Upper Mesozoic: ch13, ch15
Week
9, Chapters
13 and 15
Phanerozoic Eonothem
The Upper Mesozoic
Ammonite from the Lower
Mesozoic of NE Mexico, note its large size, 1.6 m in maximun
diameter
Back to Course Syllabus || Back to Course Plan (weekly schedule)
|
Visit this web site: UCMP
to review the
History of Life of this interval of time |
· The Evolutionary Processes of Phanerozoic Biota; From Eukaryotes to Animalia
· Paleoecology: || Types of marine environments: the plankton
· The K/T Mass extinction: Crisis in the history of life
· Animals diversified on land and invaded freshwater habitats
Click here for a summary of Mesozoic Bio-events: ||
The ammonites Visit this site to undestand: What is an Ammonite? How did Ammonites evolve? How did Ammonites live? What do their shells reveal about the Ammonite?
View superb Lower Cretaceous ammonites
Read Chapters nine and ten of your
textbook
Review the story of plate tectonics
For a more simplistic model visit this site <http://www.pbs.org/wgbh/aso/tryit/tectonics>
<http://www.enchantedlearning.com/subjects/astronomy/planets/earth/Continents.shtml>
Paleogeography: The
Fragmentation of Pangaea begins in the upper Triassic
- Divisions of time
- Chronstratigraphic Divisions: The Triassic System || The Jurassic System ||The Cretaceous System
- The Invertebrates: Protista: Foraminifera Radiolaria and Coccoliths || Mollusks: gastropods, bivalves, cephalopods -- ammonites||
- Mesozoic Mammals
- The Plants: The angiosperms: Flowering plants
Phanerozoic Eonothem
See
Chronostratigraphic Division
of the Mesozoic Eratherm
This Eonothem is often referred to as the tine of "Visible Life". Organisms with skeletons or hard shells appeared by the first time in the geological record. The Phanerozoic Eonothem spans from 543 mya through today. The Phanerozoic is divided into three Erathems, from older to younger: Paleozoic, Mesozoic, and Cenozoic.
The
Mesozoic is divided into three time systems: the Triassic (245-208
Million Years Ago), the Jurassic (208-146 Million Years Ago), and the Cretaceous
(146-65 Million Years Ago).
The Lower Mesozoic = Triassic + Jurassic Sytems
The Lower Mesozoic is an informal division of the Mesozoic Erathem which includes the lower two systems: the Triassic and the Jurassic. See Chronostratigraphic Chart
Summary of Lower Mesozoic Events: Important facts in the history of Mesozoic life
The Mesozoic is divided into three time systems: the
Triassic (245-208 Million Years Ago), the Jurassic (208-146 Million Years Ago),
and the Cretaceous (146-65 Million Years Ago).
Mesozoic means "middle life", and is the time
during which the world fauna changed drastically from that which had been seen
in the Paleozoic. Dinosaurs, which are perhaps the most popular organisms of
the Mesozoic, evolved in the Triassic, but were not very diverse until the
Jurassic. Except for birds, dinosaurs became extinct at the end of the
Cretaceous. Some of the last dinosaurs to have lived are found in the late
Cretaceous deposits of
The Mesozoic was also a time of great change in the
terrestrial vegetation. The Lower Mesozoic was dominated by ferns, cycads, ginkgophytes, bennettitaleans,
and other unusual plants. Modern gymnosperms, such as conifers, first appeared
in their current recognizable forms in the early Triassic. By the middle part
of the Cretaceous System, the earliest angiosperms had appeared and began to
diversify, largely taking over from the other plant groups.
The breakup of Pangaea can be divided into four stages:
a. The first stage involved the separation of North
America from Africa during the Late Triassic, followed by the sepa¬ration of North America from
The breakup of Pangaea influenced global climatic and at¬mospheric circulation patterns. While the temperature gradi¬ent from the tropics to the poles gradually increased during the Mesozoic, overall global temperatures remained equable.
Among the marine invertebrates, survivors of the Permian ex¬tinction diversified and gave rise to increasingly
complex Mesozoic marine invertebrate communities.
