Comparative Anatomy Exam 1

Chordata

Comes from the notochord

An internal rod-like, semirigid, fluid-engorged structure enclosed in a sheath

1. dorsal hollow nerve cord

2. notochord

3. endostyle or thyroid gland

4. pharyngeal gill pouches or slits

5. postanal tail

What are the 5 basic characteristics of all chordates?

- bilateral symmetry

- anterioposterior axis

- coelom

- tube-within-a-tube body plan

- metamerism (segmentation)

- cephalization (head region)

What are some features that chordates share with some invertebrates?

Notochord

- extends the length of the body and lies btw the gut tract and nervous system; dorsal

- stiffens the body, providing skeletal scaffolding for attachment of swimming muscles

Protochordates and jawless vertebrates

The notochord persists throughout life in

Entirely displaced by vertebrates but persists as invertebral discs

In most vertebrates, the notochord is

Dorsal hollow nerve cord

- the single cord is dorsal to the alimentary canal and is tubular

- the anterior end enlarges to form the brain (cephalization)

- produced by the infolding of ectodermal cells on the dorsal side of the body

Ventral to the alimentary canal and solid

In most vertebrates, the nerve cord is

Pharyngeal gill slits

Lead from the pharyngeal cavity to the outside

Pharyngeal pouches

Give rise to a variety of structures, including the Eustachian tube, middle ear cavity, fossils and parathyroid glands in tetrapods

Perforated pharynx

Functions as a filter-feeding apparatus in protochordates

Capillary network

With gas-permeable walls, fishes added a

• evolved into gills

Endostyle or thyroid gland

- found in all chordates

- was recognized as a shared chordate characteristic

Postanal tails

- provided motility for larval tunicates and amphioxus to swim; invertebrates

- was increased in fishes but became smaller or vestigial in later lineages; terrestrial vertebrates

- coccyx: tail bone

Classification

- Hierarchical system of grouping organisms into different taxonomic levels (taxons)

- established in 1753 by Linnaeus

- binomial system: 2-worded scientific name

Wise humans

Homo sapiens

Kingdom Animalia

>2.5 mil species

Phylum Chordata

- 56,000 species

- 5 distinct characteristics

Subphylum Urochordata

- tunicates (inverts)

- > 3,000 species

Subphylum Cephalochordata

- lancelets (inverts)

- 30 species

- earliest chordate fossil 550 mybp

Subphylum Vertebrata

- backboned chordates

Chordate features:

1. vertebral column: series of cartilaginous or bony elements

2. cranium

3. endoskeleton of cartilage or bone

4. hox genes

5. neural crest

Cyclostomes

Agnathans - jawless fishes

Class Mixini (hagfishes)

- 70 species

- lack jaws, eyes, fins

- skeleton comprised of notochord and cartilaginous skull

- covered in slime

Class Cephalospidomorphil (lampreys)

- 25 species

- have notochord, cartilagious vertebral column

- lack jaws and appendages (fins)

- covered in slime

- oldest vertebral fossils (510 mybp)

Class Chondrichythes (cartilagious fishes)

- Fossils 380 mybp

- 1,000 species

Subclass Dipneusti (fleshy-finned fishes)

- lungfishes

- 10 species

- South America, Africa, Australia

Subclass Crossopterygii (lobe-finned fishes)

- coelacanth

- 2 species

- skeletal elements of limbs similar to amphibians

- ancestral stock to tetrapods

Subclass Actinopterygii (ray-finned fishes)

- 26,000 species

- rays: support for the fins

3 distinct lineages for ray-finned fishes are distinguished by:

- form of tail

- form of scales (presence/ absence)

- structure of swim bladder

Superorder Chondrostei

- sturgeons and paddlefishes

- 25 species

- modern ones lack a complete bony skeleton

- hardened cartilage vertebral column

- notochord as adults

- bones associated w/ skull

- weak jaw

- lack scales

- heterocercal tail (notochord in upper lobe)

Superorder Holostei

- bowfin and gars

- 8 species

- ganoid scales: thick, non-overlapping

- slightly heterocercal tail (notochord to base of upper lobe)

