Taxon of the week: Euphanerops

Having been treated to a dinosaur last time in taxon of the week, this week I’ve decided to go for an obscure Palaeozoic fish.  This fish is pretty obscure even for a Palaeozoic fish; so obscure, in fact, that it doesn’t even have its own Wikipedia article.  I speak, as you’ll know if you bothered to follow that link, of the Devonian jawless fish Euphanerops.

Screen Shot 2014-03-06 at 09.50.15

Euphanerops in all its fossilised glory (Sansom et al, 2013)

Loathe as I am to introduce even more palaeontological nudity to The Dinosirs, Euphanerops is a so-called ‘naked anaspid’, a group that look similar, but not the same, as modern lampreys.  The naked anaspids consist of a handful of taxa that are united by the fact that they look a bit like members of a larger group, the anaspids, but don’t have their distinctive bony scales.  Both groups look like they lie somewhere on the gnathostome stem-lineage, which we met when we looked at heterostracans a few weeks ago.  As we saw then, these stem-gnathostome groups are extremely important in understanding vertebrate evolution as they provide our only morphological information on how characters like jaws and paired fins evolved in vertebrates.

miguasha.ca Euphanerops

A lamprey-like reconstruction of Euphanerops. Ten points if you can spot the mistake before getting to the end of the post. (From miguahsha.ca)

The specific area onto which Euphanerops sheds light is the evolution of paired fins.  Jawed vertebrates today all possess paired fins, whether as traditional ‘fins’ or as limbs in tetrapods (although some, like snakes, have secondarily lost them).  Modern jawless vertebrates, the lampreys and the hagfish, have no paired fins, they have only single ‘median’ fins down their midline.  Unfortunately this gives us no information regarding how paired fins evolved, for all we know they may have just popped into existence.  One avenue of investigation in solving the puzzle is evolutionary developmental studies (evo-devo), where the development of modern animals is studied for clues.  This gives us intriguing hints, for example paired fins seem to develop in similar ways to both gill arches and median fins, suggesting a possible shared evolutionary origin.  They can also be induced to develop along a lateral line along the sides of the body.   However, if we want to know how the structure changed morphologically we have but one recourse.  To the fossil record!

SansomPhyloOrig

A cartoon phylogeny of vertebrates with handy colour-coded fins. Green for dorsal fins, blue for anal fins and red for paired fins. Mixes arise from combinations (from Sansom et al, 2013).

Fossils clear up the picture quite a lot.  The earliest ‘paired fins’ we see are in groups like the thelodonts and the (clothed) anaspids, but these are all paired ‘fin-folds’, fin-like structures that lie paired along the body in vaguely the same place as pectoral fins, but which have no skeleton supporting them. Some heterostracans, such as Pteraspisalso have bony paired fin-like projections from their head-shields, but it looks like these are just convergent adaptations rather than actually being fins. Osteostracans, a group with a wide array of fancy head shields, have the first paired fins as we know them today, with a skeleton on the inside (like your limb bones).  They only had pectoral paired fins (ie. the front fins of a fish, or your arms), and the skeleton was made of cartilage, but they were paired fins nonetheless, although some groups of osteostracan secondarily lost them again.  Later, in jawed groups such as the placoderms, we finally see the full complement, of pectoral and pelvic paired fins.

anaspid fin folds wikipedia

Anaspids (of the clothed variety) with fin-folds coloured in green (from Wikipedia).

Combined with the molecular evidence this progression from no paired fins to paired fin-folds to paired fins with skeleton has been used to propose an evolutionary mechanism.  The story runs that lampreys and hagfish have a single stripe of ‘fin-competency’ down their midline, where fins can develop.  This stripe was somehow double and spread onto the sides of groups such as anaspids, allowing paired fin-folds to develop on the sides as well.  These paired ‘fin-competency’ zones then began to interact with the developmental tissue that bone is formed from, leading to skeletonisation of the fin in later groups, and eventually to the complex fin skeletons we see today.

Yonei-Tamura

This figure shows the proposed spread of a line of ‘fin-competency’ first from the midline onto the flanks to create ‘fin-flaps’ in various places, and then interacting with other developmental tissues to create the familiar skeletonised fins we see today at the bottom (from Yonei-Tamura et al, 2008)

This seems like a good explanation, and fits the evidence well.  Euphanerops makes the picture a bit more complicated however.  The genus has been known for a long time, and is also interesting in that some fossils appear to preserve a lamprey-like gill skeleton, which would imply that this is ancestral for gnathostomes.  Our interests lie however in the realm of paired fins, and in 2013, a fossil was described as having paired fins.  In itself this is not unusual, as the similar anaspids sometimes have paired fins in a position roughly where pectoral fins are in modern fish.  Euphanerops however has paired fins where the anal fin is in a modern fish, ie. between the anus and the tail.  This state of affairs is not known in any modern fish, or in any other extinct ones we know of.

Paired fin comparison

The paired anal fins of Euphanerops fossilised above and outline below (from Sansom et al, 2013)

This has interesting implications for the evolution of paired fins.  It seems that rather than just following a progression from no fins to paired fins, evolution had a period of ‘experimentation’ with paired fins in different places before settling on the paired fins we see today.  This fits in with our overall picture of evolution: while it can be tempting to think that it ‘progresses’ towards an aim, in fact it occurs piecemeal, leaving behind a mosaic of different ‘experiments’ with morphologies.  It’s also worth noting that lines of fin competency idea of fin evolution mentioned before isn’t overturned by Euphanerops and its paired fins, but our picture of paired fin evolution is broadened.

Screen Shot 2014-03-06 at 09.49.35

Euphanerops restored with paired anal fins! (Sansom et al 2013)

So, far from being merely an unclothed anaspid and a Twitter handle that rolls off the tongue, Euphanerops and its paired fins have much to tell us about both paired fin evolution and wider evolutionary principles.  Like Limusaurus last week it also illustrates how palaeontological and molecular methods can be used in a synthesis to better understand evolution.   Pretty impressive all round for a fish that not even Wikipedia loves*.

*But I love you Euphanerops!.

 

References

Sansom et al (2013) Unusual anal fin in a Devonian jawless vertebrate reveals complex origins of paired appendages.

Janvier et al (2006) Lamprey-like gills in a gnathostome-related Devonian jawless vertebrate.

Yonei-Tamura et al (2008) Competent stripes for diverse positions of limbs/fins in gnathostome embryos.

Johansen (2010) Evolution of paired fins and the lateral somatic frontier.

