The Bob Nicholls artwork I featured yesterday got some of you talking about a particularly famous denizen of the Jurassic seas. Namely, the gigantic, edentulous pachycormiform actinopterygian Leedsichthys problematicus from the Callovian Oxford Clay Formation. Hold on – – isn’t that a… a… fish? How on earth can I justify this inexcusable off-topicness?
Well, quite easily actually. The gigantic size of Leedsichthys (more on that below) means that it can’t be ignored whenever we discuss trophic interactions in the Middle Jurassic seas. Perhaps it was preyed on by the large, contemporaneous pliosaurs (see Martill 1988, Hudson et al. 1991, Martill et al. 1994), and it’s even been suggested that smaller marine reptiles – like metriorhynchid crocs – swam up to it and took chunks out of it on occasion. That’s not such an unreasonable idea, given that some living odontocetes have been reported to behave in a similar fashion (however, read on). Its carcass must have provided a phenomenal resource for scavenging marine reptiles and all manner of other organisms. In short, Leedsichthys is ‘very relevant’ if you’re interested in marine reptiles [different versions of Leedsichthys, as portrayed in popular media, shown above. Image provided by Jeff Liston, used with permission].
I also have quite a soft spot for Leedsichthys, having assisted in the 2002 excavation of Ariston, one of the most complete specimens yet found (Liston 2006) (this dig featured in the 2003 TV series The Big Monster Dig, broadcast on the UK TV channel Channel 4). In the adjacent image, that’s me lying on my belly in the middle. It’s a good arse shot. Anyway, we all love gigantic fishes, even those of us devoted to tetrapods…
While Leedsichthys was named in 1889, it’s only in the past three decades that it’s become well known among palaeontologists and palaeontology enthusiasts, and only in the past ten or so years has it become represented in the popular media. However, things have gone horribly astray, and it’s time to set the record straight.
The popularisation of Leedsichthys began with a semi-popular article published by Dave Martill in Geology Today (Martill 1986a). Because it featured a life restoration – the first ever published (so far as I know) – it has effectively become the first article that most people have gone to when seeking information on this fish. Dave also wrote a technical paper, reviewing knowledge of the fish’s anatomy and palaeobiology (Martill 1988). By making extrapolations from the size of the tail and estimated size of the gill arch apparatus, Dave estimated a lower total length of 13.5 m for Leedsichthys, and a possible upper limit of 27.6 m. The latter measurement is larger than an average Blue whale Balaenoptera musculus (the record for which is 33.5 m). Unsurprisingly, the 27 m estimate is the one that’s become repeated most often. Since Dave’s work, Leedsichthys has been re-visited by Jeff Liston for his PhD project: see Liston (2004, 2006, 2008) and Liston & Noè (2004). Jeff’s work has shown that various ideas that are now frequently promoted about Leedsichthys – namely, those regarding its size, its shape and proportions, and its alleged interaction with a metriorhynchid – are erroneous.
Out with the old, please
It’s notable that quite a few recent artistic renditions of Leedsichthys are (essentially) carbon-copies of the incredibly ugly, armour-plated version produced for the BBC television series Sea Monsters [visible in the slide used at the top], broadcast in 2003 and featuring a time-travelling Nigel Marven. This series was produced by Impossible Pictures, and it may or may not mean anything that Marven (playing himself) was also featured in series 3 of Impossible’s Primeval; this time round he met his end at the jaws of a giant theropod, a great scene. Sorry for the spoiler. Unfortunately, the Sea Monsters Leedsichthys – itself based mostly on a drawing produced by Paul Pollicott and published by Martill (1986a) – is substantially inaccurate. Its pectoral fins are too large in proportion to the body, the deep, dorsally convex head (creating a ‘humped’ appearance) is not accurate, and the body is not long enough. I base these assertions on Jeff’s work: a more accurate Leedsichthys [produced by Bob Nicholls] is shown below. Note the absence of the ‘hump’, the far longer, slimmer body, and the different fin proportions. This should now become the standard template for this fish: the old version – you can see versions of it at wikipedia and elsewhere on the web – is utterly and unquestionably inaccurate.
What about the size? The 13-27 m length extrapolated by Dave used data from a smaller relative, Asthenocormus, and also assumed that things like the ratio of gill basket width to total size scaled isometrically across the group. Alas, both assumptions are unlikely to be correct. More recent investigation has shown that a total length of 9 m is more like it (Liston & Noè 2004). Read this research before producing yet more over-sized renditions of this stupendous animal (for more thoughts on this and other issues, see Big Dead Fish).
