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.

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What’s New(s): 11/04/2014

Avid readers of TDS, we have again not published as often as we’d have liked to over the last few weeks, as deadlines are piling up over here in TDS Towers. Fear not, as below is a bountiful harvest of palaeontological news, five of the most succulent morsels, handpicked by Richard and I, for your entertainment.

Embry-old

Fossilised creatures generally, even those as big as dinosaurs are pretty rare. The forces of nature and preservation all stack up against palaeontologists when we try and find fossils. So when very small fossilised early stage embryos from over 500-million-years-ago are found, it certainly doesn’t go unnoticed. Whilst not new to science, the latest publication of fossil embryo’s gives some much needed insight into how such small and delicate structures were fossilised. Researchers from Missouri and Virginia Tech have found fossilised embryos in the Shuijingtuo Formation (China) which are around 500 million years-old (from the Cambrian period). Despite not being the oldest fossilised embryos (the fossil record of embryos stretches back beyond 580 Mya in the Doushantuo Formation, Pre-Cambrian), the Shuijingtuo embryos contain the soft tissue impressions of the chorion (the fertilisation envelope). The authors also suggest that in this fossil deposit, the preservation of these soft tissues is more common due to these tissues being (somehow) selectively phosphatized. At this point, how these small and rare embryos got to be preserved is all that is known of the Shuijingtuo embryos, but future discoveries on what organisms these embryos belonged to, or even better preserved embryonic soft tissues will prove to be very exciting reads in the months and years to come.

Whilst not the embryos in question, they have caused a massive stir over the years.

Ancient ‘Sp-eye-ders’ from M(ontce)A(u-les-Mines Lage)RS(tätte)

I’m (Ryan) a huge arachnophobe. So I wasn’t best pleased when Richard brought this (albeit interesting) tidbit of news to my attention. A new extinct species of harvestman from the Carboniferous, Hastocularis argus, was recently discovered in France which has allowed the authors to comment on the evolution of the group. It’s also thrown up some eye-opening surprises. Before I continue on the subject, the jovial title of this story is wrong. Whilst harvestmen are arachnids, they aren’t spiders, they’re actually more closely related to mites. Regardless, the discovery of H. argus has allowed Garwood et al. to investigate the origins of harvestmen more closely, as the exoskeletons of these arachnids are rarely preserved in the fossil record. With the creation of a new mite suborder, Tetrophthalmi (which includes H. argus and the Devonian species, Eophalangium sheari), Garwood et al. have, contrary to previous beliefs, argued that the diversification of modern harvestmen occured later in geological time (Carboniferous, rather than Devonian).

The (albeit not so scary looking) Hastocularis argus rendered in full 3D glory.

The (albeit not so scary looking) Hastocularis argus rendered in full 3D glory.

Modern harvestmen have just a single set of eyes, the medial pair (central). However, the 305-million-year-old H. argus has two pairs of eyes, a medial and a lateral (outer) pair. In the same paper, Garwood et al. report that work on modern harvestmen has revealed that despite the passage of over 300 million years, they still retain some genetic framework for these lost lateral eyes. This paper (despite being on arachnids *shudders*) is pretty great, as it combines modern 3D visualisation techniques (CT scanning), phylogenetics and some genetic work in order to really get a handle on the origins of a previously poorly known group. This again proves that the combination of palaeontology and biology is a real ‘dream team’ when it comes to unearthing evolutionary relationships.

 Cambrian heart-thropod’s gets palaeontologists’ blood pumping

I genuinely rewarded myself with a break after making that title, the puns have (if I do say so myself) been exceptional this week. Regardless, a fascinating insight into the evolution of the cardiovascular system has been published in Nature Communications this week (7th April). An exceptional specimen of Fuxianhuia protensa, a 520-million-year-old arthropod from Chenjiang deposits has been described, and with a cardovascular system almost intact. Even though the phylogenetic placement of Fuxianhuia is controversial to say the least, in 2012 it was discovered that Fuxianhuia had a relatively complex brain, suggesting by the early Cambrian, arthropods already had similar visual capabilities as modern insects.

 

Fuxianhuia reconstruction from Ma et al. (2014). a) cardiovascular system and CNS; b) whole body reconstruction; c) cardiovascular system in relation to the gut.

Fuxianhuia reconstruction from Ma et al. (2014). a) cardiovascular system and CNS; b) whole body reconstruction; c) cardiovascular system in relation to the gut.

Perhaps it is a tad unsurprising that this latest Fuxianhuia discovery reveals that the cardiovascular system of arthropods from the early Cambrian were relatively advanced, and more than able to keep the ‘complex’ brain oxygenated with blood. The combination of an advanced cardiovascular and neural/visual system has led Ma et al. to conclude that F. protensa had well developed sensory (using vision and its antennae) system, and in life it was a highly mobile forager. They also conclude that even by the Cambrian Explosion, arthropods had evolved many advanced biological systems.

