Origin of chalicotheres revisited
Chalicotheres are traditionally considered ‘aberrant’ perissodactyls
because chalicotheres superficially looked like horses (Figs 1–4). Chalicotheres had their genesis in the Eocene and lasted to the Early Pleistocene (48mya – 2mya) across North America, Europe and Africa.
The presence of clawed feet (Figs 1, 4) in a hoofed clade is the traditionally acknowledged problem here. Even so, this hypothesis continues to be taught at the university and museum level with no one (to my knowledge) working on this issue other than Hooker and Dashzeveg 2004 who supported the perissodactyl hypothesis.
If there’s a better phylogenetic fit,
the large reptile tree (LRT, 2339 taxa) should be able to recover it. The obvious place to look would be around the base of the Artiodactyla, the outgroup for the Perissodactyla where taxa still had claws and the LRT nested Agriochoerus latifrons, ‘the artiodactyl with thumbs’ – and claws (Figs 1–3).
Basal primates, like Notharctus and Megaladapis (Fig 2) are artiodactyl and Agriochoerus latifrons outgroup taxa in the LRT. That’s where the vestigial thumbs (Fig 3) and claws came from.
Figure 1. Chalicotheres tested in the LRT. Agriochoerus latifrons is an outgroup taxon at the base of the Artiodactyla.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg?w=122″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg?w=416″ class=”size-full wp-image-93944″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg” alt=”Figure 1. Chalicotheres tested in the LRT. Agriochoerus latifrons is an outgroup taxon at the base of the Artiodactyla.” width=”584″ height=”1439″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg?w=584&h=1439 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg?w=61&h=150 61w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg?w=122&h=300 122w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicotheres2scale588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Chalicotheres tested in the LRT. Agriochoerus latifrons is an outgroup taxon at the base of the Artiodactyla.
According to Wikipedia – Chalicotheriidae,
“As the early evolution of perissodactyls is still unresolved, their closest relatives among other perissodactyl groups is obscure.”
“They are generally placed as part of the clade Ancylopoda alongside their close relatives Lophiodontidae.”
“Their forelimbs were specialized to reach, grasp, and strip or sweep plants to the mouth. The pelvis and hindlimbs were specialized to stand upright, and to sit for hours while feeding, like the living gelada monkey.”
In paleontology the origin = early evolution of most clades will always remain unresolved. That’s just the history of this science. So don’t look for resolution in this blogpost where many clade origins have been recovered by minimizing taxon exclusion.
I do this because making discoveries is interesting and no one else appears to be interested in the finger-to-hoof topic.
Figure 2. Skulls of chalicotheres tested in the LRT. Agriochoerus latifrons is an outgroup taxon.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg?w=103″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg?w=351″ class=”size-full wp-image-93946″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg” alt=”Figure 2. Skulls of chalicotheres tested in the LRT. Agriochoerus latifrons is an outgroup taxon.” width=”584″ height=”1704″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg?w=584&h=1704 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg?w=51&h=150 51w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg?w=103&h=300 103w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/chalicothere_origins588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 2. Skulls of chalicotheres tested in the LRT. Agriochoerus latifrons is an outgroup taxon. Note the ‘perfect’ fit when the mandible of Agriochoerus latifrons is scaled to the skull of Macrotherium.
The addition of Macrotherium
(Fig 1) to the LRT (subset Fig 5) moved tested chalicotheres, like Anisodon and Chalicotherium (Figs 1, 2) closer to the base of the Artiodactyla.
Narrow-skulled Lophiodon and Eolophiodon are also close relatives
in the LRT (Fig 5), as mentioned above.
Figure 6. Manus and pes of Nasua, Notharctus and Agriochoerus latifrons compared.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg?w=253″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg?w=584″ class=”size-full wp-image-89308″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg” alt=”Figure 6. Manus and pes of Nasua, Notharctus and Agriochoerus latifrons compared.” width=”584″ height=”693″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg?w=584&h=693 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg?w=126&h=150 126w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg?w=253&h=300 253w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/10/notharctus-agriochoerus-manus-pes588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Manus and pes of Nasua, Notharctus and Agriochoerus latifrons compared.
Figure 4. Moropus manus and pes.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/moropus_feet.jpg?w=290″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/moropus_feet.jpg?w=290″ class=”size-full wp-image-93950″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/moropus_feet.jpg” alt=”Figure 4. Moropus manus and pes.” width=”290″ height=”246″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/moropus_feet.jpg 290w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/moropus_feet.jpg?w=150&h=127 150w” sizes=”(max-width: 290px) 100vw, 290px” />
Figure 4. Moropus manus and pes.
According to the AMNH website:
“The Chalicotheres are perhaps the most bizarre perissodactyls to have ever lived. While other perissodactyls possess hooves, Chalicotheres have secondarily evolved claws. Like brontotheres, the origins of chalicotheres is shrouded in mystery. No one is certain exactly how they are related to other perissodactyls, although they retain features in their feet and dentition that indicate that they are perissodactyls, despite their unusual appearance.”
The LRT indicates chalicothere claws were not secondarily evolved, because in the LRT relatives have similar claws.
The LRT provided a novel origin for twin-horned brontotheres alongside twin-horned arsinoitheres a few days ago here.
The LRT continues to fill
phylogenetic vacuums and repair traditional errors by minimizing taxon exclusion.
Figure 5. Subset of the LRT focusing on Artiodactyla (including Perissodactyla). Chalicotheres now nest here as basal taxa close to Agriochoerus latifrons.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/artiodactylalrt7.30.2025.jpg?w=66″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/artiodactylalrt7.30.2025.jpg?w=224″ class=”size-full wp-image-93953″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/artiodactylalrt7.30.2025.jpg” alt=”Figure 5. Subset of the LRT focusing on Artiodactyla (including Perissodactyla). Chalicotheres now nest here as basal taxa close to Agriochoerus latifrons. ” width=”584″ height=”2675″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/artiodactylalrt7.30.2025.jpg?w=584&h=2675 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/artiodactylalrt7.30.2025.jpg?w=33&h=150 33w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/07/artiodactylalrt7.30.2025.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 5. Subset of the LRT focusing on Artiodactyla (including Perissodactyla). Chalicotheres now nest here as basal taxa close to Agriochoerus latifrons. Presently a traditional chalicothere, Grangeria, nests with pigs and hippos, pending better data.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here. Sorry it took so long.
References
Colbert EH 1934. Chalicotheres from Mongolia and China in the American museum. Bulletin of the American Museum of Natural History 67(8):353–387.
Hooker JJ and Dashzeveg D 2004: The origin of chalicotheres (Perissodactyla, Mammalia) – Palaeontology: 47(6):1363–1386.
wiki/Chalicotheriidae
amnh.org/paleontology/perissodactyl/chalicotheriidae
Source: https://pterosaurheresies.wordpress.com/2025/07/31/origin-of-chalicotheres-revisited/
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