''Latenivenatrix'' (meaning "hiding huntress") is a genus of troodontid known from one species, ''L. mcmasterae''. Along with the contemporary '' Stenonychosaurus'', it is known from the non-tooth fossils formerly assigned to the genus '' Troodon''. Although described as separate, it has been considered a junior synonym of ''Stenonychosaurus''.

Discovery and specimens

The type specimen or holotype 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 '' Troodon''. It had been collected in 1968 by Irene Vanderloh in the Dinosaur Park Formation strata from Alberta, southern Canada. The specimen has preserved some skull bones ( frontals, parietals, postorbital, 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 The pelvis (plural pelves or pelvises) is the lower part of the trunk, between the abdomen and the thighs (sometimes also called pelvic region), together with its embedded skeleton (sometimes also called bony pelvis, or pelvic skeleton). The ...

), TMP 1982.019.0023 (a partial skull), and TMP 1992.036.575 (a right dentary 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'', ''Talos'', and ''

Urbacodon ''Urbacodon'' ("URBAC tooth") is a genus of troodontid dinosaur, a type of small carnivore. It lived in Uzbekistan during the early Late Cretaceous Period, about 95 million years ago. On 9 September 2004, a lower jaw of a small theropod w ...

'', 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