CHAPTER 14—LIFE OF THE MESOZOIC
CHAPTER OVERVIEW
Climate during the Mesozoic was affected by the changing locations of continents, major marine
transgressions and regressions and the formation of the great mountain systems. At no other time in the
Earth’s history had there been such diversity in the morphology of vertebrates, especially the dinosaurs. In
addition, birds and mammals were beginning their evolution.
Terrestrial invertebrates of the Mesozoic offer a good indication of their evolutionary history. However,
their marine counterparts, which are used for worldwide correlations, are much better stratigraphic
markers (index fossils). A detailed history of Mesozoic vertebrates is given beginning with amphibians
then moving to a classification of reptiles based on skull types, and finally discussing another grouping
based on pelvic bone morphology. This history gives a clear and concise understanding of the
relationships among dinosaurs.
The first appearance of birds and mammals is discussed in this chapter giving some of the evolutionary
similarities between those groups and earlier classes of vertebrates. Terrestrial plants, which include the
cycads, showed such extensive diversification during the Mesozoic that it is also called the “Age of the
Cycads”. The third great episode of plant history is introduced by the angiosperms (plants that have
enclosed seeds and flowers). Both terrestrial and extraterrestrial causes of mass extinctions that occur at
the end of the Mesozoic are thoroughly described from several view points.
LEARNING OBJECTIVES
By reading and completing information within this chapter, you should gain an understanding of the
following concepts:
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Describe the relationship between climate and continental configuration and sea levels during
the Mesozoic.
Explain the main factors that influence climate considering the following: solar radiation,
continental configuration and dimensions, location of mountain systems and bridges, the
carbon dioxide in the atmosphere, the location of the poles in reference to the continents and
changes in the Earth’s axis and orbit.
Describe the establishment and expansion of the following marine invertebrates: bivalves,
corals, echinoids, cephalopods, wrinkled septa and sutures, belemnites, snails and
crustaceans, and protistans.
Describe the major groups of amphibians and the major forms that are classified under each.
Discuss two divisions of dinosaurs that are based on the arrangement of bones in the hip
region.
Describe the characteristics of the more common groups of dinosaurs.
Explain what dinosaur members are classified as Ornithischians (bird-hipped) and which are
classified as Saurischians (lizard-hipped).
Discuss the concept of adaptive radiation including what problems and solutions were
encountered by flying (aerial) and marine reptiles.
Describe the evolutionary significance of Archaeopteryx.
Discuss the evolutionary history of mammals in the Mesozoic Era using dentition as a means
of classification.
Describe some of the more important Phytoplankton including how some have been used for
correlations.
Discuss the three segments of the history of land plants including cycads and angiosperms.
Explain some of the more current views on terrestrial and extraterrestrial causes for mass
extinctions at the end of the Mesozoic Era.
CHAPTER OUTLINE
I.
Climate Controls It All
A. Influences on Climate
Chapter 14—Life of the Mesozoic
B. Continents and Currents
C. Cretaceous Cooling
II.
Mesozoic Invertebrates
A. Bivalves
B. Corals
C. Echinoids
D. Cephalopods
E. Wrinkled Septa and Sutures
F. Belemnites
G. Snails and Crustaceans
H. Protistans
III.
Mesozoic Vertebrates
A. The Rise of Modern Amphibians
B. The Triassic Transition
C. Basal Archosaurs
IV.
Dinosaurs: “Terrifying Lizards”
A. Lizard-Hipped Bipedal Meat-Eaters (Saurischian Theropods)
B. Lizard-Hipped Quadrupedal Plant-Eaters (Saurischian Sauropodomorphs)
C. Bird-Hipped Plant-Eaters (Ornithischians)
D. Stegosaurs (“Plated” Quadrupedal Ornithischians)
E. Ceratopsians (Horn-Faced Dinosaurs)
V.
Dinosaurs: Cold-Blooded, Warm-Blooded, or Both?
VI.
Dinosaur Parenting
VII.
The Flying Archosaurs
A. Triassic Gliders
B. The Flying Pterosaurs
VIII.
Return to the Sea
A. Nothosaurs and Placodonts
B. Plesiosaurs
C. Ichthyosaurs
D. Mosasaurs
E. Sea Turtles
IX.
The Rise of the Birds
X.
The Mammalian Vanguard
XI.
Sea Plants and Phytoplankton
A. Marine Phytoplankton
B. Dinoflagellates
C. Coccolithophorids
D. Silicoflagellates and Diatoms
XII.
Land Plants
A. Gymnosperms
B. Angiosperms
XIII.
