The Australian Museum has a long history of presenting lectures and seminars on a variety of scientific and cultural topics. That tradition continues with the Australian Museum Research Institute Seminar Series, a platform for AMRI scientists, associates and collaborators to present recent research and findings to their peers.

Since 2020, many of these presentations have been delivered online. Below you can find some of these recordings.

New discoveries in temnospondyl palaeontology

Presented by Lachlan Hart

Technical Officer, Palaeontology, Australian Museum; and PhD Candidate, University of New South Wales

Recorded Wednesday 27 September 2023

Lachlan Hart has had a life-long fascination with vertebrate palaeontology, which he loves sharing with others. He is a Technical Officer in Palaeontology at the Australian Museum and is in the final year of his PhD at UNSW. Lachlan will be sharing his research concerning ancient amphibians, which has been central to his PhD research. Temnospondyls are a group of extinct amphibians that lived before, and during, the time of the dinosaurs. Throughout their time on Earth, they survived two mass extinctions and spread to every continent. This seminar will present new taxonomic discoveries of temnospondyls which have helped us understand more about these great survivors.

I do research on temnospondyl amphibians, but what exactly is a temnospondyl? They're an extinct group of very diverse amphibians that were alive during the Carboniferous through to the Cretaceous periods. That's a span of 110 million years, which is longer than all of the non-avian dinosaurs. They used to be called the labrynthodonts, so if you're old school you might have heard that word instead of temnospondyls, but now they're known as temnospondyls instead. Their closest living relatives are amphibians like salamanders and frogs, although as you can see from this picture here, some looked a lot more like crocodiles than what we generally considered an amphibian to look like.

They're not a new group known to science by any means. In fact, they even featured in the Crystal Palace structures in London, although our interpretation of what they looked like has changed a lot since those statues were built in 1850, which is probably a good thing. When I say they're diverse, I really mean it. As you can see here, here are some of the wide array of skull shapes that we see in temnospondyls. Some had very, very long snouts like a modern gharial. Some had much more robust skulls like a crocodile might have, and some had things that were kind of in between, a bit like a giant salamander. But wait, there's more! So here we have another collection of very weird temnospondyl skulls. Some looked like they were shaped a bit like footballs, and others looked a bit like toilet seats.

So why are temnospondyls important? So, temnospondyls survived two of Earth's Big Five mass extinction events, including the one at the end of the Permian Period, which wiped out over 80% of all living things. This gives us a really good case study into how animals, especially vertebrates, respond to global change after global catastrophes like mass extinction events. And those catastrophes are often associated with global warming events. And temnospondyls are particularly cool to research in Australia because you have a great record of them, especially in the Triassic Period. And the very last ones that were alive also lived in Australia, in Victoria.

So let's just have a little bit of a closer look at that fossil record. As I mentioned, they had a very long duration on Earth, a very successful duration on Earth. The ones that we look at in Australia span this timeframe. There's one known from the Permian, just a little bit before that arrow but this is mainly what we look at when we look at temnospondyls from Australia. So yes, that Mesozoic time bracket that Matt was talking about at the start. As I mentioned, we have a really great record of them in the Triassic of Australia. There's over 35 of them known from most of the states in Australia, Western Australia, New South Wales, Tasmania and Queensland. It drops off after the end of the Triassic Period. And by drops off, I mean there's only two known from the Jurassic Period and one of them is quite questionable. And then there's only one currently known from the Cretaceous and that's from Victoria.

So let's start at the Triassic Period because that seems like a good place to start when we're looking at the diversity of temnospondyls. And we're going to start with this one. So this is the one that has been in the news recently. I'm going to give you a bit more of a backstory about this fossil and how it was discovered and how it came to be in our collections and how I came to research it. So this particular fossil was known as the Kincumber Amphibian. So it's a type of temnospondyl called a brachyopoid and we know that from the shape of its skull, that parabolic head shape. And it was found on the central coast of New South Wales at Kincumber quarry. It was in rocks that were purchased for the construction of a retaining wall. And it was found in the mid-90s and it was acquired by the Australian Museum in the year 2000 and it's been in the collection since then. So one thing that makes this fossil really cool and unique is that it's got an articulated skeleton, so it's got the head attached to the body and it's got most of the body there as well and it's also got the soft tissue outline. That's all the black that you can see there on the fossil and that makes it one of the most complete temnospondyls known from all of Australia.

