Halszkaraptor (meaning "Halszka's seizer") is a genus of dromaeosaurid dinosaur from Mongolia that lived during the Late Cretaceous period. It contains only one known species, Halszkaraptor escuilliei.
Scientists compared the type specimen (holotype) to the bones of extant crocodilians and aquatic birds, and found evidence of a semiaquatic lifestyle. A phylogenetic analysis revealed it was a member of the basal subfamily Halszkaraptorinae along with Mahakala and Hulsanpes.
The holotype of Halszkaraptor likely came from the Djadochta Formation at Ukha Tolgod in southern Mongolia, and was illegally removed by fossil poachers. It found its way to Japan and Great Britain, being owned by several collectors for some years until the Eldonia company of fossil dealer François Escuillié obtained it. He identified it as a new species, and in 2015 took it to Brussels, showing it to paleontologists Pascal Godefroit and Andrea Cau for further verification. After verifying its authenticity, among other means by a synchrotron of the European Synchrotron Radiation Facility, Cau and other prominent paleontologists described the genus in a detailed study published in the journal Nature. After negotiations, Escuillié consented to the fossil being returned to the Mongolian authorities.
The type species Halszkaraptor escuilliei was in 2017 named and described by Andrea Cau, Vincent Beyrand, Dennis F. A. E. Voeten, Vincent Fernandez, Paul Tafforeau, Koen Stein, Rinchen Barsbold, Khishigjav Tsogtbaatar, Philip John Currie and Pascal Godefroit. The generic name combines a reference to the late Polish paleontologist Halszka Osmólska, who was involved in many expeditions to Mongolia and named the closely related Hulsanpes, with Latin raptor, "robber". The specific name honours Escuillié for having made the specimen available to science.
The holotype, MPC D-102/109, was found in a layer of orange sandstone of the Bayn Dzak Member of the Djadochta Formation, dating from the late Campanian. It consists of a relatively complete skeleton with skull. In 2017, the fossil was not further prepared. Work by the fossil dealers had at that point generally exposed the left side of the skeleton. The synchrotron revealed that the bones continued into the rock and that the piece was probably not a chimaera, an artificial assembly of bones of disparate species, though the top of the snout had been restored with plaster and some elements had been reattached to the rock by glue. The skeleton is largely articulated and not compressed. It represents a subadult individual, about one year old.
Halszkaraptor was about the size of a mallard duck. The head was about seven centimetres long, the neck twenty centimetres, the back thirteen centimetres and the sacrum five centimetres.
The describing authors indicated some distinguishing traits. Some of these were autapomorphies, unique derived characters. The premaxilla, the front snout bone, forms a flattened snout, occupying 32% of the snout length. The premaxilla bears eleven teeth. The jugal bone is rod-shaped and its ascending branch occupies only a tenth of the bar behind the eye socket, not reaching the orbit. The neck is extremely elongated, representing half of the snout-vent length. The postzygapophyses, rear joint processes, of the neck vertebrae bear no epipophyses, additional processes on their upper rim. The neck vertebrae have extremely reduced neural spines: on the second to fifth vertebrae these are only low ridges and subsequent neck vertebrae lack them completely. In the second to fifth neck vertebrae the normally paired postzygapophyses have fused into a single lobe-shaped process. The neural spines of the tail vertebrae are extremely shortened: at the first three tail vertebrae they are formed like low bumps and subsequent tail vertebrae lack them completely. The chevrons of the tail base are large with a pentagonal profile. The first phalanx of the third finger has 47% of the length of the third metacarpal.
Furthermore, a unique combination is present of traits that in themselves are not unique. The external bony nostril is situated behind the main body of the premaxilla, the point where it connects to the front branch of the maxilla. The descending branch of the postorbital bone is rod-shaped. The number of vertebrae of the neck and back totals twenty-two. Only the seventh, eighth and ninth neck vertebrae have pleurocoels, pneumatic depressions on their sides. The transition between the tail base and the middle tail is situated at the seventh to eight vertebra. The third finger is longer than the second finger.
The snout, though elongated, is transversely expanded in front, creating a spoon-shaped profile in top view. It is also flat, its width 180% of its height. The top profile in side view is hollow. The expanded area consists of a relatively long premaxilla. This bone is internally excavated by a system of air chambers. From a larger chamber in the rear, neurovascular channels permeate the entire bone, not just the sides as with Neovenator, but the top also. These channels probably housed electro-sensory organs. Each premaxilla bears eleven teeth, a record for the entire Dinosauria. Theropods normally have four premaxillary teeth and the previous record for this group was seven, with spinosaurids. These teeth are very closely packed, touching each other, and are very elongated, gradually curving to behind. The teeth in the maxilla, their number estimated at twenty to twenty-five, are more robust, curve only at their tips and are spaced at a larger distance. They are more transversely flattened, with an oval cross-section.