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They are difficult to analyze in terms of origins, and scientists have debated which is the closest relative to the shelled creature for a long time. Some say that they come from reptiles, others maintain they are related to snakes, while some place them in the same category as birds.The embryology further proves the ancestry of turtles coming from birds. The turtle is almost exact compared to a chicken except for the turtle's shell.

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Lower Cretaceous (~120 m.y.a.)

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Descent with Modification -
It is passing traits from parent to offspring. The fact of any type of turtle or tortoise is helping make or laying hundreds of eggs to be hatched shows descent. Over the millions of years, the children are slightly changing to become better. They are evolving to fix themselves to hopefully live longer such as over time, building up a shell that covers a turtles entire body. Or the claws on fins or legs to help mate.
Natural Selection -
After analyzing the evolution of Testudines, they follow stabilizing selection. Over time, the extremes in the population that are unlike other are usually the ones to be killed off. The turtles with the mixed color or the tortoise with the medium-length claw is more likely to survive than a light green tuetle or a tortoise with almost no claws.

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Turtles have been evolving for about 220 million years. They evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell that offered protection at every stage of its evolution. Turtles most likely had a gradualism evolution due to the progress and change over such a long period. Examples were shown in the protein analysis and the anatomical similarities.

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Sea turtles have flippers on with small claws only for mating due to them constantly being in the ocean

Snapping turtles have webbed toes and claws for mating, swimming, as well as moving on land

Giant Tortoises don’t have any flippers, webbing, or claws because they spend the large majority of their lives on dry land

They changed their flippers and claws due to the changing habitats

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Having the taxonomic classification shows the relatedness between multiple organisms. It shows going down the list how many categories they have in common, the more they relate, the more similar the organism.

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Animals are eukaryotic, multicellular and heterotrophic organisms

They have multiple cells with mitochondria

They depend on other organisms for food

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It was the giant tortoise that tipped Darwin off to the diversity of the Galapagos.

In the form of one particular individual, Lonesome George, the sole surviving member of the Pinta Island race, the giant tortoise is the symbol of extreme fragility of the Galapagos islands, and a reminder of the need for conservation.

The Galapagos tortoises are native to seven of the Galapagos Islands

It has impacted the giant tortoise population by helping it grow, many tortoises were becoming extinct and them being able to separate and make their own species, they would grow as a total population

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the male mounts the back of the female

mating takes place at any point throughout the year but has seasonal peaks between January and August.

males compete for mates by standing on their hind legs and stretching their necks out to see whose is higher

the shorter turtle backs off and the more dominant continues mating.

Males bellow loudly and bob their heads to attract females

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between April and November (warm weather)

takes place in water

males mount the females and insert their tails into the cloacal

females will often store sperm from males for future mating seasons so they can still lay eggs but don’t need a mate

Hatchlings emerge from their soft shells 55 to 125 days after the mama snapping turtle lays the eggs

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Common Name: Giant Tortoise
Kingdom: Animalia
Phylum: Chordata
Class: Sauropsida
Order: Testudines
Family: Testudinidae
Genus: Chelonoidis
Species: Aldabrachelys

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Common Name: Snapping Turtle
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Family: Chelydridae
Genus: Chelydra
Species: Chelonia Serpentina

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Common Name: Sea turtle
Kingdom: Animalia
Phylum: Chordata
Class: Reptilia
Order: Testudines
Family: Cheloniidae
Genus: Chelonia
Species: Chelonia Mydas

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Mating season occurs several weeks prior to nesting season

Nonrandom mating

During the warmer months

Two or more males may mate with a single female

Claws on males are used to grasp females while mating

Mating occurs in water at the surface or underneath the water.

Several males will compete for a female

Females mate with multiple males to 1-fertilize all her eggs and 2-ensure diversity of population

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Giant tortoises have two drastically different shaped shells in their subspecies

The effectiveness of the two shells is one, the dome shaped shell

The domed tortoises tend to be much larger in size and do not have the upward thrust to the front of their carapace; they live on the larger, higher islands with humid highlands where forage is generally abundant and easily available

Saddle-backed shells evolved on the arid islands in response to the lack of available food during drought.  The front of the carapace angles upward, allowing the tortoise to extend its head higher to reach the higher vegetation, such as cactus pads.

