. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 184 ANNALS OF THE SOUTH AFRICAN MUSEUM by Boonstra (1965) in the dinocephalian Struthiocephalus and by Cox (1959) in Kingoria. A well-defined anteroposteriorly directed groove separates the two facets and possibly transmitted a blood-vessel or nerve. There are no indica- tions of an extrastapedial process such as found by Ewer (1961) in Dapto- cephalus or of a sharp 'tympanic' opisthotic process such as is found in Kingoria (Cox, 1959), and it seems unlikely that a tympanum was present in life. In se
. Annals of the South African Museum = Annale van die Suid-Afrikaanse Museum. Natural history. 184 ANNALS OF THE SOUTH AFRICAN MUSEUM by Boonstra (1965) in the dinocephalian Struthiocephalus and by Cox (1959) in Kingoria. A well-defined anteroposteriorly directed groove separates the two facets and possibly transmitted a blood-vessel or nerve. There are no indica- tions of an extrastapedial process such as found by Ewer (1961) in Dapto- cephalus or of a sharp 'tympanic' opisthotic process such as is found in Kingoria (Cox, 1959), and it seems unlikely that a tympanum was present in life. In several specimens of Lystrosaurus a pair of short, curved rods (Fig. 21) was found, usually in the pterygoid region of the skull. Barry (1968) considers that they are ossified ceratohyals. They are often found in association with the stapes, and a strong possibility exists that in life they articulated with the median, ventral facets of the stapes (Barry, 1968). Other records of preserved portions of the hypobranchial skeleton in dicynodonts are a basihyal in Pris- terodon (Barry, 1967) and a pair of rods in Kingoria and Daptocephalus (Cox, 1959; Ewer, 1961). MED F* I cm Fig. 21. Lystrosaurus declivis. Nat. Mus. No. Stapes and ceratohyals in articulation, ventral view. THE DERMOCRANIUM The snout region The snout and adjacent skull roof are the most variable portions of the Lystrosaurus skull, but several characteristics of the region are common to all variants and can thus be used for diagnosis of the genus. The snout is always strongly developed and ventrally extended, but the nasal apertures have not accompanied this ventral growth and remain relatively high in the skull. In some forms the snout cur\es down smoothly from the frontal surface, while in others the anterior surface of the snout is a remarkable flat plane, separated from the frontal plane by a transverse frontonasal ridge. The premaxilla has an extensive facial portion, more extensive than in any Dicynodon
Size: 2120px × 1179px
Photo credit: © Library Book Collection / Alamy / Afripics
License: Licensed
Model Released: No
Keywords: ., bookcentury1800, bookdecade1890, booksubjectnaturalhistory, booky
