The Transition of Life to Land Flashcards
For Exam 3, May 6th (25 cards)
What was the climate doing at the beginning of the Paleozoic?
The extensive glaciation of the Proterozoic was slowing down, and ocean levels began to rise as ice melted (warm temps and high sea levels)
What was the Great Ordovician Biodiversification Event (GOBE)?
A large increase in diversity of life:
- Expansion of species in lower level taxonomies (species, genera, family)
- More diverse ecological niches to reduce competition (such as tiering and burrowing to spread out the way things live)
How was the GOBE different from the Cambrian Explosion?
Cambrian - major groups of animals appear (higher level taxonomies) and pretty much everything lived in the same way (on the seafloor)
What is paedomorphosis? Why might it develop? What are some examples?
Retaining juvenile features as an adult (i.e. reaching sexual maturity at a younger age)
If the environment is stressful, it may be more useful to reach sexual maturity faster (short life span) or to have other features that make survival easier (such as cute juvenile features)
E.g. axolotls retain their juvenile gills despite having lungs
Dog evolution is also paedomorphic
What happened at the end of the Ordovician?
A large land mass headed towards the pole, leading to the formation of ice sheets
Runaway albedo and sea level fall (regression) led to mass extinction of marine organisms
After the Ordovician’s ups and downs (GOBE then mass extinction), we have the Devonian. What was beginning to form at this time? What was life doing?
Pangea
Plant were beginning to move to land
What sorts of challenges would plants have to deal with in order to survive the transition from water to land? What were some adaptations that helped deal with this?
Overcoming gravity, drying out, reproduction, and obtaining nutrients
Nutrients to stabilize the plant stem
Roots to physically anchor them and gather said nutrients
What features did the first plants on land have?
They were non-vascular (no specialized tissues to move water through their body)
- Size limited + close to the ground
- Live in moist places
- Reproduce through spores, which require constant moisture
E.g. moss
After non-vascular plants came to land, we see vascular ones follow. What features did they have?
Stronger stems; efficient transport of water and nutrients through their body; taller growth; development of real seeds
How did the development of seeds impact the spread of plant life on land?
Seeds have protective coverings that keep the embryos alive for a long time without drying out
This expands the dispersal of plants far away from the water
What climate shift did we see as plants spread across land? How do we know?
More plants = more photosynthesis = more oxygen = cooler temps
We can see this through proxy data of C13 (which was increasing, indicating a rise of photosynthesis b/c the C12 is breaking down)
Once plants go to land, so do animals. What challenges do they face in this transition?
Gravity, dehydration, reproduction, finding food, vision, hearing, smelling
What is an exaptation? How did these help animals their transition to land?
A structure that evolved for one function but is co-opted for another
Many aquatic animals had traits that helped them with the challenges of living on land
What were the first animals to move to land? What exaptations did they have?
Anthropods like insects and spiders
- Exoskeletons (external coatings that prevent them from drying out and provide physical support)
- Book lungs (flap-like structures that allow for breathing on land as long as there is some moisture)
Where did jaws in fish come from? Why would a fish have jaws?
Fish had multiple sets of gilled arches, two of which get larger and move forward to form jaws
This makes it easier to breath, but was later exapted for feeding
What are jawless vs jawed fish called?
Jawless = agnathans
Jaws = gnathostomes
What other exaptations did aquatic animals have for their move to land?
Lungs and limbs
Why would a fish have lungs?
Living in low oxygen aquatic environments
Getting extra oxygen from the air
Helpful for drought periods
Why would a fish have limbs?
Extra bones = sturdy structure = use them to push along the ground =
- Help them move between close bodies of water
- Temporarily escape danger to land
- Aid in shallow water hunting
What features do we see appear as animals became more terrestrial?
Loss of finned tails
Broad, heavy ribs to support internal organs and protect against gravity
Strengthened limb attachment areas
Separation from head and shoulders (neck muscles)
What transitional features did animals have at this time? (Both fish-like and land animal-like)
Scales, fins, gills, lungs, neck, ribs, flat head, ear notches
How did the climate of the late Devonian (caused by the spread of plants) aid animals in their transition to land?
The cool, wet climate helped them to stay moist and not dry out on land
What are amniotes?
Modern reptiles and mammals, which first appear in the fossil record at this time
What adaptations did early amniotes have?
Amniotic eggs: an embryo encased in layers of semi-permeable membranes that protect it from drying out
Skin coverings: scales prevent desiccation and protect them from UV light (scales can later be modified into armor, feathers, etc.)
