lecture 16

Lecture Objectives2

• Overview of phylogeny of animals

• Review characteristics that define animals

• Discuss evolutionary timeline and factors influencing diversification and extinction

Phylogeny of Animals

• Examination of a phylogenetic tree

• Review of characteristics that define animals:

  • Heterotrophic: Animals must consume food from other sources, not produce it internally.

  • Internal Digestion: Animals digest food internally.

  • Multicellularity: Composed of multiple cells with specialized functions.

  • Mobility: Many animals show movement at some point in their life cycle.

  • Nervous System: Most animals possess a nervous system, with sponges being an exception.

Evolutionary History Timeline

• Overview of major themes and patterns:

  • Diversification Factors: Explains how some events promote species growth while others lead to extinction.

  • Extinction Events: Five major extinction events will be discussed in relation to animal evolution.

  • Understanding how extinction can pave the way for diversification,

    • Example: Cambrian Explosion.

Cambrian Explosion

• Timeframe: Occurred around 5-504 million years ago.

• Significant diversification seen in the fossil record during this period:

  • Modern groups like sponges, arthropods, mollusks, and early vertebrates appeared.

• Theories of Punctuation: The theory of punctuated equilibrium suggests periods of little change punctuated by bursts of evolution.

Factors Contributing to Cambrian Diversification

• Increased oxygen levels, conducive for animal development:

  • Documented exponential rise in global oxygen levels correlating with Cambrian period.

• Development of habitats such as warm, shallow lagoons fostering niche diversity.

• Evolution and diversification influenced by Hox genes, which regulate body segment development.

Key Developments in Evolutionary History

• Evolution of Vertebrates:

  • Formation of modern spinal columns around 420-405 million years ago.

  • Development of jaws led to the rise of bony fishes and diversification of predators.

• Colonization of Land:

  • Transition from aquatic to terrestrial life among lobe-finned fishes (sarcopterygians).

  • Key characteristics facilitating this transition: evolution of lungs and supportive limbs.

Major Clades

• Overview of evolution leading to mammals, birds, and reptiles:

  • Bifurcation of reptiles into both mammals and birds during the Pennsylvania period.

  • Significant diversification post the K/T extinction event 65 million years ago, allowing for mammalian species to thrive.

Trends in Animal Evolution

• Notable trends include:

  • Centralization: Nervous systems evolve towards a centralized structure (e.g., spinal cord, brain).

  • Stabilization: Critical sensory structures become localized in head regions, enhancing sensory processing as organisms interact with their environment.

Conclusion

• Recap of key evolutionary concepts to focus on for future study:

  • Pathways of evolutionary change, diversification, and extinction events.

  • Importance of geological and biological factors in shaping the diversity of life.

Lecture Objectives

• Overview of phylogeny of animals, highlighting the evolutionary relationships and lineages.

• Review characteristics that define animals, emphasizing unique traits setting them apart from other life forms.

• Discuss evolutionary timeline and the multifaceted factors influencing diversification and extinction of animal species.

Phylogeny of Animals

• Examination of a phylogenetic tree, illustrating the evolutionary pathways and ancestry of different animal groups.

Characteristics that Define Animals:

• Heterotrophic: Animals must consume food from external sources, relying on organic materials rather than producing their own nutrients internally through photosynthesis.

• Internal Digestion: Animals have specialized internal systems for digesting food, allowing for efficient breakdown and absorption of nutrients.

• Multicellularity: Composed of multiple cells which have specialized functions; this structural complexity leads to diverse physiological processes.

• Mobility: Many animals exhibit movement at some stage in their life cycle, using various adaptations to navigate their environments.

• Nervous System: Most animals possess a nervous system, allowing for coordination and response to stimuli; however, this is an exception in sponges, which lack a nervous system.

Evolutionary History Timeline

• Overview of major themes and patterns observable in animal evolution:

  • Diversification Factors: Analyzing how major events such as climate change, habitat formation, and genetic mutations contribute to the growth of species, while other events lead to mass extinctions.

  • Extinction Events: Five major extinction events will be elucidated in relation to animal evolution, discussing their causes and consequences.

  • Understanding how extinction events can create empty ecological niches, paving the way for diversification in the following epochs, exemplified by the Cambrian Explosion.

Cambrian Explosion

• Timeframe: Occurred approximately 541 to 485 million years ago, marking a pivotal era in the history of life.

