Posts Tagged 'ornithischians'

Welcoming Zhanghenglong

It has been a while coming on the Musings, but here’s something that’s bordering on traditional palaeontology. However, it is based on ornithischians, so obviously doesn’t quite count. That is a joke before I start getting all the complaints in the comments – I’m genuinely pleased to finally be on a paper that focuses on the other side of the Dinosauria after all my saurischian work. Anyway, long term readers will remember this post from back in 2011 about creating plaster jackets in the field. This was from a trip down in Henan were we turned up a number of specimens (and interestingly, Xu Xing was called away up to Zhucheng becuase of the discovery of what would turn out be Zhuchengtyrannus). At the time we had something that looked like a hadrosaur of some sort, and the blocks you can see us removing in the other post form the core of the new paper.

So say hello to Zhanghenglong, a basal hadrosauroid from the Late Cretaceous. Somewhat inevitably there’s not much of it, though there is a good maxilla (shown below) and dentary, as well as dorsal vertebrae, ribs, a scapula and a tibia. Phylogenetically it comes out as a hadrosauroid, but very close to the base of Hadrosauridae and gives some additional support to the idea of an Asian origin for hadrosaur groups with the nearest relatives to hadrosaurs being from Asia, as are the earliest lambeosaurines at at least a couple of members of the hadrosaurines. Happily the full paper is at PLoS ONE so all the information is fully accessible if you want more.

 

Xing H, Wang D, Han F, Sullivan C, Ma Q, et al. (2014) A New Basal Hadrosauroid Dinosaur (Dinosauria: Ornithopoda) with Transitional Features from the Late Cretaceous of Henan Province, China. PLoS ONE 9(6): e98821. doi:10.1371/journal.pone.0098821

Guest Post: A phylogeny of ankylosaurian dinosaurs

At least a few parts of the dinosaurian family tree are still relatively little studied and are controversial. One of these is the ankylosaurian dinosaurs, though a new paper seeks to delve into this problem and produced a new and comprehensive analysis. Lead author Rick Thompson takes us through it:

In 1842 Richard Owen coined the term “dinosaur”, helping to imbue the world with a fascination for the gigantic ‘terrible lizards’ of the prehistoric world. Owen’s work was based on the fossil remains of three distinct archosaurs; Megalosaurus and Iguanadon have become fixed in our consciousness as archetypal dinosaurs, while the third, Hylaeosaurus, is very much the ‘ugly-duckling’ of the trio. Hylaeosaurus is a member of the Ankylosauria, a group of Middle Jurassic to the Late Cretaceous heavily armoured herbivorous dinosaurs, closely related to the stegosaurs in the clade Thyreophora. The story of Hylaeosaurus somewhat mirrors that of its ankylosaur relatives; fragmentary, difficult to study and lacking the popularity of its theropod, ornithopod and sauropod cousins. The ankylosaurs barely even worked their way into Jurassic Park (apparently Ankylosaurus does appear in Jurassic Park III – if you can stand it…)! The lasting image of the Ankylosauria in the public consciousness is the classic battle between Ankylosaurus and Tyrannosaurus, with the ankylosaur determinedly swinging its tail club towards the leg of its powerful foe. Indeed, it is the presence of the tail club, widely regarded as a defensive weapon that could shatter bone (Arbour et al. 2009), which has helped to raise the profile of this fascinating dinosaur group.

Of course ankylosaurs are more than just a dinosaur with a weaponized tail. The Ankylosauria includes over 50 valid taxa, only a fraction of which possess this idiosyncratic armament. Fragmentary ankylosaur specimens have been recovered from every continent on Earth, though their record in North America and Asia is by far the best. It is their extensive covering of dermal armour, particularly that of the skull, that has proved to be both the blessing and bane of ankylosaur palaeontology. The high level of morphological diversity in the armour is probably responsible for the large number of ankylosaur taxa. The cranial ossifications completely cover the bony sutures of the skull, simultaneously providing a unique pattern to identify new species, while destroying a wealth of cranial characters that could help to resolve the interrelationships of the wider clade. Thus the evolution of the Ankylosauria is very poorly understood, and presents a tough challenge for systematic palaeontologists.

