Glossary P
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Placerias
This large, four legged herbivore lived in the Late Triassic period. It
lived on the plains where it grazed in large herds, eating low-lying plants
like ferns. It grew up to 3 metres long and weighed up to 1 tonne.
PLACODONT
(pronounced PLAK-uh-dont) Placodonts (meaning: "plate-like or flat
teeth") were chunky, relatively-sedentary marine reptiles that lived
in shallow seas during the Triassic Period, going extinct at the end of
the Triassic. Many of these sauropterygian diapsids had turtle-like shells
(dermal armor) and sprawling legs. Placodonts ate shellfish which were
crushed between their strong, flat teeth. Placodonts included Placodus,
Placochelys, the armored Henodus, and Claudiosaurus. They were not dinosaurs.
PLACODERM
Placoderms (meaning: "plated skin") were armored fish that evolved
during the Silurian Period, about 420 million years ago. They diviersified
and came to dominate the seas by the Devonian. They went extinct bout
355 million years ago. They had hinged bony armor on their head and thorax.
They had no teeth, but did have bony ridges that acted like teeth. Some
placoderms included the Antiarchi (like Bothriolepis), Dunkleosteus (the
largest placoderm), Groenlandapsis, and Phyllolepis. Placoderms were early
fish, not dinosaurs.
PLACODUS
Placodus was a marine reptile (a placodont) that lived in shallow seas
during the early to middle Triassic Period. This air-breather had four
legs, a short neck, a very large, wide head and two types of teeth (peg-like
teeth in the front and large, flat teeth in the sides of the mouth). Its
long tail was flattened and may have had a fin. Unlike Plesiosaurs and
Ichthyosaurs, Placodus was not a very strong swimmer. It was about 7 feet
(2.15 m) long. It ate shellfish, like oysters and clams, which were pried
open with peg-like teeth and crushed between the flat teeth. Fossils have
been found in Europe. Placodus was not a dinosaur.
Plains
Huge expanses of flat land inhabited by a mixture of low growing vegetation.
This would have been covered in ferns not grasses in the Mesozoic era.
Plankton
Plankton are numerous, primarily microscopic, swimming animals at the
base of the marine food chain. The name is derived from the Greek “planktos”,
meaning drifting.
PLANICOXA
Planicoxa was a plant-eating dinosaur that lived during the early Cretaceous
Period. This iguanodintid (spiked-thumb plant-eater) was found in eastern
Utah, USA. Planicoxa was named by DiCroce and Carpenter in 2001; the type
species is P. venenica.
PLANT EATER
Plant-eating animals are also called herbivores. Most dinosaurs were plant-eaters.
Plant-eaters are also called primary consumers.
PLANTIGRADE
Animals that are plantigrade walk in a flat-footed manner. This is a relatively
slow way of walking since most of the foot comes in contact with the ground.
Most reptiles (like alligators), amphibians (like frogs) and early mammals
(plus people and bears) are plantigrade. (Compare with digitigrade.)
PLATECARPUS
Platecarpus was a mosasaur, an extinct marine reptile that lived in the
seas during the late Cretaceous Period. They were about 14 feet (4.3 m)
long. They swam by moving the long tail and used the short flippers to
steer. They had sharp teeth and ate fish and squid. Fossils have been
found in Europe. They were not dinosaurs.
PLATEOSAURIDS
(pronounced PLAT-ee-oh-SAWR-ids) Plateosaurids (meaning: "flat lizards")
were prosauropod dinosaurs that lived from the late Triassic period to
the early Jurassic period. These quadrupedal herbivores had a long neck,
a small head, bulky body, a long tail and long snout. They ranged in length
from 5-26 ft long (1.5-8 m). These dinosaurs ate leaves high in the trees
(like conifers and cycads) with sharp, leaf-shaped teeth. Many plateosaurids
lived in herds in what is now Europe, Africa, Asia, North America, and
South America. Plateosaurids included Plateosaurus, Ammosaurus, Coloradisaurus,
Euskelosaurus, Massospondylus, and Mussaurus.
Plateosaurus
This huge, four-legged herbivore lived in the Triassic period. It was
a prosauropod, one of the first of the giant dinosaurs and was approximately
nine metres long and weighed four tonnes.
