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Age of Animals

Cretaceous Period, 145.0 - 66.0 MYA + 2025 Update

Cretaceous Period
  • FA flowering plants (angiosperms) - The modern types of flowering plant became common some time in the middle of the Cretaceous. Hardwood trees slowly replaced the conifers as the dominant trees of the forests (see Figure 09a). These new plants provided fruits, flowers and nectar as new sources of food, causing great changes in all life on land.
  • Dinosaurs continued to dominate the land. But the fauna was very different from that of the late Jurassic. Large sauropods were rare, and the medium-sized coelurosaurs had been replaced by the ostrich-like ornithomimids, which included the duck-billed hadrosaurs and the armoured ankylosaurs and ceratopsians. The 30 feet long sea monsters called mosasaurs were the descendants of nothosaurs.
  • Carnivorous mammals such as Repenomamus were beginning to come out of the shadows. A complete fossil of this animal was found at the base of the Yixian Formation in northeastern China. On its left side, under the ribs where a mammal's stomach might well have been, lies a fragmentary and disarticulated skeleton of a young dinosaur about 14 cm long. The devourer of this little dinosaur was more than a meter long, and is estimated to have weighed 4 - 6 kg.

Figure 09a Cretaceous Period [view large image]
  • The smallest North American dinosaur fossil (50 cm high, weighed 2 kg) has been identified to be predator of small animals. The clawed dinosaur was slight, ran on two legs and had dagger-like teeth. It had an enlarged sickle-shaped claw on its second toe. This cat-sized dinosaur is called Hesperonychus (western claw).
    		•
    Cat-like Crocodile Another cat-like fossil by the name of Pakasuchus was uncovered in East Africa. It seems that this creature had embarked on a failed attempt to evolve from crocodile to cat around 100 million years ago. It has nasal openings on the front of their skulls implying land living. By contrast, surviving crocodilians all have nares on the tops of their heads for breathing while partially submerged. The specimen had a short, broad, cat-like skull but the bone arrangement is otherwise distinctively crocodilian. It had mammalian teeth but retained the scaly armour on its tail. At about 50 cm long from nose to tail, these reptiles would have been active, agile hunters of insects and other small preys. This kind of creature disappeared around the same time as the

    Figure 09b Cat-like Crocodile [view large image]

    		 extinction of dinosaurs. But the ancestors of modern crocodiles were able to weather the storm and prosper ever since.
  • A cretaceous dinosaur fossil (Tianyulong Confuciusi) with long feather-like structures sticking up from its body has been discovered in Liaoning, China (Figure 09c). Based on the bones present, it looks like it was small, active, agile, and probably eating a mix of insects, small vertebrates and plants. This one is special because it is from the lineage of which is ornithischian,
    Tianyulong Dinosaur Skin Characteristics thought to become extinct at the end of the Triassic Period, and the feathered dinosaurs belong exclusively to the saurischian lineage (Figure 09d). It is suggested that if these are protofeathers, then they might not related in any way to flight. The fact that the filaments over the tail are so long and stiff, points to a possible display function. Figure 09d shows the progression of dinosaur skin characteristics from scaly skin to

    Figure 09c Tianyulong Confuciusi [view large image]

    Figure 09d Dinosaur Skin Characteristics

    		filamentous proto-feathers and onto pennaceous feathers. This surprising discovery raises fresh questions about the evolution of feathers.
  • There was another mass extinction of marine and land life forms at the end of the Cretaceous period. Principal casualties are the dinosaurs and ammonites. A 10 km diameter asteroid hit the north coast of the present-day Yucatan (the impact created a sharp sediment boundary between the Cretaceous and the Tertiary periods called the K-T boundary). It caused about 75% of the previously existing plant and animal species to disappear. No species of land animal weighing more than about 25 kg survived into the Tertiary.


    • [2025 Update]

    Can you describe the sequence of events that caused the extinction of the dinosaurs?

