Lecture 12 Flashcards
1
Q
Jaws in vertebrates
A
- first vertebrates in Cambrian had no jaws and earliest vertebrates had no appendages
- first fish with jaws were placoderms
2
Q
Graph Balloon Diagram
A
- where balloon starts out at bottom is time when it originated and where it peters out at top is when they went extinct
- width corresponds to how many species there are
3
Q
Jawless fish phylogney
A
- start acquiring appendages–>tetrapods then acquire jaws
- ray fin fish have paired appendages
- 1/2 of all living vertebrates are ray fin fish
4
Q
Why no more that 4 appendages
A
- it’s possible some early on had multiple paired appendages
- accident of evolutionary history–>fish that gave rise to tetrapods only had two sets of paired appendages
5
Q
Ray-fins
A
-long bony (but not actual bone so probably cartilaginous) structures that the fin ray attaches to
6
Q
Lobe fin
A
-appendages built like ours
7
Q
Rhipidistian and Labyrinthodont
A
- what lobe fin looks like
- shoulder girdle like ours and have bones in them
- compare to early tetrapod like Labyrinthodont (amphibian) have same structures but also has a hand
- somehow Rhipidistian transformed into Labyrinthodont
- transformation is easy and hard at same time
- turned swimming organ into a land organ
- underlying structure has a lot in common
- key change in anatomy is that you evolve fingers instead of having fin structures
- homologous limb bones, increased strength of attachment of humerus to shoulder girdle
8
Q
Evolution of the pelvic girdle
A
- lobefin fish–>tetrapods
- happened early in the Devonian
9
Q
Acanthostega
A
- first tetrapod
- fish like: has internal gills, vertebral column, tail fin like fish
- tetrapod like: bones of skull, legs
- unique: limb girdles built for swimming, not walking, 7-8 toes rather than 5 (used for swimming through weeds)
- transitional fossil between fish and tetrapods
- basal ancestors of amphibians and amniotes
10
Q
Gills and Lungs
A
- lobe fin fish had both
- lived in water that would become stagnant or in shallow streams
- breathed with gills when oxygen level in water was high but if it wasn’t they’d use there lungs
- we have lungs because fish had lungs
11
Q
Primitive number of digits for tetrapods
A
-7-8 (not 5)
12
Q
Why did fish need legs?
A
-end of every season ponds would dry out so in order to survive they needed legs to get to next pond
13
Q
In Utero
A
- have gill slits
- fore limb buds and hind limb buds give rise to hands, legs, and feet
- how do you build these?–>patterning of limb buds–>condensation of cartilage cell–>bone as bud–>limb
14
Q
Patterning of limb buds
A
- Zone of polarizing activity (in mesenchyme) contains signals that instruct developing limb bud to develop using A/P axis
- FGF-8 signals shh expression in posterior mesoderm and shh then stimulates FGF-4 to be expressed in posterior part of Apical Ectodermal Ridge
- these events means there is a co-dependence between FGF-4 and Shh for subsequent expression and maintenance
- Cells on AER have specific fate in forming limbs
- Shh and Zone of PA induces AER to produce growth factor which stimulates mesenchymal cells to multiply
- can interrupt it by removing apical epidermis ridge-how they determined the entities were sending molecular signals
15
Q
Limb buds
A
- grow from closest to body out
- grow along axes
- correct budding depends on correct specification of axes