• Significant diversification observed in the fossil record during this period, with the emergence of modern representative groups such as sponges, arthropods, mollusks, and early vertebrates.

• Theories of Punctuation: The theory of punctuated equilibrium posits that evolutionary development is marked by isolated episodes of rapid speciation between long periods of little or no change.

Factors Contributing to Cambrian Diversification

• Increased Oxygen Levels: Documented exponential rise in global oxygen levels correlates with animal development, enabling more complex life forms to thrive.

• Habitat Development: Formation of diverse habitats, such as warm, shallow lagoons, fostering ecological niches and supporting a variety of life forms.

• The role of Hox Genes: Essential in regulating body segment development and contributing to the complexity of body plans in animals.

Key Developments in Evolutionary History

• Evolution of Vertebrates: The formation of modern spinal columns around 420-405 million years ago was crucial for vertebrate evolution.

• Development of Jaws: Led to the rise of bony fishes, creating opportunities for diversification of predatory species.

• Colonization of Land: Details the transition from aquatic to terrestrial life among lobe-finned fishes (sarcopterygians), driven by adaptations such as the evolution of lungs and supportive limbs facilitating movement on land.

Major Clades

• Overview of the evolutionary lineage leading to mammals, birds, and reptiles:

  • Bifurcation of Reptiles: Occurred during the Pennsylvania period, leading to the distinct evolutionary paths of mammals and birds.

  • Significant diversification followed the K/T extinction event around 65 million years ago, creating ecological opportunities that allowed mammalian species to prosper and evolve rapidly.

Trends in Animal Evolution

• Notable Trends: includes:

  • Centralization: A trend whereby nervous systems evolve towards a more centralized structure, exemplified by the spinal cord evolution and the development of a brain.

  • Stabilization: Critical sensory structures tend to become localized in head regions, improving sensory processing and interaction with environmental stimuli, enhancing survival and reproductive success.

Conclusion

• Recap of Key Evolutionary Concepts: a focus for future studies should include the pathways of evolutionary change, the interplay of diversification and extinction events, and recognizing the importance of geological and biological factors that shape the diversity of life on Earth.

Ordovician Period and Fish Evolution

• The Ordovician period, spanning from about 485 to 444 million years ago, is a significant time in the evolution of life and particularly marked by the diversification of marine life, including the early evolution of fish.

• Early jawless fish, known as agnathans, began to dominate the seas, showcasing diverse feeding strategies and adaptations to various aquatic environments.

Devonian Period: Age of Fishes

• The Devonian, often termed the "Age of Fishes," lasted from approximately 419 to 359 million years ago. This era witnessed unprecedented diversification of fish, with both jawless (agnathans) and jawed fish (Gnathostomata) evolving.

• Lobed-Finned Fishes: Among the key evolutionary developments during the Devonian were the lobed-finned fishes (sarcopterygians). These fish possess fleshy, lobed pectoral and pelvic fins that are more robust than those of ray-finned fishes, allowing for better mobility in shallow waters and adaptability to a variety of environments.

• Key adaptations such as lungs and the ability to breathe air are believed to have evolved during this period, setting the stage for future terrestrial vertebrates.

Transition to Terrestrial Life: Tetrapod’s

• The advancement in lobed-finned fish anatomy eventually paved the way for the evolution of tetrapod’s, the first vertebrates to venture onto land.

• This transition occurred primarily in the late Devonian, around 360 million years ago. Important fossils like Tiktaalik illustrate the transitional forms between fish and early tetrapod’s, showcasing adaptations for breathing air and supporting body weight on land.

Triassic, Jurassic, and Cretaceous Periods: Evolution of Tetrapod’s

• Triassic Period (approximately 252 to 201 million years ago): Marked the emergence of early amphibians and reptiles. Early reptiles began to diverge and adapt, laying the groundwork for the vast diversity that would follow.

• Jurassic Period (approximately 201 to 145 million years ago): Characterized by the diversification of dinosaurs and the rise of mammals. The evolution of distinct terrestrial ecosystems, including diverse landscapes and plant life, facilitated the adaptive radiation of many tetrapod lineages.

• Cretaceous Period (approximately 145 to 66 million years ago): Featured the continued evolution and dominance of dinosaurs. Birds evolved during this time, showcasing the successful adaptation of tetrapods to a variety of terrestrial environments. This period ended with the mass extinction event that led to the disappearance of the non-avian dinosaurs, drastically altering the evolutionary landscape.

