ZoomDinosaurs.com Dinosaur and Paleontology Dictionary

AMARGASAURUS (pronounced uh-MARG-uh-SAWR-us) Amargasaurus was a diplodocid sauropod from the early Cretaceous period, about 131 million-125 million years ago. It was about 33 feet (10 m) long and weighed roughly 5000 kg. It had a double row of spines along its neck, back, and tail.

AMBER Amber is a yellowish, fossilized tree resin (from conifers) that sometimes contains bits of trapped matter.

AMBULOCETUS Ambulocetus natans (meaning "walking whale that swims") is an extinct mammal the size of a sea lion, 10 feet (3 m) long and about 650 pounds. Its limbs allowed it to swim and could also support it on land. It had long, powerful jaws with shark-like teeth, a small brain, and a pelvis fused to its backbone (like land-dwelling mammals but unlike whales). It may have been an ancestor of the whales - it may have evolved from animals like Mesonychid. Ambulocetus was found (in 1993) and named (in 1994) by Hans Thewissen in Pakistan.

AMBLYDACTYLUS Amblydactylus is a dinosaur known only from its fossilized footprints; it is an ichnogenus. It was probably a hadrosaur, a duck-billed dinosaur. Fossils of parallel tracks have been found in Canada, and are probably evidence of herds of these dinosaurs.

AMEBELODON Amebelodon, commonly known as a "Shovel Tusker," was a huge, plant-eating mammal that lived in herds during the Early middle Miocene (about 15 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, probable 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. Classification: Order Proboscidea, Suborder Elephantoidea, Family Gomphothere (closely related to Platybelodon).

AMMONITE (pronounced AM-uh-nite) Ammonite was an early mollusk, a fast-moving predatory marine invertebrate (a cephalopod). These animals were protected by a shell (usually spiral-coiled) that contained many air filled chambers; the animal lived only in the outer chamber. Ammonites ranged in size from under an inch to about 9 feet (3 m) in diameter. They appeared during the Devonian and went extinct during the K-T extinction, 65 million years ago. The closest living relative of the ammonite is the chambered nautilus. Ammonites were named for Amun (also spelled Ammon), an ancient Egyptian God who is pictured as having ram's horns behind each ear (which look like ammonites). Ammonite fossils are found in great quantities and are used as an index fossil.

AMMOSAURUS (pronounced AM-uh-SAWR-us) Ammosaurus (meaning "sandy-ground lizard") was a large, long-necked, small-headed, quadrupedal, plant-eating plateosaurid prosauropod dinosaur from the early Jurassic period, about 198 million to 187 million years ago. It had a bulky body, small feet, big hands with thumb claws and a long tail. It was about 14 feet (4 m) long, weighing roughly 290 kg. Four incomplete skeletons (juvenile & adult) have been found in Connecticut, Arizona, USA, and perhaps Nova Scotia, Canada. Ammosaurus was named by paleontologist O. Marsh in 1891.

AMNIOTE (pronounced AM-nee-oat) Amniotes are animals whose eggs contain an amnion, a membrane that surrounds the embryo and helps retain fluids. This lets an animal lay eggs other than in the water (without having them dry out). Mammals, amphibians, birds, dinosaurs, turtles, and lizards are amniotes.

AMPELOSAURUS (pronounced AM-pel-o-SAWR-us) Ampelosaurus (meaning "vineyard lizard") was a large, long-necked, small-headed, quadrupedal, plant-eating Titanosaurid sauropod dinosaur from the late Cretaceous period, about 198 million to 187 million years ago. It had a armored, bulky body, a long neck and a long tail. It was about 50 feet (15 m) long. An incomplete fossil (including dermal plates) was found in south-central France. Ampelosaurus was named by paleontologist Le Loeuff in 1995. The type species is A. atacis.

AMPHIBIAN (pronounced am-FIB-ee-in) Amphibians (meaning "double life") are vertebrate animals that live in the water during their early life (breathing through gills), but usually live on land as adults (and breathe with lungs). There are three groups (orders) of living amphibians: newts and salamanders (urodeles); frogs and toads (anurans); and caecilians (the worm-like gymnophiones).

