more examples...

cephalization
​is the evolutionary development producing a centralized nervous system and the development of a head and brain. cephalization and bilateral symmetry go hand in hand since all cephalized organisms exhibit  
bilateral symmetry.
Their sense organs/tissues are concentrated on/near the anterior of the organism as it moves forward = head region.
Uncephalized animals include cnidarians, some mollusks, and echinoderms.

Kingdom Animalia

advantages of being a Deuterostome which is (<1% of all animals):
more yolk proteins can be stored in the cell which allows embryos to develop further before hatching, bypassing a larval stage.

can you suggest why??

notochords

are flexible fibrous/elastic sheaths found along the dorsal surface of all chordate embryos. notochord cells are derived from mesoderm. notochords direct development along the midline as chordate embryos develop. 
lancelets exhibit notochords during maturity. tunicates only exhibit notochords during their larval stage. these are invertebrate chordates.
In most vertebrates (but the hagfish), the notochord becomes part of the vertebral column's intervertebral discs. 

symmetry:
asymmetry
radial symmetry
bilateral symmetry

from the relatively simple...

acoelomic

Types of eyes

to the more complex...

the majority of coelomic invertebrates develop as protostomes ="first mouth". protostomes exhibit an oral end that develops from the first developmental opening.
deuterostomes = "second mouth". deuterostomes exhibit an oral end that develops from the second opening. the first opening (blastopore) becomes the anus.

segmentation:

unsegmented
segmented

flight permits animals to traverse physical barriers, live in safer locations away from ground-dwelling predators, and access new food sources that cant be reached by competitors on the ground. 

the eye

the evolution of flight exhibits a remarkable degree of convergent evolution between 3 groups of flyers alive today...
bees, birds, and bats
and
1 group no longer seen in our skies...the pterosaur.

coelomic

cephalization:
uncephalized
cephalized

Chiropteran (bat) flight
Bats are the only truly flying mammals. Although there's little fossil evidence showing how bats evolved, phylogenic analysis suggests that bats are likely related to flying (well, really gliding) lemurs (which isn't really even a lemur but a dermopteran).
Bats first appeared in the Eocene epoch 56 to 33.9 mya. It is theorized that bats evolved true flight from a gliding arboreal ancestor, therefore suggesting top down development, by using their wing membrane to glide while they evolved their flight stroke. This uropatagium membrane stretches from a bat's rear legs and is supported by very long phalange bones. Other flight modifications include a modified pectoral girdle, a smaller radius,  a large humerus and ulna and claws. Bats have only been around for 60 million years so are the youngest group of flying vertebrates compared to birds who have been soaring the skies for over 150 million years.

4. 

3. 

Kingdom Animalia

​Phylum Porifera






​

Phylum Cnidaria





​

​Phylum Platyhelminthes







​
Phylum Nematoda








Phylum Annelida








Phylum Arthropoda










Phylum Mollusca









Phylum Echinodermata









Phylum Chordata





​

exoskeleton advantages

Avian flight
Archaeopteryx was the modern birds first cousin. 
Evolved from Dromaeosaurs (raptors), they also fit the bottom up theory. Modern birds are tree dwelling but keep in mind they've had 150 million years to adjust their niche. Although many of the flight adaptations of birds parallel those of pterosaurs, modern bird wings exhibit an elongated radius, ulna, modified carpals, fused clavicles and furculas = wishbones. All of these features evolved from modifications of dromaeosaurian bones. Modern birds also exhibit their just one phalange (#2) at the tip of their wings, a modification of the clawed raptor claw.  

pseudocoelomic

Pterosaurian flight
Pterosaur means "wing lizard" in Greek. They were the largest vertebrate ever known to fly. the evolution of flight in pterosaurs is separate from the evolution of flight in modern birds and bats offering an excellent example of convergent evolution.
Large pterosaurs exhibited wing spans over 12 meters and were most likely gliders while small pterosaurs were capable of powered flight, with their hollow bones and many skeletal processes which allowed for flight muscle attachment. ​Pterosaurs lived in a non-arboreal environment so the "ground up" theory of flight origin fits.

let's look at mollusk
​ eye evolution...

tissues are made up of many cells that are similar, have the same origin and perform similar functions. different tissues carry out different functions which is faster and more efficient. tissues 
​ enable a division of labor.

organs are composed of two or more tissues designed to carry out a particular function. groups of organs with related functions make up an organ systems.

the evolution of flight

hydrostatic skeleton advantages

2. 

what about the  evolution of...
the loss of flight!

