The Geology Section (C) of the Leicester Literary and Philosophical Society presents

Dynamic dinosaurs!

Cutting edge approaches to ecology and behaviour

Annual Saturday Seminar, 15 March 2008

9.00 am – 5.00 pm

Ken Edwards Building, LT1

University of Leicester

Everyone knows about dinosaurs, don’t they? We have all seen them chasing across the big screen, or in various natural history-style programmes on the television. But what do we really know about these apparently familiar animals, and how can scientists determine where they lived, what they looked like, how fast they ran, what they ate, and how their brains worked? New research, new technologies, and new fossils have led to major changes in the way dinosaurs are studied, and are revolutionising our understanding of many areas of dinosaur biology. We have brought together a group of leading international dinosaur experts, all skilled in communicating in an understandable way, to address this exciting area of science. They will present a series of fully illustrated, accessible talks and discuss the latest developments in dinosaur research; developments which will challenge what we all think we already know about these iconic animals.

Registration

We have a limited number of free tickets (not including lunch) for pre-university age students and for one accompanying teacher per group. These will be allocated on a first-come-first-served basis and must be booked in advance. Please indicate when booking how many tickets are for students.

Otherwise, Tickets for the Seminar are £18.00 with a buffet lunch or £12.00 without lunch. There are a limited number of free child places for under 16 year olds accompanied by a paying adult, although an additional charge of £6 is required if they would like lunch.

Please purchase tickets by downloading and completing the online form. For more details of the Seminar, please contact either Mark Evans (mark.evans@leicester.gov.uk) or Joanne Norris (j.e.norris@ntlworld.com; 0116 2833127).

Conference Programme

09.00

Assemble

Opening

Dr Joanne E. Norris, Chairman, Geology Section (C), Leicester Literary and Philosophical Society

Feathered dinosaurs, flying dinosaurs, and birds

Dr David M. Unwin (Dept for Museum Studies, Univ. of Leicester)

Abstract

The evolution of bird brains and flight

Dr Angela C. Milner (Palaeontology Dept, Natural History Museum, London)

Abstract

Coffee

Chewing machines: modelling feeding in early herbivorous dinosaurs

Laura B. Porro (Dept of Earth Sciences, Univ. of Cambridge)

Abstract

Duck-billed dentistry: evidence for hadrosaur diet from tooth microwear

Vince Williams (Dept of Geology, Univ. of Leicester)

Abstract

Lunch

‘The bounce has gone from my bungee’: reconstructing dinosaur biomaterials

Dr Phillip L. Manning (School of Earth, Atmospheric & Environmental Sciences & The Manchester Museum, Univ. of Manchester)

Abstract

Dinosaur evolution on a dynamic Earth: new approaches to geographic and palaeoecological questions

Dr Paul Upchurch (Dept of Earth Sciences, University College, London)

Abstract

Tea

Running with dinosaurs: physics, physiology and fossils

Dr Bill Sellers (Faculty of Life Sciences, Univ. of Manchester)

Abstract

Into the unknowns: estimates, assumptions and validation in dinosaur biomechanics

Dr John R. Hutchinson (Royal Veterinary College, Univ. of London)

Abstract

Discussion

Concluding Remarks & Close

Reception. To be held in Seminar Rooms in the Ken Edwards building

Conference abstracts

Feathered dinosaurs, flying dinosaurs, and birds

David M. Unwin

Department for Museum Studies, University of Leicester

Abstract

Feathers are surely one of the most extraordinary of all organic structures. Essentially outgrowths of the skin built from strands of protein, these remarkable adaptations surpass anything yet designed by the human hand. Tough, strong, durable, waterproof and incredibly light, feathers serve an extraordinary variety of functions. Endowed with wings constructed from these biological wonders, birds achieve unmatchable flight performances as seen in the oceanic distances covered by the albatross, the speed of a falcon and the almost magical hovering ability of humming birds. Nestling beneath our eiderdowns we thank their insulatory ability, as do King Penguins bent beneath Antarctic snowstorms. Waterproofed, ducks do not sink, camouflaged, the Nightjar hides, adorned, the Peacock, parrots and pink flamingos strive to pass on their genes. Birds, the only animals alive today that bear feathers, are defined by them and owe much of their extraordinary success (some 10,000 species and a 150 million year history) to these evolutionary marvels.