PLATE TECTONICS
Plate tectonics is the now-established theory that chunks of the Earth's
crust (plates) float on the surface and change both position and size
over time.
PLATYBELODON
Platybelodon, commonly known as a "Shovel Tusker," was a huge,
plant-eating mammal that lived in herds during the middle to late Miocene
(roughly 25 million years ago). This elephant-like browser had a shovel-shaped,
scoop-like lower jaw (mandible). This huge mouth had sharp teeth at the
front edge; these teeth were probably used for cutting leaves to eat.
Flat cheek teeth ground up the leaves. It also had 2 small, forward and
downward-pointing tusks toward the front of the upper jaw, probably used
for defense against predators. It lived in wet parts of prairies and ate
soft plants (including water plants). It was 20 ft (6 m) long, was 9 ft
(2.8 m) tall at the shoulder and weighed about 4.5 tons (4 tonnes). Fossils
have been found in North America, eastern Europe, Africa, and northwestern
China (these animals probaly crossed via the Siberian land bridge between
the continents). Classification: Order Proboscidea, Suborder Elephantoidea,
Family Gomphothere (closely related to Amebelodon).
PLATYHYSTRIX
Platyhystrix (meaning: "flat porcupine") was an ancient amphibian
that had flat, blade-like spines on its back (it was not a dinosaur).
It may have had a sail on its back, was anchored by spines; the sail may
have been used to regulate its body temperature and/or for protection.
This early land animal was about 3 feet (1 m) long. It walked on four
short, sprawling legs and had a short tail. A meat-eater, it had conical
teeth. Platyhystrix lived during the Permian period. Fossils have been
found in Texas, USA. Classification: Class amphibian, Subclass Labyrinthodontidae,
Order Temnospondyl, family Dissorophid, genus Platyhystrix.
PLATYPTERGIUS
Platypterygius (meaning: "flat wing") was an Ichthyosaur (not
a dinosaur), a reptile with flipper-like limbs that lived in the water
(but breathed air). It was 23 feet (7 m) long, was dolphin-like and had
large eyes. It dates from the early Cretaceous Period in Queensland, Australia.
PLATYRRHINI
The platyrrhini are the living new world monkeys (living in South and
Central America and southern Mexico), like the Howler Monkeys Squirrel
Monkeys, Sakis, Uakaris, Capuchin Monkeys, Woolly Monkeys, Spider Monkeys
and their relatives. They are arboreal (living in trees) and herbivore
(plant-eaters). (The platyrrhini include the Family Cebidae and Family
Callithricidae.)
PLATYSPERMS
Platysperms (meaning: "flat seeds") are plants with flattened
ovules. Platysperms include gingkos, conifers, glossopterids, and cordaites.
PLEISTOCENE
The Pleistocene was an epoch of geologic time that lasted from 1.8 million
to 11,000 years ago; it was a period of widespread glaciation and large
Ice Age animals (caled Pleistocene Megafauna). The first humans (Homo
sapiens) evolved during the Pleistocene. Mammoths, mastodons, saber-toothed
cats, giant ground sloths, and other Ice Age mammals evolved. A mass extinction
of large mammals and many birds occurred about 10,000 years ago, probably
caused by Ice Ages.
PLESIADAPSIS
Plesiadapis was a mammal that lived from the late Paleocene and the early
Eocene (roughly 65 million years ago). It was 2.5 feet (80 cm) long. A
quadruped (it walked on four legs), it had a long, bushy tail, long legs,
and long, clawed fingers and toes. It may have lived in trees part of
the time. Plesiadapis had long, large, rodent-like incisors (pointed teeth)
at the front of the mouth and wide, flat grinding teeth (molars) at the
rear of the jaws. The snout was long. It may have eaten insects. Fossils
have been found in Cernay, France, and Colorado, USA. There is some debate
about Plesiadapis' classification; it is either a primate or a close relative
of the primates. Plesiadapis was named by Gervais in 1877.
PLESIOMORPHY
Plesiomorphy (meaning: "old form") is a primitive character
of a group.
Plesiosaur
Plesiosaurs were one of a number of different groups of marine reptiles,
including marine crocodiles and ichthyosaurs. They descended from land-living
creatures that had returned to the sea. These medium-sized reptiles lived
from the Triassic period to the end of the Cretaceous period. They inhabited
freshwater and marine environments feeding mainly on fish. Fossil evidence
shows they were much more common in marine environments and ate ammonites
as well as fish.Palaeontologists are divided on how closely plesiosaurs
are related to these other marine groups. However, it is clear that they
were only very distantly related to the dinosaurs.
