Alnashetri (alvarezsauroid from Argentina) redescribed

[Ben Creisler]

Ben Creisler

bcre...@gmail.com

A new paper:

[Morrison Formation YPM 9163 and Calamosaurus foxi assigned to Alvarezsauroidea]

Peter J. Makovicky, Jonathan S. Mitchell, Jorge G. Meso, Federico A. Gianechini, Ignacio Cerda & Sebastian Apesteguía (2026)
Argentine fossil rewrites evolutionary history of a baffling dinosaur clade
Nature (advance online publication)
doi: https://doi.org/10.1038/s41586-026-10194-3
https://www.nature.com/articles/s41586-026-10194-3


Alvarezsauroids are an enigmatic clade of predominantly small-bodied theropod dinosaurs that are known mainly from the Jurassic to Cretaceous periods of Asia and South America. Late Cretaceous alvarezsauroids possess specialized forelimbs adapted for digging, minute supernumerary teeth and heightened sensory capacities6, and are interpreted as myrmecophagous. They are hypothesized to exhibit evolutionary miniaturization coupled to their dietary specialization. Fragmentary South American taxa are traditionally arrayed as a paraphyletic grade with respect to the Late Cretaceous Asian subclade Parvicursorinae, invoking dispersal to explain their disjunct distributions. Here we describe a skeleton of the alvarezsauroid Alnashetri cerropoliciensis representing to our knowledge the most complete and smallest South American taxon to date. We also recognize two alvarezsauroids among historic taxa from the Northern Hemisphere. Phylogenetic analysis recovers Alnashetri among basal non-alvarezsaurids, rendering South American taxa polyphyletic. Combined with the new taxa recognized here, our biogeographical analyses infer a Pangaean ancestral distribution for Alvarezsauroidea, with vicariance dominating the early history of the clade. The early branching position of Alnashetri among larger-bodied relatives revises best-fit models of body size evolution in alvarezsauroids—we find no support for evolutionary miniaturization but, rather, find support for repeated evolution within a narrow body size range.

Supplementary Information is free

****

News:

90-million-year-old ‘missing link’ bird-like dinosaur discovered

https://www.purdueexponent.org/news/national/90-million-year-old-missing-link-bird-like-dinosaur-discovered/article_c9bdff93-351c-56d3-9ab5-b5d14fffde16.html

https://phys.org/news/2026-02-tiny-dinosaur-big-impact-million.html

https://www.eurekalert.org/news-releases/1117307

https://www.newscientist.com/article/2517011-tiny-predatory-dinosaur-weighed-less-than-a-chicken/

[Mickey Mortimer]

Interestingly, Haplocheirus is not recovered as an alvarezsauroid, but is instead even more stem-ward than therizinosaurs, being the first branching maniraptoran.

Mickey Mortimer

[Tim Williams]

If _Calamosaurus foxi_ (originally _Calamospondylus foxi_) is an alvarezsauroid, it would be among the largest members of the group.  Naish et al. (2001) estimated the body length at 3.5m (based on a comparison of the two cervicals with those of _Compsognathus longipes_), which would make _C.foxi_ even larger than _Kol ghuva_.

--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.
To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CAMR9O1L_UUMX-9%3DYtGPDzS-V7Gp-E-mDp0MSFJ0FScdQinVgBQ%40mail.gmail.com.

[Gregory Paul]

There was another paper that also removed Haplocheirus from alvarezsaurs. If so, then the original hypothesis that the group may be closer to derived birds than Archaeopteryx may be revived. 

GSPaul

--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.
To view this discussion visit

https://groups.google.com/d/msgid/DinosaurMailingGroup/fd0210e8-f3bc-412f-8daa-ad3672a31287n%40googlegroups.com

.

[Mickey Mortimer]

Well, my analysis in the Hartman et al. (2019) Hesperornithoides description recovered it as a compsognathid, a placement originally proposed non-quantitatively by Alifanov and Saveliev (2011:184). Similarly, Choiniere et al. (2011) found the braincase anatomy of parvicursorines was more similar to avialans than to Haplocheirus, suggesting homoplasy or alvarezsauroid polyphyly. Among published phylogenetic analyses, Lee and Worthy (2011) recovered Haplocheirus as the basalmost ornithomimosaur in their Bayesian reanalysis of a TWiG matrix, not separated from compsognathids by a majority bootstrap value.  Agnolin et al. (2022) have since contested Choiniere et al.'s alvarezsauroid characters in Haplocheirus, and concluded "there are some features reminiscent to ornithomimosaurs and different from those of alvarezsaurs." 

