CVA - Unit 1. Vertebrate History and Lineages

Phylogeny

the evolutionary history of lineages

Ontogeny

the development of individuals

Metamerism

segmentation of body structures (along the anteroposterior axis)

Bilateral symmetry

distinct anterior / posterior regions; midsagittal plane can divide the body into mirrored halves

Cephalization

the increased localization of nerves and sensory structures into a distinct, dominant head

Adaptation

a hereditary modification of a phenotype that increases the probability of survival

Preadaptation

structure or behavior possesses the necessary form or function before the biological role arises

Morphologies can be similar based on which three criteria?

1. Homology

2. Analogy

3. Homoplasy

Homology

similarity based on common ancestry (often detected via embryology)

Analogy

similarity of function

Homoplasy

similarity of resemblance (usually refers to similarities in structure that do NOT result from common evolutionary origin)

_______ and ______ evolution often lead to homoplasy.

Convergent, parallel

Parallelism

closely related species that diverged relatively recently develop similar specializations

Convergent evolution (convergence)

distantly related and morphologically dissimilar species become more similar in descendants

Heterochrony

changes in the relative timing of developmental processes in descendants relative to ancestral species

Paedomorphosis

retention of embryonic or larval characteristics into adulthood

Peramorphosis

development of structures is extended, creating new morphologies

Clade

all the descendants of a common ancestor

Non-rank nomenclature

names assigned to lineages originating from each branch point (node)

Plesiomorphic traits

ancestral (“primitive”) traits

Symplesiomorphy

shared ancestral characteristics

Apomorphic traits

derived traits

Autapomorphy

unique derived characteristics

Synapomorphy

shared derived characteristics

(These are the ONLY traits that provide information re: phylogenetic relationships)

Parsimony

tendency towards the simplest explanation (“Occam’s razor”)

Principle of parsimony

fewest number of changes from ancestral to derived trait is most parsimonious

Monophyletic group

ALL descendants of a common ancestor are included

Paraphyletic group

includes common ancestor, but one or more descendants are omitted

Polyphyletic group

members do NOT share a common ancestor

Crown group

smallest clade that includes ALL living members of a group and any fossils (usually the top of the phylogenetic tree)

Stem group

extinct basal members of a clade not included in the crown group, (often lacking some synapomorphies) but are more closely related to the crown group than any other group

Why can phylogenies be considered “hypotheses”?

They are based on incomplete data and are subject to change with new evidence.

Remember: The fossil record is NOT complete. It takes a while to become a fossil. The information we have today could change tomorrow!

Why can traits be considered primitive, but not living organisms?

Organismal phenotypes are often a mosaic, or a mishmash, of ancestral and derived traits. We can use “primitive” or “ancestral” to describe the traits, but not the living organism.

A simple mono/pary/polyphyly diagram. :)

True or False: By definition, crown groups are considered paraphyletic.

False

The airfoils of pterosaurs and bats are _____ as wings, but _____ as forelimbs.

analogous, homoplastic

Vertebrates are metazoans. Metazoan is just a fancy word for saying…

animal

What are some key features that all metazoans share?

1. Multicellular - allows for division of labor and cell specialization

2. Heterotrophic

3. Eukaryotic

4. Motile for at least part of life cycle

5. Sexual reproduction (mostly)

6. Embryonic development

7. Exhibit some form of body symmetry

8. Have body plans with germ layers

Heterotrophy(ic)

does not make its own food; obtains energy by eating other organisms or organic matter

What are metazoans thought to have evolved from?

Colonial choanoflagellates

(These resemble the choanocytes, or goblet cells, found in sponges.)

List the key features of deuterostome development.

1. Anus forms first

2. Radial cleavage

3. Coelom forms from mesodermal pouches extending off of the gut (enterocoely)

List the key features of protostome development.

1. Mouth forms first, at or near blastopore

2. Spiral cleavage

3. Mesoderm forms as a block of tissue and will eventually split to become the coelom (schizocoely)

What are two major protostome lineages discussed in class?

1. Ecdysozoans (ex. arthropods, nematodes)

2. Lophotrochozoans (ex. mollusks)

What are two major deuterostome lineages discussed in class?

1. Ambulacrarians (ex. echinoderms, acorn worms)

2. Chordates (ex. lancelets, tunicates, vertebrates)

Pharyngotremy

“perforated pharynx”

(A series of pharyngeal pouches arises as
diverticula of the endoderm of the foregut on
either side of the pharynx. These become the
arches, which form supporting structures of
soft and skeletal tissues. Between pouches are cleft-like depressions, or pharyngeal clefts, which may rupture to
form slits and provide passage from the
pharynx to the outside.)

Why is pharyngotremy vital to aquatic vertebrates?