Late Cretaceous Catastrophe
A. Did a Bolide Impact Cause the Mass Extictions?
B. Evidence: Iridium and Shocked Quartz
Chapter 14—Life of the Mesozoic
C.
D.
E.
F.
The Chicxulub Structure
Did Global Volcanism Cause Mass Extinctions?
Did Environmental Change Cause the Mass Extinctions?
Did a Combination of Factors Cause the Mass Extinctions?
Chapter 14—Life of the Mesozoic
KEY TERMS (Pages 405–449)
adaptive radiation (431): The diversity that develops among species as each adapts to a different set of
environmental conditions. An example is the pterosaurs that existed from late Triassic until late
Cretaceous.
Ammonites (411): Ammonoid cephalopods having more complex sutural patterns than either cevatites or
goniates.
ammonoid (411): An extinct group of cephalopods, with coiled, chambered conches and having septa
with crenulated margins.
Ammonoidea (410): An order of cephalopods that arose during the Paleozoic area and that has wrinkled
sutures.
angiosperm (442): An advanced group of plants having floral reproductive structures and seeds in a
closed ovary. The “flowering plants” which appeared in the Cretaceous.
ankylosaur (428): Heavily armored dinosaurs which followed stegosaurs during the Cretaceous. These
bulky, squat ornithischians were completely covered by closely fitted bony plates that protected the entire
length of their 6-meter backsides. The head was small and also armored. The teeth were small and
weak.
archosaur (415): Advanced reptiles of a group called diapsids, which includes thecodonts, “dinosaurs,”
pterosaurs, and crocodiles.
belemnite (412): Members of the molluscan class Cephalopoda, having straight internal shells.
bolide (444): A meteorite, asteroid, or comet that explodes on striking the Earth.
ceratite (410): A large group of ammonoid cephalopods having suture patterns intermediate between
goniates and ammonites.
ceratospian (428): The quadrupedal ornithischian dinosaurs characterized by the development of
prominent horns of the head.
chloroplast (440): Internal orgonelles that allow plankton to photosynthesize their food. Forms that
possess this feature are called phytoplankton and are members of Protista.
coccolith (440): Secreted coverings of discoidal calcareous platelets. They are secreted by
coccolithophorids, which are marine, planktonic, biflagellate, golden-brown algae.
coevolution (443): Coevolution occurs when two or more different organisms develop a close and
reciprocal relationship in which the evolution of one organism is partially dependent on the evolution of the
other.
convergence (evolutionary) (415): The process by which similarity of form or structure arises among
different organisms as a result of their becoming adapted to similar habits. Example: seals, porpoises
(mammals), penguins (aves), shark (fish), all have elongated forms suited for swimming.
crustacean (413): A subphylum of the phylum Arthropoda that includes such well-known living animals as
lobsters, crabs, shrimp, barnacles and ostrocods.
diatom (441): Microscopic golden-brown algae (chrysophytes) that secrete a delicate siliceous frustule
(shell).
Chapter 14—Life of the Mesozoic
dinosaur (417): Any reptile belonging to the subclass Archosaura, distinguished from other reptiles
especially by features of the pelvic bone.
docodont (438): A group of small, primitive late Jurassic mammals possibly ancestral to the living
monotremes.
ectothermic (429): Cold-blooded animals such as reptiles and dinosaurs which have little or no ability to
maintain a uniform body temperature by physiological processes. Some ectotherms, however, may
regulate their body temperature to a certain degree by seeking either sun or shade in response to
temperature needs.
endothermic (430): Animals such as mammals and birds that maintain a constant body temperature by
physiologic production of heat internally and the radiation of excess heat away from the body.
foraminifera (413): An order of mostly marine, unicellular protozoans that secrete tests (shells) that are
usually composed of calcium carbonate.
frustule (411): The siliceous covering that is secreted by diatoms. It is usually composed of an upper part
(the epitheca) and a lower part (the hypotheca) that fit together like a lid on a box.
gastropod (413): Any mollusk having a single calcareous shell that is closed at the apex, sometimes
spiraled. Not chambered and generally asymmetrical.
goniatite (411): One of the three large groups of ammonoid cephalopods with sutures forming a pattern
of simple lobes and saddles and thus not as complex as either the ceratites or the ammonites.
gymnosperm (442): Plants whose seeds are commonly in cones and never enclosed in an ovary.
