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Invasion of the land

Page history last edited by Charles Forstbauer 10 years, 1 month ago

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Here's a video of evolution... starting with creatures of the water and ending with the evolution of land animals, this video also explains a bit about each picture and its time period.


Totaled 5/28 CF


Land Invasion

When invertebrates came onto land, their support system, respiratory system, reproductive methods, excretory system, and ways to regulate temperature did not match their new environment. Therefore, they had to adapt to their surroundings by changing the following:


1) Support

The vertebrates needed the structure of bones (muscles support bones), a higher density (water has a low density)


2) Water

a) Gills -> Now that the inverts were on land, and their gills needed O2, their gills had to be kept moist. Therefore, hiding in damp places like caves was ideal for them. Also, if their gills were not kept moist, they would mostly dry up causing the inverts to not be able to breathe and die, this was obviously one of the negative drawbacks for them to transfer on land.

b) Dont Sweat -> These land animals did not sweat, since they have scales, therefore they do not release water by sweating.

c) Eggs -> Their eggs developed waterproof layers to make sure the egg could survive on land instead of in water as it had previously. The eggs needed to be more durable, which caused eggs to develop a protective layer on the shell to keep the offspring safe.

d) Waste -> NH4, Uric Acid, Urea (In decreasing order of how strong each is) had to be condensed and excreted on land in different ways than in water, since in water how strong the animal's waste was did not matter. In the water, the animal could literally simply diffuse it out without a problem, continually pumping water through themselves (like a fish). On land, the waste had to be handled in a different manner. I am going to make an inference here, but i think this is how our bodies came to be more complex and advanced. On land animals need a system (excretory probably) to help get rid of this toxic waste safely, which is most likely why we have kidneys and bladders at our advantage.

e) These fish also had to figure out a way to keep water in. before they mostly tried to keep water out of their body, but now due to the lack of it, they must figure out a way to keep it in. 

3) Body Temperature

Water animals do not need to work hard to maintain their temperature.

Yet when these animals transferred over to land, the temperature was drastically different, causing cold-blooded animals to appear in hot environments. The only setback of these cold-blooded animals was that they move slower in colder temperatures. When temperatures go below 40 degrees F for Iguanas, for example, their bodies freeze and go into a hibernation mode.


Vertebrates are a well-known group of animals that includes mammals, birds, reptiles, amphibians, and fish. The defining characteristic of vertebrates is their backbone, an anatomical feature that first appeared in the fossil record about 500 million years ago, during the Ordovician period. In this article, we'll look at the various groups of vertebrates in the order in which they evolved to create a picture of how vertebrate evolution unfolded to the present day.


Jawless Fish (Class Agnatha)

The first vertebrates were the jawless fish (Class Agnatha). These fish-like animals had hard bony plates that covered their bodies and as their name implies, they did not have jaws. Additionally, these early fish did not have paired fins. The jawless fish are thought to have relied on filter feeding to capture their food, and most likely would have sucked water and debris from the seafloor into their mouth, releasing water and waste out of their gills.

The jawless fish that lived during the Ordovician period all went extinct by the end of the Devonian period. Yet today there are some species of fish that lack jaws (such as lampreys, and hagfish). These modern day jawless fish are not direct survivors of the Class Agnatha but are instead distant cousins of the cartilaginous fish.


Armored Fish (Class Placodermi)

The armored fish evolved during the Silurian period. Like their predecessors, they too lacked jaw bones but possessed paired fins. The armored fish diversified during the Devonian period but declined and fell into extinction by the end of the Permian period.


Cartilaginous Fish (Class Chondrichthyes)

Cartilaginous fish, better known as sharks, skates, and rays evolved during the Silurian period. Cartilaginous fish have skeletons composed of cartilage, not bone. They also differ from other fish in that they lack swim bladders and lungs.


Bony Fish (Class Osteichthyes)

Members of the Class Osteichthyes first arose during the late Silurian. The majority of modern fish belong to this group (note that some classification schemes recognize the Class Actnopterygii instead of Osteichthyes). Bony fish diverged into two groups, one that evolved into modern fish, the other that evolved into lungfish, lobe-finned fish, and fleshy-finned fish. The fleshy finned fish gave rise to the amphibians.


Amphibians (Class Amphibia)

Amphibians were the first vertebrates to venture out onto land. Early amphibians retained many fish-like characteristics but during the Carboniferous period amphibians diversified. They retained close ties to water though, producing fish-like eggs that lacked a hard protective coating and requiring moist environments to keep their skin damp. Additionally, amphibians underwent larval phases that were entirely aquatic and only the adult animals were able to tackle land habitats.


