Dinosaur Exam 3

Triassic faunas

• Almost no Ornithiscians

• Relatively small

• Oldest well-preserved remains are early Triassic

• Dominated by archaic mammal and reptile groups and labyrinthodont amphibians

Late Triassic to Early Jurassic distribution

Cosmopolitan —> faunas are very similar throughout the world

Middle Jurassic onwards distribution

Endemic faunas developed as the continents divided

Late Triassic dinosaur faunas

• Theropods include basal members such as Herrerasaurus and Coelophysis

• Prosauropods first appear and are abundant

• Ornithischians are rare and poorly known

End Triassic extinctions

• ~200 mya

• Rhynchosaurs, most labyrinthodonts, large mammal relatives like dicynodonts, and large crocodylian relatives (aetosaurs, rauisuchids, phytosaurs) go extinct

• Large marine extinction

• Immense volcanic activity

• Increased atmospheric CO2

  • Greenhouse conditions

Early Jurassic dinosaur faunas

• Low diversity

• No rapid radiation after End Triassic extinctions

• Prosauropods common —> sauropods rare

• Basal theropods

• Ornithischians growing more common

Middle Jurassic dinosaur faunas

• Poorly known part of the fossil record

• Sauropods are common but not diverse

• Ornithischians begin to diversify

  • Ankylosaurs, stegosaurs, and basal members

• Theropods are diverse

When did Ornithischians begin to diversify?

Middle Jurassic

Late Jurassic dinosaur faunas

• Sauropods dominate

• Large theropods such as Allosaurus are present with small coelurosaurs including the earliest bird, Archaeopteryx

• Ornithischians are diverse but not common

  • Ornithopods, ceratopsians, ankylosaurs, stegosaurs

• Some endemism as Pangaea begins to split up

Early Cretaceous dinosaur faunas

• Gondwana and Laurasia begin to develop endemic faunas

• Basal ceratopsians such as Psittacosaurus common in Laurasian faunas

• Iguanodonts are common in Gondwanan and Laurasian faunas

• Sauropods common, mainly titanosaurs

• Coelurosaurs, including birds, are diverse

When did the first flowering plants (angiosperms) appear?

Early Cretaceous

Early floras

Dominated by conifers, cycads, and ginkgoes

Cretaceous Terrestrial Revolution

The diversification of angiosperms and the related insect pollinators and herbivores in the Cretaceous

Late Cretaceous dinosaur faunas

• Best known part of Mesozoic

• Laurasia

  • Faunas of North America, Europe, and Asia are similar

  • Ceratopsians, ankylosaurs and hadrosaurs are common

  • Tyrannosaurids are the dominant large theropod

  • Titanosaur sauropods are present in many areas but not in the best known faunas of northern North America

• Gondwana

  • Faunas of South America, Africa, Madagascar, India, Australia, and Antarctica are similar

    • Rich known faunas in South America and Madagascar

  • Titanosaur sauropods are common

  • Ornithischians are rare

    • No ceratopsians or pachycephalosaurs

  • Abelisaurid ceratosaurs are the dominant large theropod

Vicariance

Geographic distribution of groups within a taxon due to the breakup of regions by non-biological forces —> taxa have not moved, the Earth has changed

Dispersal

Geographic distribution due to movement of organisms between regions

How features that are not preserved are inferred using phylogeny and optimization

If we know the conditions in living animals they can be optimized (mapped) on a cladogram to infer the condition in extinct relatives for which we have no data —> if all living relatives have the same condition we would infer that the extinct forms have that condition

Character optimization

• Infer genomic information about extinct taxa using genomes of living animals

• Ancestral gene sequences inferred using the sequences of the living representatives and outgroups

• Proteins can be manufactured from the inferred ancestral genome sequence and subjected to experiments

• Can be done for the archosaur common ancestor of birds and crocodylians, but not for dinosaurs

  • Large size of many non-avian dinosaurs may have required them to evolve new features that are not found in living archosaurs

