (small shelly fauna).

• First hard parts (exoskeletons, spines, shells).

• First complex eyes (supports Light Switch Hypothesis).

• First non-vascular land plants begin appearing near end of Cambrian

• First true body plans for most major animal phyla.

Ordovician

AGE OF MULLUSKS

• Continental Movements:

• Laurentia, Siberia, and Baltica separate early → merge into Gondwana by mid-Ordovician.

• Highest sea levels of the Paleozoic; vast shallow seas.

• Climate:

• Early climate extremely hot (114°F water temps!).

• High CO₂ → strong greenhouse effect.

• Late Ordovician: glaciation → mass extinction.

• Organisms Alive:

• HUGE diversification: 4× more marine genera than Cambrian.

• Dominated by suspension/filter feeders.

• Mollusks explode in diversity (bivalves, gastropods, cephalopods).

• Trilobites, brachiopods, graptolites, echinoderms all diversify.

• New predatory arthropods (eurypterids).

• First starfish, brittle stars, sea lilies.

• Ostracoderms (armored jawless fish) appear.

• Evolutionary Firsts:

• First true vertebrates (ostracoderms).

• First bony armor/plates/scales in vertebrates.

• First fungi (mycorrhizae).

• First terrestrial plants expand (bryophytes, liverworts).

• First corals (reef-forming corals appear).

• End-Ordovician Extinction:

• Caused by glaciation, volcanism, and possibly a hypernova.

Silurian

• Continental Movements:

• Gondwana covers equator & much of S. Hemisphere.

• Massive ocean Panthalassa covers the north.

• Sea levels rise early then fall later.

• Climate:

• Warm, stable; glaciers retreat.

• Low oxygen levels (30–60% of modern).

• Organisms Alive:

• Brachiopods, corals, crinoids, mollusks, trilobites common.

• Eurypterids (sea scorpions) diverse and HUGE.

• Leeches appear.

• Major radiation of jawless fish.

• Evolutionary Firsts:

• First jawed fish (placoderms).

• First cartilaginous fish (Chondrichthyes → sharks, rays, skates).

• First bony fish (Osteichthyes).

• First true jaws evolved from gill arches.

• First vascular plants (Cooksonia).

• First terrestrial animals:

  • Millipede (Pneumodesmus)

  • Early arachnids.

Devonian

AGE OF FISHES

• Continental Movements:

• Laurentia + Baltica collide → Laurussia.

• Laurussia + Gondwana start approaching (Pangaea forming).

• Climate:

• Warm (86°F sea temps).

• High sea levels; later periods experience anoxia.

• Organisms Alive:

• Huge reef systems.

• First ammonites and nautiloids.

• Placoderms dominate; Dunkleosteus is top predator.

• Cartilaginous fish diversify.

• First ray-finned & lobe-finned fish.

• dunkleosteus was top predator

• Evolutionary Firsts:

• First lobefin fishes (coelacanths, lungfish, osteolepiforms).

• First tetrapods (Acanthostega, Ichthyostega, Tiktaalik).

• First insects.

• First true forests (lycophytes, ferns, horsetails).

• First seed plants.

• First plants with true wood (Archaeopteris).

• End-Devonian Extinction:

• Triggered by cooling from CO₂ drop due to plant expansion.

• Major loss of jawless fish, corals, placoderms.

Carboniferous (mississippian and pennsylvanian)

• Continental Movements:

• Pangaea forms.

• Gondwana remains in south.

• Extensive equatorial swamp forests.

• Climate:

• Early Carboniferous: warm (68°F).

• Mid Carboniferous: cool (54°F).

• Very high oxygen levels → giant arthropods!

• Faster Earth rotation → stronger winds (Coriolis effect).

• Organisms Alive:

• Sharks and rays dominate after placoderms vanish.

• Many bizarre fish forms.

• Carboniferous = Age of Giant Arthropods:

  • Arthropleura (2.6 m millipede)

  • Meganeura (giant dragonfly)

  • Gigantoscorpio

• Verdant swamp forests with ferns, lycopods, first gymnosperms.

• Evolutionary Firsts:

• First reptiles (Hylonomus).

• First amniote egg (huge evolution milestone!).

• First cycads & early gymnosperms.

• First protoconifers.

• Largest amphibian diversity in history.

• End-Carboniferous Climate Shift:

• Becomes cool + arid → rainforest collapse

name the periods in order

Cambrian, Ordovician, Silurian, Devonian, Carboniferous (Mississippian, Pennsylvanian), Permian, Triassic, Jurassic, Cretaceous, Paleocene, Eocene, Oligocene, Miocene, Pliocene, Holocene

• paleozoic (Cambrian, Ordovician, Silurian, Devonian, Mississippian, Pennsylvanian, Permian)

• Mesozoic (Triassic, Jurassic, Cretaceous)

• Cenozoic (Paleocene, Eocene, Oligocene, Miocene, Pliocene, Holocene)

Camels Often Sit Down Carefully (mississippian, pennsylvanian) Perhaps Their Joints Creak.

