Phylogeny vs Ontogeny: large Agriochoerus latifrons now nests with small Ectocion ralstonensis in the LRT

I did not see this coming.
Large Agriochoerus latifrons now nests with small Ectocion ralstonensis in the LRT, apparently in an adult and juvenile interrelationship.

Previously the two taxa were separated by one or two nodes.
Both were slightly rescored.

The small taxon
has a shorter rostrum, larger orbit, reduced zygomatic arch and where the postfrontal might have been, there’s a broken spot on the temple.

Click on the links above to see the data.

Agriochoerus latifrons
(Leidy 1850, 1869; Wortman 1895, O’Harra 1920, Late Eocene to Oligocene, 38–16mya)  is known as the artiodactyl with thumbs. It has a tooth pattern with large lateral upper canines followed by a diastema. The lower canines align behind the uppers during occlusion, which is different from most synapsids. In the LRT, this taxon is the basalmost artiodactyl. Agriochoerus has slender, vestigial thumbs. Smaller Ectocion ralstonensis appears to be a juvenile of this genus and species.

Ectocion ralstonensis
(Cope 1882 a, e, Granger 1915; Late Paleocene; 11 cm skull length) is generally considered a member of the Phenacodontidae, like Phenacodus, but here nests It nests close to Agriochoerus latifrons, perhaps as a juvenile given its small size, large orbit and short rostrum.

After analysis the the MPTs
(number of most parsimonious trees) became reduced.

Taxa with premolars replacing the canines have lost their clade status in the LRT. This cannot be, so the LRT has not been updated to reflect this error.

This goes to show have fragile parts of the mammal subset still are.

Experimental deletion of the juvenile Ectocion ralstonensis did not resolve this issue.

Setbacks like this are part of the process. Will keep you informed of progress.

Like archosaurs (= other archosauromorphs)
mammals ontogeny is allometric = change in morphology while growing to adulthood. This makes recovering a phylogenetic tree more difficult, since juveniles have a different morphology from adults… and in some cases different morphologies for each gender.

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

References
Cope ED 1882a. Contributions to the history of the Vertebrata of the lower Eocene of Wyoming and New Mexico, made during 1881. Proceedings of the American Philosophical Society: 139-197.
Cope ED 1882e. Note on Eocene Mammalia. American Naturalist 16:522.
Leidy J 1850. [Abstract of remarks made before a meeting of the Academy of Natural Sciences of Philadelphia, December 17th, 1850]. Proceedings of the Academy of Natural Sciences of Philadelphia 5(1):121-122.
Leidy J 1869. Extinct Mammals of Dakota and Nebraska:Including an account of some allied forms from other localities, together with a synopsis of the mammalian remains of North America., Journal of the Academy of Natural Sciences, Philadelphia 2(7): 135–141.
O’Harra CC 1920. The White River Badlands. South Dakota School of Mines. 13: 1–181 + plates.
Thewissen JGM 1990. Evolution of Paleocene and Eocene phenacodontidae (Mammalia, Condylarthra). University of Michigan Papers on Paleontology 29:1-107.
Wortman JL 1895. On the osteology of Agriochoerus. Bulletin of the American Museum of Natural History 7(4):145–179.

wiki/Agriochoerus
wiki/Ectocion

Source: https://pterosaurheresies.wordpress.com/2026/05/03/phylogeny-vs-ontogeny-large-agriochoerus-latifrons-now-nests-with-small-ectocion-ralstonensis-in-the-lrt/