Triassic and Jurassic land-plant communities were
composed of seedless plants and gymnosperms. Angiosperms, or flower¬ing plants, evolved during the Early Cretaceous,
diversified rapidly, and soon became the dominant land plants.
Dinosaurs evolved during the Upper Triassic, but were
most abundant and diverse during the Jurassic and Cretaceous. Based on pelvic
structure, two distinct orders of dinosaurs are recognized-Saurischia
(lizard-hipped) and Ornithischia (bird¬hipped).
Pterosaurs were the first flying vertebrate animals.
Small pterosaurs were probably active, wing-flapping fliers, while large ones
may have depended more on thermal updrafts and soaring to stay aloft. At least
one pterosaur species had hair or feathers, so it was likely endothermic.
The fish-eating, porpoise-like ichthyosaurs were
thoroughly adapted to an aquatic life. Female ichthyosaurs probably re¬tained eggs within their bodies and gave birth to live
young. Plesiosaurs were heavy-bodied marine reptiles that probably came ashore
to lay eggs.
Crocodiles become the dominant freshwater predators
during the Jurassic. Turtles and lizards were present during most of the
Mesozoic, but by the Cretaceous snakes evolved from lizards.
Birds probably evolved from
small carnivorous dinosaurs. The oldest known bird, Archaeopteryx) appeared
during the Jurassic, but few other Mesozoic birds are known. Protoavis in Triassic rocks may represent a bird older than
Archaeopteryx.
The earliest mammals evolved during the Upper Triassic,
but they are difficult to distinguish from advanced cynodonts.
Details of the teeth, the middle ear, and lower jaw are used to distinguish the
two.
Several types of Mesozoic mammals existed, but all were
small, and their diversity was low. A group of Mesozoic mammals known as eupantotheres gave rise to both marsupials and pla¬centals during the Cretaceous.
Because the continents were close together during much of
the Mesozoic and climates were mild even at high latitudes, animals and plants
dispersed widely.
Mesozoic mass extinctions account for the disappearance
of dinosaurs, several other groups of reptiles, and a number of marine
invertebrates. One hypothesis holds that the extinc¬tions
were caused by the impact of a large meteorite. Many pa¬leontologists
reject the meteorite proposal and claim that withdrawal of epeiric
seas and climatic changes can account for these extinctions.
Introduction to the Tetrapoda: The Four-Legged Vertebrates
The word "Tetrapoda" means "four
legs" in Greek. Amphibians, reptiles (including dinosaurs and birds) and
mammals are the major groups of the Tetrapoda.
Dinosaurs, one of the most successful groups of animals
(in terms of longevity) that have ever lived, evolved into many diverse sizes
and shapes, with many equally diverse modes of living. The term "Dinosauria" was invented by Sir Richard Owen in 1842
to describe these "fearfully great reptiles," specifically Megalosaurus, Iguanodon, and Hylaeosaurus,
the only three dinosaurs known at the time. The creatures that we normally
think of as dinosaurs lived during the Mesozoic Era, from late in the Triassic
period (about 225 million years ago) until the end of the Cretaceous (about 65
million years ago). But we now know that they actually live on today as the
birds.
Some things to keep in mind about dinosaurs:
Not everything big and dead is a dinosaur. All too often, books written (or movies made) for a popular audience include animals such as mammoths, mastodons, pterosaurs, plesiosaurs, ichthyosaurs, and the sail-backed Dimetrodon.
Dinosaurs are a specific subgroup of the archosaurs, a group that also includes crocodiles,
pterosaurs, and birds. Although pterosaurs are closely related to dinosaurs,
they are not true dinosaurs. Even more distantly related to dinosaurs are the
marine reptiles, which include the plesiosaurs and ichthyosaurs.
Mammoths and mastodons are mammals and did not appear
until many millions of years after the close of the Cretaceous period.
Dimetrodon is neither a reptile nor a mammal, but a basal synapsid, i.e., an early relative of the ancestors of mammals.
