by the Palaeontology [online] team
We’re now into our sixth volume — and calendar year — at Palaeontology [online]. Over the years, we have introduced a lot of fossil groups, concepts from palaeontology and overviews of different parts of our field. An intention when we started was also to provide the occasional overview of happenings in the world of palaeontology: to reflect new developments and highlight some current ideas. To that end, we have chosen to start 2016 by looking back over the past year, and forward into the next. In this article, members of the Palaeontology [online] team have chosen their favourite papers from 2015, and indicated what they hope to be up to over the next 12 months. So without further ado, here is team Palaeontology [online]!
My favourite paper of 2015 — Porro et al. (2015): One of the most important events in the history of life on Earth was the colonization of land by vertebrates, which was fundamental to the group’s subsequent success and modern diversity. Study of the fossil record has allowed palaeontologists to reconstruct this transition in some detail, using a number of fossils of early tetrapods that show the step-by-step transformation from a body adapted for life in water to one adapted for life on land. Acanthostega is one such animal: it lived during the Devonian period (about 365 million years ago) and combines a range of fish-like and tetrapod-like features. A paper published last year by Laura Porro, Emily Rayfield and Jenny Clack used computed tomography (CT) to describe the fossil in unprecedented detail. Acanthostega was originally described in the 1950s by the Swedish palaeontologist Erik Jarvik, and revised in the late 1980s by Clack, an English palaeontologist. The new study by Porro and colleagues was able to build on previous descriptions by constructing a three-dimensional (3D) computer model of Acanthostega, revealing previously hidden and poorly known aspects of the fossil’s shape and structure, or morphology (Fig. 1). This paper provides an excellent case study of the value of CT for studying fossils in great detail. It also serves as a timely reminder that detailed descriptions of fossils remain the foundation of the science of palaeontology.
My plans for 2016: One of the main goals of my research over the next year will be to investigate the evolution of symmetry. In particular, I hope to address how and why echinoderms — sea urchins, starfish and related marine creatures — evolved five-fold symmetry, a characteristic that is rare among modern animals, but common to all living species in the echinoderm group. Intriguingly, the fossil record of echinoderms shows that they were not always like this. Fossil echinoderms displayed a range of different types of symmetry, from bilateral, or mirror-plane, to three-fold and five-fold, but only the last of these remains today. I will analyse early fossil echinoderms using computer modelling to test hypotheses about why five-fold symmetry came to dominate the group.
My favourite paper of 2015 — Brasier et al. (2015): When it comes to looking at ancient life, some of the hard questions hinge on interpretations of what you see in the rock. Does a particular structure represent something that was once living, or is it non-biological in origin? If the former, what kind of organism might it have been, and how do we tell? Answering these questions in an objective way can be very challenging, and interpretations depend in equal parts on the geological setting of a fossil (and hence its taphonomy, or preservation), and on educated speculation from biology — plus, ideally, a healthy dose of scepticism. The authors of one of my favourite papers from 2015 approach these questions using new ways of studying fossils. In this study, they analyse three putative fossil deposits to show the power of a range of cutting-edge methods. In one technique (focused-ion beam, or FIB), they use charged molecules called ions to create very thin wafers of a 3.46-billion-year-old putative fossil from an Australian rock called the Apex chert. Analysing these with very high-resolution transmission electron microscopy, they suggest that structures previously thought to be the fossils of early cells are more likely to be clay-like minerals altered by high-temperature fluids. They use related methods to create 3D reconstructions of some 3.43-billion-year-old structures from another Australian rock called the Strelley Pool Formation. The authors propose that these structures represent some of the earliest known organisms, single cells eking out an existence between sand grains. They finish by analysing structures that are widely accepted to be fossils, from a 1.88-billion-year-old rock found in Canada, the Gunflint Chert. They suggest that one particularly complex organism may be multicellular (Fig. 2) — and if so, very few organisms like it are alive today. I appreciate the authors’ approach in this paper because it demonstrates that by using new techniques and pushing boundaries, we can start to unravel the interplay between geology and biology in complex structures. As a result, interpretations of ancient fossils can be based on an increasingly wide array of evidence. On another level, I believe that to create 3D models of fossils as small as 10 micrometres across is a stunning technological achievement that deserves recognition in itself.
My plans for 2016: One goal for my research in 2016 is to publish work on specimens that document major evolutionary transitions. Over the past few years, I’ve been applying high-resolution CT to a number of fossils rather removed from my usual comfort zone of insects and arachnids. I hope that by using digital visualization to study these, my colleagues and I can provide a little extra information on fossils dating from soon after the evolution of hard parts, and after life first made its way onto land. But I am also expecting to work on a creepy-crawly or two!
