106 



the glenoid fossa, causing the zygomatic arch to take on a roughly triangular form (tapering 

 anteriorly) when viewed dorsally. In the remaining forms, the broadest point was situated 

 anterior to the fossa, causing the arches to take on their typical arched morphology. Of 

 these two forms, the apomorphic state 0 describes a synapomorphy of the mustelids 

 (including the lutrines) and the pinnipeds, with only Zalophus, Erignathus, and Lobodon 

 independently reversing to the primitive condition (state 1). 



51) relative position of zygomatic arches: 0 = lower than tooth row; 1 = level with tooth 

 row; 2 = higher than tooth row (Ridgway 1972). 



The increase in orbit size noted for phocids (King 1972, 1983) has apparently been 

 achieved with some unique changes involving the zygomatic arch (see the following 

 character also). For instance, simply dropping the zygomatic arches will increase orbit 

 diameter (Howell 1928). An extreme dropping of the zygomatic arches (state 0) has been 

 described as peculiar to Ommatophoca, contributing to the proportionately huge (even for 

 a phocid) orbit and eyeballs characteristic of this genus (Mivart 1885; King 1969, 1972, 

 1983; Ridgway 1972; Ray 1981). However, this extreme condition was never observed 

 consistently in this study, even for Ommatophoca. Instead, parallel instances of the 

 apomorphic intermediate condition (a slight dropping of the zygomatic arches - state 1 ) 

 were found in Odobenus and in the monachines internal to Mirounga spp., except for 

 Monachus monachus which reverted to the plesiomorphic condition (state 2). 



52) direction of arch of anterior portion of jugal: 0 = downwards; 1 = flat, no distinct 

 arch; 2 = upwards (Mivart 1885) (state 2 - Fig. 19). 



In noting the immense orbits of Ommatophoca, Mivart (1885) made mention of a 

 distinctive downward arch to the zygomatic arches in this genus. Although most obvious 

 in Ommatophoca, this latter feature is common among monachines, and appears to be 

 related to a unique elongation of the maxillo-jugal suture associated with the dropping of 

 the zygomatic arches in this group (see previous character). In most carnivores, the typical 

 morphology of the jugal is of a rather compact bone, with the body being narrower than 

 its articulating ends. Together with the relatively restricted, roughly vertical articulations 

 of the jugal with the squamosal, and especially with the maxilla, this gives the ventral 

 border of the jugal a distinctive upward arch. In those monachines with lowered zygomatic 

 arches, and in Ommatophoca in particular, the maxillo-jugal suture is greatly elongated 

 posteriorly, and the jugal tapers anteriorly. As well, the elongation of the suture results in 

 its horizontal rotation, so that the ventral margin of the jugal is now primarily composed 

 of that portion contributing to the suture, and the jugal now possesses a characteristic 

 downward arch (or, at least, is flat, with no arch in either direction). The upward arch, 

 which is associated with the narrower body, remains, but is no longer as obvious, having 

 been shifted posteriorly and diminished in amplitude. 



The possible connection between an elongated maxillo-jugal suture and the previous 

 character is supported by their similar distributions. Flat or downward arching jugals (both 

 of which are apomorphic) also diagnose the clade demonstrating the lowered zygomatic 

 arches (lobodontines and Monachus spp.). A downwardly arching jugal is limited within 

 this clade to Lobodon, Monachus spp., and Ommatophoca, but with reversals in Monachus 

 monachus and Monachus schauinslandi to states 2 and 1 respectively. However, a flat 



