Things just got strange: A referred Shuvuuia specimen has a Gallimimus-type skull

A recent dive into the life and ecology
of the Late Cretaceous Mongolian tiny theropod, Shuvuuia deserti (Chiappe, Norell and Clark 1998; Figs. 1–2) sheds new light on the inner ear and sclerotic ring of this remarkable dinosaur. Choiniere et al. 2021 considered Shuvuuia a nocturnal scratch-digger based on its morphology and comparative anatomy.

Figure 1. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally. Click to enlarge.
Figure 1. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks or large dinosaurs. The forelimb is very strong. Perhaps these taxa rest vertically and run horizontally.

Several specimens attributed to Shuvuuia
have been described. Two have skulls. The holotype is IGM 100/1304 (Fig. 1). It did not preserve a sclerotic ring. Everyone agrees Shuvuuia was a descendant of the larger alvarezsaurid, Hapolocheirus (Fig. 1).

Figure 2. Haplocheirus and Shuvuuia skulls and sclerotic rings compared.

Choiniere et al. 2021 used the sclerotic ring from the referred specimen
of Shuvuuia, IGM 100/0977 (Figs. 1–2) for their study on nocturnal dinosaurs. The identity of the referred specimen was never in question because it also had that iconic stunted forelimb with a large ungual 1. If other manual digits were present, buried in the matrix, they are not yet visible.

Figure 2. Comparisons of two specimens attributed the Shuvuuia, Note the claw and scale bar on the upper left is actually 3x larger than the MPD claw, here shown at the same length.

A problem arises
in phylogenetic analysis. When tested in the large reptile tree (LRT, 1841+ taxa) the slightly larger 0977 specimen does not nest with the Shuvuuia holotype 1304 specimen. Instead the 0977 specimen nests with a much larger, coeval, big-eyed, toothless, struthiomimid, Gallimimus (Fig. 3). In the LRT 54 steps are added to the MPT when the referred specimen is forced to nest with the holotype of Shuvuuia.

Figure 3. Gallimimus skull. Compare to figures 1 and 2.
Figure 3. Gallimimus skull. Compare to the IGM 100/0977 skull in figures 1 and 2.

Convergence is rampant with the Vertebrata.
Sure those stunted foreclaws are similar, but let’s not get caught “Pulling a Larry Martin” (= cherry-picking outstanding traits). Rather test ALL the available traits to determine where on the cladogram your taxon nests. Create a reconstruction so you know the way the bones went together in life. When more data comes to light, be willing to make changes, as I will as this situation continues to unfold.

Choiniere et al. 2021 considered Shuvuuia to be a nocturnal predator
based on the specimens they employed and comparisons to living and extinct taxa. They used the holotype skull for the inner ear data. They used the Gallimimus sister skull for the optic data.

Choiniere et al. reported a 92% correspondence of their optical ratio method
to known nocturnal vs. non-nocturnal bird taxa. In the course of study I found out that large-eyed Apus, the swift, and Struthio, the ostrich, are essentially sleepless taxa (see below). These two scored with non-nocturnal birds. Choiniere did not appear to indicate a ‘sleepless’ category apart from nocturnal vs. non-nocturnal.

According to ScienceMag.org
“Contrary to popular belief, ostriches don’t sleep with their heads in the sand. In fact, to all appearances, they never sleep at all: their eyes stay open, although they appear to doze off from time to time.” Consider the situation. On the plains of Africa, ostriches cannot risk letting their guard down. So they sleep and dream standing up with eyes open, in groups. Yes, you will find pics of ostriches lying down with eyes closed, surrounded by friends, during daylight hours. Wikipedia also reports, “Ostriches are diurnal, but may be active on moonlit nights.”… so ‘either or’ in the case of birds and dinos should probably include a little gray zone in between.

Wikipedia reports on the Common swift,
“non-breeding individuals may spend up to ten months in continuous flight.” So swifts sleep on the wing for who knows how long or when.

Many birds sleep with one eye open
in the dark, looking for trouble.

The kiwi (Apteryx) is a flightless nocturnal theropod.
Their optic ratio in this taxon is not larger than in many diurnal birds.

When you have something to say
and you’re going to say it in a paper with 12 co-authors, make sure the taxa you test are indeed the taxa you intend to test. Do this before you send grad students off to the collections with their micrometers and digital calipers to measure scleral rings and endoosseus cochlear ducts. Reconstruct your skulls and skeletons. Add your taxon to your cladogram. Do the work. Show the pros and cons. Be ready to bail on your project if results slip into the gray zone. Greet critics with open arms. They will take you to places you were never aware of (Thank you NB). Many workers have tried to figure out the niche and lifestyle of extinct taxa. That makes paleo come alive. It’s always good to hear an idea that is well supported.

References
Chiappe LM, Norell MA and Clark JM 1998. The skull of a relative of the stem-group bird Mononykus. Nature, 392(6673): 275-278.
Choiniere JN et al. (+12 co-authors) 2021. Evolution of vision and hearing modalities in theropod dinosaurs Science 372 (6542): 610-613 DOI: 10.1126/science.abe7941

https://www.sciencemag.org/news/2011/08/video-ostriches-are-stealth-sleepers

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