 

What’s new/s 03/03/14

What’s news has been neglected a bit over the last few weeks, but fear not! Here are five exciting palaeo news stories from the last month or so:

Placoderm faces

For no particularly good reason, placoderms are a group close to my heart.  This group of fish existed during the Devonian, and are the earliest example of vertebrate with jaws in the fossil record,  As well as being generally awesome, they are also crucial to understanding how gnathostomes, the jawed vertebrates, evolved from their jawless ancestors.  Dupret et al have CT imaged a primitive placoderm, Romundina, and have shown that it has a mixture of jawless fish (‘agnathan’) and gnathostome  cranial  characters.  As with so much of evolution, the transition to attaining jaws seems to have been piecemeal, part by part, an example of mosaic evolution, with cerebral proportions remaining largely unchanged with the evolution of jaws.

Romundina

Romundina in all its glory. This is the head with front end to the left, the large, round holes are the orbits. (from phys.org)

Even more Burgess Shale

The Cambrian is famous for the weird and wonderful fossil taxa that existed during it, and the most famous Cambrian fossil site is the Burgess Shale, in the Canadian Rockies.  Since the early 20th century the incredible preservation of this site has given us an invaluable window into life 500 million years ago.  While the Burgess Shale animals were famously argued by Stephen Jay Gould to represent experimentations in body plans alien to anything alive today, more recent work has shown that actually these animals are early relatives of groups such as arthropods (ie. insects, crustaceans etc) and vertebrates (ie. you).  The other week another site was described from the Burgess Shale; hopefully this will mean we’ll see lots of new Cambrian beasties over the next few years, as well as more information on known ones,  continuing to fill in our picture of early animal evolution.

Burgessnew

A range of weird and wonderful Cambrian fossils from the new assemblage. (from Caron et al)

Aquatic Acanthostega

We already met Acanthostega, the earliest known tetrapod, a few weeks ago, when we were looking at Tiktaalik and the transition of vertebrates onto land.   Acanthostega possesses a mixture of aquatic and terrestrial qualities: like a fish, it has gills and a tail fin, but like a modern tetrapod it had digits and a ‘neck’ between the head and body.  This has been taken to demonstrate that tetrapods actually evolve many ‘adaptations to land’, such as digits, while the still lived in water, in contrast to the historical view that a (presumably rather optimistic) fish crawled onto land and only then adapted to it. Recent work by Neenan et al suggests that Acanthostega’s jaw was adapted to aquatic, rather than terrestrial, feeding, which they argue refutes recent suggestions that it might have fed on land, or at least above water.

Optimistic fish

An optimistic fish (from Pixar.wikia.com)

Playing around with flight

Imagine, if you will, a bird.  Chances are that you’re imagining something that’s probably feathered and beaked*.  The fossil record, however, shows us that many traits that we associate with birds, such as feathers and beaks, evolved before birds came into existence as a group.  Feathers are perhaps the best example, found in many dinosaurs not particularly closely related to birds, but it is also true of various skeletal characters.  Work by Mark Puttick and others shows that this is the case with the comparatively long forelimbs of birds, which originated before the origins of the group, amongst earlier dinosaurs.  Gliding dinosaurs like Microraptor suggest that many groups were independently evolutionarily ‘playing around’ with feathered gliding, it was just the birds that happened to evolve powered flight and make it through to today.

*If not, you may want to double check that you know what a bird is.

Microraptor

Microraptor: Evolutionary experimentation with flight? (from nhm.co.uk)

Primitive live birth in ichthyosaurs

As we’ve seen before on The Dinosirs, ichthyosaurs were a very successful group of Mesozoic reptiles, highly adapted to an aquatic life.  One oft quoted adaptation viviparity, or live birth, as a fully aquatic amniote can’t get back onto land to lay eggs.  This is also seen in other groups of marine reptile, such as plesiosaurs and mosasaurs.  However, a recent paper by Motani and others has suggested that actually live birth was present in ichthyosaurs’ terrestrial ancestors before they became aquatic.  They argue this based on a fossil of a very early ichthyosaur, Chaohusaurus, which appears to have been fossilised giving birth.  While this is fairly common in ichthyosaur fossils, all previous fossils have been found giving birth to babies tail first as in modern day whales, possibly as an adaptation to prevent suffocation.  This fossil demonstrates that Chaohusaurus  gave birth head first, as in most terrestrial vertebrates.  Motani et al argue that this demonstrates that ichthyosaurs evolved from terrestrial viviparous ‘head first’ ancestors, only later switching round as an adaptation to marine life as in whales today.  This is contrary to the traditional view, but does fit with our picture of modern reptiles: many groups of lizard are viviparous.

Viviparity icthyo

Chaohusaurus.: green, red and blue below are the ribs, paddle and tail of the mother respectively. Small ichthyosaur can be seen com in out headfirst in yellow. (from Motani et al)

 

References

Dupret et al (2014) A primitive placoderms sheds light on the origin of the jawed vertebrate face, Nature

Caron et al (2014) A new phyllopod bed-like assemblage from the Burgess Shale of the Canadian Rockies, Nature communications

Neenan et al (2014) Feeding biomechanics in Acanthostega and across the fish-tetrapod transition, Proc. Roy. Soc. B

Puttick et al (2014) High rates of evolution preceded the origin of birds, Evolution

Motani et al (2014) Terrestrial origin of viviparity in Mesozoic marine reptiles indicated by Early Triassic embryonic fossils, PLOS One

Taxon of the Week: Limusaurus

As a treat, this week’s Taxon of the Week is a dinosaur. Even better, it’s a dinosaur with very small hands. Despite it’s small hands, it’s managed to cement itself amidst a pretty sizeable debate, yes ladies and and gentle, this week’s TotW is Limusaurus inextricabilis.

The facts

Limusaurus was discovered in 2009 by Xing Xu, a Chinese palaeontologist whose seemingly always discovering a new species of dinosaur (over 30 valid species to date). At around 1.7m in length (roughly the size of a large-ish dog), Limusaurus was far from the biggest and most exciting looking new dinosaur of 2009, however, it was certainly a bit weird:

  • For starters it’s the first Asian ceratosaur ever described. Yes, you heard right a ceratosaur.
  • For your main course, it’s herbiverous.
  • To finish off with dessert, it’s got a beak.
Limusurus. Not your average ceratosaur.

Limusurus. Not your average ceratosaur.

True, whilst indeed not your average ceratosaur (or for that matter, theropod) such traits aren’t that weird in primarily carniverous clades. Within Theropoda, there’s many secondarily herbiverous taxa, incl. everyone’s favourite weirdo taxon, the therizinosaurs. Let’s also not forget the well known beaked herbiverous theropods, ornithomimosaurs. Oh, and did you know crocodylomorphs had a crack at beaks and herbivory (of course they did). Even though I keep harping on about its small hands, for frak’s sake, just take a look at alvarezsaurs (with even more pathetic arms than T. rex). So why exactly am I taking the time to blog about Limusaurus?