​evolutionary adaptations

                 Insect flight


     Insects were fling high over 400 mya, right around the time plants started to spread across land and mature into forests. They were the first animals to evolve flight. Recent studies strongly suggest that insects evolved the ability to fly just once with modifications to this ability evolving over millions of years. Data suggests modern day insect wings evolved from pre-existing structures such as tracheal gills or a part of the ancestral insects' thorax.
     The oldest known winged insect is the 325 million years old Palaeodictyoptera which gave rise to over 30 ancestral branches of winged insects. Palaeodictyoptera exhibited four lateral wings located on its thorax. ​Studies of Palaeodictyoptera nymphs support the theory that jointed thoracic lobes initially permitted the insect to glide and eventually evolved the musculature that permitted active flight. Flight sped up the colonization of our planet by insects, making them the most successful of animals. 

the first known eye was found on a trilobite over 5oo mya. This Cambrian period in our planets evolution, followed by millions of years of evolution, set the stage for the many types of eyes we
"see" ​ today.
spiders sport tiny eyes with scanning optics,  scallops exhibit 70+ eyes displayed on their mantle each with 2 retina, birds have vision several times better than primates. 

coelom:
acoelomic
pseudocoelomic
coelomic

endoskeleton disadvantages

exoskeleton disadvantages

The PAX6 gene is highly conserved and codes for a  transcription factor responsible for regulating many genes involved in embryonic eye development and adult homeostasis.

5. 

 when it absorbs a photon, 11-cis retinal isomerizes to trans retinal enabling rhodopsin to activate transducin, its G protein. 

are all wings the same...?

7. 

it all started with light-sensitive proteins in bacteria that permitted movement to/away from light = +/- phototaxis
photoreceptors (like rhodopsin) contain light sensitive photopigments, proteins that absorb light and experience structural changes that initiate action potentials which can be interpreted by the organism 

and ask yourself this...
did flight developed from the ground up or from the trees down??

Cephalopods exhibit sensory organs specialized for use in aquatic environments. Their eyes contain an iris, lens, vitreous cavity, photoreceptors.
This eye functions like a camera and can be compared to
​ vertebrate eyes.
Mollusk and vertebrate eyes evolved independently from one another =
​ convergent evolution.

Kingdom Animalia includes
​ several phyla:
​Phylum Porifera
Phylum Cnidaria
Phylum Platyhelminthes
Phylum Nematoda
Phylum Annelida
Phylum Arthropoda
Phylum Mollusca
Phylum Echinodermata
​Phylum Chordata

6. 

radial symmetry is advantageous to slow moving or sessile animals. there's an even distribution of sensory receptors all around their body so radially symmetrical animals can sense danger and/or obtain food from any direction.

Since flying is a behavior and behaviors do not leave fossil records, to understand how/why flight began, three factors must be considered:
1. the phylogeny (origin) of the group
2. the structures that permitted flight and how they differ from their nearest non flying relative
3. the environment in which the group lived at the time it developed flight

endoskeleton advantages

having bilaterally symmetrical bodies allows animals to move 
forward in a straight line. animals able to move quickly and efficiently are more successful and are selected for than those less efficient at doing so. 

embryonic development:
protostome vs
​deuterostome

1. 

organization level:
cellular
tissue
organ
​ organ system

and for fun... :)

Fossilized flight modifications included...
1. front limbs w/modified phalange bones that served as wing spines 
2. sternum with a keel for center of gravity/balance
3. lightweight hollow but strong bones
4. modified epidermal fibers which were precursors to feathers 

Animal Evolution Part II

skeleton:
​hydrostatic skeleton
exoskeleton
endoskeleton