#alvarezsaurid

[stavrosskundromichalis]

Scene from the Late Cretaceous Allen Formation in Argentina. Two male Kelumapusaura machi are giving a group of azhdarchid pterosaurs (Aerotitan sudamericanus) and a poor little Bonapartenykus ultimus a fright.

[alphynix]

Manipulonyx reshetovi was an alvarezsaurid theropod dinosaur that lived during the Late Cretaceous, about 70 million years ago, in what is now Mongolia.

Although only known from a partial skeleton, based on its close relatives it would have been about 50cm long (~1'8"), with a narrow snout, a coat of fluffy down-like feathers, long slender legs, and short stout arms with massively enlarged thumb claws. 

Notably the fossil specimen has the best preserved hands known from the parvicursorine subfamily of alvarezsaurs, revealing a surprising arrangement of three ossified conical spikes around the thumb. These hand spikes were positioned pointing forwards, backwards, and inwards, and may have improved the ability to grip with just one functional finger.

"Spike-like" hand bones were also previously reported in 2009 in another parvicursorine, Ceratonykus, suggesting that these structures weren't unique to Manipulonyx.

The paper describing Manipulonyx proposes that alvarezsaurs were ovivores, using their hands to carry and then break open eggs, but I'm personally very skeptical of this idea. I think the myrmecophagy interpretation for these little dinosaurs is still much more likely – they probably did opportunistically raid eggs when they could get them, like many modern predators do, but being specialized for just egg-eating is a big claim that definitely needs more evidence.

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References:

Alifanov, V. R., and R. Barsbold. "Ceratonykus oculatus gen. et sp. nov., a new dinosaur (? Theropoda, Alvarezsauria) from the Late Cretaceous of Mongolia." Paleontological Journal 43.1 (2009): 94-106. https://doi.org/10.1134/S0031030109010109

Averianov, A. O., A. V. Lopatin, and A. A. Atuchin. "Forelimb structure and function in a new Late Cretaceous parvicursorine theropod dinosaur from Mongolia." Proceedings of the Zoological Institute RAS 329.4 (2025): 382-408. https://doi.org/10.31610/trudyzin/2025.329.4.382

Senter, Philip J. "Restudy of shoulder motion in the theropod dinosaur Mononykus olecranus (Alvarezsauridae)." PeerJ 11 (2023): e16605. https://doi.org/10.7717/peerj.16605

Wikipedia contributors. “Alvarezsauridae” Wikipedia, 02 Jan. 2026, https://en.wikipedia.org/wiki/Alvarezsauridae

Wikipedia contributors. “Manipulonyx” Wikipedia, 19 Jan. 2026, https://en.wikipedia.org/wiki/Manipulonyx

[olessan]

The lil steppies were not much exaggerated

[surfsupenthusiastnumerouno]

MONONYKUS, I LOVE YOU. 😭

[bralebradycneme]

Here it is, the dinosaur that I've based my username of. Bradycneme Draculae.

[harpagornis]

Were alvarezsaurids egg-eaters?

Manipulonyx by Conner Ashbridge.

Alvarezsaurids are highly unusual dinosaurs in that they have short but powerful forelimbs with thick claws. Typically they are interpreted as analogous to modern anteaters and similar mammals, using their claws to dig for termites and ants. However, a 2025 paper on the newly discovered Manipulonyx, a taxa with odd carpal spikes, have noted that the forelimbs are too short to reach termite mounds. Instead, these animals are interpreted as egg eaters, using the forelimbs to grab and pierce dinosaur egg shells.

While an interesting hypothesis, I feel it has its own share of problems. If alvarezsaurid arms are two short to reach termite mounds, they surely are also too small to reach eggs, as most dinosaurs (including some Mesozoic birds) burried their eggs on the ground. I also question the ecology of an obligate egg-eater; there are modern snakes of the genus Dasypeltis and Elaschistodon that do feed primarily on eggs, but they're cold blooded animals. An endothermic dinosaurs would likely have to feed on multiple eggs per day, and there would have been times of absence like dry seasons or harsh winters.

Additionally, dinosaurs usually develop hand spikes when engaging in interpecific combat; many modern birds with spurs can attest to this. I doubt that the spikes of Manipulonyx, being hard and inert, would have been better to collect eggs than to simply fight other Manipulonyx.

Overall, the mystery of alvarezsaurid diet continues.

[percivalias]

The Maniraptoran Alphabet (Part 3)

Part 3/5 of my dinosaur alphabet! Some of my favorite species in the whole set in this batch, but I'll let you guess which ones those are :)

[shiningcindyz]

Day 29