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External Characteristics:
~Thick and hard scales
~Waterproof skin
~Medium to large in size
~Wide jaws
~Large teeth
~Brown, Gray, Black, Olive, or sometimes greenish or reddish
~Strong, elongated skull
~Eyes and nostrils on top of head
Internal Characteristics:
~Cold-blooded
~Same characteristics as Reptiles (largest reptiles)
Behavior Characteristics:
~Carnivores
~Open mouth to keep cool
~Oviparous
~Build nests to protect babies
Habitat Characteristics:
~Live in or around water but can also survive on land
~Live in warm environments

https://www.thoughtco.com/guide-to-crocodilians-130685

https://a-z-animals.com/animals/crocodile/

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Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Alligatoridae
Genus: Alligator
Species: Alligator Mississippiensis

Comparison:
~Has the widest snout of the three organisms
~Moves fast on land
~Smallest of the organisms

https://a-z-animals.com/animals/alligator/

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Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Crocodylidae

Genus: Crocodylus
Species: Crocodylus Cataphractus

Comparison:
~Third transparent eyelid
~More pointed/V shaped snout
~Slower on land and in water than alligators

https://a-z-animals.com/animals/crocodile/
https://owlcation.com/stem/Whats-the-difference-between-alligators-and-crocodiles

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Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Crocodilia
Family: Gavialidae
Genus: Gavialis
Species: Gavialis gangeticus

Comparison:
~Has the longest, most slender snout of the organisms
~Bulbous growth at end of snout
~Weak legs that struggle to move on land

https://a-z-animals.com/animals/gharial/

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These three species are all related to each other because they have the same classifications up to the order (Crocodilia). This tells us that they must have evolved from the same species in order to be so closely related to one another. Taxonomy is an important way to show the relatedness of species because it shows how classification levels can be similar with related species.

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Directional Selection
Over time, crocodilians have adapted to organisms with the best possible traits. Like in crocodiles, those who are stronger and have a good smell attract females which is what will mate and over time produce more of. Also, in Gharials, males that have a loud noise and are strong will mate and reproduce leading to one side reproducing more than the other. These certain traits are more likely to be favored in an environment than other weaker traits. This is why an extreme phenotype is favored in a common crocodilian community.

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My taxonomic group has evolved from one species because of fossils recorded back to older times. These fossils have related structures that crocodilians have today. This also goes along with the common anatomy of certain organisms in my taxonomic group like the skull and body shape. These fossils help to show that they have evolved from one common ancestor. Also, the development of babies in my taxonomic group is the same, meaning that the way reproduction occurs has not changed. Lastly, the similarities between DNA and chromosomes in crocodilians add to the theory of Descent with Modification. All the organisms in my taxonomic group have 32 chromosomes with a very similar pattern in the structure. Overall, this evidence leads to the theory that over time crocodilians have evolved from one common ancestor with changes over time.

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~Emigration/Immigration does not impact the gene flow because the crocodilian species stays in the environment it is living in and does not migrate
~Each specific species in the taxonomic group has adapted based on the habitat it is living in
~Since the groups are not moving from habitat to habitat, the species will remain the same and change a little over time based on how the habitat the organism is living in changes
~This impacts evolution because it causes change to slow down because the organisms in the taxonomic group are not rapidly changing based on adapting to new settings

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Evolutionary Mechanisms: Nonrandom  Mating

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Evolutionary Mechanisms: Nonrandom  Mating

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~Mates are chosen off of characteristics meaning that it is not random and is selected by the best traits
~In Alligators, mates are chosen by aural, visual, tactile and olfactory cues along with smells
~In gharials, females use the gangus to impress males
~This influences evolution because only the best form of traits are passed onto the next generation
~The weaker traits in the taxonomic group dies out while the stronger thrives and changes the group as a whole
~If weaker traits were passed on it would influence how Crocodiles, Alligators, and Gharials look and act today

