Are We Shrink-Wrapping Ichthyosaur Tails?

(Don't start with a disclaimer... DON'T START WITH A DISCLAIMER!)

Disclaimer: I'm not trained in palaeontology or fluid mechanics, but after recently illustrating a few ichthyosaurs for a project, I wondered if I was reconstructing their tails too conservatively. I had a poke around the internet and tried to translate it into some coherent thoughts. A water tunnel, tame engineer, and unlimited access to ichthyosaurs would have been useful, but in the absence of all of that, I just had fudge it. And fudge it I did.

The Current Popular Look For Ichthyosaur Tails

If you look at palaeoart depicting ichthyosaurs (including six of the seven I just did... pfft!), a good chunk of it shows animals with tails which are more-or-less cylindrical, following the form of the vertebral column under the surface, skimmed with some muscle and skin, and terminating in a thunniform ('tuna-esque') caudal fin, the lower lobe of which displays a prominent ridge where the vertebrae continue beneath the fin's surface. The top lobe is generally depicted as skinnier than the bottom. But is this the most likely look for ichthyosaurs, and is it worth taking a peak at modern aquatic vertebrates to see how they're doing it?

A horribly-shrink-wrapped Ophthalmosaurus, with a stupidly-long tail. By me. Illustration: copyright © 2003 OUMNH/Gareth Monger

Caudal Fins

The caudal fins of aquatic vertebrates vary greatly in form, reflecting the locomotive styles and ecological niches of their owners. Ocean-going predators, including cetaceans, sharks, and billfish (sailfish, marlins, etc.) have evolved caudal fin shapes which allow them to reach the speeds necessary to run down swift prey and there are broad similarities brought about by convergence. The differences in the orientation of the caudal fin of fishes and reptiles, and mammals, reflect the evolutionary origins of those fins. The ancestors of aquatic reptiles presumably walked with a sprawling gait, their vertebral columns flexing from side to side, resulting in the same undulating motion in water and, therefore, a vertically oriented caudal fin. Cetaceans' terrestrial ancestors walked with an erect gait and cetaceans swim with a vertical undulation and developed a horizontally oriented caudal fin.

Predatory marine vertebrates: A. Atlantic sailfish (Istiophorus albicans); B. tiger shark (Galeocerdo cuvier); C. harbour porpoise (Phocoena phocoena); D. the Jurassic ichthyosaur, Opthalmosaurus. Image: Gareth Monger.

Streamlining Peduncles

Some of these animals also bear modified structures which improve the efficiency of their stroke. The part of the body after the anal fin (broadly speaking, the tail) is called the caudal peduncle, and contains the muscles which drive the caudal fin. It also includes the bony or cartilaginous skeleton, depending on the group to which it belongs. (In cetaceans, the peduncle is also called the tail stock.) In order to generate forward thrust, the caudal fin beats laterally in fish and reptiles, and vertically in mammals. The peduncle must also displace water during the stroke, but pushing the peduncle through water can reduce the efficiency of the caudal fin. Drag created by the peduncle during the stroke is energy wasted which could be converted to forward thrust by the caudal fin. In addition to this, water made turbulent having passed over the animal's body and fins then flows to the caudal fin. The caudal fin is less efficient in this disturbed, turbulent water than in smooth, laminar water.

Many species improve upon these inefficiencies by having peduncles which are streamlined to cut down hydrodynamic drag during the swimming stroke. For example, many sharks' peduncles are dorsoventrally-flattened to ovals when viewed in cross-section, which might be expected anyway because the muscles are grouped either side of the vertebral column – though the overlying tissues produce more-angular apexes to the oval than is achieved by the muscle mass alone.  This produces a lower profile that cuts through the water more easily during lateral beating of the tail. If the stroke generates less turbulence, the animal can transfer more of its energy to the caudal fin to be turned into forward thrust. The cross-section of the cetacean peduncle is similar, except that its oval is oriented vertically.

The peduncle and caudal fin of the harbour porpoise. The cross-section through the peduncle shows the streamlined dorsal and ventral surfaces. Image: Gareth Monger.

Caudal Keels as Laminar Flow Generators

Caudal keel as a possible laminar flow generator.
Image: Gareth Monger.

An additional feature of some fish peduncles is a 'caudal keel' situated on the outermost margins. This is sometimes formed by harder structures such as scales in animals which possess scales – a bit like ridge tiles on a roof. The keels' locations towards the distal end of the peduncle may also partially stabilise the flow of turbulent water as it passes from the animal's body and over its caudal fin. It's less efficient for the caudal fin to push against turbulent water during its stroke, but a longer caudal keel, as seen in some sharks, might convert some of the turbulence to laminar flow. This presumes that a given ichthyosaur's integument didn't sufficiently produce laminar flow on its own.

