Cartorhynchus: helping ichthyosaurs crawl back into the mainstream.

Over the last 12 months or so, I’ve been researching ichthyosaurs for my masters project, and since then, I’ve been working on publishing my results. As such, I’ve learnt a fair bit of ichthyosaur palaeobiology and systematics. I’m no expert, but at this early stage in my academic career, I can say that at the moment, ichthyosaurs (specifically ichthyosaur endocranial anatomy) are my ‘specialisation(s)’, perhaps even making me an ichthyo-sir (heh). To this end, Motani et al.’s recent publication in Nature was massive news for ichthyosaur palaeobiologists. And that’s why it’s got its own little blog post.

What’s all the fuss about then? This year (2014) marked the anniversary of the 200 years since the first appearance of ichthyosaurs in scientific literature, and ichthyosaurs are closely associated with palaeontological celebrities, both historical (Mary Anning) and rather more recent (Alfred Romer). In those 200 years, we’ve learnt a lot about ichthyosaurs, and whilst they’re not ‘some kind of fish-lizard’, they are diapsid reptiles that were some of the first tetrapods to evolve a thunniform (fish/tuna-like) bodyplan, which aided them in their marine adventures. We know what colour some of them were thanks to melanosomes (Lindgren et al. 2014), we also know that they gave birth to live young, like mammals and some sharks do. We have exceptional fossils of ichthyosaurs actually giving birth, and others with amazing detailed and undisturbed soft tissue outlines. However despite all these amazing discoveries, we still don’t know a whole lot about two major aspects of ichthyosaur palaeobiology: their precise biomechanical function (we can’t create fancy 3D digital models due to the lack of 3D specimens, most ichthyosaur remains are mostly pancake-flat, even the really awesome ones) and perhaps more importantly, how they place in wider diapsid phylogeny.

The miracle of ichthyosaur birth, over 200 million years-ago. Very cool.

The miracle of ichthyosaur birth, over 200 million years-ago. Very cool.

Now before I go any further, it might be a good idea to explain what I mean by diapsid. Diapsida is a group of organisms (more specifically tetrapods) that have two temporal fenestrae (holes) in each side of their heads. Now this is a pretty large group, including archosaurs (dinosaurs, birds and crocs), lizards, snakes and tuataras. So whilst we have some vague idea where ichthyosaurs lie within this pretty large evolutionary tree, we’re not entirely sure. Why? Well because we don’t have transitionary fossils, ichthyosaurs previously (before Motani et al. 2014) appeared in the fossil record as highly adapted marine reptiles, well suited to the marine environment (remember, they look like fishes). So without any hint of which precise group of terrestrial organisms they evolved from, the topic of where ichthyosaurs came from is highly debated. So much in fact that in 2006, a very prominent ichthyosaur worker, Michael Maisch declared that the placement of ichthyosaurs within Diapsida was “…impossible…” (Maisch et al. 2006) without more basal specimens.

The internal phylogeny of ichthyosaurs isn’t a much better state either, with tree topologies changing at every opportunity of the last 10 years or so, threatening to change again when new systematic methods are applied. This again is largely due to the lack of well preserved three-dimensional specimens. But it’s not all doom and gloom, amazingly preserved specimens like those used in Lindgren et al. 2014 have shown us the colour of these ancient fish-dolphins (joke name, please don’t take it seriously), and Fischer et al. 2013’s discovery of Malawania has helped, to some degree, solve the internal phylogeny of at least neoichthyosaurs and ophthalmosaurs (ichthyosaurs from the Jurassic onwards). And obviously, my work on ichthyosaur endocranial and neuroanatomy from an exceptionally three-dimensionally preserved specimen will be hopefully  well received (more on that in the coming months). So it’s not all doom and gloom. But still, ichthyosaurs aren’t exactly the Brangelina of the palaeontological scene, no sir, those celebrity couples occupying all the headlines are dinosaur discoveries such as Deinocheirus and Dreadnoughtus, and the number of ichthyosaur workers isn’t exactly huge.

