Vertebrate Evolution and Earth's History

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Questions and Answers

Which characteristic is NOT associated with cyclostomes?

A muscular tongue with keratinous teeth

Rudimentary vertebral precursors

The presence of a jaw (correct)

A single nostril

What unique feature do hagfish possess that assists them in their scavenger lifestyle?

A protrusible jaw with sharp teeth

A complex, multi-chambered heart

Multiple slime glands (correct)

Paired fins for propulsion

How do adult lampreys typically obtain their nutrition, differing from their larval stage?

Photosynthesis

Scavenging dead organisms

Parasitizing other fish (correct)

Filter feeding

What is the term for the larval stage of lampreys?

Ammocoetes Signup and view all the answers

During their spawning cycle, adult lampreys that migrate from lakes and oceans utilize which type of behavior?

Anadromous migration Signup and view all the answers

How do larval lampreys facilitate the movement of water over their gills?

Flowthrough ventilation Signup and view all the answers

What is the typical ratio of female to male hagfish?

100:1 Signup and view all the answers

Which of the following describes the location of the mouth on an adult lamprey?

Located under the oral hood Signup and view all the answers

Which geological period is NOT considered part of the 'Age of the Fishes'?

Permian Signup and view all the answers

What feature does Pikaia possess that places it within the clade Chordata?

Notochord and V-shaped myomeres Signup and view all the answers

Which of the following is NOT a synapomorphy of Haikouella?

Cranium Signup and view all the answers

What discovery helped scientists determine that Conodonts were members of the clade Vertebrata?

The discovery of whole fossils with myomeres, teeth, paired eyes, and notochord. Signup and view all the answers

What is one piece of evidence supporting the hypothesis that vertebrates originated in a marine environment?

Early fossils were found in marine sediment. Signup and view all the answers

What distinguishes the Quaternary period from other periods in the fossil record?

The emergence of the genus Homo. Signup and view all the answers

Which of the following best describes the transition between the 'Age of the Dinosaurs' and the rise of mammals?

The Tertiary period marked the rise of mammals after the decline of the dinosaurs. Signup and view all the answers

Which feature of Hagfishes provides evidence of the original vertebrate condition in terms of body fluids?

Concentrated body fluids. Signup and view all the answers

What factor initially prevented sea lampreys from entering Lake Erie?

Niagara Falls acting as a physical obstruction. Signup and view all the answers

What was the consequence of lamprey invasion in the Great Lakes prior to control measures?

Collapse of the Lake Trout fisheries. Signup and view all the answers

What characteristic is shared by ostracoderms?

Possession of true bone. Signup and view all the answers

What major evolutionary development is associated with the Gnathostomata?

The origin of paired pectoral and pelvic limbs. Signup and view all the answers

Which of the following best describes the function of the conus arteriosus found in Gnathostome hearts?

Regulating blood flow leaving the heart. Signup and view all the answers

In mammals, how are teeth attached to the jaw?

Set in sockets and attached by periodontal ligaments. Signup and view all the answers

What is the evolutionary source of gnathostome jaws?

Formation from the mandibular arch, with the hyoid arch providing support. Signup and view all the answers

What major genetic event allowed the development of jaws in animals?

The duplication of HOX genes. Signup and view all the answers

Study Notes

Agnathans and Gnathostomes

Agnathans are jawless fish, including hagfish and lampreys
Gnathostomes are jawed fishes
Gnathostomes evolved from Agnathans
Differences between the two groups include the presence of jaws in Gnathostomes

Geologic Time and the Fossil Record

Earth formed over many years
Periods/epochs are distinguished by changes in landmasses, organisms, or asteroid impacts
"-zoic" means "animal," referring to the appearance of animal life after Precambrian
Ordovician, Silurian, and Devonian periods are known as the "Age of the Fishes"
Permian, Triassic, Jurassic, and Cretaceous periods are known as the "Age of the Dinosaurs"
Tertiary period marked the start of mammals
Quaternary period marks the appearance of the genus Homo - Pleistocene era is the caveman era
Holocene era is the modern human era

What Did the Earliest Vertebrates Look Like?