    ChatGPT said:
    The extinction of the dinosaurs, known as the Cretaceous-Paleogene (K-Pg,     also known as K-T) extinction event, occurred approximately 66 million years ago and was a complex sequence of events triggered by an asteroid impact, compounded by other environmental factors.
    Here's an outline of the likely sequence:
    ________________________________________
    1. The Asteroid Impact
    " Size and Location: A 10-15 kilometer-wide asteroid struck the Yucatán Peninsula, forming the Chicxulub crater.
    " Initial Effects:
    o Extreme heat: The impact released immense energy, creating temperatures high enough to incinerate nearby life instantly.
    o Shockwaves: The collision generated powerful seismic waves, causing massive earthquakes and tsunamis.
    ________________________________________
    2. Global Firestorms and Dust Ejection
    " Ejected Material: Billions of tons of rock and sulfur were vaporized and blasted into the atmosphere.
    " Firestorms: Friction from the re-entering debris heated the atmosphere, sparking global wildfires.
    " Dust Cloud: A thick layer of debris enveloped the planet, blocking sunlight.
    ________________________________________
    3. "Impact Winter"
    " Darkened Skies: The lack of sunlight caused a dramatic drop in temperatures, leading to a "nuclear winter"-like effect.
    " Photosynthesis Collapse: Plants and phytoplankton, the base of the food chain, could no longer perform photosynthesis, disrupting ecosystems worldwide.
    ________________________________________
    4. Acid Rain and Ocean Acidification
    " Sulfur Aerosols: Vaporized sulfur reacted with water to form sulfuric acid, resulting in acid rain.
    " Ocean Chemistry: Acidification of the oceans harmed marine life, especially organisms with calcium carbonate shells.
    ________________________________________
    5. Long-Term Effects
    " Climate Instability: The Earth's climate fluctuated between cooling (from the dust cloud) and warming (from increased CO2 from fires and decomposing biomass).
    " Mass Extinctions: About 75% of species, including all non-avian dinosaurs, went extinct. Survivors included small mammals, birds, and certain reptiles.
    ________________________________________
    6. Compounding Factors
    " Deccan Traps Volcanism: Massive volcanic eruptions in present-day India occurred around the same time, releasing greenhouse gases and further stressing ecosystems.
    " Synergistic     (combined effect greater than the sum of their separate effects) Stress: The combined effects of the asteroid impact and volcanic activity created an environment too hostile for most species.
    ________________________________________
    Recovery and the Rise of Mammals
    " After the extinction, ecological niches     (un-occupied place "suitable for life") opened up, allowing mammals to diversify and eventually dominate terrestrial ecosystems.
    ________________________________________
    This sequence highlights the interplay of catastrophic events that led to one of Earth's most dramatic mass extinctions.

    See a 36 mins video on "Dino-extinction"

     Why and how do smaller animals survive the impact?

    ChatGPT said:
    Smaller animals had several advantages that increased their chances of survival during the catastrophic events of the Cretaceous-Paleogene (K-Pg) extinction. Here's a breakdown of why and how smaller animals survived:
    ________________________________________
    Why Smaller Animals Survived
    1. Lower Food Requirements
    o Smaller animals needed less food to survive compared to large dinosaurs, which required vast amounts of plant or animal matter.
    o In the aftermath of the asteroid impact, global food chains collapsed, favoring organisms with minimal energy needs.
    2. Burrowing and Shelter
    o Many small animals, like mammals and certain reptiles, could burrow underground or hide in sheltered environments.
    o These refuges provided protection from extreme heat, firestorms, and the harsh conditions of the "impact winter."
    3. Generalist Diets
    o Small survivors often had adaptable, generalist diets. They could eat a wide variety of foods, including seeds, insects, and detritus, which remained available even in devastated ecosystems.
    4. Thermoregulation
    o Some small animals, like mammals, were warm-blooded, enabling them to maintain body heat in the cold, dark post-impact world.
    o Others, like reptiles and amphibians, were cold-blooded but could slow their metabolisms, helping them endure periods of scarcity.
    5. Reproductive Strategies
    o Short lifespans and high reproductive rates allowed smaller animals to recover their populations quickly after the extinction event.
    ________________________________________
    How Smaller Animals Survived
    1. Burrowing and Hiding
    o Animals such as early mammals and burrowing reptiles sought refuge underground or in crevices, protecting them from the initial heat blast, falling debris, and subsequent fires.
    2. Exploiting Niches
    o After the extinction of larger species, smaller animals moved into ecological niches with reduced competition.
    o Detritivores (organisms that feed on dead organic material) thrived on the abundance of decaying matter.
    3. Dormancy and Hibernation
    o Some species could enter dormant states (e.g., torpor or estivation), conserving energy during periods of food scarcity and extreme cold.
    4. Mobility and Small-Scale Ecosystems
    o Smaller animals required less space and could exploit microhabitats that larger animals couldn't.
    o They could also migrate more easily to areas with slightly better conditions.
    5. Resilience to Environmental Stress
    o With simpler biological systems and smaller size, many species were better suited to survive rapid changes in temperature and habitat compared to large, specialized dinosaurs.
    ________________________________________
    Examples of Survivors
    " Mammals: Burrowing or semi-aquatic mammals fed on insects and seeds.
    " Birds: As descendants of dinosaurs, birds that were small and adaptable survived by feeding on seeds or scavenging.
    " Amphibians and Reptiles: Many reptiles and amphibians endured due to their lower metabolic rates and ability to enter states of metabolic inactivity.
    " Insects: Insects with short life cycles and high reproductive rates quickly repopulated the devastated landscapes.
    ________________________________________

    In summary, small animals survived the extinction event through a combination of physical traits (size, metabolism, sheltering behaviors) and ecological adaptability (generalist diets, resilience). Their survival allowed them to thrive and diversify in the post-impact world, eventually shaping the modern biosphere.

