Spot-tail Shark, Carcharhinus sorrah
Northern Territory Coast
Natural sciences collection NTM S.13990-001
Sharks draw great fascination for many people, often as a combination of fear and admiration for the top-order predators of the sea. There are over 50 species of shark in Northern Territory waters, coming in all sorts of shapes and sizes: from Wobbegong sharks with seaweed-like tassels covering their face; others with hammer-shaped heads; freshwater sharks with unusual spear-like teeth; to large Tiger sharks with intricate vertical markings on the body.
Sharks are an important and, considering their size, often significant component of natural science collections. Scientists use these collections as they seek to better document the biodiversity and biology of marine ecosystems, thus informing the development of management and conservation programs. At the Museum and Art Gallery of the Northern Territory (MAGNT), we regularly host researchers who come to measure, collect tissue samples or inspect the stomach contents of sharks. But one of our most famous sharks, that turns heads on any behind the scenes tour of our Wet Store facility, is a two headed shark found by a fisherman from inside a pregnant female off the Northern Territory coast in 1994.
There is actually some literature on the topic of two-headed sharks – firstly as a curiosity, but also as a baseline to gauge potential environmental change and impact. It has been suggested that while rarely sighted now, the two-headed phenomena may become more common as overfishing affects global populations of sharks leading to reduced genetic diversity and increased deformities, or as other environmental changes interfere with embryonic development. There are two kinds of two-headed sharks: one where they are effectively con-joined twins with the bodies fused but having separate heads; and then the much rarer developmental condition where the cartilaginous backbone splits into two and the head is then replicated (known as or axial bifurcation). We performed an x-ray (radiograph) of the MAGNT specimen which revealed it to be a result of the twin scenario, with two rows of vertebrae recognisable along most of the length.
The Natural Sciences section of MAGNT frequently receives queries and specimens of animals from members of the public who suspect they might have found something a bit out of the ordinary. One of our most common queries is the fearless looking, but usually harmless, Northern Mouse Spider Missulena pruinosa, which can turn up in backyard pools at the start of the Tropical build-up. We also have a citizen science project effectively fishing for new species by looking for the ‘worm of death’ being a colloquial name for a group of pink worm-like gobies with big fang-like teeth. These are occasionally foul hooked by Barramundi fishers. While the two-headed shark is an extreme example and anomaly, we are always interested in helping to identify unusual animals, which may perhaps be species new to the region or new to science – a real possibility in the species rich, poorly explored and remote waters of the Northern Territory.