Supramyomorpha D’ELÍA et al., 2019

Flynn, Lawrence J., Jacobs, Louis L., Kimura, Yuri & Lindsay, Everett H., 2019, Rodent Suborders, Fossil Imprint 75 (3 - 4), pp. 292-298 : 295

Suborder Supramyomorpha D’ELÍA et al., 2019

Suborder Supramyomorpha (see Appendix) is the crown clade of myodonts (muroids plus dipodoids) with anomaluroids, pedetids, castorids (beavers), and geomorphs (the group for geomyids, heteromyids, and extinct eomyids). This clade supplants in part the classical Myomorpha, which has been used to contain myodonts, the geomorphs, and formerly in some classifications the glirids. The name invokes living myomorphous rodents but encompasses rodents with a wide array of structures. D’Elía et al. (2019) proposed this taxon at subordinal rank in their analysis of recent developments in rodent systematics.

Despite the name, only later muroids have myomorphous jaw musculature. Myomorphy is derived from hystricomorphy by inclination of the zygomatic plate ( Lindsay 1977), which pinches the oval infraorbital foramen into a keyhole. Hystricomorphy appears to be primitive for myodonts, anomalurids and pedetids. On the other hand, geomorphs and beavers exhibit sciuromorphy ( Korth 1994), and differ much from muroids in the sculpted fossa on the snout that seats the masseter muscle, with the small infraorbital foramen ventral to the fossa.

Supramyomorphs have primitive (sciurognathous) jaw structure. The incisor enamel is dominantly uniserial. Detailed variation in uniserial microstructure associates some muroid subgroups but, in other cases, suggests morphological homoplasy across that superfamily ( Kalthoff 2000). One family, the Pedetidae , diverges from the others in displaying multiserial incisor enamel, apparently an independent acquisition. Like jaw musculature, incisor microstructure may show homoplasy ( Wood 1955).

Many basal members of some clades (myodonts, early anomaluroids and early geomorphs) show a generalized molar structure, basically four-cusped with connecting lophs, called the “cricetid plan” (see Flynn et al. 1985). The “cricetid plan” includes presence of a hypocone on upper molars, which is seen in all groups, but the pattern is secondarily modified in geomorphs. A myodont synapomorphy is reduction of the cheek tooth row from the usual 4/4 tooth formula: myodonts lack a lower premolar and only a few species retain a small last upper premolar.