PLEISTOCENE
(pronounced PLEES-toh-seen) The Pleistocene was an epoch in geologic time
that lasted from 1.8 million years ago until about 10,000 years ago (it
was at the beginning of the Quaternary period). During this epoch, the
first humans (Homo sapiens) evolved. Mammoths, mastodons, saber-toothed
cats, giant ground sloths, and other Pleistocene megafauna (huge animals)
lived. A mass extinction of large mammals and many birds happened about
10,000 years ago (at the end of this epoch), probably caused by climate
changes (the last Ice Age ended).
PLEUROCOELS
Pleurocoels are openings in the sides of the vertebrae of some large theropod
dinosaurs (like Tyrannosaurus rex). These openings decrease the weight
of the bone. They may have also been used for other purposes, such as
an air-sac system that is used by modern birds in which the vertebrae
contain a series of air-sacs which are connected to the lungs.
PLEUROCOELUS
(pronounced PLOOR-oh-SEEL-us ) Pleurocoelus (meaning: "hollow-sided
(vertebrae)") was a small brachiosaurid sauropod dinosaur that lived
during the early Cretaceous Period, about 131-119 million years ago. This
plant-eater had a long neck, long tail, bulky body, and a small, narrow
head. The front legs were longer then the rear legs, giving it a giraffe-like
stance. The fourth toe or each rear leg had a small claw (this is rare
for sauropods). The vertebrae had long, deep cavities in them (hence the
dinosaur's name). Pleurocoelus was about 30 ft (8.8 m) long. Fosils were
found in USA (Maryland, Texas, and Utah). The type species is P. nanus.
Pleurocoelus was named by paleontologist O. Marsh in 1888.
PLIOCENE
(pronounced PLEE-oh-seen) The Pliocene was an epoch in geologic time that
lasted from 5-1.8 million years ago (it was at the end of the Tertiary
period). During this epoch, the first hominids (australopithecines) andmodern
forms of whales appeared. The ancient shark megalodon swam the seas during
this time.
PLIOPLATECARPUS
(pronounced PLEE-oh-PLAT-ee-CAR-pus) Plioplatecarpus was a mosasaur, a
marine reptile that swam in shallow seas during the late Cretaceous Period.
They were not dinosaurs. These powerful swimmers were about 20 feet (6
m) long. They had a big head, large brain, big eyes, four flippers, and
a tail that ended in a fin. Carnivores, they had sharp teeth, which they
used to catch fish and cephalopods. Fossils have been found in North America.
One Plioplatecarpus fossils was found with a fossilized embryo inside
it; this seems to indicate that Plioplatecarpus gave bith to live young.
Plioplatecarpus was named by Dollo in 1884; the type species is Plioplatecarpus
marshii (named to honor O. Marsh).
Pliosaur
A sub-group of the plesiosaurs, which flourished throughout the Mesozoic
era. Pliosaurs were characterised by a large head, short neck and tail,
and long, paddle-like limbs. They were ferocious predators. One species
called Liopleurodon was the largest and heaviest known carnivore.
PLOTOSAURUS
(pronounced PLOAT-oh-SAWR-us) Plotosaurus was a mosasaur, a marine reptile
that swam in shallow seas during the late Cretaceous Period. These powerful
swimmers were about 33 feet (10 m) long. They had four flippers and a
tail that ended in a fin. These carnivores had sharp teeth and ate fish,
squid, and perhaps shellfish. Fossils have been found in North America.
They were not dinosaurs.
Podocarp
There is evidence of these huge trees from the LateTriassic to the Cretaceous
period. They were usually the tallest in the forest, spreading their branches
above the tree canopy to catch the most light.
