BIOL 2003 Lecture Notes - Lecture 13: World Wide Fund For Nature, Thylacine, Osteichthyes
Vertebrates and Phylum Chordates
October 23, 2015
*Vertebrates are a subphylum of Chordata
Tree of Life not ladder of life
• Some of the chordates and their invertebrate relatives
• The linear model is an illusion, can only talk about one thing at a time however the animals are
really a tree
• All of life could be put on a linear model however the model implies a linear sequence where one
evolves into the other and that would be incorrect
• Animal on the left is a hemichordate (in the deuterostome category)
Tree of Life
1) branches—not a linear sequence
2) relationships are hypotheses not fact
• You start at a common ancestors and there is a common ancestor for all of life.
• As you go up the tree species diverge through morphology
• All the animals that live today are on the tips of the trees
• The tree morphology replaced the linear morphology
• At the bottom you have a common ancestor of all vertebrates and then it branches from there
• Fish share a common ancestor with us
• Branching pattern that is thought to be the branching pattern of evolution
• Bony fish share more common features with us then the hagfish
• Remember that this a hypothesis – not a fact
• Clade: common ancestor and everything derived from it and they share more characteristics
with each other than the rest of the group
• Placaderms have come part from being one clade to a bunch of individual groups
• Don’t memorize a clade, these things change
Perspective: vertebrates in time and context
• Only ~2 – 5% of species
• Less than 60,000 species
o Vs. over 2 million species
• Only 1 phyla
o Vs. ~34 invertebrate phyla
• Vertebrates are only a small part of animal diversity
Human-Induced Threats and Extinctions
• Conservation issues
• And what species are most at risk
• 50,000 years of extinctions
o Much of this is human induced
o Humans have been affecting diversity for thousands of years
o The pace of extinction is occurring more rapidly
▪ Moa bird
▪ The dodo
▪ Tasmanian tiger
▪ ^examples
• Global wildlife populations down by half since 1970 (World Wildlife Foundation)
• In our life time we will see huge decreases in the number of species and the population of a
species
find more resources at oneclass.com
find more resources at oneclass.com
Document Summary
*vertebrates are a subphylum of chordata (cid:498)tree(cid:499) of life not (cid:498)ladder(cid:499) of life really a (cid:498)tree(cid:499) (cid:498)tree of life(cid:499: branches not a linear sequence, relationships are hypotheses not fact. Perspective: vertebrates in time and context: only 1 phyla, vs. ~34 invertebrate phyla, vertebrates are only a small part of animal diversity. In our life time we will see huge decreases in the number of species and the population of a species. Chordate characteristics: notochord, longitudanal strut, above the pharynx. Just below the dorsal hollow: along the upper side of the body cavity, right above you find the notochord made of a different kind of structure (not bones and not cartilage, made of cells and fibrous sheath. Is contained in a sheath that prevents it from bulging out the sides. In aquatic chordates: pharyngeal gill slit, gill arches between slits. In tetrapods: gill arches give rise to a variety of structures:
