For many millions of years after the first animals began to crawl onto land in the early Paleozoic,
the Earth still lacked the big, charismatic animals of later eras. Unlike the mammals of
the Cenozoic or the dinosaurs of the Mesozoic, land animals for most of the Paleozoic were
either very small or were burdened by a need to return to water frequently. On a Paleozoic safari,
there wouldn't be the familiar sights of big herds of grazing herbivores or large
predators stalking them. But towards the end of the Paleozoic, things started to change,
and by the beginning of the Permian period, vertebrates had become better adapted for land,
pioneering the ecological niches that define terrestrial life today. Together, these pioneers
formed the first large land animal fauna, and although they took many evolutionary pathways,
many of them converged on one very specific adaptation largely unseen in the modern world.
Fifteen million years into the Permian, and the climate is still getting warmer and drier,
as the swamp forests of the Carboniferous continue to give way to dry land. Just like
in the Carboniferous, drier areas like these are mostly populated by seed-bearing plants.
But these forests of primitive Walchian conifers harbor animals that share their ability to live
beyond the wetlands. Insects and other arthropods have inhabited drier areas of the continents for
many millions of years now, since their aquatic ancestors already had an exoskeleton that was
pre-adapted to prevent water loss. Meanwhile our primitive tetrapod ancestors had moist skin and
eggs that needed to be laid in water, preventing them from fully colonizing the land. But back in
the Carboniferous period, one group of tetrapods, the amniotes, broke free of this restriction. They
evolved both dry skin and eggs that could be laid on land, allowing them to become
fully terrestrial. Both of the two main amniote groups, Sauropsida and Synapsida, started out as
small insect eaters, and many of them still fill this niche in the early Permian. Despite their
lizard-like appearances, none of these creatures are reptiles as we know them. All modern reptiles,
from turtles to snakes to crocodiles and birds, belong to a group of diapsid sauropsids called
Sauria, and there's no evidence for any saurians at this point in the early Permian. And although
diapsids had been around since the Carboniferous, early Permian diapsids like the Araeoscelidians
were still outnumbered by more primitive varieties of sauropod scurrying through the undergrowth. One
major group was Captorhinidae. While they may not look like much, the mouths of some species
harbored multiple rows of teeth like a shark's. And even though they were only distant cousins
to the reptiles we have today, recent discoveries have shown that at least some could detach their
tails mid-vertebra in much the same way that lizards do. While the captorhinids and diapsids
belong to the eureptile branch of Sauropsida, there was another long-lost branch of sauropsids
that has left no descendants in the modern world: the parareptiles. Lots of parareptiles
were also small carnivores, and while many were primitive looking like the lanthanosuchoids, a
bolosaurid called Eudibamus cursoris is the first two-legged vertebrate known in the fossil record,
fifty million years before the first dinosaur. Meanwhile, there were small insectivores on the
synapsid side of the tree as well, including the eothyrids. Like all synapsids, these fanged
hunters were more closely related to mammals than to any reptile. But while the eothyrids and
other small amniotes preyed on insects, there were larger predators on the prowl for larger
prey. Among the sauropsids, some captorhinids and parareptiles were large enough to prey on
other tetrapods, but unlike in later periods that would be dominated by enormous skyscraper-sized
reptiles, in the early Permian a 6-foot captorhinid it is just about the largest sauropsid
you'll get. Among the synapsids, the varanopids were some of the most prolific medium-sized
predators. Thanks to some extraordinary paleontological finds, we have an unusually
good deal of information about their anatomy and behavior. Fossils from earlier in the Permian
show that they had scales shaped like those of a lizard or snake, and a fossilized burrow from
much later in the Permian contains what may be the earliest known evidence for parental care
in the fossil record: an adult varanopid huddled with younger individuals of different ages. This
parental care could have evolved separately from the care we see in modern mammals, but
it could also mean that parental care originated near the beginning of the synapsid family tree,
and that nearly all synapsids inherited it. Even though synapsid eggs are amniotic,
they are not quite as waterproof as the eggs of most modern reptiles and birds, and they needed to
be kept from drying out. Perhaps parental care was a solution to this problem. And while in modern
mammals, milk is used to nourish the young, it may have originated as a secretion meant to keep early
synapsid eggs moist. In modern times, terrestrial predators mostly subsist on other land animals,
but early Permian predators often fed on aquatic animals as well. In the swamps, sharks,
other fish, and primitive amphibious tetrapods were still in abundance. Not all of these
primitive tetrapods were as water dependent as a typical amphibian. Several groups of non-amniote
tetrapods had independently evolved to become more terrestrial, although they presumably still
had to lay their eggs in water. some members of Seymouriamorpha possessed dry skin and muscular
legs, which helped when hunting small animals on land as adults. Although they were long considered
to be relatives of the amniotes, their position within the tetrapods is now uncertain. Meanwhile
another group of tetrapods, the dissorophoids, had evolved towards life on land as well. They
were members of the ancient group Temnospondyli, and were close relatives of modern amphibians. In
addition to their terrestrial adaptations, a lot of them had armor on their backs as protection
against predators. One dissorophoid, Platyhystrix rugosus, sported a little sail on its back. But
it was far from the only Permian creature with such ornamentation. While many of the terrestrial
food chains in the early Permian were based on aquatic food sources or insects, some tetrapods
had begun to exploit a new food source: plants. The first major group of herbivores tetrapods
was Diadectidae. They were not amniotes, but were close relatives, and had remained the most
prolific herbivores for the last 20-or-so million years, with some growing up to ten feet in length.