     The strategy for life in adverse environments starts from hibernation to immobilize deep underground. Can you fill in their response in between these extremes?

    ChatGPT said:
    Life strategies for survival in adverse environments likely form a continuum between the extremes of active hibernation and total immobilization. Here's how these strategies might be filled in:
    1. Active Hibernation
    " Key Features:
    o Reduced metabolic rate to conserve energy.
    o Periodic activity to maintain homeostasis, repair damage, or respond to stressors.
    " Examples:
    o Earth microbes like Deinococcus radiodurans can remain dormant but repair DNA rapidly when conditions improve.
    o Arctic ground squirrels hibernate and lower body temperature close to freezing but periodically rewarm.
    ________________________________________
    2. Dormancy with Occasional Activity
    " Key Features:
    o Organisms remain in a dormant state until triggered by environmental cues (e.g., temperature, moisture, or light).
    " Examples:
    o Desert plants like resurrection ferns can survive prolonged desiccation, only reviving when rehydrated.
    o Spores of bacteria like Bacillus subtilis stay dormant until they detect favorable conditions.
    ________________________________________
    3. Metabolic Reduction
    " Key Features:
    o Cells maintain essential functions (e.g., ion gradients across membranes, minimal ATP synthesis) while drastically slowing growth and reproduction.
    " Examples:
    o Certain deep-ocean microbes maintain life at extremely low energy fluxes, akin to "barely alive."
    " Implication for Extraterrestrial Life:
    o On Mars or Europa, life in subsurface brines might rely on trace metabolic activity, using radiolysis products or geothermal energy.
    ________________________________________
    4. Energy Hoarding
    " Key Features:
    o Storage of energy-rich compounds during favorable periods for use during prolonged harsh conditions.
    " Examples:
    o Arctic tundra animals store fat reserves.
    o Microbes accumulate polyhydroxyalkanoates (PHA), a biopolymer, for energy storage.
    ________________________________________
    5. Adaptive Symbiosis
    " Key Features:
    o Organisms partner to share resources, mitigating environmental challenges.
    " Examples:
    o Lichens, a partnership between fungi and photosynthetic algae or cyanobacteria, thrive in harsh conditions by combining strengths.
    " Implication for Extraterrestrial Life:
    o Symbiosis might be essential for survival in extreme environments, where one organism scavenges energy from inorganic reactions and shares it.
    ________________________________________
    6. Extreme Longevity Mechanisms
    " Key Features:
    o Organisms evolve highly durable molecular machinery to survive over geological timescales.
    " Examples:
    o Tardigrades survive extreme radiation by producing damage-protective proteins.
    o Seeds and spores remain viable for thousands of years in permafrost or deserts.
    ________________________________________
    7. Quasi-Immobilization
    " Key Features:
    o Life enters a state of molecular stasis, with all non-critical functions halted.
    " Examples:
    o Bacteria encased in salt crystals (Halobacterium) show metabolic traces even after tens of thousands of years.
    " Relevance to Mars:
    o Deep subsurface microbes might live in salt deposits, metabolizing very slowly due to low water activity.
    ________________________________________
    8. Complete Immobilization
    " Key Features:
    o Organisms suspend all activity, existing in a vitrified or desiccated state until rehydration or energy input resumes processes.
    " Examples:
    o Anhydrobiotic organisms, such as tardigrades and rotifers, survive by replacing water in their cells with protective sugars.
    o Microbes in Antarctica's frozen lakes endure immobilized states but revive when summer light melts surface ice.
    ________________________________________

    Evolutionary Implications
    Life adapting to extremes tends to prioritize durability, resource efficiency, and adaptability over rapid growth or reproduction. This trade-off allows survival in niches previously considered uninhabitable.
    ________________________________________

