Evolutionary Biology: Vertebrates Quiz

Agnathans and Gnathostomes

• Agnatha are jawless fish, while Gnathostomes have jaws.
• Jawless fish, like lampreys and hagfish, are an early group of vertebrates.
• Fish with jaws, like sharks and bony fish, are a more recent group of vertebrates.

Geologic Time & The Fossil Record

• Earth formed over many years.
• Geologic periods are distinguished by changes in landmasses, organisms, or asteroid impacts.
• "-zoic" in a period name denotes an "age of animals".
• The Precambrian period is the earliest in which animal life is recorded.
• The Ordovician, Silurian and Devonian are often called the "Age of the Fishes"
• The Permian, Triassic, Jurassic, and Cretaceous periods are known as the "Age of the Dinosaurs".
• The Tertiary period is when mammals first appeared.
• The Quaternary is when humans (Genus Homo) appeared.
•  Pleistocene is the period when early humans (cavemen) lived.
•  Holocene is the period when modern humans live.

What Did the Earliest Vertebrates Look Like?

• Pikaia was found in the Burgess Shale in British Columbia.
• Pikaia was an invertebrate that possessed a notochord and V-shaped myomeres.
• Pikaia is placed within the Chordata clade and is possibly a cephalochordate.

Early Vertebrate Evidence

• Haikouella is a small fish-like organism.
• Haikouella has chordate features like a dorsal nerve cord and notochord.
• Haikouella also shows features of vertebrates like pharyngeal muscles and eyes.
• Haikouella has a possible link, but is not definitive as a vertebrate.

Conodonts

• Conodonts were odd tooth-like fossils, found in ancient marine sediments.
• Fossils show myomeres, teeth, paired eyes, and notochords.
• Conodonts were probably vertebrates.
• Their exact placement within vertebrate phylogeny is uncertain.

Environment of Early Vertebrate Evolution

• Earliest vertebrate fossils were found in marine sediments.
• Nonvertebrate chordates and deuterostome invertebrates are also of marine origin and had body fluids similar to their surroundings.
• Hagfish have similar body fluid concentrations as their marine surroundings, similar to the likely original vertebrate condition.

Simplified Phylogeny of Early Vertebrates

• The diagram shows relationships between groups, including cyclostomes, agnathans, and gnathostomes.
• The chart distinguishes extinct (dagger) groups from extant (asterisk) ones.

Cyclostomes - Extant Jawless Fish

• Agnatha includes hagfish and lampreys.
• Cyclostomes lack internal bone structures.
• They lack paired fins and scales.
• Cyclostomes lack jaws, complex reproductive structures, and usually have a single nostril.
• Cyclostomes typically have a velum that acts as a pump for their pharynx.
• They have cartilage-like precursor vertebrae called arcualia.
• Cyclostomes have single circulatory systems, and some have a muscular tongue with teeth.

Myxiniformes - Hagfishes

• Hagfishes have approximately 75 species.
• They are a type of jawless fish that range up to 0.5 meters long.
• They are marine, cold-water scavengers.
• Hagfishes have slime glands that produce defensive slime.
• They have a single opening at the front of their head for water.
• Gill openings are located far back.
• Males are out numbered by females.

Petromyzontida - Lampreys

• Lampreys comprise some 40 species, and are either freshwater or marine.
• They range from 10 cm to 1 m in length.
• Lampreys are found in temperate waters, and can be free living or parasitic.

Lamprey Spawning Cycle

• Adults migrate to spawning streams.
• Fertilization is external.
• Larvae called ammocoetes hatch and remain in streams for 3-7 years.
• Ammocoetes then undergo metamorphosis to adult free-living forms.
• Free-living forms do not feed as adults, and die after spawning.
• Parasitic forms return to the ocean or lakes to live as parasites on other fish.

Humans vs. Lampreys

• Sea lampreys migrated into the Great Lakes via the canals.
• The lamprey invasion decimated the Great Lakes fishery.
• Control measures have helped regulate the lamprey population.

Ostracoderms

• Ostracoderms were the first unambiguous vertebrate fossils.
• They were jawless but had bone.
•  Ostracoderms had median fins (dorsal, anal, caudal).
• Ostracoderms possess heavy armor plating.

Gnathostome Derived Characters

• Jaws and teeth permit firm grasps and greater food consumption.
• Paired pectoral and pelvic fins facilitate greater movement.
• Two sets of paired limbs, better movement.
• Jointed gill arches facilitate a double pump ventilation mechanism.
• Vertebral column with segmented vertebrae.
• Nerve fibers have myelin sheaths.
• Epaxial and hypaxial musculature within the trunk.
• Ribs between myomers that facilitate movement.
• The vertebrate heart has a conus arteriosus in addition to the sinus venosus, atria, ventricles

Gnathostome Body Plan

• Horizontal septum divides the trunk into dorsal and ventral hypaxial components.
• Three semicircular canals in inner ear.
• The fish has two nostrils, leading to olfactory tracts..
• The fish has jaws with teeth.
• The fish has a spiracle.
• Jointed gill arches are internal to gills, with gill rakers.
• The fish has hypobranchial muscles that attach to the pectoral girdle.
• The fish has a heart with a conus arteriosus, between the ventricle and ventral aorta.

Extant Gnathostome Teeth

• Some cartilaginous fishes have tooth whorls on their jawbones.
• Modern bony fishes have teeth in different forms, depending upon the group.
•  Modern mammals have teeth in sockets and attached to jawbone with periodontal ligaments.

Origin of Jaws

• Gnathostome jaws formed from the mandibular arch.
• The hyoid arch supports the jaws.
• HOX gene duplication events allow for jaw structures.

Cyclostome vs. Gnathostome Gill Placement

• Cyclostome gills are positioned internally.
• Gnathostome gills are positioned externally within gill arches.

Vertebrate Nose

• Cyclostomes have a single nostril (monorhiny).
• Gnathostomes have two nostrils (diplorhiny).
• Nasal capsules are close to the forebrain in cyclostomes (short forebrain).
• Nasal capsules are more anterior in gnathostomes (longer forebrain).

Origin of Paired Appendages

• Pectoral fins were the first paired appendages.
• Fish used bending (flexing) their bodies and tail to move through water.
• Gnathostomes have distinct head and neck regions.

Advantages of Fins

• Caudal fins push fish through the water.
• Other fins (pectoral, pelvic, dorsal, and anal) help steer fish.
• Pectoral and pelvic fins control pitching and acting as brakes.
• Unpaired dorsal and anal fins prevent a fish from rolling or yawing.

Test your knowledge on the evolution of vertebrates and their characteristics in this quiz. Explore important concepts related to geological periods, notable fossils, and the differences between various vertebrate groups. Perfect for students of evolutionary biology or paleontology.