ZoomDinosaurs.com Dinosaur and Paleontology Dictionary

AGATHAUMAS (pronounced ag-ah-THAW-mas ) Agathaumas (meaning "great wonder") was a ceratopsid resembling Triceratops. This horned plant-eater dates from the late Cretaceous period. Fossils (only a few bones from the hip area) have been found in western North America. It was named by paleontologist Cope in 1872. The type species is A. sylvestris. This genus is a nomen dubium.

AGE An age is a unit of geological time which is distinguished by some feature (like an Ice Age). An age is shorter than epoch, usually lasting from a few millions of years to about a hundred million years.

AGILISAURUS (pronounced AJ-il-eh-SAWR-us) Agilisaurus (meaning "agile lizard") was a lightly-built dinosaur that was about 3.5-4 feet (1.2-1.7 m) long and weighed roughly 40 kg. This plant-eater lived during the middle Jurassic period, about 170 million years ago. It was perhaps a hypsilophodontid. A nearly complete skeleton was found in China. Agilisaurus was named by Peng in 1990. The type species is A. louderbecki.

AGROSAURUS (pronounced AG-roh-SAWR-us) Agrosaurus (meaning "wild country lizard") was an ornithischian dinosaur, a primitive prosauropod about 6.5-10 feet (2-3 m) long, weighing perhaps 18-30 pounds (40-70 kg). This small bipedal plant-eater had a long tail, short arms, and lived during the late Triassic period, about 225-213 million years ago. It was thought to be the first fossil found in Australia, but has since been found to a mislabeled fossil from Britain (Wales). Only a few bones were found. Agrosaurus was named by Seeley in 1891. The type species is A. macgillvrayi, but Agrosaurus is a nomen dubium and is probably the same as Thecodontosaurus antiquus.

ALAMOSAURUS (pronounced Al-uh-moe-SAWR-us) Alamosaurus (meaning "Ojo Alamo [New Mexico] lizard" ) was a long-necked, whip-tailed dinosaur about 69 feet (21 m) long and weighed perhaps 33 tons (30000 kg). It was a quadrupedal, plant-eater from New Mexico, Texas, and Utah, USA during the late Cretaceous period, about 73 million to 65 million years ago. It was a sauropod and a Titanosaurid that may have had some body armor. It was named by Gilmore in 1922. The type species is A. sanjuanensis.

ALBERTOSAURUS (pronounced al-BUR-toh-SAWR-us) Albertosaurus was a large, meat-eating dinosaur from the late Cretaceous period. It was a theropod related to T. rex. Albertosaurus was about 8.6 m long and weighed about 2500 kg. The type species is A. sarcophagus.

ALECTROSAURUS (pronounced ah-LECK-troh-SAWR-us) Alectrosaurus [meaning "Alectra's lizard," Alectra was one of the furies in classical mythology] was a huge, bipedal, meat-eating dinosaur from the late Cretaceous period, about 98 million to 88 million years ago. It was a tyrannosaurid, a theropod related to T. rex, but it had larger arms and claws and very long jaws with many teeth. Unlike most tyrannosaurids, its skull was smooth on top. It was about 25-30 feet (8-9 m) long and weighed perhaps 1.5 tons. It had powerful legs, tiny arms, and a stiff, pointed tail. Partial skeletons have been found in the Gobi Desert in Mongolia. Alectrosaurus was named by paleontologist C. W. Gilmore in 1933. The type species is A. olseni.

ALGOASAURUS (pronounced al-GOH-a-SAWR-us) Algoasaurus (meaning "Algoa Bay (South Africa) lizard") is doubtful genus of dinosaurs; it is known from only a few bones found in Africa. This long-necked, long-tailed plant-eater (a neosauropod and perhaps a titanosaurid) was about 30 ft (9 m) long. It lived during the early Cretaceous period, about 145-135 million years ago. The type species is A. bauri. Algoasaurus was named by the paleontologist Broom in 1904.

ALIORAMUS (pronounced AL-ee-uh-RAY-mus) Alioramus, meaning "different branch," was a large, bipedal, meat-eating dinosaur from the late Cretaceous period, about 73 million to 65 million years ago. It was a tyrannosaurid theropod about 16-20 feet (5-6 m) long, perhaps weighing up to 1 ton. It had 6 tiny horns on its snout; four in a row on the lower snout plus a horizontal pair near the eyes. It had powerful legs, tiny arms, and a stiff, pointed tail. It had more teeth and a longer skull than other tyrannosaurids. A single, fragmentary skeleton was found in Mongolia. Alioramus was named by Kurzanov in 1976. The type species is A. remotus.

ALIWALIA (pronounced ahl-ih-WAHL-ee-ah) Aliwalia (named for Aliwal North, South Africa) was a carnivorous dinosaur known from only a few bones found in south Africa. This meat-eater (a theropod) was about 25 ft (8 m) long and weighed about 1500 kg. It lived during the late Triassic period, about 145-135 million years ago. The type species is A. rex. Aliwalia was named by the paleontologist Galton in 1985. The type species is A. rex.

ALLIGATOR Alligators are large reptiles. Primitive alligators evolved during the late Triassic period.

ALLOPATRIC SPECIATION Allopatric speciation is the formation of new species after a population has been separated geographically. Over time, the two isolated populations diverge genetically. Allopatric speciation is probably the major mode of speciation (the formation of new species). Compare with parapatric speciation and sympatry.

ALLOPATRY Allopatry means occupying different geographic locations. Compare with parapatry and sympatry.

