Pan Tetrapoda Flashcards
(44 cards)
Crown Tetrapoda (352) is defined by the split between
Amniota and Amphibia
Stem Tetrapods
Rhizodontids, ‘Osteolepiforms’, Panderichthyes, Tiktaalik, Acanthostega, Ichthyostega, Whatcheeridae
Rhizodontids
Stem Tetrapods
- shallow marine and freshwater
- largest freshwater “fish”
- shoulder girdle and brain case well preserved
- reduced dorsal, anal, and pelvic fins
“Osteolepiforms”
Paraphyletic Stem Tetrapods
- ventral cranial fissure, large choanae, tetrapod skull patterning
- 1t evidence of bone marrow
Tiktaalik
Found on Ellesmere Island
-flat skull, no dorsal, anal fin, retains lepidotrichia, pectoral fin expanded, enlarged pelvis
- more tetrapod like shoulder girdle
- operculum lost
–pectoral girdle not attached to head = neck mobility
-enlarged ribs
-elongated snout
Acanthostega
Stem Tetrapod found in Greenland
- digits! At least 8
- lacked ossified wrists
- shoulder girdle
- retains well-developed gill arch and skeleton
- pectoral girdle detached from skull
Icthyostega
Stem tetrapods found in Greenland
- very similar to Acanthostega
- limbs, vertebrae, ribs
- pelvic appendage “catching up”
- more capable to terrestrial locomotion, but is primarily aquatic
Whatcheeridae
Stem Tetrapods found in Scotland
- foot has 5 digits
- 5 robust digits +1 extra, so 6 is primitive
What are the Fin/Limb Character Transformations of Vertebrates?
Fins to Limb - separation of the pectoral girdle from head, basically a neck!
Fin/Limb positioning along AP axis
Fins to Limb - separation of pectoral girdle from head
Neck!
Spinal Cord
- dual innervation of pectoral fins by cranial and spinal nerves in non-tetrapod gnathostomes
- hypothesized caudal shift of Hox expression shifted innervationpattern of “forelimbs” in tetrapods
—response of part displacement of the pectoral girdle along tetrapod stem
Fin/Limb positioning along AP axis- Hox genes
Forelimb, interlimb, hindlimb: Hox expression in LP
- anterior limit for expression - key features
General Limb Development
1) Hox expression field determines AP positioning of limb buds (somatopluere, core of LP,, etc)
2) Limb Buds - outgrowth of LP mesenchyme + surface ectoderm
3) Fibroblast growth factor (Fgf) 10 expression in LP mesenchyme establishes Apical Ectodermal Region (AER) in adjacent ectoderm
4) AER expression for fgf4 and 8, which maintains 10 expression in LP
A) appositional growth of limb bud
B) co-optation of Hox exp filled patterns proximal-distal axis
—girdle-style pod-zeugopod-autopod
5) AER exp 4 and 8 which establishes and maintains zone of polarizing activity (ZPA)
6) ZPA establishes Shh gradient = patterns AP axis
- morph. Identities of digits - Shh gradient
7) DV axis = WNT (dorsal)Engrailed/En (ventral) gradient
Appendicular Skeleton - Gnathostome
“Internal” Fin structure = girdles w/o radials
What are the components of the Pectoral Girdle of Vertebrates
Cleithrum, scapula, coracoid, clavicle, etc
Cleithrum
Part of pectoral girdle in vertebrates
Large, dorsal; serves as attachment to upper cucullaris muscles
Scapula and coracoid does what
Start sepration
Scapula
Part of pectoral girdle
Glenoid fossa
Coracoid
Part of pectoral girdle
Will brace shoulder girdle against sternum
Clavicle
Part of pec. Girdle
Braces shoulder girdle to sternum; attached
In Gnathostomes, there are paired fins, what are its structures?
From dorsal to ventral:
Lepidotrichia
Radials
Left to right:
Propterygium, mesopterygium, metapterygium
In Chondrichthyes and Osteichthyes, what are the structures of limbs?
Along the stem, there is a reduction of the basal elements, radials are restricted to metapterygium
Along Stem Actinopterygia: there is a relative enlargement of petapterygium
Pan Actinisia + Pan-Dipnoa: established metapterygium axis
Pan TetrapodaL reduction of lepidotrichia, meta= stylopod and zeugopod +carpals/tarsals
- Radials = digits
- Digit 4 = meta, Digits 1-3 pre axial digits, Digit 5 = postaxial
What is the spiracle?
A hole near the eye and is a respiratory structure
IN Stem Tetrapods Acanthostega and Icthyostega, it is a spiracular notch = otic/tympanic note
Spiracle = fenestra vestibuli
Hyomandibular = stapes
Ears: Organ of Balance
Evolved from lateral line system
Turning Head
Lag in endolymph, movement displaces hair cells
Via C VIII/vestibulocochlear nerve
Christa, macula