Mononykus trying, the meme that couldn't be due to it's preposterously pathetic forelimbs. Hastily drawn by me.

Mononykus trying, the meme that couldn’t be due to it’s preposterously pathetic forelimbs. Hastily drawn by me.

A debate as simple as 1, 2, 3

If you’re a fan of dinosaurs/palaeontology then you should be aware that birds evolved from theropod dinosaurs. News flash: this isn’t new. This notion really started to gain ground after seminal work by John Ostrom in the late 1960s/early 1970s (including that famous drawing of the ‘naked Deinonychus‘ as Richard likes to call it) who noted a lot of avian-like features in Deinonychus. On top of that, palaeontological records show multiple transitional forms between smaller theropods and birds (e.g. the ever eminent Archaeopteryx), and even some of the larger theropods show avian affinities (e.g. the cranial pneumatic sinuses found in Alioramus). Those are only a select few pieces of evidence that have made the evolutionary link between birds and theropods almost undeniable, there’s a so many more, it’s astounding (incl. inferred behaviour, such as avian sleeping positions in theropods: Xu & Norell 2004, and apparent egg brooding behaviour in Oviraptor: Norell et al. 1995). Watch the video if you need more peer reviewed proof that dinosaurs (even if they did look a bit like birds) were awesome. Try and show a little respect.

However, there’s always new discoveries that just love to get people arguing. The issue revolves around digit homology/identity. Essential, theropods (via evolution) ‘lost’ two fingers (digits) to arrive at the three-fingered hand seen in most theropods (aside from the aforementioned ‘weird taxa’, who lost more than 2). The same is true for birds. However, the debate revolves around which digits are lost, and which 3 form the fingers of the hand. In tetanurans (essentially the more advanced theropods, and by extension birds), it has long been thought that digits IV and V were lost, leaving a three-fingered hand consisting of digits I, II and III. Now, you’d expect birds, by being derived tetanurans to have this digital formula.  Well that would be nice wouldn’t it. Unfortunately the question of I,II,II or II,III,IV in modern birds has been debated for a very long time. New evidence in the mid-late 1990s from developmental and genetic studies showed us that the three digits of the avian hand actually developed from digits II, III and IV. Gasp, a spanner in the works!

This new evidence was then used (rather wrongly) to attempt to oppose the hypothesis that birds evolved from dinosaurs (Feduccia 2002). While I agree, the 90s developmental evidence from modern birds creates some novel evolutionary dynamics to investigate, it cannot be used to deny the whole host of other evidence that links dinosaurs to birds. Following on from the developmental studies, genetic studies in the early 2000s showed that during the ontogeny of some birds, the digit identity would change from the initial II,III,IV to I,II,III. This led to the occurrence of the ‘Frame Shift’ hypothesis, which suggests that certain genetic pathways associated with dinosaur/avian digit identity allow for ‘rapid’ changing of digit homology throughout dinosaurian/avian evolution (at it’s core, and that’s a very simplified summary). Not to be bogged down by detail (genetics isn’t my strong suit), developmental geneticists thought they’d cracked it, and that the change in digit identity over avian/dinosaurian evolution was likely to have been caused by these frame shifts.

Feduccia's (2002) argument in a nutshell.

Feduccia’s (2002) argument in a nutshell.

Enter Limusaurus. So, finally, we come to Limusaurus’ role in all of this. In 2009, Xu et al. looked at Limusaurus’ small hands and went “you know what, that’s a reduced digit I” (NOT ACTUAL QUOTE), which makes Limusaurus’ digit identity II, III, IV. As we discovered right at the start of this article (before the I made my lack of genetics knowledge crystal clear), Limusaurus is a ceratosaur, which isn’t a tetanuran, but a more primitive theropod, meaning that the II,III,IV digit identity may well be shared by most/all tetanurans, with Limusaurus representing an intermediate of sorts. Thus Xu et al. state that the digit identity of Limusaurus is more in favour of a slower, stepwise acquisition of the digit identity seen in advanced tetanurans, and eventually birds. But, as the famous saying goes, you know what small hands means…(small gloves?)

That’s right, a big controversy.

If you're confused (don't worry, so am I), this may help.

If you’re confused (don’t worry, so am I), this may help.

The small gloves are off

The Xu et al. (2009) caused a fairly serious debate, with authors such as Vargas et al. arguing that the digit condition seen in Limusaurus is derived, and based on developmental and genetic work that they (Vargas et al.) carried out, suggest that faster genetic shifts occurred in the evolution of birds. Xu et al. quickly responded (and quoted  Arthur Conan Doyle in a somewhat dramatic conclusion) and argued that the shift proposed by Vargas is not likely when the digit (and manus) morphology of fossil tetanurans is considered.

I’d sincerely like to end this post with a succinct conclusion, saying that the debate has, over the last few years been wrapped up. However, such large debates in palaeontology, due to the very nature of our field (i.e. everything we love is dead) are rarely fully resolved. This case is no exception. Researchers from Yale (Bever et al. 2011) and other top world universities have stated time and time again that the frame shift hypothesis is still viable in the context of avian evolution, and in a recent summary by Xu and Mackem, Xu is not so sure, saying neither hypothesis has evidence to topple the other. Not one for revelling in an unnecessarily depressing ending (*coughs* Firefly) I’ll leave you with this: yes, we can’t always find all the answers to big questions in palaeontology and evolution, but by creating a synergistic relationship between palaeontology and biology (genetics, evo devo etc.), future discoveries in both fields are sure to shed some light on even the biggest of debates.

If you’d like to read more on this subject, and weren’t put off by my murdering of the genetics side of things, then I’d highly recommend the aforementioned Xu & Mackem (2013) paper for a recent summary of the field (see references below, it’s in bold).

References

Xu, X. et al. (2009). A Jurassic ceratosaur from China helps clarify avian digit homologies. Nature 459, 940-944.

Xu, X. & Mackem, S. (2013). Tracing the Evolution of Avian Wing Digits. Current Biology 23, R538–R544 (and references therein).

Bever, G., S. et al. (2011). Finding the frame shift: digit loss, developmental variability, and the origin of the avian hand. EVOLUTION & DEVELOPMENT 13:3, 269–279.

Vargas, A.O., Wagner, G.P. & Gauthier, J.A. in Nature Proceedings (2009).

Vargas, A.O. & Wagner, G.P. Frame-shifts of digit identity in bird evolution and Cyclopamine-treated wings. Evolution & Development 11, 163-169 (2009).

Young, R. L. et al. (2011). Identity of the avian wing digits: problems resolved and unsolved. Dev Dyn. 2011 May;240(5):1042-53.

Taxon of the Week: Beelzebufo.

Yet again, Richard and I are falling behind on delivering on the blog front. For that, we apologise. The next 7 days (hopefully) should bring numerous posts to make up for lost time, including an opinion piece!

