 Alternately, a 2011 phylogenetic study by Ximena Vélez-Zuazoa and Ingi Agnarsson, based on nuclear and mitochondrial genes, found close relationships between the smalltail shark, the daggernose shark ("Isogomphodon oxyrhynchus"), the blacknose shark ("C. acronotus"), and the finetooth shark ("C. isodon").The Pacific smalltail shark ("C. cerdale") was once mistakenly synonymized with "C. porosus", until 2011 when José Castro resurrected it as a distinct taxon.An undescribed species closely similar to "C. porosus" is known from Southeast Asia.