Pikaia, from the Burgess Shale beds in British Columbia, was an invertebrate chordate
It possessed a notochord and V-shaped myomeres, placing it in the Chordata clade
Possibly a cephalochordate

Early Vertebrate Evidence

Haikouella, a small fish-like animal from early Cambrian beds in Haikou, China, displayed chordate synapomorphies (dorsal nerve cord, notochord, pharynx)
It also exhibited vertebrate synapomorphies (pharyngeal muscles, paired eyes, enlarged brain)
However, Haikouella lacked a cranium and a distinct forebrain, suggesting it is not a vertebrate, but possibly a sister group

Conodonts

Conodonts were odd tooth-like fossils discovered in Paleozoic marine sediments
Fossils in the 1980's showed myomeres, teeth, paired eyes, notochord
These are almost certainly members of the clade Vertebrata, though their exact position remains uncertain

Environment of Early Vertebrate Evolution

Earliest fossils were found in marine sediments
Nonvertebrate chordates and deuterostome invertebrates originated in the marine environment, displaying body fluid concentrations similar to their surroundings
Hagfishes also show these characteristics

Simplified Phylogeny of Early Vertebrates

Phylogeny diagram showing extinct and extant jawless (Agnatha) and jawed (Gnathostomes) vertebrate groups
Extinct groups are indicated with + signs

Cyclostomes - Extant Jawless Fish

Agnatha (jawless) include hagfish and lampreys
Lack of internal ossification, paired fins, scales, and jaws
Lack complex reproductive structures
Single nostril
Have a velum (pump)-pharynx
Have rudimentary vertebral precursors (arcualia)
Single circulation
Muscular tongue with keratinous teeth

Myxiniformes - Hagfishes

~75 species, ~0.5m long marine cold water scavengers
Slime glands (90-200)
Single opening for water intake (olfaction and gill ventilation)
Gill openings moved posteriorly (burying head in prey)
5-16 pairs of gill openings
Females outnumber males 100:1

Petromyzontida - Lampreys

~40 species, both freshwater and marine, free-living and parasitic
10 cm to 1 m in length
Temperate waters

Lamprey Spawning Cycle

Adults migrate from lakes or oceans to small streams in late winter/spring
Build nests, eggs hatch in ~2 weeks, releasing ammocoetes (larval stage)
Ammocoetes filter feed and remain in the larval stage for 3-7 years
Free-living lampreys don't feed as adults and die after spawning
Parasitic species migrate back to lakes/oceans and live as parasites

Humans vs. Lampreys

Sea lamprey (Petromyzon marinus) moved into Lake Ontario
Niagara Falls used to be a barrier
Construction of canals in 1913-1918 allowed the lamprey to enter Lake Erie and then spread
Lamprey invasion resulted in a collapse of Lake Trout fisheries by 1950
Control measures were implemented

Ostracoderms

First unambiguous vertebrate fossils
Jawless, possessing true bone
Median fins (dorsal, anal, caudal)
Heavy armor plating

Gnathostome Derived Characters

Jaws and teeth, allowing for a firmer grip and increased food access
Two sets of paired limbs (pectoral and pelvic), improving movement
Jointed gill arches for double-pump ventilation
Vertebral column with segmented vertebrae (protecting the spinal cord/ providing structural support)
Nerve fibers possessing myelin sheaths to increase their efficiency
Epaxial and hypaxial muscles enabling efficient movement
Ribs connecting myomeres for more efficient locomotion
Heart with additional parts, such as the conus arteriosus, improving circulation

Gnathostome Body Plan

Horizontal septum divides trunk muscles
Three semicircular canals in the inner ear
Two olfactory tracts, leading to two nostrils
Jaws with teeth
Jointed gill arches
Internal gill rakers preventing food from entering the gills
Hypobranchial muscles connecting to the pectoral girdle
Heart with conus arteriosus between ventricle and ventral aorta

Extant Gnathostome Teeth

Differences in tooth structure (placement, and attachment style) across distinct vertebrate groups (e.g., chondrichthyans, bony fish, amphibians, reptiles, mammals)

Origin of Jaws

Gnathostome jaws formed from the mandibular arch; the hyoid arch forming the jaw supports.
HOX genes duplication event allowed complex jaw structures

Cyclostome vs. Gnathostome Gill Placement

Cyclostomes have gills located internally, while Gnathostomes have gills in a more external position

Vertebrate Nose

Cyclostomes have single nostrils (monorhiny)
Gnathostomes have double nostrils (diplorhiny)
Nasal capsules are close to the forebrain in cyclostomes, making it short; in Gnathostomes, the nasal capsules are more anterior, resulting in a longer brain.

Origin of Paired Appendages

Pectoral fins were the first paired appendages
Fish swim by flexing their bodies and tail in a wave motion with lateral fin movements

Advantages of Fins

Caudal fin propels the fish through water
Other fins (e.g., pectoral and pelvic) control direction and act as brakes

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Description

Explore the fascinating evolution of vertebrates from jawless Agnathans to jawed Gnathostomes. This quiz covers significant geologic periods and the characteristics of early vertebrates. Test your knowledge on the timeline of Earth and the major transitions in the history of life.