Anyway, on with the show. If you follow palaeontological news in any sense, then you’ll probably have heard about a new marine reptile called Atopodentatus. If you haven’t heard of Atopodentatus, imagine if you will the offspring of a basal sauropterygian, Predator, and Cthulu that potentially could have filter fed. Or, you could just check out Brian Switek’s well written Atopodentatus article (with pretty pictures). That’s right, this week we’re going against the grain, and focusing in on a big Cretaceous amphibian, that’s made for a big controversy. I assure you, it’s going to be ribbeting.

Big facts: “we’re gonna need a bigger pond”.

This week, our TotW is Beelzebufo ampinga. Before we knuckle down and attempt to remove the f(r)og from the controversy, let’s get down to the basics. B. ampinga was discovered in 2007 by a team from Stony Brook University from the Maevarano Fm, Madagascar, the remains dated to 70-65Ma (late Cretaceous). The initial paper had little to work with, as the holotype only consists of a few cranial elements, with a few vertebrae, a urostyle and a tibiofibula. However, even with such few remains, the initial size estimates for Beelzebufo are astonishing: with a length of over 40cm, and its head alone estimated at half that in width (20cm!). This immediately bestows Beelzebufo with the crown of the largest frog to ever have lived. Beelzebufo was initially placed within the Ceratophryinae (the common horned frogs), which is unusual and is the basis of most of the controversy surrounding B. ampinga (more on that later). Due to it’s phylogenetic position, Beelzebufo has hyperossification in the skull, stabilising connections between the upper jaw and the skull, a huge mouth, oh, and sharp teeth. What does this mean? Well, like all other ceratophyrines Beelzebufo probably was carniverous, and by being so large, many agree that it would have been an ambush predator of small vertebrates, such as small/baby dinosaurs. So a frog that eats dinosaurs, no wonder they called it Devil Frog.

Evans2008

The holotype of Beelzebufo. Bones that were discovered in white. Modified from Evans et al. (2008).

Earlier in 2014, Beelzebufo was back. This time a (open access!) paper was published, showing off many new specimens of the Devil Frog. These specimens (64 since 2007) were far more complete than the original published findings, and have shown us that it was far weirder than previously imagined. It also gave us a more complete picture of B. ampinga as an organism and as a species. By looking at the squamosal of different individuals it became apparent that there was a lot of intraspecific variation present in B. ampinga, with a size difference of up to 20% present between certain individuals. This has found to be caused by different individuals having different bone growth rates and patterns. Now, the simplest explanation is everyone’s favourite, sexual dimorphism (in modern ceratophryines, the females are larger than males in 90% of cases). However, studies on extant frogs have shown that bone growth patterns and maturation times in anurans can be dependent on other factors such as seasonal food and water availability, as well as temperature.

SOON.

SOON.

Another intriguing fact is that Madagascar at that time was seasonal arid, with dry periods being especially water-sparse. So how does a large amphibian like Beelzebufo cope? Again, material from the 2014 publication (Evans et al. 2014) helps us to possible answer this. Hyperossification (especially in the skull) is prevalent in Beelzebufo. This is apparent in the initial discovery also, but combine this with evidence from Evans et al. (2014), features such as the loss of a tympanic membrane, tall neural spines and cranial exostosis go some way towards confirming that Beelzebufo was a burrower. Thus enabling it to escape desiccation during extreme dry spells. Not only did Evans et al. (2014) provide us with a wealth of new information on an important fossil anuran, but it also came with some fantastic 3D skeletal morphological reconstructions.

Evans2014

The aforementioned pretty digital reconstruction. Also, those posterolateral flanges, phwoar. Modified from Evans et al. (2014).

Big controversy

As has been eluded to, Beelzebufo caused a big splash. Evans et al. (2008) placed B. ampinga within Ceratophryinae, a subfamily found only in South America, based on mainly cranial characters and a supporting phylogenetic analysis. Evans commented that the discovery of a late Cretaceous ceratophryine in this area is ‘unexpected’. Indeed, if you look at the palaeobiogeography it still looks squiffy, with the Madagascar-Seychelles-India tectonic plate losing contact from South America 120 million years-ago. However, even this is debated. Multiple lines of evidence now suggest some land-link was present between South America and Madagascar, including many molecular studies (ratite birds, iguanin lizards et al.) and physical similarities present between South American and Madagascan dinosaurs, crocodyliforms and mammal. So a ceratophryine from the Cretaceous of Madagascar isn’t so crazy, right?

Wrong. Two years after the initial Evans publication Ruane et al. (2010) carried out rigorous testing on the phylogenetic position of Beelzebufo. In Evans et al. (2008), it was apparently established that B. ampinga was a crown-group Ceratophryinae, and a sister taxon to the living Ceratophrys. Ruane et al. had a big problem with this reasoning, stating that the relationship between Beelzebufo and Ceratophrys is supported by 1 out of 81 characterstics, support values for the relationship between these two were also low in the phylogenetic study. Ruane et al. (2010) used molecular phylogenies (with data from extant anurans) in tandem with Beelzebufo, using it as a calibration point, to calculate the timings of the emergence of the MRCA (most recent common ancestor) of modern ceratophryines. With Beelzebufo used in this way, the emergence time of the ceratophryine MRCA was way before the times calculated by other studies, using well established datasets.Ruane et al. came to the conclusion that contrary to Evans’ initial hypothesis, Beelzebufo was a) not a sister taxon of Ceratophrys or b) definitely not a crown-group ceratophryine. However, Ruane et al. don’t really give us more than that, apart from saying it might be some sort of stem-group ceratophryine or a crown-group Hyloidea (a superfamily). If were throwing ballpark ideas around for the phylogenetic position of Beelzebufo, then I’m gunning for a stem-group Hynerian.

dominarrygelxvi

Dominar Rygel XVI, a fine example of Hynerian for all those nerds who don’t watch Farscape.

The Evanpire Strikes back

Not one for lying down Evans et al. (2014), now armed with many more specimens than last time around, resurrected the phylogenetic controversy surrounding B. ampinga. In the 2014 publication, the phylogenetic position of Beelzebufo was restored to the initial hypothesis, stating that Beelzebufo was indeed a crown-group ceratophryine, with this relationship holding true even when different tree-making steps and calibration points were used. Evans et al. also deal with many of the issues raised by Ruane et al. For example, Ruane et al. argue that the low support values between Beelzebufo and Ceratophrys indicate that they might not be sister taxon (and hence Beelzebufo isn’t part of the ceratophryine crown-group). Yet Evans et al. point out that support values are low even in studies that solely consider extant ceratophryids.

