Chordata (vertebrates and invertebrates)

synapomorphies of chordata

• notochord

• dorsal hollow nerve cord

• post-anal tail

what is the notochord made of and what is its function?

• it is a stiff, flexible rod of collagen

• derived from mesoderm

• support and muscle attachment

what does the notochord become in vertebrates?

vertebrae

dorsal hollow nerve cord

• formed from the folding of the ectoderm during embryonic development

• becomes the CNS

• located dorsal to the gut

what are other key features of chordates that are not synapomorphies?

• pharyngeal slits

• closed circulatory system

• segmentation

how do chordates reproduce?

• sexually

• dioecious

• internal or external fertilization

what type of environments do chordates live in?

• diverse environments

• trend of movement from water —> land

pharyngeal slits

• water is brought into the pharynx (a muscled organ that brings water into the mouth via cilia), which then passes through openings to the outside (the pharyngeal slits)

• feeding and respiration

why are pharyngeal slits not considered a synapomorphy of chordates?

• they were present before chordates diverged

• they are not unique to chordates

key features of tunicates (aka sea squirts)

• have a tunic: a thick cellulose body covering

• lack chordate features as adults

• mostly sessile, one swimming species

• marine

• invertebrates

how do tunicates feed?

• incurrent and excurrent siphons

• filter feeders

why are tunicates still considered chordates if they lack key chordate features?

• they have these features as larvae, but lose them as adults when they undergo metamorphosis

larvacean tunicate

• free-living

• do not undergo metamorphosis —> retain chordate features throughout life

how are hagfish and lampreys related?

they are sister to each other

key features of hagfish

• no bones or jaw

• vertebrae are lost/reduced

• have cranium made of cartilage

• “teeth” made of keratin

• have skin and slime for defense

• predators on polychaetas, or scavengers

key features of lampreys

• no bones or jaw

• have cartilaginous vertebrae

• have a sucker-like mouth with rasping teeth

• filter feeders or predators

  • some adults are ectoparasites on fish

• fresh or salt water

which lineages were the first to evolve bones?

• ostracoderms and placoderms

Ostracoderms

• jawless

• have bony external armored plates, but still have cartilage endoskeleton

• filter feeders

• non-monophyletic

Placoderms

• one of the first vertebrates to have true bony jaws with true bony teeth

• bony armored exoskeleton, cartilaginous endoskeleton

how did jaws evolve?

anterior gill arches (cartilage that supports pharyngeal slits) were modified into bony jaws with teeth

gnathostomes

• vertebrates w/ jaws

• placoderms, chondrichthyes, bony fishes, tetrapods

agnatha

• lack jaws

• hagfish, lampreys, ostracoderms

Chondrichthyes

• cartilaginous fish (lost bones)

• flexible cartilage skeleton

• vertebrates

• sharks, rays, sawfish, skates, chimeras

• mostly predators, some scavengers

• true jaws (made of cartilage)

• fast swimmers

• diverse reproductive strategies

• dermal denticles: small, tooth-like scales on the skin that are homologous to vertebrate teeth

lancelets

• sandy sediments

• small marine animals

• are filter feeders

  • use pharynx and slits

  • lack siphons

• segmented muscles

• intervebrates

  

which chordates are vertebrates vs invertebrates?

• vertebrates: hagfish, lampreys, ostracoderms, placoderms, chondrichthyes, bony fish, tetrapods

• invertebrates: lancelets and tunicates

What are osteichthyes and which lineages do they include?

• bony fish

• includes ray-finned fish, coelacanths, lungfishes

key features of osteichthyes

• chordates

• vertebrates

• have jaws

ray finned fish (Actinopterygii)

• largest group of boney fish

• freshwater and marine

• diverse feeding strategies, but almost always use suction feeding

lobe finned fish

• most extinct, but coleocanths and lungfish are extant

• lungfish have gills and lungs —> can survive out of water longer

• have bones, but no bony spines as part of their fins

  • fins are joined to the body by a single bone instead

how are the bones of lobe-finned fish and ray-finned fish related to tetrapod limbs?

• the bones of lobe-finned fish are homologous to tetrapod limbs

• the bones of ray-finned fish are not homologous to tetrapod limbs

key innovations involved in the transition to life on land for tetrapods

• fins —> limbs

• lungs

• modifications to skin

• internal fertilization

• shelled eggs

how did lungs evolve?

• evolved in the MRCA of bony fish

• evolved from swim bladders

• lived in low oxygen environment —> air pocket evolved from digestive tract

  • in ray fish —> pocket became swim bladder

  • in lung fish —> pocket became lungs

what is the function of the swim bladder?

buoyancy

which lineage was the first to transition to land?

amphibians

which lineages are part of tetrapods?

amphibians, mammals, lepidosaurs, turtles, birds, crocodilians

key features of amphibians

• vertebrates

• skin used for respiration —> allowed them to depend less on water (but are still need a moist environment)

• some live mostly on land and reproduce in water, some are entirely aquatic

  • some lost lungs

  • metamorphosis from tadpole larva with gills into adults with lungs

• not amniotes

key features of amniotes

• impermeable skin

• efficient kidneys

• amniote egg which prevents dessication —> allowed them to live in dry environments

• no metamorphic larval stage

• some lay eggs, some don’t

what lineages do amniotes include

mammals, lepidosaurs, turtles, birds, and crocodilians

key features of mammals

• hair

• sweat glands

• mammary glands

• 4-chambered heart

what are the 3 major groups of mammals?

• Prototherians

• Marsupials

• Eutherians

prototherians

• lay eggs

• provide milk, but lack nipples

• ex. platypus

marsupials

• have placenta

• young are born undeveloped and develop in a pouch

• ex. kangaroos

eutherians

• larger placenta

• young are born developed

• ex. humans

examples of convergence in mammalian evolution

• similar body morphology in eutherians and marsupials, despite living in geographically isolated regions

3 major groups within repitles

• lepidosaurs: tuataras, snakes and lizards (squamata)

• testudines: turtles and tortoises

• archosaurs: birds, crocodiles, dinosaurs

what are some features that are conserved amongst birds that allowed for the evolution of flight?

• endothermy

• feathers

• hollow bones

• high metabolic rate

• efficient respiration through air sacs

what type of heart do archosaurs have

4-chambered (like mammals) due to convergent evolution

are reptiles monophyletic?

• no, they are paraphyletic (must include birds to be monophyletic)