Geomyoidea
Encyclopedia
Geomyoidea is a superfamily of rodent
that contains the pocket gophers (Geomyidae), the kangaroo rats and mice (Heteromyidae
), and their fossil
relatives.
, the fossil record, molecular analyses
, and biogeography
all support this relationship.
Geomyoids are most noticeably characterized by the position of the infraorbital canal
. Unlike all other rodents who have the opening of the infraorbital canal facing forward, geomyoids have an infraorbital canal that faces to the side. Instead of passing through the zygoma
, the infraorbital canal of geomyoids has moved to the side of the snout
. This condition is so pronounced and the snout so narrow in heteromyids that the infraorbital canals from either side connect. Essentially, if the skull
of a heteromyid is viewed from the side, the viewer can see directly through it.
Modern geomyoids are mostly restricted to North America, but some representatives have extended their range into South America since the Great American Interchange
. Fossil taxa are known from throughout Laurasia
.
does not pass through the infraorbital canal; it cannot due to the position of the canal. Some authorities consider the geomyoids related to squirrel
s, beaver
s, and mountain beaver
s on this basis.
The masseter muscle does attach directly behind the zygomatic arch in a manner very different from sciuromorphs. Some authorities consider geomyoids myomorphs based on this feature. This suggests they may be related to mice
, jerboas
, and perhaps dormice
.
Cladogram showing interrelationships among geomyoid families following Korth et al. (1991):
Rodent
Rodentia is an order of mammals also known as rodents, characterised by two continuously growing incisors in the upper and lower jaws which must be kept short by gnawing....
that contains the pocket gophers (Geomyidae), the kangaroo rats and mice (Heteromyidae
Heteromyidae
The family of rodents that include kangaroo rats, kangaroo mice and rock pocket mice is the Heteromyidae family. Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the Heteromys and Liomys genera are also found in forests and...
), and their fossil
Fossil
Fossils are the preserved remains or traces of animals , plants, and other organisms from the remote past...
relatives.
Characteristics
Although dissimilar in overall appearance, gophers have been united with kangaroo rats into a common superfamily for a considerable period of time. The superfamily Geomyoidea is among the few superfamilial relationships in rodents that is not subject to much controversy. Overall morphologyMorphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
, the fossil record, molecular analyses
Molecular phylogeny
Molecular phylogenetics is the analysis of hereditary molecular differences, mainly in DNA sequences, to gain information on an organism's evolutionary relationships. The result of a molecular phylogenetic analysis is expressed in a phylogenetic tree...
, and biogeography
Biogeography
Biogeography is the study of the distribution of species , organisms, and ecosystems in space and through geological time. Organisms and biological communities vary in a highly regular fashion along geographic gradients of latitude, elevation, isolation and habitat area...
all support this relationship.
Geomyoids are most noticeably characterized by the position of the infraorbital canal
Infraorbital canal
Not to be confused with the infraorbital groove and infraorbital foramen, which are on opposite ends of the canal.One of the canals of the orbital surface of the maxilla, the infraorbital canal, opens just below the margin of the orbit...
. Unlike all other rodents who have the opening of the infraorbital canal facing forward, geomyoids have an infraorbital canal that faces to the side. Instead of passing through the zygoma
Zygomatic arch
The zygomatic arch or cheek bone is formed by the zygomatic process of temporal bone and the temporal process of the zygomatic bone , the two being united by an oblique suture; the tendon of the Temporalis passes medial to the arch to gain insertion into the coronoid process...
, the infraorbital canal of geomyoids has moved to the side of the snout
Rostrum (anatomy)
The term rostrum is used for a number of unrelated structures in different groups of animals:*In crustaceans, the rostrum is the forward extension of the carapace in front of the eyes....
. This condition is so pronounced and the snout so narrow in heteromyids that the infraorbital canals from either side connect. Essentially, if the skull
Skull
The skull is a bony structure in the head of many animals that supports the structures of the face and forms a cavity for the brain.The skull is composed of two parts: the cranium and the mandible. A skull without a mandible is only a cranium. Animals that have skulls are called craniates...
of a heteromyid is viewed from the side, the viewer can see directly through it.
Modern geomyoids are mostly restricted to North America, but some representatives have extended their range into South America since the Great American Interchange
Great American Interchange
The Great American Interchange was an important paleozoogeographic event in which land and freshwater fauna migrated from North America via Central America to South America and vice versa, as the volcanic Isthmus of Panama rose up from the sea floor and bridged the formerly separated continents...
