Chapter 18: Questions & Answers

Most lizards and snakes are oviparous, but some are ovoviviparous or have placental viviparity. Compare these methods of reproduction in squamates.

--Oviparous: lay shelled, elliptical eggs beneath logs, under rocks, or in holes in the ground --Viviparous: giving birth to well-formed, live young; some are nourished by the placentae --Ovoviviparous: young receive nourishment only from their yolk sac.

What is the function of the allantois?

Forms a sac that stores metabolic waste

Describe ways in which amniotes are more functionally or structurally suited for terrestriality than were the earliest tetrapods.

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What is meant by a "kinetic" skull, and what benefit does it confer? How are snakes able to eat large prey?

A kinetic skull has movable joints; it allows predators to seize and manipulate prey; it increases effective closing force of the jaw musculature

What are the four membranes associated with amniotic eggs?

Amnion Allantois Chorion Yolk sac

What is the function of amnion?

Encloses the embryo in fluid, cushioning the embryo and providing an aqueous medium for growth

How might nest temperature affect egg development in turtles?

High temperature = females Low temperature = males

How might nest temperature affect egg development in crocodilians?

High temperature = males Low temperature = females

What is the function of the "pit" in pit vipers?

Identify heat signatures to the 0.003rd degree

What is the function of the Jacobson's organ in snakes and lizards?

Identify scents

Why are "reptiles," as traditionally defined, a paraphyletic group? How has cladistics taxonomy revised Reptilia to make it monophyletic?

Originally, birds were in their own class. Cladistic taxonomists made birds an order within Class Reptilia to make it a monophyletic group.

What is the function of the yolk sac?

Stores nutrients

What is the function of the chorion?

Surrounds entire contents of egg; forms an efficient respiratory organ for removing carbon dioxide and acquiring oxygen (like the allantois, is highly vascularized)

Amniotes are divided into three groups based on their skull morphologies. What are these three groups, and how do the skulls differ? Which living amniotes, if any, originated from each of these three groups?

Synapsid: contains a pair of lateral temporal openings and an orbit; all mammals Anapsid: contains an orbit; turtles Diapsid: contains a pair of dorsal temporal openings, a pair of lateral temporal openings, and an orbit; reptiles and birds

How do crocodilians breathe when their mouths are full of food?

They have a complete secondary palate.

Describe the principal structural features of turtles that distinguish them from any other nonavian reptilian order.

They have a shell consisting of a dorsal carapace and a ventral plastron; their ribs are fused to their shell; they can retract into their shell for protection.

Why are tuataras (Sphenodon) of special interest to biologists? Why are they rare?

Tuataras are the sole survivors of the sphenodontid lineage; their populations are extremely low due to island domestication and their very low reproduction rates