I actually wanted to further talk about this sketch from last night a little, as it not only serves as an full body depiction of the animal but also a cheek in tongue critique of the paper describing Manipulonyx.
This animal, an alvarezsaur, is known from various bones, most importantly a complete hand that reveals novel structures for this group. Specifically osteoderms sitting on the side and palm of the hand. The authors speculated that these structures would have a specific, practical purpose and proposed that they would be used for grabbing, transporting and opening larger dinosaur eggs.
While this appears an interesting idea and I certainly think that occasional consumption of eggs wasn’t off the table for this animals I doubt that they were specialized in this way. At least to the degree that it actively shaped their limbs.
And here is why I think that:
Eggs are a very seasonal treat. While certain areas with a stable climate can see a year long supply of eggs from different species, the Nemegt formation, where this animal was found, is unlikely to provide such a stable egg supply. The climate was quite seasonal, in winter maybe even reached freezing temperatures occasionally. Not ideal when you have to wait months for your main source of food to return.
Which brings us to the next point. Animals today, that are specialized in egg consumption are usually “cold blooded”, as these are usually too rare of a treat to fuel more active creatures.
The fossils of Manipulonyx were indeed found in the vicinity of larger dinosaur eggs but being found together with them doesn’t mean the animal predated on these. Beyond that the paper doesn’t provide a taphonomic explanation for the locality, meaning: how did this fossils end up here? Were they preserved in situ or were the fossils maybe transported, how long did it take for the fossils to accumulate?
The limbs of Manipulonyx do not look like they would be great for transporting eggs. Especially the palmar osteoderm seems in the way when trying to hold anything, I wouldn’t the surprised if the hand overall was actually quite rigid.
The idea of these animal would go after eggs that they can wrap their arms around begs the question what juvenile Manipulonyx would eat. Did smaller/younger individuals simply go for smaller eggs? Would there be ontogenetic niche shift? That seems, in my eyes, unlikely.
So what did they use their arms for? Please take everything you read here with a grain of salt, as an artist who hasn’t seen the fossils personally I can only provide limited insight into this. Non of what you read here is peer reviewed research. Non the less I think there are some alternative ideas what is animal did that seem, for the moment, more likely to me.
Most prominently I see two possibility, both related and based on observations on modern birds:
Display, the age old argument, I know, but tons of spikes on really short arms just don’t seem really practical. But with some flashy colors… who knows, I am not kink shaming.
Intraspecific combat. Many modern day birds have wing spurs, often times visible even in the bone. They might look weird but many birds are known for beating each other with their wings, the arms of Manipulonyx were short yes, but I think they would still allow for some wrestling matches. In birds they are also used for defense but given the arm length of Manipulonyx I think that’s not as likely ;)
