Living Fossils 2. The Abyss

Living Fossils 2.

The Abyss

 

This entry is going to focus on 2 species of fish that occupy some of the darkest depths of our vastly unexplored oceans. They are two species of a group of animals that are seemingly as old as time itself. I am of course talking about sharks, an ancient taxa dating back 420 million years to the Silurian period. The Silurian period itself is determined by a mass extinction event which wiped out 60% of all life on earth along with the evolution of bony and jawed fish including the earliest known fossils of fish determined to be sharks. 

To get a real sense of the timescale I will put it another way by comparing it, to arguably the most well known dinosaur, Tyrannosaurus rex (T-rex). The time between T-rex and man is 65 million years, whereas the time between T-rex and the earliest known sharks is an estimated 353 million years. Meaning that the timescale of T-rex to man can fit in the time difference around 5.5 times. Throughout this entire time, sharks in some form or another have been present from Edestus in the Carboniferous and Helicoprion in the Permian, which survived the greatest mass extinction in earths history, where 95% of all life was wiped out, to the fabled Megalodon whose mighty jaws are in the header image of this series. The 2 shark species in this entry are throwbacks to these bygone ages, creatures that look alien and ancient by every degree, but that only makes them more interesting right?

Helicoprion

Frilled Shark (Chlamydoslachus anguineus)

 

Citron / CC-BY-SA-3.0

The First footage

The frilled shark itself is one of the most worlds most primitive living sharks. Although the frilled shark was first identified and described in 1879, it was not until 2004 when the first footage of a live frilled shark in its natural habitat emerged. They are serpent like sharks with a broad, blunt snout coupled with a large mouth which houses over 300 needle sharp three-pronged teeth situated in 25 rows inside the jaw. Behind this fearsome looking jaw lies six 'frilled' gills which gives the shark its name. The frilled shark is thought to reach an average size of up to 2 meters. The body is a dark brown or grey in colour with a large anal fin and small pectoral and dorsal fins. This appearance, as well as making the shark look like an eel, is thought to contribute to ancient legends of sea serpents but this is disputed due to the deep sea nature of the fish and its small size leading some to consider that that the frilled shark once had a larger relative which made the oceans its home.

 

Frilled sharp jaw + teeth (Source: OpenCage)

 Although it is unknown how this shark exactly hunts, hypotheses based upon the size and shape of the shark have given us an educated insight. Scientists believe that the frilled shark actively hunts prey up to one and a half times its own size, due to its numerous inward angled teeth along with a wide opening jaw, the manner in which it hunts is though to be similar to a snake by curving its body and striking forward, with there being a likelihood of the shark using crevices as well as caves located throughout continental slopes to find food, a realistic rationale for their slender eel like appearance.From sharks that have been examined their diet consists of around 60% cephlapods. However, this is speculation. Its slow moving tendencies may suggest they take advantage of injured or weak squid or perhaps even closing its gills creating a negative pressure which will suck any proximal prey into the sharks mouth.

The frilled shark is by all means a deep water fish, rarely, if never at all, visiting the surface. They are commonly found between 50-200 meters down, although odd specimens have been seen at around 1200 meters. The skeleton of the shark for this reason is simple and poorly calcified, a way of compensating for the nutrient poor depths of the ocean. The depths of the ocean are also much colder then the surface and for this reason the frilled shark has a lethargic metabolic system but large liver full of low density lipids, enabling it to maintain its position in the water with very little effort.The range of the frilled shark is almost worldwide although the physical distribution is patchy. Populations of frilled shark occur on the outer continental shelves and slopes of Norway and northern Scotland, whilst other populations can be found in the eastern Pacific off California, Chile and the west Pacific off Japan and even the Indian Ocean off the South African coast.

The Frilled shark is classified as near threatened mainly due to their long gestation period and low reproductive output. The frilled shark has the longest gestation of any vertebrate at a staggering 3 and a half years. Typically 6 pups are born but few of these reach adulthood. Alongside this, accidental fishing and a high susceptibility to the effects of water pollution could have serious impacts on remaining frilled shark populations.

Goblin Shark (Mitsukurina owstoni)

 

The goblin shark is a very poorly understood deep sea shark. It is the only extant species of shark from a linage going back 125 million years. The goblin shark can grow between 3 and 4 meters and is often characterised by its unique pinkish skin, which unlike previously thought is not due to pink pigments in the skin but in fact due to a translucent dermis, making the shark somewhat transparent. The goblin shark also has a distinctive long, slender and flat snout, almost like a sword blade, which decreases in size depending upon the age of the shark. The jaws of the shark are highly protrusile and can be extended almost to the length of the snout, although the jaws are only elongated when hunting, when not, they are held against the underside of the head. Inside the mouth of the goblin shark, long, sharp fang like teeth are present leading the shark to sometimes be referred to as 'snaggle-toothed'. The flat snout of the goblin shark also includes numerous electro-sensitive ampullae of Lorenzini which are receptors used to pick up the electric fields of other creatures. 

The body of the goblin shark is slender and flabby. The anatomy of the shark suggests its lifestyle is fairly inactive and sluggish, much like the frilled shark, its skeleton is basic and poorly calcified. The sharks fins are also poorly developed and small, typical of a slow swimming shark. Based upon these anatomic features it is probable that the goblin shark is an ambush predator. A large, neutrally buoyant liver means they would be able to drift towards prey with minimal motion. A mixture between their small eyes and the electrical receptors on the snout are used to help detect prey, then once in range the specialised jaws launch forward to capture the prey item.

The goblin shark is found in depths from 40 meters to 1200 meters. They have been caught in all 3 major oceans indicating a worldwide distribution although how complete or fragmented this may be is a matter of complete speculation.

The lack of complete information on both of the above species is reason enough to get out there and explore our oceans in more depth. The fact we know more about the surface of the moon is frankly quite sad. These 2 sharks in particular, are 2 of the oldest living groups of animals on the planet & with the world changing as rapidly as it is, it is unknown how much more time we will have with these unusual but incredible species.

The jaw in action!

Birdman.

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