11.1 Macroevolutionary patterns and processes in the fossil record
4 min read•august 7, 2024
The fossil record reveals fascinating patterns of evolutionary change over time. From to gradual shifts, organisms adapt to changing environments and interactions. These processes shape the diversity of life we see today and in the past.
and are key drivers of biodiversity trends. New species emerge through various mechanisms, while extinctions, both gradual and catastrophic, reshape the tree of life. Understanding these patterns helps us grasp the dynamic nature of evolution.
Patterns of Evolutionary Change
Rates and Patterns of Morphological Change
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- Punctuated equilibrium proposes evolutionary change occurs in rapid bursts followed by long periods of (little to no change)
- suggests evolutionary change happens slowly and steadily over time through the accumulation of small changes
- Supported by many examples of gradual change in the fossil record (horse evolution)
- Stasis is a period of little to no over long periods of time
- Can last for millions of years (coelacanth, horseshoe crab)
- Morphological change refers to changes in the physical form, structure, and appearance of organisms over time
- Includes changes in size, shape, and the presence or absence of features (development of feathers in dinosaurs)
- Evolutionary rates describe the speed at which evolutionary changes occur
- Can be rapid (punctuated equilibrium) or slow (gradualism)
- Vary across different lineages and time periods (rapid evolution of mammals after the K-Pg extinction)
Factors Influencing Evolutionary Patterns
- can drive evolutionary change by altering
- Climate change, habitat shifts, and changes in resource availability (evolution of drought-resistant plants during aridification)
- Interactions between species, such as competition and predation, can influence evolutionary patterns
- Arms races between predators and prey (evolution of faster cheetahs and gazelles)
- Developmental and genetic constraints can limit the range of possible morphological changes
- Bauplan (body plan) constraints (tetrapod limb structure)
- , such as novel traits or behaviors, can open up new adaptive opportunities and influence evolutionary patterns
- Evolution of flight in birds and bats enabling the exploitation of new niches
Speciation and Extinction
Speciation Processes
- Speciation is the formation of new species from existing species
- Requires reproductive isolation and genetic divergence (Darwin's finches)
- is a speciation process that results in the splitting of a lineage into two or more descendant lineages
- Occurs through adaptive radiation or allopatric speciation (cichlid fish in African lakes)
- is a speciation process involving the gradual transformation of one species into another over time without splitting
- Occurs through the accumulation of changes within a single lineage (Homo erectus to Homo sapiens)
Extinction Patterns and Causes
- Extinction is the disappearance of a species or higher taxonomic group
- Can be caused by various factors, including environmental changes, competition, and mass extinction events (dinosaur extinction at the end of the Cretaceous)
- refers to the continuous, low-level extinction of species over time
- Occurs at a relatively constant rate (1-5 species per year)
- are events characterized by the rapid and widespread loss of a significant proportion of Earth's biodiversity
- Caused by catastrophic events such as asteroid impacts, volcanic eruptions, and climate change (End-Permian extinction)
- refers to the non-random patterns of extinction, where certain taxa are more prone to extinction than others
- Influenced by factors such as body size, specialization, and geographic range (selective extinction of large mammals during the Pleistocene)
Diversity Trends
Patterns of Diversity Through Time
- refer to changes in the number and variety of species or higher taxa over geological time
- Can be studied at various taxonomic levels (species, genera, families) and spatial scales (local, regional, global)
- The fossil record shows a general increase in diversity over time, punctuated by occasional declines due to mass extinctions
- marked a rapid increase in animal diversity (appearance of most modern phyla)
- Diversity rebounds and recovers after mass extinction events, often with the rise of new dominant groups
- after the K-Pg extinction (rise of primates, carnivores, and ungulates)
- Diversity patterns can vary across different taxonomic groups and geographic regions
- Marine vs. terrestrial diversity trends (higher diversity in marine environments)
- Latitudinal diversity gradients (higher diversity in the tropics compared to polar regions)
Factors Influencing Diversity Patterns
- , such as competition and predation, can shape diversity patterns
- and resource specialization (diverse herbivorous dinosaurs in the Jurassic)
- Environmental factors, including climate, habitat heterogeneity, and productivity, influence diversity
- Warm, stable climates often associated with higher diversity (Eocene Epoch)
- , such as continental drift and sea level changes, can affect diversity by altering geographic ranges and creating or removing barriers
- Pangaea breakup and the formation of new oceans and continents (isolation of marsupials in Australia)
- Evolutionary innovations and adaptations can drive diversification by opening up new ecological opportunities
- Evolution of grasses and the diversification of grazing mammals (horses, antelope)
Key Terms to Review (20)
Anagenesis: Anagenesis refers to the gradual evolutionary process by which a single species evolves into a different species over time without branching into multiple lineages. This transformation can occur through small, incremental changes in the traits and characteristics of the organism, resulting in a lineage that is distinctly different from its ancestral form. Anagenesis is significant as it showcases how species adapt and evolve in response to environmental pressures, contributing to macroevolutionary patterns observed in the fossil record.
Background extinction: Background extinction refers to the ongoing, gradual process of species becoming extinct over time due to various environmental and biological factors, as opposed to mass extinction events which occur suddenly and affect a large number of species simultaneously. This concept highlights the normal, natural rate of extinction that has occurred throughout Earth's history, contributing to the dynamic nature of ecosystems and biodiversity.
Cambrian Explosion: The Cambrian Explosion refers to a remarkable period of rapid diversification of life that occurred around 541 million years ago, marking the beginning of the Paleozoic Era. This event is characterized by the sudden appearance of many major groups of marine invertebrates in the fossil record, establishing a foundation for modern ecosystems and evolutionary processes.