Naturally, the prominence of feathers means that their structure, properties and, above all, their origin have attracted a great deal of scientific interest. How did they first evolve? Under what circumstances did this take place, why did it happen? These are vital questions to which studies of feather construction and development have offered some clues, but far from complete answers.

Of course, the fossil record is the obvious place to search for evidence but, until recently, it too provided relatively little to go on. This might seem surprising, after all, Archaeopteryx, the oldest known bird, dating back to the Upper Jurassic, has been known since the mid 19^th century and is justifiably famous for its remarkably well preserved feathers. They are almost identical to those of modern birds, however, and while they and numerous other finds of fossil feathers in younger rocks confirm that all birds back to the earliest forms were feathered, they reveal little about the origins of these undoubtedly ancient structures.

Logically, it would seem that feathers must have appeared before Archaeopteryx and passed through their early stages of evolution in the ancestors of birds. But who were birds’ ancestors? This question has been strenuously debated for much of the last two centuries and many different candidates have been put forward over the years: small, lizard-like gliders; those membrane-winged reptilian fliers the pterosaurs; and, unlikely as it may seem, even relatives of crocodiles. The answer, however, is dinosaurs, or, more precisely, theropods, carnivores that came in all shapes and sizes and epitomised, for most people, by those cinematic bad guys – Velociraptor and Tyrannosaurus rex.

The notion that birds are descended from dinosaurs dates back to the mid 1800’s when it was first proposed by T. H. Huxley, an early supporter of evolutionary theory who became famous as Darwin’s Bulldog. This idea only reentered serious consideration in the late 20^th century following the discovery of theropods such as Deinonychus that had unique bird-like features such as a furcula (wishbone). Moreover, shorn of its feathers, Archaeopteryx looked extraordinarily like a small theropod – indeed, the similarities are so great that several examples of this early bird were initially misidentified as theropod dinosaurs. There was one problem, however. No feathers. At least some theropods must have had them, it was argued, but presumably they had failed to survive the processes of fossilisation. This sounded reasonable, although the existence of bird fossils with feather impressions, most notably Archaeopteryx, preserved in the same deposits as a small dinosaur that conspicuously lacked such features, was slightly worrying.

Then, in the late 1990’s, came a scientific bombshell – Sinosauropteryx, a dinosaur, with feathers. Preserved in fine-grained lake sediments deposited in the Early Cretaceous, about 128 million years ago, in what is now north-east China, this turkey-sized theropod exhibits clear traces of skin bearing tiny, hair-like protofeathers: ‘dino-fuzz’. At least, that is what some researchers claimed, but others were not so sure and wanted more and better evidence. Thankfully, basic economics – selling fossils is far more lucrative than tilling the earth – solved the problem and the Chinese lake deposits began to produce lots and lots and lots more fossils, among them many beautifully preserved small theropods – with feathers. Some bore ‘dino-fuzz’, some had rather simple, but clearly feather-like structures and some came with feathers that were indistinguishable from the feathers of early birds fossilised in the same rocks.

(Right): Feather evolution. Stage I: simple filament. Stage II: splitting of filament into barbs. Stage III: orientation of barbs into a planar structure, development of shaft. Stage IV: evolution of hooks linking barbs into a single continuous vane. (Modified from Xu, 2006, Integrative Zoology 1: 4-11)

(Left): Head and neck of Sinosauropteryx showing dense pelt (black) of fine, filament-like protofeathers (dino-fuzz). (Photo courtesy of Ji Qiang and Ji Shuan, Geol. Inst. Beijing)

So far, more than ten different kinds of feathered theropods have been found in China and they have already revealed a great deal about some of the key stages in feather evolution. The first stage was no more than a simple, hollow, tube-like outgrowth – the dino-fuzz found in Sinosauropteryx and several other small theropods.