The fuzzy phylogenetic positioning given to Beelzebufo by Ruane et al. (maybe stem-group this, or crown-group that) is put under fire by Evans et al. I’ve already said that the Cretaceous MRCA emergence time is Ruane’s main argument against B. ampinga as a crown-group ceratophryine, however what I’ve not yet said (and what Evan’s et al. 2014 love to point out) is that Ruane et al. almost positively place another mid-late Cretaceous frog, Baurubatrachus as a ceratophryid (crown and/or stem), which still means that the MRCA is somewhere in the Cretaceous. Evans was quick (p.54) to point out that Ruane et al. at this point were being somewhat hypocritical in this regard. Finally, Evans points out that the hyperossification present in Beelzebufo is also present in living ceratophryids, another compelling line of evidence in support of the crown-group hypothesis. Despite being confident in their findings, Evans et al. still give a passing mention of the notion that hyperossification (and other ceratophryid characters) may be present due to convergent evolution, however, for the time being (and to conclude!) Beelzebufo appears to be (for the time being) a crown group ceratophryid. *Sighs*.

You've made it past the long-winded bit. Well done, have a pretty picture.

You’ve made it past the long-winded bit. Well done, have a pretty picture.

Big importance

Well done, you’ve made it through a very poorly written account of the s**t-storm which is the phylogenetic positioning of Beelzebufo. By this point, you’ve probably seen the words crown, stem, Beelzebufo, et al. and ceratophryine/d/inae enough to last multiple lifetimes, so then, why should we care about Beelzebufo and it’s position within the ‘tree of life’. You should care for two reasons: 1) the timing of the emergence of ceratophryids, 2) the importance of correctly using fossils in phylogenetic studies.

All glory to the importance of Beelzebufo. You will obey.

All glory to the importance of Beelzebufo. You will obey.

You should remember that the biogeography of Madagascar in the Cretaceous creates problems for the ceratophryid hypothesis. Ali et al. (2008, 2009 2011) have recently noted that land bridges between Madagascar and South America were severed by 115-112Ma. If this is true, (and presuming Beelzebufo and undiscovered others didn’t raft across the seaways, which is actually a large presumption, giving the thick skinned Beelzebufo would weather the salty waters well, for a frog) this pushes the emergence time of ceratophryids to before these dates. This is again contrary to studies that have found the emergence times of crown-group Hyloideans (a superfamily if you remember) to be around 88Ma. As has been stated many times of this blog, any fossil, even an incomplete specimen, if found in the certain places at certain times can cause palaeontologists/phylogeneticists/biologists to have to seriously reconsider the state of the field.

This leads nicely onto the second reason why Beelzebufo is important. Hypocritical arguments aside, Ruane et al., using Beelzebufo as an example, shows how any study using fossils as certain anchor points in phylogenetic studies MUST look closely at the phylogenetic position (and the evidence behind it) of the fossil taxa, and decide if this is appropriate. Any mistakes when involving fossil taxa in these studies affects conclusions with wide reaching implications, such as the divergence/emergence times of certain, and sometimes, very large clades.

And finally, Beelzebufo kinda looks like Hypno Toad. That’s pretty rad.

References

  • Evans, S. E. et al. (2008). A giant frog with South American affinities from the Late Cretaceous of Madagascar. Proc. Natl. Acad. Sci. USA 105: 2951–2956.
  • Evans S. E. et al. (2014). New Material of Beelzebufo, a Hyperossified Frog (Amphibia: Anura) from the Late Cretaceous of Madagascar. PLoS ONE 9(1): e87236. doi:10.1371/journal.pone.0087236
  • Ruane S. et al. (2011). Phylogenetic relationships of the Cretaceous frog Beelzebufo from Madagascar and the placement of fossil constraints based on temporal and phylogenetic evidence. J Evol Biol 24: 274–285.
  • Ali J. R., Aitchison J. C. (2008). Gondwana to Asia: plate tectonics, paleogeography and the biological connectivity of the Indian sub-continent from the Middle Jurassic through end Eocene (166–35 Ma). Earth-Science Reviews 88: 145–166.
  • Ali J. R., Aitchison J. C. (2009). Kerguelen Plateau and the Late Cretaceous southern-continent bioconnection hypothesis: tales from a topographical ocean. J Biogeogr 36: 1778–1784.
  • Ali J. R., Krause D. W. (2011). Late Cretaceous bioconnections between Indo-Madagascar and Antarctica: refutation of the Gunnerus Ridge causeway hypothesis. J Biogeogr 38: 1855–1872.

TOTW: Pteraspis

In the spirit of Ryan’s last TOTW, this week we will be looking at a member of the group of animals that my current work focuses on: Pteraspis, a heterostracan from the Early Devonian period.

The heterostracans were a group of armoured jawless fish, or ‘ostracoderm’, which lived in both saltwater and freshwater environments from the Ordovician to the Devonian period.  They were notable for their characteristic armour, with which they evolved a wide range of forms during their existence: some encased in box-like plates, others in smaller tesserae, some with flattened bodies, others with bizarre pointy nasal structures.  I’ll probably be subjecting you to a post on heterostracan morphological diversity later on, so don’t worry too much about taking notes.

Heterostraci1

Various types of heterostracan. Pteraspis is in the bottom right. (from Wikipedia)

Heterostracans are important to palaeobiology because, despite being jawless themselves, they lie somewhere on the ‘stem’ of the phylogenetic tree of the gnathostomes, or jawed vertebrates.  In the phylogeny below, the only two living clades are the gnathostomes (jawed fish, including us), which have jaws, paired fins and a bony skeleton, and the cyclostomes (hagfish and lampreys), which have neither jaws, paired fins nor bone.  This means that fossils are the only way we have of learning about how these characters evolved.  Heterostracans themselves are particularly interesting due to their bone, one of the first occurrences of this tissue amongst vertebrates.

Gnath phylo

A cladogram of vertebrate relationships. Note how all stem gnathostomes are jawless . Extinct groups marked with a cross. (from Purnell, 2002)

Enter our hero, Pteraspis.  This 20cm long animal is pretty famous as heterostracans go, and can usually be found swimming his way through any marine Devonian diorama (there’s a particularly good one in the National Museum of Scotland, Edinburgh).  The most striking thing about Pteraspis initially is its large bony head shield.  This is characteristic of all heterostracans, although the types of plate forming it and the shape vary dependent on the species.  Characters peculiar to Pteraspis and related genera are the long rostral (ie. nose) section and the large dorsal spine.  Also worth noting are the characters it lacked.  It had no paired fins, although it’s been suggested that the two wing-like protrusions coming out of its head shield served a similar function.  It also had no jaws or teeth.

