Proposed re-organization of Rodentia taxa between Order and Family
Rodentia is the most speciose mammalian order, comprising of about 40% of all living mammals (Behringer et al. 2006). Rodentia is also one of the most "diverse" orders, in a sense that all living members are divided into ~35 families. Compared to Chiroptera, the second most speciose mammalian order, there are no taxonomic ranks between order and family on iNaturalist for Rodentia, nor are there any acknowledged by iNat's external mammal authority, the Mammal Diversity Database (MDD). The lack of such ranks potentially isolates rodent observations at the order level, and transitively limits the potential for a rodent observation to reach a specific identification (e.g. a rodent is "clearly" a caviomorph, but the discrepancies between a slender capybara [Caviidae] and a large agouti [Dasyproctidae] is less apparent to the user, so they leave their ID at "Rodentia"). Additionally, the lack of ranks between order and family make navigating the rodent section of our taxonomic tree potentially more overwhelming, as users see a wall of families with similar vernaculars and scientific names instead of suborders and superfamilies that contain members of more immediately diagnosable relatability.
Even in acknowledgment of these issues, it is understandable why iNat and the MDD do not recognize ranks between order and family. The relatedness between the rodent families has historically been very difficult to understand due to the independent emergence of traits found across distantly related taxa. For a long time, the tenability of groups - particularly suborders such as Castiomorpha and Myomorpha - was dubious. However, the proposal I suggest below follows Fabre et al. 2012. It is an extremely adequate overview of recent phylogenetic work done on rodents and validates the relatedness of certain families (including the tenability of the rodent suborders). With this study in mind (and with slight modifications to accommodate the families recently split [e.g. Zenkrellidae, Sminthidae] - as acknowledged by the MDD), here is my suggested revision of Rodentia (new taxonomic entries are bolded for clarity):
Order Rodentia
↪ Suborder Anomaluromorpha
.....↪ Anomaluridae
.....↪ Pedetidae
.....↪ Zenkrellidae
↪ Suborder Castorimorpha
.....↪ Castoridae
.....↪ Geomyidae
.....↪ Heteromyidae
↪ Suborder Ctenohystrica
.....↪ Infraorder Hystricognathi
..........↪ Parvorder Caviomorpha
...............↪ Superfamily Cavioidea
....................↪ Caviidae
....................↪ Cuniculidae
....................↪ Dasyproctidae
....................↪ Dinomyidae
...............↪ Superfamily Chinchilloidea
....................↪ Abrocomidae
....................↪ Chinchillidae
...............↪ Superfamily Erethizontoidea
....................↪ Erethizontidae
...............↪ Superfamily Octodontoidea
....................↪ Capromyidae
....................↪ Ctenomyidae
....................↪ Echimyidae
....................↪ Octodontidae
..........↪ Bathyergidae
..........↪ Heterocephalidae
..........↪ Hystricidae
..........↪ Petromuridae
..........↪ Thryonomyidae
.....↪ Superfamily Ctenodactyloidea
..........↪ Ctenodactylidae
..........↪ Diatomyidae
↪ Suborder Myomorpha
.....↪ Superfamily Dipodoidea
..........↪ Dipodidae
..........↪ Sminthidae
..........↪ Zapodidae
.....↪ Superfamily Muroidea
..........↪ Cricetidae
..........↪ Calomyscidae
..........↪ Muridae
..........↪ Nesomyidae
..........↪ Platacanthomyidae
..........↪ Spalacidae
↪ Suborder Sciuromorpha
.....↪ Aplodontidae
.....↪ Gliridae
.....↪ Sciuridae