The next stage was simple – splitting of the end of the filament led to the appearance of barbs that initially formed a tuft on a stalk and eventually, as splitting progressed, to a down-like feather. Early feathers of this type are preserved in several theropods including Sinornithosaurus, a chicken-sized cousin of Velociraptor and Dilong a much smaller relative of the king – T. rex. Does this mean that our beloved killer was downy? Perhaps not. Fossilised impressions seem to show that T. rex had a scaly skin and probably didn’t need the insulatory fuzz borne by its diminutive ancestor.

Moving further up the theropod family tree and closer to birds, fossils of Caudipteryx another turkey-sized theropod that belongs to a group called oviraptorosaurs (mistakenly thought to be egg-eaters, but now considered omnivorous, or possibly even herbivorous), reveal two major developments in feather evolution – the appearance of a distinct central shaft and the orientation of barbs into a single plane.

(Right): Microraptor, a four-winged feathered dinosaur from the Early Cretaceous of China. (Portia Sloan 2003)

(Left): Caudipteryx (courtesy of Jim Robins Art)

The final stage of feather evolution saw the appearance of barbules that hooked together the barbs to form a continuous surface, the vane. Asymmetric development of the vane such that the portion on one side of the shaft was narrower than that on the other rendered the feather ready for flight. Feathers of this type are found in all modern flying birds and in many extinct forms including Archaeopteryx. Rather surprisingly, they have also been found in a small Magpie-sized theropod dinosaur called Microraptor where, even more surprisingly, they adorn both the arms and the legs, forming not just two, but four wings.

Undoubtedly, the early evolution of feathers was more complex than the simple picture presented here, but even this represents a tremendous advance over our understanding only a decade ago. Moreover, this basic scenario is strongly supported by studies of the development of feathers which show a sequence of development that matches up quite well to that seen in theropods as they successively become more closely related to birds. But, what does this tell us about why feathers evolved in the first place and what implications does it have for our understanding of dinosaur biology and evolution?

Until recently it was widely believed that the origin of feathers was directly related to the evolution of bird flight. Fossils of feathered dinosaurs show that this cannot be true since neither the dino-fuzz, nor those dinosaurs that bear it, show any identifiable adaptations for flight. More likely in these early stages it acted primarily as insulation, endowing theropods with greater control over their body temperature which, in turn, suggests that their physiology may have been more like that of birds than that of reptiles.

As feathers evolved it seems likely that in more advanced, and increasingly bird-like theropods they acquired several functions perhaps serving as camouflage or for display, or possibly even for waterproofing. Later, with the development of a vane, came the possibility of co-option for flight. Presumably, at this point, theropods such as Microraptor and its relatives had adapted to an arboreal life style, and were using their feathered wings to glide and flap their way through the sky. From here evolution was only a very short step away from Archaeopteryx and the first birds, although whether Microraptor with its weird combination of four wings was directly on the path to birds, or represents one of several lineages that became airborne, just one of which eventually evolved into birds, is still hotly debated.

Feathered dinosaurs count among the most important and exciting scientific discoveries of all time. They provide the first real evidence for key stages in the origin and evolution of feathers; they demonstrate beyond any reasonable doubt that birds descended from dinosaurs; and they reveal a completely new picture of dinosaurs, showing them as they really were, dressed up in all their feathery finery.

Additional reading

American Museum of Natural History. 2001. First dinosaur found with its body covering intact; displays primitive feathers from head to tail. http://www.amnh.org/science/specials/dinobird.html.

Chiappe, L. 2007. Glorified Dinosaurs. The Origin and Early Evolution of Birds. Wiley-Liss. 192pp.

Prum, R. O. & Brush, A. 2003. The feather or the bird, which came first? Scientific American, March 2003.

The evolution of bird brains and flight

Angela Milner

Department of Palaeontology, The Natural History Museum, London

Abstract

It is now almost universally agreed that birds are the descendants of small meat-eating dinosaurs called maniraptorans. The evidence from skeletons is very clear but very little is known about timing and sequence of the huge changes in the brain took place in order to integrate and control wing movements, eyesight and balance – all essential for becoming airborne and staying in control up in the air.

