''Latenivenatrix'', meaning "hiding huntress", is a genus of large

troodontid Troodontidae is a clade of bird-like theropod dinosaurs from the Late Jurassic to Late Cretaceous. During most of the 20th century, troodontid fossils were few and incomplete and they have therefore been allied, at various times, with many dinos ...

known from a single species, ''L. mcmasterae''. Along with the contemporary '' Stenonychosaurus'', it is known from non-tooth fossils that were formerly assigned to the now potentially dubious genus ''

Troodon ''Troodon'' ( ; ''Troödon'' in older sources) is a controversial genus of relatively small, bird-like theropod dinosaurs definitively known from the Campanian age of the Late Cretaceous period (about 77 million years ago). It includes at l ...

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

Discovery and specimens

The type specimen, or

holotype A holotype (Latin: ''holotypus'') is a single physical example (or illustration) of an organism used when the species (or lower-ranked taxon) was formally described. It is either the single such physical example (or illustration) or one of s ...

, 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 '' Stenonychosaurus''. In 1987, it was referred to ''

''. It was 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 a Provinces and territories of Canada, province in Canada. It is a part of Western Canada and is one of the three Canadian Prairies, prairie provinces. Alberta is bordered by British Columbia to its west, Saskatchewan to its east, t ...

Canada Canada is a country in North America. Its Provinces and territories of Canada, ten provinces and three territories extend from the Atlantic Ocean to the Pacific Ocean and northward into the Arctic Ocean, making it the world's List of coun ...

. The specimen has preserved some skull bones, such as the 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 ve ...

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

gastralia Gastralia (: 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 these reptil ...

, a fairly complete arm, and incomplete legs. Moreover, three additional specimens from the same locality are referred to ''L. mcmasterae''. These include UALVP 55804 (a partial

pelvis The pelvis (: pelves or pelvises) is the lower part of an Anatomy, anatomical Trunk (anatomy), trunk, between the human abdomen, abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also c ...

), TMP 1982.019.0023 (a partial skull), and TMP 1992.036.575 (a right

dentary In jawed vertebrates, the mandible (from the Latin ''mandibula'', 'for chewing'), lower jaw, or jawbone is a bone that makes up the lowerand typically more mobilecomponent of the mouth (the upper jaw being known as the maxilla). The jawbone ...

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

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

Paleopathology

A parietal bone catalogued as TMP 79.8.1 bears a "

pathological Pathology is the study of disease. The word ''pathology'' also refers to the study of disease in general, incorporating a wide range of biology research fields and medical practices. However, when used in the context of modern medical treatme ...

aperture". In 1985, Phil Currie hypothesized that this aperture was caused by a cyst. Tanke and Rothschild interpreted it as a possible bite wound in 1999. One hatchling specimen may have suffered from a

congenital defect A birth defect 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 range from mild to severe. Birth de ...

, which resulted 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