Put Eggs On My Plate Please, Henry

End of the Carboniferous

• middle Carboniferous: Cooling reduced temperatures and drying of the climate lead to Carboniferous Rainforest collapse

• Amphibians, the dominant vertebrates at the time, fared poorly through this event with large losses in biodiversity;

  • Reptiles continued to diversify due to key adaptations that let them survive in the drier habitat:

    • Specifically the hard-shelled egg and scales, both of which retain water better than their amphibian counterparts

Early Permian and land masses

• end of the Paleozoic Era (1/3 that make up the phanerozoic)

• the earth was still in an ice age, but it began to recede in the early Permian

  • Also started wet and dried out

  • Many animal groups which survived the Carboniferous with only a few species rapidly diversified.

• land masses: 

  • Northwestern Gondwana collided with and joined southern Laurussia, resulting in the Alleghenian orogeny, occurring in the region that would become North America —> forms PANGEA (the supercontinent). 

• marine life:

  • Mollusks, brachiopods, and echinoderms were common

  • Most dominant life forms were:

    • Ammonites

    • Fusulinids – a shelled amoeba-like protist

    • A Nautilus-like mollusk, Cooperoceras texanum

• terrestrial life — plants

  • Several new groups of seed plants

    • First cycads

    • Conifers radiated

  • dominant plants were conifers, ginkoes, and cycads

• insects followed plants into new habitats and broadly diversified

Terrestrial life in the Permian — Amniote Radiation

• Amniotes were the animals that evolved from amphibians but could lay eggs on land, so they were no longer amphibians.

• Actually evolved in Carboniferous

• Since they could range far from water, they quickly evolved to fill many available niches

• The earliest amniotes had anapsid skulls with no opening behind the eye – inherited from fishes and early amphibians

Terrestrial life in the Permian — Synapsids

• diverged from anapsids

  • skulls have one skull opening behind the eye socket.

  • Became dominant animals in the Permian

  • Never evolved capacity to excrete uric acid instead of urea

  • Now known as stem-mammals

• transitional mammals

• Early synapsids had large heavy forelimbs and a lighter hind limb with a greater range of movement

  • No ankle joint

  • Toes long and splayed sideways

  • Forelimbs kept animals upright and hind limbs had momentum

Permian terrestrial life — Amniote Radiation— Diapsids

• are amniotes with two skull openings behind the eye socket.

  • evolve from the sauropsids, the sister group of synapsids

  • Includes all dominant terrestrial groups of the Mesozoic and all living amniotes except for mammals

  • Reptiles and bird (reptiles and birds are more modern than mammals in terms of skulls)

• reptilian but not dinosaurs yet

• early synapsids were all carnivorous

• dimetrodon was most powerful land predator — is NOT A DINOSAUR (it’s more closely related to mammals) and it’s big fin on the back is used for thermoregulation

Evolution of Herbivory

• most plant material is hard to digest

  • cellulose can only be broken down if chewed well and manage to get fermenting bacteria to work symbiotically with them

  • some plant material is high in protein or sugar, but rarer and often have toxins (only small animals can specialize on these)

• So three pathways:

  • 1) Small animals that specialize on high calorie foods, such as juices, fruits, or seeds

    • Small mammals, birds, insects

  • 2) Eat lots of low calorie plants and enlist gut bacteria as symbionts

    • Large grazing animals

  • 3) Omnivory – large animals that are indiscriminant and eat anything in large volumes

    • Bears

• vegetarianism depends greatly on body size

  • as animals got bigger, they might have evolved herbivory

• need symbiotic bacteria to help digest cellulose

  • most bacteria only do well in a narrow range of temperatures

  • thermoregulation is needed

Evolution of Thermoregulation

• Body functions are determined by enzymes and enzymes work best at an optimal temperature, so all organisms have an optimal temperature.

  • Endothermic animals regulate body temperature internally.

    • High metabolic costs

• Ectothermic animals regulate body temperature externally by behavioral thermoregulation

  • Behavioral thermoregulation means that an animal uses it’s behavior to regulate body temperature.

  • Means there is trade-off between activities and balancing body temperature

Permian continental shifts and therapsids

• Shifting continental geography resulted in major biogeographic changes.

  • Creation of Pangaea

  • Changed the climate from wet to dry

• dominant permian plants were conifers, ginkoes, and cycads

• The changing climate of Pangaea also affected animals

  • Since most early synapsids had a narrow temperature distribution and couldn’t thermoregulate, they were restricted to warm areas and were much reduced in diversity

• Instead, their descendants, called therapsids, radiated and diversified

therapsids and evolution of therapsids

• mammal-like reptiles; a group of synapsid reptile that have key mammalian features, such as having their legs vertically beneath their bodies

• synapsid descendants with larger skull openings — more powerful jaws; better locomotion

• come from synapsids

• evolution led to three new advanced forms in the later Permian:

  • Theriodonts

    • includes gorgonopsians (the dominant predators in the late Permian; had saberteeth and a large gaping jaw with slamming action

  • cynodonts

  • dicynodonts

theriodonts (evolution of therapsids)

Carnivores with low flat snouts and very effective jaws

cynodonts (evolution of therapsids)

• small to medium-sized carnivores or herbivores; most mammal-like therapsids

  • Jaw and teeth adapted to chew – led to many jaw, tooth, and skull features seen today

