''Latenivenatrix'' (meaning "hiding huntress") is a genus of

troodontid Troodontidae is a clade of bird-like theropod dinosaurs. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinosaurian lineages. More recent fossil disco ...

known from one species, ''L. mcmasterae''. Along with the contemporary ''

Stenonychosaurus ''Stenonychosaurus'' (meaning "narrow claw lizard") is a genus of troodontid dinosaur from the Late Cretaceous Dinosaur Park Formation of Alberta, Canada, as well as possibly the Two Medicine Formation. The type and only species, ''S. inequ ...

'', it is known from the non-tooth fossils formerly assigned to the genus ''

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a wastebasket taxon and a dubious genus of relatively small, bird-like dinosaurs known definitively from the Campanian age of the Late Cretaceous period (about 77 mya). It includes at leas ...

''. Although described as separate, it has been considered a junior synonym of ''Stenonychosaurus''.

Discovery and specimens

The type specimen or

holotype A holotype is a single physical example (or illustration) of an organism, known to have been used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of sever ...

of ''Latenivenatrix'', CMN 12340, was originally described in 1969 by Dale Alan Russell and referred by him to the genus ''

''. In 1987 it was referred to ''

''. It had been collected in 1968 by Irene Vanderloh in the

Dinosaur Park Formation The Dinosaur Park Formation is the uppermost member of the Belly River Group (also known as the Judith River Group), a major geologic unit in southern Alberta. It was deposited during the Campanian stage of the Late Cretaceous, between about 76. ...

strata from

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 ...

, southern

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 ...

. The specimen has preserved some skull bones ( frontals, parietals,

postorbital The ''postorbital'' is one of the bones in vertebrate skulls which forms a portion of the dermal skull roof and, sometimes, a ring about the orbit. Generally, it is located behind the postfrontal and posteriorly to the orbital fenestra. In some ...

, basioccipital and basisphenoid), four vertebrae and four ribs, some chevrons and

gastralia Gastralia (singular gastralium) are dermal bones found in the ventral body wall of modern crocodilians and tuatara, and many prehistoric tetrapods. They are found between the sternum and pelvis, and do not articulate with the vertebrae. In thes ...

, fairly complete forelimb and incomplete hindlimbs. Moreover, three additional specimens coming from the same locality are referred to the same species. These include UALVP 55804 (a partial pelvis), TMP 1982.019.0023 (a partial skull), and TMP 1992.036.575 (a right

dentary In anatomy, the mandible, lower jaw or jawbone is the largest, strongest and lowest bone in the human facial skeleton. It forms the lower jaw and holds the lower teeth in place. The mandible sits beneath the maxilla. It is the only movable bone ...

and several left

metatarsals The metatarsal bones, or metatarsus, are a group of five long bones in the foot, located between the tarsal bones of the hind- and mid-foot and the phalanges of the toes. Lacking individual names, the metatarsal bones are numbered from the me ...

). ''Latenivenatrix'' was suggested to be distinguishable from ''Stenonychosaurus'' due to the structure of its frontals and metatarsal III, although later analyses found these characters to be individually variable, and also present in specimens of ''Stenonychosaurus.''

Description

With an estimated skull length of and a full body length of , ''Latenivenatrix'' is the largest troodontid known. It was described as distinguishable from other troodontids thanks to the following diagnostic (autapomorphic) traits residing in the pelvis: the pubis is retroverted forming a 17° angle; the pubic shaft is anteriorly curved; a large muscle scar on the lateral surface of the pubic shaft is present, slightly proximal to the pubic boot (this is seen also in dromaeosaurid ''

Hesperonychus ''Hesperonychus'' (meaning "western claw") was a small, carnivorous dinosaur. It was a member of the family Dromaeosauridae, along with its larger relatives ''Deinonychus'' and ''Velociraptor''. There is one described species, ''Hesperonychus el ...

''). Other traits argued to further distinguish ''Latenivenatrix'' from other derived troodontids (particularly its close relative ''Stenonychosaurus'') are: the triangular shape of each frontal bone which also does have a single deep groove in the frontonasal contact surface; a concave anterior surface of metatarsal III. While this trait appears to be absent in other derived troodontids such as ''

Saurornithoides ''Saurornithoides'' ( ) is a genus of troodontid maniraptoran dinosaur, which lived during the Late Cretaceous period. These creatures were predators, which could run fast on their hind legs and had excellent sight and hearing. The name is deri ...

'', ''Talos'', and '' Urbacodon'', it appears to be present in ''

Philovenator ''Philovenator'' (literally meaning "love hunter") is an extinct genus of troodontid paravian dinosaurs from the Wulansuhai Formation (dated to the Campanian age, sometime between 75 and 71 million years ago) of Inner Mongolia, China. Its spec ...

'' as well and not clearly verifiable in several species. A later re-analysis of the stratigraphic positions of known specimens of ''Latenivenatrix'' and ''Stenonychosaurus'' (including specimens not included in the initial description of ''L. mcmasterae'') also found stratigraphic overlap between the two proposed taxa. Due to this stratigraphic overlap, as well as the lack of definitive diagnostic characters, the variable presence of characters originally described as autapomorphic of ''Latenivenatrix'' in specimens of ''Stenonychosaurus'', and the extensive overlap of frontals of both in morphospace, ''L. mcmasterae'' was considered to be a junior synonym of ''S. inequalis''.

Phylogeny

''Latenivenatrix'' was found to be a derived troodontid (part of the newly defined

Troodontinae Troodontinae is a subfamily of troodontid dinosaurs. The subfamily was first used in 2017 for the group of troodontids descended from the last common ancestor of '' Gobivenator mongoliensis'' and ''Zanabazar junior,'' but has been redefined to be ...

), probably related to coeval Asian forms such as ''

Linhevenator ''Linhevenator'' is a genus of short-armed Troodontidae, troodontid theropod dinosaur from the Late Cretaceous (Campanian) Bayan Mandahu Formation of Bayan Mandahu, Inner Mongolia, China. Discovery The type species ''Linhevenator tani'' was na ...

'' and ''

''.

Paleobiology

''Latenivenatrix'' was the largest troodontid known, with a maximum total body length estimated to 3.5 m (11.5 ft). As a derived troodontid, it was probably a semi-omnivorous bipedal with loss of the skills of a primitive flyer.

Paleopathology

A parietal bone catalogued as TMP 79.8.1 bears a "pathological aperture". In 1985 Phil Currie hypothesized that this aperture was caused by a cyst, but in 1999 Tanke and Rothschild interpreted it as a possible bite wound. One hatchling specimen may have suffered from a

congenital defect A birth defect, also known as a congenital disorder, is an abnormal condition that is present at birth regardless of its cause. Birth defects may result in disabilities that may be physical, intellectual, or developmental. The disabilities can r ...

resulting in the front part of its jaw being twisted.Molnar, R. E., 2001, Theropod paleopathology: a literature survey: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 337-363.

References