Marine Vertebrate Evolution

Intended Learning Outcomes

• Compare and contrast the evolutionary pathways of different marine vertebrate groups
• Identify homologous and analogous structures among marine vertebrates
• Analyze the functional adaptations in the body systems of marine vertebrates

Evolution

• Evolution describes changes in inherited traits of biological populations across generations
• Evolution explains how species arise, adapt, and sometimes face extinction due to genetic variations and environmental pressures

Key Aspects of Evolution

• Descent with Modification means offspring inherit traits from parents, but variations happen due to mutations, recombination, and other genetic processes
• Natural Selection leads organisms with advantageous traits to survive and reproduce more successfully, passing those traits to the next generation
• Genetic Drift describes random changes in allele frequencies over time, notably in small populations
• Mutation refers to changes in DNA sequences that create genetic diversity
• Speciation involves forming new species when populations diverge and become reproductively isolated

Evidence for Evolution

• Fossil Records show transitional forms between ancient and modern species
• Comparative Anatomy reveals similar structures in different species, suggesting common ancestry (homologous structures)
• Genetics shows DNA similarities to indicate evolutionary relationships
• Biogeography, or the distribution of species, supports evolutionary patterns
• Embryology reveals similar developmental stages in different species, pointing to shared ancestry

Evolutionary Relationships

• Evolutionary relationships are connections between species or organisms based on common ancestry and evolutionary history
• These relationships explain how different species are related and how they evolved from shared ancestors over time

Homologous Structures

• Homologous structures share the same origin but can have different functions
• An example is the forelimbs of humans, bats, whales, and cats, which have the same bone structure but serve different purposes
• Homologous Structures indicate common ancestry

Homology

• Similar structures that are due to shared ancestry may have different functions, such as the human arm and bat wing
• Homology is the result of divergent evolution, where species evolve different functions from a shared ancestral trait
• Homology helps in reconstructing evolutionary relationships or phylogeny
• Forelimbs of mammals like the human arm, whale flipper, and bat wing share bone structure despite different functions

Analogous Structures

• Analogous structures serve similar functions but have different evolutionary origins
• Wings of birds and insects are an example, both used for flying but evolved independently
• Analogous Structures indicate convergent evolution (different ancestors but similar adaptations due to similar environments)

Analogy

• Similar structures are due to similar function, not ancestry, as is seen in bird wings and insect wings
• Analogy results from similarity in structures due to convergent evolution, not common ancestry
• Different species evolve similar adaptations due to similar environmental pressures and functions
• Analogy shows how natural selection can lead to similar solutions in different evolutionary lineages
• Wings of birds, bats, and insects enable flying, but they evolved independently

Vestigial Structures

• Vestigial structures are body parts that have lost their original function through evolution
• Examples of Vestigial Structures include whale pelvis bones, the human appendix, and flightless bird wings
• Vestigial Structures indicate evolutionary change over time

Divergent Evolution

• Divergent Evolution happens when species with a common ancestor evolve into different forms by adapting to different environments
• Darwin's finches on the Galápagos Islands evolved different beak shapes based on their food sources

Divergent Evolution Characteristics

• Common ancestry is followed by different adaptations
• Groups from the same common ancestor evolve and accumulate differences, forming new species
• Divergent Evolution occurs as a response to changes in abiotic factors like a change in environmental conditions, or when a new niche becomes available
• Divergent Evolution takes place in response to changes in biotic factors such as increased or decreased pressure from competition or predation
• Divergent Evolution leads to speciation and works on the basis of variation within the gene pool of a population
  • Allopatric and peripatric speciation occurs when the reproductive barrier is caused by a physical or geographical barrier
  • Sympatric and parapatric speciation take place within the same geographical area
• Organisms may develop homologous structures which are anatomically similar structures that are present in the common ancestor that persist within the diverged organisms, although have evolved dissimilar functions

Convergent Evolution

• Convergent Evolution is when unrelated species develop similar traits due to similar environmental pressures
• Example: Sharks (fish) and dolphins (mammals) have streamlined bodies for swimming, despite being evolutionarily distant.

