In herpetologist Richard Wells’ controversial 1985 paper, A classification of the Amphibia and Reptilia of Australia, he described what he considered a new species of crocodile known as Crocodilus pethericki. Wells noticed that many specimens considered to be saltwater crocodiles in the springs and headwaters of the Finnis and Reynolds Rivers in the Top End southwest of Darwin have a number of physiological differences. He noted their short tails, large heads, relatively small body, and their large size, reaching 15 to 18 ft on average. The Petherick’s crocodile also has fewer scutes (bony scales) on the sides of their body compared to that of saltwater crocodiles, and have darker scales and whitish-blue eyes. Wells also noticed their much more aggressive behaviour.
The holotype, (a specimen upon which the description of a new species is based) of Pethrick's crocodile is "Sweetheart", a 17-foot long crocodile infamous for attacking boats in the 70’s around the Finnis River. In July of 1979, Sweetheart was caught alive by the Northern Territory Parks and Wildlife Commission but sadly drowned while being taken to Darwin after getting entangled with a log and not being able to free itself due to the use of flaxedil, a muscle relaxant they used to help capture the animal. Sweetheart’s taxidermized body is now kept at the Museum and Art Gallery of the Northern Territory in Darwin.
The Brinken and Marithiel Aboriginal People who inhabit the Petherick’s crocodile range are very fearful of them, which they call "kunbiyen" or "mulkyinun" and clearly differentiate them from saltwater crocodiles. The recognition of Petherick’s crocodile is split, with many arguing it as a genuine species due to the clear anatomical differences, while others believe Wells misidentified the physiological changes large and old saltwater crocodiles undergo. Wells refutes skeptics, as he, and the locals, have seen infant and young adult specimens.
Sweetheart's corpse being taken to Darwin
The taxidermized remains of Sweetheart (note the large head and black scales)