  • Descendants became mammals

dicynodonts (evolution of therapsids)

• dominant herbivores of the late Permian – first truly abundant worldwide herbivores

  • Have specialized palate to allow breathing and chewing at same time

  • Very short snouts, almost no teeth except for tusk-like canines; had beak-like jaw

  • Ranged from rat-sized to cow-sized

  • Best known dicynodont is Lystrosaurus

    • Dominant grazer

The Great Dying (Permian Extinction) — CAUSES

• Two extinction events

  • Mid-Permian – caused by shifts in the tectonic plates when Pangaea came together, which caused the landmass to dry out

    • Took place over millions of year

  • Late Permian – Abrupt catastrophic event

    • Took place rapidly – within one million years

• sea levels were low and near shore environments were reduced when most major landmasses collected into Pangaea in middle Permian

  • partly why so many ocean animals went extinct

• asteroid impact

• radiation generated by the impact

  • caused enough heat to generate fires

• The impact would have blown a mass of vaporized rock and steam high above the atmosphere

  • Would form an immense dust cloud that would settle out through the atmosphere during a period of weeks to years.

    • This would cut down on the sun’s rays so that plants and phytoplankton cannot photosynthesize

    • The dust would also cause freezing temperatures within days of the impact – stay freezing for months

      • Catastrophic for non-thermoregulating organisms

• Once the dust and aerosols have settled, the enormous amount of water vapor and CO2 released into the atmosphere generate a greenhouse gas effect that will elevate the planet’s temperature for 1000 years

• impact triggered massive plume eruption

  • largest known volcanic eruption occurred

    • plume tectonics – a giant pulse of heat comes rising to the surface as a plume

    • as the plum approaches the surface, the plume melts the crust to develop a flat head of basalt magma

  • Penetrating the crust of the earth, the plume generates enormous volcanic eruptions that pour hundreds of thousand of km3 of basalt over the surface

    • Flood basalt

• The plume event would have produced a tremendous amount of sulfate aerosols that would have added to the debris and contributed to the rapid global cooling, causing ice caps

• Once the plume has finally ended, the dispersion of the aerosols would reverse the glaciation and cause a very rapid climate shift in the opposite direction

• acid rain, ozone depletion, and a massive dose of CO2 would have set in

• it’s also possible that the CO2, methane, and other gases in the atmosphere supersaturated the ocean, resulting in an anoxic environrment (without oxygen)

The Great Extinction (Permian Extinction) — EFFECTS

• the end of the Paleozoic

  • fauna changed so dramatically that this ended an entire era

• extinctions

  • trilobites

  • families of crinoids, corals, and cephalopods

  • 75% of known amphibian families

  • 80% of reptilian families

  • 2/3 of amphibians, reptiles, and therapsids

• affects evolution

• at the end of the Permian extinction, synapsids were the dominant large land animals

• diapsids were present but not nearly as numerous or diverse as synapsids

• synapsids faired more poorly during the mass extinction than diapsids

• allowed diapsid reptiles to take over and become the dominant large animals on land and at sea

• without P-T extinction, we may never have had dinosaurs, and mammals might be very different and humans might have existed much earlier

• marine invertebrates suffered the greatest losses

• was the only known mass extinction of insects ever (wipes out some of the biggest)

• Plant abundances and distributions changed profoundly – forests virtually disappeared

  • Gymnosperms and seed ferns were replaced by mosses and liverworts

How do mass extinctions affect evolution? (The Great Extinction — EFFECTS)

1. Open spots that need filling

   1. The ecosystem is like a big puzzle and mass extinctions remove several pieces. This leaves opportunities for new species to fill those niches and become the missing puzzle pieces. New species won’t be the same as the old species. Mass extinctions remove the incumbent effect – once a species is there and established, it’s difficult to remove, even though it is possible through natural selection.

2.  New habitats

   1. mass extinction events are perpetuated by large natural disasters; often greatly change the landscape and climate; in turn causes animals to adapt to the new habitat; new species created

3. New biological inventions

   1. occasionally a lineage will evolve a body plan that allows it to do things that have never been done before. much more opportunity to be successful when there are many empty niches

      1. examples: the first eukayotes, tetrapods, flights

who did cynodonts derive from?

What were the Permian precursors to mammals?

therapsids, a group of synapsids that evolved from earlier pelycosaurs. These animals developed several mammalian-like traits, such as more mammal-like jaw and teeth structures, limbs positioned more under the body, and possibly even warm-bloodedness

How did herbivory evolve and why was this difficult?

herbivory evolved from animals having gut bacteria and the inability to digest plants properly. they also need thermoregulation.

Mary Ann Mantell

found the first known dinosaur

sees a dark shiny object in pile of rocks near the side of the road —> ends up being several large teeth

Gideon Mantell

• avid collector of fossils

• took the teeth that Mary found.

• he knew that they had to belong to some species of gigantic plant eater

• Named the specimen Iguanodon (similar teeth to the iguana)

Sir Richard Owen

• English naturalist and influential 19th-century scientist.