Traditionally the Ankylosauria is split into two families, the Ankylosauridae and Nodosauridae. The Ankylosauridae includes many of the more recognisable taxa including Ankylosaurus and Euoplocephalus. Ankylosaurids are generally identified by their short-broad skulls, which are ornamented with horn-like ossifications above (supraorbital), behind (squamosal) and below (quadratojugal) the eye, along with the presence of a tail club. The Nodosauridae generally have a more elongate skull, with a domed skull roof (parietal region) and boss-like rather than horn-like cranial ossifications. Their trunk armour often incorporates spike-like ossifications along their flanks, though no tail club is present. In recent years, a number of ankylosaurs, such Gastonia and the aptly named Gargoyleosaurus, have been found to possess combinations of these classic traits, thus blurring the distinction between ankylosaurids and nodosaurids. This has led some authors to erect a new group of ankylosaurs, the Polacanthidae, which includes many of these recent discoveries, along with a few older, fragmentary genera like Owen’s Hylaeosaurus.

 

A mounted skeleton of Gastonia burgei. Note the large shield over the pelvis, a character suggested to unite polacanthid taxa. Photo by Susie Maidment.

The validity of the polacanthid hypothesis has proved hard to test cladistically, as the majority of ankylosaur character sets are either heavily biased towards the skull, or include a limited number of taxa. As many of the potential polacanthid taxa are fragmentary, or predominantly postcranial, the incorporation of these taxa into ankylosaur phylogeny has been problematic. Studies including some polacanthid genera place them either towards the root of the Ankylosauridae, or as a new family (Polacanthidae), sister to the Ankylosauridae. During my Master’s Degree in Biosystematics at Imperial College, London, I was lucky enough to get the opportunity to try to resolve some of these issues in ankylosaur evolution. Paul Barrett and Susie Maidment offered me the chance to revise and update the unpublished PhD thesis of Jolyon Parish on ankylosaur phylogeny. My aim was to expand the taxon sample of Parish’s thesis, as well as modify his extensive character set. In this way I hoped to produce a ‘palaeontological total evidence’ phylogeny of the Ankylosauria, which included all valid taxa regardless of completeness, and a roughly even mix of cranial and postcranial characters.

The results of this project were recently published in the Journal of Systematic Palaeontology, and give some new insights into ankylosaur evolution. Encouragingly our data did support the traditional split between the nodosaurids and ankylosaurids; however, no polacanthid clade was recovered. Instead, all taxa that have been affiliated with the Polacanthidae by various authors (and Ankylosauridae by others) were resolved within the Nodosauridae. In the strict consensus tree (the tree which summarizes all of the information that each of the shortest possible evolutionary trees agree upon) the nodosaurid clade formed a polytomy – that is, we could say nothing about the internal relationships of the group. This poor resolution of the clade was in fact caused by a number of unstable taxa, whose position on the tree is highly variable. Unsurprisingly three of these unstable taxa have previously been attributed to the Polacanthidae. To counteract their influence we produced a derivative strict reduced consensus tree (shown in the figure). This tree prunes unstable taxa from the strict consensus tree, greatly increasing resolution. In this phylogeny it is clear that the ‘polacanthid’ taxa form a basal grade of nodosaurid dinosaurs, while the traditional nodosaurids (clade D) form a polytomy.

This result simultaneously highlights the strengths and weaknesses of the ‘palaeontological total evidence’ approach. By including all taxa (regardless of completeness) and a character set sampled from the whole skeleton, a large amount of missing data was guaranteed. This lowers the resolution of the tree, as seen in the traditional nodosaurid clade. However, it is the inclusion of such a broad sample of characters and taxa that has allowed completely new relationships to be revealed, placing ‘polacanthid’ taxa in the Nodosauridae. The problems have been further confounded by the extensive cranial ossification of the taxa. The variation in such complex ornamentation is exceptionally hard to capture using traditional discrete characters. This makes it very hard to test for presence of the evolutionary signal in the ornamentation. In the future, a study which incorporates extensive measurements of the cranial armour could better capture this variation, and more clearly reveal the relationships of the group. This is particularly important for the Nodosauridae, many of which are primarily distinguished by their cranial ornamentation.

The phylogeny of the Ankylosauridae was much better resolved, and broadly in agreement with existing studies, if the ‘polacanthid’ taxa are discounted. Again in this clade we see that the basal lineages do not conform to the traditional view of the Ankylosauridae, often having elongate skulls. The tip of the tail has not been recovered in many of these taxa, so the presence of a tail club is uncertain. However, our tree is the first cladistic analysis to place an ankylosaur that clearly lacks a tail club within the Ankylosauridae. Zhongyaunsaurus was originally described as a nodosaurid, though this assignment was subsequently corrected by Ken Carpenter (Carpenter et al. 2008). Our phylogeny confirms that Zhongyaunsaurus was indeed an ankylosaurid, and suggests that the most characteristic trait of the Ankylosauria is only present in the most derived ankylosaurids.