. Fossil taxa are known from throughout Laurasia
Laurasia
In paleogeography, Laurasia was the northernmost of two supercontinents that formed part of the Pangaea supercontinent from approximately...
.
Relation to other rodents
Geomyoids have been considered to be either sciuromorphous or myomorphous depending on the authority. The masseter muscleMasseter muscle
In human anatomy, the masseter is one of the muscles of mastication.In the animal kingdom, it is particularly powerful in herbivores to facilitate chewing of plant matter.-Origin and insertion of the two heads:...
does not pass through the infraorbital canal; it cannot due to the position of the canal. Some authorities consider the geomyoids related to squirrel
Squirrel
Squirrels belong to a large family of small or medium-sized rodents called the Sciuridae. The family includes tree squirrels, ground squirrels, chipmunks, marmots , flying squirrels, and prairie dogs. Squirrels are indigenous to the Americas, Eurasia, and Africa and have been introduced to Australia...
s, beaver
Beaver
The beaver is a primarily nocturnal, large, semi-aquatic rodent. Castor includes two extant species, North American Beaver and Eurasian Beaver . Beavers are known for building dams, canals, and lodges . They are the second-largest rodent in the world...
s, and mountain beaver
Mountain Beaver
The Mountain Beaver is the most primitive extant rodent. Not to be confused with the North American beaver Castor canadensis, or its relative the Eurasian beaver, Castor fiber, it has several common names including Aplodontia, Boomer, Ground Bear, and Giant Mole...
s on this basis.
The masseter muscle does attach directly behind the zygomatic arch in a manner very different from sciuromorphs. Some authorities consider geomyoids myomorphs based on this feature. This suggests they may be related to mice
Muroidea
Muroidea is a large superfamily of rodents. It includes hamsters, gerbils, true mice and rats, and many other relatives. They occupy a vast variety of habitats on every continent except Antarctica. Some authorities have placed all members of this group into a single family, Muridae, due to...
, jerboas
Dipodoidea
Dipodoidea is a superfamily of rodents that includes Jumping mice and Jerboas....
, and perhaps dormice
Dormouse
Dormice are rodents of the family Gliridae. Dormice are mostly found in Europe, although some live in Africa and Asia. They are particularly known for their long periods of hibernation...
.
Taxonomy
The family †Eomyidae is alternatively referred to as a member of the superfamily Geomyoidea or as a separate superfamily (†Eomyoidea) within the shared infraorder Geomorpha. †Florentiamyidae and †Heliscomyidae are usually placed within the superfamily Geomyoidea regardless of if eomyids are treated as a separate superfamily or not (Korth et al., 1991). McKenna and Bell (1997) do not recognize heliscomyids as a distinct family, placing the one or two heliscomyid genera in Geomyoidea incertae sedis. Sometimes the pocket gophers and heteromyids are placed as separate subfamilies within a single family (Geomyidae). These subfamilies are Geomyinae and Heteromyinae respectively.- Superfamily Geomyoidea
- Genus †Griphomys incertae sedisIncertae sedis, is a term used to define a taxonomic group where its broader relationships are unknown or undefined. Uncertainty at specific taxonomic levels is attributed by , , and similar terms.-Examples:*The fossil plant Paradinandra suecica could not be assigned to any...
- Genus †Meliakrouniomys incertae sedis
- Family †EomyidaeEomyidaeEomyidae is a family of extinct rodents from North America and Eurasia related to modern day pocket gophers and kangaroo rats. The family includes the earliest known gliding rodent, Eomys -References:...
- Family †HeliscomyidaeHeliscomyidaeHeliscomyidae is a family of extinct rodents from the mid-Tertiary of North America related to pocket gophers and kangaroo rats and their relatives . The family contains four genera, Apletotomeus, Heliscomys, Passaliscomys, and Tylionomys...
- Family †Florentiamyidae
- Family Geomyidae - pocket gophers
- Family HeteromyidaeHeteromyidaeThe family of rodents that include kangaroo rats, kangaroo mice and rock pocket mice is the Heteromyidae family. Most heteromyids live in complex burrows within the deserts and grasslands of western North America, though species within the Heteromys and Liomys genera are also found in forests and...
- kangaroo rats and mice, pocket mice
- Genus †Griphomys incertae sedis
Cladogram showing interrelationships among geomyoid families following Korth et al. (1991):