Diversity of Amniotes

Question 1

What is a synapomorphy of all amniotes?

Answer 1

they were developed from an amniotic egg

Question 2

What are the layers/sacs contained within the amniotic egg?

Answer 2

The amnion (surrounds the embryo), the allantois (stores metabolic wastes from the embryo) and the chorion (surrounds and cushions the embryo), as well as the yolk sac which provides nutrients to the embryo

Question 3

Where are the amniotic sacs and embryo positioned in basal amniotes? What is the purpose of this? What type of fertilization is required?

Answer 3

Within the hard/leathery shell, protects against desiccation, infection as well as predation, constrains the amount of gases (oxygen and carbon dioxide) being diffused into and out of cells, internal fertilization is required

Question 4

How was the amniotic egg modified for derived amniotes?

Answer 4

shell is hardened with calcium so its harder to bite/tear through, has pores for gas exchange, and in most derived amniotes the membranous sacs are replaced with placenta

Question 5

What do basal amniotes without a preserved amniotic egg have?

Answer 5

Upper palate with palatal denticles which are small teeth on the roof of the mouth for food processing, they use costal ventilation, they have a well developed ankle joint for limb driven locomotion

Question 6

Describe anapsid amniote skulls (bones)

Answer 6

Only have lower temporal fenestra and it is supported by four bones? postorbital, squamosal, and jugal

Question 7

What are the two clades of amniotes that are anapsids? Describe them.

Answer 7

1. Parareptilia: several related groups of sauropsids from late Paleozoic and early Mesozoic, includes Mesosaurs which are the earliest reptile to return to sea, they are carnivorous predators with small needle-like teeth as well as the Pareiasaurs which are large herbivores and their skulls have multiple bony protrusions
2. Captorhinidae: eureptiles from Paleozoic, can be up to 3m in length, they have multiple rows of teeth for grinding plant food

Question 8

What are the oldest known amniotes?

Answer 8

Hylonomous (more well known), as well as Paleothrys, they are small and lizard like and they feed on insects, they have anapsid skulls

Question 9

What are the two diapsid clades of basal amniotes?

Answer 9

1. Younginidae: 2 species, small and lizard like, hindlimbs are more developed to produce more propulsive force, the Thadeosaurus has a long tail
2. Ichthyopterygia: aquatic, convergently gained aquatic features (dorsal fin, flipper like limbs, homocercal tail)

Question 10

What is a euryapsid? What clades of amniotes are diapsids/euryapsids?

Answer 10

Upper temporal fenestrae only, surrounded by post-orbital squamosal and parietal bones.
Archosauromorpha, Lepidosauromorpha, Ichthyopterygia, and Younginidae

Question 11

What are the four fossil testudines and their skull types?

Answer 11

Pappochelys (modified diapsid skull), Eunotosaurus (between anapsid and diapsid, the fenestra can be covered by bony laminae) Odontochelys (anapsid, no carapace), Proganochelys (anapsid with both carapace and plastron)

Question 12

What are the three evolutionary theories for extant testudines?

Answer 12

A: testudines are within Parareptilia, supported by the anapsid skull modified from diapsid condition and plastron evolved before carapace
B: testudines in Archosauromorpha, currently the most likely, supported by molecular and anatomical evidence
C: testudines in Lepidosauria, least likely