It was a member of the Hesperornithes, flightless toothed seabirds of the Cretaceous. Among these, it belonged to the Hesperornithidae, along with Hesperornis, the well-known namesake genus.[3] C. arctica is the largest known member of the Hesperornithes, reaching a length of 2.5 metres (8.2 ft). It also represents one of the last known members of the lineage.[1] Unlike its relatives which are mainly known from subtropical or tropical waters, this species seems to have ranged in temperate or even subarctic areas.