Unfortunately our study has done little to help the plight of the earliest known ankylosaur, Hylaeosaurus. Our analysis suggests that it is a member of the Nodosauridae, but its removal from the reduced consensus tree feels like a sad continuation of its rather anonymous history. Never the less, our study has helped to reveal a new perspective on the Ankylosauria. Although the ankylosaurid-nodosaurid dichotomy has been maintained, it appears that the classical characters of these groups only apply to the most derived of their forms. The earliest lineages of each family show greater levels of diversity in their armour and body form. This has made their classification difficult, and without more fossils, or newer forms of character, it is likely to remain so. There is still much work to do in order to understand the evolution of this extraordinary group of animals, but hopefully our study can serve to trigger a new wave of research in the coming years.

 

 

Yet more hadrosaur heads

The Musings seems to be have been on a bit of an unintentional roll for hadrosaur heads recently. There were some Lambeosaurus heads to go with Nipponosaurus but now here’s something of a flood. Steve Cohen, who kindly supplied a bunch of AMNH pterosaurs, has sent in this set of heads from the halls of the AMNH and it’s a nice example of the variety of crests and expansions seen in the group.

While some of these genera have made appearances on these pages before (like this Corythosaurus and while not shown here, don’t forget the amazing Tsintaosaurus) this is good chance to smush them all together and make them much easier to compare and contrast. A couple have also been flipped to put everything in left lateral view, though this means that the nicely labelled Saurolophus as the bottom is now covered in mirror writing.

Here then are (in order): Corythosaurus, Hypacrosaurus, Kritosaurus, Lambeosaurus, Prosaurolophus and finally Saurolophus.

Camptosaurus

Another super-later entry from the Oxford Museum back catalogue, this is Camptosaurus. I’m not one who is deeply into my ornithischian systematics, but as far as I’m aware this is fairly uncontroversially close to Dryosaurus and Dysolotosaurus and the like and thus in the dryosaur clade that is basal to the iguanodontians and hadrosaurs.

I’d much rather comment on the mount which is superb. It’s a shame about the wooden batten in the cabinet, but well, that’s part of the furniture. But the suspension of pieces in space like this without an obvious big metal armature is really nice to see. OK so yeah, the specimen is largely visible from only one side, but this offset by the superb way it’s put up and I really like this.

Dryosaurus skull

In addition to the mounted skeleton shown yesterday, as usual the Carnegie provided a little extra something. In this case it’s a nearly complete skull of a young Dryosaurus (the label lies in the orbit and it’s facing to the left).

I must confess to knowing little about this ornithischian (also true of many ornithischians I admit) though it helps illustrate one small point. Not that long ago, it was thought that sometime in the Middle to Late Jurassic there was a landbridge from Africa to North America. This was invoked to explain the apparent incredible similarity between the Tendaguru and Morrison faunas. Both had Dryosaurus, and Allosaurus and Brachiosaurus, and both had stegosaurs and diplodocids.

However, better examination of the available material makes the Tendaguru brachiosaur not Brachiosaurus, the allosaur not Allosaurus and the small ornithopod is Dysolotosaurus and not Dryosaurus. In short, there’s no need to invoke a special land-bridge since the two faunas are not identical. Similar sure, with each having representatives of the same families, but that’s hardly surprising – look to the modern world and the two continents feature felids, canids, mustelids, bovids and others and such comparable faunas are quite normal.

Gular armour

Stegosaurs are, understandably, famous for their combination of spike and bony plates that give them a distinctive profile even when compared to other dinosaurs. However in addition to these more obvious bits of armour (and let’s face it, some of them are really obvious) is the gular armour. For those not familiar, the former word refers to the throat (most often used by me at least when talking about the gular pouches of various pterosaurs) and as you can see here this armour is a series of tiny bony ossicles that lie almost like chainmail around the throat and base of the neck (here in Stegosaurus). To my knowledge these are pretty rare in stegosaurs and I can easily imagine that they fall away or simply don’t preserve given their small size.

Hesperosaurus mjosi

This will be bordering on my shortest post ever as i really have noting to say beyond, what a lovely and dramatic mount. What a lovely and dramatic mount.

Tianyulong


Although I have seen this specimen before (and indeed others) this is the first time it’s been ‘out’ and available. Like many things published in Nature and Science and similar journals, the specimens might be very interesting and important, but the restrictions of space means you may only get a small photo of the material and a couple of close-ups: no lavish 10 colour plates or multiple views of important elements for you (though the supplementary data increasingly helps out).

