Grangeria gobiensis links the extant rock hyrax to extinct chalicotheres

Chalicotheres are… a little different.
How chalicotheres came to be has been a traditional enigma.

According to Wikipedia – Chalicotheridae
“Chalicotheres can be first identified with certainty around 46 million years ago, in the Eocene of Asia. The family is thought to have evolved there, but appeared in North America by the Eocene. As the early evolution of perissodactyls is still unresolved, their closest relatives among other perissodactyl groups is obscure.”

“A 2004 cladistic study (Holbrook et al 2004) recovers chalicotheres as the sister group to Lophiodontidae, and the combined group (Ancylopoda) as sister to all modern perissodactyls (which includes Equoidea and Ceratomorpha), with the brontotheres as the most distantly related within the order Perissodactyla.”

In the LRT Lophiodon recently moved to the Marsupialia from the Chalicotheridae.

Figure 1. The rock hyrax, Procavia, shown to scale with several chalicotheres. ” data-image-caption=”

Figure 1. The rock hyrax, Procavia, shown to scale with several chalicotheres.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/chalicotherium588.jpg?w=122″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/chalicotherium588.jpg?w=415″ tabindex=”0″ role=”button” class=”size-full wp-image-87217″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/chalicotherium588.jpg” alt=”Figure 1. The rock hyrax, Procavia, shown to scale with several chalicotheres.” width=”584″ height=”1441″ />

Figure 1. The rock hyrax, Procavia, shown to scale with several chalicotheres.

A short while ago,
the large reptile tree (LRT, 2320 taxa) nested Procavia, the extant rock hyrax (Figs 1–3) with chalicotheres and liptoterns, like Diadiaphorus (Fig 1). Today a poorly known small chalicothere, Grangeria gobiensis (Colbert 1934, Figs 2, 3), appears to support this hypothesis as a transitional taxon: a small chalicothere with large incisors and small hooves, like Procavia, rather than the large claws in derived chalicotheres (Fig 1).

Figure 2. The skulls of Procavia and several chalicotheres to scale. ” data-image-caption=”

Figure 2. The skulls of Procavia and several chalicotheres to scale.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/diadiaphorus_procavia_skulls588.jpg?w=163″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/diadiaphorus_procavia_skulls588.jpg?w=558″ tabindex=”0″ role=”button” class=”size-full wp-image-87218″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/diadiaphorus_procavia_skulls588.jpg” alt=”Figure 2. The skulls of Procavia and several chalicotheres to scale. ” width=”584″ height=”1073″ />

Figure 2. The skulls of Procavia, Grngeria and several chalicotheres to scale. Note the reduction of the tusk like incisors in Grangeria.

Unfortunately
too little is known of Grangeria gobiensis to score it in the LRT. The line drawing Colbert made of the skull (Fig 2) appears to be complete, but it is a chimaera created from several specimens of various sizes. The same method was used to reconstruct the manus and pes (Fig 3).

Figure 3. Grangeria and Procavia manus and pes skeletal elements compared, not to scale. ” data-image-caption=”

Figure 3. Grangeria and Procavia manus and pes skeletal elements compared, not to scale.

” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/grangeria.manus_.pes588.jpg?w=150″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/grangeria.manus_.pes588.jpg?w=512″ tabindex=”0″ role=”button” class=”size-full wp-image-87220″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/grangeria.manus_.pes588.jpg” alt=”Figure 3. Grangeria and Procavia manus and pes skeletal elements compared, not to scale.” width=”584″ height=”1168″ />

Figure 3. Grangeria and Procavia manus and pes skeletal elements compared, not to scale.

Does the extant hyrax resemble
the last common ancestor of hyraxes and chalicotheres? We’ll find out if and when that ghost taxon is ever discovered and described. For now Procavia, the rock hyrax, appears to be a late survivor of that earlier radiation that gave us little-changed hyraxes and highly derived chalicotheres.

This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.

References
Ameghino F 1887. Reports of the Princeton University Expeditions to Patagonia, 1896-1899. J. B. Hatcher in charge. 338pp.
Colbert EH 1934. Chalicotheres from Mongolia and China in the American Museum. Bulletin of the American Museum of Natural History 67: 353–387.
Hatcher JB and Scott WB 1910. Reports of the Princeton University Expeditions to Patagonia 7(1-3):
Holbrook LT Lucas SG and Emry RJ 2004. Skulls of the Eocene Perissodactyls (Mammalia) Homogalax and Isectolophus. Journal of Vertebrate Paleontology 24. (4) 951-956.
Pallas PS 1766. Miscellanea zoologica. AP van Cleef, La Haye, 224 pp.

wiki/Procavia
wiki/Diadiaphorus
wiki/Chalicotheriidae
wiki/Chalicotherium
wiki/Moropus
wik/Anisodon

A living chalicothere + liptotern: Procavia, the rock hyrax