1. Evolution of alternation of generations
To enhance dispersal, land plants evolved alternation of generations: The multicellular haploid generation alternates with a multicellular generation composed of diploid cells. Specifically, the diploid zygote develops by mitosis into a multicellular spore-producing plant, called a sporophyte, while still attached to and supported by the haploid gamete-producing plant, called a gametophyte.
2. Evolution of vascular plants
These plants produce elongate cells for the internal transport of water and other materials. Xylem cells transport water and dissolved nutrients, and phloem cells transport carbohydrates produced by photosynthesis . As a result, vascular plants are taller and able to photosynthesize over a much wider range of conditions than plants dependent solely on surface moisture. Opened the way to the development of trees and forests.
3. Evolution of pollen and seeds (gymnosperm)
Differences between seed plants and spore-dispersing vascular plants. a)spores are not dispersed b)Male and female gamestes are brought together c)seeds develop which replaces the unicellular spores as the dispersal unit
4. Evolution of the flowering plants (angiosperms)
Flower, Carpel (closed vessel), double fertilization (one sperm nucleus fuses with the egg and a second sperm fuses with two haploid nuclei, and the development of fruits
-Some biologists pointed to the presence or absence of a cavity, or coelom, surrounding the gut, dividing bilaterians into three groups: those without a body cavity (acoelomates) and those with a body cavity (coelomates and pseudocoelomates, which differ in the embryonic origin of the cells lining the cavity). NO SUPPORT FROM MOLECULAR STUDIES
-In the phylum Cnidaria, which includes jellyfish and sea anemones, the embryo has two germ layers, the endoderm and the ectoderm, from which the adult tissues develop. These animals are therefore called diploblastic. Bilaterally symmetrical animals, the Bilateria, are triploblastic, with a third germ layer, the mesoderm, lying between the endoderm and ectoderm, which develops into muscles and connective tissues
- protostomes (from the Greek for "first mouth") and deuterostomes (from the Greek for "second mouth"). In protostomes, the earliest-forming opening to the internal cavity of the developing embryo, called the blastopore, becomes the mouth. In deuterostomes, the blastopore becomes the anus.
Bilaterian animals can be divided into two major groups, the deuterostomes and protostomes. Protostomes can be further subdivided into lophotrochozoans and ecdysozoans.
Ordovician Period (485-443 million years ago) was a time of renewed animal diversification, especially the evolution of heavily skeletonized animals in the world's oceans.
The number of genera recorded by fossils increased fivefold, suggesting that species diversity might have increased by an order of magnitude (most genera contain multiple species). The Ordovician radiation established a marine ecosystem that persisted for more than 200 million years.
Land plants evolved during the Ordovician Period
At the end of the Permian Period, 252 million years ago, environmental catastrophe eliminated most genera in the oceans. Paleozoic coral-like cnidarians become extinct, as did the trilobites. Brachiopods survived as a group, but most species disappeared. As noted in Chapter 23, the trigger for this devastation was massive volcanism that unleashed global warming, ocean acidification, and oxygen loss from subsurface oceans.
Bivalves and gastropods diversified; new groups of arthropods radiated, including the ancestors of the crabs and shrimps we see today; and surviving cnidarians evolved a new capacity to make skeletons of calcium carbonate
Flies, beetles, bees, wasps, butterflies, and moths radiated later, beginning in the early Mesozoic Era. Their rise in diversity parallels that of the flowering plants and reflects coevolution of flowering plants and the insects that both pollinate and feed on them.
Dominating terrestrial ecosystems until the end of the Cretaceous Period, 66 million years ago, when another mass extinction, caused by a catastrophic asteroid impact, eliminated nearly all dinosaur species