Archaeopteryx, the earliest known bird, dating back 147 million years, is an important ‘half-way house’ in the investigation of the dinosaurian origin of birds since it shares many skeletal characters with maniraptoran theropod dinosaurs and has an almost modern flight feather arrangement shared with birds. The braincase of the holotype London specimen lends itself uniquely to modern non-invasive investigative methods, since it is preserved with little crushing. Computed tomography (CT) scanning and computerized 3-D reconstruction have been used to investigate the detailed anatomy of the braincase and compare it to theropod dinosaurs and birds. Because the brain fits very tightly inside the braincase, it leaves an impression on the internal bone surface. This has also allowed us to visualize the brain shape, size and volume and to reconstruct the inner ear for the first time. The proportions of the brain lobes and the structure of the inner ear show that Archaeopteryx's brain was bird-like and ‘flight ready’.

(Right): 3D reconstruction of the brain of Archaeopteryx

(Left): Archaeopteryx, the earliest known bird

Recently discovered Cretaceous bird and maniraptoran dinosaur fossils, particularly from Liaoning in China, have provided important insights into the theropod-bird transition and the evolution of flight. Unfortunately, they don’t help much with studying how the brain evolved in response to the development of flight because their skeletons are all very flattened. Very few bird fossils preserve the braincase from which brain endocasts can be reconstructed.  However, CT analysis of two Lower Eocene birds from the London Clay of England, Odontopteryx and Prophaethon, demonstrate that they possessed brains comparable in size and shape to those of living seabirds, indicating that the bird brain had reached an evolutionary level close to that of Recent species by that time. However, the brain region responsible for many advanced functions including binocular vision, had not developed fully by the Eocene. These early seabirds nevertheless represent the earliest evidence of ‘modern’ bird brains in the fossil record and have important implications for the evolution of avian cognitive ability leading to the huge diversity of modern birds from chickens to owls and parrots.

References and further reading

Chiappe, L. 2007. Glorified Dinosaurs. The Origin and Evolution of Birds. Hoboken, NJ; John Wiley & Sons, 263 pp.

Domínguez Alonso, P., Milner, A. C., Ketcham, R. A., Cookson, M. J. and Rowe, T. B. 2004. The avian nature of the brain and inner ear of Archaeopteryx. Nature, 430, 666-669.

Milner, A. C. 2002.  Dino-birds. The Natural History Museum, London, 64 pp.

Zhou, Z. 2004. The origin and early evolution of birds: discoveries, disputes and perspectives from fossil evidence. Naturwissenschaften, 91, 455-471.

Chewing machines: modelling feeding in early herbivorous dinosaurs

Laura Porro

Department of Earth Sciences, University of Cambridge, Cambridge, UK

lbp24@esc.cam.ac.uk

Abstract

Understanding the feeding behaviour of dinosaurs allows us to reconstruct the palaeobiology of individual taxa, as well as investigate broader evolutionary questions: how did dinosaurs adapt to their environment? How do complex feeding mechanisms evolve? Do functional innovations drive adaptive radiations? In addition to cranial anatomy, researchers now have access to a number of novel techniques¹ that can potentially shed new light on dinosaur feeding strategies.

Figure 1. (A) Reconstruction of Heterodontosaurus tucki (© Gregory S Paul, used with permission); (B) cranium of Heterodontosaurus tucki

One such technique is finite element analysis (FEA), a method widely used in mechanical engineering and orthopedics to reconstruct and visualize deformation, stress, and strain in complex 3D structures during function. Over the past decade, FEA has been applied increasingly to both living and extinct animals².  The use of FEA to predict mechanical behaviour in extinct taxa requires assumptions to be made when applying input parameters such as material properties, muscle and bite forces, and constraints; thus, caution must be taken when interpreting results³. By asking appropriate questions and recognizing the limitations of the technique (through sensitivity testing), we can have greater confidence in predictions made by FEA.