Convergent Evolution Characteristics

• There is different ancestry but similar adaptations, such as in sharks vs. Dolphins (streamlined bodies)
• Organisms that are not closely related independently evolve similar features
• Convergent Evolution causes the evolution of similar body forms, colors, organs, and other adaptions that make up the organism's phenotype
• Convergent Evolution creates analogous structures or 'homoplasies', which have similar forms or functions between diverged species but were not present in the common ancestor of the two
• Convergent Evolution occurs when organisms are required to adapt to similar environmental conditions and when two different organisms occupy a similar niche
• Convergent Evolution can rise through mimicry complexes where organisms evolve to replicate the morphology of other species
• Benefits from Mimicry
• Batesian mimicry benefits by way of protection when imitating the phenotype of an organism that is toxic or otherwise dangerous
• Müllerian mimicry benefits by mimicking the a resource or interaction by being mistaken for the model

Parallel Evolution

• Parallel evolution is when closely related species evolve in similar ways after diverging from a common ancestor
• Marsupials in Australia and placental mammals elsewhere (like flying squirrels) evolved similarly

Co-evolution

• Co-evolution is when two species evolve in response to each other
• Flowers and pollinators like hummingbirds and tubular flowers

Studying Evolutionary Relationships

• Phylogeny is the evolutionary history and relationships of species or groups of organisms
• Phylogeny deals with the evolutionary development of a species or group over time and is typically represented as a phylogenetic tree which is concerned with the historical development of a species from its evolutionary ancestors
• Phylogenetic Trees show evolutionary history and relationships among species
• Cladograms show how organisms are related based on shared characteristics
• Molecular Evidence or DNA and protein similarities help trace ancestry
• Ontogeny is the history of an individual.
  • It deals with the lifecycle of an organism within a single generation, the development of an individual organism from fertilization to maturity
  • Ontogeny is concerned with the individual development of an organism, including all stages of growth, from embryo to adult

Phylogeny & Ontogeny Comparison

• Phylogeny focuses on evolutionary relationships of species across generations, and its timeframe spans a long time in evolutionary history
• Phylogeny studies species or populations
• Ontogeny focuses on developmental stages of a single organism within the lifespan of an individual, studying individual organisms

Historical Predecessors to Evolution

• The concept of evolution is often associated with Charles Darwin, it predates him
• Ancient Greek philosophers proposed ideas about change in organisms over 2,500 years ago
  • Anaximanders of Miletus suggested a progression from fish-like creatures to land animals
  • Empedocles imagined bizarre combinations of beings, arguing that only practical forms survived
• Pre-Darwinian evolution ideas were more poetic than scientific, but laid the groundwork for evolution before Darwin

Ancient Times (~400 BCE - 1500s)

• ~400 BCE – Aristotle, "Father of Zoology," documented various marine vertebrates in Historia Animalium
• 77 CE – Pliny the Elder described marine life, fish, and marine mammals in Natural History
• Middle Ages (~500-1500s) – Knowledge of marine vertebrates remained stagnant and primarily recorded in folklore

Age of Exploration (1500s-1700s)

• 1500s-1600s – Ferdinand Magellan and Sir Francis Drake documented marine species during voyages
• 1692 – John Ray published Synopsis Methodica Animalium Quadrupedum et Serpentini Generis, a classification system for animals, including marine vertebrates

Carl von Linné (Carolus Linnaeus)

• Swedish biologist who believed species were fixed and unchangeable
• Created a naming system for plants and animals that forms the basis of modern taxonomy (binomial)
• Argued for the immutability of species, aligning with the biblical view of creation from Genesis

18th Century (1700s)

• 1735 – Carl Linnaeus introduced Systema Naturae, classifying marine vertebrates in his binomial nomenclature system
• 1768-1779 – Captain James Cook's voyages led to marine species discoveries thanks to naturalists like Joseph Banks documenting fish and marine mammals
• 1788 – Pierre Joseph Bonnaterre published Tableau Encyclopédique et Méthodique des Trois Règnes de la Nature, focusing on fish taxonomy

19th Century (1800s) - Foundations of Modern Marine Biology

• 1801 – Georges Cuvier published Le Règne Animal, establishing comparative anatomy and recognizing cetaceans as mammals
• 1839 – Charles Darwin's Voyage of the Beagle detailed marine vertebrate observations, influencing evolutionary theory
• 1859 – Darwin published On the Origin of Species, explaining natural selection and profoundly impacting marine vertebrate studies
• Charles Darwin's key contribution was not the idea of evolution itself but the conditions and mechanism behind it
  • Reproductive Potential causes species to increase in number if unchecked, leading to potential overpopulation
  • Competition As numbers grow, resources become scarce, resulting in individual competition
  • Natural Selection allows competition that selects those with superior adaptations, allowing them to pass on their traits

