134 



The morphologies of the bony tentorium and bony falx (see the following character) appear 

 to largely depend on the parietal contribution to each (see characters #118 and 119). In 

 those forms lacking such a contribution (i.e.. the phocids generally), both structures are 

 reduced. The bony tentorium, in particular, is reasonably compact in such cases, and fails 

 to reach the floor of the braincase (Nojima 1990). In contrast, the bony tentorium is much 

 expanded in those species with a processus tentoricus. frequently extending to the petrosal 

 apex. or. more commonly, to the floor of the braincase (Wyss 1987: Nojima 1990). 

 However, this relationship is not absolute, as canids obtain state 0 despite possessing a 

 processus tentoricus (Nojima 1990). As well, we noted that a ventral extension to the 

 petrosal apex was only found in the phocids. and not in any forms with a distinct processus 

 tentoricus [although the presence of this structure in Histhophoca and Pagophilus is 

 unclear (see Xojima 1990)]. 



The somewhat aberrant morphology of the canids causes the primitive state for the 

 caniforms to be equivocal. However, as Nojima (1990) indicates that all feloids possess 

 state 2. this state is likely plesiomorphic for the caniforms. if not the carnivores as a whole. 

 This condition is retained throughout the caniforms. before the phocids derive state 0 

 ancestrally. This very much reduced bony tentorium is common to all phocids. with the 

 phocines Halickoerus and Histhophoca (possibly as a synapomorphy with Erignathus and 

 Pagophilus: ACCTRAN optimization) independently deriving a tentorium that approaches 

 the petrosal apex. 



121) morphology of bony falx proper: 0 = absent: 1 = sail-shaped: 2 = vertical; 3 = inverse 

 sail (Nojima 1990: pers. obs.). 



In carnivores, the bony falx is not nearly so ubiquitous as the bony tentorium, being found 

 only in Ursus spp. and the pinnipeds (Nojima 1990). Despite this limited distribution, the 

 bony falx does possess several distinct morphologies that our observations reveal are 

 generally dependent on the contribution of the parietal (see character #119). A sail-shaped 

 bony falx. in which the falx arcs posterodorsally from the anterior junction of the two 

 halves of the bony tentorium, is generally restricted to the phocids. which generally lack 

 a parietal contribution to the falx. The contribution of the parietal in the otarioids fills out 

 the bony falx. causing it to extend directly dorsally (state 2) or to arc anterodorsally (state 

 3). However, these trends are again not absolute, with most phocid specimens obtaining 

 state 2. As well, although the parietal frequently contributes to states 2 and 3. this was 

 not necessarily always the case. In Ursus. the bony falx is only partial, despite a parietal 

 contribution, and fails to reach the dorsal wall of the skull (Nojima 1990). We have chosen 

 to distinguish this partial bony falx (see the following character) from the bony falx proper 

 examined here. So. together with the complete lack of a bony falx in the remaining ursids 

 (Nojima 1990). Ursus has been scored as lacking the bony falx. 



The possession of a bony falx is a derived characteristic within the Caniformia. and is a 

 synapomorphy of Lutra and the pinnipeds. For this group, a vertical bony falx is primitive 

 and largely retained throughout. A further derivation to the reduced sail-shaped 

 morphology occurs a number of times within the phocids: Cysrophora. Halickoerus, 

 Monachus schauinslandi. Pusa caspica. and Pusa sibirica. DELTRAN optimization holds 

 these all to be independent derivations, whereas ACCTRAN 1 optimization indicates this 