Not all dinosaurs lived at the same time. Different
dinosaurs lived at different times. Despite the portrayals in movies like King
Kong and
The Dinosaurs are not extinct: Technically, based on
features of the skeleton, most people studying dinosaurs consider birds to be
dinosaurs.
This shocking realization makes even the smallest
hummingbird a legitimate dinosaur. So rather than refer to
"dinosaurs" and birds as discrete, separate groups, it is best to
refer to the traditional, extinct animals as "non-avian dinosaurs"
and birds as well as birds, or "avian dinosaurs." It is incorrect to
say that dinosaurs are extinct, because they have left living descendants in the
form of cockatoos, cassowaries, and their pals —
just like modern vertebrates are still vertebrates even though their Cambrian ancestors are
long extinct. So at thanksgiving what you eat is a dinosaur we called a turkey
The Evolutionary Process of
Phanerozoic Life
Major groups of animals
are already present in the Phanerozoic, at the
beginning of the Cambrian System, thier phylogenetic development is
shown in the following diagrams as shown below:
The opisthokonts (Greek: ??????- (opisth?-) = "rear, posterior" + ?????? (kontos) = "pole" i.e. flagellum) are a broad group of eukaryotes, including both the animal and fungus kingdoms, together with the phylum Choanozoa of the protist kingdom. Both genetic and ultrastructural studies strongly support that opisthokonts form a monophyletic group. One common characteristic is that flagellate cells, such as most animal sperm and chytrid spores, propel themselves with a single posterior flagellum. This gives the groups its name. In contrast, flagellate cells in other eukaryote groups propel themselves with one or more anterior flagella.
See Biological Principles for a review of these concepts
Anapsida: amniote group whose skull does not have openings near the temples. The clade Anapsida includes turtles and all their extinct relatives. The anapsids once consisted of many groups, many of which could be considered to have been quite successful until their extinction. Today, only one group of anapsids remains ( Chelonia -- the turtles), which truly could be called an evolutionary success story.
Diapsids ("two
arches"): are a group of tetrapod animals
that developed two holes (temporal fenestra) in each
side of their skulls, about 300 million years ago during the late Carboniferous
period. Living diapsids are extremely diverse, and
include all birds, crocodiles, lizards, snakes, and tuataras. All members
of the group called the Reptilia, except for the anapsids (turtles and their ilk), and a few extinct groups,
are diapsids. The main diagnostic physical character
for a diapsid is the presence of two openings on each
side of the skull; the upper and lower temporal openings. Even the birds are
considered diapsids (and hence reptiles), because
they are descended from certain dinosaurs (which are also diapsids),
and ancestrally have the paired skull openings along with other physical
characteristics that unite them with diapsids. Thus,
they are considered diapsids by their ancestry, which
is illuminated by shared derived traits.
Synapsids ('fused arch') also known as Theropsids ('beast face'), and traditionally described as 'mammal-like reptiles' , are a group of amniotes (the other being the sauropsids) that developed one opening in their skull (temporal fenestra) behind each eye, about 320 million years ago (mya) during the late Carboniferous Period. The mammals of today are but one branch of the Synapsida, a great vertebrate group with a 300 million year history. Pre-mammalian synapsids -- including the famous "finback" Dimetrodon dominated the land vertebrate fauna of the Permian and early Triassic before losing ground to the diversifying dinosaurs and other archosaurs. These pre-mammalian groups of synapsids have at times been called "mammal-like reptiles". This term is now discouraged because although many had characteristics in common with mammals, none of them were actually reptiles.
Euryapsida are a group of tetrapod
animals that are distinguished by a single opening behind the orbit (temporal fenestra). They are different from Synapsida
by the precise placement of the opening below. It is now commonly believed that
euryapsids are in fact diapsids
(having two fenestrae) that lost the upper temporal fenestra.
Back to Unit Plan
NOTES
ON THE CLASSIFICATION OF
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Organisms affected: Dinos, ammonite, planktonic protista, land plants
Causes of the K/T Extinction:
Plate Tectonics:
Climatic Fluctuations:
Volcanic Eruptions:
Asteroid Impact: