''Albertonykus'' (meaning "

Alberta Alberta ( ) is one of the thirteen provinces and territories of Canada. It is part of Western Canada and is one of the three prairie provinces. Alberta is bordered by British Columbia to the west, Saskatchewan to the east, the Northwest Ter ...

claw") is an

alvarezsaurid Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...

dinosaur Dinosaurs are a diverse group of reptiles of the clade Dinosauria. They first appeared during the Triassic period, between 243 and 233.23 million years ago (mya), although the exact origin and timing of the evolution of dinosaurs is t ...

from the

Maastrichtian The Maastrichtian () is, in the ICS geologic timescale, the latest age (uppermost stage) of the Late Cretaceous Epoch or Upper Cretaceous Series, the Cretaceous Period or System, and of the Mesozoic Era or Erathem. It spanned the interval from ...

-age (

Upper Cretaceous The Late Cretaceous (100.5–66 Ma) is the younger of two epochs into which the Cretaceous Period is divided in the geologic time scale. Rock strata from this epoch form the Upper Cretaceous Series. The Cretaceous is named after ''creta'', the ...

) rocks of the

Horseshoe Canyon Formation The Horseshoe Canyon Formation is a stratigraphic unit of the Western Canada Sedimentary Basin in southwestern Alberta. It takes its name from Horseshoe Canyon, an area of badlands near Drumheller. The Horseshoe Canyon Formation is part of the ...

of Alberta,

Canada Canada is a country in North America. Its ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, covering over , making it the world's second-largest country by tot ...

. It is known from forelimb and hindlimb remains from multiple individuals. All but two of the specimens come from a

bonebed A bone bed is any geological stratum or deposit that contains bones of whatever kind. Inevitably, such deposits are sedimentary in nature. Not a formal term, it tends to be used more to describe especially dense collections such as Lagerstätte. ...

dominated by ''

Albertosaurus ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...

'', located at the top of Unit 4 of the Horseshoe Canyon Formation,Larson, D. W., Brinkman, D. B., & Bell, P. R. (2010). Faunal assemblages from the upper Horseshoe Canyon Formation, an early Maastrichtian cool-climate assemblage from Alberta, with special reference to the Albertosaurus sarcophagus bonebed This article is one of a series of papers published in this Special Issue on the theme Albertosaurus. Canadian Journal of Earth Sciences, 47(9), 1159-1181. dating to ~68.5 million years ago. ''Albertonykus'' is interpreted as having fed on wood-nesting

termite Termites are small insects that live in colonies and have distinct castes (eusocial) and feed on wood or other dead plant matter. Termites comprise the infraorder Isoptera, or alternatively the epifamily Termitoidae, within the order Blattode ...

s because the forelimbs appear specialized for digging, but are too short for burrowing. ''Albertonykus'' is the earliest-known

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

n alvarezsaurid. Isolated bones of alvarezsaurids are known from late Maastrichtian rocks in

Montana Montana () is a state in the Mountain West division of the Western United States. It is bordered by Idaho to the west, North Dakota and South Dakota to the east, Wyoming to the south, and the Canadian provinces of Alberta, British Columbi ...

and

Wyoming Wyoming () is a U.S. state, state in the Mountain states, Mountain West subregion of the Western United States. It is bordered by Montana to the north and northwest, South Dakota and Nebraska to the east, Idaho to the west, Utah to the south ...

(

USA The United States of America (U.S.A. or USA), commonly known as the United States (U.S. or US) or America, is a country Continental United States, primarily located in North America. It consists of 50 U.S. state, states, a Washington, D.C., ...

). The bones now belonged to a new genus, ''

Trierarchuncus ''Trierarchuncus'' (meaning "captain hook," after its single-clawed hands) is a monotypic genus of alvarezsaurid theropod which includes a single species, ''Trierarchuncus prairiensis'', which is known from fossils found in deposits of the Hell Cr ...

''. The

type species In zoological nomenclature, a type species (''species typica'') is the species name with which the name of a genus or subgenus is considered to be permanently taxonomically associated, i.e., the species that contains the biological type specimen ...

is ''A. borealis'', described by Nicholas Longrich and Philip Currie in 2009. The specific name (''borealis'') means "north".

Discovery

Dry Island Buffalo Jump Horseshoe Canyon by Nick Longrich

Until the 1990s it was unknown that dinosaurs like ''Albertonykus'' existed. A chain of new discoveries from Asia and South America exposed the existence of these previously unknown theropod dinosaurs.Brian Switek, ''Smithsonian Magazine'', http://dinosaur.smithsonianmag.com/2008/10/06/a-dinosaur-that-ate-termites-for-breakfast/ North American finds remained rare. The bones of ''Albertonykus'' were discovered through a coincidental association with a much larger theropod dinosaur. In 1910,

paleontologist Paleontology (), also spelled palaeontology or palæontology, is the scientific study of life that existed prior to, and sometimes including, the start of the Holocene epoch (roughly 11,700 years before present). It includes the study of fossi ...

Barnum Brown Barnum Brown (February 12, 1873 – February 5, 1963), commonly referred to as Mr. Bones, was an American paleontologist. Named after the circus showman P. T. Barnum, he discovered the first documented remains of ''Tyrannosaurus'' during a career ...

and his crew found a site filled with the bones of the gigantic

tyrannosaurid Tyrannosauridae (or tyrannosaurids, meaning "tyrant lizards") is a family of coelurosaurian theropod dinosaurs that comprises two subfamilies containing up to thirteen genera, including the eponymous ''Tyrannosaurus''. The exact number of genera ...

Albertosaurus sarcophagus ''Albertosaurus'' (; meaning "Alberta lizard") is a genus of tyrannosaurid theropod dinosaurs that lived in western North America during the Late Cretaceous Period, about 71 million years ago. The type species, ''A. sarcophagus'', was app ...

''. They unearthed the remains of at least nine different specimens of ''Albertosaurus'' in the single site, but stopped digging after just two weeks.Nick Longrich, ''University of Calgary'', Renewed quarrying in the ''Albertosaurus'' bonebed in Dry Island Provincial Park again produced the remains of over twenty specimens of ''Albertosaurus'', and the quarry has yet to be fully excavated. It is not known why so many tyrannosaurs were found in one place: paleontologist Nick Longrich speculated that the site was part of a

predator trap A predator trap is a natural hazard where prey animals become trapped or incapacitated, and the attracted predators suffer the same fate. More predators, scavengers, insects and birds become attracted to this mounting accumulation of carrion, until ...

, where trapped prey animals drew predators to their deaths. At the same site, over a dozen arm and leg bones belonging to an unknown species of small theropod were in 2002 excavated by a team of scientist led by

Philip John Currie Philip John Currie (born March 13, 1949) is a Canadian palaeontologist and museum curator who helped found the Royal Tyrrell Museum of Palaeontology in Drumheller, Alberta and is now a professor at the University of Alberta in Edmonton. In the ...

of the

University of Alberta The University of Alberta, also known as U of A or UAlberta, is a public research university located in Edmonton, Alberta, Canada. It was founded in 1908 by Alexander Cameron Rutherford,"A Gentleman of Strathcona – Alexander Cameron Rutherfor ...

. The bones were then stored at the

Royal Tyrrell Museum The Royal Tyrrell Museum of Palaeontology (RTMP, and often referred to as the Royal Tyrrell Museum) is a palaeontology museum and research facility in Drumheller, Alberta, Canada. The museum was named in honour of Joseph Burr Tyrrell, and is situa ...

in Alberta.Ken Than, ''National Geographic News'', http://news.nationalgeographic.com/news/2008/09/080925-smallest-dinosaur.htmlJeanna Bryner, ''MSNBC.com'', http://www.nbcnews.com/id/26856262 In 2005 Nick Longrich, then a student at the

University of Calgary The University of Calgary (U of C or UCalgary) is a public research university located in Calgary, Alberta, Canada. The University of Calgary started in 1944 as the Calgary branch of the University of Alberta, founded in 1908, prior to being ins ...

, happened upon the small fossils while comparing ''Albertosaurus'' claws to other dinosaur species. Longrich recognized the fossils as alvarezsaurid, concluding that they represented a new species. Other fragments of ''Albertonykus'' were then recognized in the collections, which had not been identified as a separate species.

Description

''Albertonykus'' is the smallest known

alvarezsauridae Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...

ever discovered in North America, measuring long and weighing . Alvarezsaurs typically had slender hind legs, long rigid tails, and unusually short arms that were powerfully built to support a large claw. Although no skull bones of ''Albertonykus'' have been found, related animals from

Mongolia Mongolia; Mongolian script: , , ; lit. "Mongol Nation" or "State of Mongolia" () is a landlocked country in East Asia, bordered by Russia to the north and China to the south. It covers an area of , with a population of just 3.3 million, ...

show that they likely had long, slender snouts filled with tiny teeth similar to those of armadillos and anteaters. It is likely that ''Albertonykus'' ate insects, using its large thumb claw to tear open rotten logs to find its prey. As in other alvarezsaurs, the forelimbs of ''Albertonykus'' were specialized for digging, but were too short to permit burrowing. Unfortunately at this time the skeleton of ''Albertonykus'' is not complete, but its Mongolian relatives give us a distinct idea of what the rest of the skeleton would have looked like. Possible prey items were evaluated and compared with the fossil record of social insects.

Ant Ants are eusocial insects of the family Formicidae and, along with the related wasps and bees, belong to the order Hymenoptera. Ants evolved from vespoid wasp ancestors in the Cretaceous period. More than 13,800 of an estimated total of 22 ...

s were not an important part of the ecosystem during the Cretaceous, and mound-building termites do not appear until the Eocene. This leaves the possibility that ''Albertonykus'' preyed on wood-nesting termites. This hypothesis was tested by examining

petrified wood Petrified wood, also known as petrified tree (from Ancient Greek meaning 'rock' or 'stone'; literally 'wood turned into stone'), is the name given to a special type of ''fossilized wood'', the fossilized remains of terrestrial vegetation. ''P ...

from the

, where ''Albertonykus'' was found. The wood found there frequently contains borings, which resemble those of termites.

Classification

''Albertonykus'' is a member of an unusual

theropod Theropoda (; ), whose members are known as theropods, is a dinosaur clade that is characterized by hollow bones and three toes and claws on each limb. Theropods are generally classed as a group of saurischian dinosaurs. They were ancestrally c ...

group known as the

Alvarezsauridae Alvarezsauridae is a family of small, long-legged dinosaurs. Although originally thought to represent the earliest known flightless birds, they are now thought to be an early diverging branch of maniraptoran theropods. Alvarezsaurids were highly ...

and is one of only a few alvarezsaurid fossils that has been found outside of South America and Asia. After a phylogenetic analysis, it was shown that ''Albertonykus'' is a member of the Asian

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English term, ...

Mononykini, which supported the hypothesis that the alvarezsaurs originated in South America, and then dispersed to Asia through North America. The unearthing of ''Albertonykus'' provided important information into the biology of the Alvarezsauridae.

References

External links

Small 'Dr. Seuss'-like dinosaur dug up in Alberta
news report at CBC.ca {{Taxonbar, from=Q131750 Fossils of Canada Alvarezsaurids Late Cretaceous dinosaurs of North America Fossil taxa described in 2009 Taxa named by Philip J. Currie Paleontology in Alberta