Decent with modification

State Fossils, Early Vertebrates, and the Deep Time Narrative

• Spiders, ticks, scorpions are mentioned along with a fossil context; the state fossil of New York is a eurypterid (sea scorpion), an ancient arthropod representative from the early fossil record.
• The lecture frames a timeline: invertebrate chordates → the first vertebrate chordates → fishes → amphibians → reptiles → mammals.
• The discussion centers on the age of fishes, a key interval in vertebrate origin, and the transition toward tetrapods and land vertebrates.

The Age of Fishes and the Origin of Vertebrates

• Fishes mark the rise of vertebrates; the lineage then moves to amphibians, then to reptiles, then to mammals.
• Among fishes, the sarcopterygians (lobe-finned fishes) are highlighted as having fin-like limbs that eventually develop into legs (a prelude to tetrapods).
• These lobe-finned fishes could walk on the ocean bottom using leg-like fins.
• The coelacanth is highlighted as a famous example: a lobe-finned fish historically considered extinct for about $70\,\text{million years}$, until a living specimen was found.
  • The genus Latimeria was identified after a fishing vessel catch off South Africa; a captain alerted Marie Latimer (the director of the natural history museum there), who recognized the significance.
  • The discovery involved contacting a renowned ichthyologist; travel and verification were slower due to the era, but it confirmed the persistence of this ancient lineage.
  • Video footage and captive individuals have been observed since; anecdotes include a live specimen in captivity and a sighting in DC.

Visuals of Low-Pinned Fishes and Early Vertebrate Transitions

• Reference images show lobe-finned fishes as transitional forms toward tetrapods; the narrative emphasizes the morphological bridge from fins to limbs.
• Timeframe noted: continuing through the Paleozoic into the Mesozoic, with gaps in detail but a clear trajectory toward terrestrial vertebrates.

Amphibians and Stem Mammals: The Tetrapod Bridge

• In the Paleozoic to Mesozoic timeframe, skulls of sizable amphibians are described (they could reach sizes comparable to crocodilians).
• Some vertebrates near the fish-to-land transition are described as stem mammals, specifically synapsids, which have skull openings (single temporal opening) distinct from diapsids.
• The so-called sail-backed reptile is identified as a stem mammal: the organism often associated with Dimetrodon, a non-dinosaur, and not a true reptile.
• Distinctions:
  • Synapsids: lineage leading toward mammals; characterized by a single temporal opening in the skull.
  • Diapsids: lineage including the later dinosaurs, with two skull openings.
• The example of a sail-backed animal (often misnamed in casual discussions) is clarified as a stem mammal, not a dinosaur.

The Mesozoic Era: Dinosaurs and Hip Structure

• The Mesozoic is the “age of dinosaurs.” Dinosaurs captured popular imagination through media (e.g., Jurassic Park). Key points:
  • Theropods: bipedal dinosaurs (two-legged), including Tyrannosaurus rex and raptors (e.g., Coelophysis is referenced as a diaphysis-like genus; the exact spelling in the transcript shows some variability).
  • Saurischian vs Ornithischian hip structures are implied through discussion of hip anatomy; theropods are generally considered to be theropod saurischians.
  • Quadrapedal, lumbering herbivores include Triceratops, Stegosaurus, Ankylosaurus.
  • Predators versus herbivores: a mix of ecological roles across the groups.
• Stegosaurus: notable for two rows of plates along the back.
  • The plates were once thought to be primarily for defense; they may have had a role in thermoregulation as well, given the vertebrate physiology debates of the era.
• Theropods and other predators: emphasis on two-legged and often predatory lifestyles within the theropod group, with herbivorous counterparts in other lineages.
• Convergent evolution example: dolphins are cited as a non-dinosaur reptilian lineage that evolved a dolphin-like body shape due to marine environmental pressures, illustrating how similar selective pressures produce similar forms across distant lineages.

Marine Reptiles and Ichthyosaurs

• Large marine reptiles are described as apex predators of their time; several could reach sizes comparable to small whales.
• Ichthyosaurs: marine reptiles adapted to ocean life; some lineages gave live birth, with fossil evidence documenting birthing events.