Swimming croc vs mega-fish
Finally, if you’ve seen illustrations that show a metriorhynchid crocodilian (an animal of about 3 m in total length) swimming up to a Leedsichthys and biting it, you’ll be interested to know this is not mere artistic whimsy, but is in fact based directly on an interpretation in the literature [in the illustration by Colin Swift, shown below, the metriorhynchid is near the fish’s dorsal fin. A Liopleurodon attacks the fish’s pectoral fin at the same time]. While reviewing stomach contents reported for Oxford Clay metriorhynchids, Martill (1986b) noted that a Leedsichthys frontal bone, held in the collections of the Peterborough Museum, ‘has a large tooth of Metriorhynchus embedded in it towards the margin’ (p. 623) (despite viewing this specimen several times, I seem not to have any photos of it). New bone growth around the tooth showed that healing had occurred. It was therefore proposed that the metriorhynchid had attacked the fish, and that the fish had survived and started to heal its wound. Given that the ‘frontal’ (read on) was over a metre long, and given the discrepancy in size between a metriorhynchid and an adult Leedsichthys, this interaction might imply that metriorhynchids acted in a similar fashion to cookie-cutter sharks: that they swam up to giant animals and took chunks out of them. As mentioned earlier, interactions of this sort have been observed in cetaceans, as False killer whales Pseudorca crassidens have been filmed biting chunks out of Sperm whales Physeter macrocephalus (Paul 1998).
However, there are two problems with this otherwise appealing notion. Firstly, the bone identified by Dave as a frontal is not a frontal: frontals are absent in Leedsichthys (the skull is roofed by parietals and postparietals only, with a rostrodermethmoid, nasals and antorbitals located more anteriorly), and the bone is actually a hyomandibula (Liston 2008). Secondly, the bone around the embedded tooth does NOT display any sort of reaction, and hence there is no evidence for healing (Liston, PhD thesis). So, while a reptile did bite this Leedsichthys specimen, it was more likely scavenging on a dead one, not attacking a live one. Indeed, as Jeff notes in his thesis, it’s difficult to imagine how a marine crocodilian might have bitten into a hyomandibula unless that bone was already partially disarticulated from the rest of the skull. Other evidence points towards the possibility that metriorhynchids sometimes scavenged from submerged vertebrate carcasses (Forrest 2003).
Incidentally, some Leedsichthys fin rays (perhaps representing the dorsal fin in one specimen, and a pectoral fin in another) do bear evidence of attack by large predators. What look like curving bite marks appear to have been made by plesiosaurs [another Bob Nicholls piece shown here. While more accurate in proportions and shape than most other versions, this reconstruction is now out of date and has been superceded by Bob’s CG version shown above (the greenish one)].
As is well known, I, ordinarily, only blog about tetrapods. Today that rule has been broken, and I feel the shame. But I felt compelled to do it, given the amount of incorrect data that’s out there about this fish. I hope this one little article starts to turn the tide and make a different.
Finally – if this has interested you, it is mandatory that you attend Sea Dragons of Avalon: the early radiations of the marine reptiles and recovery from the Triassic-Jurassic faunal crisis, with special reference to Street in Somerset and the wider British record (Street, Somerset, UK, July 30th-August 1st): follow the links here for more information.
Refs – –
Forrest, R. 2003. Evidence for scavenging by the marine crocodile Metriorhynchus on the carcass of a plesiosaur. Proceedings of the Geologists’ Association 114, 363-366.
Hudson, J. D., Martill, D. M. & Page, K. N. 1991. Introduction. In Martill, D. M. & Hudson, J. D. (eds) Fossils of the Oxford Clay. The Palaeontological Association (London), pp. 11-34.
Liston, J. 2004. An overview of the pachycormiform Leedsichthys. In Arratia, G. & Tintori, A. (eds) Mesozoic Fishes 3 – Systematics, Paleoenvironments and Biodiversity. Verlag Dr. Friedrich Pfeil (München), pp. 379-390.
– . 2006. From Glasgow to the Star Pit and Stuttgart: a short journey around the world’s longest fish. Glasgow Naturalist 24 (4), 59-71.
– . 2008. A review of the characters of the edentulous pachycormiforms Leedsichthys, Asthenocormus and Martillichthys nov. gen. In Arratia, G., Schultze, H.-P. & Wilson, M. V. H. (eds) Mesozoic Fishes 4 – Homology and Phylogeny. Verlag Dr. Friedrich Pfeil, München, pp. 181-198.
– . & Noè, L. F. 2004. The tail of the Jurassic fish Leedsichthys problematicus (Osteichthyes: Actinopterygii) collected by Alfred Nicholson Leeds – an example of the importance of historical records in palaeontology. Archives of Natural History 31, 237-253.
Martill, D. M. 1986a. The world’s largest fish. Geology Today 2, 61-63.
– . 1986b. The diet of Metriorhynchus, a Mesozoic marine crocodile. Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 1986, 621-625.
– . 1988. Leedsichthys problematicus, a giant filter-feeding teleost from the Jurassic of England and France. Neues Jahrbuch fur Geologie und Paläontologie, Monatshefte 1988, 670-680.
– ., Taylor, M. A., Duff, K. L., Riding, J. B. & Bown, P. R. 1994. The trophic structure of the biota of the Peterborough Member, Oxford Clay Formation (Jurassic), UK. Journal of the Geological Society, London 151, 173-194.
Marven, N. & James, J. 2003. Sea Monsters: Prehistoric Predators of the Deep. BBC Books, London.
Paul, G. S. 1998. Terramegathermy and Cope’s rule in the land of titans. Modern Geology 23, 179-217.