Cainotherium: part of an overlooked primate radiation convergent with ungulates
According to Wikipedia – Cainotherium
“Cainotherium is an extinct genus of rabbit-sized prehistoric even-toed ungulates.”
Cainotherium (Fig 1) had sharp hooves and no thumb, as in traditional basal ungulates.
Unfortunately, that would be a prime example of “Pulling a Larry Martin” = labeling a taxon based on a few traits – rather than the preferred last common ancestor method after phylogenetic analysis. That’s how convergence is identified. Case in point:
Figure 1. Cainotherium skull compared to scale with that of Notharctus.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg?w=297″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg?w=584″ class=”size-full wp-image-94132″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg” alt=”Figure 1. Cainotherium skull compared to scale with that of Notharctus. ” width=”584″ height=”589″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg?w=584&h=589 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg?w=150&h=150 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg?w=297&h=300 297w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium-notharctus588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Cainotherium skull compared to scale with that of Notharctus.
Here, based on the last common ancestor method
in the large reptile tree (LRT, 2338 taxa, subset Fig 3) Cainotherium is no longer a phylogenetic ungulate. Now it nests basal to chalicotheres and lophiodons, in a primate clade close to the giant lemur, Megaladapis and the ‘artiodactyl with thumbs’ Agriochoerus latifrons.
So hooves appeared several times by convergence within the Mammalia in the LRT.
Fig. 2. Cainotherium used to nest in the LRT at the base of the Artiodactyla or even-toed ungulates. Now it nests as a member of the recently recovered hoofed primate clade.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg?w=584″ class=”size-full wp-image-26685″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg” alt=”Fig. 1. Cainotherium nests at the base of the Artiodactyla or even-toed ungulates. I wonder if it had five fingers, even if vestiges, given that Ancodus, a derived artiodactyl, retains five fingers. ” width=”584″ height=”401″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg?w=584&h=401 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg?w=150&h=103 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg?w=300&h=206 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2017/04/cainotherium_588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Fig. 2. Cainotherium used to nest in the LRT at the base of the Artiodactyla or even-toed ungulates. Now it nests as a member of the recently recovered hoofed primate clade.
According to Wikipedia – Cainotherium
“The skeletal anatomy of these hare-like animals suggest they, along with other members of Cainotheriidae, belong to the artiodactyl suborder Tylopoda, together with oreodonts and modern camelids.
Suggest? Would it not be better to test a wide gamut of taxa in order to determine hypothetical interrelationships? Usually hoofed mammals are ungulates – but the LRT is recovering a small clade that is not related to pigs, camels and deer.
“Species had cloven hooves, similar to those of bovids or deer, although the shape and length of the limbs suggests that the living animals moved by leaping, like a rabbit.
Basal primates, like lemurs, also like to leap.
“The shape of the teeth also suggests a rabbit-like diet of nibbled vegetation, while the size of the auditory bulla and shape of the brain suggest that it would have had good senses of hearing and smell.”
Figure 3. Subset of the LRT focusing on basal placental1 taxa. Here Cainotherium is part of a radiation of hoofed primates.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium.radiation588.jpg?w=83″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium.radiation588.jpg?w=283″ class=”size-full wp-image-94141″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium.radiation588.jpg” alt=”Figure 3. Subset of the LRT focusing on basal placental1 taxa. Here Cainotherium is part of a radiation of hoofed primates. ” width=”584″ height=”2115″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium.radiation588.jpg?w=584&h=2115 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium.radiation588.jpg?w=83&h=300 83w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/08/cainotherium.radiation588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 3. Subset of the LRT focusing on basal placental1 taxa. Here Cainotherium is part of a radiation of hoofed primates.
Cainotherium renggeri
(Bravard 1828, 1835; 30cm in length; Eocene to Early Miocene) was considered a rabbit-sized artiodactyl. Here it nests at the base of a convergent radiation within the primates.
The LRT just made Cainotherium and chalicotheres a new branch of Primates. It’s unsettling for the moment, but all new hypotheses that break invalid paradigms go through the same routine of mental processing. It takes longer for some people to accept.
Taxa like Cainotherium are likely one reason
why it has taken so long to resolve interrelationships within the Mammalia. The other main reason is also a product of the human filter: reliance on tradition and authority along with freshman naiveté. No one is immune from the influence of the human filter.
Expanding the taxon list seems to help overcome inherent limitations.
References
Bravard A 1828. Monographie de la montagne de Perrier pres d’lssoire (Puy-de-Dome) et de deux especes du genre Felis, decouvert dans l’une de ces couches d’alluvion; Paris; 1–47.
Bravard A 1835. Monographie du Cainotherium, nouveau genre fossile des Pachydermes, trouve dans les terrain tertiaires d’eau douce du department du Puy-de-Dome; Levrault, Paris, 1835.
Source: https://pterosaurheresies.wordpress.com/2025/08/10/cainotherium-part-of-an-overlooked-primate-radiation-convergent-with-ungulates/
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