To my shocked delight, on the afternoon of the 5th of November, 2014 I stumbled upon a fresh new ichthyosauriform, in a Nature paper. Good heavens! Could it be true? Well, of course, other wise I’d have spent the last hour typing madly about ichthyosaurs for no apparent reason. Catorhynchus lenticarpus (‘shortened snout’, ‘flexible wrist’) is a weird, small beast. At first glance, you’d be forgiven for thinking that Catorhynchus wasn’t even a ichthyosaur at all. Well, technically, it isn’t an ichthyosaur at all, it’s an ichthyosauriform.  Catorhynchus comes from the Lower Triassic, approximately 248 million years-ago, and whilst some would call it an ‘ichthyosaur’, the Ichthyosauria (essentially all of the things your properly allowed to call ‘ichthyosaurs’) didn’t occur until later on in the Triassic. So, what the hell is Catorhynchus? Simple, it’s an ichthyosauriform, an ichthyosaur-looking creature which is more closely related to Ichthyosaurus communis than to a hupesuchian? Wait, what the hell are hupehsuchians, and what do they have to do with anything?

Hupehsuchians, think ichthyosaurs but a little more 'vacant' looking.

Hupehsuchians, think ichthyosaurs but a little more ‘vacant’ looking.

Good question. Hupehsuchians are a weird bunch of marine reptiles, who you’d be very much forgiven for calling ichthyosaurs, because well, they look quite a lot like ichthyosaurs. This simple fact has led many researchers to state that ichthyopterygians and hupehsuchians were related, however, there’s been little evidence to really cement this (just because two organisms look the same/have similar features, doesn’t mean they’re closely related. For example birds and bats both have wings, but they evolved powered flight independently and convergent to each other). As I’ve previously said, this is due to the lack of really primitive fossil ‘ichthyosaurs’ as well as our fairly poor understanding of where ichthyosaurs fit relative to other diapsids. However, Catorhynchus has given us a glimmer of hope, enabling us to, for the first time, really start to understand how ichthyosaurs first came about. Now, thanks to Catorhynchus, we think that ichthyosauromorphs (which now includes hupehsuchians) originated in China in the Earliest Triassic, which was a warm tropical archipelago ‘back in the day’. This is interesting, as we know that other groups of marine reptiles, such as sauropterygians (plesiosaurs, pliosaurs et al.) may have also originated in this area at the same time, so Earliest Triassic China may have provided very good conditions to harbour the evolution of many marine reptiles.

Phylogeny of ichthyosauromorphs, modified from Motani et al. 2014.

Phylogeny of ichthyosauromorphs, modified from Motani et al. 2014.

Don’t worry, I’ll stop teasing you now, I’ll actually talk about the fossil for a bit. With a host of unusual features such as really short snout, large flippers and a short body length (the shortest of all ichthyosauromorphs, estimated at a tiny 40 cm) and a really deep lower jaw, Catorhynchus is a weird beast. Yet, despite all these abnormalities, it looks like an ichthyosaur, I mean look at those big eyes! However, it also looks like a juvenile ichthyosaur. For me, and other ichthyosaur workers I’ve spoken to, this is the main reason why people of sceptical about drawing so many big conclusions from Catorhynchus. However, other people (untrustworthy creator of reptileevolution.com) have said that it certainly can’t be an ichthyosaur, and has to be an ‘ichthyosaur-mimic’, because yeah, if it has loads of scientifically diagnostic features of an ichthyosaur the most obvious answer is that it wants you to think it’s an ichthyosaur, just to troll the scientific community, and then years later scream ‘psyche!’ to everyone, you know, because fossils love to mess with us, the jerks.

Catorhynchus fossil from Motani et al. 2014. E represents a  newborn Chaohusaurus, for comparison.

Catorhynchus fossil from Motani et al. 2014. E represents a newborn Chaohusaurus, for comparison.

