Glossary

Adaptations Changes in a lineage of organisms in response to environmental stress. Amniota Vertebrate group that includes the most recent common ancestors of living reptiles, mammals, birds, and all their descendants. amniote A tetrapod that protects the embryo of its offspring within the sealed environment of an amniotic egg reptiles, mammals, and birds are amniotes. amphibians Partly aquatic tetrapods that must return to the water to reproduce amphibians hatch from eggs in the water and live...

Leaving the Water

Now, having seen that fish did not come out of the water before they developed legs and lungs, one can return to the original question about why vertebrates left the water to begin with. A likely explanation is that for animals that could breathe and move outside of the water, the land represented a rich, new, uncharted domain. By the Late Devonian Epoch, both saltwater and freshwater habitats were populated by an abundance of fishes. Competition in the water was predicated by size No matter...

Introduction Of Prehistoric Earth

The Cambrian Period of the Paleozoic Era is known for its remarkable explosion of multicelled organisms with hard shells and exo-skeletons. The evolution of early life during the Cambrian set into motion an arms race between predator and prey that has continued to escalate over the ages with each new species of organism. From the roots of life in the Cambrian arose the first animals with backbones the vertebrates. In the vast Paleozoic oceans, fishes of many kinds became the focus of a...

Formation of Soil and Ground Cover

An important early stage in the development of a habitable terrestrial environment was the formation of a viable ground cover of soil. Soil is composed of two kinds of materials. The first kind comes from rocks. When rocks are broken up by geological processes such as erosion and weathering, they can form soil particles. Mineral elements and compounds that include silicon, aluminum, iron, oxygen, calcium, magnesium, sodium, and potassium can all be found in varying amounts in soil composed of...

Million Years Ago in Scotland

One of the most plentiful fossil locations for early terrestrial life is the Rhynie Chert in the north of Scotland. Located near the town of Rhynie, in Aberdeenshire, the site contains fossils from a time when that part of Scotland was located south of the equator, about 400 million years ago. Chert is a quartz-related mineral that occurs naturally from the breakdown of minerals in rocks or decayed organic matter. In the case of the Rhynie Chert, silica deposits literally rained down from...

Pelycosaurs The Sailbacked Synapsids

The most familiar pelycosaurs are the sailbacked Dimetrodon and Edaphosaurus. Evolving during the Early Permian, each of these animals developed a large sail on its back the sail was held upright by extremely elongated extensions of the neural arch of the back and tail bones. This large sail must have looked somewhat like a handheld fan, as it was covered by a membrane of vascularized skin skin with blood vessels running through it. The function of the sail was probably to help regulate the...

Splits in the amniote family tree

Several patterns of distinctive morphological changes began to arise in amniotes in the Carboniferous Period. These changes were most clearly expressed in the skulls of early reptiles and their kin. By the end of the Permian Period, about 251 million years ago, the die was cast for the future of amniotes that have dominated terrestrial, and sometimes marine, ecosystems ever since. A key diagnostic trait used to classify amniotes is a feature of the skull called the temporal fenestrae openings...

From fins to legs

Until about 20 years ago, a scarcity of tetrapod fossils led paleontologists to make several basic assumptions about the evolution of the first land animals. Central to an interpretation of tetrapod origins was the idea that legs developed as a means for walking on land. This idea made sense based on the timing of known fossil specimens and the best information available about the specimens' ancient habitats. These basic assumptions have changed dramatically in recent years due to a renaissance...

Weight Bearing Anatomy

Without water to support its body weight, a vertebrate out of water had to cope with the stronger pull of gravity while remaining mobile. This adaptation was accomplished through a gradual but complete overhaul of the vertebrate skeleton to maximize its weight-bearing components and limbs. The transition from fish to four-legged animal did not occur suddenly, but over the course of thousands of generations of many species of creatures. Before the fossil record begins to show unequivocal...

Near Terrestrial Tetrapods

This category includes taxa that are not quite fully terrestrial yet probably not exclusively aquatic as are most sarcopterygian fish. The animals mentioned below are grouped with the tetrapods because of the development of their skulls and because they possess a generalized set of limbs with digits. The distinction made here between near-terrestrial tetrapods and tetrapods is one of degree These animals represent an important transitional stage in the evolution of land vertebrates but also...

Major Plant Groups

Ribosomes Plants

Plants are multicellular, photosynthesizing members of the Eu-karya the domain of organisms with a eukaryote cell type that also includes animals and fungi. Most plants are green, although a select few genera have lost their green pigment during the course of their evolution. During photosynthesis, the green pigment chlorophyll that is found in plant cells uses energy from sunlight to transform carbon dioxide and water into organic compounds, including free oxygen. Land plants are most...

