23 Vertebrates Evolution and Diversity

Question 1

Chordates 2 main things

Answer 1

• bilaterally symmetrical
• are deuterostome

Question 2

4 Key Features of Chordates

Answer 2

1. Notochord - flexible rod located
   between the digestive tube and nerve
   chord
2. Dorsal, hollow nerve cord- Develops into the brain and spinal cord of the adult
3. Pharyngeal slits
   - function as suspension-feeding devices in many invertebrate chordates
   - modified in more evolved vertebrates for: Gas exchange, Hearing, Jaw support
4. Muscular, post-anal tail used for swimming

Question 3

Subphylum Cephalochordata (lancelets)

Answer 3

Most basal chordates
Segmented muscles develop from blocks of mesoderm called somites
Encoded HOX proteins are master regulators of embryonic development

Question 4

Subphylum Urochordates (tunicates)

Answer 4

gelatinous
aka sea squirts
chordate characteristics apparent in larvae stage
- tail
-notochord
-pharynx with numerous slits
- dorsal hollow nerve cord

Question 5

Vertebrate Phylogeny Timeline
Development of Features

Answer 5

got all adaptations after Cambrian explosion because of competition
1. Brain and cranium
evolve
2. vertebral column
3. the jaws, ossified
skeleton, and paired
appendages evolve
later

Question 6

What changes happened
overall within the Vertebrates

Answer 6

• Gene duplication events gave rise to additional genetic and in turn morphological complexity
  -* Vertebrae enclosed the spinal chord and replaced notochord***
• Vertebrae originally made of cartilage but later replaced by mineralized bone

Question 7

Craniates

Answer 7

in between invertebrates and vertebrates
* Possess two Hox gene clusters plus other gene duplications
* Are generally active with higher metabolic rates
* Muscular lining of digestive tract
* Have heart with 2 or more chambers and red blood cells
* Have kidneys
Groups of Craniates
- Agnatha within that the hagfish

Question 8

Craniates
- Agnatha Group

Answer 8

• jawless
• no teeth/bones but had plates
• mouth starts to calcify at pharngyl slits
• bottom dwellers
• no paired fins
  most primitive is the Hagfish

Question 9

Hagfish

Answer 9

Belong to the Craniates and the subgroup of Agnatha
- only vertebrates without jaws: hagfish and lampreys
- possess rudimentary vertebrae
– Cartilaginous skeleton & notochord. (no
skeleton, no notochord in adult)
– No jaws
– Three accessory hearts
– Lack vertebrae, cerebrum, cerebellum
– Direct development
– Glands along body produce copious amounts of slime to deter potential predators

Question 10

Characteristics of Vertebrates

Answer 10

1. Neural crest
   - Embryonic feature formed from the neural crest cells throughout the body
   - Allows for many unique vertebrate characteristics (e.g. bones and cartilage)
2. Enhanced cephalization: Skeletal elements, such as the cranium (braincase), allow for the big evolutionary feature of vertebrates
3. Vertebral column is the main support for the body axis. It allows for large size, fast movement, and protection of the nerve cord.
4. The closed circulatory system pumps oxygenated blood to cells and allows rapid metabolism, rapid movement to search for food, escape predators.

Question 11

Vertebrae

Answer 11

Somites are repetitive muscle blocks along spine to allow for efficiency
* Main support structure for trunk, making large body size and fast movements possible
* Add ribs to anchor muscles, protect internal organs
* Support for limbs
* Endoskeleton can grow continuously, unlike exoskeleton of arthropods

Question 12

Family Petromyzontida

Answer 12

• oldest vertebrates
• an ectoparasite= parasite from the outside
• lampreys in fresh/salt water
• early version of vertebral column that was a skeleton of cartilage and the covering of nerves was cartilaginous
• larvae resemble lancelets

Question 13

Advantages of Jaws and Paired Fins

Answer 13

• made animals stronger/faster
• teeth let them disable and consume food faster
• can eat food supplies they couldn’t before as agnathans
• fins and tail allow fine scale maneuvering
• are active predators so can have diverse lifestyles and nutrient sources

Question 14

Gnathostomes

Answer 14

• jawed vertebrates
• have true jaws, hinged structures that with the help of teeth, enable vertebrates to grasp food firmly
  -2 pairs of fins
• HOX gene duplication to four clusters (linked to morphological diversification)
• enlarged forebrain (better smell/vision)
• Lateral line system (organs that sense vibrations in the water)
  Hypothesis: Vertebrate jaws evolved by modification of skeletal rods that previously supported anterior pharyngeal slits. Remaining gill slits remain as site of respiration

Question 15

“Age of Fishes”