The resulting arches and clefts become persistent gill slits that pass water into the pharynx, both for filter feeding and respiration.

Why is pharyngotremy vital to terrestrial vertebrates?

Each arch has a cartilaginous and muscular component, an artery, and a cranial nerve. The arches contribute to a variety of glands, lymphatic tissues, bones, nerves, throat muscles, and heads of tetrapods.

True or False: Convergent evolution is the phenomenon where closely related species develop similar morphologies.

False

Which of the following is best defined as 'ancestral trait'?

plesiomorphy

autapomorphy

apomorphy

synapomorphy

plesiomorphy

True or False: By definition, crown groups are paraphyletic.

False

True or False: Nonvertebrate chordates have filamentous gill tissue on the pharyngeal arches.

False

From which pharyngeal arch is the facial nerve derived?

Arch 2

Which cell type is unique to cnidarians?

Cnidocytes

‘Ammocoetes’ refers to the larval form of which group?

Petromyzontiformes

In which group do we see the earliest appearance of mineralized tissues?

Conodonta

True or False: The tongue is innervated by the hypoglossal nerve in Gnathostomes.

True

The cartilaginous element that contributes to the upper jaw of gnathostomes is the __________.

palatoquadrate

The cartilaginous element that contributes to the lower jaw of gnathostomes is the _____.

Meckel's cartilage

What 4 features do all chordates share?

1. Dorsal hollow nerve cord (forms CNS)

2. Notochord (slender rod of fibrous connective tissue lying beneath and parallel to central nerve cord)

3. Endostyle (homologous with thyroid gland)

4. Postanal tail (posterior elongation of the body)

Pharyngeal bars and slits are vital to nonvertebrate chordates because they are primarily involved in…

filter feeding

True or False: All chordates have muscular segments called myomeres.

True

What are the 3 subphylums of Phylum Chordata?

1. Cephalochordata

2. Urochordata

3. Vertebrata

Subphylum Cephalochordata

• Marine chordates known for burrowing into sandy sediments

• Filter feed via buccal cirri and wheel organ

• Water flows over ciliated pharyngeal bars, exits into atrium or tunic, and goes out through atriopore

• Ciliated neurula embryo

Ex. Amphioxus, lancelets

Subphylum Urochordata

• Sessile adults with saclike bodies and tubular in/excurrent siphons

• Encased in a protective, supportive tunic that is secreted by the epidermis of the mantle 

• Free-swimming “ascidian tadpole” larvae (CNS degenerates at metamorphosis, tail and notochord are resorbed)

Ex. Tunicates, sea squirts

What are the MAJOR derived anatomical traits shared by vertebrates?

• Vertebral column

• Cranium

• Forebrain (specifically the telencephalon)

• Closed circulatory system

• Complete digestive tract

• Multilayered epidermis

• Pancreas and liver

Cyclostomes - Myxiniformes

Hagfishes

• Marine, burrowing scavengers

• Large mucus glands, internal gill openings, and a single terminal nasal opening

• Barbels around mouth

• “Tooth plates”

• Large blood sinuses and low blood pressure

• Exhibit a “knotting” behavior

Cyclostomes - Petromyzontiformes

Lampreys

• Single nasal opening on top of head

• Heart innervated by Vagus nerve

• Parasitic as adults; oral gland secretes anticoagulant

• Anadromous - ascend rivers and streams to spawn and then die afterward

• Spends most of life cycle as ammocoetes larvae, which burrow into sediment and suspension-feed

Which of the following is not a shared derived trait for Gnathostomata?

Paired pelvic fins

Branchiomeric musculature

3 semicircular canals in inner ear

Hypobranchial musculature

Branchiomeric musculature

Describe the structure of the dermal armor of ostracoderms.

Made up of aggregations of odontodes - toothlike elements in the dermis - and projections of dentine with pulp cavity and a bony base (aspidin)

Very similar to the placoid scales of sharks

Why was mineralized tissue an important radiation of early vertebrates?

It offered the basis for advanced body armor for protection, teeth for predation, and an endoskeleton for locomotion

Pectoral fins and girdles first arose in…

osteotracans

Jaws are derived from an enlarged, anterior pharyngeal arch called the…

Mandibular arch

Why did jaws in organisms likely evolve?

Initially to increase efficiency of gill ventilation, and later coopted for predation

How did jaws likely evolve?

From pharyngeal slits and branchial arches

List the generalized body plan features of Gnathostomes.