Chapter The First Land Animals

Cohen. Evolutionary Origin of Insect Wings from Ancestral Gills. Nature 385 February 13, 1997 627-630. Budd, Graham E., Anette E.S. H gstr m, and Ivan Gogin. A Myriapod-Like Arthropod from the Upper Cambrian of East Siberia. Palaeontologische Zeitschrift 75, no. 1 2001 37-41. Dudley, Robert. Atmospheric Oxygen, Giant Paleozoic Insects and the Evolution of Aerial Locomotor Performance. Journal of Experimental Biology 201 1998 1043-1050. Dunlop, Jason A. A...

Plant Adaptations for Living on Land

Plant Adaptations Marine

Plants were pioneers the first organisms to colonize dry land. Adapting for life on land required several key modifications. Gymnosperms are seed plants with a protected cone or other body for their seed embryos, such as conifers evergreen trees , seed ferns, and cycads. Gymnosperms are seed plants with a protected cone or other body for their seed embryos, such as conifers evergreen trees , seed ferns, and cycads. Plants originated in the nourishing environment of the water. Life on land...

Insecta

Insecta Thorax

Insects are members of the arthropod class Insecta. They are the largest group of organisms on the planet and account for more than half of the named species known to science. Doubtless there are tens of thousands more species of insects waiting to be detected. More The taxonomy of living insects includes 31 major groups or orders and more than 1,015 families within those groups. In addition, there are about 12 extinct groups that are known only from the fossil record. The following table...

Evolution of the Tetrapod Vertebral Column

Some of the most important clues to the lineage of early tetrapods can be traced in the evolutions of the vertebral column. While all vertebrates have a backbone, the number of vertebrae and the shape and design of the individual bones vary significantly from taxon to taxon. Such morphological features as size, shape, and volume provide excellent clues to the lifestyle of a given extinct creature. The design of vertebrae can also serve as pointers to link related taxa. To understand the...

Reptiles the first amniotes

The earliest reptile for which there is clear, undisputed fossil evidence is Hylonomus, from the Middle Carboniferous swamps of Nova Scotia it dates from about 310 million years ago. Another early reptile, Paleothyris, dates from about 300 million years ago and also comes from Nova Scotia. Superb fossils of each have been found inside fossilized tree trunks. It is presumed that the animals perished inside the exposed tree trunks while feeding on insects, millipedes, and other arthropods that...

Ozone Protection

The Earth has a layer of ozone in the upper part of the oxygen-filled lower atmosphere. Ozone is made by a reaction that takes place when ultraviolet UV radiation from the Sun strikes oxygen molecules. When sunlight strikes oxygen molecules, the molecules are split apart they recombine with other elements in the atmosphere to form the band of ozone that surrounds the planet. That ozone is Atmospheric oxygen levels have gradually increased as photosynthetic organisms have flourished. 2 The...

The Origin and Evolution of Land Plants

Prehistoric Atmospheric Oxygen

Photosynthesizing algae first arose in the oceans. As improbable as it may seem, a single species of green algae, living in the water, was likely responsible for giving rise to every form of land plant that followed. This was a monumental step in the evolution of life on Earth, yet it was also a kind of accident an accident repeated over and over until life stuck to dry land once and for all. It began when near-coastal colonies of algae mats stromatolites became exposed to the air when the...

EuRyapsida Extinct Marine Reptiles And Their Kin

The roots of the euryapsid family tree are largely uncertain, although the design of the euryapsid skull, with its single temporal fenestra, looks very much like the skull of a diapsid without the lower opening. There is consensus among paleontologists that the euryapsid skull was probably a modification of the diapsid pattern. Regardless of similarities in their skulls, most euryapsids arose during the Mesozoic as a diverse and plentiful group of reptiles that had returned to an aquatic...

Diapsida LizArds Snakes Crocodiles Birds PterosauRs DinosauRs And Extinct Kin

The diapsids include the most diverse radiation of reptile forms. With roots going back to the Late Carboniferous Period, most Paleozoic diapsids were small, long-legged, swift-running forms that lived in the shadows or ran away from the shadows, as the case may have been of the much larger amphibians, anapsids, and synapsids that dominated the terrestrial ecosystems of the Permian. With the coming of the disastrous end-Permian mass extinction, the status of many life-forms was changed forever....

Early Tetrapods

The discovery of Ichthyostega in 1932 pushed back the known origin of tetrapods to the Late Devonian. Prior to that, the earliest known tetrapods were the much more derived and amphibianlike specimens from the Carboniferous. The discovery of Ichthyostega provided some excellent clues to the early adaptation of lobe-finned fishes to life on land, but the discovery presented some puzzles as well. While some Carboniferous tetrapods were clearly optimized for living on land, those of the Late...

