Cranial Morphology and Multituberculate Relationships

Abstract

OverviewThe comparative description of multituberculate crania has provided a solid morphological data base for the character analysis, which reveals that a majority of multituberculate cranial features are merely mammalian plesiomorphies. A few specializations do exist and appear to be either peculiar to all multituberculates or evolved within the group. These include inflated vestibular apparatus in taeniolabidoids, reduced postorbital process and jugal, large premaxilla, nasal and jugular foramen, and exclusion of palatine from orbit. Previously proposed synapomorphies to relate multituberculates as a sister taxon to either monotremes or Recent therians may simply be homoplasies, that is, independent acquisition of three-boned middle ear and independent loss of septomaxilla. Therefore, multituberculates appear to have been a separate lineage in early mammalian radiation either prior to emergence of the latest common ancestor of Recent mammals or before any other mammals even evolved.“The result of this increased knowledge is to strengthen the growing conviction toward which all the recent accretions of data on the multituberculates have contributed, that these animals were not the ancestors of or closely related to monotremes, marsupials, or placentals, that any phyletic connection between them and the later three groups must have been far back toward the origin of the Mammalia, possibly even before that artificially delimited event, and that taxonomically this means that the Multituberculata form a separate subclass, Allotheria.” (Simpson, 1937, p. 761)