    Extraterrestrial Insights
    On Mars, Europa, or Enceladus, similar strategies may dominate:
    " Mars: Dormancy or extreme longevity might help life survive long dry spells underground.
    " Europa/Enceladus: Adaptive symbiosis and slow metabolic reduction could sustain life in energy-limited oceans beneath icy crusts.
    ________________________________________
    Mars
    " Environment:
    o Extremely cold (-125°C to 20°C).
    o Thin atmosphere, high radiation.
    o Subsurface water ice and brines.
    o Limited energy sources (e.g., trace geothermal heat, radiolysis).
    Applicable Strategies:
    1. Active Hibernation
    o Microbes in Martian regolith might remain dormant but "wake" periodically to repair radiation damage or metabolize transient brine moisture.
    o Similar to Earth microbes that survive freeze-thaw cycles in Antarctic permafrost.
    2. Dormancy with Occasional Activity
    o Dormant microbes could activate during rare periods of subsurface brine formation from thawing ice.
    o Seasonal variations might trigger metabolic bursts.
    3. Metabolic Reduction
    o Subsurface life near geothermal hot spots may operate on minimal energy, using radiolytic hydrogen or oxidants like perchlorates for metabolism.
    4. Energy Hoarding
    o Microbial cells might accumulate polyhydroxyalkanoates (PHA) during rare energy-rich events, sustaining them for decades.
    5. Extreme Longevity Mechanisms
    o DNA-repair proteins or protective sugars might shield cells from desiccation and radiation for millions of years.
    o Similar to ancient bacteria found viable in Earth's salt crystals.
    6. Quasi-Immobilization
    o Life deep underground might be encased in briny pockets, metabolizing trace amounts of hydrogen or methane over geologic timescales.
    ________________________________________
    Europa (moon of Jupiter)
    " Environment:
    o Subsurface global ocean beneath ~10-30 km of ice.
    o Cryovolcanism and tidal heating provide geothermal energy.
    o Potential hydrothermal vents.
    o Likely low chemical energy availability.
    Applicable Strategies:
    1. Active Hibernation
    o Microbes near hydrothermal vents could hibernate between nutrient influx events.
    2. Dormancy with Occasional Activity
    o Periodic activity might coincide with cryovolcanic or hydrothermal events introducing nutrients into local environments.
    3. Metabolic Reduction
    o Life could subsist at extremely low metabolic rates, utilizing trace chemical energy from hydrothermal activity or radiolysis-derived compounds (H2_22, O2_22).
    4. Adaptive Symbiosis
    o Symbiotic communities near vents could share resources: chemosynthetic microbes providing energy to others in exchange for nutrients.
    5. Extreme Longevity Mechanisms
    o Protective adaptations (e.g., stable membrane structures) could allow survival during extended periods of nutrient scarcity.
    6. Energy Hoarding
    o Organisms might store energy during nutrient-rich events to endure long spans of scarcity.
    7. Quasi-Immobilization
    o Microscopic life could persist in slow, quasi-stationary states within the water column, relying on minimal energy inputs from vent chemistry.
    ________________________________________
    Enceladus (moon of Saturn)
    " Environment:
    o Subsurface ocean beneath an icy crust (~20-30 km thick).
    o Jets of water vapor and organic molecules escape from surface cracks.
    o Similar to Europa but with periodic water-ice exchanges with the surface.
    Applicable Strategies:
    1. Active Hibernation
    o Microbes might activate briefly during nutrient influx caused by tidal stress and ice-water mixing.
    2. Metabolic Reduction
    o Life in the deep ocean could use radiolysis byproducts or hydrothermal energy at the ocean floor to persist in a nearly dormant state.
    3. Energy Hoarding
    o Organisms could hoard energy during active periods near hydrothermal vents or nutrient-rich currents caused by tidal forces.
    4. Dormancy with Occasional Activity
    o Cryovolcanism and tidal flexing might intermittently release nutrients, allowing bursts of metabolic activity.
    5. Adaptive Symbiosis
    o Organisms might form mutualistic communities, maximizing resource utilization in nutrient-poor waters.
    6. Extreme Longevity Mechanisms
    o Membrane and protein stability could enable survival over millions of years, with occasional periods of revival.
    ________________________________________
    Key Takeaways:
    " Mars likely favors extreme dormancy, metabolic reduction, and quasi-immobilization due to limited liquid water and energy.
    " Europa and Enceladus may support more dynamic strategies, such as adaptive symbiosis or dormancy with occasional activity, near hydrothermal vents or nutrient-rich zones.
    " All these environments push life to its limits, relying on highly efficient, long-term survival mechanisms.

    , ________________________________________
    See video of Europa and Enceladus.

    BTW,
    Jupiter and Saturn's positions beyond the frost line, coupled with their large cores and the availability of gas in the protoplanetary disk, enabled them to grow into gas giants. Closer to the Sun, where rocky planets formed, and farther out, where icy but less massive planets like Uranus and Neptune exist, the conditions weren't favorable for forming gas giants.

     [End of 2025 Update}

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