Teenage Mutant Ninja Hupehsuchians, swimming in a half shell.

Because what would a blog post on TDS be without a marine reptile? (Also, it’s taken until the 4th news piece to get to a tetrapod, what is this nonsense?). Moving on swiftly, the next discovery presents a new species of marine reptile, Parahupehsuchus longus. After taking a quick look at the holotype of P. longus (pictured below) you’d be very much forgiven if you thought it was an early Triassic ichthyosaur. P. longus is in fact a hupehsuchian, which a group of diapsid reptiles from around 250 Ma, and are known exclusively from one locality, in Hubei Province (China).

An incredibly dumb looking hupehsuchian, Nanchangosaurus (a close relative to Parahupehsuchus).

An incredibly dumb looking hupehsuchian, Nanchangosaurus (a close relative to Parahupehsuchus).

So what makes Parahupehsuchus so cool? Well in its defenceP. longus has a weird expansion of its ribs (similar to the ribs of turtles, that’s how they ‘make’ their carapace) which overlap to form a ‘bony tube’. As indicated by the aforementioned pun, Chen et al. think that this is used as a defence mechanism. Whilst the fact that the same kind of defence mechanism (revolving around the expansion of the ribs) has convergently evolved in at least 2 groups of marine diapsids is fairly interesting, it’s the wider implications of this discovery that really make Parahupehsuchus cool. What does any creature needs a defence mechanism for? That’s right Captain Obvious, defence. This almost definitely means that during the early Triassic, there were large predators and a higher trophic level was present at this time. This is odd, you wouldn’t expect this trophic level to recover so quickly after the Permo-Triassic extinction event (commonly referred to as ‘when life nearly died’, so you know, it’s pretty potent). Chen et al. make 2 pretty bold claims from this one discovery, stating that the recovery from the event was faster in the marine realm (specifically faster in marine predators) and that this marine tetrapod predator trophic level is probably the first one ever to emerge in evolutionary history.

Bird’s and pterosaurs had to Cope with one another

Cope’s rule, simply put is a hypothesis that states evolutionary lineages, over time, increase in size. Pterosaurs have long been the poster child of Cope’s rule in the fossil record (along with horses) going from small rhamphorhynchids in the late Triassic to the huge (and probably flightless) azhdarchids of the Cretaceous. The study by Benson et al. set out to try and understand this apparent trend in pterosaur size evolution further. They found that up until the late Jurassic/early Cretaceous the average wingspan didn’t really go above 1m, and over the cretaceous there was a sustained increase in wingspan, until you reach the monstrous 10m+ wingspans of azhdarchids such as Quetzacoatlus northropus.

Obligatory funny, only very slightly related picture.

Obligatory funny, only very slightly related picture.

A controversial notion that it was the emergence and radiation of the (somewhat smaller) birds in the late Jurassic/early Cretaceous that drove the evolution of large size in pterosaurs. In a unexpected turn of events, Benson et al. actually suggest that this may well be the case, citing a possible combination of ‘intrinsic factors’ (such as terrestrial living in azhdarchids and other flight mechanisms in other groups) and ‘extrinsic factors’ (such the evolution of birds, which would have taken the niches occupied by small aerial feeders away from the pterosaurs) as the cause of the switch to selection of a larger body size in pterosaurs. It just goes to show that competition can be, in some cases, used to explain macroevolutionary processes and patterns.

References

Brose, J. et al.  (2014) Possible Animal Embryos from the Lower Cambrian (Stage 3) Shuijingtuo Formation, Hubei Province, South China. Journal of Paleontology: March 2014, Vol. 88, No. 2, pp. 385-394.

Garwood, R. J. et al. (2014). A Paleozoic Stem Group to Mite Harvestman Revealed through Integration of Phylogenetics and Development. Current Biology, http://dx.doi.org/10.1016/j.cub.2014.03.039.

Ma, X. et al. (2014). An exceptionally preserved arthropod cardiovascular system from the early Cambrian. Nature Communications 5, 3560, doi:10.1038/ncomms4560.

Chen X-h, et al. (2014) A Carapace-Like Bony ‘Body Tube’ in an Early Triassic Marine Reptile and the Onset of Marine Tetrapod Predation. PLoS ONE 9(4): e94396. doi:10.1371/journal.pone.0094396

Benson et al. (2014). Competition and constraint drove Cope’s rule in the evolution of giant flying reptiles. Nature Communications 5, 3567, doi:10.1038/ncomms4567.