Examples would include conifers, cycads, ginkgo, pine, and spruce.
ichthyosaurs (434): Highly specialized marine reptiles of the Mesozoic, recognized by their fishlike form.
ilium (417): One of three bones of the pelvis that is represented as the uppermost bone that is firmly
clamped to the spinal column in Saurischia.
irregular echinoids (410): Echinoids that are bilaterally symmetrical and have a flattened shell.
ischium (417): One of the three bones in the pelvis extending downward and slightly backward.
leipdosaur (415): A group of Diapsids that consists of lizards, snakes and their ancestors.
monotreme (438): The egg-laying mammals.
multituberculate (438): An early group (Jurassic) of Mesozoic mammals with tooth cusps in longitudinal
rows and other dental characteristics that suggest they may have been the earliest herbivorous mammals.
Nautiloidea (410): An order of cephalopods that arose during the Paleozoic Era that has relatively straight
sutures.
nodosaur (428): Quadrupedal ornithischians of the Jurassic that surpassed the Stegosaurs in the
Cretaceous.
nothosaur (433–434): Relatively small early Mesozoic sauropterygians that were replaced during the
Jurassic by the plesiosaurs.
Chapter 14—Life of the Mesozoic
Ornithischia (417, 423): An order of dinosaurs characterized by birdlike pelvic structures and including
such herbivores as the ornithopods, stegasaurs, ankylosaurs, and ceratopsians.
ornithopod (423): Plant-eating members of the bipedal group of ornithischians. Evolutionary history
began in the Triassic, with relatively small species that lived primarily on dry land. A representative large
Jurassic ornithopod is Camptosaurus, a bipedal dinosaur of medium size with a heavy tail, short forelimbs,
and long hind legs.
pachycephalosaur (427): A group of bipedal ornithischians that are identified by their “bone head”. The
skull of pachycephalosaurs consists mostly of solid bone with only a small space to accommodate a brain
of unimpressive size.
phytoplankton (440): Microscopic marine planktonic plants, most of which are various forms of algae.
phytosaur (415–416): Extinct aquatic, crocodile-like thecodonts of the Triassic.
placodont (434): Extinct walrus-like marine reptiles that fed principally on shellfish.
plankton (440): Minute, free-floating aquatic unicellular organisms that may grow together in impressive
colonies or aggregates.
plesiosaur (434): The group of extinct Mesozoic marine reptiles (sauropterygians) characterized by
large, paddle-shaped limbs and broad bodies, with either very long or relatively short necks.
prosauropod (422): A group of herbivorous sauropodomorpha that lived from late Triassic to early
Jurassic. Their remains have been found on all continents except Antarctica.
prototherian (439): A group of mammals that include the triconodonts, multituberculates, and the
monotremes.
pubis (417): One of three pelvic bones that is forward of the ischium.
radiolarian (413): A Protozoan that secretes a delicate, often beautifully filigreed skeleton of opaline
silica.
regular echinoid (410): Have a five-fold symmetry and a shell that is more or less spherical. Regular
echinoids were especially abundant in the Jurassic but were overtaken by irregular echinoids during the
Cretaceous.
rhynchocephalians (415): Existed during the Triassic period in which many lineages of marine reptiles
appeared and is represented today by the tautara of New Zealand.
rudist (409): Peculiarly specialized Mesozoic bivalva often having one valve in the shape of a horn coral,
covered by the other valve in the form of a lid.
Saurischia (417): An order of dinosaurs with triradiate pelvic structures, including both the gigantic
herbivorous sauropods and the carnivorous theropods.
sauropods (418, 422): Gigantic herbivorous dinosaur belonging to the order Saurischia. Characterized
by triradiate pelvic structures
sauropodomorpha (418): Term applied to typically large, quadrupedal herbivores.
septum (of cephalopod) (410): Vertical plates which serve to separate layers of tissue and provide
support in cephalopods.
Chapter 14—Life of the Mesozoic
shocked quartz (444): Distinctive parallel sets of microscopic planes found on shock quartz produced by
high-pressure shock waves such as those emanating from the impact of a large meteorite.
stishovite (444): A rare, dense, high-pressure silicate mineral that is found at Meteor Crater and other
known impact structures, as well as found in the boundary clay.
suture patterns (of cephalopod) (410): In cephalopods, the lines formed on the inside of the conch
where the edge of each chamber is partitioned.
symmetrodonts (438): A group of primitive Mesozoic mammals characterized by a symmetric triangular
arrangement of cusps on cheek teeth.
tektites (444): A rounded pitted jet-black to greenish or yellowish body of silicate glass of nonvolcanic
origin, usually walnut-sized, found in several widely separated areas of the Earth’s surface; high in silica
and low in water content; believed to be extraterrestrial in origin or formation.
temnospondyls (415): A group among the tetrapods of the late Paleozoic that were able to survive the
wave of extinctions at the end of the Permian.
therians (439): Marsupials and placental mammals.
theropoda (418): A carnivorous dinosaur belonging to the order Saurischia. Characterized by triradiate
pelvic structures.
triconodonts (438): A group of primitive Mesozoic mammals recognized primarily by the arrangement of
three principal cheek tooth cusps in a longitudinal row.