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Snapping turtles are well known for their powerful jaws

The use of their jaws is to clamp down on their prey without fail

The force of jaw relates to the size of prey they are trying to attract and kill

Common snapping turtles can clamp down with up to 656.81 newtons (N) of force

The Alligator snapping turtles usually exert 158 N

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A sea turtles flippers varies between the different species

The use of claws on their fins relate to mating habits and the time spent on land

Green Sea turtle - their large size in the water makes the large flat flippers necessary to propel through the water but have no claws due to the lack of need of having them

Leather Back sea turtles - they have claws that reach out of both front flippers to help grip way out of the sand when laying eggs on land

Flat Back sea turtles - they have one claw on each flipper used for digging, mating, and eating

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Green sea turtles weight is from 550 lbs to 1,500 lbs

Giant tortoise length ranges from 3 feet to 5 feel long

Snapping turtles have a shell variation between 8 and 18.5 inches long

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This is possible phylogenetic tree for the Green Sea Turtle.
They are set apart from all other animals by their shell. This shell is not an exoskeleton. It is a modified rib cage. This tree shows how turtles are far from crocodile relationships and are able to be divided by their diversity as a species.

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Turtles posses diverse chromosome numbers taken from extensive genomic rearrangements

Rates of evolution in turtle chromosome number are higher along phylogenetic branches where changes between sex-determining mechanisms also occur, showing strong coevolution of these traits.

Directional tests indicate that both traits evolved effectively at the same time.

This occurred near global extremes in temperature shifts over the last 200 million years

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Scientists have decoded the genome of the western painted turtle, one of the most abundant turtles on Earth.

Finding clues to their long life and ability to survive without oxygen during long winters spent hibernating in ice-covered ponds.

Comparing the turtle’s DNA to other animals, the scientists show that turtles are more closely related to birds than to lizards and snakes.

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Various alternatives for the position of the turtles have been proposed, branching off either before or after the mammals

cDNA sequences have been determined for the eye lens proteins αA- and αB-crystallin of the red-eared slider turtle

All sequences were analyzed by three phylogenetic tree reconstruction methods

7 out of 12 proteins support a sister-group relation of turtles and birds with all 3 methods

Analyses of the combined amino acid data give strong evidence that turtles are nearer to birds, showing that mammals branched off before the divergence between turtles and birds occurred

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Micro-chromosomes are indicated in dark grey. The sex chromosomes present in the homo-gametic sex are shown for representative species and alternatives present in each are indicated.
They all compare drastically, the turtle compared to the central bearded dragon look quite similar while keeping in perspective that they are both reptiles. Comparing a turtles karyotype to a humans shows their vast differences.

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Reptiles occupy a key position in vertebrate evolution by sharing the common ancestor to birds and mammals. They are likely to play a critical role by providing information to help understand genome organization and evolution in birds and mammals. The first step in learning how the genomes of this diverse group have evolved is to establish the level of conservation between different reptilian species, as well as more broadly with birds and mammals.

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Adaptive Radiation in the Galapagos Islands

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Adaptive Radiation in the Galapagos Islands

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Each island has a different subspecies of tortoise

On some larger islands there are more than one subspecies

Examples include:

Island N. Isabela - subspecies becki

Island Pinzon - subspecies duncanensis

Island Pinta - subspecies abingdoni

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The skeletal structures of forelimbs in various vertebrate animals showing the homologous of these bones.
Although these vertebrates were evolved in different directions and have different size, shape and function, they all use the same bone elements, homologous nerve systems, blood circulatory systems, and other organ systems. The arm of a turtle has the exact same components as a human, bat, and whale but a whale is swimming and a bat is flying. The similarities are there but they are all used drastically different.

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The shell growing and covering the entire back of the turtle over millions of years show the evolution of turtles and their proof of adapting to their surroundings and lifestyles

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Organisms are known only from discovered fossil remains, which are extinct today. This means they failed to survive in changing circumstances though they were successful once on earth. The turtle fossils over time show changes in shell and legs. They're shells have grown and become stronger throughout geologic time.

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Oligocene (~33 m.y.a.)

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Cretaceous (~65 m.y.a)

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Eocene (~47 m.y.a.)

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Lower Cretaceous (~125 m.y.a.)

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Cenozoic (~60 m.y.a.)

