That rare posterior extension of the palatine extends to giant Megistotherium

Megistotherium has been difficult to understand.
Now (hopefully at long last), the posterior extension of the palatine in this taxon is linking this giant member of the Carnivora with a much smaller, primitive, extant taxon, Nasua,the coatimundi, which also shares this rare trait with the raccoon, Procyon, and the binturong, Arctictis.

Click links to see images at ReptileEvolution.com.

Megistotherium osteothlastes
(Savage 1973; Miocene, 23mya; 66cm skull length) was originally considered a giant hyaenodontid creodont. After rescoring this taxon, here it nests with the much smaller, extant coatimundi, Nasua. The jaw muscles were enormous filling the high cranial crest. The large diameter canines were housed in large, laterally expanded maxillae. The brain case was narrow. The fragile postfrontals appear to have broken off. The premaxillae each include room for only one tiny tooth, if not absent altogether. A key trait is the posterior extension of the palatine far beyond the tooth row, a trait common to this clade. The fragile otic bulla = ectotympanic is missing here, perhaps via taphonomy, so was scored with a ‘?’ rather than ‘bulla absent’.

These are choices one makes when scoring taxa, taking into consideration overall  shape AND details. Feel free to argue for another nesting. Bring evidence when you do.

The great size of Megistotherium vs the much smaller size of Nasua
– and the changes that inevitably happen with Cope’s Rule – seem to be the reason why these two taxa have remained phylogenetically separated until now.

According to wiiki/Megistotherium
“Due to the paucity of material assigned to Megistotherium, size estimates for the genus have varied considerably over the years. The validity of Megistotherium has been questioned by several authors, who suggest that it is actually a junior synonym of Hyainailouros. The matter is complicated by the paucity of dentition in Megistotherium.”

No other taxa close to Hyainailouros have been tested by the LRT. The tooth roots are visible in the Megistotherium data, but the tooth crowns are missing.

Updates have been made to the LRT and the Megistotherium page.

References
Savage RJ 1973. Megistotherium, gigantic hyaenodont from Miocene of Gebel Zelten, Libya. Bulletin of the British Museum (Natural History) Geology 22(7):483–511.

wiiki/Megistotherium

pterosaurheresies.wordpress.com/2026/03/04/posterior-palate-extensions-in-the-raccoon-family/