ANYWAY. I think it’s worth pointing out that it realistically might turn out to be a juvenile, even though Motani et al. do present some evidence that it’s a fully grown adult, for example the forefins of Catorhynchus are almost as long as its skull, a feature found exclusively in adult individuals. However, it’s also worth mentioning that even despite this, Motani et al. don’t completely dismiss the possibility of this specimen being a juvenile. Essentially, I feel it’s best to take this discovery with a pinch of salt until we find a few more specimens of Catorhynchus. Despite this uncertainty, we can be fairly sure that Catorhynchus may have been amphibious. Yeah, that’s right, amphibious and NOT an amphibian. Other articles have said that Catorhynchus is an amphibian, this is incorrect, as Amphibia form their only little group of organisms, which ichthyosauromorphs aren’t part of! However, Catorhynchus is amphibious, i.e. it shares its time between land and water. How do we know this? Well from the fossil, Motani observed that the carpus may have allowed the flipper to bend in a way much like the flippers can bend in seals, and since seals have flippers for limited terrestrial locomotion, it seems likely that this was also the case for the flippers of Catorhynchus. Motani also presents a case for suction feeding in Catorhynchus, which brings the contentious debate of whether other ichthyosaurs fed via suction feeding back to the table.

To summarise Motani and friends have presented the world with a new ichthyosauromorph which, if verified with further specimens, will help us to really start to understand how ichthyosaurs (and perhaps marine reptiles more widely) first evolved, as well as to understand the place of ichthyosauromorphs within Diapsida. And since it was published in Nature, it might turn a few heads, perhaps persuading more people to join the very small field of ichthyosaur of palaeobiology. As always let us know what you think, comment below or Tweet us (or indeed, even Facebook us).

Not only was it amphibious, Catorhynchus was also the most miserable of all the ichthyosauromorphs.

Not only was it amphibious, Catorhynchus was also the most miserable of all the ichthyosauromorphs.

Deinocheirus: why beer-bellies are bad-ass and the importance of being weird

Today started out as a fairly normal day. I overslept thanks to marathonning House late into the night/morning (note: not due to working late/early on my publication, oops), I dragged myself out of bed and into the office. I then, still half-asleep checked Twitter (the morning ritual was well underway) and then suddenly, I displayed both ends of the NedryGrant excitement chart (patent pending) simultaneously. Deinocheirus. It was DeinocheirusDEINO-RUDDY-CHEIRUS! At the moment, I’m in an office full of volcanologists, so no-one understood my excitement (in fact most thought I had some form of disposition, I mean I was practically frothing at the mouth with excitement). I immediately texted Richard and all my other palaeontological friends/colleagues with two words: DEINOCHEIRUS PUBLISHED.

My face on the morning of the 22nd October 2014. (I even laughed like a Dilophosaurus).

Story time

So why was I so stupidly excited? Well, I’m glad you asked. To explain this excitement, our tale begins in 1965. It was July, and the Polish-Mongolian Palaeontological Expedition had stumbled upon a ‘monster’ find. Forelimbs and a shoulder girdle 2.4 metres long belonging to a 70 million-year-old dinosaur with surely the largest forearms of a bipedal animal ever. However, that was all they found. What in the Seven Hells was this magnificent beast? Surely these the arms of some superpredator, akin to Allosaurus or perhaps a mega-Velociraptor? Deinocheirus mirificus was (‘unusual horrible hand’) was ‘born’. For seven-years, this was the most likely explanation. In this time, palaeontologists and members of the public alike went wild with fantastical recontructions of this new and wacky beast, some even going as far as noting that the arms were used much like those of a giant sloth. Alas, in 1972 John Ostrom (the guy responsible for revolutionising the way we think about dinosaurs in relation to birds in the 60s) noted that the bones in the forearm of Deinocheirus appeared similar to those found in the ornithomimosaurs, a group of secondarily-herbiverous theropod dinosaurs very similar to modern ostriches. This agreed with the sentiments of the team that initially discovered Deinocheirus, so it was settled, the beast was in fact an ornithomimosaur. Mystery solved. Right?

Dem Claws.

Dem Claws.

