Fossils and Geology

A few weeks ago, I was demonstrating on a geology field course in Wales. It was fantastic for several reasons - I had a great time, it was out on the coast of Wales mostly on the coast, and more importantly, it reminded me of my love for geology. It's been a while since I've done some geology, about 6 years to be exact, and I really enjoyed looking at rock types, folds, faults, and all those other fun things.

One of the other things I remembered on the trip was the occasional animosity that is seen between geologists and palaeontologists. I remember in my undergrad geology classes how geologists would rant about how they hated palaeontology and fossils, and vice versa for palaeontologists regarding rocks and geology. Then in Wales, one of the lead staff members would make a face each time we found a fossil or discussed them. While I will admit to preferring fossils over rocks (obviously, I'm a palaeontologist...), there is one important thing to remember: palaeontology and geology NEED each other. And palaeontology especially would not exist without geology.

To start with the obvious side, fossils are basically rocks made of bones, shells, soft tissue, etc. of long dead animals or plants. The process of fossilisation means that the organic material is literally replaced over time with rock and mineral. This is done primarily by highly-mineralised pore water in the ground and sediment. As an animal dies and is buried by sediment, highly mineralised water flows through the sediments and around the dead body, and over time, the minerals in the water will replace the tissues of the body, primarily the hard tissue. Soft tissue is generally decayed and broken down, while the hard tissues of bone and teeth remain replaced as rock. Being able to tell what type of rock now makes up the fossils can be important in figuring out the environment that the fossil was deposited in. Even more important is that the rocks surrounding the fossils can contain clues about how the animal died and the environment in which it lived. For example ripples in sandstone tell us there was a current, while fine laminated sediment like mudstone tells us that the animal died in a quiet low-energy environment like a lake or lagoon where fine sediments settled over a long period of time to the bottom. The presence of specific minerals can tell us things as well. Pyrite is formed in low-oxygen environments, so pyritised fossils mean a low-oxygen environment like the bottom of a deep ocean. Having a background in geology can definitely help in understanding palaeontology, specifically in order to understand the environment that the plant or animal was living in.

On the other hand, palaeontology and fossils can tell us specific things about the environment and geology of an area. There are fossils called Index Fossils, which are fossils that lived for a very little amount of time, and a specific time. They are obviously identifiable, and the fact that they are only found at very specific times means that when they are found, we know exactly what time period those fossils come from. Additionally, fossils can be helpful in determining geological structures like bedding planes. Sedimentary rocks are deposited in layers called beds. These layers are deposited as horizontal beds as sediments fall from lakes or rivers, for example. Through geological processes, these beds can be folded, faulted and overturned, making it difficult to tell which way is up and what has happened geologically speaking. This is where fossils, and in particular trace fossils can come in to help clear up some of the problems. If an animal is walking around on the bottom of the ocean or lake, the footprints or traces will be on a single bedding plane. If preserved and fossilised, these traces can tell us which way was "up" on the bed when it was deposited. This can help us understand what geological processes have happened in the past in terms of folding and faulting.

Trilobite trace fossil from Wales. This showed at this particular locality that the bedding planes here were nearly vertical, and allow us to see that there was some significant folding in this area, specifically an an anticline in the bay where this was found.

So as you can see, geologists need palaeontologists, and palaeontologists need geologists. Or even better, it's important for geologists and palaeontologists to learn about each others subject. So here it is - palaeontologists: stop hating on geology and rocks! You need it! And now geologists: fossils aren't so bad, and they teach us things every day! We need each other, so stop with all the malice.

Late Cretaceous of Romania

For the last 2 weeks, I have been on fieldwork in Transylvania (western Romania) with the University of Southampton Vertebrate Palaeontology group. This is part of a long-term project between several groups including British, American, and Romanian organisations looking at the vertebrate palaeontology of this area. This is the 3rd year this Easter trip has run, and was the biggest yet (25 strong at it's largest!).

The area was first recognised as being an important vertebrate palaeontology location by Baron Franz Nopsca, the Hungarian aristocrat and palaeontologist of the late 1800's and early 1900's who is widely thought to be the kickstarter of palaeontology in the region.

