Geology Reference
In-Depth Information
The development of flowers, in particular, is a turning point in not only plant evolution
but also insect evolution. In fact, the evolution of flowers and insects is so closely re-
lated that it is considered
co-evolution.
Co-evolution is a type of
symbiosis
or relationship
between two organisms. In this case, both the plant and the insect benefit from their re-
lationship. Today some plants and insects have such closely co-evolved characteristics
that only a certain species of insect can pollinate a certain species of plant.
Recognizing All the Mesozoic Reptiles
The front-page story of Mesozoic life on earth is, quite obviously, the reptiles — specific-
ally the dinosaurs. But contrary to popular belief, not all ancient reptiles were dino-
saurs. Dinosaurs are only one branch on a family tree that includes modern reptiles
such as turtles, snakes, and lizards, along with surviving ancient reptiles such as cro-
codiles (which evolved 200 million years ago and are still around) and others.
At the end of the Paleozoic, animals called
protorothyrids,
or
stemreptiles,
were present.
(In Chapter 19 I briefly explain the relationship of the Paleozoic reptiles.) Scientists call
them stem reptiles because they form the base or stem of the reptile family tree, from
which all the other reptiles (including dinosaurs) evolved. By the beginning of the Meso-
zoic, the ancestors of all ancient and modern reptiles had evolved from the protoro-
thyrids. This includes the
archosaur
(ancestor to the dinosaurs), crocodiles, and —
much later — birds. The relationships between ancient and modern reptiles are illus-
trated in Figure 20-4.
As you can see from the simplified diagram in Figure 20-4, modern lizards, snakes, tuatu-
aras, and turtles are only distantly related to the swimming reptiles, flying reptiles, and
dinosaurs. In this section I describe the characteristics of the ancient and extinct rep-
tiles.
If it flies or swims, it's not really a dinosaur
Popular culture commonly assumes that any ancient and extinct reptile is a dinosaur.
But if it swims or flies, it is not a dinosaur! During the Mesozoic there were indeed swim-
ming and flying reptiles, which I describe here.
Figure 20-4:
The
reptile family tree.