Osteological correlates

Features on bones indicative of particular soft tissues

Archosaur features (derived features of birds and crocodylians)

• Extensive air sacs in the skull

• Unidirectional air flow during respiration

• Parental care of young

• Vocalization

• Four chambered heart with completely separated circulation in the heart

• Egg shells are hard, not leathery

• Males had a penis

• Scales and possibly feathers were composed of Beta keratin

Features of birds that may have evolved within non-avian dinosaurs

• Endothermic (warm-blooded)

  • High metabolic rate

• Incubated eggs within their nests

• High growth rate and age of sexual maturity

• Had nasal turbinates (or similar soft tissue to cool the brain)

• Completely divided blood flow

• Had a crop/gizzard

• Been active fliers

• Breathed by moving their sternum

• Extensive air sacs throughout body

• Had a cerebellum and cerebrum

• Ears sensitive to sound

• Genetic sex determination

Evidence for endothermy in non-avian dinosaurs

• Surface area does not increase as fast as volume when animals get larger

• Large animals have a problem getting rid of body heat (which is done mostly through the skin) once they have warmed up

• Bone tissues indicate that dinosaurs were active, possibly warm-blooded animals (Robert Bakker)

  • Extensive vascular canals

• Predator-prey ratios

  • There are fewer carnivores in warm-blooded communities

• Dinosaurs were built like active animals

  • Erect posture of hindlimb bones

• Dinosaurs out-competed the mammals during the Mesozoic, which cold-blooded animals could not do

• Birds are warm-blooded, and since they descended from dinosaurs then dinosaurs may have been warm-blooded

• Feathers in non-avian dinosaurs suggest that they insulated internally produced heat 

• Dinosaur localities known near the poles, only endotherms can survive those regions today

• Lipid oxidation byproducts in fossils suggest the ancestral condition in dinosaurs was endothermy

Evidence against endothermy in non-avian dinosaurs

• Vascular canals are found in reptile bones occassionally

  • Not directly linked to endothermy

• Biases of the fossil record make predator-prey ratios difficult to measure

• It is difficult to tell how active an animal is from the shape of its bones

• Mammals evolved endothermy during the Mesozoic, yet dinosaurs “out-competed” them

• Growth lines in dinosaur bone indicate they had a lower metabolism during the winter, like ectotherms

• No evidence of nasal turbinates in dinosaurs (like in birds)

Lines of Arrested Growth (LAGs)

• Mammal and bird bones do not have growth lines

  • For most, growth doesn't slow in the winter

• Growth rates in living animals are correlated with metabolic rate

  • High metabolic rates of endotherms produce faster growth

• Maximum growth rates should only consider growth during the rest of the year, and not be an average for an entire year

  • Exclude slower seasonal growth

• A 2014 calculation using whole growth rings shows dinosaurs have a mesothermic growth rate, lower than mammals and birds but higher than crocodylians

Endothermy

• Warm-blooded

• Relatively constant high body temperature

• Higher metabolic rates

• Enzymes are most effective with a narrow range of temperatures in which they are active

• Ex. birds and mammals

Ectothermy

• Cold-blooded

• Gain heat from outside the body

• Maintain a relatively constant body temperature through behavior

  • Ex. sunning themselves, evaporative cooling

• Ex. reptiles, crocodylians

Poikilotherms

Ectothermic animals that can vary their body temperature

Homeothermy

Variation in body temperature in endotherms

• Evidence suggests that large sauropods were homeothermic due to thermal inertia in the huge bodies

• Stable isotopes suggest homeothermy in many dinosaurs

End Cretaceous (K-P) extinctions

• Large marine extinction

  • Ammonites and belemnites

  • Species on sea floor were impacted less

• All dinosaur species except birds extinct

• Plants suffered extinctions in some areas

  • A “fern spike” (a layer dense with fern spores) occurred at the very end of the Cretaceous, lasting about 1,000 years