The Process Behind the Change

-Darwin emphasized observation over experimentation

• Fact: Establishing whether organisms change over time, which is well-supported by evidence
• Course: Understanding the evolution pathway, where scientists' disagreements arise
• Mechanism: Darwin asserts natural selection is the cause
• 1872-1876 – The HMS Challenger expedition extensively studied deep-sea fish and marine vertebrates
• 1890s – Louis Agassiz and Alexander Agassiz pioneered coral reef and fish studies, advancing marine vertebrate classification

20th Century (1900s) – Advances in Marine Science

• 1911 – William Beebe conducted deep-sea explorations and described deep-sea fishes
• 1934 – Beebe and Otis Barton used the Bathysphere to observe deep-sea marine vertebrates firsthand
• 1953 – Watson and Crick discovered DNA's structure, advancements in marine genetics and evolutionary studies
• 1960 – Jacques Piccard and Don Walsh descended to the Challenger Deep in the Trieste, observing deep-sea marine vertebrates
• 1977 – Hydrothermal vents and unique deep-sea fish communities were discovered by the Alvin submersible

21st Century (2000s-Present) - Modern Technological Advances

• 2000s – Satellite tagging and remote sensing revolutionized marine vertebrate tracking and conservation
• 2010 – The Census of Marine Life (2000-2010) provided a marine vertebrate database
• 2012 – James Cameron's Deepsea Challenger explored the Mariana Trench
• Present – Advances in genomics, Al, and autonomous underwater vehicles (AUVs) enhance marine vertebrate research and conservation

Marine Vertebrates Timeline

• Paleozoic Era (541-252 mya):
• Cambrian Period (541-485 mya): First chordates (early ancestor's of vertebrates) appear and Pikaia and Haikouichthys, primitive fish-like creatures emerge
• Ordovician Period (485-443 mya): Jawless fish (Agnatha), like ostracoderms, evolve, becoming the first true vertebrates and there is first evidence of cartilaginous and bony fish precursors
• Silurian Period (443-419 mya): Jawed fish (Gnathostomes) appear, including placoderms (armored fish) and Cartilaginous fish ancestors (Chondrichthyes), like early sharks such as the spiny sharks (Acanthodians), have emerged
• Devonian Period (419–359 mya): “Age of Fishes” Bony fish (Osteichthyes) diversify into lobe-finned fish (Sarcopterygii) and ray-finned fish (Actinopterygii)
  • Sharks and early ray-finned fish become dominant marine predators
  • First lungfish and coelacanths appear, some of which will give rise to tetrapods
• Carboniferous Period (359-299 mya): Cartilaginous fish (sharks and rays) diversify and First fully aquatic marine reptiles (early ancestors of ichthyosaurs) start evolving from amphibian-like tetrapods
• Permian Period (299-252 mya): Xenacanthus (freshwater shark relatives) dominate and The first marine reptiles appears, the Permian-Triassic mass extinction wipes out many marine species
• Mesozoic Era (252-66 mya)
  • Traissic Period (252-201 mya): Marine reptiles dominate, including Ichthyosaurs (fish-like reptiles) and Nothosaurs
    • There is first appearance of modern ray-finned fish and Early ancestors of sea turtles emerge.
  • Jurassic Period (201-145 mya): Ichthyosaurs thrive as top marine predators
  • Sharks and bony fish diversify, with some resembling modern species
  • Plesiosaurs and pliosaurs, long-necked and short-necked marine reptiles, evolve
  • First marine crocodiles (e.g., Metriorhynchus) appear -Cretaceous Period (145–66 mya): Mosasaurs dominate the oceans, modern sharks (Lamniformes) evolve, and Hesperornithiformes, flightless diving birds, emerge. In addition;
  • Ichthyosaurs decline and go extinct, and the End-Cretaceous mass extinction wipes out marine reptiles and many fish species
• Cenozoic Era (66 mya – Present)
  • Paleocene-Eocene Epochs (66-33 mya): Whales evolve from terrestrial ancestors, first modern sharks and rays appear and Lastly, early penguins evolve and adapt to marine environment
  • Oligocene-Miocene Epochs(33-5 mya): Domination of mammals such as whales seals, sea lions, etc
  • Pliocene-Pleistocene Epochs (5 mya –12,000 ya): Modern Whales, dolphins, and sea otters are evolved -Holocene Epoch (Present): Modern marine ecosystems are established and there's and human impact (overfishing, climate change, pollution)