Chapter 14—Life of the Mesozoic
MULTIPLE-CHOICE QUESTIONS
1.
The diatoms first appeared in the Mesozoic oceans during what geologic period?
a. Pennsylvanian
c. Jurassic
b. Triassic
d. Cretaceous
2.
The calcium carbonate secreting marine organism who internally deposits calcium carbonate on an
internal matrix and constructs tiny, shield-like structures is called a(n)
a. diatom.
c. coccolith.
b. acritarch.
d. foraminifer.
3.
The third great episode of plant history is marked by the appearance of species having enclosed
seeds and flowers. Such plants are known as
a. angiosperms.
c. chlorophytes.
b. cycads.
d. tracheophytes.
4.
Members of the molluscan class Cephalopoda that were abundant during the Mesozoic and were
characterized by elongate internal shell (conch) are called
a. nautiloids.
c. belemnites.
b. ammonites.
d. goniatites.
5.
The most important event in the terrestrial plant evolution of the Mesozoic was
a. the development of vascular tissue for fluid and nutrient transport.
b. the appearance of the gymnosperms.
c. the appearance of the angiosperms.
d. the appearance of the psilophytes.
6.
Of the following, which group became extinct at the end of the Cretaceous?
a. brachiopods
c. echinoderms
b. bryozoans
d. ammonoids
7.
One of the particularly specialized Mesozoic pelecypods that had one valve in the shape of a curved
or coiled cone and the other valve in the form of a lid was called a
a. brachiopod.
c. belemnite.
b. rudist.
d. rugose.
8.
In the Saurischians, what is the name of the bone, visible on either side of the pelvic structure,
which is firmly clamped to the spinal column?
a. ischium
c. fibia
b. ilium
d. pubis
9.
This “basal archosaurs” was lightly built with a tail and short fore limbs and walked upright on their
hind legs. It is called the
a. phytosaurs.
c. triadobatrachus.
b. hesperosuchus.
d. eocaecilia.
10.
What is the name of the basalarchosaur that were so similar to the living crocodiles that they
represent an example of evolutionary convergence?
a. pterosaurs
c. phytosaursb
b. ichthyosaurs
d. pleisosaurs
11.
What is the name of the highly specialized marine reptiles of the Mesozoic that had fishlike tails,
boneless dorsal fins, and paddle limbs for steering?
a. pterosaurs
c. phytosaurs
b. ichthyosaurs
d. plesiosaurs
Chapter 14—Life of the Mesozoic
12.
Which of the following does not represent a member of the sauropod dinosaurs?
a. apatosaurus
c. tyrannosaurus
b. plateosaurus
d. stegosaurus
13.
Which of the following features did Archaeopteryx not have?
a. a keel bone (wishbone)
c. a long tail
b. teeth
d. claw-bearing fingers
14.
The wings of the pterosaurs were supported by
a. the fusion of two fingers into a support structure.
b. all five fingers.
c. an elongated thumb.
d. an elongated fourth finger.
15.
The evolutionary process whereby new groups diverge from their ancestral lineages in order to fit
into their new surroundings is called
a. adaptive radiation.
c. punctuated equilibrium.
b. convergent evolution.
d. isolation.
16.
The largest of all of the dinosaurs were the
a. thecodonts.
b. theropods.
c. sauropods.
d. omithopods.
17.
A well-known Jurassic representative whose remains have been found in a formation of Colorado is
Apatosaurus, which was formerly known as
a. plesiosaurs.
c. pteranodon.
b. mosasaurs.
d. brontosaurus.
18.
The quadrupedal ornithischian dinosaur which was characterized by the development of prominent
horn(s) and displayed a shield-like bony frill at the back of the skull is called a(n)
a. ceratopsian.
c. ichthyosaur.
b. hadrosaur.
d. placodont.
19.
The dinosaur group with the pelvis structure that mimics that found in birds is called
a. saurischians.
c. thecodonts.
b. ornithischians.
d. therapsids.
20.
All of the theropods were typically bipedal dinosaurs were also
a. herbivores.
c. carnivores.
b. omnivores.
d. scavengers.
Chapter 14—Life of the Mesozoic
FILL IN THE BLANK
1.
Cephalopods that have a straight or gently undulating suture are placed in the subclass
while those with more complex sutures are placed in the subclass
.
2.
Reefs of the Mesozoic that often were formed of pelecypod shells rather than coral skeletons were
called
.
3.