This presentation will focus on how FEA has been used to better understand skull and jaw design in the plant-eating dinosaur Heterodontosaurus tucki (Fig. 1). Heterodontosaurus is one of the earliest and best-known members of Ornithischia, a large and diverse group of successful Mesozoic herbivores which include such well-known taxa as Triceratops, Iguanodon, and Stegosaurus. The animal features an interesting complex of characters related to feeding, some unique amongst dinosaurs (e.g., a highly differentiated dentition, very low tooth replacement rates, and high-crowned teeth) and some of which (e.g., closely-packed cheek teeth) developed independently in much later ceratopsian and ornithopod dinosaurs. Thus, heterodontosaurids represent an early radiation of plant-dinosaurs with a sophisticated feeding apparatus⁴. Despite a number of proposed hypotheses (fore-aft grinding, long-axis rotation of the lower jaws), the feeding mechanism of this animal remains unknown. Using CT-scanning, 3D models of the skull and lower jaws were created, loaded with muscle and bite forces, and assigned material properties.

Figure 2. Colour-contour finite element plot of skull deformation in Heterodontosaurus during biting (oblique view). Red indicates areas of high deformation; blue indicates areas of low deformation

FEA results (Fig. 2) suggest Heterodontosaurus used a complex jaw mechanism to process vegetation, consisting of medial translation of the lower jaws, slight rotation at the rear of the tooth row, and possibly a small amount of jaw retraction. These predictions are independently supported by: cranial anatomy (including suture morphology and lack of cranial kinesis), dental morphology, and tooth wear. Results highlight structural changes in the skull during the transition from carnivory/omnivory to herbivory and provide new information on the origin and early evolution of herbivory in ornithischian dinosaurs.

References

Barrett, P. M. & Rayfield, E. J. Ecological and evolutionary implications of dinosaur feeding behaviour. Trends in Ecology and Evolution 21, 217-224 (2006).

Rayfield, E. J. Finite element analysis and understanding the biomechanics and evolution of living and fossil organisms. Annual Review of Earth and Planetary Sciences 35, 541-76 (2007).

Alexander, R. M. Dinosaur biomechanics. Proceedings of the Royal Society of London Series B, 7 (2006).

Weishampel, D. B., Dodson, P. & Osmolska, H. The Dinosauria (University of California Press, Berkeley, 2004).

Duck-billed dentistry: evidence for hadrosaur diet from tooth microwear

Vincent Williams and Mark Purnell

Department of Geology, University of Leicester, UK

Abstract

How animals exploit and compete for finite food resources is a fundamental aspect of their ecology and represents a major evolutionary pressure, yet it is often difficult to investigate rigorously in fossil taxa. The evolution of herbivory in dinosaurs, for example, has been linked to major adaptive radiations and macroevolutionary trends, but were these driven by the appearance of new ecological niches, by innovations in feeding mechanisms, or both? The first herbivorous dinosaurs arose from carnivorous ancestors in the Late Triassic and it has been suggested that this was a response to the opening of new ecological niches. Those pioneers were saurischian but it was the ornithischians that developed herbivory to its fullest extent. Currently, models of feeding mechanisms in dinosaurs are based on analyses of functional morphology and whilst this approach generates well-constrained hypotheses, they are difficult to test.

Quantitative tooth microwear analysis is a potent tool that has been used to great effect to investigate the diets of extinct mammals but has never been applied to dinosaurs. The lack of a differentiated heterodont dentition in dinosaurs makes comparisons problematic as we cannot look at homologous facets. Also, whilst the microwear on mammals’ teeth accumulates over a lifetime, dinosaur teeth were continually shed and replaced; was their functional life long enough for diagnostic microwear textures to form? We have conducted the first quantitative analysis of tooth microwear in dinosaurs. Our results demonstrate that microwear can provide powerful insights into the precise jaw motions of dinosaur feeding and provides a robust test of functional hypotheses.