But no(?) analysis has recovered alvarezsauroids as paravians in the past 25 years, even when Haplocheirus falls out elsewhere. Alnashetri doesn't look particularly birdlike to me, although some characters are troodonty.

References- Alifanov and Saveliev, 2011. Brain structure and neurobiology of alvarezsaurians (Dinosauria), exemplified by Ceratonykus oculatus (Parvicursoridae) from the Late Cretaceous of Mongolia. Paleontological Journal. 45(2), 183-190.
Choiniere, Norell and Dyke, 2011. The anatomy of the parvicursorine braincase and its implications for alvarezsauroid systematics and evolution. Journal of Vertebrate Paleontology. Program and Abstracts 2011, 88.
Lee and Worthy, 2011. Likelihood reinstates Archaeopteryx as a primitive bird. Biology Letters. 8(2), 299-303.
Hartman, Mortimer, Wahl, Lomax, Lippincott and Lovelace, 2019. A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight. PeerJ. 7:e7247.

Agnolin, Lu, Kundrat and Xu, 2022 (online 2021). Alvarezsaurid osteology: New data on cranial anatomy. Historical Biology. 34(3), 443-452.

Mickey Mortimer

[Tim Williams]

Gregory Paul via Dinosaur Mailing Group <DinosaurMa...@googlegroups.com> wrote:

> There was another paper that also removed Haplocheirus from alvarezsaurs. If so, then the original hypothesis that the group may be closer to derived
> birds than Archaeopteryx may be revived.

I concur with Mickey.  There's no compelling evidence that alvarezsaurs are birds (avialans), or secondarily flightless.

The new _Alanashetri_ description mentions the putative ant-/termite-eating (myrmecophagous) habits of alvarezsaurids, a hypothesis that has broad support.  But it's worth noting that egg-eating (ovivorous) habits have been proposed as an alternative explanation for the specialized forelimbs of alvarezsaurids (e.g., Lü et al., 2018 doi:10.31035/cg2018005; Averianov et al., 2025  doi:10.31610/trudyzin/2025.329.4.382).  A recent investigation of the evolution of myrmecophagous mammals (Vida et al. 2025 doi.org/10.1093/evolut/qpaf121) was sceptical of myrmecophagous habits in alvarezsaurids.  Although termites and ants are estimated to have originated in the Early Cretaceous (maybe a bit earlier for termites), both appear to be minor components of terrestrial ecosystems prior to the Cenozoic.  So the relatively scarce termite and ant colonies during the Cretaceous might not have been sufficient as a food source - especially because of how energy-poor this diet is, and the volume of individual insects that would need to be consumed by highly active cursorial theropods like alvarezsaurids.  In the modern world, myrmecophagous mammals that weigh over 1 kg generally have low basal rates of metabolism and low body temperatures by mammalian standards (McNab 2009 10.1111/j.1469-7998.1984.tb02345.x).  

[Alberta Claw]

That last doi links to McNab (1984). Note that McNab (2000) later revised the upper limit of body mass in mammalian myrmecophages that retain a typical mammalian metabolism to around 10 kg, which as it happens is also about the size of the largest known parvicursorines. This is also consistent with subsequent work (including some by McNab) finding that some mammalian myrmecophages > 1 kg do not necessarily have significantly reduced metabolic rates compared to closely related species.

--
You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CA%2BnnY_ESoYoYKO18yU_NYkMHg42rKyn9E7%3DyTrGj4i9WuPo9HA%40mail.gmail.com.

[Tim Williams]

Thanks - nice catch!

The question remains: Were there enough ant or termite colonies around in the Cretaceous to support myrmecophous theropods?

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CAHLxd9P1Z9-g4-0CaW-eoNLAta%3D90exWoKF10Yi%3DnHf1Sh8VVw%40mail.gmail.com.

[Jaime Headden]

I'm sure the answer to the question is: if they are adapted for it, then it stands there were enough to feed them.