PODOKESAURUS
(pronounced POH-doh-kuh-SAWR-us) Podokesaurus (meaning: "swift-footed
lizard" in Greek) was a small, bipedal, meat-eating dinosaur from
the early Jurassic period, about 200-188 million years ago. This fast-moving
theropod was about 3.5 feet (1 m) long. This lightly-built dinosaur had
a long neck, short arms, bird-like feet (with three toes and a dewclaw),
and four-fingered hands . A single fossil was found in Massachusetts,
USA; that specimen was destroyed in a fire but a cast of it remains. The
type species is P. holyokensis, named for Mount Holyoke College, where
the fossil was found. Podokesaurus was named by US paleontologist Mignon
Talbot in 1911. The dinosaur Grallator, known only from its footprints,
may be Podokesaurus. This dinosaur may be the same as Coelophysis or perhaps
an immature Rioarribasaurus.
POEKILOPLEURON
(pronounced POH-key-loh-PLURE-on) Poekilopleuron (meaning: "varied
rib or side" in Greek) was a small, bipedal, meat-eating dinosaur
with powerful arms. It dates from the early to middle Jurassic Period
about 166-163 million years ago. This fast-moving megalosaurid theropod
was about 26 feet (8 m) long. The type species is P. bucklandii, but the
type specimen was destroyed in World War II. Poekilopleuron was named
by paleontologist Eudes-Deslongchamps in 1838. Fossils were found in northern
France. 8 to 10 stones (perhaps gastroliths) were found within the ribs
of Poekilopleuron in 1835. Poekilopleuron may be the same as Megalosaurus;
it also resembled Torvosaurus.
POIKILOTHERMS
Poikilotherms are animals whose internal temperature changes depending
on the environment. Reptiles are poikilothermic.
Polacanthus
This four legged herbivore lived in the Early Cretaceous period. It was
mainly a solitary dinosaur, though some fossils have been found amongst
Iguanodon herds. Polacanthus was heavily armoured with a thick plate of
bone over its rump and evenly spaced rows of spikes lining its back.
POLYONYAX
(pronounced pol-ee-OH-nax) Polyonax (meaning: "master over many")
was a plant-eating dinosaur from the late Cretaceous period. This ceratopsian
was about 23 ft (7 m) long. Polyonax may be a juvenile Triceratops. Fragmentary
fossils have been found in Colorado, USA. Polyonax was named by Cope in
1874. The type species is P. mortuarius. This genus is a nomen dubium.
POLYPHYLETIC
A polyphyletic group consists of organisms but not their common ancestors.
This is an artificial group which is based primarily on physical characteristics
rather than on evolutionary relationships. An example is "flying
vertebrates" which includes birds, pteranodons and bats.
Postosuchus
This large, four-legged carnivore lived in the LateTriassic period. It
inhabited river valleys and scrubland around the plains and hunted big
game. It grew up to was approximately six metres long, and could rear
up on its long back legs to a height of two metres.
PRECAMBRIAN
The Precambrian is the geological time period before the Cambrian period
(before 540 million years ago). It is the time period from when the Earth
formed until simple life-forms evolved.
Predator
An animal that preys on other animals.
PREDENTATA
Predentatan is another name for the beaked or ornithischian dinosaurs,
which have a predentary bone in the lower jaw (in front of the teeth).
PREHISTORIC
Prehistoric refers to the time before people began recording history in
writing. This time varies from culture to culture.
PREDENTARY BONE
Prenocephale (meaning: "sloping head") was a plant-eating dinosaur
that lived during the late Cretaceous Period, roughly 83.5 to 65 million
years ago. This thick-skulled ornithischian (a pachycephalosaurid similar
to Stegoceras) had a thick, dome-like skull (hence its name) with some
bony knobs protruding along the sides and the back of the head. This dinosaur
walked on two legs, had short arms had a long, stiff tail. Prenocephale
was about 7.5 feet (2.5 m) long. It is known from skulls and a few other
bones. Fossils have been found in the Nemegt Formation, Omnogov, (Mongolia),
Alberta (Canada) and Montana (USA). Prenocephale was named by paleontologists
Maryañska and Osmólska in 1974; the type species is P. prenes.
PREONDACTYLUS
Preondactylus was a primitive pterosaur that lived during the late Late
Triassic Period. It is the oldest pterosaur yet known. This flying reptile
had a wingspan of 5 feet (1.5 m) and a very short lower jaw bone. It may
have eaten insects. Fossils have been found in the Preon Valley of Udine,
northern Italy. The type species is P. buffarinii, named by Wild in 1983.
PREY
An animal is prey when another animal hunts and kills it for food.