PALEO LABORATORY # 10, PAGE 1
PALEO LAB # X – REPTILES, SYNAPSIDS AND BIRDS
The oldest-known reptiles are found in Lower Carboniferous (Mississipian)-age deposits
from Scotland and from the Mid-Carboniferous (Pennsylvanian) of Nova Scotia.
reptiles" possessed labyrinthine infolding in their teeth and assumed the sprawled posture of their
labyrinthodont amphibian (Seymouriamorph) ancestors.
However, even the earliest reptiles
showed vast improvements over the Amphibia in their adaptation to land-dwelling through the
evolution of internal fertilization and development of the amniotic egg.
This type of egg could
be laid on land and through its development the reptiles freed themselves from dependence on
the aquatic environment.
A couple of groups of these “stem reptiles”, the captorhinids and
palaeothyrids, are evidently close to the ancestry of the later “diapsid” reptiles.
Mesozoic times, reptiles completely dominated terrestrial environments and other members of
the group reinvaded the oceans and developed powers of flight.
Reptile evolution involves a
number of distinct fossil and modern groups.
The classification of the reptiles into major categories is primarily based on the position and
numbers of temporal openings on the sides of the skull.
The anapsids, which include the turtles
and primitive reptile groups such as the procolophonids, pareiasaurs and captorhinids, lack
Diapsids, including dinosaurs, the ancient flying pterosaurs and all modern
reptiles (except turtles) primitively have two temporal openings.
The euryapsids, including the
ancient swimming plesiosaurs and ichthyosaurs, had a single upper temporal opening.
synapsids, including the fin-backed pelycosaurs and “mammal-like reptiles” (therapsids), had a
single lower temporal opening. Although they have been placed within the reptiles in previous
classifications, the synapsids are now considered to belong to a distinct class of vertebrates.
EXERCISE # 1 - Observe the skull illustrations provided and the lab specimens of amphibians,
primitive reptiles, and advanced archosauromorphs. Describe the changes seen within this
"structural lineage" of skulls in terms of bones lost, bones reduced, and subsequent changes in
EXERCISE # 2 - Using the illustrations provided, identify the types of reptile temporal openings
in specimens TSU VP 051, VP 071, VP 157, VP 163 and VP 229.
EXERCISE # 3 - Observe the skull of the captorhinid
(TSU VP 069; on Shelf E4)
from the Lower Permian Arroyo Formation of Baylor County, Texas.
A. What feature of the skull makes this specimen an anapsid?
B. What is the evolutionary relationships of the captorhinids versus other reptile groups, both
ancient and modern?
The Pareisaurs were large anapsid herbivores from the Middle to Upper Permian of