Development and evolution of the carotid circulation in geomyoid rodents in relationship to their craniomorphology.
The diversity in cranial morphology of living geomyoids, including pocket gophers (Thomomys), spiny pocket mice (Heteromys and Liomys), desert pocket mice (Chaetodipus and Perognathus), and kangaroo rats and mice (Dipodomys and Microdipodops) is accompanied by only a few differences in their cephalic arterial circulation. The principal difference is the origin of the pterygopalatine artery, which serves the orbit and rostrum. In dipodomyines and perognathines it originates as a stapedial branch of the internal carotid artery and passes through the middle ear en route to the braincase. In geomyines and heteromyines it originates as an internal maxillary branch of the external carotid artery and enters the braincase directly. Either geomyines and heteromyines are convergent in this respect, or the currently recognized family Heteromyidae is paraphyletic. The stapedial artery is the same size in early embryos of T. bottae and D. merriami, but in the former species it fails to grow and disappears in juveniles. Comparison of developmental series of D. merriami and T. bottae revealed that the decline of the artery in the latter species is preceded by a greater degree of arterial coarctation, or narrowing, as it passes though the developing stapes. The loss of the stapedial artery is correlated with an enlarged masseter profundus muscle in T. bottae and with an unusually small stapes in T. bottae, H. desmarestianus, and L. salvini. I hypothesize that the primitive condition for geomyoids is the presence of both stapedial and internal maxillary arteries, that the stapedial artery was lost in geomyines and heteromyines because of the constraint on its size posed by the stapes, and that the stapedial artery was retained in dipodomyines because enlargement of the stapes accompanied bullar inflation in these taxa and lifted the constraint on the size of the stapedial artery.
Brylski
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Museum of Vertebrate Zoology, University of California, Berkeley 94720.
D000818:Animals; D005075:Biological Evolution; D001775:Blood Circulation / Q000502:physiology; D001921:Brain / Q000033:anatomy & histology / Q000098:blood supply* / Q000502:physiology; D002339:Carotid Arteries / Q000033:anatomy & histology* / Q000502:physiology; D004432:Ear, Middle / Q000033:anatomy & histology; D005123:Eye / Q000033:anatomy & histology; D007568:Jaw / Q000033:anatomy & histology; D010802:Phylogeny; D012377:Rodentia / Q000033:anatomy & histology*