Predation (the eating of one living
organism by another for
nutrition) predates the rise of commonly recognized carnivores by hundreds of millions (perhaps billions) of years. It began with
single-celled organisms that
phagocytozed and
digested other cells, and later evolved into
multicellular organisms with
specialized cells that were dedicated to breaking down other organisms. Incomplete digestion of the prey organisms, some of which survived inside the predators in a form of
endosymbiosis, might have led to
symbiogenesis that gave rise to
eukaryotes and eukaryotic
autotrophs such as
green and
red algae.
Proterozoic origin The earliest predators were
microorganisms, which engulfed and "swallowed" other smaller
cells (i.e.
phagocytosis) and
digested them internally. Because the earliest fossil record is poor, these first predators could date back anywhere between 1 and over 2.7
bya (billion years ago).
Paleozoic The degradation of
seafloor microbial mats due to the
Cambrian substrate revolution led to increased active predation among animals, likely triggering various
evolutionary arms races that contributed to the rapid
diversification during the
Cambrian explosion.
Radiodont arthropods, which produced the first
apex predators such as
Anomalocaris, quickly became the dominant carnivores of the Cambrian sea. After their decline due to the
Cambrian-Ordovician extinction event, the niches of large carnivores were taken over by
nautiloid cephalopods such as
Cameroceras and later
eurypterids such as
Jaekelopterus during the
Ordovician and
Silurian periods. The first
vertebrate carnivores appeared after the
evolution of
jawed fish, especially
armored
placoderms such as the massive
Dunkleosteus. The dominance of placoderms in the
Devonian ocean forced other fish to venture into other niches, and one clade of
bony fish, the
lobe-finned fish, became the dominant carnivores of
freshwater wetlands formed by early
land plants. Some of these fish became better adapted for breathing air and eventually giving rise to
amphibian tetrapods. These early tetrapods were large
semi-aquatic piscivores and
riparian ambush predators that hunt
terrestrial arthropods (mainly
arachnids and
myriopods), and one group in particular, the
temnospondyls, became terrestrial apex predators that hunt other tetrapods. The dominance of temnospondyls around the wetland habitats throughout the
Carboniferous forced other amphibians to evolve into
amniotes that had adaptations that allowed them to live farther away from water bodies. These amniotes began to evolve both carnivory, which was a natural transition from insectivory requiring minimal adaptation; and
herbivory, which took advantage of the abundance of
coal forest foliage but in contrast required a complex set of adaptations that was necessary for digesting the
cellulose- and
lignin-rich plant materials. After the
Carboniferous rainforest collapse, both
synapsid and
sauropsid amniotes quickly gained dominance as the top terrestrial animals during the subsequent
Permian period. Some scientists assert that
sphenacodontoid synapsids such as
Dimetrodon "were the first terrestrial vertebrate to develop the curved, serrated teeth that enable a predator to eat prey much larger than itself".
Mesozoic In the
Mesozoic, some
theropod dinosaurs such as
Tyrannosaurus rex are thought probably to have been obligate carnivores. Though the theropods were the larger carnivores, several carnivorous mammal groups were already present. Most notable are the
gobiconodontids, the
triconodontid Jugulator, the
deltatheroidans and
Cimolestes. Many of these, such as
Repenomamus,
Jugulator and
Cimolestes, were among the largest mammals in their faunal assemblages, capable of attacking dinosaurs.
Cenozoic In the early-to-mid-Cenozoic, the dominant predator forms were mammals:
hyaenodonts,
oxyaenids,
entelodonts,
ptolemaiidans,
arctocyonids and
mesonychians, representing a great diversity of
eutherian carnivores in the northern continents and
Africa. In
South America,
sparassodonts were dominant, while
Australia saw the presence of several
marsupial predators, such as the
dasyuromorphs and
thylacoleonids. From the
Miocene to the present, the dominant carnivorous mammals have been
carnivoramorphs. Most carnivorous mammals, from
dogs to
deltatheridiums, share several dental adaptations, such as
carnassial teeth, long
canines and even similar tooth replacement patterns. Most aberrant are
thylacoleonids, with a diprodontan dentition completely unlike that of any other mammal; and
eutriconodonts like gobiconodontids and
Jugulator, with a three-cusp anatomy which nevertheless functioned similarly to carnassials. ==See also==