• Coined the term “Dinosauria” in 1841, meaning “terrible lizard” (from Greek deinos + sauros)

• Recognized that fossils found by Mantell, Buckland, and others belonged to a distinct, extinct group of reptiles.

• Was a strong anti-evolutionist and used dinosaurs to argue against Lamarckian evolutionary ideas.

• Believed organisms followed divine “archetypes”—fixed patterns created by a creator.

• Helped shape early public perception of dinosaurs as huge, slow, lumbering, cold-blooded reptiles.

• Worked with sculptor Benjamin Waterhouse Hawkins to create the first life-size dinosaur models for the Crystal Palace exhibition.

• Not known for being “nice”—had a reputation for being competitive and difficult, even with other scientists

Charles R Knight

• Late 19th–early 20th century paleoartist and illustrator.

• One of the first artists to depict dinosaurs as active, agile, and dynamic, instead of slow, clumsy reptiles.

• His artwork helped shift public understanding toward a more realistic and modern view of dinosaur behavior and posture.

• Created famous pieces like Leaping Laelaps (1897), which portrayed dinosaurs in energetic, predatory motion.

• His paintings still appear in major museum halls, including the American Museum of Natural History.

• Considered one of the most influential paleoartists in history; shaped how generations visualized prehistoric life.

Were dinosaurs endothermic or ectothermic?

endothermic and were warm-blooded. their physiology was more like that of birds and mammals than that of lizards and snakes

how have our depiction of dinosaurs changed over time?

1850s:

➡ Giant, clumsy lizards
➡ Slow, cold-blooded, tail-dragging

1900s–1950s:

➡ More detailed but still reptilian and sluggish

1960s–1970s:

➡ Athletic, upright, warm-blooded
➡ Birdlike movement and behavior

Modern:

➡ Diverse, intelligent, active, and ecologically complex animals

Over time, depictions of dinosaurs shifted from slow, tail-dragging, lizard-like reptiles to active, agile, and bird-like animals. Early reconstructions showed them as lumbering, cold-blooded brutes, but discoveries in the late 20th century, especially by Ostrom and Bakker, revealed they were dynamic, warm-blooded, and far more sophisticated. Modern portrayals emphasize movement, intelligence, and ecological diversity.

Cope and Marsh Fossil Feud — Was their rivalry a good thing or not?

The contribution was that while their feud greatly advanced paleontology. They destroyed fossils to keep each them from each other, made rushed and inaccurate publication, and damaged the reputation of American science. However, their competition led to massive discoveries (over 120 new dinosaur species). I think that their feud was positive for paleontology because they probably wouldn't have discovered as much as they had without racing eachother. They accelerated the progres of paleontology, bringing public interest. I don't think either of them would have achieved as much as they did without the hatred of the other.

Dinosaurs belong to a large group of reptiles known as Archosaurs, or “ruling reptiles”

• diapsid amniote reptiles including dinosaurs, birds and crocodiles

  • also includes pterosaurs and pterodactyls

  • took over in the Triassic, did so well that it took another mass extinction event to let mammals dominate again in the Cenozoic

• became dominant by mid Triassic — did well with high temperatures

• have teeth set in sockets

• pair of opening on each side of the rear of the skull, in the temporal area

• possess a pair of large triangular openings in front of the eye cavity

• Most have powerful hind limbs

Synapsids

a group that includes therapsids (mammal-like reptiles) and mammals dominated during the Permian, almost wiped out in the Great Dying

Dinosauria

is united by many shared derived traits (synapomorphies), including:

• Reduced 4/5 digits

• Sacrum (part of spine) of three or more vertebrae

• Open hole in center of hip socket

Dinosaurs diverged very early on into two main lineages, separated primarily by differences in pelvic structure

• Ornithischia

• Saurischia

Ornithischia

“bird-hipped dinosaurs”

• Duck-billed hadrosaurs

• Horned Ceratopsians (Triceratops)

• Ankylosaurs

• Stegosaurs

Saurischia

“lizard-hipped” dinosaurs

• Herbivorous Sauropods, like Brontosaurus (Apatosaurus), Diplodocus

• Carnivorous Theropods, such as Tyrannosaurus, and Compsognathous

therapods

• the carnivorous saurischian dinosaurs

• birds evolved from these dinosaurs

archosaurs and foot/leg movement

• crocodile-like archosaurs

  • had a sprawling side-to-side gait of primitive amphibians and early reptiles

  • two groups: phytosaurs and aetosaurs

• bird-like archosaurs

  • have a forward gait which allows rapid movement

• this advance involved turning the foot from facing outward, as a relatively passive pad for a sprawling gait

• Needed a freely hinged ankle with the foot facing forward, to accommodate the front to back gait of advanced vertebrates

• Legs held vertically under the body

• with their improved stance, dinosaurs could reach an enormous size

  • though large, could still move quickly and efficiently, like a modern mammal or bird

• required a radical reshaping of the ankle joint

  • ankle joint morphology shows a great deal of complexity and variation

  • fortunately, ankle bones are small, dense, preserve well

More than other characteristics, what improvement may account for the incredible success of the dinosaurs?

their improved stance and gait. they conquered the earth, and in doing so, gave rise to a new evolutionary line destined to conquer the skies.

dinosaurs evolved many significant improvements, both skeletal and physiological. name the skeletal/morphological adaptations that allowed them to be what they were.