This is a different question compared to the oviphagous issue, where the food source is a seasonal thing, and hardly enough to force consumption. It needs be said, but Gans argued that oviphagous snakes, among the only animals that subsist entirely upon eggs, derive from within colubroid lineages that are known nest predators, and some will still consume nestlings (be it lizard, bird, etc.). This doesn't enforce the idea that egg-eating should evolve only among nest-predators, but it raises the difficulty of easing the pathway from non- to pro-oviphagy when the consumers lack oral adaptations for managing the eggshell---and exclusively avian eggs. Nest predation also occurs among snakes against lizards, crocs, turtles, where the *relative* thickness of the shell requires oral/postoral adaptations for crushing/slicing open. That occurs in the mouth/esophagous for a reason, being that other animals that consume eggs just peck the shell open, or bite it open, such as lizards, mammals, etc. No special claws are needed. But like myrmecophages, it seems a relatively lower metabolism to adjust for scarcity may comport with specialized diet that doesn't require specialized oral equipment.

Cheers,

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/CA%2BnnY_H6z1jah7iB-nWtkVa0nvEwP4aee_B3reknVUb5XMUBfw%40mail.gmail.com.

--

Jaime A. Headden

The Bite Stuff: http://qilong.wordpress.com/

"Innocent, unbiased observation is a myth" - P. B. Medawar (1969)

[Tim Williams]

 Jaime Headden <jaimeh...@gmail.com> wrote:

> I'm sure the answer to the question is: if they are adapted for it, then it stands there were enough to feed them.

Yes, good point.  The extinct mammal _Fruitafossor_ is inferred to have fed on termites, so presumably termite colonies existed in the Late Jurassic (maybe _Eopolis ekdalei_?).  Based on dentition, the original description inferred that _Fruitafossor_ had a diet similar to dasypodid armadillos, and fed primarily on insects and small invertebrates.  So not obligately myrmecophagous (termitivorous in this case).

> Nest predation also occurs among snakes against lizards, crocs, turtles, where the *relative* thickness of the shell requires oral/postoral adaptations

> for crushing/slicing open. That occurs in the mouth/esophagous for a reason, being that other animals that consume eggs just peck the shell open, or
> bite it open, such as lizards, mammals, etc. No special claws are needed. But like myrmecophages, it seems a relatively lower metabolism to adjust for
> scarcity may comport with specialized diet that doesn't require specialized oral equipment.

With regards to ovivory (egg predation) in alvarezsaurids, the working hypothesis is that the clawed forelimbs were specialized for puncturing eggs.   

In a way I'm playing devil's advocate here, because the myrmecophagy hypothesis for alvarezsaurids has solid biomechanical support, and is the favored hypothesis for good reason.  Additionally, as far as I know, it doesn't require that alvarezsaurids were obligately myrmecophagous.

[Russell Engelman]

The other option is there was some kind of termite analogue in the Mesozoic we just don't know about because the insect fossil record is so poor. Possibly something we have fossils of now but haven't recognized as eusocial yet. Kind of like how we have evidence of insect pollination by beetles, flies, and scorpionflies in bennettitaleans, but based on what is known about modern plants there is no way anyone would have suspected independent evolution of animal pollination.

Hell ants seem to have been proposed to be eusocial based on recovery of alate ("princess") and worker castes, so it seems plausible that eusociality in ants goes back at least before the Aptian.

Vermivory or grub-eating might be another option. Maybe not eating colonial insects but wood-boring grubs in rotting wood? There are a surpris8ngly large number of worm and grub-eating mammals out there, including some surprisingly large ones, not to mention the numerous cases of convergence in "woodpecker niches" between woodpeckers, the marsupial Dactylopsila, and a few other extinct mammal lineages like apatemyids. In theory all that ecospace would be open in the Mesozoic. Digging for grubs and digging for eusocial insects is going to produce similar specializations.

[Jason Brougham]

My first problem with myrmecophagy for alvarezsaurs is that, though the arms of derived ones are described as “hypertrophied” they are in fact massively reduced in length from the ancestral state. Yes, the width-to -length of the humerus, radius, and ulna are hugely increased, but that is because the whole arm is so short that it might not even protrude from the body feathers! Shuvuuia, for example, would have to press its chest against a termite colony to dig into it at all, and could only reach an inch into the colony, regardless. 