ALLOSAURUS (pronounced Al-oh-SAWR-us) Allosaurus, meaning "different lizard," was a huge, meat-eating dinosaur from the late Jurassic period, about 154 million to 144 million years ago. It was a theropod that lived in what is now the western United States. It was about 10.5 m long. The type species is A. fragilis.

ALOCODON (pronounced a-LOK-oh-don) Alocodon (meaning "furrowed tooth") is doubtful genus of dinosaurs; it is known from only a single tooth. Alocodon was a small, plant-eating dinosaur of unknown length, perhaps about 3 feet (1 m) long. It was an ornithischian from Europe (Portugal) during the late Jurassic period, about 164 million years ago. The type species is A. kuehni. Alocodon was named by the paleontologist Thulborn in 1973.

ALPHADON (pronounced AL-fa-don) Alphadon (meaning "first tooth") was a metatherian, primitive marsupial. It was not a dinosaur, but lived with the dinosaurs. Alphadon was a small omnivore, eating fruit, insects, and small animals. It was about 1 feet (30 cm) long. This tree-dweller had opposable toes and a prehensile tail which it may have used to climb trees. It lived in North America (Alberta, Canada to New Mexico, USA) during the late Cretaceous period, about 70 million years ago. The type species is A. marshi. Alphadon was named by the paleontologist Simpson in 1929. Classification: Subclass Prototheria, Order Pantotheria, Infraclass Metatheria, Genus Alphadon.

ALTICAMELUS Alticamelus (meaning "tall camel") is the old name of Aepycamelus. It was a prehistoric camel that lived from the middle through late Miocene. This giraffe-like early camel was about 10 ft (3 m) tall at the head; it had a small back hump and a short tail. It had very long legs, and small hooves on its two toes and broad pads. It probably moved in a manner similar to modern-day camels. Fossils of this mammal have been found in Colorado, USA.

ALTIRHINUS (pronounced al-ti-RINE-us) Altirhinus (meaning "high snout") was an iguanodontid, a plant-eating dinosaur about 23-26 feet (7-8 m) long. Altirhinus had a tall beak on its rounded snout and a spiked thumb on each hand. This big-nosed dinosaur may have had a good sense of smell. It walked on two long legs but could also eat on all four imbs - the arms were a bit smaller than the legs. It was an ornithischian from Mongolia during the early Cretaceous period. The type species is A. kurzanovi. Altirhinus was named by the paleontologist David Norman in 1998. Altirhinus used to be known as Iguanodon bernissartensis, (Rozhdestvensky, 1952).

ALTISPINAX (pronounced AL-tee-SPY-nax) Altispinax (meaning "high spine") is doubtful genus of dinosaurs; it is known from only a single tooth. The vertebral material originally found (which gave this dinosaur its name) has been assigned the name Becklespinax. Altispinax was a large meat-eating dinosaur of unknown length, perhaps about 30 feet (9 m) long, weighing roughly 1000 kg. It was a theropod, a bipedal, meat-eating, stiff-tailed predator from Europe (England) during the early Cretaceous period, about 123-119 million years ago. The type species is A. dunkeri. Altispinax was named by the paleontologist von Huene in 1923.

ALVAREZ, LUIS Luis Alvarez (1911-1988) was a physicist who, with his son Walter Alvarez (a geologist), hypothesized that the a huge asteroid hit the Earth 65 million years ago, causing a mass extinction. The Alvarez Theory of Extinction is widely accepted. Luis Alvarez received a Nobel Prize in physics (1968) for his work on subatomic particles.

ALVAREZ THEORY OF EXTINCTION This theory is that a large asteroid, meteor, or comet hit the Earth 65 million years ago, causing huge atmospheric and geologic disruptions, leading to a mass extinction which killed the dinosaurs and many other species.

ALVAREZSAURUS (pronounced Al-vuh-rez-SAWR-us) Alvarezsaurus was a small, lightly-built, bird-like, bipedal theropod (a meat-eating dinosaur) that was about 6 feet (2 m) long, weighing roughly 20 kg. This fast runner had very long legs, long feet, very short arms, a long, s-shaped neck, and an extremely long, thin, flat tail. The tail was over half of the dinosaur's length. It had no ridges on its back, like most other theropods. It lived during the late Cretaceous period, 80 million years ago, in what is now Argentina. It and the family of Alvarezsaurids were named for the historian Don Gregorio Alvarez by José Bonaparte in 1991. The type species is A. calvoi.

ALWALKERIA (pronounced al-wah-KEER-ee-a) Alwalkeria was a small, early theropod (a bipedal, meat-eating dinosaur). It lived during the late Triassic period, roughly 220 million years ago. An incomplete fossil was found in what is now India. It was named by Chatterjee and Creisler in 1994, honoring the British vertebrate paleontologist Alick D. Walker. The type species is A. maleriensis.

ALXASAURUS (pronounced AWL-shah-SAWR-us) Alxasaurus (meaning "Alxa [Desert of Inner Mongolia] lizard") was an advanced theropod (a meat-eating dinosaur) that was about 11.5-13 feet (3.5-4 m) long and weighed about 800-900 pounds (350 to 400 kg). This bipedal carnivore had long legs with clawed feet, relatively long arms, a long, s-shaped neck, a toothless beak, and a short tail. Alxasaurus was the most primitive therizinosauroid (bird-like asian theropods with unusual feet). It lived during the Cretaceous period, about 99 million years ago, in what is now Mongolia. It was named by paleontologists D. A. Russell and Dong in 1995. The type species is A. elesitaiensis.

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