1. Jaws formed from mandibular arch

2. Gill skeleton of jointed branchial arches with rakers

3. Hypobranchial muscles 

4. 2 olfactory tracts and nostrils

5. Spiracle

6. 3 semi-circular inner ear canals

7. Conus arteriosus of the heart

8. Horizontal septum

9. Vertebrae with centrum and ribs

Placoderms

• Extinct sister group to Gnathostomes

• Extremely diverse in size and morphology

• Thick bony shield of dermal armor on head, front of body, and pectoral fins

• Most lacked teeth, but had toothlike projections of the dermal jawbones

• Mineralized endoskeletons

• Some of the earliest known instances of viviparity (developing embryos) in vertebrates

Ex. Dunkleosteus

Acanthodians

• Extinct

• Most the size of minnows

• Heterocercal tail

• Teeth formed shark-like tooth whorl 

• Primitive, large operculum-covered gills

“Spiny sharks”

Almost half of all vertebrates can be split in terms of diversity between ___________ (ray-finned) and ___________ (lobe-finned, including tetrapods).

Actinopterygii, Sarcopterygii

What are some major shared characteristics of all Chondrichthyes?

1. “Oily” liver

2. Ampullae of Lorenzini

3. Cartilaginous skeletons

4. Placoid scales

5. Reproductive claspers in males

6. Subterminal mouths

7. Continuous tooth replacement

What two major groups comprise the Chondrichthyes?

1. Elasmobranchii (sharks and rays)

2. Holocephali (chimaeras or ratfishes)

Chondrichthyes - Elasmobranchii

• Sharks (Selachii) and skates and rays (Batoidea)

• 5 exposed gill slits

• Small or absent dorsal spiracle (often closes before birth)

Chondrichthyes - Holocephali

• Ratfishes

• Upper jaw fused to cranium

• Teeth reduced to grinding tooth plates (durophagous habits)

• Extended, fleshy operculum covering 4 gill slits

• Spiracle absent in adults

• Mostly absent placoid scales

What is the significance of the Greenland shark in regard to vertebrate longevity?

Greenlands are the longest living vertebrates known to science.

They reach sexual maturity at around 156 years of age and grow at a rate of around 1 cm per year. Their metabolisms are extremely slow, and they don’t decline as they get older, unlike other vertebrates.

Lepidotrichia

jointed bony fin rays that surround bundles of giant collagen fibers

True or False: In Osteichthyes, many species retain their cartilaginous endoskeletons.

False; most have well-ossified bony skeletons

Where did the swim/gas bladder in Osteichthyes derive from?

Embryonic tube gut

Many Osteichthyes have mouths that are…

terminal

Differentiate between Sarcopterygii and Actinopterygii based on their physical characteristics.

Sarcopterygii

• Lobe-finned

• Fins monobasal with internal bony elements (mesomeres) and muscles external to the body wall, giving them a fleshy, stalk-like appearance

• Cosmoid scales in early members

Actinopterygii

• Ray-finned

• Endoskeleton, where muscles barely extend onto the fin (if at all)

• Ganoid scales in early members; most modern species have reduced, thin elasmoid scales

Actinopterygii - Polypteriformes

Bichirs, reedfish

• Elongated bodies with heavy rhomboidal scales

• Many have lungs

• Modified heterocercal tails

Actinopterygii - Acipenseriformes

Sturgeons, paddlefish

• Have spiracles

• Secondary cartilaginous skeletons

• Most lack ganoid scales (except for sturgeons, which have enlarged scutes in lateral rows along the body)

Actinopterygii - Neopterygians 

(List the main features.)

• Dorsal (rather than ventral) gas bladder

• Basals lost from fin skeleton

• No spiracle

• Reduced heterocercal tail

• Loss of electroreceptor ampullary organs

• Increased jaw mobility (aka lateral flaring of buccal cavity)

Actinopterygii - Neopterygians - Lepisosteriformes

Gars

• Retain large, rhombic ganoid scales

• Dorsal gas bladder used for respiration and buoyancy

Actinopterygii - Neopterygians - Amiiformes

Bowfin

• Dorsal gas bladder used for respiration and buoyancy

• Thin scales made of a single layer of bone (like teleosts)

Actinopterygii - Teleosts

(Know the main features.)

• Thin, circular elasmoid scales

• Ossified vertebrate

• Dorsal gas bladder dedicated to buoyancy 

• Skull with complex jaw mobility

• Pharyngeal jaws (see image)

Tetrapods initially emerged from…

tetrapodomorph fishes

• loss of bony operculum*

• flat head and body, with long snout and dorsal eyes

• loss of dorsal and anal fins

• reduced tail fins

• likely respired via gills and gulping air

Coelocanths are extant Sarcopterygiians of subclass…

Actinistia

Lungfish are extant Sarcopterygiians from subclass…

Dipnoi

True or False: The earliest tetrapods, such as Acanthostega and Icthyostega, were mostly aquatic, despite having limbs.

True

What are the two major lineages of tetrapods?

1. Lissamphibia

2. Amniota / Reptiliomorphs

The tetrapod limb consists of supports (girdles) and ______ segments that articulate end-to-end. 

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