Geological Setting

When mentioning fieldwork in Romania, and in particular Transylvania, most people think of vampires, castles and mountains, and have no idea about the palaeontological significance (or even topography) of the region. While there are outcrops of many ages, the areas that we are interested in are of Late Cretaceous (Maastrichtian) age, deposited approximately 72-66 million years ago. This is the last time period of the Cretaceous, culminating in the end Cretaceous extinction 66 million years ago that saw the extinction of pterosaurs, non-avian dinosaurs, and many more. There are the Carpathian mountains, and also several plateaus and rivers where much of the fossils come from.

In particular, there are 2 areas of interest in Transylvania that yield Maastrichtian deposits - the lesser known sedimentary Transylvanian Basin in the area of Sebeş and Alba Iulia, and the famous Haţeg Basin to the southwest. During the Late Cretaceous, this area was characterised by an island environment, and is represented by both terrestrial and marine deposits in the area, with the younger terrestrial/continental deposits overlying the older marine sediments. Numerous islands were found in this area of the world, with Haţeg Island being one of the major islands. 

Palaeontology of the Area

Transylvanian Basin

Râpa Roşie

There are numerous sites in the Transylvanian Basin that have yielded vertebrate remains, and many different groups of animals have been found. At the river site Sebeş-Glod the theropod Balaur bondoc was found[1], which has an interesting double sickle-clawed foot and has proven to be highly controversial in it's placement among theropods. Balaur was a small theropod estimated at just 1.5m in length from an incomplete skeleton unfortunately lacking a skull. Also from Glod is the azhdarchid pterosaur Eurazhdarcho, which had a wingspan of around 3m and is known from an incomplete skeleton as well with no skull[2]. Further finds include additional dinosaurs (Zalmoxes, titanosaurid sauropods), turtles, crocodylomorphs, and more. At Petreşti (also a river site) a number of fossils have been found including pterosaurs and the ornithopod dinosaur Zalmoxes[3]. A productive site at Lancrăm has produced fossils of numerous groups including primarily titanosaurs (Magyarosaurus) and ornithopods (Telmatosaurus and Zalmoxes), but also turtles and crocodylomorphs[4]. Oarda de Jos is another river locality that may have represented a bird breeding colony[5], but also includes turtles, amphibians, fish, lizards, crocodylomophs, dinosaurs and mammals [4]. While it has been suggested that pterosaur material has been found here, this was actually a misidentified turtle [6-7]. The final site I will highlight from the Transylvanian Basin is that of Râpa Roşie, the "Red Ravine". This is a breathtaking site that reminds me of the badlands of southern Alberta, but with massive imposing red cliffs. Vertebrate fossils from here include crocodylomorphs like Allodaposuchus, turtles, azhdarchid pterosaurs, titanosaurid sauropods, ornithopods (both Telmatosaurus and Zalmoxes), ankylosaurs, and theropods[4]. In the Transylvanian Basin alone there are numerous vertebrate groups represented from several fossil-bearing localities showing just how rich this region is, and this is just a snapshot of all the localities! 

The foot of Balaur bondoc from Csiki et al. [1]

Haţeg Basin

Vadu

Sînpetru sandstone

While the Transylvanian Basin is certainly fossiliferous, the Haţeg Basin is the more famous of the two, and arguably even more fossil-rich. The first site to discuss is near the town of Sînpetru (or Sânpetru sometimes), and is the stratotype of the Sînpetru Formation. This is now a protected site so no hammering or digging is allowed, but you can still go and take a look to see if anything is there on the surface. Here, several dinosaur, crocodile, turtle and mammal fossils have been found. Not far from Sînpetru is the river site of Vadu, which is set in the middle of the basin with the Carpathian Mountains on all sides. This is a very shallow river with fossils consisting of birds, dinosaurs, crocodylomorphs and much more. Another interesting site is Tustea, which is best known for a large number of dinosaur eggs, including egg clutches, which are thought to be from the ornithopod dinosaur Telmatosaurus or the titanosaurid Magyarosaurus due to the presence of their fossils in this region as well. Additionally, turtle, crocodylomorph, mammal, and pterosaur fossils have also been found here, one of the most famous perhaps being that of the giant pterosaur Hatzegopteryx thambena, which was described first from here and another site Vălioara[8]. Finally one of the most active sites in recent years is that of the Barbat River at Pui. Numerous dinosaur fossils have been found here including the ornithopods Telmatosaurus and Zalmoxes, pterosaur fossils like the recently described short-necked azhdarchid vertebra[9], turtles (e.g. Kallokibotion), crocodylomorphs, mammals, and more. 

Artists impression of a short-necked azhdarchid pterosaur based on a cervical vertebra from the Barbat River described by Vremir et al. [9]. Image copyright Mark Witton.

