Cenozoic: ch10, ch11, ch13,ch14, ch16


 Week 12
 

Cenozoic Eonothem

The divisions of the Cenozoic

During the 65 million years of the Cenozoic Erathem (also spelled "Cainozoic"), or Age of Mammals, the world took on its modern form.  Invertebrates, fish, reptiles etc were essentially of modern types, but mammals, birds, protozoa and flowering plants still evolved and developed during this period.

Traditionally, the Cenozoic Erathem was divided into two very unequal periods, the Tertiary (which made up the bulk of the Cenozoic), and the Quaternary, which is only the last one and a half million years or so.  The Tertiary is in turn divided into Paleogene and Neogene systems

The Paleogene System is divided into three Series, the Paleocene, Eocene, and Oligocene.  During this relatively short span of time (about as long as the Triassic), the continents began to take on their present form.   General cooling and drying began before the end of the Oligocene, but was probably not a major factor until the middle Miocene.  The Paleogene might be thought of as an extension of the Mesozoic -- but with mammals.

The Neogene System traditionally comprised the Miocene and Pliocene Series.  Recent changes by the ICS appeared to eliminate the Quaternary, so that the Neogene included the Pleistocene and Holocene.

 

Paleogeography: Eocene <http://www.scotese.com/newpage9.htm>
                          Middle Miocene <http://www.scotese.com/miocene.htm>
 

Tertiary period, name for the major portion of the Cenozoic era, the most recent of the geologic eras (see Geologic Timescale, table) from around 26 to 65 million years ago. The name Tertiary was first applied about the middle of the 18th cent. to a layer of deposits, largely unconsolidated sediments, geologically younger than, and overlying, certain other deposits then known as Primary and Secondary. Later (c.1830) a fourth division, the Quaternary, was added. Although these divisions of the earth's crust seemed adequate for the region to which the designations were originally applied (parts of the Alps and plains of Italy), when the same system was later extended to other parts of Europe and to America it proved to be inapplicable. It was realized that one scheme of classification could not be applied universally: The names Primary and Secondary were generally abandoned; Tertiary and Quaternary were, and still are, used, but other geologic literature substitutes other names, including the Palaeogene and Neogene. The main divisions of the Tertiary are the Paleocene, Eocene, Oligocene, Miocene, and Pliocene epochs.

Quaternary period, younger of the two geologic periods of the Cenozoic era of geologic time (see Geologic Timescale, table) from 2 million years ago to the present. Comprising all geologic time from the end of the Tertiary period to the present, it is divided into the Pleistocene and Holocene, or Recent, epochs. It was named (1759) by Giovanni Arduino, an Italian scientist who thought that the biblical great flood was responsible for its deposits. During the early Quaternary, Europe and North America were covered by the glaciers of the Pleistocene epoch. Retreat of the glaciers led to isostatic rebound (see continent) of the crust in the Holocene. In the Quaternary the climate and present physical features of the earth continued to develop. Significant changes in sea level within historic times are demonstrated by the submergence of the temple of Jupiter Serapis near Naples and by the rising of the shores of the Baltic. The life of the Quaternary has been marked by the rise and dominance of humans.

The Meaning of the Series:
Pleist = most
Pleion = more
Meion = less
Oligos = few
Eos = dawn
Paleo = ancient

LIFE OF THE PALEOGENE

Marine life recovered
The present marine ecosystem is for the most part popŽulated by groups of animals, plants, and single-celled organisms that survived the extinction at the end of the Mesozoic Era to expand during the Cenozoic.

Many groups of benthic foraminifera, sea urchins, cheilostome bryozoans, crabs, snails, bivalves, and teleost fishes surŽvived in sufficiently large numbers to assume prominent ecological positions in Paleogene seas.

Planktonic foraminifera apŽpear to have survived the terminal Cretaceous extincŽtion, but they gave rise to a remarkably rapid evoluŽtionary radiation-one that yielded 17 new species, assigned to 8 new genera, within the first 100,000 years of Paleocene time.

Calcareous nannoplankton, which had suffered seŽvere losses at the end of the Cretaceous Period, also reŽdiversified rapidly during the Paleogene.

The corals, having been displaced as dominant reef builders by the rudists during the CreŽtaceous, failed to take rapid advantage of the rudists' demise: they built few massive reefs during Paleocene and Eocene time.

The most distinctive marine organisms of this period were the whales, which evolved during the Eocene Series from carnivorous land mammals and quickly achieved sucŽcess as large marine predators. JoinŽing the whales as replacements for the reptilian "sea monsters"-the top carnivores of the Mesozoic EraŽ were enormous sharks (Figure).

