TABLE 5-2 SYNONYMY Of SOME OF THE CRANIAL PLATES OF 

 THE EUARTHRODIRE AND THE HIGHER GNATHO- 

 5TOME 



suborbital plate which was grooved by the infraorbital 

 canal. Behind the suborbital was a smaller postsuborbital 

 and above this a preopercle, which was a long, slim, free 

 plate. Anterior to the infraorbital process of the suborbital 

 was a small postnasal, notched anteromedially by the nasal 

 opening. The postnasal was free or incorporated into the 

 shield. Both cheek and roof bore grooves marking the 

 course of the sensory canals. 



The upper jaw was formed by two superognathal plates. 

 Teeth were present in the young but replaced by cutting 

 edges in the adult. The superognathals have been identified 

 as the vomerine and palatopterygoid plates and homolog- 

 ized with the tooth plates of the chimaerid. A free palato- 

 quadrate was present and had quadrate and autopalatine 

 assifications. 



The lower jaw was formed basically of a plate lying 

 dorsolateral to Meckel's cartilage and anterior and medial 

 to that cartilage posteriorly; this has been called the mixi- 

 coronoid or inferognathal. There were articular and mental 

 ossifications in Meckel's cartilage. 



The endocranium enclosed the brain cavity. It was mainly 

 cartilaginous but was sometimes covered in various areas or 

 entirely, inside and out along with all canals and hollows, 

 by perichondral bone. Where the bone was well developed, 

 endochondral trabeculae were within it. The notochord 

 varied from unchanged to obliterated in the basal plate. The 

 eye had a sclerotic ring of four bony plates. The nasal 

 capsules were sometimes an integral part of the endocra- 

 nium and sometimes separate. 



The hyoid arch and branchial arches are not known, but 

 it is assumed that these fishes were aphetohyoideans and 

 operculate. 



Antiarch Stensio (1948) has described the antiarch Bothrt- 

 olepis (Figure 5-23). The mouth was small and ventral, and 

 the eyes were on top of the head along with the nasal open- 

 ings. The head was somewhat flattened. These relationships 

 suggest a sluggish, bottom living habit. The head articulated 

 with the pectoral girdle, much as in the euarthrodire, ex- 

 cept that the main socket was on the pectoral girdle. The 

 cranial roof was joined with the cheek and inuch reduced 

 in size. There was a spiracular opening above and behind 

 the angle of the mouth. The jaws are suggestive of those of 



the euarthrodire. The endocranium was unossified except 

 for one small, Y-shaped bone of unknown position. There 

 were three scleral plates in the eye ring. The visceral skele- 

 ton is largely unknown, but there were several ventral peri- 

 chondral ossifications associated with the hyoid arch. 



nucha! 



postpineal 



sclerotic rin 

 rostral 



premedian. 



lateral. 



lower jaw 



paranuchol- 

 morginol 



postmorginal 



preloteral 



rostral premedian 



nasal opening_J^. jL.__ sclerotic ring 



.lateral 



extralateral 



paranuchal- marginal 

 postmorginal nuchal 



B 



intermandibular cartilage 

 Meckel's cartilage 

 palotoquodrate cortilai 



pineal 

 postpineal 

 endolymphatic foramen 



superior gnathal 



inferior gnathal 



iai cartilage 



extramandibular plate 

 submandibular plate 



Figure 5-23. Head skeleton of Bothn'o/ep/s canadensis. A, lateral 

 view; B, dorsal view; C, ventral view. (After Stensio 1931, 1948) 



GNATHOSTOME FISHES • 127 



