Jr. Wible et Ja. Hopson, HOMOLOGIES OF THE PROOTIC CANAL IN MAMMALS AND NONMAMMALIAN CYNODONTS, Journal of vertebrate paleontology, 15(2), 1995, pp. 331-356
The term prootic canal has been used to describe vascular canals in th
e adult petrosal bones of extant monotremes and marsupials and presume
d vascular canals in the petrosals of extinct ''non-tribosphenic'' mam
mals (i.e., morganucodontids, docodontids, triconodontids, multituberc
ulates, Vincelestes). Study of the ontogeny of these canals in extant
mammals and of their morphology in extinct mammals reveals that the te
rm prootic canal has actually been applied to four different arrangeme
nts of canals. The prootic canal variously encloses the prootic sinus
(most extinct ''nontribosphenic'' mammals), the prootic sinus in compa
ny with the ramus superior of the stapedial artery (the platypus Ornit
horhynchus and most multituberculates), the prootic sinus and the late
ral head vein (the echidna Tachyglossus), and the lateral head vein al
one (didelphid, caenolestid, and some dasyurid marsupials). We propose
restricting the term prootic canal to the canal enclosing the prootic
sinus (middle cerebral vein) at its exit from the cranial cavity. As
so defined, the prootic canal is a canal that: (1) in extinct ''non-tr
ibosphenic'' mammals passes through the lateral trough of the petrosal
; (2) in the platypus forms between the petrosal and lamina obturans a
nd also transmits a meningeal branch of the ramus superior; (3) in the
echidna forms within the petrosal bone; and (4) in marsupials forms b
etween the petrosal and squamosal. Several presumed vascular canals in
non-mammalian cynodonts have been proposed as precursors of the canal
enclosing the prootic sinus in mammals. We review the vascular struct
ures of the ear region and lateral braincase in non-mammalian cynodont
s and conclude that the most likely precursor is a canal through the l
ateral flange of the prootic similar to those interpreted as enclosing
the prootic sinus in Probainognathus jenseni and Massetognathus pascu
ali. However, until a prootic canal is found in other non-mammalian cy
nodonts, those in Probainognathus and Massetagnathus are most reasonab
ly viewed, given current phylogenies, as acquisitions independent of t
he prootic canal in mammals.