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After hatch-lings reach the water they generally remain solitary until they mate

Sea turtles spend most of their lives in the water

Sea turtles will return to the same nesting grounds at which they were born

When females come to the shore they dig out a nest in the ground with their back flippers, bury their clutch of eggs and return to the ocean

After hatching, the young may take as long as a week to dig themselves out of the nest

Sea turtles are found in all warm and temperate waters throughout the world and migrate hundreds of miles between nesting and feeding grounds

Most sea turtles undergo long migrations, some as far as 1400 miles, between their feeding grounds and the beaches where they nest

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Adult male and female sea turtles are equal in size

Sea turtles are characterized by a large, streamlined shell

Depending on the species, sea turtles range can be olive-green, yellow, greenish-brown, reddish-brown, or black in color

Limbs are flippers adapted for swimming. Sea turtles are awkward and vulnerable on land

Only one or two claws are present on each fore flipper

A sea turtle cannot retract its limbs under its shell as a land turtle can

Sea turtles have large upper eyelids that protect their eyes

The bony shell is composed of broadened, fused ribs, and the backbone is attached to the carapace

A sea turtle's large, bony shell provides protection from predation and abrasion

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(Chelonioidea)

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primarily vegetarian diet

Saddle-backed tortoises tend to inhabit the hotter, drier islands with sparse vegetation

Domed tortoises inhabit the cooler, wetter islands with lush ground vegetation.

Galapagos tortoises are cold-blooded animals. They spend much of their day soaking up the sun to warm themselves. When  the temperature cools, tortoises sleep partially submerged in mud, water or brush to keep warm

Tortoises are extremely peaceful creatures.

The tortoises are slow-moving reptiles with an average long-distance walking speed of 0.3 km/h

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Can even reach up to 5 feet in length

Giant tortoises have either a round, dome-shaped shell or a saddle-back shell

Average lifespan of over 100 years

Male Galapagos tortoises can reach up to 573 pounds, although generally they average 475 pounds

Females are usually smaller than males and reach up to 300 pounds

The giant tortoise has five front claws and four claws on the back. They help the tortoise navigate through sometimes rugged terrain

Giant tortoises have thick scales all over their limbs, neck and pointed head

Their limbs vary from dark grey to black in color. The thickness of their skin helps protect them from the sun, but their hard shell is still very important for protecting their soft endoskeletons

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The mental state of these species always reflects furiousness

On sensing something uncanny, they emit a hissing sound

These species are mostly active during the nighttime

They cannot pretend to hide under the shells due to their giant body size. This is why they have adapted to the mechanism of snapping

These species catch hold of their prey with the help of their beaks

These species like to dwell in the watery areas

During the time of breeding these species inhabit on the land

One can easily spot these species around the lakes, ponds and shallow water areas

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A shell that covers their back, normally between 8 and 18 1/2 inches long

A snapping turtle's mouth is shaped like a strong, bony beak with no teeth

Their skin is rough with characteristic bumps, called tubercles, on their necks and legs

The feet are webbed and have strong claws

Turtles have hard plate that covers the stomach, this is called a plastron - A snapping turtle's plastron is small and leaves much of their body exposed

This means that they cannot pull their head and legs into their shell for protection against predators so snapping turtles make up for this lack of body armor with an aggressive temperament

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(Chelydra serpentina)

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Some species live in seasonally cold climates with growing seasons of only about three months

Others live in the tropics and grow year-round

Some tortoises rarely see water

Some turtles spend virtually their entire lives in it, be it in a single small pond or traveling the vast open ocean

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After hatch-lings reach the water they generally remain solitary until they mate

An unhappy turtle will withdraw into its shell, physically and emotionally give up

Their neck offers a significant flexibility which is mainly due to the eight cervical vertebrae

The number of eggs which the females deposit can be as many as hundred or sometimes only just one or two. the small turtles generally lay no more than two eggs; large turtles, on the other hand, lay more than a dozen

Many turtles show a stereotypical nest-digging behavior

They usually employ their hind limbs while digging egg chambers

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Physical Characteristics shared by all of the Organisms

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Physical Characteristics shared by all of the Organisms

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Shells

No teeth

Hard, flat surfaces on their jaws that allow them to grip and tear off bits of plants or animals for feeding

Backbone

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(Aldabrachelys gigantea)