Real anteaters have long, strong, forelimbs. Derived alvarezsaurs are more like Apteryx, the Kiwi, in forelimb length. BUT, the muscle attachments on alvarezsaur forelimb are indisputably disproportionately large, which is puzzling.

I recently built a model of Trierachunchus and when I had the plastic skull on an armature wire, I found that the tip of the snout could not even reach the manual unguals. It could not kink its neck enough to get its mouth to where the arms were digging, it would have to take a step back.

Dr. Roger Benson told me that the living analogue he sees is Peddles, the Spring Hare: a long-legged, rodent with a disproportionately short but powerfully built forelimb. It is used in burrowing, apparently, when the animal is already down its hole and cannot reach forward with its hindlimb anymore, the forelimbs dig to extend the burrow. Benson is a lot smarter than I, so I like his idea.

From: dinosaurma...@googlegroups.com <dinosaurma...@googlegroups.com> on behalf of Russell Engelman <neovena...@gmail.com>
Date: Thursday, March 5, 2026 at 9:55 AM
To: Dinosaur Mailing Group <dinosaurma...@googlegroups.com>
Subject: Re: [DMG] Re: Alnashetri (alvarezsauroid from Argentina) redescribed

EXTERNAL SENDER

--

You received this message because you are subscribed to the Google Groups "Dinosaur Mailing Group" group.
To unsubscribe from this group and stop receiving emails from it, send an email to DinosaurMailingG...@googlegroups.com.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/32971e32-a2e3-42aa-b593-2d2bf7735af5n%40googlegroups.com.

[Jason Brougham]

Sorry that is Pedetes the Spring Hare. Microsoft  auto-uncorrected my spelling.

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/MN2PR14MB3950D8D44687E84CADE4AC74DB7DA%40MN2PR14MB3950.namprd14.prod.outlook.com.

[Gregory Paul]

Like when a person noted that a preprint says specious rather than speciose. Spell check:(

GSPaul

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/MN2PR14MB3950F4CE170A33A303034D34DB7DA%40MN2PR14MB3950.namprd14.prod.outlook.com.

[Jura]

I am similarly skeptical of the whole "termite eater" / "ant specialist" hypotheses for alvarezsaurs. I would argue that the hypothesis of their ecology is less well-supported than it is just strangely popular. The biomechanical data are not that strong. As Jason Brougham brought up, heavily muscled arms with effectively no reach are not all that useful for burrowing, much less for tearing into termite mounds. They more resemble python spurs than pangolin arms. Alvarezsaur hyoids are also not special, suggesting a relatively unspecialized tongue that would have been of limited use for capturing insects hidden in tunnels. Then there's the alleged "owl-like" hearing which appears to be based on a generous read of the original paper (Choiniere et al. 2021, who used this mostly as evidence for nocturnality), and has not withstood a critical re-examination (see Manley and Koppl 2025). 

Refs

Choiniere, J.N., Neenan, J.M., Schmitz, L., Ford, D.P., Chapelle, K.E., Balanoff, A.M., Sipla, J.S., Georgi, J.A., Walsh, S.A., Norell, M.A. and Xu, X., 2021. Evolution of vision and hearing modalities in theropod dinosaurs. Science, 372(6542), pp.610-613. 

Manley, G.A. and Köppl, C., 2025. When dinosaurs hear like barn owls: pitfalls and caveats in assessing hearing in dinosaurs. Biology Letters, 21(5).

[Jaime Headden]

The issue with the forelimbs is, as Jason notes, they are enormously strong. Moreover, Senter and others have described forelimb attitude and posture and motion consistent with scratch digging, meaning regardless of whether one feels they are not "large enough," they are uniquely exapted for a function consistent with the very behavior that modern myrmecophages are notable for. *Depsite* their extremely small size. One thing that is being lost in this discussion, however, is that the forelimbs of almost every modern myrmecophage are also used for locomotion, a point Albert (-onykus) made: https://albertonykus.blogspot.com/2020/05/making-sense-of-alvarezsaurid.html . So now we should be wondering what  myrmecophage forelimbs might look like if they weren't used to walk or climb with?

Cheers,

To view this discussion visit https://groups.google.com/d/msgid/DinosaurMailingGroup/8985195a-8e66-496f-bf32-71694812c90bn%40googlegroups.com.