Early Jawed Fishes: Placoderms Flashcards

Questions and Answers

What is the class of the placoderms?

Chondrichthyes

Placodermi (correct)

Ostracodermi

Osteichthyes

What adaptive advantages did placoderms show over ostracoderms?

Several adaptive advantages

What was the first fish feature acquired by the placoderms?

Lower jaw

What advantage did the lower jaw provide for placoderms?

Diversified eating habits Signup and view all the answers

What did lampreys use their jawless mouths for?

Aggressive feeding Signup and view all the answers

How did placoderms differ in feeding compared to ostracoderms?

They could swim and eat other animals. Signup and view all the answers

In what way were ostracoderms typically limited in their movement?

Moving only in one plane, along the bottom of the pond Signup and view all the answers

What were the fins of placoderms necessary for?

Stability during swimming Signup and view all the answers

How did placoderms utilize their swimming environment differently?

Used the entire water column Signup and view all the answers

Better extensions off the body to either side greatly increased (blank), (blank), and (blank) were strongly selected.

stability during swimming, paired pectoral fins, pelvic fins Signup and view all the answers

The earliest of these paired fins had (blank) and appear to be simply (blank), but as time went by, a (blank) allowed for greater control during swimming.

broad bases, extensions of the body wall, narrower base Signup and view all the answers

What embryological structure is suggested to have evolved into the lower jaw?

Gill arches Signup and view all the answers

From what do the lower jaw and gill arches derive embryologically?

Neural crest cells Signup and view all the answers

Anatomically, the same cranial nerve that innervates the muscles of the gill arch innervates the (blank) and in sharks, the muscles that work the gill arches also work the (blank).

lower jaw, lower jaw Signup and view all the answers

What does the term 'placoderms' translate to?

Shell skins Signup and view all the answers

What is the classification for sharks?

Chondrichthyans Signup and view all the answers

What do you call bony fish, the largest group that diversified from early jawed fishes?

Osteicthyans Signup and view all the answers

Placoderms are now extinct.

True Signup and view all the answers

What covers the head and neck of placoderms?

Large bony plates Signup and view all the answers

What is a characteristic of the large bony plates of placoderms?

Bulky and heavy Signup and view all the answers

Which group diversified widely among early jawed fishes?

Placoderms Signup and view all the answers

What improvements did the placoderms showcase in anatomy?

Lower jaw anatomy and better shearing plates for shredding prey Signup and view all the answers

What paired fins did placoderms develop?

Pelvic fins Signup and view all the answers

How long could Dunkleosteus terrelli grow?

Up to six meters in length Signup and view all the answers

What did most placoderms also have in addition to gills?

Lungs Signup and view all the answers

Placoderms survived for about sixty million years before going extinct at the end of the Devonian period during a time of anoxia called the (blank).

Hangenberg Event Signup and view all the answers

Study Notes

The Placoderms Overview

Placoderms, belonging to the class Placodermi, were among the earliest jawed fishes.
They showcased adaptive advantages compared to ostracoderms, demonstrating evolutionary progress.

Evolution of the Lower Jaw

The development of a lower jaw marked a significant evolution in vertebrates, facilitating diverse feeding strategies.
Unlike lampreys, which used their jawless mouths aggressively, most ostracoderms were limited to suction feeding from the bottom.

Mobility and Feeding Habits

Placoderms were predatory, capable of swimming towards and consuming ostracoderms and other animals.
They utilized the entire water column for movement, contrasting with ostracoderms that primarily stayed on the pond bottom.

Anatomical Features

Improved body extensions enhanced stability during swimming, with paired pectoral and pelvic fins becoming essential.
Early paired fins had broad bases as body wall extensions, while later adaptations featured narrower bases for enhanced swimming control.

Evolutionary Insights

The lower jaw likely evolved from gill arches found in ostracoderms, supported by both embryological and anatomical evidence.
Lower jaws and gill arches share a common embryological origin from neural crest cells.

Cranial Nerves and Muscle Innervation

The cranial nerve that innervates gill arch muscles also innervates the lower jaw muscles, indicating a muscle coordination link between these structures.

Distinct Characteristics

The term "placoderms" translates to "shell skins," referring to their bony external features.
They had large, heavy bony plates covering their head and neck, which may have increased drag while swimming.

Diversity and Extinction

Placoderms experienced significant diversification during their existence, particularly noted for lower jaw enhancements and advanced shredding plates for prey.
They developed paired pelvic fins and survived for around sixty million years before becoming extinct at the end of the Devonian period during the Hangenberg Event.

Notable Species

Dunkleosteus terrelli was a prominent species among placoderms, reaching lengths of up to six meters.
Most placoderms possessed both lungs and gills, allowing for versatile gas exchange during their aquatic life.

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Description

Test your knowledge about the early jawed fishes known as placoderms. This quiz covers their classification, evolutionary advantages, and significant features like the lower jaw. Perfect for students of paleontology or those interested in evolutionary biology.