Despite their primitive origins, fossil evidence suggests that they had upright limb posture and
an ability to chew their food long before any amniotes evolved these features. Some amniotes
took advantage of this food source as well. Unlike Eudibamus, some bolosaurid parareptiles evolved
herbivorous diets, including Bolosaurus itself. But the most impressive herbivores of the time
were synapsids. The Edaphosaurids were a group of mostly herbivores, all of which had large sails on
their backs. The largest genus, Edaphosaurus, included some species that grew to ten feet
long. The caseids were another group of synapsid herbivores. They were probably relatives of the
eothyrids, and both groups possessed a distinctive overbite. Caseids were a minor part of this fauna,
but within the next 10 million years they would diversify and produce 20-foot giants,
becoming the largest land animals of their time. The biggest early Permian herbivores were
probably too large for most predators to hunt, but there were some carnivorous synapsids that
rose to the occasion. The ophiacodontids started out small in the Carboniferous,
but had quickly produced 10-foot carnivores like Ophiacodon itself by the time the Permian started,
and 15 million years later, Ophiacodon and its relatives were still some of the largest predators
on land. But there was another, more advanced group of carnivores. The sphenacodontians were
relatives of the edaphosaurs, but they had a few distinguishing characteristics. The bone
around the two largest teeth was thickened and the front tooth sockets were deeper, both presumably
reinforcing their teeth when biting. The front teeth were adapted for grabbing and the back teeth
were better for slicing. This type of dentition, in which there are two different types of tooth,
is what lends its name to the most famous sphenacodontian: Dimetrodon. This animal also
had a sail, but it had evolved separately from its edaphosaurid relatives. Most sphenacodontians were
small and lacked sails, but throughout the early Permian, the group produced many large
species of Dimetrodon, and by this point in the Permian, Ctenospondylus and Secodontosaurus had
recently joined the ranks. Why do we see so many instances of sails evolving in such a short time,
when they are completely absent from the modern world. The most commonly suggested function for
a large thin sale is thermoregulation, allowing the animal to warm up blood by pumping it into
the sail where the Sun could heat it easily. This was probably useful to these early land creatures
because unlike large animals for most other periods, they were probably completely cold
blooded. This fauna was unusual in other ways. For one, there was a lower herbivore to-carnivore
ratio that in most later warm-blooded faunas. Part of this was probably because a cold-blooded
predator burns through food less quickly, so more of them can be sustained on a given amount of
prey. Another reason may have been the way these food chains were structured, since many carnivores
were feeding on aquatic creatures and insects instead of just the herbivorous vertebrates.
This fauna had remained relatively unchanged for the last 20 million years, but the first wave
of new Permian land vertebrates was beginning to take shape in the world of 284 million years ago,
and Permian land ecosystems were about to start evolving at a much more rapid
pace. While Dimetrodon and the other sailbacks would eventually be left behind, a few other
sphenacodontians would continue to accumulate new adaptations that would allow them to keep
up. These adaptations would define not only the next waves of synapsid radiations, but would
also ensure the continued success of the last living sphenacodontians to this day: the mammals.