Quiz 1 - Phylogeny + Placozoans Flashcards
what makes a vertebrate a vertebrate
cranium
phylum chordata
what are the benefits of the worm like body plan
efficient digestion
what is disparity
morphological differences between major groups
what is diversity
number of species
why would one phylum be more diverse or disparate than another?
disparate phylum means more morphological changes between the phyls, less physical similarites
more diverse phyla means a higher number of species in this phyla than another - could be due to a basal split or an evolutionary change that only occurred in that phyla
what was Darwin’s Dilemma
the seemingly rapid radiation of animals in the cambrian as this does not fit with the gradual change of evolution
- no fossil record evidence for this gradual change in the Cambrian
why is hard to find pre-cambrian fossils
likely soft bodied animals, difficult to fossilize
what is the oldest known fossils
bacteria - 3.5 bya
found in Australia
what were found 3.4 bya found in shallow water ecosystems, microbial like mixed in with sediment that made a layer of organisms in the sediment record?
stromatolites - 3.4 bya
What was the proteinaceous micro fossils that are said to emerge 3 bya that resemble pollen
acritarchs
what are ichnofossils?
trace fossils
- preserved in sedimentary rocks that record biological activity
has any trace fossil ever been accepted?
yes, trace fossil dating back to 560 mya were accepted
when did the ediacaran begin? when did it end? when did the biota flourish
spanned from 635-543 mya
biota floursihed in 575 mya
what is the poster fossil for ediacaran? it was found about 565 mya
rangeomorphs
what do rangeomorphs look similar too
sea pens, but with fractal repitition
what was the first pre-cambrian fossil to ever be named?
Charnia
- benthic, anchored to sea floor, lived in deep water, didn’t photosynthesize, no feed apparatus
What is the oldest triploblastic bilaterian fossil discovered 555 mya
Kimberella
what is the kimberella fossil a stem group of
molluscs
- it has radula marks which is a synaptomorphy of modern molluscs
what is the difference between a stem and crown group
crown = last common ancestor of all living + extinct fossils (monophyletic)
stem = series of entirely extinct organisms that lead up to the crown group (paraphyletic)
what is phylogeny
map of evol relationships btw organisms\
evol relatedness, similarities and differences of common ancestor
phyylogeny is inferred - changing all the time
what is evolution
based on common ancestry + shared derived characters - change in heritable characters over millions of years
what is taxonomy
classification system of organism based on common ancestors
arrangement of organisms based on descent
what is cladistics?
based on shared characters that can trace them back to a common ancestor
what helps placozoans stick
gland cells on ventral side
what are placozoans covered in
dorsal and ventral ciliated cells
what did metazoans evolve from 1.4 bya?
some flagellated cells
do placozoans have sexual/embryonic cells?
nope, they have 4-5 somatic cell types
the incisal cells in placozoans are missing what…
nuclei
what is the rarest type of cell found in placozoans
crystal cells
- along perimeter of placozoan
- little, cup like cells wuth inorganic crystal inside
what cell type was thought to be the pre-cursor to statocyst cells that help with orientation in placozoans
crystal cells
how do placozoans eat?
phagocytosis / external digestion on ventral side
where are placozoans found
mostly tropical and subtropics
what are some derived features of placozoans with metazoans
loss of ribosomal protein genes
mtDNA showed mitochondral features only seen in poriferans + cnidarians
what are some shared features of placozoans with fungi and choanoflagellates?
intrgenic spacers (introns) large mtDNA
placozoan have some genes that are similar to metazoans… what are they
Pax Genes - not found in placozoans but some variant of Pax gene found
Hox Genes
how does the term GENES B4 PHENES apply to placozoans
they have the genetic makeup to build new metazoans, but just had yet to be expressed
Pax gene variant + Hox gene (sort of…)
Pax genes are found in poriferna sand cnidairnas but not in placozoans… but they did find what in placozoans?
TripPaxB - an early version of the Pax gene from the same gene family
expressed differently in placozoans
what are pax genes
control developmental genes that encode nuclear transcription factors - help make the nervous and sensory organs/systems
*mechanosensory systems
hox genes are a type of…. what genes
homeobox genes
- involved in regualtion of development
what is the hox gene function
patterning of the body
symmetry (something placozoans lack)
do placozoans have hox genes
not really… they found homeobox genes in placozoans but their expressed differently
explain the conclusions of the dellaporta 2006 paper on placozoan phylogeny i nthe metazoan tree
placos more basal than sponges based on mtDNA bc of shared features w choanflagellates + fungi
why were sponges always thought to be the most basal
because of the choanoflagellate / chanocyte connection and the filter feeding
how many homeobox genes have been identified in trichoplax adhereans
6 homeoboc genes
explain Butschli placula hypothesis
flagellated protozoans formed a benthi-vagile, plate-like metazoan = placozoan
developped a 2 layered placula that had an upper ectoderm + lower endoderm
invagination of endodermal layer led to benthic animal
the second mystery of placozoans is about their diversity… are they just one species? explain why or why not
diverse halophytes in subtropic oceans - each clade has its own niche based on its genetics… placozoans could be more diverse than originally thought
it used to be thought there was only 1 species of placozoans… how many are known now
3 species
what is the third mystery of placozoan
life cycles and reproduction
mostly reproduce asexually (binary fission or budding) but never seen them sexually reproduce
what is convergent evolution
not monophyletic related, but evolved similar traits from have to adapt to similar environments/similar functions