• fully improved stance, rapid gait

• feathers 

• pneumatic bone

dinosaurs evolved many significant improvements, both skeletal and physiological. name the physiological/behavioral adaptations

• advanced respiratory system (air sacs)

• rapid growth rates

• uric acid excretory system

• endothermy (warm blood)

• complex social behavior

pneumatic bones (dinosaur skeletal/morphological adaptations)

• most dino bones were not solid, but filled with air spaces, some occupied by structures called air sacs

• modern birds have similar bones, rely on air sacs for buoyancy, breathing, etc

• would have allowed dinosaurs to become very large, but still relatively lightweight

  • could move faster, be more maneuverable for their size

• neck bons (vertebrae) are filled with these air spaces

• similar pneumatic bones have been found in theropods and other dinosaurs

• may be a preadaptation for flight in birds

advanced respiratory system (air sacs) (dinosaur physiological/behavioral adaptations)

• tied with the pneumatic bones, birds have numerous large air sacs

  • critical part of their respiratory system

• gives them incredibly efficient flow-through ventilation

• upright stance also aids in respiration

  • makes respiration, lung expansion more efficient, especially while running

uric acid excretory system (dinosaur physiological/behavioral adaptations)

• makes them better adapted to the more arid Triassic environment

• uric acid requires less water than systems based on ammonia and urea

rapid growth rates (dinosaur physiological/behavioral adaptations)

• advantage over competitors

• important for the largest herbivores and carnivores

• can be measured by looking at rings in their bone structure

  • bones formed growth rings, analogous to growth in rings in trees

• growth rings indicate very rapid growth, especially as a teenager (5 tons in 4 years, 2kg a day from age 14 to 18)

• by counting growth rings, we can tell age

  • most sauropods probably lived 70-80

  • most theropods probably lived 20-30

superior metabolism and endothermy (dinosaur physiological/behavioral adaptations)

• an erect stance and active gait had to required an efficient metabolism

• dinosaurs must have been warm blooded

• studies show that Saurischians (theropods and sauropods) had low metabolic rates and were probably ectothermic

• ornithischians were endothermic

  • some had higher metabolic rates than mammals, much like birds

evidence that at least some dinosaurs were warm blooded

• erect stance

• rapid gait (run, gallop) - trackways

• feathered dinosaurs — insulation

• predator/prey ratios

  • warm-blooded animals (endothermic) need more energy to sustain themselves than cold-blooded animals (ectothermic)

  • ectothermic (cold blooded) communities have high predatory/prey ratios

    • a large number of gators can be sustained by relatively small number of fish

  • endothermic (warm blooded) communities have low predatory/prey ratios

    • it takes a lot of zebras to sustain a small number of lions

gastroliths

• along with coprolites, it tell us something about feeding behaviors

• they are large stones that dinosaurs swallowed to help them grind their food

• 2003 discovery of well-preserved dinosaur shed new light on dinosaur physiology

  • brachylophosaurus (duck-billed herbivorous dinosaur) specimen named “Leonardo”

  • showed large stretches of actual skin, with well-preserved scales, tendons, etc

  • found that his last meal included plenty of well-chewed leaves digested into tiny bits (contained ferns, conifers, and flowering plants, parasites)

dinosaur complex social behavior (dinosaur physiological/behavioral adaptations)

• they were successful in part due to their evolution of complex social behavior

• rarity of good fossil finds requires a big assumption

  • very easy to make mistakes

  • example: Oviraptor was first specimen found near a nest thought to belong to another species, so interpreted remains as an egg-stealer. turned out it was just a good mother dinosaur who was caring for her eggs

• behavior we can deduce from fossils:

  • speed and gait

  • herding

  • pack hunting

  • aggression (male-male competition)

  • courtship behavior (display etc)

  • parental behavior

ichnology

• study of tracks and traces animals left behind

• gives clues to dinosaur behavior

• study things such as:

  • tracks and trackways provide data on speed, gait, behavior. distance between footprints, and distance between alternate prints of he same foot lets us estimate height, stride length, speed, normal gait

  • coprolites

  • nets and eggs. tells us a lot about dinosaur behavior

• also reveal predator/prey interactions, and social behavior such as herding

• there’s evidence of pack hunting

dinosaur speed and gait (ichnology— behavior we can deduce from fossils)

• some smaller sprinters could go 30-40mph

• large dinosaurs could run about as fast as an elephant (slow)

• triceratops could probably keep up with a charging rhinoceros

• t-rex probably had a top speed of about 9-13mph

• distance between footprints, and distance between alternate prints of he same foot lets us estimate height, stride length, speed, normal gait

dinosaur herding (behavior we can deduce from fossils)

ichnology also reveal predator/prey interactions, and social behavior such as herding

• some traveled in herds, with young in the center, adults surrounding them to protect them from predators

several morphological features suggest dinosaurs relied on visual displays for communication (behavior we can deduce from fossils)

• display behavior usually occurs when

  • males display to court females

  • males display to defend their territories

  • males establish dominance heirarchies

• features that suggest display behavior:

  • horns

  • frills

  • spikes

  • crests

  • thickened skulls

• Good circumstantial evidence that such structures are display structures

  • In sexually dimorphic species, well-developed structures are limited to one sex (presumably the male)

  • In species with large numbers of specimens, these structures only appear on mature individuals (as in modern animals)

• thickened skulls of pachycephalosaurus seemed to have evolved for good old-fashioned head butting

• triceratops frill bones show combat scars, suggests horn and frills were not just ornamental, but used for fighting

• long feathers on the epidexipteryx seemed designed for display, not functional for flight

• color patterns

  • understanding color tells us things about animal’s behavior

  • example: microraptor was thought to be nocturnal because of its large eye sockets, but is recently discovered to be iridescent

• certain dinosaurs may have used their crests to generate sounds for vocal displays

dinosaur colors — visual communication and species identification in modern animals helped determine dinosaur colors

• dinosaurs often reconstructed in bright colors

• no colors preserved, pigments too delicate

• there are visible patterns, however, in the size and type of scales or tubercules or melanosomes

  • different shapes mean different colors

• some fossils contained pigment structures called melanosaomes which are also found in fossilized feathers or skin. We can look at modern birds to see what kind of melanosomes give certain colors and apply it to dinosaurs. Psittacosaurus was light on its stomach and dark on its back.

• they had stripes, black and white markings, counter shading

coloniality

• often find groups of nests together of similar types

• dinosaurs behave very much like modern colonial waterbirds

dinosaur eggs and nests

• All dinosaurs laid eggs, but only a handful of species have been found together with their nests

• nested like gulls, herons, and ibises do today

• they returned to the same location year after year to nest

• one nest held the remains of 15 babies each 3ft long

  • lots of eggshell fragments

  • baby’s teeth were warn, indicating it had been feeding for some time

  • suggested that the baby must have spent some time in the nest, being cared for by their parents

• they were colonial

• evidence shows that some young were altricial

• evidence also shows some were precocial

altricial

young that were developmentally immobile for a significant period after hatching/birth

precocial

young that are mobile shortly after hatching/birth

• in one fossil nest, the top parts of the eggs were broken into fragments, but the bottoms of the shells were intact

• These newborn dinosaurs must have immediately left the nest

Problems with Jurassic Park

• T rex, velociraptor, and triceratops all lived during the Cretaceous

• movie shows triceratops dun as big as an actual triceratops

  • nowhere close to the actual size

• velociraptors are much more like Deinonychus

The Mesozoic: AGE OF REPTILES — Triassic

• supercontinent Pangaea still united most landmasses together

• climate was hot and dry and seasonal

  • very hot summers and cold winters

• Permian extinction caused massive damage to ecosystems

  • oceans, the massive loss of genera left the fauna very uniform

    • new species, so could become populous

• dominant ocean vertebrates included nautiloids, ammonoids (not ammonites), gastropods, echinoderms, and bivalves

  • reduced diversity because of Permian

• early Triassic, Ichthysauria (group of reptiles) returned to the ocean

  • by mid-triassic, they were dominant in the oceans

• sauropterygia (aquatic reptiles)

• plesiosaurs evolved during late Triassic from nothosaurs

• Nothosaurs — early tiassic marine sautopterygian reptiles

• turtles, another group of primitive reptiles took to the water during early triassic

• Pleuromeia, a lychophyte was one of the most common plants

• conifers, gymnosperms began to recover from Permian. ferns did well in the triassic and gymnosperms eventually recovered

• spiders, scorpions, millipedes, and centipedes survived the Permian extinction, as well as some groups of beetles

• grasshoppers and lepidopterans (butterflies and moths) evolved in the Triassic

• crocodilians did well during the Triassic and greatly diversified

• By the late Triassic, the first true flying Pterosaurs had evolved

Sauropterygia (Triassic)

a group of aquatic reptiles that flourished during the Triassic, but most went extinct during the mass extinction event at the end of the Triassic except for the plesiosaurs

• nothosaurs

• plesiosaurs

• pachypleurosaurus

nothosaurs (Triassic)

early Triassic marine sauropterygian reptiles

• Lived like seals, spending most of their time in water but living on land.

• 10 ft in length

• Ate fish and cephalopods

• Gave rise to plesiosaurs

plesiosaurs

• evolved from reptiles that returned to sea (nothosaurs) during the late Triassic

the turtles (Triassic)

primitive reptiles that also took to the water during the early Triassic

two main groups of reptiles that survived the Permian extinction were the ___

therapsids (mammal-like reptiles) went extinct during mid Triassic

archosaurs (diapsid amniotes that includes dinosaurs, birds, and crocodilians) became dominant by mid Triassic as they did well with high temperatures

ornithodira (Triassic) evolved into two important groups

Pterosauria

Dinosauromorpha — gave rise to dinosaurs

The Triassic — Dinosaurs; when did dinosaurs first evolve?