Atmospheric Carbon Dioxide and Oxygen

Life on land requires oxygen and carbon dioxide. Nearly all types of organisms use oxygen to obtain energy from organic compounds. Oxygen is an essential fuel for body tissues. Plants need carbon dioxide CO2 for photosynthesis. Carbon dioxide comes from animals when they exhale and from decaying organic matter, and is absorbed by water from the atmosphere. This exchange between living organisms and the environment is a critical factor that affects the development of all life. The explosion of...

Lobe Finned Fishes

Lobe-finned fishes the sarcopterygians rose during the Early Devonian Period and were the first dominant group of bony fishes. Their numbers dwindled by the end of the Paleozoic with the rise of the ray-finned fishes, but not before some members of this group evolved to become the first limbed vertebrates. Four groups of sar-copterygians are recognized. Porolepiformes an early group of sarcopterygians, now extinct. Osteolepiformes advanced group of sarcopterygians, now extinct, although they...

Hemiptera Sucking Insects

What are known as the true bugs or Hemiptera are part of an enormously diverse order with roots going back to the Permian Period. Basal members of this group were probably predators, with mouthparts originally designed to suck fluids from other animals. These same mouthparts were adapted over time to feed on plants, and most hemipterans were, and continue to be, plant eaters. The rise and diversity of the hemipterans coincides with the spread of gymnosperm plants. Extinct members of this group,...

Therapsida

The therapsids arose during the Middle Permian, following the decline of the pelycosaurs. This diverse collection of later synap-sids persisted until the Early Jurassic Epoch the therapsids were displaced by diapsids, a group that included lizards and the early dinosaurs. With the therapsids, the elongated, sprawling body plan of the pelycosaurs gave way to the compact, sturdier build seen in many theraspids. A reduced tail and longer legs suggest that these animals were becoming better walkers...

Eurypterids and Scorpions

Fish With Pinchers

Arachnids have roots in the Silurian Period, in the form of aquatic, scorpionlike creatures called eurypterids, or sea scorpions. The eurypterids are an extinct group of arthropods that lived primarily in brackish freshwater environments and lagoons. Most species were small, but some spectacular examples such as Pterygotus routinely reached lengths of more than six feet 1.8 m . Larger still was a fossil specimen of the eurypterid Jaekelopterus Early Devonian, Germany described in 2007. Based on...

Odonata Giant Fliers

Dragonflies and mayflies are among the most ancient winged insects. Early mayflies are known from the Early Carboniferous the first dragonflies are known from the Late Carboniferous. Fossil mayflies had secondary wings that were about the same size as the primary wings. This is unlike modern species, in which the second pair of wings is greatly reduced in size. Also unlike their modern descendants, which do not eat, Paleozoic mayflies had sucking mouthparts for extracting juices from plants....

Arachnida spiders and scorpions

The arthropod group Arachnida includes the spiders, scorpions, ticks, and their kin. Their heads and thorax are fused and protected by a carapace, or hard outer covering. Arachnids have from zero to four pairs of eyes, eight legs, and a complex set of anterior appendages associated with grabbing food, tearing it apart, and preparing it for ingestion. The appendages used by arachnids for securing food are notoriously effective and deadly. A pair of smaller appendages, called che-licerae, is...

Amniote origins

Amniotic Egg

Prior to the appearance of amniotes, all tetrapods reproduced in the water. With most extant amphibians, fertilization takes place externally the same can be assumed for the earliest tetrapods. Typically, when two amphibians mate underwater, the male discharges sperm onto mature eggs that are being released from the body of the female. The egg mass is covered in a gelatinous substance this sticky substance adheres the eggs to a surface such as a rock. Soon, an aquatic larva hatches from each...

Early Diapsids

The fossil record of Late Paleozoic diapsids is not complete enough to define their evolutionary relationships. Certain anatomical trends can be seen in their development, however, and that development became more and more specialized and advantageous as diapsids of various kinds diversified in the Triassic. Among these adaptations were long legs for running, long necks for added flexibility, lighter skulls, and the specialization of teeth for the consumption of both meat and plants. One of the...

Diversification of EARLY tetrapods the Carboniferous and permian periods

Carboniferous And Permian Periods

The beginning of the Carboniferous Period, 360 million years ago, was a time of expanding horizons for all terrestrial life. Plants were extending their domain in all directions, gaining ground and pushing out farther from the shorelines of the oceans, lakes, and streams where they originated. Insects and other arthropods were thriving in the vast vegetative coal forests that accumulated around the coastal plains. The annual climate was so evenly temperate that there were no distinct seasons....