• Freshwater animals like turtles, fish, amphibians and crocodilians suffered less than fully terrestrial animals

Impact Theory

• Leading hypothesis for the cause of the extinction of non-avian dinosaurs

• Iridium is a rare earth element that is 10,000 times more common in extraterrestrial dust and meteorites than in the Earth’s crust

• At an end-Cretaceous rock section at Gubbio, Italy, Walter Alvarez found a sharp increase in Iridium

• In 1980 he and his father proposed the theory that the extinction was caused by the impact of an extraterrestrial object

• Soon after the discovery of Iridium, the same layers produced granules of quartz that were “shocked”

• Shocked quartz results from extremely strong stresses, and is rare on Earth except in volcanic eruptions and meteor craters

• Shocked quartz and iridium were soon found in a number of localities around the world preserving the K-P boundary

• Tektites are found at known meteor impact sites and at times of suspected large impacts

  • Occur at the K-P boundary in deep sea cores 

• Chicxulub crater in the Yucatan

Alternative hypothesis for the extinction of non-avian dinosaurs

• Climates change during the Cretaceous

• Became warmer until about 90 mya then gradually cooling until the very end 66 mya, rising again just before the end of the Cretaceous

• Sea level dropped very low at the end of the Cretaceous

• This caused the continental seaway across North America to disappear, so that much of the continental shelf was above water

• Probably caused some marine invertebrate extinction

• Greenhouse conditions resulting from volcanic eruptions

How extinctions are studied in the fossil record

• Extinction is recognized by the disappearance in the fossil record of a species or group of species present in older rocks

• Examining taxa a particular taxonomic level

• Species-level diversity is largely artifactual because species have limited geographic ranges, and species diversity often reflects only the abundance of available rocks in an area or at a particular time, or the number of geographically separated sites

• Pseudoextinctions, in which one taxon evolves into another (like dinosaurs and birds), must be recognized and ignored

• Fossil record has many biases and gaps

Evidence for dinosaur diets

• Indirect

  • Tooth structure and correlations with diet in living animals

  • Gastroliths

  • Stable isotopes

    • May reflect the diet of animals, since the food is metabolized and its byproducts incorporated into bone and teeth

• Direct

  • Fossilized stomach contents

  • Coprolites

    • Rarely associated with skeletons, so difficult to identify the maker

  • Tooth marks on bone indicate prey

  • Fossilized predator-prey interactions

How trackways are used to estimate speed

• Most trackways preserve stride length

• The length of the limbs can be inferred from the size of the footprint and the identity of the trackmaker

• In general, stride increases with speed

  • Relationship differs between species

• Dimensionless speed (DS)

  DS = speed/√(leg length x gravity)

  Estimating leg length and assuming gravity has always been 9.8 m/sec2, we can calculate speed from DS

Evidence for color in feathers and eggshells

• Study pigment cells (melanosomes)

• Different melanosomes of bird feathers have different shapes

• Pigment chemicals or their decay products can sometimes be found preserved in fossils

• Only the colors due to melanosomes have been reconstructed

  • Does not account for other types of pigment cells

Biomolecules known in non-avian dinosaurs

• Once fossils petrify, they trap molecules with the bone matrix, as do cross-linkages

• Studies in 2018 and 2019 found that crosslinking processes such as glycoxidation and lipoxidation could preserve as flexible 3D polymers

• Proteins such as keratin and collagen but not DNA are known from non-avian dinosaur fossils

How DNA and amino acid sequences are used to infer phylogeny

• Same gene or protein in different organisms is aligned

• Aligning them shows which sites on the gene are the same in all species and which are variable

• Alignment is complicated because there are gaps and insertions in some sequences

How to sex dinosaurs

• Must be differences in the skeletons of the two sexes (sexual dimorphism)

• When female birds lay eggs, calcium is taken from the bone to be deposited in the egg

  • Often first deposited as medullary bone

  • Only present in some females