• first true dinosaurs evolved by late-Triassic

  • hunted in packs

  • some bipedal

  • had flexible hip, faster

  • had lightweight hollow bones

late-Triassic, dinosaurs diversified and the true _____ had evolved

FLYING Pterosaurs

the first ____ evolved near the end of the Triassic Period from the nearly extinct Therapsids

mammals; early mammals were very small, mainly herbivores or insectivores and therefore were not in direct competition with the Archosaurs or later dinosaurs. first monotremes, arboreal, nocturnal, laid eggs

Triassic Extinction

• Pangaea began to break up at the end of the Triassic

• huge volcanic eruptions began to occur

• Triassic period ended with a mass extinction, particularly severe in the oceans

  • 22% of marine families went extinct

    • conodonts

    • all marine reptiles except for ichthyosaurs and plesiosaurs

    • many brachiopods, gastropods, and mollusks

• other groups that went extinct included

  • important clades of large archosaurian reptiles

  • large labyrinthodont amphibians,

  • groups of small reptiles,

  • some synapsids (except for the proto-mammals).

• Some of the early, primitive dinosaurs also became extinct, but more adaptive ones survived to evolve into the Jurassic.

The Mesozoic: AGE OF REPTILES — Jurassic

• By the beginning of the Jurassic, Pangaea started drifting into Laurasia and Gondwana

  • Mountains rose on sea floor, raising sea levels

• This created more coastlines and shifted the climate from dry to humid – temps up to 86°F

• tree-like cycads, tree ferns, ginkoes, and conifers took over the now moist landscape

• mid Jurassic, the oceans teemed with life

  • plesiosaurs

  • ichthyosaurs

  • giant marine crocodiles

  • large sharks

  • ammonites

  • reefs— there were corals but majority of reefs were built by mollusks

• ammonites and other cephalopods, crustaceans, and true starfish had become common

• skies were also becoming filled with winged vertebrates – NOT dinosaurs

• Early species had long, fully toothed jaws and long tails, while later forms had a highly reduced tail, and some lacked teeth.

• Many sported furry coats made up of hair-like filaments known as pycnofibers, which covered their bodies and parts of their wings

• end of Jurassic, climate began to cool

The Jurassic — Non Reptiles

• the first jumping frog evolved (first frog evolved in the Permian)

• earliest shelled turtles appeared

The Jurassic — Mammals

• things are beginning to look similar in terms of mammals

• vilevolodon — sugar glider

• castrocauda — early beaver

• etc

Lush conditions gave rise to new and extraordinary kinds of dinosaurs — Jurassic Sauropods

• all huge, long neck dinos (10-52 tons)

• apatosaurus

• diplocodus

• brachiosaurus

• camarasaurus — most common

The Jurassic — Theropod Saurischians

• there were many theropods in the Jurassic

  • many were 20ft long on average

• Allosaurus was the top predator of the Jurassic

  • 50ft tall, 28ft long, most abundant predator

The Jurassic — Ornithiscian Dinosaurs

• bird hipped

  • pubis pointing backward

• mainly herbivorous dinosaurs

The Jurassic — Cryptoclidus

a plesiosaur that resembled the Loch Ness Monster with four huge flippers, a short tail and a longer, flexible neck. had a long snout and curved sharp teeth which aided in catching small fish, shrimp and squid.

The Jurassic — Pterosaurs

• flying reptiles, first vertebrates to have evolved flight.

• Their wings were formed by a membrane of skin, muscle, and other tissues stretching from the ankles to a dramatically lengthened fourth finger

The Mesozoic: AGE OF REPTILES — The Cretaceous

• early Cretaceous, Pangaea continued to brake up into modern continents of North America, Europe, and Asia

• Gondwana followed, forming South America, Africa, Australia, and Antarctica

  • Not in modern positions yet though

• Broad shallow seas across North America and Europe

• at first, cooling climate (from Jurassic)

  • very wet

  • evidence of snow

• after first 6my, temps increased again and remained warm for rest of period

  • Warming may have been due to volcanic activity which produced large amounts of CO2

  • sea levels were high

• Flowering Plants (Angiosperms) evolved!

  • Aided by the appearance of bees – coevolution

• Many leafy trees appeared and gymnosperms continued to thrive

• rise of mammals — Mammals were still very small but abundant

• Marsupials and placental mammals evolved about 115 mya

• oceans were filled with large, toothy, fast organisms

  • ichthyosaurs were probably outcompeted by plesiosaurs and went extinct by mid cretaceous

  • mosasaurs evolved from aquatic lizards in late Cretaceous; quickly diversified

  • sea turtles evolved during cretaceous, resembled modern sea turtles

• rise of birds — by early cretaceous, there were many birds

The Cretaceous - Sauropods

• titanosaurs — a diverse group of sauropods that included some of the largest animals that ever walked the Earth; had smaller heads than other sauropods and larger nostrils

• argentinosaurus

The Cretaceous — Ornithischia

• many ornithischia still around

ankylosaurs — herbivorous quadrupeds armored with body scales

The Cretaceous — Theropods

• ornithomimosaurs — theropods which looked like ostriches

• dromaeosaurs — feathered theropods

The Cretaceous — Pterosaurs

quetzalcoatlus — advanced toothless pterosaurs some of the largest flying animals of all time 

• wingspan of ~40ft

The Cretaceous — mammals evolved from _____

therapsids

characteristics of mammals

• Have hair

• Suckle young

• Are endothermic (warm-blooded)

key features had to evolve to form mammals — rise of mammals (cretaceous)

