Chordates

How many extant vertebrate species? extinct?

70000

>100x extinct

Two major groups of vertebrates? describe each

non amniotes (mostly aquatic)

embryo protected by membranes

amniotes (mostly trestrial)

additional 3 membranes, one being amnion

Animals in each group?

non amniotes:

• Jawless fishes (“Agnathans”)

• Cartilaginous fishes (Chondrichthyes)

• Bony fishes (“Osteichthyes”)

• Amphibians (salamanders, frogs, caecilians)

amniotes:

“Reptiles"

• Turtles (Testudines)

• Lepidosauria (lizards, snakes, tuatara)

• Crocodilia

• Birds (Aves) (technically reptiles due to close ancestry to crocodilia)

• Mammals

Systematics (examples)

= evolutionary classification

reflects evolutionary relationships and for organization

Chinese algae eater > fish

Aracari > bird

Central stoneroller > fish

Taxon

Named taxonomic unit at any level (plural=taxa)

Binomial nomenclature

scientific naming of species, standardized by Linnaeus (1700s) (genus, species) (unique for all)

Homo sapiens (Humans)

Felis concolor (cougar)

Hierarchy of classification (name all, which italicized? what should they reflect?)

Higher levels more inclusive

lower less

Kingdom (e.g., Animalia)
Phylum (e.g., Chordata)
Class (e.g., Mammalia)

Order (e.g., Carnivora)

Family (e.g., Felidae)

Genus (e.g., Felis)

Species (e.g., concolor)

reflect a degree of relatedness, shared ancestry, not how similar

Phylogenetic systematics (what is it, what are ancestors, can they change or are they set in stone?)

hierarchy based on ancestry

ancestor is nodes

can change as hypotheses and evolutionary relationships change

Monophyletic taxa

group, share a common ancestor, includes all descendants

One line in, no line out

natural groupings

How do we identify monophyletic groups? (Apomorphy, Plesiomorphy, synapomorphy, symplesiomorphy)

derived/apomorphic characters

Apomorphy= character different from ancestral (novel/derived trait) (the guy that got it first)

feather in birds

hair in mammals

jaws in vertebrates

Plesiomorphy= ancestral character (og trait)

synapomorphy (shared derived) helps find common ancestry. feathers in all birds, meaning common ancestor.

Notochord in chordates, common ancestor

symplesiomorphy doesnt indicate recent.

Mammals with hair are close to eachother but animals without hair arent inheritaely close due to that absence

homologous

there is a chance that traits evolved independently in different lineages. Birds and mammals being warm blooded for example. To know if from same ancestor, they have to be homologous, where likeness is due to shared ancestry.

Analogous

resemblance between species, but different branches

similar roles but independent

also called homoplasy (plas = form)

Causes of Homoplasy/Analogous

Convergent evolution: evolve independently in animals that have diverged for a long time (bats and birds, wings)

Parallel evolution: evolved independently but diverged recently (elongate hind legs in jerboa (africa) and kangaroo rat (NA)

Evolutionary reversal: re-evolution (streamlined body and fins of aquated whales and dolphins, whereas sharks retained there still)

All of these independent evolution, not inherited

polyphyletic taxa

artificial grouping, two more distant lineages

ex. “aquatic vertebrates”

more than one line going in, none going out

paraphyletic taxa

dont include all species derived from common ancestor

cant be selective about which to choose and which to not choose

Pongidae, Hominidae

One in, one out

Traditonal Groups

traditional groups are paraphyletic mostly

some polyphyletic

Paraphyletic:

Dinosaurs if birds excluded

“reptiles” and “fishes”

Polyphyletic:

warm blooded (birds and mammals)

Sister groups

two closest lineages (birds and saurischian dino)

Crown groups

extant species, ends of branches

Stem groups

extinct groups, stems of branches

Three subphyla of Chordata

Vertebrata

plus non vertebrates:

cephalochordata (lancelets)

Urochordata (tunicates, sea squirts)

Who are chordates closely related to? why?

close: Echinodermata (sea stars) and phylum Hemichordata

They are the only deuterostomes (synamorphy)

Deuterostomes vs protostomes

Blastopore=

Deu: second mouth, first came the anus

Pro: first mouth, first came mouth

Five synapomorphies of chordates

1. Notochord (rod for support and muscle, replaced by vertebrae in most)

2. Dorsal Hollow nerve chord (forms spinal chord, induced by notochord, not just nerve chord has to be dorsal hollow)

3. Postanal tail (segmented muscular tail, all chordates during embryonic)

4. Pharyngeal (gill) slits (pair openings anterior pharynx, first as feeding, respiration in fish)

5. Endostyle/Thyroid gland (endostyle in adult non vert, and larval lampreys, secretes mucus, ciliated glandular tissue on pharynx floor)

Cephalochordata (what, lifestyle, myomeres)

25 fishlike species (lancelet or amphioxus)

burrowing, sedentary

elongation notochord aids in burrowing, past the head.

pharyngeal slits for feeding, not gas exchange

Myomeres = blocks of striated muscle (like salmon)

contraction of myomeres bends the body

Cephalo= head

Urochordate

Tunicates, sea squirts

Uro=tail

2000 marine species

sedentary