Pteraspis_NT

A reconstruction of Pteraspis (from Wikipedia)

As the vast majority of living vertebrates have jaws and teeth, it might be quite hard to imagine how Pteraspis would have fed. The two groups of living jawless fish- hagfish and lampreys- have highly specialised mouthparts: the former for deep sea scavenging and the other as a ‘sucker’. Heterostracan mouthparts aren’t similar to either of these however, and they also have a more generalised swimming body plan; one thing they do have though is a series of oral plates.  These were parts of the head shield (not teeth!) that lay over the oral cavity.  Many functions have been suggested: scooping sediment, grabbing onto prey and suspension feeding.  Patterns of wear seem to exclude scooping and tiny little outwards pointing denticles on the plates would have prevented big prey from entering the mouth.  As such it seems that heterostracans like Pteraspis would have suspension fed on small animals, like many groups of animal today.

Het smile

A heterostracan similar to Pteraspis giving us an oral platy grin. (from Purnell, 2002)

Pteraspis and the heterostracans have a lot to tell us about how the jawed vertebrates evolved.  They possess bone, but no jaws or paired fins, immediately telling us that these characters of the gnathostome body plan didn’t evolve together.  Although we’ve not really discussed it here, the structure of their bone itself can also teach us about the evolution of bone, and how it came to prominence as a tissue. These animals, completely different to anything living in the oceans today, also present their own mysteries, such as how they fed without jaws.  We’ve only briefly talked about heterostracans here, but fear not! There’s plenty more to talk about in the future.

References

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: Hauffiopteryx

In keeping with Richard’s aquatic theme for the previous TotW, this week the ichthyosaur Hauffiopteryx typicus has the honour of being the last TotW of January 2014. It also has the honour of being the first post to announce some exciting work (unpublished at time of writing) being carried out by Ryan on the first 3D reconstruction of an ichthyosaur (amongst other firsts, see below!).

During the Mesozoic, marine environments were very different. In modern oceans, marine reptiles (turtles, sea snakes, marine iguanas, saltwater crocs etc.) aren’t hugely important in the grand scheme of things, with only around 100 species around today (compared to the 30,000 ish species of teleost fish swimming about). However, take it back to the Mesozoic (especially from the Jurassic onwards, for everything except ichthyosaurs) and marine reptiles dominated the higher trophic levels, with 5 big groups (ichthyosaurs, plesiosaurs, pliosaurs, mosasaurs and thalattosuchians) emerging by the Cretaceous. We see a huge range in morphological diversity, from long necked plesiosaurs (e.g. Elasmosaurus,  and the amazingly named Attenborosaurus), pliosaurs with heads reaching over 2.5m in length, crocodiles trying to be sharks, and finally ichthyosaurs.

marinrep

TIL: pliosaur taxonomy consists of just ‘pliosaur’ and ‘big pliosaur’.

nessieseadragon

A more useful figure detailing different Mesozoic marine reptiles (Motani 2010).

Whilst ichthyosaurs seem a little less awesome than ‘shark crocs‘, Predator X and the Loch Ness Monster, ichthyosaurs have a wealth of published literature that makes them really cool. Looking at the organisms’ gross anatomy, it looks fish-like, and true, it is the first tetrapod to adapt a fish-like body plan, allowing them to adopt (over the course of the Triassic and the early Jurassic) a more thunniform body plan, aiding more efficient swimiming. This has led ichthyosaurs to conquer both shallow sea and open ocean environments.  Ichthyosaurs also have incredible eyesight (see Motani 1999), allowing them to be efficient deep-water predators. Speaking of feeding, they also may adopt suction feeding (although heavily debated). Shastasaurus is also the largest marine reptile ever described (take that Predator X). They’ve also been shown to give birth to live young, as modern whales and some sharks do. As well the aforementioned cool stuff, ichthyosaurs have made a splash (heh) in Nature recently, with an ichthyosaur (along with a mosasaur) providing the first direct evidence of skin pigmentation in the fossil record which aren’t feathers. This has lead to the conclusion that ichthyosaurs may have been dark coloured all over (rather than countershading, seen in some modern cetaceans, for example).

the_dapper_ichthyosaur_conundrum_by_robthedoodler-d4uh3vs

If you’re not convinced yet that ichthyosaurs are cool, here are some dapper gentlemen ichthyosaurs. (From RobTheDoodler, DeviantArt).

However, poor little Hauffiopteryx, as yet, has received little attention. Up until 2008 the genus Hauffiopteryx was previously described as just another species of Stenopterygius (S. hauffianus, von Huene 1931). In 2008, Maisch et al. redescribed S. haffianus specimens, leading to the establishment of a new genus, Hauffiopteryx , with H. typicus being the only species within it. H. typicus has significantly larger orbits and a much more slender rostrum (snout) than S. hauffianus (amongst other apomorphies).

Hauffiopteryx_NT

Reconstruction of Hauffiopteryx typicus, (c) N. Tamura.

More Hauffiopteryx trivia:

  • Up to 3m long
  • From the Toarcian (early Jurassic, 182.7-181.8 Ma) of England, Luxembourg and Germany.
  • Small size thought to possibly indicate ventures into shallower waters to feed.

Yet, in 2011 Caine & Benton described 8 rediscovered specimens (initially from Somerset, England), all infants and juveniles. These 8 individuals (both H. typicus and S. triscissus) are all remarkably preserved (with some soft tissue preservation). One specimen in particular, M1399, may well turn out to be incredibly important. 

hauff_caine&benton

Skull of M1399, right lateral view.

As you can see from the pictures of M1399, it is exceptionally preserved in 3D, which is uncommon in the usually laterally compressed ichthyosaur fossil material. This is extremely exciting, because it means we can CT scan it and explore the cranial anatomy of ichthyosaurs in three dimensions. Which by the way, has never really been done before (aside for some work on ichthyosaur teeth, see references), and is even more amazing considering M1399 is a wee juvenile. And that’s exactly what I’ve been up to lately. For the past few months I’ve been beavering away in the tomography lab, attempting to create M1399’s (which I’ve come to affectionately call ‘The Hauff’) 3D cranial reconstruction. So far results have been really interesting, we’ve seen some things which (according to my research so far) has never been seen in ichthyosaurs before. Due to the great 3D preservation, we’re hoping to reconstruct one of the first ichthyosaur endocast (and maybe alongside some more functional/musculature stuff). Unfortunately that’s all I can say right now, as it’s still a long way off from being published (hopefully later this year/2015). As soon as I can tell you guys more, I’ll post right here on TDS.

M1399_after_a_web_0

M1399 (left lateral view). What a beauty. From JESBI collection page.

References

Motani, R. et al. (1999). Large eyes in deep diving ichthyosaurs. Nature 402, 747.

Lindgren, J. et al. (2014). Skin pigmentation provides of convergent melanism in extinct marine reptiles. Nature doi:10.1038/nature12899.