Unfortunately not. Fast forward a little over 40 years later to October 2013, and we still hadn’t found any more remains of the all-too mysterious Deinocheirus. That was all to change. At the SVP 2013 Symposium (one of the biggest annual events in palaeontology) there were hushed, exciting whisperings of new Deinocheirus material (apparently, I couldn’t afford to go). And then, a speaker emerged and confirmed it, Deinocheirus was back, the mystery was apparently solved. New material had been discovered and we now had a 95% complete skeleton to work with. However, this wasn’t fully shown at SVP, and the entire palaeontological community had to wait with baited breath until the work was published. One of the greatest mysteries of 20th and 21st century dinosaur palaeontology had been solved, but we had to wait. It was agonising. Personally, I grew up enthralled with the mystery of Deinocheirus as did many palaeontologists, both young and old, so to be kept in the dark like this was painful.

The Big Reveal

Fast forward again, exactly (pretty much) to a year later. Late October 2014. A dreary-eyed, 20-something-year-old palaeo grad-student is almost hyperventilating over an image he found on Twitter. Ladies and gentlemen, Deinocheirus has landed. And bloody hell if it isn’t the weirdest thing we’ve ever seen.

Deinocheirus-990x980

The Beer-Bellied weirdo in all it’s glory. Deinocheirus mirificus.

Mystery Solved

Standing almost as tall as T. rex, and weighing in at a hefty 6 tonnes Deinocheirus is the biggest ornithomimosaur to dateSo it was big, no biggie right (heh)? Wrong, in addition to it’s monstrous size it’s also (and I might have already said this) bloody weird. With a really deep lower jaw, no teeth, huge forearms, relatively small hindlimbs, a big old “beer belly” (the best description of dinosaur’s anatomy ever, thanks Tom Holtz!) and tall neural spines (similar to those seen in SpinosaurusDeinocheirus sure is different to the ‘typical’ ornithomimosaurian body plan of Galimimus, with long legs and many other features that suggested it was a fast runner. Quite the opposite, Deinocheirus was a big, sluggish brute with a huge appetite. After 50 years, the mystery of Deinocheirus seems to be solved then, it’s a incredibly odd looking, slow moving, bulky, T. rex sized, beer-bellied behemoth. Myth busted, right?

Skeletal reconstruction of Deinocheirus mirificus. Modified from Lee et al. 2014.

Skeletal reconstruction of Deinocheirus mirificus. Modified from Lee et al. 2014.

Again, wrong. These new specimens are that good that we can already begin to hypothesise how Deinocheirus actually lived out it’s seemingly odd, slow lifestyle. Deinocheirus was discovered in the Nemegt Formation, a deposit which is 70 Million years-old (Late Cretaceous), and was an ecosystem similar to that of the Okavango delta today. First off, over 1400 gastroliths were present, probably used to aid in digestion of food, (mainly plants) making up for the lack of teeth. The morphology of it’s jaws and its broad bill (similar to those found in hadrosaurs and ducks) suggest that certain muscles associated with biting were small, meaning that Deinocheirus probably ate soft (and possibly water-dwelling) plants. But there wasn’t just some stones in that big beer belly, no sir! Evidence of a half-eaten fish was found as well, indicating that Deinocheirus was no means a fussy eater, and probably a ‘megaomnivore’ eating pretty much anything it could get it could swallow. This seems to fit well, especially when you consider Deinocheirus’ place in the Nemegt ecosystem, as generalist ‘all you can eat’ type deal (finally, a dinosaur I can relate to) it wouldn’t be in such harsh competition with the other herbiverous dinosaurs in the area that mostly ate plant matter from trees. However, not only do you need to outcompete you friendly neighborhood herbivores to keep on truckin’ in a Cretaceous world, you also need to be not eaten yourself. The main threat in the Nemegt ecosystem was probably the 12 metre long, 5 ton tyrannosaur, Tarbosaurus. However, Deinocheirus seemingly has an answer to everything by sacrificing speed for bulk and size, it was probably too big (and bloody hell, those claws) for Tarbosaurus to safely take on.

Deinocheirus_fin_colcorr_lres

Deinocheirus in situ. Image credit: Andrey Atuchin.

