Acheroraptor temertyorum lived in what is now Montana about 67–66 million years ago. It is one of the few named small dromaeosaurids from the latest Maastrichtian Hell Creek ecosystem. Nearly everything diagnostic comes from an upper jaw and a nearby lower jaw, not from a complete skull or skeleton.
Quick facts
| Scientific name | Acheroraptor temertyorum Evans, Larson & Currie, 2013 |
|---|---|
| Group | Theropoda, Dromaeosauridae; recovered in Saurornitholestinae by a 2022 analysis |
| Age | Latest Cretaceous, about 67–66 million years ago |
| Range | Hell Creek Formation, Garfield County, Montana, USA |
| Holotype | ROM 63777, an almost complete right maxilla with teeth |
| Referred material | ROM 63778, an almost complete left dentary without teeth |
| Length | About 3 m in a museum comparison, not a direct skeletal measurement |
| Mass | About 40 kg in the same broad comparison |
| Diet | Carnivorous |
How much of the animal is actually known?
ROM 63777 preserves nine tooth positions, distinctive openings and internal walls of an elongated maxilla.
ROM 63778 was found four metres away and fits in size, but it was not articulated with the holotype.
Ridged, recurved crowns link some isolated Hell Creek and Lance teeth to this jaw pattern.
No confirmed vertebra, limb, pelvis, tail or specialised second-toe claw belongs to the genus.
Name, locality and specimens
David Evans, Derek Larson and Philip Currie named the genus in 2013. Acheroraptor combines Acheron, the river of suffering in Greek mythology, with the Latin word for robber, echoing the name Hell Creek. The species honours James and Louise Temerty for their support of the Royal Ontario Museum.
The holotype came from reddish coarse sandstone roughly 45 kilometres southwest of Jordan, Montana. ROM 63778 lay in the same bone-bearing horizon about four metres away. Its size matches the upper jaw, so the bones may represent one animal, but the mixed deposit and lack of contact make that uncertain. The original paper credits CK Preparations with collecting and preparing the material without naming a single person who first saw it in the field.
What the jaws preserve
The tooth-bearing part of ROM 63777 is 92 millimetres long and contains nine sockets. Complete crowns remain in the third, fifth and seventh positions, while other sockets record teeth at different replacement stages. The bone is slightly crushed and crossed by a large crack, yet it preserves the combination used to diagnose the genus.
The front of the maxilla is comparatively long. A large maxillary opening lies low in the antorbital depression, and the internal wall projects far backwards into the antorbital opening. ROM 63778 preserves fifteen visible tooth sockets and probably held one or two more. Its fused interdental plates and Meckelian groove support a eudromaeosaur identity, but a toothless isolated dentary is harder to assign to one genus.
The crowns are narrow, strongly recurved and blade-like. Their front serrations are finer than those on the rear edge, and several longitudinal ridges run towards the tip. Similar isolated teeth had once been labelled Dromaeosaurus, Saurornitholestes or even Velociraptor. The connected upper jaw showed that many may instead belong to Acheroraptor, although not every small serrated tooth from Hell Creek can be assigned automatically.
Classification changed after CT work
The original analysis placed Acheroraptor among velociraptorines, close to Asian forms. A broader analysis in the same study left many eudromaeosaurs unresolved. In 2022, researchers used CT data and revised maxillary characters to recover Acheroraptor in Saurornitholestinae. Under that result, its long jaw resembles Asian velociraptorines through convergence rather than especially close ancestry.
The later placement is a tested hypothesis, not a final answer. Two jaw bones provide only a small fraction of the characters used in dinosaur phylogeny. A complete skull or associated postcranial skeleton could still alter its position.
Size, feeding and Hell Creek life
The Royal Ontario Museum presented a scale estimate of roughly three metres and 40 kilograms. Those numbers are not measurements of a preserved body. Tail length, limb proportions, maturity and individual variation are unknown, so the figures should be read as a broad comparison with better known relatives.
Recurved, compressed teeth with two serrated edges directly support carnivory. They do not identify prey. No stomach content, coprolite or attributable bite trace is known. A mechanical model of the referred dentary suggested rapid cutting bites and a weaker jaw than in Saurornitholestes, but that result depends on one incomplete bone whose referral is itself provisional.
Acheroraptor shared the Hell Creek landscape with Tyrannosaurus, Triceratops, hadrosaurs and many smaller vertebrates. Their presence does not establish a particular prey relationship. Small terrestrial animals also fossilise poorly, which helps explain why teeth are much commoner than associated dromaeosaur skeletons.
Evidence and reconstruction
| Level | What belongs here |
|---|---|
| Direct | Maxillary openings, jaw proportions, replacement teeth and serrated ridged crowns |
| Supported inference | Carnivory, an elongated snout and a feathered dromaeosaur body plan |
| Disputed | Exact subfamily, attribution of isolated teeth and identity of the lower jaw |
| Unknown | Precise size, colour, speed, social behaviour and preferred prey |
Frequently asked questions
Are Acheroraptor and Velociraptor the same dinosaur?
No. They are separate genera from different continents. Acheroraptor was first recovered near velociraptorines, but a later CT-based analysis placed it among North American saurornitholestines.
Has the sickle claw of Acheroraptor been found?
No confirmed foot claw belongs to its type material. The genus is known from an upper jaw and a provisionally referred lower jaw.
Who discovered Acheroraptor?
The 2013 description does not identify one field discoverer. CK Preparations collected and prepared the material, and the Royal Ontario Museum acquired the specimens.
Was Acheroraptor feathered?
No feathers occur with the fossils. Plumage is a strong inference from its dromaeosaurid relationships, but feather length, pattern and colour are unknown.