The Tree of Life Flashcards
What is the “Tree of Life” and what does it represent?
The “Tree of Life” is a depiction of all life on Earth, including living and extinct species. It shows that all species are genetically linked and can reveal common genes between human and non-human species. It includes both past lineages and species.
What is systematics and what does it aim to achieve?
Systematics is the field that reconstructs phylogenetic relationships. It aims to understand the broad relationships among discovered species, even though only a small fraction of all species have been discovered and fully studied.
Why are most species on Earth still undiscovered?
Most species are undiscovered because poorly known clades have unique environments, small organisms, or diversity that is difficult to study. Additionally, much of Earth’s diversity likely exists within poorly known groups like fungi, mites, and nematodes.
What are the major evolutionary steps in the phylogenetic tree that need to be memorized?
Eukaryotes: formation of nucleus and sex
Plants
Animals: muscle cells, head
Vertebrates: skeleton with backbone
Tetrapods: legs
What is the difference between mass extinction and background extinction?
Mass extinction is a rapid loss of species over a short geological time (millions of years) due to catastrophic events, while background extinction refers to the regular, gradual extinction of species over time, accounting for most extinctions (~80%).
What were the causes and consequences of the Late Permian mass extinction?
The Late Permian mass extinction, also called the “Great Dying,” occurred ~252 million years ago and caused the extinction of 81% of marine species and 70% of terrestrial vertebrates. Potential causes include volcanic eruptions, increased CO₂ levels, climate change, and methane release. It allowed dinosaurs, crocodilians, and mammal ancestors to diversify later.
What was the cause of the Late Cretaceous mass extinction, and what was its major consequence?
The Late Cretaceous mass extinction, which wiped out the non-avian dinosaurs, was likely caused by the impact of a large asteroid. As a result, mammals and flowering plants diversified, marking the end of the Mesozoic era and the beginning of the Cenozoic era.
What key events occurred during the Precambrian era?
During the Precambrian era, life originated (~4 billion years ago), cyanobacteria began producing oxygen, causing the oxygenation event (~2.4 billion years ago), and multicellular animals first appeared around 1 billion years ago.
What key evolutionary developments occurred during the Paleozoic era?
The Paleozoic era saw the Cambrian explosion, with a sudden abundance of marine animal fossils, and the appearance of life on land, including the first tetrapods around 450 million years ago.
What evolutionary milestones characterize the Mesozoic and Cenozoic eras?
The Mesozoic era is known for the evolution of dinosaurs and mammals, while the Cenozoic era marks the rise of hominids and the evolution of primates.
How is background extinction studied, and why is it important?
Background extinction is studied using fossils, phylogenies, and observed species losses in recent times. It is important because it helps determine extinction rates, allowing us to better understand and conserve current species.
What is the diversification rate (D), and how is it calculated?
The diversification rate (D) is the difference between the speciation rate (S) and the extinction rate (E), calculated as D = S - E. It represents the net rate of increase or decrease in species over time.
What happens when the diversification rate (D) is positive or negative?
When D is positive (D > 0), the number of species increases exponentially. When D is negative (D < 0), the number of species declines.
What assumptions does the simple model of diversification rate make, and why might these assumptions be unrealistic?
The model assumes no limits on species numbers, a constant diversification rate over time, and a constant rate across lineages. These assumptions are likely unrealistic, but the model remains useful for making predictions and comparisons.
