Dwarf sperm whale modern day whale. Characteristic of sperm whales, the left nostril is markedly larger than the right, and it has a spermaceti organ on its skull. The brain weighs around . The eyes are adapted for low-light environments. The dwarf sperm whale has 14 to 24 teeth, rarely 26, in the lower jaw that are sharp, slightly curved backwards, and–like other sperm whales–lack enamel. The teeth rarely exceed in length, smaller than those of the pygmy sperm whale. At most, 6 teeth are in the upper jaws, though in modern sperm whales, upper teeth are defunct. Unique to "Kogia", there is
Whale shark , with a weight of around . In 2011, more than 400 whale sharks gathered off the Yucatan Coast. It was one of the largest gatherings of whale sharks recorded. Aggregations in that area are among the most reliable seasonal gatherings known for whale sharks, with large numbers occurring in most years between May and September. Associated ecotourism has grown rapidly to unsustainable levels. Neither mating nor pupping of whale sharks has been observed. The capture of a female in July 1996 that was pregnant with 300 pups indicated whale sharks are ovoviviparous. The eggs remain in the body and