We also know a few more tricks that Deinocheirus had up its exceedingly large sleeves. Remember those Spinosaurus-like neural spines? They were probably there to support the bulky beer belly, similar to an “asymmetrical cable-stayed bridge“. It also had broadended tip-toes (pedal unguals, to be technical), allowing it not to sink when wading into wetter areas. And those claws? No longer used as lethal disembowlers, but for digging/plant gathering. So Deinocheirus seemingly was perfectly adapted to life on the braided, meandering rivers of the Nemegt ecosystem, unafraid of pesky Tarbosaurus, perfectly content to munch away until its heart (and beer belly) was content, and then waddling to the next patch of river to devour (and P.S Deinocheirus didn’t half walk funny).

And the moral of the story is…

By now, you’ve probably found literally hundreds of grammatical and spelling errors, due to the fact that I’ve been excitedly vomiting words onto my laptop in wave after wave of dino-induced mania. Yes it’s weird, and yes I love it because it’s pretty much me in dinosaur form, but why is this important? You’ll probably see this on IFLS (I F***ing Love Science) in a summary post, with ‘weird fat dinosaur discovered’ alongside ‘cure for cancer found’ and ‘artificial intelligence finally sorted’, making palaeontology, yet again look like the stupid and childish sibling of all the other sciences (e.g. “dino with big nose discovered”, unfortunately not a joke). But this is more than just some crazy guys with beards and stetsons finding a random pile of bones and shouting eureka until Nature finally publishes their work. Oh no. This, as well as many other finds over the last year shows us just how extreme dinosaurs can get. In the past 12 months, we’ve had a new, now with more swimming (TM) Spinosaurus recontruction, Dreadnoughtus, possibly the largest dinosaur ever, as well as long-snouted and pygmy tyrannosaurs. Not to mention feathered ornithischians (R). Dinosaurs have often been regarded as evolutionary extremes, and we’re only now beginning to understand just how these extreme animals lived and evolved.This understanding allows us to further understand evolution works, and how organisms can evolve in various environments and under different conditions.Not only is Deinocheirus a weird and wonderful beast, but when we look at it as a living, breathing animal, rather than a poster-child for all things weird and wonderful, we can begin to further understand  the evolutionary processes involved in theropods, a group which would garner the evolution of an incredibly diverse and successful group of animals, the birds. Deinocheirus exemplifies that palaeontologists, by investigating extremely adapted animals, such as dinosaurs, can further the understanding of the the process of evolution, one of the most important processes on Earth, and just how far it can go, and what wonderfully strange creatures it can help to explain.

So there you have it. Deinocheirus. It sure is a good day to be a palaeontologist.

What’s New(s) 31/01/14

So, only four days late putting this up.  I’ll save the things happening this week for Fridays post, but fear not! Plenty occurred in the paleontological world last week.  Some of it’s even non-Mesozoic (gasp!).

journal.pone.0084709.g020

Look at those ichthyosaurs go! Diversity remains roughly constant with the Jurassic throughout their Cretaceous range. From Fischer et al.

The last hurrah of the ichthyosaurs.  This group of iconic Mesozoic marine reptiles, who recently starred in TOTW, didn’t quite make it all the way to the K/T party, and went extinct during the late Cretaceous.  Traditionally the group has been seen as going out on a bit of a whimper after a lengthy decline from the Jurassic.  New work on European ichthyosaurs by Fischer et al has shown that this picture isn’t necessarily correct, with ichthyosaurs showing a pretty stable diversity throughout their existence, at least in Europe.

Screen Shot 2014-02-04 at 10.23.53

Polypterus having a breathe. From Graham et al.

Stem tetrapods can breathe easy with the news that Polypterus, a basal ray-finned fish, breathes air through its spiracles.   These large paired openings on its had have previously been argued to have a use in air breathing, but Graham et al have for the first time demonstrated this to actually be the case.  Stem tetrapods (the lineage of fish leading up to terrestrial vertebrates, including our friend Tiktaalik) possessed spiracles which have been linked to the transition to air breathing, and this work supports this argument.

Silesaur

Reconstruction of the size of NHMUK R16303 (grey) in comparison to a more normally sized silesaurid. From Barrett et al.