Caudal Keels as Boundary Layer Fences

The keels might also function as 'boundary layer fences', which serve to reduce slippage of water passing across the caudal fin towards the lobes of the fins. In other words, if the water flows in any other direction not associated with the forward thrust, thrust is lost and the animal must work harder. Imagine balancing a tray on one hand. If the tray is loaded with marbles and it leans slightly, it's fairly easy for all of the marbles to roll together, and the tray will tip, spilling all of the marbles at one end. If there's a small ridge at the centre, it will help to prevent each half of the tray's marbles from slipping to the other side, and it will be easier to control the tray.

Locations of caudal keels for the Atlantic sailfish (Istiophorus albicans) and the porbeagle shark (Lamna nasus). NB: The cross-section for the sailfish is an extrapolated from available photos of live animals. Image: Gareth Monger.

It's entirely possible that ichthyosaurs employed a similar system, combining a dorsoventrally-compressed peduncle and some sort of keel, to improve stroke efficiency. After two weeks of looking over literature and images online, I stumbled over a paper by Theagarten Lingham-Soliar (2016), which I wish I had a fortnight ago. Lingham-Soliar looked at convergence in lamnid sharks and Jurassic ichthyosaurs, and interpreted the soft-tissue remains in a particular ichthyosaur fossil (funnily enough, the photo later on in this article) as the impression of the animal's twisted-over peduncle. It's sometimes hard to interpret these soft tissue remains, not least because some earlier examples may have been enhanced, but if the fossil remains are suggesting chunky peduncles, it would make sense for them to find their way into artistic reconstructions.

Speculative diagram showing sections through the tail of Ophthalmosaurus. Vertebral column is shown in white, against body outline. Positions for possible keel-like structure indicated by arrows and pink dashed line. Image: Gareth Monger

So if peduncles are in, what of the ridge in the lower lobe, as defined by the distal vertebrae within the caudal fin? I can only approximate since I don't have ready access to an ichthyosaur skeleton, and I haven't yet found a detailed diagram of ichthyosaur musculature. That ridge has always been a feature of my ichthyosaur reconstructions, but those vertebrae are relatively small – they're only half the diameter of the smaller vertebrae in the peduncle, just in front of the caudal fin, forming a fairly narrow column. The majority of the caudal fin comprises soft tissue, presumably including some muscle which would be necessary to perform the adjustments to the fin's form during the stroke, i.e., preventing too much flexing which might negate the improvements brought about by the keel (re: boundary layer fence). Cetaceans do this, and their caudal fins are not especially skinny structures. It's feasible that an ichthyosaur's caudal fin vertebrae would have been bound in enough connective fibres, muscle and other tissues that they might not have been discernible in a healthy individual, and the upper lobe might not look too different to the lower.

Two highlighted caudal vertebrae, one just inside, and one just outside, the caudal fin. Note the those in the fin are approximately half the diameter of some of their nearest neighbours in the peduncle. Photo: Daderot. CC0 1.0; Digital overlays: Gareth Monger

So, considering that ichthyosaurs' forms shows them to be powerful, efficient swimmers, it's not totally unreasonable to at least consider that they might have evolved the anatomy to allow them to live as active, effective predators. And whilst the wider, flattened peduncle is likely, it doesn't automatically follow that they would have had keels as sharply defined as those found in sharks and other fish. Without knowing much about the sorts of integuments that various ichthyosaurs possessed, we can't know if specialised integument was used in a similar manner to the scutes of sailfish and their kin. I'm inclined to think scuted/scaled keels are a bit of a stretch. But a bit of definition to the peduncle might be likely.

Different ichthyosaur species were subjected to different selective pressures and, as with extant aquatic vertebrates, we should expect some variation in the external appearances of the myriad ichthyosaur species.

Lateral view of the chunky Ophthalmosaurus (based on Sander 2000), and a dorsal view extrapolated (well, fudged) from an anterior skeletal (McGowan & Motani 2003), and various pics of the great mount at Peterborough Museum. This dorsal view shows off the wider peduncle, but this still might be a tad skinny. Gotta find a decent ichthyosaur muscle reconstruction! Image: Gareth Monger.

Generalised ichthyosaurs, shown from different angles and displaying their chunky peduncles. 'Pedunkies'? Illustration: Gareth Monger).

The ophthalmosaurid ichthyosaur, Nannopterygius, reconstructed with a keeled peduncle. Illustration: Gareth Monger.