My favourite paper of 2015 — Costidis and Rommel (2015): Vertebrate paleontology requires a detailed understanding of modern animals, particularly their skeletal and soft-tissue anatomy, so that we can make inferences about the biology of extinct animals. We have additional motivation to study the head anatomy of whales, because humans may be dramatically impacting the behaviour of these animals with naval sonar, shipping noise and other human-made sounds and activities. Beaked whales, a rarely seen group of deep-diving toothed whales that use echolocation, seem to have a particularly rough time — for example, events in which they have become stranded on land have been associated with naval use of sonar. Dissections of stranded whales have shown signs of decompression sickness, indicated by fat embolisms (similar to blood clots but with fat) in the tissues surrounding the ear and other specialized sound-reception areas in the heads of these animals. The authors of this study take a detailed anatomical look at the veins (notoriously difficult to study under most circumstances) in the heads of a number of specimens of beaked whales, with a specific focus on the sound-reception regions (Fig. 3). They find intricate connections between blood vessels and acoustic fat bodies (specialized areas important for sound reception and production). This has implications for how nitrogen gas moves between the blood and fat tissue (important for avoiding decompression sickness on deep dives), and for fat clots that may be caused by trauma induced by responses to naval sonar deployment. My favorite part of this paper was the 3D PDF with isolated anatomical regions that one can rotate in the digital version of the paper! This study really embraces modern technological advances and I look forward to seeing more from these great anatomists (and citing them in my work on fossil whales).
My plans for 2016: I plan to continue my work on corals, which uses both morphological and molecular data sets to investigate how living and fossil corals are related. This work will make it easier to put fossils into groups with modern corals to form a more accurate and complete coral family tree, and may also help to plan for their conservation (which is critical given the present biodiversity crisis). Other work in the pipeline includes more projects on whale inner ears and brain evolution in both extant and fossil animals, as well as some new work on dinosaurs from the Transantarctic Mountains!
My favourite paper of 2015 — Molnar et al. (2015): I have quite an interest in how we can work out how much a joint would move from bones alone. If we are to reconstruct how extinct forms such as dinosaurs moved, we need to know how much their joints could move. The trouble is that you can’t just take bones and wiggle them together, because in life all the soft tissues around them — cartilage, muscles, skin, ligaments — affect the range of motion. Molnar and colleagues did a great study looking into the range of motion of vertebrae in extinct and extant crocodylomorphs, the group that includes crocodiles and their relatives. They physically measured dead specimens at various stages of dissection, and also used computer-based CT and animation techniques — a really cool combination. Their study agreed with the idea that osteoderms (bony structures in the skin) in early crocodylomorphs helped to stabilize the back.
My plans for 2016: This year should see the publication of a book on dinosaur tracks that I’ve been editing along with Annette Richter and Daniel Marty. It’s been several years in the making, but we’re finally on the home stretch, and it will be great to see it come out. I’m also hoping to make serious headway on a follow-up to my 2014 paper with Steve Gatesy. Perhaps more exciting, though, is that this year I’ll get my first PhD student. She’ll be studying plesiosaur neck hydrodynamics, and I’m looking forward to seeing that project come to life and evolve. Aside from research, I’ll be developing some new courses to teach on evolution and locomotion, as well as continuing my current teaching in those areas.
Suggestions for further reading:
Brasier, M. D., Antcliffe, J., Saunders, M. & Wacey, D. Changing the picture of Earth’s earliest fossils (3.5–1.9 Ga) with new approaches and new discoveries. Proceedings of the National Academy of Sciences 112, 4859–4864 (2015). DOI: 10.1073/pnas.1405338111
Costidis, A. M. & Rommel, S. A. The extracranial venous system in the heads of beaked whales, with implications on diving physiology and pathogenesis. Journal of Morphology 1, 34–64 (2015). DOI: 10.1002/jmor.20437
Falkingham, P. L. & Gatesy, S. M. The birth of a dinosaur footprint: Subsurface 3D motion reconstruction and discrete element simulation reveal track ontogeny. Proceedings of the National Academy of Sciences 111, 18279–18284 (2014). DOI: 10.1073/pnas.1416252111
Molnar, J., Pierce, S. E., Bhullar, B.-A. S., Turner, A. H. & Hutchinson, J. R. Morphological and functional changes in the vertebral column with increasing aquatic adaptation in crocodylomorphs. Royal Society Open Science 2, 150439 (2015). DOI: 10.1098/rsos.150439
Porro, L. B., Rayfield, E. J. & Clack, J. A. Descriptive anatomy and three-dimensional reconstruction of the skull of the early tetrapod Acanthostega gunnari Jarvik, 1952. PLoS ONE 10, e0124731 (2015). DOI: 10.1371/journal.pone.0124731
Zamora, S. & Rahman, I. A. Deciphering the early evolution of echinoderms with Cambrian fossils. Palaeontology 57, 1105–1119 (2014). DOI: 10.1111/pala.12138