Other newcomers to the ocean margins were the penŽguins, a group of swimming birds of Eocene origin, and possibly the pinnipeds, the group that includes walruses, seals, and sea lions. It is widely believed that the pinŽnipeds evolved before the beginning of the Neogene System, although this group left no known Paleogene fossil record.

Flowering plants rose to dominance
Land
plants did not experience major evolutionary changes early in Paleogene time. Instead, the greatest change in terrestrial vegetation was ecological: flowerŽing plants assumed a much larger role after the termiŽnal Cretaceous extinction, while gymnosperms and ferns played a lesser role. In the process, modern famŽilies of flowering plants evolved. By the beginning of Oligocene time, some 34 million years ago, about half of all genera of flowering plants were ones that are alive today, and although many modern plant genera had not yet evolved, forests had taken on a distinctly modern appearance.

One major event in plant evolution that did take place during the Paleogene interval was the origin of the grasses, although these usually low-growing flowerŽing plants did not reach their full ecological potential until Late Oligocene and Miocene times. Once they were able to survive the effects of heavy grazing, grasses quickly spread to form vast expanses of grasslands.

Chordates (phylum Chordata)
Are deuterostome coelomates whose nearest relatives in the animal kingdom are the echinoderms, the only other deuterostomes. However, unlike echinoderms, chordates are characterized by a notochord, jointed appendages, and segmentation.

Four features characterize the chordates and have played an important role in the evolution of the phylum (figure 34.2):
1. A single, hollow nerve cord runs just beneath the dorsal surface of the animal. In vertebrates, the dorŽsal nerve cord differentiates into the brain and spinal cord.
2. A flexible rod, the notochord, forms on the dorsal side of the primitive gut in the early embryo and is present at some developmental stage in all chorŽdates. The notochord is located just below the nerve cord. The notochord may persist throughout the life cycle of some chordates or be displaced durŽing embryonic development, as in most vertebrates, by the vertebral column that forms around the nerve cord.
3. Pharyngeal slits connect the pharynx, a muscular tube that links the mouth cavity and the esophagus, with the outside. In terrestrial vertebrates, the slits do not actually connect to the outside and are better termed pharyngeal pouches. Pharyngeal pouches are present in the embryos of all vertebrates. They become slits, open to the outside in animals with gills, but disappear in those lacking gills. The presence of these structures in all vertebrate embryos provides evŽidence of their aquatic ancestry.
4. Chordates have a postanal tail that extends beyond the anus, at least during their embryonic developŽment. Nearly all other animals have a terminal anus.

The Nonvertebrate Chordates
Nonvertebrate chordates have a notochord but no backbone.
The tunicates (subphylum Urochordata) are a group of about 1250 species of marine animals. Most of them are sessile as adults, with only the larvae having a notochord and nerve cord. As adults, they exhibit neither a major body cavity nor visible signs of segmentation. Most species occur in shallow waters, but some are found at great depths.

Lancelets are scaleless, fishlike marine chordates a few centimeters long that occur widely in shallow water throughŽout the oceans of the world. Lancelets (subphylum Cephalochordata) were given their English name because they resemble a lancet-a small, two-edged surgical knife. There are about 23 species of this subphylum. Most of them belong to the genus BranchioŽstoma, formerly called Amphioxus, a name still used widely. In lancelets, the notochord runs the entire length of the dorsal nerve cord and persists throughŽout the animal's life.

Characteristics of Vertebrates
The evolution of vertebrates involved invasions of sea, land, and air.
Vertebrates (subphylum Vertebrata) are chordates with a spinal column. The name vertebrate comes from the indiŽvidual bony or cartilaginous segments called vertebrae that make up the spine. Vertebrates differ from the tunicates and lancelets in two important respects:
1. Vertebral column. In all vertebrates except the earliest fishes, the notochord is replaced during the course of embryonic development by a vertebral colŽumn (figure 34.8). The column is a series of bony or cartilaginous vertebrae that enclose and protect the dorsal nerve cord like a sleeve.
2. Head. Vertebrates have a distinct and wellŽ differentiated head; the brain is fully encased within a protective box, the skull or cranium, made of bone or cartilage. For this reason, the vertebrates are someŽtimes called the craniate chordates.
In addition to these two key characteristics, vertebrates differ from other chordates in other important respects:
A. Neural crest. A unique group of embryonic cells called the neural crest contributes to the development of many vertebrate structures. These cells develop on the crest of the neural tube as it forms by invaginaŽtion and pinching together of the neural plate. Neural crest cells then migrate to various locations in the developing embryo, where they participate in the development of a variety of structures.
B. Internal organs. Internal organs characteristic of vertebrates include a liver, kidneys, and endocrine glands. The ductless endocrine glands secrete horŽmones that help regulate many of the body's funcŽtions. All vertebrates have a heart and a closed circuŽlatory system. In both their circulatory and their excretory functions, vertebrates differ markedly from other animals.
C. Endoskeleton. The endoskeleton of most verteŽbrates is made of cartilage or bone. Cartilage and bone are specialized tissue containing fibers of the protein collagen compacted together. Bone also contains crystals of a calcium phosphate salt. Bone forms in two stages. First, collagen is laid down in a matrix of fibers along stress lines to provide flexibility, and then calcium minerals infiltrate the fibers, providing rigidity. The great advantage of bone over chitin as a structural material is that bone is strong without being brittle. The vertebrate enŽdoskeleton makes possible the great size and extraŽordinary powers of movement that characterize this group.