 Interpretations and observations

Little Magyarosaurus being tormented by a flock of
Hatzegopteryx - a possible use of terrestrial stalking. Image
copyright Mark Witton.

Interpreting the palaeoecology and palaeobiology of different animals in this region has been a heavily debated and hot topic in palaeontology over the last few decades. Island dwarfism is a process that applies today to animals living on islands where their size is limited and over many generations animals get smaller and smaller as their resources are limited. Nopsca first suggested this was what had happened on Haţeg Island in the Late Cretaceous since most of the dinosaurs in particular are significantly smaller than their contemporaries in other parts of the world. For example, Magyarosaurus was a titanosaurid sauropod dinosaur, a kind of large long-necked dinosaur. Unlike what we are used to seeing as the giant long-necked dinosaurs like Apatosaurus, this dinosaur was less than 2m tall. Additionally the ankylosaur Struthiosaurus is smaller than other members of its group. Currently, very few theropod remains are known, and the best known is that of Balaur, which is similar in size to a small chicken at approximately 50 cm high and 2 m long. With theropods being so rare, what would the main predator in such an environment be? Well one thought is that the giant pterosaur Hatzegopteryx terrorised the land animals as the major predator[10]. With this animal being by far the largest found so far, this is a well supported theory. These points all suggest that the Late Cretaceous islands of Romania were a strange and dangerous place to live.

New finds?

 

Corvin Castle in Hunedoara

Barbat River in the snow

Unfortunately I can't reveal too much about our trip yet as there are publications imminent and forthcoming, but I will say that we had a very productive year. We visited a number of sites in both the Transylvanian and Haţeg Basins, and found a lot of bone. Some highlights include some pterosaur material (both cranial and postcranial), a partial ornithopod dinosaur skeleton, and some additional bits and bobs. We had a great time wading through rivers, getting snowed on, checking out little museums, and some of us even got to go see a castle (although not the famous Dracula castle, it's still an awesome castle). 

Keep following for news on the new finds as they become available. I'll update when we have more news!

Special thanks to Prospectiuni and the National Geographic Society for funding for this trip. Without them, this trip would not be possible!

References

1. Csiki, Z., et al. 2010. An aberrant island-dwelling theropod dinosaur from the Late Cretaceous of Romania. PNAS 107: 15357-15361.

2. Vremir, M., et al. 2013. A new azhdarchid pterosaur from the Late Cretaceous Transylvanian Basin, Romania: Implications for azhdarchid diversity and distribution. PLoS One 8: e54268.

3. Vremir, M., et al. 2014. Petreşti-Arini — An important but ephemeral Upper Cretaceous continental vertebrate site in the southwestern Transylvanian Basin, Romania. Cretaceous Research 49: 13-38.

4. Vremir, M. 2010. New faunal elements from the Late Cretaceous (Maastrichtian) continental deposits of Sebeş area (Transylvania). Terra Sebus. Act Musei Sabesiensis 2: 635-684.

5. Dyke, GJ., et al. 2014. A drowned Mesozoic bird breeding colony from the Late Cretaceous of Transylvania. Naturwissenschaften 99: 435-442.

6. Grellet-Tinner, G., and Codrea, VA. In Press. Thalassodromeus sebesensis, an out of place and out of time Gondwana tapejarid pterosaur. Gondwana Research. In Press - online July 2014.

7. Dyke, GJ., et al. In Press. Thalassodromeus sebesensis — A new name for an old turtle. Comment on "Thalassodromeus sebesensis, an out of place and out of time Gondwana tapejarid pterosaur", Grellet-Tinner and Codrea (online July 2014 DOI 10.1016/j.gr.2014.06.002). Gondwana Research. In Press - online August 2014.

8. Buffetaut, E., et al. 2003. Giant azhdarchid pterosaurs from the terminal Cretaceous of Transylvania (western Romania). Geological Society, London, Special Publications 217: 91-104.

9. Vremir, M., et al. 2015. A medium-sized robust-necked azhdarchid pterosaur (Pterodactyloidea: Azhdarchidae) from the Maastrichtian of Pui (Haţeg Basin, Transylvania, Romania). American Museum Noviciates 3827:1-16.

10. Witton, MP., and Naish, D. 2008. A reappraisal of azhdarchid pterosaur functional morphology and paleo-ecology. PLoS ONE 3: e2271.