• jaws

• Teeth and tooth replacement

• Hearing

• Brains

• Locomotion

• Thermoregulation

• Reproduction

• live birth

Jaws (key features had to evolve to form mammals — rise of mammals (cretaceous))

cynodonts evolved the masseter, a large muscle that runs from the skull under the cheekbone to the outer side of the lower jaw

• Most powerful muscle that closes the jaw

• Made jaw movements more precise and easier to control

• Biting became more powerful

• Force of bite delivered directly through teeth, instead of through jaw hinge

hearing (key features had to evolve to form mammals — rise of mammals (cretaceous))

early cynodonts transmitted ground-borne vibrations through the forelimbs and shoulder girdle to the brain

• Hearing system evolved to detect sound through the air

• Middle ear-bones became suspended from skull

• Don’t have to listen to yourself chew as much

• Only advanced mammals evolved the complex spiral inner ear

brains (key features had to evolve to form mammals — rise of mammals (cretaceous))

As jaw and ears evolved, brain got bigger and bigger to accommodate senses and more complex behavior

locomotion (key features had to evolve to form mammals — rise of mammals (cretaceous))

Cynodonts had wheelbarrow locomotion

• Hindlimbs evolved to become semi-erect, which brought feet closer together

• Ankle changed to give more direct propulsion in line of travel

• Spine evolved greater stiffness so that power would be transmitted more efficiently, more flexible necks

thermoregulation (key features had to evolve to form mammals — rise of mammals (cretaceous))

Means you have a much faster metabolism to keep body warmer

• Cynodonts evolved diaphragm to allow more efficient respiration

  • Have to breathe more with faster metabolism

• Evolved fur for insulation

reproduction (key features had to evolve to form mammals — rise of mammals (cretaceous))

Suckling – evolved from a special gland that reptiles had to secrete moisture for the eggs while incubating them

• Hatchlings may have licked gland to gain moisture

• Gradually, nutrients were secreted too = milk

• Suckling demands full and flexible cheeks, which mammals evolved

live birth (key features had to evolve to form mammals — rise of mammals (cretaceous))

first mammals (monotremes) laid eggs

• Has evolved independently many times – 90 times

• Live birth is easier than egg laying in small animals

• Probably evolved during Cretaceous

Rise of birds: By early Cretaceous, there were many birds. The origin of flight has nothing to do with feathers. Name the four hypotheses of the origin of Flight

• birds had:

  • shorter tail feathers and shorter tail

  • shorter body

  • center of mass closer to wings

  • shoulder joint that allowed wings to be raised

• hypotheses of origin of flight:

  • the arboreal hypothesis

  • the cursorial hypothesis

  • the running raptor hypothesis

  • the display and fighting hypothesis

The arboreal hypothesis (origin of flight)

• flight evolved by birds jumping out of trees

• suggests small feathered dinosaurs first glided from branches, making it a plausible path since gliding is common in tree-dwelling animals.

• Can’t be because body types of early birds and therapods were not evolved to live in trees

the cursorial hypothesis (origin of flight)

• a fast-running reptile would learn to flap its winged arms and eventually fly

• proposes that running dinosaurs used their feathered arms to generate lift

• less supported because running alone doesn’t create much lift.

• Can’t be because before flight, wings would cause increased drag

the running raptor (origin of flight)

Running with synchronized movement of wings to give forward thrust and allow more rapid movement over ground

• argues that early predators leapt onto prey from above, using controlled falls that could later evolve into true flight.

Wing thrust would have to become more powerful that leg thrust

the display and fighting hypothesis (origin of flight)

theropods had long display feathers that they would flap for mates or territoriality and flapping would give it lift off the ground during fighting

• suggests feathers originally evolved for display or aggressive interactions, and those movements were eventually co-opted into flapping.

• How does a bird flap enough during fighting to really fly?

The Cretaceous-Tertiary (KT) Extinction

• the end of the dinosaurs

• was a mass extinction of three-quarters of the plant and animal species on Earth

  • occurred over a geologically short period of time approximately 66 million years ago.

• It marked the end of the Cretaceous period and with it, the entire Mesozoic Era, opening the Cenozoic Era that continues today

• huge asteroid impact

• The impact would have sent tidal waves crashing against all the continents and started a chain reaction of volcanic eruptions

• the asteroid would have vaporized, sending up a huge cloud of dust into atmosphere

  • Blockage of Sunlight - Would cause global winter of darkness up to 3 months

• Short-term global warming – immediately after the impact, the heat from the impact would have raised global temperatures by as much as 30C for up to 30 days

  • Followed by the winter of darkness for up to 3 months

• Global Wildfires would have broken out instantly

• Acid Rain – may have occurred caused by nitrous acids in atmosphere, but not much evidence

• Long Term Global Warming followed all of these (but less than a million years)

• with the exception of a few reptilian species like leatherback sea turtle and crocodiles, no tetrapods weighing more than 55 lbs surived

• all non-avian dinosaurs, pterosaurs, mosasaurs, and plesiosaurs went extinct

• ammonites went extinct