'The bounce has gone from my bungee’: reconstructing dinosaur biomaterials

Phillip L. Manning,

School of Earth, Atmospheric & Environmental Sciences and

The Manchester Museum,

University of Manchester, Manchester, M13 9PL

phil.manning@manchester.ac.uk

Abstract

Bones, tendons and ligaments of extant vertebrates are both tough and flexible composite materials that have evolved to provide many important properties to aid the locomotor abilities of animals. These structural biomaterials form the basis of the musculoskletal system of all extant and extinct vertebrates. The intimate relationship of biomaterials, such as that between collagen and the mineral component of bone, define their properties and behaviour, from skull to postcranial elements. Whilst fossil bone, tendon and ligament offer information on the size and form of structural materials, the all important soft-tissues that were integral to the performance of such composite biomaterials have usually long since gone. The rare circumstances where soft-tissue structures are preserved in the fossil record offer a two-dimensional glimpse of the once three-dimensional composite materials so critical in life.

The application of imaging technology, combined with recently developed analytical techniques has the potential to reveal much about the growth, structure and properties of ancient biomaterials. The combined use of high-resolution CT scanning, with nanoindentation of materials chosen by applying the principle of the extant phylogenetic bracket (EPB), can help resurrect some mechanical properties from fossil bone. However, an understanding of the relative distribution of organic to inorganic components of vertebrate structural biomaterials might be further elucidated by combining imaging, EPB and proteomic techniques.

Remarkably well-preserved soft-tissue structures in the skin, tendon and bone of a large, late Cretaceous hadrosaur have been imaged using infra-red and electron microscopic techniques, with biomolecules recovered from the structures using proteomic techniques have revealed extremely rare organic information and detail at the micrometer-scale. This information has been used to reconstruct the structure, form and function of skeletal and integument biomaterials from this dinosaur.

The advantages and disadvantages of such high-fidelity information will be discussed, in terms of potential use and the problems associated with handling large and often complex datasets. An example of the locomotary advantage to be gained by the inclusion of biomaterials will also be discussed when modelling the elastic recoil in the vertebral column of bipedal dinosaurs during locomotion. It is suggested that the inclusion of elastic structures within such models are crucial to understanding the locomotor ability of bipedal dinosaurs, having a significant impact on optimum speed and efficiency.

The inclusion of progressively accurate structural biomaterials, based upon fossil and the EPB, can only serve to improve the fidelity of locomotary, finite element and behavioural models for dinosaurs and other extinct vertebrates.

Dinosaur evolution on a dynamic Earth: new approaches to geographic and palaeoecological questions

Paul Upchurch

Department of Earth Sciences, University College, London

Abstract

Many biologists are interested in the factors that determine the geographic distributions of organisms. One important theme concerns "ecology": that is, certain organisms are found in particular places because they possess the environments and resources the organisms need. Another theme is "history". For example, the movement of continents and changes in sea level can result in a group of organisms becoming isolated from the rest of the world.

Palaeontologists are also interested in the complex relationship between ecology and history and would like to understand the factors that control the geographic distributions of extinct species.

Recent advances mean that palaeontologists now have access to a wide range of powerful analytical tools that can be used to test ideas concerning the ecology and history of extinct organisms. One set of approaches searches for patterns in the evolutionary relationships of organisms in order to determine whether the formation and destruction of geographic barriers (such as mountain chains, deserts or oceans) have left a lasting impression on species distributions. Another set of approaches uses Geographic Information Systems (GIS) to plot the distributions of fossils on palaeogeographic maps in order to search for ecological relationships between different species. These studies reveal that the distributions of dinosaurs were strongly influenced by the break-up of Pangaea (the supercontinent that existed between approximately 250 and 90 million years ago). Similarly, GIS-based studies are shedding light on the habitats preferred by particular dinosaur groups, and are also testing claims regarding the diets of plant-eating dinosaurs.