Overview of the Evolution of Vertebrates
The first vertebrates evolved in the oceans about 470 milŽlion years ago. They were jawless fishes with a single caudal fin. Many of them looked like a flat hot dog, with a hole at one end and a fin at the other. The appearance of a hinged jaw was a major advancement, opening up new food opŽtions, and jawed fishes became the dominant creatures in the sea.
 

Mammals radiated dramatically in the Paleocene and Eocene
The mammals, having inherited the world from the diŽnosaurs, underwent a remarkably rapid adaptive radiaŽtion during the early part of the Cenozoic Era (Figure 18-3). It is this radiation that gave the era its informal name: the Age of Mammals. It was probably primarily through predation rather than competition that the diŽnosaurs had prevented the mammals from undergoing any great evolutionary expansion during Mesozoic time.

Early in the Paleocene Epoch, when they first had the world to themselves, mammals were small creatures, most of which resembled modern rodents; no mammal seems to have been substantially larger than a goodŽ sized dog.

12 million years later, however, by the end of Early Eocene time, mammals had diversified to the extent that most of their modern orders were in existence (see Figure). Bats already fluttered through the night air for example, and, as we have seen, large whales swam the oceans.

Among the Paleocene mammals were groups that had survived from Cretaceous time, such as marsupials, rodent like forms called multituberculates, and the placental mammals called insectivores.

Primates, the order to which humans belong, evolved beŽfore the end of the Paleocene. Although these small animals were quite different from monkeys, apes, or humans in many respects, by Early Eocene time they were climbing with grasping hind limbs and forelimbs that foreŽshadowed our own hands and feet.

Primitive doglike mammalian carnivores known as mesonychids were common early in the Paleocene (Figure 18-6). The relatively primitive carnivorous mammals known as creoŽdonts diversified during the Paleocene were doglike or catlike in their adaptations.

The earliest members of the horse family had evolved by the end of Paleocene time; the first such animals were no larger than small dogs, but by the end of the epoch, larger herbivorous mammals, some the size of cows, had appeared.

The diversity of mammals continued to increase in the Eocene Epoch. The number of mammalian families doubled to nearly a hundred, approximating that of the world today.

Modern varieties of hoofed herbivores appeared they are known as ungulates, and they are divided into

odd-toed ungulates (living horses, tapirs, and rhinos) and

even-toed ungulates, or cloven-hoofed animals (cattle, antelopes, sheep, goats, pigs, bison, camels, and their relatives).

The odd-toed ungulates expanded before the even-toed group did, but primitive even-toed ungulates were also present early in the Eocene.

Among the carnivorous mammals, mesonychids and creodonts were rare in most regions of the world after Eocene time. They were replaced by members of the Carnivora, the order to which most modern mammalian carnivores belong. For example, the dog, cat, and weasel families, which had their origins in Eocene time, radiated during the Oligocene Epoch to produce such advanced forms as large saber-toothed cats, bear Žlike dogs, and animals that resembled modern wolves.
 

Early Paleogene birds were large
New terrestrial predators of the Paleocene Epoch inŽcluded not only mammals, but also the diatrymas, which were huge flightless birds with powerful clawed feet and enormous slicing beaks (Figure). The diatrymas disappeared toward the end of the Eocene Epoch.

The monstrous diatrymas were not the only birds of the Eocene, but flying birds were much less diverse then than they are today, Most species were large shoreŽbirds that waded in shallow water when not in flight

Frogs and insects were modernized in Paleogene time
As for other forms of vertebrate life, reptiles and amŽphibians were relatively inconspicuous during PaleoŽgene time. The first record of the Ranidae, the largest family of living frogs, is in the Eocene Series, but the fossil record of this group of fragile animals is poor, so we do not know precisely when the Ranidae originated or attained high diversity.
   

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