References

Bernvi, D. 2016. Ontogenetic Influences on Endothermy in the Great White Shark (Carcharodon carcharias). 10.13140/RG.2.1.2888.5367

Fish, F. E. (<-- seriously?). Biomechanical Perspective on the Origin of Cetacean Flukes. research.net

Lingham-Solia, T. 1999. Rare Soft Tissue Preservation Showing Fibrous Structures in an Ichthyosaur From the Lower Lias (Jurassic) of England. The Royal Society, 266, 2367–2373.

Lingham-Solia, T. 2016. Convergence in Thunniform Anatomy in Lamnid Sharks and Jurassic Ichthyosaurs. Integrative and Comparative Biology, Volume 56, Issue 6, 1 December 2016, Pages 1323–1336, https://doi.org/10.1093/icb/icw125

Martill, D. N. 1995. An Ichthyosaur With Preserved Soft Tissue From the Sinemurian of Southern England. Palaeontology, Vol. 38, Part 4, 1995, pp. 897–903, 1 p1.

Motani, R. 2005. Evolution of Fish-Shaped Reptiles (Reptilia: Ichthyopterygia) in their Physical Environments and Constraints. arjournals.annualreviews.org

Naish, D. 2008. Ichthyosaur Skin Impressions. http://scienceblogs.com/tetrapodzoology/

Sagong, W., Jeon W-P., Choi H. 2013. Hydrodynamic Characteristics of the Sailfish (Istiophorus platypterus) and Swordfish (Xiphias gladius) in Gliding Postures at Their Cruise Speeds. PLoS ONE 8(12): e81223. doi:10.1371/journal.pone.0081323

Veterian Key: Cetaceans. https://veteriankey.com/cetaceans/

Walters, V. 1962. Body Form and Swimming Performance in the Sogmbroid Fishes. Zoologist, 2:143-149.

#FordVNaish Cartoon Follow-Up

#FordVNaish cartoon follow-up

So the talk was talked, the tweet-storm rained itself out and the write-ups were written (see here, here and here). Several people produced some nice memes and cartoons commenting on, and parodying, the aquatic dinosaur theory, which will hopefully continue to circulate for as long as the book does. I knocked out a few single-framers which are dumped here for the sake of posterity.

Ford vs. Naish - 'Too Big To Walk'

Too Big To Walk

Tuesday night saw the much anticipated head-to-head between aquatic dinosaur proponent, Brian J Ford, and British palaeo sense speaker, Darren Naish.

To get you up to speed, Ford has a written a pretty hefty book, published by HarperCollins, which outlines his theory that ALL non-avian dinosaurs were necessarily aquatic, as demonstrated by numerous anatomical details across the whole non-avian group. To promote his book, Ford has embarked on an informal lecture tour, giving talks at institutions and on cruises.

#FordVNaish: a well-attended event. (Photo: G. Monger.)

Ford is very much a lone wolf in respect of this theory, and one might wonder what harm there is in an individual pushing his ideas against the immense weight of established palaeontology. He’s one guy and if his ideas are bat shit crazy, what’s the problem?

Fringe Theory

The problem is basically two-fold:

First of all, Ford is taking his theory directly to his audience, which most of the time won't comprise individuals with any kind of working knowledge of biological or palaeontological principles. A critical and enquiring mind will almost certainly enable an audience member to identify some sweeping and unsubstantiated claims, but many people will take Ford’s claims at face value. After all, palaeontology is not that new a science, and it sounds reasonable that Ford has the benefit of all that available knowledge. In short, there must be something already in the myriad studies to support his claims.

Secondly, Ford’s theory is legitimised by the mainstream coverage it receives. HarperCollins gave him a book deal, fergawdsake! They’re not some loony creationist publishing outfit that only ever publishes anti-science. They’re a big deal. They have standards.

Even the BBC provided him with a platform, much to the consternation of many scientists. Whack-job pseudoscientists touting fringe theories don’t seem so oddball to the general public when an organisation like the BBC helps increase their audience size – or when a publishing house like HarperCollins is happy to associate with them.

#FordVNaish

So Ford came to London to plug his book at a new regular event dubbed New Lands, held at Conway Hall. In the interest of maintaining some semblance of balance (and, presumably, integrity) the organisers pushed for another speaker to attend in order to defend the ‘dinosaurs are not obligate water dwellers’ position of modern palaeontology. The format was simple and digestible. Ford made his claims and then Dr Darren Naish answered those claims. After a few minutes’ break, the audience and speakers reconvened, and a Q&A session was held.

