List of reasons why multituberculates were not competitively excluded by rodents

<figure>List of multie skulls by Adams et al 2019.</figure>

You might have figured something is happening, something evil. So allow me to distract you with this article not at all related to that.

Why multituberculates were not replaced by rodents:

• The last unambiguous multies, ptilodontoideans like Ectypodus, were generalists (Ostrander 1984). This goes against principles of competitive exclusion in which only specialised forms remain. Compare for example monotremes and marsupials, the highly specialised former possibly outcompeted by the latter, but even this has been called into question (Phillips 2009).
• Multituberculates disappear in many areas before rodents arrived. For exaple kogaionids diversified in the Cretaceous and Paleocene of Balkanatolia, but there is an interval of 18 million years before kogaionids disappearing in the PETM and the first apparence of rodents in Balkanatolia; this vaccuum of both groups in fact allowed the evolution of local mammals like pleuraspidotheriids and polydolopiforms (Métais 2018). Corriebaatar suggests an Early Cretaceous Australian presence, yet the few Cenomanian and Cenozoic Australian fossil sites show no evidence of multituberculates, providing an interval of over 100 million years between the presence of multituberculates and rodents in Australia. The fossil reccord of Africa and Indo-Madagascar is notoriously poor, but again large intervals are observed between the last multituberculate presence (Krause 2017) and the mid-Cenozoic arrivals of rodents to these landmasses.
• Most damningly Brocklehurst 2021 has shown that multituberculates actually constrained placental dievrsity in the northern continents, with placentals only diversifying after multies declined. This paints the precise polar opposite of the rodent competition hypothesis: multituberculates were so efficient at competing with placental mammals that they kept rodents in place until they died out.

References (that aren’t already linked)

Ostrander, Gregg (1 January 1984). “The Early Oligocene (Chadronian) Raben Ranch Local Fauna, Northwest Nebraska: Multituberculata; with Comments on the Extinction of the Allotheria”. Transactions of the Nebraska Academy of Sciences and Affiliated Societies.

Phillips, MJ; Bennett, TH; Lee, MS (October 2009). “Molecules, morphology, and ecology indicate a recent, amphibious ancestry for echidnas”. Proc. Natl. Acad. Sci. U.S.A. 106 (40): 17089–94. Bibcode:2009PNAS..10617089P. doi:10.1073/pnas.0904649106. PMC 2761324. PMID 19805098.

Métais, Grégoire; Coster, Pauline M.; Kappelman, John R.; Licht, Alexis; Ocakoğlu, Faruk; Taylor, Michael H.; Beard, K. Christopher (2018–11–14). “Eocene metatherians from Anatolia illuminate the assembly of an island fauna during Deep Time”. PLoS One. 13 (11): e0206181. doi:10.1371/journal.pone.0206181. ISSN 1932–6203. PMC 6235269. PMID 30427946.

Krause, David W.; Hoffmann, Simone; Werning, Sarah (December 2017). “First postcranial remains of Multituberculata (Allotheria, Mammalia) from Gondwana”. Cretaceous Research. 80: 91–100. doi:10.1016/j.cretres.2017.08.009.