- teeth

Superorder Teleostei

- >26,000 species

- scales are absent- thin, lightweight, overlapping, mostly rounded (cycloid, ctenoid)

- tail: homocercal (equal lobes)

- operculum: gill covering, aids in gas exchange

Class Amphibia

- >4,000 species

- first tetrapod group

- Amphios: living a double life (most split their life btw aquatic and terrestrial stages) (larval)

- ancestral group: most likely to be Crossopteryian fish

- similarities: front limbs bones, digits, dentition, flattered skull, skull bones, “neck-like region

Earliest fossil: Ichthyostega

- 4 limbs

- similar skeletal structure to modern amphibians but still retained fish characters (dorsal fin on tail)

- some scales

- 360 mybp

Subclass Lissamphibia

- modern amphibians

- smooth, living a double life

- thinnest skin

Order Anura

Frog and toads

Order Gymnophiona

Caecilians

Order Caudata

Salamander

Class Reptilia

- >8,000 species

- includes turtles, crocodilians, lizards, snakes, and tuatara

- lots of fossils due to size and morphological characters

* snakes are the best *

3 skull lineages

1. anapsid

2. diapsid

3. synapsid

Anapsid

- without arch

- no temporal openings

- turtles and tortoises

Diapsid

- 2 arches

- 2 temporal openings

- tuatara, crocodilians

- lizards, snakes

- fossil reptiles, birds

Synapsid

- with arch

- 1 temporal opening

- fossil reptiles, mammals

Order Testudinata

- turtles and tortoises

- anapsid skull

- >400 species

Order Crocodylia

- alligators, crocodiles, caimans, gharials

- 28 species

- diapsid skull

Order Rhynocephalia

- tuatara

- 1 species

- diapsid skull

- 3 lines

Suborder Lacertilia

- lizards

- fossils 240 mybp

Suborder Amphisbaenia

- worm lizards: worm-like, ringed

- >200 species

Suborder Serpentes

- snakes

- fossils 200 mybp, fragile and lacking large bones

- <2,500 species

Class Aves

- 9,000 species

- diapsid skull

- “Glorified Feathered Reptiles”

- fossils at 150 mybp Archaeopteryx lithographica

Subclass Neornithes

New bird

Superorder Paleognathae (ancient jaw)

- 5 orders

- many holes

- upper jaw

- flat sternum; flightless birds

Superorder Neognathes (new jaw)

- 23 orders

- 2 openings

- upper jaw

- keeled sternum

Order Passeriformes

- largest group of > 5,000 species

Class Mammalia

- appeared about 225 mya and evolved from small mammal-like reptiles

- after dinosaur extinction mammals flourished

- synapsid skull

3 dentitions:

1. thecodont

2. heterodont (incisors, canines, premolars, molars)

3. diphydont (milk teeth, permanent teeth); 2 sets of teeth in lifetime

Age of mammals

- Cenozoic era lasted 65 million years

- coincides w/ mass extinctions of Ruling Reptiles

- ancestral reptile group: Therapsids

- probably 1 lineage of reptilian ancestor

Therapsids

- synapsid skull

- middle ear ossicle(s)

- limbs under body

- bipedal

- thecodont

- increased brain capacity

- separation btw thoracic & abdominal cavities

Subclass Prototheria

- egg-laying mammals

- first wild beast

- Order Monotremata: one opening (cloaca-chamber w/vent to outside)

- 3 living species (leathery shelled)

- fossils at 200 mybp; probably several groups at one time; Australian region

Subclass Theria

- wild beast

- diverged into 2 distinct groups at 160 mybp; recognized as 2 Infraclass

- Infraclass Metatheria: after wild beast

- Infraclass Eutheria: true wild beast

Infraclass Metatheria: marsupials

- 7 orders, 250 species

- Australian region (most), South America, Central America, North America

- viviparous: short-term placenta, weak hormonal system

Infraclass Eutheria: placental mammals

- 18 orders, 6,000 species

- viviparous: better placental connection

Classification of humans

Kingdom Animilia

Phylum Chordata

Subphylum Vertebrata

Class Mammalia

Subclass Theria

Infraclass Eutheria

Order Primates

Family Hominidae

Genus Homo

Species Homo sapiens