Cladogenesis: Cladogenesis is the process of evolutionary branching in which a lineage splits into two or more distinct lineages, leading to increased biodiversity. This occurs when a species diverges into different forms, often due to factors like environmental changes or geographical barriers, resulting in the creation of new species from a common ancestor. Cladogenesis is essential for understanding macroevolutionary patterns and processes, as it highlights the branching nature of evolutionary history and how different groups of organisms arise over time.
Diversity Trends: Diversity trends refer to the patterns and changes in the variety of life forms over geological time, as evidenced by the fossil record. These trends can show how different groups of organisms have emerged, evolved, and gone extinct, reflecting broader macroevolutionary processes that shape biodiversity. Understanding these trends helps in analyzing the influences of environmental changes, extinction events, and the adaptive radiations of species throughout Earth's history.
Ecological interactions: Ecological interactions refer to the various relationships and dynamics that occur between different organisms and their environment, influencing species distribution, behavior, and evolution. These interactions can be direct, such as predation or competition, or indirect, such as mutualism and commensalism, affecting population dynamics over time. Understanding these interactions is crucial to comprehending macroevolutionary patterns and processes as they help shape the biodiversity observed in the fossil record.
Environmental Changes: Environmental changes refer to the shifts in the Earth's natural systems and climate that can influence ecosystems, species distribution, and the overall landscape over time. These changes can be gradual or abrupt and include factors such as climate change, geological events, sea-level rise, and habitat destruction, which all play significant roles in shaping macroevolutionary patterns and processes observed in the fossil record.
Evolutionary innovations: Evolutionary innovations refer to novel traits or features that arise through the process of evolution, allowing organisms to adapt to their environment and enhancing their chances of survival and reproduction. These innovations can lead to significant changes in the structure, function, or behavior of organisms, ultimately contributing to biodiversity and the emergence of new species.
Extinction: Extinction refers to the complete disappearance of a species or group of organisms from the Earth, resulting in a permanent loss of biodiversity. It serves as a crucial process in the evolutionary timeline, impacting ecosystems and influencing the course of life's history. Understanding extinction helps to uncover patterns of survival and adaptation, as well as the consequences of environmental changes over geological time scales.
Extinction selectivity: Extinction selectivity refers to the concept that certain species are more likely to go extinct than others during mass extinction events or periods of environmental change. This selectivity is influenced by various factors, such as species traits, ecological roles, and environmental conditions. Understanding extinction selectivity is crucial for interpreting macroevolutionary patterns and processes as it sheds light on how different groups respond to environmental stressors over geological time scales.
Gradualism: Gradualism is the concept in evolutionary biology that proposes species evolve slowly and steadily over long periods of time, rather than through sudden changes or large-scale transformations. This idea connects to macroevolutionary patterns and processes by illustrating how small, incremental changes can accumulate, leading to significant evolutionary developments as seen in the fossil record.
Mammalian diversification: Mammalian diversification refers to the evolutionary process through which mammals have expanded and adapted into various forms and ecological niches over time. This process is marked by the emergence of a wide variety of mammal species, resulting from both adaptive radiation and natural selection, and has played a crucial role in shaping the fossil record as well as understanding macroevolutionary trends.
Mass extinctions: Mass extinctions are significant and rapid decreases in biodiversity, characterized by the widespread loss of species across multiple taxa. These events have played a crucial role in shaping the history of life on Earth, influencing evolutionary processes and ecological communities, and often leading to the emergence of new species and ecosystems in their aftermath.
Morphological change: Morphological change refers to alterations in the structure, shape, and form of organisms over time, often driven by evolutionary processes. This concept is vital for understanding how species adapt to their environments and how these adaptations are reflected in the fossil record. It highlights the dynamic relationship between organisms and their ecosystems and can provide insights into macroevolutionary patterns.
Niche partitioning: Niche partitioning refers to the process by which different species in an ecosystem utilize various resources or habitats to minimize competition and coexist. This concept is crucial for understanding how species diversify and adapt in different environments, especially during events of rapid evolutionary change, where multiple species evolve from a common ancestor and occupy distinct ecological roles.
Punctuated equilibrium: Punctuated equilibrium is a theory in evolutionary biology that suggests species experience long periods of stability interrupted by brief episodes of rapid change. This concept contrasts with the traditional view of gradual evolution and highlights the significance of geological and environmental events in driving these rapid changes, which can be observed in the fossil record and in adaptive radiations.
Selective pressures: Selective pressures are environmental factors that influence the survival and reproduction of individuals within a population. These pressures can include predation, competition for resources, disease, and climate conditions, and they play a crucial role in shaping the evolutionary trajectory of species over time. In the context of macroevolutionary patterns and processes in the fossil record, understanding selective pressures helps to explain how species adapt to their environments and how these adaptations can lead to speciation or extinction events.
Speciation: Speciation is the evolutionary process by which new biological species arise from existing ones, typically through mechanisms like genetic divergence and reproductive isolation. This process contributes to biodiversity and is influenced by various factors, including geographic separation and environmental changes that promote adaptation over time.
Stasis: Stasis refers to a period of little or no evolutionary change in a species or group, often lasting for millions of years. This concept is essential for understanding how some organisms can maintain stable characteristics over long geological timescales, which plays a significant role in the patterns and processes seen in the fossil record.
Tectonic events: Tectonic events refer to significant geological occurrences driven by the movement of Earth's tectonic plates, such as earthquakes, volcanic eruptions, and the formation of mountain ranges. These events play a crucial role in shaping Earth's landscape and influencing biological evolution by altering habitats, climate, and geographic barriers, ultimately impacting macroevolutionary patterns and processes in the fossil record.