Motani, R. (2005). Evolution of fish-shaped reptiles (Reptilia: Ichthyopterygia) in their physical environments and   constraints. Annu. Rev. Earth Planet. Sci. 33, 395–420.

Motani, R. (2009). The Evolution of Marine Reptiles. Evo Edu Outreach 2, 224-235.

Fröbisch, N., B. et al. (2013). Macropredatory ichthyosaur from the Middle Triassic and the origin of modern trophic  networks. PNAS, 110(4), 1393-1397.

Sanders, P., M. et al. (2011). Short-Snouted Toothless Ichthyosaur from China Suggests Late Triassic Diversification of Suction Feeding Ichthyosaurs. PLoS ONE 6(5): e19480.

Motani R. et al. (2013) Absence of Suction Feeding Ichthyosaurs and Its Implications for Triassic Mesopelagic Paleoecology. PLoS ONE 8(12): e66075. doi:10.1371/journal.pone.0066075

Caine, H. & Benton M., J. (2011). Ichthyosauria from the Upper Lias of Strawberry Bank, England. Palaeontology 54 (5), 1069-1093.

Motani, R. (2005) Detailed tooth morphology in a durophagous ichthyosaur captured by 3D laser scanner,
Journal of Vertebrate Paleontology, 25:2, 462-465, DOI: 10.1671/0272-4634(2005)025[0462:DTMIAD]2.0.CO;2

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

Taxon of the Week: Postosuchus

In this week’s TotW, Ryan takes us through the posto child of the ‘rauisuchians’, Postosuchus.

When someone mentions the Mesozoic, you instantly think about dinosaurs. Admit it, it’s fine, there’s no judgement on this blog. You also will predominately think about dinosaurs from the Jurassic and the Cretaceous, with good old T. rex and co. (allosaurs, carcharodontosaurs, spinosaurs etc.) ruling the roost at the top of the food chain, whilst sauropod behemoths (amongst other ridiculously sized herbivores) wandering about in herds etc. etc. However, the Triassic (seemingly the Cretaceous and Jurassic’s ugly sister) is often forgotten about. Yes, we don’t have things which are outrageously large or ridiculously bipedal (or do we..?), but in the Triassic, crurotarsans (crocodile-line archosaurs) were having a bit of a field day.

awesomesozoic

The image that immediately springs to mind as soon as you mention ‘Jurassic’ or ‘Cretaceous’. Clearly.

Here on TDS, we think the Triassic (as well as plenty other eras, not just the Jurassic and Cretaceous) is pretty awesome too. The Triassic was a time of recovery, the Permian-Triassic mass extinction event had been and gone (and almost taken all of life on Earth with it). Dinosaurs were just starting out, and sitting on top of the food chain was, you guessed it, Postosuchus. If you look at the skull of Postosuchus kirkpatricki below, look carefully. Back in the 1980s famous palaeontologists thought Postosuchus (along with Poposaurus) could be a tyrannosaur ancestor. You can see where they’re coming from. Postosuchus was first discovered in 1922, and for 60 odd years after that, people didn’t really know what to make of it. First reports penned it as a Coelophysis, 20 years later, other finds were thought to belong to a new phytosaur. It wasn’t up until 1985 that the holotype, a well preserved skull and some postcranial remains, of Postosuchus kirkpatricki was formally announced. 

BronzePostosuchus

Totally not a dinosaur. No seriously.

Weighing in at almost 300kg, at reaching almost 4m when fully grown, Postosuchus was one (if not the) largest predator in the Triassic. With good long distance vision, a decent sense of smell, and a possible Jacobson’s organ, and oh, not to mention, over 7cm dagger-like teeth, this killing machine well may have taken down a fair few aetosaurs in it’s time (not a small feat). So fairly fearsome, but not as impressive as the theropods that were to come later in the Mesozoic, surely? Well, again, no.

tumblr_m3zd8iT4YA1rrpn3bo1_500

These coelophysoids clearly came to the wrong neighbourhood.

What makes Postosuchus (and many other ‘rauisuchians‘) so interesting are its hindlimbs. One of the major dinosaurian innovations was the erect hindlimb posture, enabling more efficient locomotion. In the Triassic, descendants of crocodiles (who now have the ‘sprawling’ hindlimb posture) such as Postosuchus had a go at this hindlimb arrangement (evolutionary speaking). Whilst debated, many palaeontologists view Postosuchus (amongst other Triassic crurotarsans) as being bipeds (or at the very least facultative bipeds). So that means Postosuchus could use it’s forelimbs to kill things as well as it’s terrifyingly huge mouth (like bears do). To summarise, Postosuchus is a nightmare-inducing, killer croc-bear from back in time. It also raises the question (to be investigated by a future blog post on TDS, hopefully) of why exactly did dinosaurs survive through to the Jurassic, and rauisuchians go extinct, and why did crurotarsans go back to being solely quadrupedal?

biobeast-sm

Killer croc-bear from back in time. (Thank you internet).

Told you the Triassic was awesome. (Also, more to come on the locomotory strategies of Triassic crurotarsans to come, right after I finish my final 4th year exams…).

Bonus picture (because it’s cool and reasonably accurate, although not as accurate as the previous picture):

Postosuchus_mural

There’s no escape from the Post(o) Man (not actually a man).

References

  • Case, E. C. (1922). “New reptiles and Stegocephalians from the Upper Triassic of western Texas”. Carnegie Institution of Washington Publication 321: 1–84.
  • Case, E. C. (1932). “On the caudal region of Coelophysis sp. and on some new or little known forms from the Upper Triassic of western Texas”. University of Michigan Museum of Paleontology Contributions 4 (3): 81–91.
  • Case, E. C. (1943). “A new form of Phytosaur pelvis”. American Journal of Science 241 (3): 201–203. doi:10.2475/ajs.241.3.201.
  • Chatterjee, S. (1985). “Postosuchus, a new Thecodontian reptile from the Triassic of Texas and the origin of Tyrannosaurs”. Philosophical Transactions of the Royal Society of London. Series B, Biological Sciences 309 (1139): 395–460. doi:10.1098/rstb.1985.0092.
  • Drymala, S. & Bader, K. (2012). Assessing predator-prey interactions through the identification of bite marks on an aetosaur (Pseudosuchia) osteoderm from the Upper Triassic (Norian) Chinle Formation in Petrified Forest National Park (Arizona, USA). Journal of Vertebrate Palaeontology, Program and Abstracts 2012, p89.

What’s New(s): 6/01/2014 incl.; Naked Dinosaurs, Saudi Arabian dinosaurs and Ichthyosaur storms.