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Divergent Evolution
~The crocodilian species are diverging as time goes on because each species lives in different parts of the world
~Each organism in the taxonomic group has different conditions based on the environment it lives in
~The species will continue to grow apart because as the environment changes, the organism will change with it
~This leads to divergent evolution because the species will only grow farther apart from its ancestors as the habitat changes from what it used to be
~Alligators, Crocodiles, and Gharials evolved from the same species of Archosaurs and are close relatives of birds

https://news.ucsc.edu/2014/12/crocodile-genomes.html

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Gradual Speciation
~The changes in the crocodilian species are very slow
~Crocodilians are one of the most closely related species to their ancestors (Archosaurs)
~Very little change has occurred over the years meaning that the change in the species is extremely gradual
~Crocodiles, Alligators, and Gharials all have characteristics from their ancestors which has gone almost unchanged over time
~When changes do occur, they stay this way for a long period of time
For example; leg shape and jaw shape

https://news.ucsc.edu/2014/12/crocodile-genomes.html

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~Alligator, Crocodile, and Gharial babies are developed in the same way as each other
~All crocodilians reproduce by laying eggs
~These eggs are laid in nests built for incubation
~Most female crocodilians reach sexual maturity at an average of 10 years
~Gender is based upon the temperature of the nest
~All eggs hatch at the same time

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This diagram shows the three different species in my taxonomic group compared to some related species, and some species that are not so similar. The species in my taxonomic group have evolved from one similar species that is closely related to what it is now. This means that the traits that it has today are similar to the traits that the relative species had. The evolutionary key shows that the species in my group have not evolved that much because it is taking a slower time to evolve which is why it is so similar to its older species.

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DNA bar coding is used to find the differences between the different species in this taxonomic group. In one certain study, a partial cytochrome c oxidase subunit 1 gene is used as a marker to indicate the differences between two types of crocodiles and a gharial. This forensic study outlines the differences between the species by showing the differences between the alignment in the DNA of each organism. This technique also helps by showing the differences between each species of gharials and other crocodilians. Not only does it highlight the inter specific differences, but also the similarities created by the different species.

https://www.ncbi.nlm.nih.gov/pubmed/23718785

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Evidence of Evolution: Fossil Record Explanation

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Evidence of Evolution: Fossil Record Explanation

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The fossils found from earlier times in the past help to support the theory of evolution because these fossils are related to the bones found in crocodilians today. The shapes of the head, body, and legs show a close resemblance to the current crocodilian's bone structure.

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5. Mesosuchia
Age: Late Liassic to Early Jurassic

http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/Crocodylomorpha/Fossilrecord.html

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2. Sarcosuchus
Age: Early Cretaceous Period

http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/Crocodylomorpha/Fossilrecord.html

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Evidence of Evolution: Chromosomal Analysis

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Evidence of Evolution: Chromosomal Analysis

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Similarities:
~The alligator, crocodile, and gharial all have 16 pairs of chromosomes (32 overall)
~Chromosome 19 and 20 are small and round
~Chromosomes 26 and up are smaller, dot-like shapes in the karyotypes
~The beginning chromosomes of the karyotypes are long and opposite to the ending chromosomes
~No sex chromosomes found in crocodilians

Explanation: The similarities in chromosomes shows that the organisms are related internally by their structure. Not only are their bones similar but also the chromosomes inside of them. There is very little difference between the chromosomes in the different organisms meaning that they are very related.

https://www.ncbi.nlm.nih.gov/pubmed/7720416

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4. Protosuchia
Age: Late Triassic to Early Jurassic

http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/Crocodylomorpha/Fossilrecord.html

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3. Pelagosaurus
Age: Late Liassic to Early Jurassic

http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/Crocodylomorpha/Fossilrecord.html

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1. Borealosuchus Sternbergii
Age: Late Cretaceous to the Eucene

http://palaeo.gly.bris.ac.uk/Palaeofiles/Fossilgroups/Crocodylomorpha/Fossilrecord.html