SVP abstracts 23: Alvarezsaurids identified as termite eaters again

Qin et al. 2020 suggest
alvarezsaurids, tiny theropods with odd hook-like hands, were termite eaters. According to tradition and Qin et al. alvarezsaurids would have used their strong, hook-like fore claws to rip open termite nests.

By contrast,
earlier a tick bird analog (Figs. 1, 2) was proposed here.

Figure 3. Giant Deinocheirus, a contemporary of Mononykus, might have served as the host and dining room for a series of ever smaller and more specialized parasite eaters.

Figure 3. Giant Deinocheirus, a contemporary of Mononykus, might have served as the host and dining room for a series of ever smaller and more specialized parasite eaters.

From the Qin et al. abstract:
“Alvarezsauroidea is a group of bizarre theropods with highly specialized anatomy. Some of the late-branching members of this clade evolved extremely small body size—as small as early birds.”

“Alvarezsauroids until now have generally been overlooked in studies of theropod body mass evolution because they lacked sufficient lineage sampling and because the evidence for skeletal maturity of tiny specimens was lacking. Moreover, unlike the evolution of flight in paravians, the phylogenetically independent reduction in alvarezsauroid body mass lacks an obvious functional correlate.”

Unless they became parasite pluckers, like tick birds.

“The recent discoveries of early-branching alvarezsauroid fossils from China make a more thorough investigation of body mass evolution in this clade possible.”

Haplocheirus (Fig. 1) nests at the base of the alvarezaurids in the large reptile tree (LRT, 1751+ taxa) and in all other studies. These close relatives of velociraptors are traditionally portrayed as capable of leaping on the backs of larger dinosaurs. That’s where the ticks are, hiding among the feathers. That explains the phylogenetic miniaturization of alvarezsaurids, widely recognized as convergent with birds.

“We conducted detailed osteohistological analysis and bone co-ossification comparisons for Chinese alvarezsauroids, including the Late Jurassic Haplocheirus sollers, Aorun zhaoi, and Shishugounykus inexpectus, the Early Cretaceous relatively large-sized alvarezsauroids Xiyunykus pengi and Bannykus wulatensis, and the Late Cretaceous alvarezsauroid Xixianykus zhangi.”

In the LRT Aorun does not nest with alvarezsaurids, but at a much more basal node. Several of the others have not yet been tested due to their partial and often post-cranial only remains. Often these authors consider the large fore claws ideal for ripping open termite mounds.

“Together with previously published histological data and observations of anatomical characters such as bone ossification, we present a general age and ontogeny estimation for alvarezsauroid specimens. We use our results to estimate adult body mass of all alvarezsauroids and to critically assess the hypothesis of lineage-specific size decrease in Alvarezsauroidea.”

Figure 3. Tickbirds sitting atop a pair of rhinos, perhaps a modern analog for mononykids.

Figure 2. Tickbirds sitting atop a pair of rhinos, perhaps a modern analog for mononykids.

“Our results reveal that size evolution within alvarezsauroids had an initially divergent start followed by a single body size miniaturization event. This miniaturization process started at around 90 million years ago, had a significantly high rate, and culminated in parvicursorines that attained the smallest non-paravian dinosaur body masses in its final stage. Alvarezsauroid lineage richness increased after the miniaturization began, and potentially involved a secondary radiation of small-sized taxa at the end of the Cretaceous. Our results also support the idea that these late-branching small-sized alvarezsauroids occupied an obligate myrmecophagous (termite-eating) ecological niche. This hypothesis is also supported by their unusual low growth rates strategies revealed by our osteohistological studies, and their highly specialized anatomical features indicated by previous research.”

Analog extant termite eaters (anteaters, pangolins) are not tiny, bird-shaped taxa. Analog extant tick pluckers (Fig. 2) are bird-shaped taxa. Authors Michael Benton and David Hone, are part of the contingent promoting the unlikely termite-eater hypothesis.


References
Qin Z, Zhao Q, Choiniere J, Benton M and Xu X 2020. Comparative osteohistology of alvarezsaurs informs hypotheses for their body size evolution. SVP abstracts 2020.

https://pterosaurheresies.wordpress.com/2020/05/21/mononykus-and-shuvuuia-cretaceous-tickbirds/

https://www.smithsonianmag.com/science-nature/a-new-ant-eating-dinosaur-xixianykus-67587048/

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