Thanks in part to Darren Naish’s prevalence on social media, the event was well-publicised, especially among palaeontology workers and enthusiasts, and it seemed (to me, anyway) that it was those people who comprised the majority of the audience. Indeed, many of those in attendance knew each other, and as @scyrene tweeted, it resembled a mini TetZooCon.

Brian J Ford's Presentation

So after Scott Wood's introduction, Ford opened straight away with what boiled down to, “All modern palaeoart is wrong and silly, and palaeontologists hate me and are petty and small-minded, and also wrong.” A more-gentle approach might have helped his cause – and would have been more friendly! – since it’s impossible to denigrate scientific consensus on so basic a level without also seeming to have a pop those people, however informal their interest, who subscribe to those theories. It’s probably fair to say that Ford put a lot of backs up with his opening comments, and it said as much about his attitude towards the scientific community as it did about what he thought of the  model for dinosaurian lifestyles.

Ford adheres to the Greek pronunciation for Triceratops, pronouncing it with a hard ‘c’ throughout. His dedication to classical Greek fell short of dressing like Theophrastus and stalking up and down the lecture theatre making pronouncements from a scroll. (Er, what? - Ed) Ford proceeded to argue that dinosaurs were not dynamic, and the ideas perpetuated in modern palaeoart were ridiculous. Examples were provided, but all I got from that was that he's never seen a large mammal, like a rhino or a hippo, throwing its weight around. Also used as examples were numerous video clips of CG dinosaurs and their relatives, generally used as poor examples of palaeo restoration, in support of Ford's position. However, many of these, such as the WWD clips, are pushing twenty years old. There was a lot of cherry-picking going on, but picking holes in old, or even new, palaeoart is not the same as scientifically disproving a theory.

Edmontosaurus was selected as an animal which definitely lived an aquatic lifestyle, on account of its footprints' proximity to water, and the recovery of its fossils from petrified swamp beds. Also, sauropods didn’t need tails to balance; tails are dead weights, don't you know?! And gigantism always favours an aquatic lifestyle, never mind that sauropod skeletons are nothing like extant giant aquatic vertebrates' skeletons.

Curiously, Ford ignored the vastly disparate nature of the various dinosaur groups. Sure, it must help him make his point if he can ignore as many uncomfortable truths as possible, but ten year olds watching his talk on some Cunard cruise are going to wonder if he really knows his stuff. Some of Ford's anti-terrestriality arguments were based on out-dated reconstruction of Spinosaurus. He then moved to the newer Ibrahim et al reconstruction to point out that he was right all along, but then trashed it when it didn't agree with him.

Take-home: Non-Avian dinosaurs were too big to live on land, and inhabited bodies of water sufficiently deep to support their bodies. And suggestion to the contrary is absurd, and all palaeontologists are silly and small-minded.

Darren Naish's Presentation

Darren's main line of attack was to go through Ford's arguments, and offer some science – which had been sorely lacking for the previous thirty-or-so minutes. He started by giving a very brief overview of the main dinosaur groups and pointing out that the aquatic dinosaur theory is misinformation; the aquatic dinosaur claim is old, familiar, and robustly discredited. Ford cherrypicks his data. (He does; we all sat through him doing it!)

Contrary to Ford's assertions, Tyrannosaurus fossils, their trace fossils, coprolites, and fossils found in association with them, all support terrestriality. Darren pointed out that non-bird dinosaurs lacked aquatic specialisation, with the exception of a couple of weirdo theropods such as Spinosaurus and Halszkaraptor, and we were shown slides showing the evolutionary changes seen in animals which are aquatic.

Despite Ford's claims, aquatic animals do not want pneumatised bodies. They want dense bones. Also, buoyancy studies of dinosaurs support terrestriality. As mentioned, Darren acknowledged that some dinosaurs were likely semi-aquatic. Ford frequently referred to Spinosaurus's sail as a fin, but Darren pointed out that its sail is unlike those in fish. Despite the presence of a sail in chameleons, they're not aquatic either.

Are sauropods too heavy to walk? No - bones and soft tissue support life on land. Were those tails too big for living on land? Their anatomy says no; the tail is not a dead counterweight. it anchors the caudofemoralis muscles for pulling the femur back and powering locomotion.

In order to support his claims, Ford is dismissive of geology - like creationists! The Mesozoic was not a hothouse environment full of deep, warm swamps. The vast majority of dinosaur footprints were made on land and those thought to be made in water are highly questionable.

Critically, the isotopic signature in dinosaur bones supports a terrestrial lifestyle – but not for Spinosaurus.