Conclusion

• The evolution of fish during the Ordovician and Devonian periods set the stage for significant ecological developments, leading to the emergence of tetrapods and their eventual diversification into numerous terrestrial forms through the Triassic, Jurassic, and Cretaceous periods. This evolutionary trajectory showcases the intricate relationships between aquatic and terrestrial life forms and underscores key adaptations essential for survival in diverse environments.

Major Clades: Amphibians, Birds, and Reptiles

• Amphibians: Represent the first group of vertebrates to become adapted to life on land, evolving from lobe-finned fishes during the late Devonian period. Key adaptations include the development of lungs and limbs, which enable locomotion and respiration in terrestrial environments. Over time, amphibians underwent significant diversification, giving rise to modern groups such as frogs, salamanders, and caecilians.

• Birds: Evolved from theropod dinosaurs during the late Jurassic period, characterized by feathers, a lightweight skeletal structure, and adaptations for flight. The evolution of birds exemplifies the survival of certain lineages following extinction events. Their unique adaptations have allowed them to occupy various ecological niches on land and in the air.

• Reptiles: Evolved from early amphibians, developing key adaptations such as amniotic eggs that allow for reproduction on land, as well as features that minimize water loss. Reptiles diversified greatly during the Mesozoic era, with significant groups including dinosaurs, crocodilians, and modern lizards and snakes.

Five Major Extinction Events

1. Late Ordovician Extinction (approximately 444 million years ago): Triggered by a short, intense ice age, this event caused the extinction of nearly 85% of marine species, including many types of fish.

2. Late Devonian Extinction (approximately 375 million years ago): A prolonged event over several million years that affected primarily marine life, with significant losses among reef-building organisms and jawless fish.

3. Permian-Triassic Extinction (approximately 252 million years ago): The most devastating extinction event, where about 96% of marine species and 70% of terrestrial vertebrate species vanished, paving the way for the rise of reptiles.

4. Triassic-Jurassic Extinction (approximately 201 million years ago): An event that led to the extinction of many reptiles and amphibians, allowing dinosaurs to dominate during the Jurassic period.

5. Cretaceous-Paleogene Extinction (approximately 66 million years ago): Often attributed to a massive asteroid impact, this event led to the extinction of approximately 75% of all species, including non-avian dinosaurs, but allowing birds and mammals to thrive afterward.

Phylogenetic Relationships of Major Animal Clades

Overview of Evolution and Diversification

• Animals are categorized into major clades based on evolutionary relationships derived from shared characteristics and genetics.

• Key clades include: Vertebrates, Chordates, Arthropods, Mollusks, and Annelids.

Timeline of Animal Evolution/Diversification

1. Origin of Animals: Emerged approximately 600 million years ago.

2. Cambrian Explosion (541-485 million years ago): A significant increase in the diversity of life forms, including sponges, arthropods, and early vertebrates.

3. Ordovician Period (485-444 million years ago): Marked by the evolution of early jawless fish (agnathans).

4. Devonian Period (419-359 million years ago): Known as the "Age of Fishes," significant diversification of both jawless and jawed fish.

5. Transition to Terrestrial Life (Late Devonian): Evolution of tetrapods from lobe-finned fishes.

6. Mesozoic Era: Evolution of amphibians, reptiles, and birds marked key diversification events.

7. K/T Extinction Event (66 million years ago): Significant extinction of non-avian dinosaurs allowing mammals to diversify.

Factors Promoting Diversification

• Increased Oxygen Levels: Documented rise in oxygen during the Cambrian period supported more complex life forms.

• Ecological Niches: Formation of diverse habitats, such as lagoons, allowed for greater specialization and diversification.

• Evolution of Key Structures: Developments like jaws in vertebrates opened new feeding strategies.

• Genetic Mutations: Changes in genetics facilitated adaptations to varying environments.

Major Extinction Events

1. Late Ordovician Extinction: ~85% of marine species lost due to an ice age.

2. Late Devonian Extinction: Prolonged event affecting primarily marine life; significant losses among reef-building organisms.

3. Permian-Triassic Extinction: Most severe; ~96% of marine and ~70% of terrestrial vertebrates extinct, paving way for reptiles.

4. Triassic-Jurassic Extinction: Led to dominance of dinosaurs in the Jurassic period.

5. Cretaceous-Paleogene Extinction: ~75% of species, including non-avian dinosaurs, perished, leading to mammalian diversification afterward.