AMPHICOELIAS (pronounced am-fee-SEEL-ee-yus) Amphicoelias (meaning "double cavities") was a diplodocid sauropod dinosaur. It was a long-necked, whip-tailed, quadrupedal, plant-eater about 65 ft (20 m) long weighing roughly 100000 kg. Amphicoelias dates from the late Jurassic period, about 150-140 million years ago. Amphicoelias was named by paleontologist Cope in 1877. A single, enormous fossilized vertebra of A. fragillium (8 ft = 2.4 m) was found in Colorado, USA, but has since disappeared (based on Cope's description, the animal that belonged to this fossil would have been 170 feet long). A few other fossils were found belonging to the type species, A. altus. Amphicoelias is a doubtful genus.

AMPHICYON Amphicyon (meaning "two dog"),also known as the bear-dog, was probably the biggest land-dwelling carnivore of its time. This extinct mammal about the size of a modern grizzly bear, about 6.5 ft (2 m) long. (although it looked like a bear with wolf's teeth, it wasn't a bear). It walked on four sturdy legs, had a short tail, thick neck. Amphicyon ate meat and plants. This predator lived about 30 million years ago to about 14 million years ago, during the mid-Tertiary. Fossils of Amphicyon have been found in Europe (France and Germany) and North America (Nebraska, USA). Classification: Class Mammalia, Order Carnivora, Family Amphicyonidae (bear-dogs), Genus Amphicyon.

AMPHICOELUS VERTEBRAE Amphicoelus vertebrae are vertebrae in which the main body is concave in the front (anterior) and back (posterior). Compare with opisthocoelus vertebrae.

AMPHIOXUS (pronounced AM-fee-OX-us) Amphioxus (meaning "both sides sharp") are small, flattened ocean animals - a type of lancelet (lancelets are the most fish-like of the invertebrates). Instead of having a true vertebral column, Amphioxus have a notochord (a hollow dorsal nerve cord) and gills. They eat small organic particles floating in the water, using a mouth (without jaws), filtering the food through gill slits. The sexes are separate. Classification: Kingdom Animalia, Phylum Chordata, Subphylum Cephalochordata (lancelets), Genus Amphioxus, many species.

AMPHISAURUS (pronounced AM-fee-SAWR-us) Amphisaurus (meaning "near lizard") is a dubious genus of dinosaur, actually Anchisaurus polyzelus. It was named by Marsh in 1882.

AMTOSAURUS (pronounced AM-toe-SAWR-us) Amtosaurus (meaning "Amtgay [Mongolia] lizard") was probably an ankylosaur, an armored dinosaur (or perhaps a hadrosaur) from the late Cretaceous period, roughly 95-85 million years ago. This plant-eater may have been about 15-23 ft (4.5-7 m) long, weighing roughly 800 kg. Only a partial skull was found in Mongolia. Amtosaurus was named by paleontologist Marsh in 1882. The type species is A. magnus.

AMUROSAURUS Amurosaurus (meaning lizard from the Amur river basin, in far eastern Russia) is a newly-discovered plant-eating dinosaur. Two almost complete fossils of this lambeosaurine hadrosaur (duck-billed dinosaur) were found in Russia. Amurosaurus was named by Yuri Bolotsky (who discovered the fossils near Blagoveshchensk) and Kurzanov in 1995. This genus is a nomen nudum, one that has not yet been formally described. The type species is A. riabinini.

AMYGDALODON (pronounced am-ig-DAL-oh-don) Amygdalodon (meaning "almond tooth") is a dinosaur known from only a tooth found in Argentina. This long-necked, long-necked, plant-eater was about 11.5 ft (13.5 m) long and weighed about 14800 kg. It lived during the middle Jurassic period. This sauropod was named by Cabrera in 1947. The type species is A. atagonicus.

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