“Through shoal and shining flock and froth and freath and freaky frisky flashers, like a liner, The Bearsden shark coasts casually, kinglily, killingly casual, casing the scales, lazily pacing and chasing, lord of the place, of the plaice, lordly diner.”The Bearsden Shark, Edwin Morgan.
Glasgow was a very different place 330 million years ago. What is now the largest city in Scotland, covered in sandstone buildings frequently splattered by rain, was once a warm shallow sea teeming with marine life. This ranged from molluscs, corals and fish to now extinct creatures such as straight coned Belemnites (ancient relatives of squids) and Sea Scorpions (which could grow bigger than a human!). Just like in today seas, sharks were a key part of this ancient ecosystem. At this point in their history, sharks and their close relatives were still in their early evolutionary days and, just like any teenagers, were going through “a phase”. They were experimenting with different body types and features not found in modern sharks. One of the weirdest shark-like creatures from this time was unearthed in the Bearsden area of Glasgow in 1982 by a local fossil collector named Stan Wood. This shark is known scientifically as Akmonistion zangerli (meaning “Zangerles anvil sail”) but it is more commonly referred to as “The Bearsden Shark”.
The 1982 Bearsden Shark fossil was quite an astonishing find. The cartilaginous fishes (a group that contains Sharks, Rays and Chimera fish), despite having existed on Planet Earth for over 400 million years, actually have a poor fossil record. This is because their skeletons are almost entirely made up of cartilage instead of bone. Cartilage is relatively soft and doesn’t fossilise well at all. So as a result an ancient shark’s body is almost always lost to time. The only exception is their teeth which due to being hard and resilient, and the sharks shedding and replacing them frequently, are more commonly preserved. In fact much of what we know about a number of extinct sharks (including the famous Megalodon) only comes from fossilised teeth. This limits what we can discern about the rest of their anatomy. But the Bearsden Shark was different. The fossil that Stan Wood found in 1982 preserved not just the teeth but the entire body. This happened because, by a stroke of luck, the Bearsden Shark was buried by thick mud very quickly after it died. This protected the carcass from being broken down by scavengers, decay and/or the surrounding environment. The preservation was so good that palaeontologists were able to identify muscles, blood vessels and even its last meal! It’s truly a unique fossil, and if you want to see it for yourself it’s on display at Glasgow University’s Huntarian Museum.
The Bearsden Shark belonged to a group of extinct relatives of sharks known as the Stethacanthidae. This group is known as the “Ironing Board Sharks” due to their most iconic feature; a large ironing-board like structure attached to their back. This board extends outwards into a wide, flat surface covered in small spines and is often described as being like an upturned ironing board or an anvil in shape (hence Akmonistion’s name meaning “anvil sail”). This structure is known scientifically as a “Spine Brush Complex” and only appears in male Ironing Board Sharks. So from this we can already deduce that the Bearsden Shark was male. What could possibly have been the purpose of this bizarre ironing board/brush structure? Palaeontologists still don’t know for sure! The fact that this structure only appears in males could indicate that they were display structures. The male with the largest board would be “more impressive” to the females and more intimidating to rival males. As a result over millions of years this board could evolve to become larger and more extravagant. Another suggestion is that the spines on the board could somehow have allowed males to attach themselves to a female during mating. Outside of this structure the Bearsden Shark (and its relatives) also possessed a patch of spines on the top their head (again only in males) and long thin strips trailing from their front fins (which palaeontologists also don’t know the function of!). Put this all together and you get a unique looking animal that would have been distinctly recognisable if you were out scuba diving in the Carboniferous seas. These features would also have affected the Bearsden Shark’s lifestyle outside of courtship. They meant that it wasn’t as streamlined and hydrodynamic as other sharks. Therefore it wouldn’t have been a fast swimmer and instead it would have cruised the sea floor, snapping at any small fish that wandered too close.
Akmonistion has not only influenced the field of palaeontology (by increasing our understanding of early sharks and their relatives) but has also been an influence on the local community of Bearsden. In 2016 a cairn and plaque were placed on the site of its discovery to simultaneously commemorate it and inform people about it. The Bearsden Shark is even the subject of a poem by Edwin Morgan, which I quoted at the beginning of this blog article. It’s a fun read and I’ve provided a link to it in the “References and Further Reading” below. Not many prehistoric animals can say that they have a poem in their honour!
The Bearsden Shark is an astonishing animal of earths’ past, and a great example of how diverse and wonderful sharks and their relatives both were and are. The week this blog article is coming out is the same week as “Shark Week”, a week-long event that is supposed to celebrate and educate people about sharks. While some places promote incorrect, negative ideas and stereotypes about sharks I hope that through the story of the Bearsden Shark you can catch a glimpse at their rich history, and why they absolutely should NOT be seen as simply monsters.
M. I. Coates & S. E. K. Sequeira (2001) A new stethacanthid chondrichthyan from the lower Carboniferous of Bearsden, Scotland, Journal of Vertebrate Paleontology, 21:3, 438-459, DOI: 10.1671/0272-4634(2001)021[0438:ANSCFT]2.0.CO;2
BBC News, “Shark ‘fossil wonder’ find commemorated at Bearsden site”, Glasgow & West, BBC News, https://www.bbc.co.uk/news/uk-scotland-glasgow-west-35092689