Antediluvian Beasts of the East: Errimonykus colayae

The ice forms brittle plates as it encapsulates the cold, dark sea. Whale-sized mosasaurs swim beneath the ice, their lizard-like scales gleaming in the beams of sun which pierce through the crusty surface of the water. This is no place for the light of heart. Only the toughest of dinosaurs live here, including herds of battle-worn hadrosaurs which nibble at the ice for water, heading back to the shore to eat low-lying shrubs. 

Other, more ferocious dinosaurs live here. Amongst them are the tyrannosauroids, which use their large hands and claws to swipe and and impale their victims. The tyrannosauroids vex the hadrosaur herds, the frequent appearance of their sleek feathered coats in the mist above the ocean making the beaked herbivores nervous. The tyrannosaurs, however, are not the hadrosaurs main worries. Rather, their anxiety comes from other, smaller predators. 

One such hadrosaur has the misfortune of being at constant war with these small hunters. He is a large bull, and at 12 meters, he has little to worry about from the tyrannosaurs. However, he must live in constant pain from the attacks of Erimmonykus colayae. These small predators gnaw at the hadrosaur’s tough hide, constantly biting and tasting the herbivore’s flesh. Biting and gnawing and biting and gnawing seem to be the constant actions of the dromaeosaurs. The predators’ teeth have grown blunt from their use, and will soon be replaced by new sets of fangs. In the meantime, the bluntness of the dromaeosaurs’ teeth makes life for the hadrosaur even more miserable, as the fangs cause bruising and are a constant itch. This hadrosaur is particularly unfortunate, as five of the dromaeosaurs have latched on to his flesh for around a year. Erimmonykus attack the hadrosaur in a very sadistic way, waiting for the wounds they’ve inflicted on the poor dinosaur to heal before once again feeding on the flesh of the herbivore. The bull hadrosaur will also have to cope with the burden of the dromaeosaurs’ weight, which increases greatly the longer he carries them with him. He may find salvation if the dromaeosaurs find better-tasting meat, but Erimmonykus rarely leave their victims. Such is life in these harsh lands. 

Erimmonykus colayae was a dromaeosaurid, or “raptor” dinosaur of the subfamily pseudolovecrafinae recently described by Outis, Nemo, Nein & Young (2016) in the journal Introspective Advances in Theropods. Like other pseudolovecrafinines, the skull of E. colayae was robust and elongated. The sharp, serrated teeth of this animal formed 20-degree angles with the animal’s upper jaw, while the bottom teeth were isosceles and serrated on both sides. Large eyes would have been present in the animal, likely for spotting prey in the dark. Finally, a short body and large tail would have given the animal a bird-like appearance.

The most incredible adaptation of E. colayae was its odd foot morphology. Unlike other dromaeosaurs, the claws of E. colayae bore large areas of muscle attachment, seemingly to grasp on to objects for an extended amount of time. However, the lower leg of E. colayae is simplified, bearing resemblance to that of an ostrich. This morphology suggest that E. colayae did not use its highly adapted claws to navigate trees, but rather to cling on to the ground or perhaps more likely into prey items.


The claw of Errimonykus colayae.


Parasitism as a possible lifestyle for dromaeosaurs has previously been discussed in scientific literature (Fraser, 2014). In fact, this lifestyle has also been discussed to be the reason why dinosaurs like Triceratops and Stegosaurus evolved frills and bony plates. These structures would have protected the herbivores from being latched onto by dromaeosaurs. However, E. colayae seems to have taken this lifestyle even further, as it seems to have been able to latch onto prey for long periods of time. E. colayae comes from the far north  of the continent Appalachia in an area dubbed “Errim” by Outis, Nemo, Nein & Young (2016). The locality from which the holotype of E. colayae was discovered also bore the remains of basal hadrosaurid dinosaurs. As hadrosaurs did not evolve any structures like the plates of Stegosaurus on their back, they would have been the perfect targets for E. colayae to latch onto. The claws of E. colayae would have slashed into the skin of these herbivores, their serrated undersides catching on the flesh of the poor hadrosaurs. The dromaeosaurs would nibble on the exposed tissue of the animal. The pain must have been excruciating.

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E. colayae by the author. Pencils on paper, 2016.

Unfortunately for E. colayae, the Late Cretaceous would soon draw to a close. The meteorite that would slam into the Yucatan Peninsula would also send large waves crashing through the seas surrounding Appalachia. With it, the Errim ecosystem would be destroyed. No longer would E. colayae irritate herbivores for long amounts of time. The most sadistic predator in Earth’s history would go extinct.


Outis NG, Nemo FI, Nein BS, Young NY. 2016. A new dromaeosaurid coelurosaur theropod  from a new geographic area pertaining to the continent Appalachia and its implications for dromaeosaur parasitism. Introspective Advances in Theropods 1295: 332-560.

Fraser G. 2014. “Bizarre Structures” Point to Dromaeosaurs as Parasites and a New
Theory for the Origin of Avian Flight. The Journal of Paleontological Sciences 1: 1-27.


  1. I’ve always found parasites interesting, and I have recently been looking into different kinds of parasitic behavior in insects for my own curiosity. Is the sub-family name a reference to the science fiction/horror writer H. P. Lovecraft? One last comment – I think it is beyond dispute that humans are the most sadistic predators in Earth’s history.


    1. I think the authors were referencing H. P. Lovecraft, but you’d have to check the paper to be sure (I didn’t pay much attention to the etymology section, especially since I wanted to get out the news in a timely matter). Check with the link I provided to the paper (it’s open access).


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