Take-home: Decades of evidence and studies support a terrestrial lifestyle for non-avian dinosaurs, although a couple of known species show evidence for being semi-aquatic. Aside from those exceptions, no non-avian dinosaurs show any specialisation towards an aquatic lifestyle.

Q&A/Who Won?

The bar was shut during the break, which resulted in the sort of wailing and gnashing of teeth that you would expect from a bunch of scientists. People started sweating and panicking, but then John Conway remembered he’d seen a pub only a hundred yards away, and everybody pulled themselves together.

After the break, a Q&A session provided the speakers with the opportunity to address some of their differences through answering questions from the audience, and New Lands’ organiser, Scott Wood, refereed the responses and kept things on track. Among the many excellent questions were, “Would dinosaurs with heavy bone structures, such as Triceratops and Ankylosaurus, sink in water?” and “If Darren was more outrageous and sweary, would he have a HarperCollins publishing deal?”

Darren Naish and Brian J Ford (Photograph: G. Monger.)

Unfortunately I was still busy live-tweeting, and the faster pace of the Q&A session meant that I didn’t manage to tweet all of the questions, and I didn’t record any of the replies. But it’s fair to say that the speakers’ answers were in line with their presentations, and there were no surprises. That said, there was a fraction of what felt like ‘rolling back’ by Ford, where he made it clear that he wasn’t saying that even the biggest sauropods didn’t migrate to land in order to carry out certain activities, such as egg-laying. This was certainly at odds with his overall tone regarding the preposterousness of dinosaurs living out of water. He worked hard to convince us that these animals simply couldn’t do it, and then, almost flippantly, remarked, “Well, I’m not saying they couldn’t come out to lay their eggs!”

For me, this rather summed up Ford’s theory – and maybe Ford himself. Despite the Boris-eque bluster and theatrics, Ford simply didn’t speak with conviction. Certainly not the conviction of a scientist who has put his ideas to the test. Not even the conviction of the weirdo in the pub who genuinely, genuinely believes that David Icke is right about the Royal Family. Unlike the weirdo in the pub who can quote his subject chapter and verse, Ford cannot. There’s nothing to quote. We were provided with a string of barely-relevant anecdotes, insults and easily-refutable observations.

On that point, I’m not suggesting that all Darren had to do was turn up and list the studies that refuted Ford’s claims whilst trying not be rude, but in many ways, that was all that was required. Ford hadn’t undone any accepted principles. There was no palaeontology-shattering peer-reviewed paper which Ford could roll up and bop Darren on the nose with and say, “Toddle off home, Naish – you’re finished!” We were just subjected to his unsubstantiated ideas, punctuated with playground-style verbal attacks on palaeo workers. Saying somebody else's theory is silly does not substantiate your own.

But Darren did provide as much information as the time and format would allow and was very well prepared, which is to be expected from someone who is an expert in their subject and has already challenged Ford's claims on several occasions. Who won the debate is largely moot, since Ford is promoting a book, the release of which is imminent, and HarperCollins is hardly going to pull it on the strength of Ford's thrashing at the hands of Darren. A win for Darren would be to see the buzz surrounding the debate help inform people before they accept Ford's theories wholesale. Tuesday was about countering Ford in the hope that it will go some way to mitigating the damage that Ford and his book will do to the public's understanding of palaeontology. Hopefully Ford's book will simply be remembered as one of those weird little blips, like Hoyle's and Wickramasinghe's Archaeopteryx, the Primordial Bird: A Case of Fossil Forgery. They enjoy their fifteen minutes but ultimately, no one takes the seriously.

When all is said and done, Ford’s negativity towards the science community is telling. If he isn’t interested in winning over scientists, he’s trying to win over the public. And if he isn’t doing it for science, he’s doing it for money. Too Big To Walk is Brian J Ford’s snake oil.

(Illustration: Gareth Monger.)

After the event, Darren Naish posted supplemental information here. The opening paragraph: "This document corrects various additional claims made by Brian J. Ford and is intended as a supplement to my talk given at Conway Hall on Tuesday 15th May 2018. Needless to say, there was insufficient time in the talk to fit in all of these additional corrections and comments."

For those who couldn't attend, I filmed the event with my co-author, Andy Brain, from my other blog, Beware! The Zine. TetZoo now has the files, and barring a couple of minutes clipped from the end of the Q&A, we hope we got some usable video/audio.

(The details recorded throughout this write-up were hastily posted to Twitter during the event itself, before being presented here. Although I've taken care to post accurately, there remains the possibility that paraphrasing and abbreviating for the live tweeting has introduced slight errors.)