Nautiloids and the Chambered Nautilus

• Nautiloids (including nautiluses) are emphasized as ancient cephalopods with chambered shells.
• Some nautiloids grew to very large sizes (the speaker notes seeing references to diameters up to about $8\,\text{ft}$ in books).
• The chambered nautilus (a living representative in the modern oceans) exists around the Philippines, Madagascar, the Pacific, and the Indian Ocean.
• How buoyancy works: the shell contains gas-filled chambers that render the animal neutrally buoyant, reducing the energy needed to stay afloat.
• The nautiloids are framed as an ancient predator group that existed long before the rise of fishes as dominant predators in some ocean realms.

The Cenozoic Era: Megalodon and Modern Marine Mammals

• The Cenozoic begins about $7.5\times 10^7\,\text{years ago}$ and continues to the present, marked by the rise of mammals.
• Megalodon (a huge prehistoric shark) is highlighted with a reconstructed jaw that could accommodate a large bite; a life-size replica jaw was shown to illustrate its enormous size and predation on large whales and other large fishes.
• Narwhals: a living representative of large cetaceans; a fossil narwhal skull was found in the Norfolk/Norwood area near the local campus, with faculty noting the discovery.

Neanderthals, Humans, and Interbreeding

• The skull of a Neanderthal is shown as a reference point for human evolution and diversity.
• Humans and Neanderthals interbred: Neanderthals are not a separate species from Homo sapiens; rather, they mixed with modern humans.
• A personal DNA reflection: the speaker mentions having about $85\%\%$ more Neanderthal DNA than other tested individuals (a tongue-in-cheek claim about individual ancestry);
  • This admission is tied to the idea that Neanderthal DNA is present in modern humans, with varying levels depending on ancestry, particularly Northern European populations who were cold-adapted.

Extinctions Through Deep Time

• The Paleozoic-to-Mesozoic transition is framed by the Great Die-off (Permian-Triassic extinction) as the largest known mass extinction event.
• The end of the Mesozoic (Cretaceous-Paleogene boundary, often denoted K-Pg), wiped out most dinosaurs and many other lineages while allowing birds (dinosaurs) and crocodilians to survive.
• Mammals were suppressed during much of the Mesozoic but rebounded afterward, giving rise to Cenozoic mammalian diversity.

North American Megafauna and Late Pleistocene Extinctions

• In North America, large mammals included mammoths (including woolly mammoths) and mastodons; they inhabited widespread regions
  • Both mammoths and mastodons persisted across North America and went extinct roughly around the end of the last Ice Age, around $1\,0\text{ thousand years ago}$, with estimates often centered near $10\,000\,\text{years ago}$.
• Extinction hypotheses include climate change and human hunting pressure, with evidence suggesting humans hunted these large mammals.
• Dog-assisted hunts are mentioned as a potential factor in the human-megavention dynamic.
• Other contemporaneous large mammals include rhino-like mammals, ground sloths, and large camel-like species in various North American habitats.
• For further study, the lecturer notes that natural history museums (e.g., Albany, Ottawa) house strong fossil collections relevant to these topics.

Administrative and Study Guidance

• The assignment for the next session involves answering questions in a provided report; the questions align with the material presented and are intended to be answerable given the lecture notes and textbook content.
• The expectation is to type up answers and bring them to the next class; an estimated hour of work is suggested for completing the task.
• The lecturer emphasizes that the material should be present in the report, and that the questions are designed to be answerable using the content from lectures and readings.

Key Takeaways and Connections

• Evolutionary throughlines: From invertebrate chordates to the earliest vertebrates; vertebrate evolution proceeds from fishes to tetrapods to amniotes, then to mammals.
• Major transitions: lobed-finned fishes as a bridge to land animals; synapsids as stem mammals; dinosaurs as major Mesozoic fauna with distinct hip anatomies; marine reptiles and cephalopods as dominant marine predators in their eras.
• Extinction and resilience: mass extinctions reshape life – mammalian radiations after the KT boundary; long-term shifts in predator-prey dynamics; the survival of birds and crocodiles across major extinction events.
• Human evolution and genetics: Neanderthal DNA admixture in modern humans; population differences in Neanderthal ancestry; implications for understanding human diversity and shared ancestry.
• Practical implications: fossil discoveries (e.g., Neanderthals, narwhals, ichthyosaurs) illuminate ancient environments, adaptive strategies, and the interconnectedness of life across deep time; museum collections can be valuable educational resources.

If you need this organized differently (e.g., more diagrams, a glossary, or a separate section for each time interval with dates and key taxa), tell me and I can adjust the notes accordingly.