Not that I can do much more here as the damned thing was quite some way from the glass and at an odd angle, but hey, at least it’s a couple of new images of this interesting and potentially profoundly important specimen.

Getting in late

Iguanacolossus

So everyone already knows about the two new igunaodontians that are out there, Hippodraco and Iguanacolossus. I’m a bit late to the part with all the palaeoart stuff going on, but I did promise Jim Kirkland, Andy Milner and Don DeBlieux that I’d blog about it so I’d better had. The paper is in PLoS One and so is freely available here who want to see it. This of course follows hot on the heels of Kukufeldia, and Darren Naish’s review of the last two years of igunaodontian taxonomic revisions and the host of newly erected names. Everyone has gone on about the year of the ceratopsians but these guys have had a good 2009-10 as well.

Hippdraco

Given the coverage of the new taxa, I really will cut things short here as there is little to add to the host of other blog posts. However, Jim was kind enough to send me a ton of images some of which I have not spotted on other reports so I’ve dropped them in here for your edification. Congratulations to Jim and the team and best of luck with future finds.

Continue reading ‘Getting in late’

Guest Post: introducing Kukufeldia

Today Paul Barrett generously gives up his time to write about the newly named igunaodonitan dinosaur Kukufeldia and the problems of providing definitions and diagnoses of new taxa in the fossil record:

Continue reading ‘Guest Post: introducing Kukufeldia’

Guest Post: presenting Diabloceratops eatoni

Dr. James Kirkland (L), and Paleontologist Don Bileux (R) who discovered the skull, answer questions about the Ceratopsian skull from children from the Cosgriff Catholic School. Scott Sommerdorf / The Salt Lake Tribune

This newly named ceratopsian dinosaur, based on a superbly preserved and amazing looking skull has already been doing the rounds in the media and on various blogs. Lead author Jim Kirkland has been good enough to pen this guest post on the discovery of the specimen and its importance in terms of  the evolution of the group and the characters of the skull within the clade.

Continue reading ‘Guest Post: presenting Diabloceratops eatoni’

Ossified tendons

Let’s face it, although it would be far less catchy it would be more accurate to call this the ‘theropod and pterosaur and occasionally other things’ blog more than the Archosaur Musings, but since that is where my knowledge and interests lie, that’s what you tend to get. However I am trying to at least get some more ornithischians, birds and crocs in here but bear with me if it takes a while and tends to be short.

Here though I want to mention one defining characteristic of the Ornithischia as it actually relates to both theropods and pterosaurs, if rather obliquely, namely the ossified tendons of the spine. Many of you are probably familiar with these already since they crop up in various ecological and mechanical discussions about how tails work (especially with the old one about hadrosaurs swimming). For those who don’t however, the short version is that ornithischians have a series of elongate little bones that run alongside the vertebral column, especially close to the sacrum.

I say ‘bones’ and in a sense they are, though they are not like normal skeletal elements but are tendons that have been turned into bones. This is actually more familiar that you might think – you may well have noticed how tough some tendons are in a turkey carcass compared to a chicken and this is a result of the same process. Ossified tendons are quite literally those that are partially, or fully turned to bony tissue. Those tendons that take heavy loads often have this happen to them as seen in turkeys or for an extinct examplw the nyctosaurid pterosaurs.

These are present in pretty much all ornithischians (stegosaurs don’t have them), though don’t always show up in juvenile animals and some have far more than others. They are typically concentrated on the vertebrae of the sacrum but do appear on the dorsals and caudals too in most cases. They are typically long and thin and lie subparallel to each other, though famously in the hadrosaurs they form a lattice work on the tail. Here’s a not very good image showing then in Psittacosaurus (above) and Yinlong (below). In the former they appear as a series of stripes and in the latter as some rods (though badly broken) but between the two it should give you an idea of what I mena and demonstrate that they are not part of the vertebrae themselves.

So, where’s the relevance to dromaeosaurs and pterosaurs? Well in some cases, (with Tianyulong being a notable example) there can be loads of ossified tendons binding the tail up in a tight mass of little splints of bone. This can look very similar to the situation in both dromaeosaurs and some rhamphorhynchoid pterosaurs where the tail is similarly bound up. However, in the latter cases this is a result of those (normally) little articulations on the vertebrae (the pre and postzygopophyses) being enormously extended into long thin rods. The tails can therefore look superficially similar between the two groups, but close examination should reveal the fact that in the ornithischians, the rods of bone are not part of the vertebrae by lying on top of them. It’s actually a rather nice demonstration of solving the same problem (stiffening the tail in this case) in two different ways as well as the convergence between the dromaeosaur and rhamphorhynchoid tails.

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