''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. inequalis ...

'', 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 least ...

''. 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 seve ...

of ''Latenivenatrix'', CMN 12340, was originally described in 1969 by

Dale Alan Russell Dale Alan Russell (27 December 1937 – 21 December 2019) was an American-Canadian geologist and palaeontologist. Throughout his career Russell worked as the Curator of Fossil Vertebrates at the Canadian Museum of Nature, Research Professor at ...

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 7 ...

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 tota ...

. 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 v ...

, basioccipital and basisphenoid), four vertebrae and four ribs, some chevrons and gastralia, 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). ''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''). 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'', ''Talos'', and '' Urbacodon'', it appears to be present in '' Philovenator'' 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), probably related to coeval Asian forms such as '' Linhevenator'' and '' Philovenator''.

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 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