INTRODUCTION

The braincase described here belongs to an ichthyodectiform teleost. It shows a well-developed ethmopalatine (a synapomorphy of all but the most primitive of ichthyodectiforms), as well as the following combination of features: median parietals meeting in front of a large supraoccipital, large intercalar that forms a significant part of the hyomandibular facet as well as the skull roof, a jugular canal opening into the floor of a deep subtemporal fossa and continuing to run posteriorly beneath the intercalar. Some of these features are only found in more derived ichthyodectiforms (see below). Ichthyodectiforms are an extinct group of about 30 species of primitive teleosts ranging in time from the Bathonian to Maastrichtian. Most were marine fishes and many had structural adaptations suggesting they were fast open water swimmers. Some must have been the top predators of their day. The phylogeny of ichthyodectiforms has been addressed on several occasions (Bardack 1965; Patterson and Rosen 1977; Maisey 1991; Stewart 1999; Taverne and Chanet 2000). There is broad agreement among these authors; at least for the better known taxa. The phylogeny and derivative classification given in Figure 1 is that of Maisey (1991) and may be used as reference for the following description.

Detailed information on braincase structure is not known for all ichthyodectiforms, and therefore comparisons of this braincase with others are more detailed for some taxa than for others. The braincase of the most primitive ichthyodectiforms such as Occithrissops and Allothrissops remain largely unknown, except for the skull roof and ethmoid regions. At the other extreme, species of Ichthyodectes, Gillicus and Xiphactinus are virtually completely known. Therefore, comparisons are inevitably biased towards those taxa.