Giant Silesaurids!  Silesaurids are a group of Triassic archosaurs thought to be somewhere near the base of the dinosaur lineage, and so are important to understanding early dinosaur evolution.  Previously silesaurids have all been fairly small animals, particularly when compared to their later dinosaurian brethren.  Barrett et al have, however, described the femur of an unprecedentedly large silesaurid from Tanzania.  This specimen, with the catchy name NHMUK R16303, shows that silesaurids gained bigger sizes than previously thought, bigger than some early dinosaurs, with implications for ideas of why and how dinosaurs were so successful.

Penguinterrogation

The paper just has pictures of bits of broken femur in, so instead here’s a picture of a penguin undergoing what appears to be some kind of interview. From Wikipedia.

An ancient seabird has been described from the Palaeocene of New Zealand by Mayr and Scofield, and unlike everything else described from this locality it isn’t a penguin!  While I love penguins as much as the next man, this fleshes out the picture of the avian fauna of this area shortly after the K/T extinction.  It also continues to expand the picture of the diversity of birds in the Palaeocene, showing that the dinosaurs were still doing pretty well.  Extinct indeed.

800px-Fishfinger1

Apologies for the decline in picture usefulness through this post, but it was a either this or a complicated schematic of the action of Hox genes which I’d have done a poor job of explaining.   From Wikipedia.

Fish fingers. For a long time, scientists have been trying to reconcile the digits of tetrapods with fishes’ fins.  These two structures that are superficially similar, but frustratingly different in layout.  While fossil data has been building up a picture of this transition, ‘evo-devo’ studies have also been providing valuable information.  One such recent study, by Woltering et al, suggests that the digits of tetrapods aren’t in fact homologous (ie. evolutionarily the same) to the fin radials in a fishes’fin.  This is based upon the expression of Hox genes (genes that dictate the layout of a developing organ) in zebrafish and mice.  When Hox genes from the fish were expressed in developing mice, they only affected development in the proximal parts (ie. arm) of the limb, suggesting fish don’t use the ‘digit-causing’ part of their genetic toolkit.  This in turn suggests the two structures are not homologous.

Taxon of the Week: Tiktaalik

Following all of the giant-rauisuchian based excitement of last week’s TOTW, I’ve decided to calm it down a bit by looking at an unassuming fish.  This particular unassuming fish has been in the news recently, and illustrates a transition without which there would be no Postosuchus, no mammals and (perhaps worst of all) no ‘Dinosirs’.  The fish of which I speak is, of course, the Devonian tetrapodomorph Tiktaalik roseae, but before we look at it closely, let’s have a look at the bigger evolutionary picture into which it fits.

Vertebrates that live on land are known as tetrapods, and all possess (or at least their ancestors possessed) four limbs with digits: amphibians, lizards, crocodiles, birds and mammals are all modern tetrapods. Despite their many obvious differences from what you’d typically think of as a ‘fish’, tetrapods are actually the largest group of lobe-finned fish, or sarcopterygians, named for their fins’ fleshy bases.  The only other modern groups of sarcopterygian are lungfish and the famous ‘living fossil’ coelacanth.

An African Lungfish: note fleshy-based lobe fins (from bbc.co.uk)

An African Lungfish: note fleshy-based lobe fins, as compared to the rayed fins of your goldfish. (from bbc.co.uk)

The most obvious difference between tetrapods and other fish is that the latter are aquatic and the former mainly terrestrial (with the exception of groups that went back into water, like whales and icthyosaurs).  At some point during the evolution of tetrapods they switched from an aquatic lifestyle to a terrestrial one, and this pretty drastic transition is of great interest to palaeontologists.   Originally pictured as being a case of fish struggling onto land and then evolving limbs, in recent(ish) years very early tetrapods from the Late Devonian (~365 Mya), such as Acanthostega and Ichthyostega, have changed this view.  These fossils have four limbs with digits, but appear to be fully aquatic, suggesting that the tetrapod body plan evolved in water first, only later proving handy (pun obviously intended) on land.

Acanth tol.web

Acanthostega having a swim with its digit-y limbs (from tol.web).

