By Megan Beaton, Laura Buennemeyer, and Catherine Romano

 Exploring the evolution of the inner ear Dorudon atrox million years ago  Exploring the evolution of hind limbs to a vestigial structure Maiacetus inuus million years ago

 Vestigial Structure- homologous characters in an organism that has lost all or most of their original function  Vertigo- extreme dizziness, which can be caused by the ear  Myosin- motor proteins found in eukaryotic tissues that are responsible for motility  Myoblasts- a type of stem cell that exists in muscles  Somitic myoblasts- causes the stem cells that develop in vertebrates to migrate  Cetacean- mammals adapted to aquatic life, including whales, dolphins, and porpoises  Echolocation- the ability to sense objects in the environments by hearing echoes from those objects

 Approximately 50 million years ago, the ancestors of modern day whales were four legged terrestrial mammals about the size of a raccoon  Thick bone density made it easier escape predators in the water  The inner ear adapted to allow the whales to move quickly under water and avoid vertigo Zygorhiza kochii Late Eocene (39-37) million years ago

On land- 50 million years ago (Packistis) Aquatic- 34 million years ago (Dorudon) Total evolutionary process- approximately 15 million years total Hind limbs- started 41 million years ago; finished 34 million years ago (Gaviocetus) Inner ear- started 47 million years ago (Dalanistes)

 In the 5 th week of gestation, the genes responsible for hind limb development are no longer expressed  Initial limb outgrowth requires…  Apical ectodermal ridge (AER)- signaling center for the hind limb bud regulated by Fgf8 protein  Distal margin of limb bud  Zone of polarizing activity (ZPA)- signaling center that maintains initial limb outgrowth  Posterior connective tissue

 Hand2 gene- a regulator of Sonic Hedgehog (Shh) transcription and required for cell survival  Hand2 is not expressed in the hind limb developing embryo after the 5 th week of development  Shh- mediates the signaling activity of ZPA  Fgf8- protein that is coupled with AER and is not detectable or functional in the hind limb development

 Muscles are formed when myosin evades limb buds  Myogenetic cells attracted to limb bud by signals sent out by the AER and ZPA  Hind limb bud induces somitic myoblasts to migrate  Myogenic cells are found in both the fore limbs and hind limbs

 The inner ear canal of whales is 3 times smaller than that of the human ear  The evolution of the inner ear was a key point of no return  Today, with the size of their ear canal, a terrestrial whale would only be able to crawl at a slow pace  The ear is extremely specialized for the aquatic lifestyle

 Examine the relationship between size of hind limbs and whale length  Explore differences with balance, feeding techniques, swimming depth, life span, speed, and location in the ocean.  Study carried out by examination of different whales and different pods of whales  Examine other species with similar vestigial structures, and see if the evolutionary paths are similar