The lines formed on the inside of an ammonite shell (conch) where the edge of each chamber’s
partition meets the inner wall are called
.
4.
The class members of phylum Echinodermata that are characterized by a fivefold symmetry and a
shell or test that is nearly spherical are
.
5.
The order of dinosaurs that is called lizard-hipped and includes Allosaurus and Tyrannosaurus is
called
.
6.
The cigar-shaped cephalopods that became common during the Mesozoic and are considered the
ancestors of Triassic squids are called
.
7.
What order do bird-hipped dinosaurs belong to that includes stegosaurs and ceratopsians?
.
8.
In dinosaurs, the uppermost pelvic bone which is firmly clamped to the spinal column is
called
.
9.
The large massive paddle swimmers, often called “swan lizards”, that attain an overall length in
excess of 12 meters, are called
.
10.
The form of flying reptile of the late Triassic to late Cretaceous that attests to the adaptive success
of these flying reptiles is called
.
11.
The first undisputed fossil bird that is considered a close evolutionary link between small, bipedal
theropods and modern birds was
.
12.
The dentition type of this group of mammals is described as cheek teeth in which three cusps are
aligned in a row. Some members were as large as cats and may have preyed on smaller
invertebrates; this group was called
.
13.
The evolutionary process of producing similar forms in unrelated organisms is called
14.
Saurischians are divided into two groups: _______________ (bipedal meat-eaters) and
___________________ (large quadrupedal herbivores).
15.
_______________, the first undisputed fossil bird, is a close evolutionary link between small,
bipedal therapods and modern birds.
.
Chapter 14—Life of the Mesozoic
TRUE-FALSE
1.
Coccoliths are extremely useful in stratigraphic correlation of Cretaceous to Holocene
rocks.
2.
Angiosperms provide many examples of co-evolution with Mesozoic insects, reptiles,
mammals, and birds.
3.
Cycads were particularly abundant land plants during the Jurassic.
4.
Angiosperms are seed-bearing plants in which true flowers have not developed.
5.
Diatoms are small microscopic organisms made of calcareous ooze called chalk.
6.
Rudists of the Jurassic and Cretaceous are grouped with bivalvia.
7.
Ammonoid cephalopods are subdivided into ceratites, goniatites and belemnoids based
on the complexity of suture patterns.
8.
Theropods, ceratosaurs, and sauropods are grouped under Ornithischian dinosaurs.
9.
The suture patterns of the gonatitic ammonoids are gently undulating or straight.
10.
Mammals are divided into two groups: the prototherians that include triconodonts,
multituberculates, and monotremes; and the therians that include both marsupials and
placental mammals.
Chapter 14—Life of the Mesozoic
ANSWER KEY
Multiple Choice
1. d
2. c
3. a
4. c
5. c
6. d
7. b
8. b
9. b
10. c
11. b
12. a
13. a
14. d
15. a
16. c
17. d
18. a
19. b
20. c
Fill Ins
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
13.
14.
15.
True/False
nautioloid, ammonoid
rudistids
suture
echinoids
saurischians
beleminites
Ornithischian
ilium
plesiosaurs
pterosaurs
archaeopteryx
triconodonts
convergence
theropoda,
sauropodomorpha
archaeopteryx
1.
2.
3.
4.
5.
6.
7.
8.
9.
10.
T
T
T
F
F
T
F
F
F
T
Chapter 14—Life of the Mesozoic
RESPONSES TO QUESTIONS ACCOMPANYING SELECTED FIGURES
FIGURE 14–3 (p. 409) Unlike many clams and mussels, the two valves of Gryphaea differ from one
another in size and in shape.
FIGURE 14–9 (p. 422) The most widely accepted explanation for the wrinkled edges of ammonoid septa
is that they added strength to the outer wall of the shell. This afforded protection against the pressures
existing at great depths in the open ocean.
FIGURE 14–12 (p. 414) Radiolarians are placed in the Kingdom Protoctista.
FIGURE 14–16 (p. 416) The crocodile is an example of convergent evolution with Rutiodon.
FIGURE 14–17 (p. 417) Predatory groups of dinosaurs in the figure are the theropods, ceratosaurs,
carnosaurs, and coelurosaurs.
FIGURE 14–22 (p. 420) In the drawing of the skeleton of Ornithomimus, the bone attached to the veterbral
column is the illium. The pubis is the forwardly directed bone in front of the leg bones, and the ischium is
at the rear of the leg bones. These bones are paired, so that there are really a total of six.
FIGURE 14–56 (p. 441) The plates, on which the coccosphere is constructed, are called coccoliths.
FIGURE 14–58 (p. 441) Diatoms are members of the Kingdom Protoctista.