So this is a photo from the Museum archives around the time that the fossil was discovered. We postulate that it came from this layer here but unfortunately that has not been ascertained and apparently according to the quarry owner who I spoke to just recently, it's a very hard layer to reach. This is the man, his name is Mihail Mihailidis. He's the man who purchased the rocks for building the retaining wall at his house. It was a landscaper named David King who actually found the fossil when he had finished building the wall. He was taking off the top layer of dirt and the fossil just appeared from underneath the dirt. It was quite an amazing story.

The story is so amazing that it caused a bit of a media circus. As you can see here, it was lapped up by the media. They all loved it. Just because I think it's a great story and it's a great fossil. So one man that you might have seen featured in some of those photos was this person here. This man, he's Dr Stephen Godfrey. He's actually a Canadian palaeontologist who specialises in dinosaurs, not amphibians. But his connection was that he was actually in Sydney at the time the fossil was discovered because he was working on what was called the Dinosaur World Tour. That just happened to have its tour stop there in Sydney in early 1997 when Mahail brought the fossil to the Museum's attention. A lot of people saw the fossil there for the first time in early 1997, including myself. So that's me with my family posing outside the Dinosaur World Tour. I'm the one in the hat and my dad's the one with the moustache. That was the first time that I saw the fossil as a 12-year-old on that world tour. So it's quite a serendipitous thing that I got to work on over 20 years later.

It was very delicately cut down with a rock saw before it was put into our collections. As you can see, the rock there is quite thick. It was very dense, and it was very hard initially looking at the fossil to work out what was going on with the bones. And so as a bit of an out there idea, Matt (McCurry) and I decided to contact the Australian Border Force and ask if we could use their high-powered x-ray scanners to scan the fossil to see if it could penetrate into the rock so we could see the underside of the skull. Because as I have alluded to before, the fossil is preserved belly up, which means we can't see the top of its head, we can't see sutures of the skull or its eyes or anything like that. And so it would have been good to penetrate it with a high-powered machine like an x-ray to see into the fossil itself. Now legally, I can't show you the images generated when we went to the Border Force, but I can tell you that it didn't actually provide anything very useful to us. We put it through a scanner that was a bit like this, but that's not the exact model. Again, for legal reasons, I cannot show you the exact models of the things that they, the equipment that they use there. But these are some of the methods that we attempted. As I said, unfortunately, it didn't give us anything very useful.

So I was left to describe the fossil at face value, take some high-quality photographs with the help of the Museum's Tom Peachey. And this was our interpretation of what was preserved on the fossil. So as I mentioned before, it's a type of temnospondyl called a brachyopoid, which is easily identified due to its head shape and the proportions of its head. But it's larger than other Triassic types of brachyopoid. And it was eventually identified as a new type of temnospondyl due to a unique combination of nine different characteristics. Here's a bit of a close-up of the head. So unfortunately, the head area of the fossil is quite squashed, which would have happened post-mortem. But there were a few unique details that we could pull out of here. One really cool aspect here is the mandible, which is on this side here. It's still partially articulated. So it's still partially attached to the jaw as it would have been in life. Here's the midsection of the animal. So we've actually got some of the soft tissue here around the hand, which is unique. We don't often see the soft tissue preserved, especially around the hands of temnospondyls, which is quite cool. Unfortunately, we couldn't work out if it had webbing between its fingers, that would have been even more exciting. But it's still very cool to have that. This bone here, which you see here, is called the interclavicle bone. That's a very characteristic bone of temnospondyls. What we found in this one, it's smaller than we see in other closely related animals.

So, speaking of close relations, we ran a phylogenetic analysis to see where it fell out in relation to its other closely related family members. So you can see it's there. This is the whole superfamily. And it sits here, which shows that it's more closely related to species from India and South America than it is from Australian species, which is quite interesting. And there it is again with the branch support calculated. So one other really cool thing about this fossil is it shows that there's an evolution of increased size, especially the width of the skull across this entire clade, which confirms an earlier theory that larger animals of this family called chigutisaurs were present in Australia very early on in the evolution in history in the early Triassic. It shows that they were evolving to large sizes, very close to the beginning of the Triassic period, which is just after that mass extinction event at the end of the Permian period.