Answer 15

During late Silurian & early Devonian periods (~420-400 MYA), the gnathosomes largely replace agnathans
2 groups alive today:
1. Class Chondricthyes:
Sharks and rays - Have cartilaginous
skeletons “Cartilaginous fishes”
2. Class Osteichthyes or “Bony fish”

Question 16

Class Chondrichthyes

Answer 16

• lost bones in favor of cartilage is a derived condition that emerged after they diverged from gnathostomes
• lost ability to calcify
  ex: sharks , rays
  Evidence:
• Most species have some calcium in skeleton
• Traces of bone found in scales, base of teeth, and on vertebrae surface
• Bonelike tissues are found in some early shark fossils

Question 17

Sharks

Answer 17

Chondrichthyes
- Swift, though not highly maneuverable
swimmers
- Carnivorous and filter feeder: Hinged jaws, teeth from scales, intestinal spiral valve increases surface area
- Sharp vision, no color; olfaction from
paired nostrils; detect electrical fields;
lateral line detects low-frequency
vibrations; inner ear
Internal fertilization
– Oviparous eggs hatch outside
– Ovoviviparous eggs hatch inside
– Viviparous live young born nourished
by placenta

Question 18

Superclass Osteichthyes or
“Bony fish”

Answer 18

• Ossified endoskeleton of calcium
  phosphate, dermal scales
• Maneuverable swimmers
• Neutrally buoyant (swim bladder)
• Acute senses (lateral line)
• Gill-breathers (operculum)
  Variable Reproduction
  – External & internal fertilization
  Three extant fish classes:
  1 Actinopterygii, ray-finned
  2 Actinistia, lobe-finned
  (coelocanths),
  3 Dipnoi, lungfishes

Question 19

Class Actinopterygii

Answer 19

Sub class of Osteichthyes
Ray-finned fishes (muscular)
– e.g. bass, trout, perch, tuna, herring, eels
– Fins supported by long flexible rays
– Fins may be modified for maneuvering, defense, and other functions

Question 20

Class Actinistia (Coelacanths!)

Answer 20

Sub class of Osteichthyes
Lobe-finned fishes with muscular pectoral &
pelvic fins supported by extensions of bony
skeleton
– Many large, bottom dwellers that may have
used muscular fins to “walk” along the
bottom
– Devonian coelacanths mostly freshwater
animals with lungs, but others entered sea

Question 21

Class Dipnoi

Answer 21

Sub class of Osteichthyes
* A Devonian lungfish probably ancestor of
amphibians & all other tetrapods
– Generally, inhabit stagnant ponds & swamps
– Can gulp air into lungs connected to the pharynx
– Also have gills; main organs for gas exchange in Australian lungfishes
– Developed lobed walking fins to move from one pond to another
– During dry season, some lungfishes can burrow into mud & aestivate (~hibernation)

Question 22

Tetrapod

Answer 22

• aquatic to terrestrial transition species
• During Devonian, plants begin providing organic material at water’s edge
• Lobe-fin & lungfish abundant - Buccal breathing*, leg-like paddles
• The pectoral and pelvic fins of some lobe-finned fish evolved into the limbs and
  feet of tetrapods
• Tetrapods are gnathostomes that have limbs
• first tetrapod’s spending long time on land were amphibians
  IMPORTANT transitional species= tiktaalik, Acanthostega

Question 23

Tiktaalik

Answer 23

super important transition species for water to land
Fish Characteristics
- Had gills and a lung . Gills had reduced bony covering
- had fins for swimming
- scales covering it’s body
Tetrapod Characteristics
- flat heads with eyes on top
- Ear notches. Larger than seen in other Devonian fish.
- Had a full set of ribs – needed for breathing and support out of water

Question 24

Acanthostega

Answer 24

super important transition species for water to land
- Prehistoric tetrapod of the Late Devonian Period and among the first tetrapods to have
recognizable limbs.
Tetrapod Characterisitic
- Had a neck so could move its head around (fish shoulders are directly connected to skull)
- Fin skeleton. Fins have an internal structure similar to limbed animals. Probably not used for walking but could support animal’s weight
Lifestyle
- hunted small fish in shallows and terrestrial arthropods

Question 25

Characteristics of Tetrapods

Answer 25

• Four “feet”
• Feet have digits to transmit muscle force to ground
• a neck of 1 or more vertebrae
• Bones of pelvic girdle are fused to vertebrae so it can support weight of back legs
• No gill slits – instead pharyngeal clefts give rise to facial structures and glands
• These general characteristics continue to evolve in the tetrapod lineages, eg. pectoral limbs became wings

Question 26

Amphibian Orders

Answer 26

Order Urodela – Salamanders, retain tails as adults
Order Anura – Frogs, lack tails as adults
Order Apoda – Caecilians, lack legs
Limitation: Amphibians need to return to water to lay eggs and for development of larvae