What is a vertebrate/ vertebrate phylogeny Flashcards
define tetrapoda
tetrapodomorpha
tetrapod
tetrapoda - the last common ancestor of all living tetrapods and all of its descendants (i.e. crown group tetrapods)
tetrapodomorpha - sister group to lungfish (crown group tetrapods and all their stem group relatives)
tetrapod - any animal primitively possessing four limbs
When was the Devonian
416-360 Mya
Describe the early flora of the Devonian
vascular plants originated in the Silurian ,and major radiation on land took place in the early Devonian
they are small with limited root systems and simply branching structure
the largest, a lycophyte called Asteroxylon grew to 40cm.
late flora of the late Devonian
some of these plants are found together with tetrapod remains. greater size and complexity than early Devonian plants.
pro gymnosperm is the largest, Archaeopteris - grew to 20m and formed the first true forests. growth rings indicate seasonally unfavourable conditions
fern-like shrub called Rhacophyton grew to 1.5m .
formed extensive monotypic stands.
comment on the distribution of tetrapods
must have been found in freshwater deposits, but they remains are spread so widely around the continents that their ancestors must have been able to disperse around coastlines. but caution must be taken when inferring the specific context in which tetrapods evolved depending on where the remains have been found.
Devonian stem tetrapods - Ichthyostega
comment on their hearing
and what the features of the vertebral column indicate about their movement
First to be discovered.
derived characters place it way off the main line of tetrapod evolution.
Ichthyostega probably had gills and an ear specialised for hearing both underwater and overwater.
differentiation of regions of vertebral column indicates limited vertical abdominal flexion. restricted hip and shoulder joint mobility suggests seal - like movement on land.
Devonian stem tetrapods - Acanthostega
Smaller than Ichthyostega, Never found together - different ecological differentiation.
almost entirely aqauatic - paddles like limbs, large caudal fin - rays for fine control, large gill chamber, exensive lateral line system. feeding apparatus sepcizlied for aquatic feeding.
Acanthostega - what were the findings from using synchrotron microtomograhpy ?
what was inferred from the growth rings in the cortical bone?
imaging of several humerus bones allows growth rate to be inferred from growth rings in the Cortical bone.
Acanthostega therefore, seems to have an extended juvenile phase of 6-10 years
forelimb ossification did not begin to occur until animals were almost fully grown - humerus remained almost fully cartilaginous during the growth phase supporting the notion that Acanthostega was fully aquatic - at least in juvenile stage.
Please provide what is known about the Devonian stem tetrapods Ichthyostega and Acanthostega?
What feature suggests that they were largely aquatic?
What features suggested bottom dwelling or shallow water existence?
what functionally important, dervied characters typical of tetrapods are found? List the 8 characters.
what primitive characters of fish that were lost in later tetrapods?
they seem to have had gills - suggesting aquatic
relatively large predators
dorso-ventrally flattened form, dorsally placed eyes, lack of dorsal fins. suggest a bottom dwelling/ shallow water existence.
8 characters are: choanae, stapes, neck, limbs, digest, laterally-facing glenoid, large pelvic girdle, enlarged ribs
both taxa retained characters of fish that were lost in later tetrapods: spiracles, internal gills, lateral line system running through groove in bone, caudal fin with rays
mosaic of primitive and derived characters represent transitional forms!
What is the giant surprise relating to digits?
what does it suggest about pentadactyly
All of the Devonian stem tetrapods are polydactylous.
Ichthyosteaga - 7 digits on hind limb
Acanthostega - 8 digits on forelimb
suggests that it is not the basal state for tetrapods but primitive to crown-group tetrapoda. don’t know whether it is through accident or selection.
tetrapodomorph fish - tetrapods arose from within the sarcopterygii (lobe finned fish).
What are elpistostegalians ? How are they similar to to Devonian tetrapods?
what derived characters do they possess? 6 of them
what primitive characters of fish are retained?
they are the sister taxa to tetrapods within the tetrapodomorphoda
similar body form, size, predatory haits
flattened head, large temporal notches, choanae, neck, limb bone and digit homologues, enlarged ribs
functional fins, gills, scales