Christmas is a time of rest, festive cheer, spending time with loved ones and (probably most importantly) food.       This is seemingly not the case for academics. Firstly, Richard and I have been busy revising for our January finals, so whilst we’ve tried to give you a few juicy morsels over to tide you over the festive season, we’ve not really had chance to bring you the latest news. Coupled with this is that over this year’s festive period there’s been a lot of palaeontology going on. Holiday, what holiday?

blog

PhD Comics, get used to laughing (and crying) along to them as a postgrad.

So here is a What’s News(s) bumper edition, with 5 of the biggest news stories in palaeontology over the festive period. This week, we’ve got Saudi Arabian dinosaurs, naked dinosaurs, ichthyosaurs, body-size trends in evolution and some Hungarian palaeoneurobiology! Since we don’t want to spam you, we might start evolving our What’s New(s) sections so they are weekly, rather than as-and-when the news comes out (unless it’s really cool).

The first Saudi Arabian dinosaurs. Like has been previously stated, new dinosaur finds aren’t rare occurrences. They happen roughly every 1.5 weeks. Big deal right. Wrong (again). Benjamin Kear’s team have discovered a few caudal vertebrae and some teeth from Saudi Arabia, from the Maastrichtian (75 Ma, ish), and have confidently identified the vertebrae to be from a titanosaur, and the teeth to be from an abelisaurid. The confidence of these groupings is the first time that fossils the Arabian peninsula have been able to be classified as dinosaurian without contention. It also stretches the palaeogeographical ranges of titanosaurs and abelisaurids to the northern margin of Gondwana, whilst showing us (with just one find) that dinosaur ecology in this area may have been quite diverse in the mid-late Cretaceous. The papers also open access (over here on PloS One).

saudidinos

A-C: vertebra of a titanosaur from Saudi Arabia; D-F: tooth of a abelisaurid (again from Saudi Arabia). From Kear et al. (2013).

Naked dinosaurs a common sight during the Mesozoic. For a pretty ‘young’ blog, we’ve already mentioned naked dinosaurs (ooo err!) twice. That says a lot about Richard and I. Moving swiftly on… Since the discovery of the feathered Sinosauropteryx in 1996 (and a plethora of other feathered Chinese dinosaurs since) has caused a bit of frenzy. So much so, that even the Jurassic Park conceded, and created this monstrosity (they’ve now de-conceded, and have yet again ignored feathered dinosaurs). Since 1996, palaeontologists have endeavoured to find just how far back feathers go in the dinosaur lineage. Up until the early 2000s, we thought we had it covered, and that feathers were ancestral to theropods (with discoveries such as Dilong paradoxus, a feathered tyrannosaur sparking fierce debate over whether good old T. rex  had a majestic feathered coat). Yet, as always, it only takes one discovery to turn everything upside down. Pscittacosaurus was that discovery. Pscittacosaurus is a ceratopsian (basal relative to the frilled dinosaur celebrity Triceratops), but with some proto-feathers. Crazy times.

bakker deino

Richard’s favourite naked dinosaur, Deinonychus (which probably wasn’t naked at all).

Paul Barrett then set about to try and solve just where the feathered dinosaur bus stopped. He and his team looked at all of the dinosaur skin impressions found to date, looking for any sign of feathers (or similar structures) and then considered the data is a evolutionary context. He concluded that despite Pscittacosaurus, most ornithischians (ceratopsians, ornithopods, pachycephalosaurs and thyreophorans) and sauropods would have had scales. With the majority of dinosaurian clades having scales rather than feathers, Barrett tentatively concluded (at SVP 2013, in sunny Los Angeles) that scales were probably the ancestral condition in dinosaurs.  But by now we know that all it takes is one feathered dinosaurs from the Triassic (or even the early Jurassic) to upheave this study.

The I(chthyosaur) of the Storm. Quick bit of local (for British palaeontologists  anyhow) news for everyone. After heavy storms (no, seriously, before any Americans/Canadians/anywhere with ‘proper weather’ complain) a 1.5 m long partial ichthyosaur skeleton has been revealed at the base of a cliff in Dorset, and is being restored by the Jurassic Coast Heritage organisation. Three ichthyosaurs have been revealed in similar ways after storms in the past year along the Jurassic Coast. So remember kids, 80mp/h winds and floods aren’t all bad.

Ichthyosaur_hharder

That’s right, icthyosaurs can fly. And then they become storms. True story (Not actually true).

Growing fields: body-size trends throughout the fossil record. Whilst by no means is the study of body-size trends through evolutionary history a new field, but Mark Bell has just published a brilliant, relatively short and Open Access (whoop!) introduction to body-size trends in the fossil record. The article really does make you feel rather small (literally). It also goes through some long established rules on body-size evolution (e.g Cope’s rule), whilst also noting some nice examples of giganticism and dwarfism in the fossil record. Finally, he also states that new computer simulations/software maybe able to help us to further understand these trends in the future.

Bell_gigantism_Figure-1

Where’s Wally, PhyloPic edition. (From Bell 2013 and PhyloPic).

The very Hung-a-ry dinosaur brain. This gem of palaeontological news really does show how fieldwork and digital analysis can produce fantastic results. A new find of a partial skull of Hungarosaurus (from, you guessed it, Hungary) has enabled Hungarian palaeontologists to made a cast of the endocranial cavity, allowing them to analyse the braincase of this European anklyosaur. Initial results suggest that the cerebellum (area of the brain associated with motor control) is larger in volume than other ankylosaurs. This may well mean that Hungarosaurus was better able to run than other anklyosaurs (well known for not being the fastest of starters…).

hungarybrain

Endocast of Hungarosaurus. cbl=cerebellum (roughly circled, from Osi et al. 2013)

References:

Kear BP, Rich TH, Vickers-Rich P, Ali MA, Al-Mufarreh YA, et al. (2013) First Dinosaurs from Saudi Arabia. PLoS ONE 8(12): e84041. doi:10.1371/journal.pone.0084041

Mayr, G., Peters, D. S., Plodowski, G. & Vogel, O. Naturwissenschaften 89, 361–365 (2002)

Zheng, X.-T., You, H.-L., Xu, X. & Dong, Z.-M. Nature 458, 333–336 (2009).

http://www.nature.com/news/feathers-were-the-exception-rather-than-the-rule-for-dinosaurs-1.14379

http://www.bbc.co.uk/news/uk-england-dorset-25548426

http://www.palaeontologyonline.com/articles/2014/trends-body-size-evolution-fossil-record-growing-field/

Ősi, Attila, Pereda Suberbiola, Xabier, and Földes, Tamás. 2014. Partial skull and endocranial cast of the ankylosaurian dinosaur Hungarosaurus from the Late Cretaceous of Hungary: implications for locomotion, Palaeontologia Electronica Vol. 17, Issue 1; 1A; 18p;
palaeo-electronica.org/content/2014/612-skull-of-hungarosaurus