And if you weren't aware already, this article did come out about a month ago now. And it's been well received and well-read in the Journal of Vertebrate Palaeontology. And so again, we name this thing Arenaerpeton supinatus which translates to the supine sand creeper, which is a reference to the fact that it was the fossils preserved lying on its back in a block of sandstone. And just to complete the full circle, as I showed you before, there was quite a bit of a media storm, and it was quite a fulfilling feeling to add my own bit of that to the story of this fossil when all the media hit.

So that's the Triassic period and as I said, we've done a little bit now in filling some of the gaps in evolution of temnospondyls during the Triassic. So what about the Jurassic? As I mentioned before, the Jurassic is quite depauperate for temnospondyls and in fact, it's quite depauperate for all fossils in Australia, vertebrates. So we have this one, this is a temnospondyl called Siderops, which is one of the most complete temnospondyls known from Australia, which is a beautiful fossil. But then we also have this. This is all that's known of another temnospondyl called Austropelor. And that's why I mentioned at the start that this one is a bit of a questionable taxon. From the Jurassic of Australia, we also have a sauropod called Rhoetosaurus, which is known from basically just this, although there's apparently a few other bones out there known from it. But that leg is the holotype. And then there's this amazing fossil called Ozraptor, which is apparently a theropod dinosaur. And that's it. That's all that is known from the Jurassic of Australia as far as terrestrial vertebrates go.

However, in New South Wales, we have a really great fossil site called the Talbragar Fossil Fish Beds that's dated from the Jurassic period. And as the name suggests, it doesn't have any terrestrial vertebrates, but it's full of especially fish. There's also fossil plants, insects, and there's an example of one of the common fish species that we see there. The site has been excavated for over 130 years by both professional palaeontologists and amateur fossil collectors. And so until recently, we were pretty confident that we weren't going to find any other vertebrates besides fish at the site until a couple of years ago. So a couple of years ago during a routine visit to the site, one of the visitors, Jochen Brocks, found this tooth. It was identified at the time by, I believe, Matt, as something that didn't quite look like a tooth that belonged to a fish. And so when I started my PhD, this was handed to me to work out what it was. The first step was to get better detail of the tooth, and that was done by putting it into a microCT scanner. We got great surface detail as well as internal detail of the tooth. Of particular note was the tooth in cross section. So we can see three cross sections of the tooth here on the left hand side, going from the apex, the point of the tooth, down towards the root. As you can see here, these black lines here are something that we call plicidentine, which is what gave temnospondyls their original taxonomic name, which was labrynthodonts, because it looks a bit like a labyrinth when it's looked at under a microscope. This type of infolding of the enamel of the teeth is not seen in any other animal that we would find in a deposit such as the Talbragar Fossil Fish Beds. So this led us to eliminate all other possibilities and to hypothesise that this tooth actually did belong to a temnospondyl.

This is a very significant discovery because it is the first tetrapod, first terrestrial vertebrate known from this site, which has been excavated for 130 years. It's also the first fossil of a supposed temnospondyl that has been found in New South Wales from the Jurassic period. So again, we're filling in those gaps. The paper came out a couple of years ago and that's also formed one of the chapters from my PhD.

Just to quickly summarise that, it was the first tetrapod over 130 years, and it shows that temnospondyls were present in New South Wales in the Jurassic period. Now one persistent question about this is how did this tooth actually get there? So the theory about the Talbragar fossil fish beds, or one of the theories about the Talbragar fossil fish beds and how it was formed, is that it was formed due to some sort of anoxic event. Some people have hypothesised due to ash flow. So when the water of the fish beds became anoxic, all the fish that were trapped in those water bodies died. If you're an amphibian, like temnospondyls, you have the ability to get out of water when it starts turning yucky. So that's one of the theories that how this tooth got there. It was shed or dropped or possibly knocked out when a temnospondyl was fleeing the water when the water started becoming less hospitable. Another theory is that it was transported from another site, so it got washed down in some sort of water or mud flow down towards the fossil fish beds and was eventually embedded there. And yeah, so then that's adding a little bit more to the story of the temnospondyls in the Mesozoic. It's been quite a good journey to fill in some of those evolutionary gaps in the Triassic and Jurassic periods. And my next stop is working on the Cretaceous and hopefully adding some new information from what we know from there. But with that, I'd like to thank you all for letting me talk through your lunchtime!

AMRI Student Forum

The AMRI Student Forum showcases the research done by students utilising the Australian Museum's unique expertise and collections.

Learn more

Explore previous seminars and lectures