As the continents drifted apart, each became a separate evolutionary arena with lineages of plants and animals that diverged from those on other continents.
Continental drift explains much about the former and current distribution of organisms.
Australian flora and fauna contrast sharply from that of the rest of the world.
Marsupial mammals fill ecological roles in Australia analogous to those filled by placental mammals on other continents.
Marsupials probably evolved first in what is now North America and reached Australia via South America and Antarctica while the continents were still joined.
The breakup of the southern continents set Australia adrift.
In Australia, marsupials diversified and the few early eutherians became extinct.
On other continents, marsupials became extinct and eutherians diversified.
Concept 26.6 New information has revised our understanding of the tree of life
In recent decades, molecular data have provided new insights into the evolutionary relationships of life’s diverse forms.
The first taxonomic schemes divided organisms into plant and animal kingdoms.
In 1969, R. H. Whittaker argued for a five-kingdom system: Monera, Protista, Plantae, Fungi, and Animalia.
The five-kingdom system recognized that there are two fundamentally different types of cells: prokaryotic (the kingdom Monera) and eukaryotic (the other four kingdoms).
Three kingdoms of multicellular eukaryotes were distinguished by nutrition, in part.
Plants are autotrophic, making organic food by photosynthesis.
Most fungi are decomposers with extracellular digestion and absorptive nutrition.
Most animals ingest food and digest it within specialized cavities.
In Whittaker’s system, Protista included all eukaryotes that did not fit the definition of plants, fungi, or animals.
Most protists are unicellular.
Lecture Outline for Campbell/Reece Biology, 7th Edition, © Pearson Education, Inc. 26-17