Various fish-like animals have been described that have body plans somewhere between these early aquatic tetrapods and the ancestral fishy form, and which are more closely related to tetrapods than the next closest group of sarcopterygians, the lungfish.  These animals are known as ‘tetrapodomorphs’, and show an evolutionary trajectory towards air breathing and a four-finned body plan, while still retaining fish-like characters such as gills and fin rays.  It has been suggested that this was as a result of them living in shallow rivers during the oxygen-poor Late Devonian, where being able to breathe air as well as oxygen dissolved in water would have been advantageous, as would being able to navigate shallow, relatively predator free, water.

Tikphylo

A phylogeny of selected tetrapodomorphs and tetrapods, showing the change in body plan from ‘fish-like’ to ‘tetrapod-like’. (adapted from Daeschler et al, 2006)

Enter TiktaalikTiktaalik is something of a celebrity amongst tetrapodomorph fish. Described in 2006 from fossils found on Ellesmere Island in Nunavut, Canada, its name means ‘Burbot’ in Inuktitut.  It was subsequently popularised by one of its discoverers, Neil Shubin, in his book ‘Your Inner Fish’ (recommended), and is even the star (or possibly victim) of its own song on Youtube.  This stardom is well deserved, as Tiktaalik gives us a good deal of interesting information on the water-land transition.

A burbot reacts with indifference to the news that a tetrapodomorph has been named after it.

A burbot reacts with indifference to news of its namesake.

The original fossil material of Tiktaalik consisted of a pretty spectacularly articulated front half of the animal, possessing a number of interesting features.  The animal was pretty ‘fish-like’, but with some tetrapod-like characters, such as large shoulders bones and pectoral fins with wrist-like joints, a neck, and a robust ribcage.  These qualities, together with the shallow river environment in which it appears to have lived, led to the suggestion that it might have used its robust fore-fins to prop it up in ‘press-ups’, lifting its head (with the help of its neck) above water to breathe.  While there was no knowledge of the back half of Tiktaalik itself,  the small pelves (plural of pelvis) of other tetrapodomorph fossils like Panderichthys, led to a ‘front-wheel drive’ picture of tetrapodomorphs moving largely with the fore-fins, with  ‘four-wheel drive’ locomotion, with all four fins (or limbs), being a tetrapod innovation.

Tiktaalik wiki

Front-wheel drive Tiktaalik (from wikipedia)

Earlier this week however, the back half of Tiktaalik (or at least some of it) was described, and it transpires that this picture of exclusively ‘front wheel drive’ tetrapodomorphs is incorrect.  Tiktaaliks pelvis and parts of the hind limb were recovered, and it turns out that its hind-fins were as large as its fore-fins, with a fairly good range of movement.  While still compatible with their function as ‘props’ mentioned above, this also suggests that it would have been able to do more in terms of fin-based movement, with the possibility of underwater gaits, like the ‘walking’ seen in African lungfish.  It also changes our picture of the evolution of limbs, suggesting that tetrapodomorphs became ‘four-wheel drive’ before the evolution of tetrapods.

Tiktaalik comparison

The change in beefiness of hind-quarters/rear fins in Tiktaalik from the original description, above, to the recent paper, below (images from Daeschler at al 2006 and 2014 respectively)

While this recent information has changed our picture of Tiktaalik, it just adds to its importance as a source of information on the water land-transition.  This unassuming Devonian fish, along with various other fishy friends, helps illustrate that many of the changes that we associate with living on land, such as breathing air and having limbs, actually evolved as adaptations to aquatic life.  This transition also acts as a prime example of the mosaic nature of evolution: tetrapods didn’t evolve gradually from a fish-like form to a tetrapod-like form, but instead evolved tetrapod-like characters piecemeal while retaining ‘primitive’ ones. This mosaic theme is one that comes up time and time again in evolution, and is one that we’ll be discussing in future blog posts.

Some more Tiktaalik revelling in all their newly reconstructed glory.

Some more Tiktaalik revelling in all their newly reconstructed glory (image from bbc.co.uk)

Further reading