5 - Jaws and Paired Fins

This set of flashcards covers crucial concepts related to the origin of jaws and paired fins in Gnathostomata, as discussed in Zoology 224 lecture notes.

What does Gnathostomata refer to?

A group of vertebrates characterized by the presence of jaws.

What major evolutionary advance is associated with the origin of jaws?

The evolution of jaws led to the development of paired fins and increased success among vertebrates.

What are paired fins believed to have eventually evolved into?

Limbs.

What does the term 'metamerism' refer to in zoology?

Segmentation or repetition of body parts in vertebrates.

What is the significance of branchial arches in vertebrate anatomy?

They are skeletal supports that form between embryonic pharyngeal slits and play a role in jaw evolution.

What is the first branchial arch called?

Mandibular arch.

What are the two main elements of the mandibular arch?

Palatoquadrate (dorsal) and Meckel’s cartilage (ventral).

What role does the hyomandibula play in jaw evolution?

It supports the jaws in early gnathostomes, aiding in the suspension of the lower jaw.

What are the two prevailing hypotheses for the origin of paired fins?

Gegenbaur's hypothesis and the fin-fold hypothesis.

What does Gegenbaur’s hypothesis suggest about paired fins?

That they arose from branchial structures.

Describe the fin-fold hypothesis in simple terms.

It proposes paired fins originated from continuous ventro-lateral folds along the body.

How do the pectoral fins relate to tetrapod anatomy?

They are homologous to the tetrapod forelimb.

Name one key element formed from the mandibular arch in early gnathostomes.

Palatoquadrate or Meckel's cartilage.

What does the term 'branchial arch' refer to?

Structural supports between pharyngeal slits; important in both respiration and jaw evolution.

Why is the term 'gill arch' considered incorrect in this context?

Because it implies respiratory tissue which is not present in the jaw-forming arch.

What is the second branchial arch known as?

Hyoid arch.

What is one important structure that develops from the hyoid arch?

Hyomandibula.

What two groups of gnathostomes are discussed in relation to teeth evolution?

Placoderms and acanthodians.

What is the significance of the fossil Entelognathus?

It is classified in the discussion of early gnathostomes but not strictly a placoderm.

Why is it crucial to understand the theories of jaw evolution?

They provide insight into vertebrate evolutionary history.

What is a key focus of the course regarding jaws and paired fins?

To understand the hypotheses and their evidential support.

What characterizes the serial metamerism of vertebrates?

Repeated segments from anterior to posterior in the body.

Which segment of the branchial arch gives rise to the upper jaw in early gnathostomes?

Palatoquadrate.

What is the role of researchers in the context of theories of jaw evolution?

They modify and present new hypotheses based on advancing knowledge.

What historical figure proposed the archipterygium hypothesis?

Karl Gegenbaur.

In which year was Gegenbaur's theory published?

1877.

What might the future of research on jaw and paired fin evolution involve?

Continued exploration and discovery using new scientific techniques.

What is the anatomical term for the largest dorsal element of the mandibular arch?

Palatoquadrate is the largest dorsal element of the mandibular arch.

What are the early gnathostomes mentioned in the lecture?

Placoderms and acanthodians.

What type of structure do branchial arches evolve into in adult vertebrates?

Cartilage or bone.

How does the presence of teeth in placoderms contribute to research?

It helps understand the evolution of teeth.

What forms to support the gills in adult fish?

Branchial arches.

What does the term 'ventro-lateral folds' refer to in the fin-fold hypothesis?

Continuous tissue folds that became divided into fins.

What is a common error students should avoid regarding the term 'gill arch'?

Using it instead of 'branchial arch' in exams.

Why is the hyoid arch important to jaw evolution?

It aids in the support of the jaw structure.

What is emphasized for students with regard to the understanding of hypotheses in this course?

The need to differentiate between established facts and ongoing research.

What is a key takeaway regarding the origin of jaws from this course?

The origin is complex and supported by various hypotheses, still debated in research.