Amniotes and Mammals lecture Flashcards
What is a crown group? Give a course-relevant example
A derived monophyletic group; Amniota
What are the Amniota synapomorphies?
Amniotic egg
Claws or nails at the end of digits
Egg tooth
Genitalia for internal fertilization
At least 2 sacral vertebrae
Formation of astragalus
Loss of water breathing and lateral line system
What structures are conserved between the amniotic egg and amphibian/fish egg?
Yolk and chorion
What structures does the amniotic egg have that the amphibian/fish egg doesn’t?
Allantois, amnion, and chorioallantoic membrane
What limits the fish/amphibian egg from moving onto land?
Lacks an outer shell to avoid desiccation. It is dependent on water for gas exchange, waste management, and moitsure
What is the function of the yolk sac?
Nutrition
What is the function of the amnion?
Encapsulates embryo, protective against mechanical forces
What is the function of the chorion?
Encapsulates embryo and extraembryonic tissues (including amnion), protection for embryo, gas exchange, and provides structure for the yolk sac
What is the function of the allantois?
Storage of metabolic waste and gas exchange, ‘mini bladder’
What is the chorioallantoic membrane?
It is synthesized from an old character (chorion) and new character (allantois) for gas exchange and waste storage
Why do amniotes require an allantois?
Embryos are unable to diffuse metabolic waste into their surroundings like fish/amphibians can. Also necessary for gas exchange for the same reason
What germ layers make up the yolk sac? Outside to inside
Mesoderm and endoderm
What germ layers make up the allantois? Outside to inside
Mesoderm and endoderm
What germ layers make up the chorioallantoic membrane? Outside to inside
Ectoderm, mesoderm, and endoderm
What germ layers make up the amnion? Outside to inside
Mesoderm, ectoderm
What germ layers make up the chorion? Outside to inside
Ectoderm, mesoderm
Why is declawing a cat considered unethical?
Claws and nails have a tight connection/association with the end of the digit through lots of connective tissue, so removing them is like amputating the most distal phalange
What germ layers make up the egg tooth?
Ectoderm and neural crest
What tissue makes up the caruncle?
Keratin
Why do (most) squamates have an egg tooth rather than a caruncle?
Egg teeth are much harder, which is needed to break free of the leathery shell that encapsulates the embryo
What is the Shh gene?
Sonic hedgehog, it is analogous to HOX genes and allows for symmetry of tissues
Which clade does not have Shh expression?
Tuatara
What are the steps for penile development?
External genital initiation, Shh expression, and cloacal separation
Which two clades do not have external penises?
Anoles and Tuataras