Reptiles (Class Reptilia)

Reptiles arose during the Carboniferous period and quickly took over as the dominant vertebrate of the land. Reptiles freed themselves from aquatic habitats where amphibians had not. Reptiles developed hard-shelled eggs that could be laid on dry land. They had dry skin made of scales that served as protection and helped retain moisture. Reptiles developed larger and more powerful legs than those of amphibians. The placement of the reptilian legs beneath the body (instead of at the side as in amphibians) enabled them greater mobility.


Birds (Class Aves)

Sometime during the early Jurassic, two groups of reptiles gained the ability to fly and one of these groups later gave rise to the birds. Birds developed a range of adaptations that enabled flight such as feathers, hollow bones, and warm-bloodedness.

Mammals (Class Mammalia)

Mammals, like birds, evolved from a reptilian ancestor. Mammals developed a four-chambered heart, hair covering, and most do not lay eggs and instead give birth to live young (the exception is the monotremes).


Progression of Vertebrate Evolution

The following table shows the progression of vertebrate evolution (organisms listed at the top of the table evolved earlier than those lower in the table :

Animal Group Key Features
Jawless Fish - no jaws
- no paired fins
- gave rise to placoderms, cartilaginous and bony fish
Placoderms - no jaws
- armored fish
Cartilaginous fish - cartilage skeletons
- no swim bladder
- no lungs
- internal fertilization
Bony fish - gills
- lungs
- swim bladder
- some developed fleshy fins (gave rise to amphibians)
Amphibians - first vertebrates to venture out onto land
- remained quite tied to aquatic habitats
- external fertilization
- eggs had no amnion or shell
- moist skin
Reptiles - scales
- hard-shelled eggs
- stronger legs positioned directly beneath body
Birds - feathers
- hollow bones
Mammals - fur
- mammary glands
- warmblooded


This is a really interesting article about why animals left the sea for land. They explain things such as how we evolved from walking with 4 legs to walking on 2, with specific research to back it up. For example, a biological anthropologist in the Washington University of St. Louis found that walking on two legs costs humans only one-quarter the energy used by chimpanzees that knuckle-walk on four legs.

Here is the link to the article on livescience.com = http://www.msnbc.msn.com/id/20265184/ns/technology_and_science-science/page/2/


This website has many different types of reasonings to why and how animals went from sea to sea/land animals to land animals.  



Evolved Lungs 

     Fish exchange gases through their gills, which are usually covered by a hard surrounding.  However once animals began to come onto land, gills wouldn't have been as efficienct because they would dry out, and diffusion happens in wet surfaces.  For this reason animals began to get internal lungs that could be kept moist so that gasses could diffuse.


Different Nitrogenous waste

     Fish get rid of there nitrogenouse waste with a very toxic ammonia.  Since they swim and llive in water, they can get away with it.  But on land, the waste needs to be less concentrated, and this is done with water being added.  This started with Urea , and then even the Uric Acid that humans have which is 95% water.


Cold to Warm Blooded 

     Water temperature changes very slowley compared to air temperature.  That is why fish are well off being cold blooded, however many reptiles would benefit being warm blooded.  With the rapidly changing climate on land, many species evolved to having warm blood.  This is something that was needed to evolve because with warm blood, and animal could survive in all kinds of conditions differing in climate, while a cold blooded animal would need to "warm up."


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This video shows why being cold blooded is a disadvantage.  As the temperatures drop, the cold blooded iguana cannot function properly because it cannot produce its own heat which is necessary for body functioning.  At this point it is vulnerable to pretators, which is why being warm blooded on land is an advantage.

     Being warm blooded does however come at a price.  Maintaining warm blood takes energy, which is why it is not always advantages.  Animals use most of the energy that they consume through food to maintain their body temperature, which makes less for attaining mass.  Therefore while animals can live just about anywhere on land because of their warm blood, they need to consume more to maintain that warm blood.


Cartilage to Bones

     Bones serve a very important role in the invasion of land.  Fish can regulate the amount of gasses that they have in their system in order to swim at whatever water level they need to.  This is important because without needing bigger muscles to support themselves, fish dont need bones for that muscle to attach to.  But on land, the densities of the air and body differ much greater, therefore the need for bigger muscles to support the animal, and in return denser and stronger bones for the muscles to attach to.

     A rib cage is a good example of this in two different ways.

          1.  The denser bones are perfect for attaching muscles to that are important for the movement of an animal.  With cartilage, the muscles would have to be much smaller in order not to break the cartilage, which would not allow the animal to be an effective predator.

          2.  The ribcage also helps with respiration.  Since the lungs have to be kept inside of the body, the oxygen needs to be brought into the lungs.  Before with diffusion in the gills, the oxygen was just there in the water.  But on land, a diaphragm is needed to move the lungs to inhale and exhale gasses.  This could only be done with bones strong enough to allow such a muscle to attach itself and contract.

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