Meniscotherium: now a marsupial in the LRT
Williamson and Lucas 1992 wrote,
“In a phylogenetic analysis of ungulate relationships, Prothero et al 1988 prsented a hypothesis of the relationships of Meniscotherium similar to ours, i.e., that Meniscotherium is a phenacodontid most closely related to Ectocion.”
Note the restrictions: “ungulate relationships” and “is a phenacodontid”. The large reptile tree (LRT, 2338 taxa) is not hampered by such restrictions.
Figure 1. Meniscotherium compared to Hyopsodus and Orthaspidotherium, marsupials, not placentals.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg?w=74″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg?w=253″ class=”size-full wp-image-92411″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg” alt=”Figure 1. Meniscotherium compared to Hyopsodus and Orthaspidotherium, marsupials, not placentals. ” width=”584″ height=”2360″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg?w=584&h=2360 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg?w=37&h=150 37w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg?w=74&h=300 74w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Meniscotherium compared to Hyopsodus and Orthaspidotherium, marsupials, not placentals.
By expanding the taxon list
the LRT just nested Eocene Meniscotherium (Fig 1) with extinct Orthaspidotherium, Periptychius and Hyopsodus all derived from the extant pouchless marsupial, Monodelphis domestica. All prior authors assumed a placental status for Meniscotherium.
Turns out that assumption was false.
Figure 1. Drawing and museum mount of Meniscotherium.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg?w=300″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg?w=584″ class=”size-full wp-image-92414″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg” alt=”Figure 1. Drawing and museum mount of Meniscotherium.” width=”584″ height=”585″ srcset=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg?w=584&h=585 584w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg?w=150&h=150 150w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg?w=300&h=300 300w, https://pterosaurheresies.wordpress.com/wp-content/uploads/2025/04/meniscotherium_overall588.jpg 588w” sizes=”(max-width: 584px) 100vw, 584px” />
Figure 1. Drawing and museum mount of Meniscotherium.
Meniscotherium tapiacitum
(Cope 1874; Williamson and Lucas 1992; Middle Eocene 54-38 mya; 25-50 cm long) nests in a marsupial clade near Monodelphis domestica. If this is a placental, it will be by convergence with the other placental clades.
This appears to be a novel hypothesis of interrelationships.
If not please provide a citation so I can promote it here.
References
Cope ED 1874. Report of the Chief of Engineers for. 1874 Vol. II, Pt. II, Appendix FFa of Appendix FF, pp. 115-130.
Williamson TE and Lucas SG 1992. Meniscotherium (Mammalia, “Condylarthra”) from the Palaeocene-Eocene of Westeran North America. New Mexico Museum of Natural Hstory and Science Bulletin 1.
Source: https://pterosaurheresies.wordpress.com/2025/04/13/meniscotherium-now-a-marsupial-in-the-lrt/