Running with dinosaurs: physics, physiology and fossils

Bill Sellers

Faculty of Life Sciences, University of Manchester

Abstract

Traditional techniques for reconstructing gait in fossil dinosaurs either involve complex animatronic machines or stop motion animation techniques. These techniques rely on a good knowledge of the skeletal anatomy and a familiarity with the range of locomotor styles seen in modern animals. These are mixed with a great deal of artistic skill and often produce visually stunning results. However using these approaches it is impossible to say whether the animal could actually have moved as portrayed. The movements used are anatomically possible but in all likelihood if the animal had actually tried to move like this then it would have fallen over. Even had it managed to stay upright it would not have minimised its cost of locomotion as living animals do. These difficulties can be overcome if we include both Newtonian physics and musculoskeletal physiology in conjunction with skeletal anatomy in our reconstructions. To do this we create a computer model of the musculoskeletal system of our target vertebrate fossil. The limbs and body are reconstructed as jointed segments, and the muscles and tendons are force generators that power the movement. This requires us to make estimates of various soft tissue parameters which are generally not preserved in the fossil record so we use a combination of phylogenetic and functional bracketing to estimate these values from living animals. The computer model is then imported into a physics simulator which solves the equations of motion so that the model moves appropriately given the forces applied by the muscles, by contact with the ground, and by gravity. Unfortunately such a model will not spontaneously walk or run so we use a genetic algorithm search procedure to find muscle activation patterns that optimise global parameters such as minimising energy cost or maximising speed. The end result is the generation of stable gait that is anatomically, physiologically and physically possible. At the same time the gait can represent an objective estimate of the most energetically efficient gait, or alternatively the fastest gait possible for a given animal. Sadly current technology does not produce gaits that look as good as the more artistic techniques and this new technique highlights the uncertainty inherent in all attempts at gait reconstruction. However ultimately it is a very powerful approach for the scientific understanding of dinosaur gait and we predict that as the technology advances it will also find a place assisting more artistic reconstructions.

Into the unknowns: estimates, assumptions and validation in dinosaur biomechanics

John R. Hutchinson

Royal Veterinary College, University of London

Abstract

R.M. Alexander kick-started the field of dinosaur biomechanics in the late 70s-early 80s, showing that dinosaur speeds could be estimated from footprints, and dinosaur posture and gait could be qualitatively assessed from basic bone biomechanics. Since then the tools for studying dinosaur biomechanics have grown so that, unlike in Alexander's earlier studies, they no longer pose a major limit on the kinds of questions that can be asked. It is easy to animate a 3D dinosaur moving dynamically and have it look believable to a layperson. But it is very difficult to base that motion on firm scientific principles. The public may assume that without a time machine, nothing can be resolved scientifically, or on the other hand that we already know the basic principles of animal locomotion well enough to reconstruct dinosaur movement in high detail and confidence.  Neither of these extreme views is correct. This is what makes dinosaur functional analysis an exciting, vibrant and challenging scientific field, and one that is still in its tentative early stages.

Despite innovations in technical procedures and improvements of evidence, all dinosaur functional studies must confront the errors introduced into their quantitative and qualitative estimates by: (1) unknown parameters such as body dimensions and musculoskeletal anatomy of the limbs; (2) assumptions about how mechanical systems function (e.g., moment arms of muscles); (3) abstraction of complex dynamic systems into simpler representations (e.g., 3D into 2D); and (4) inadequate fundamental understanding of how living organisms actually function. I will address these critical issues with examples from my research (Fig. 1), particularly on theropod locomotor biomechanics, using them as springboards to explore the broader field of dinosaur functional analysis.

I will outline where I think we can improve on the problems of ambiguity, examine which specific parameters or assumptions may always involve a large margin of error, and assess how much these problems matter for reaching valid scientific conclusions about dinosaur palaeobiology and evolution. How much does what we don't know matter-what kinds of "error bars" are there on estimates of posture, gait or speed? Does it hurt the field to focus intensely on such issues?

A closing issue is how to deal with pressure from outside of science. The media and public alike thirst for animations of dinosaur movement, and both would like firm science behind it all. But how can one balance scientific ambiguity versus clarity and popular appeal-are the two at loggerheads? Is this a wonderful opportunity for science education, or shouldn't we worry about ambiguity and instead focus on getting ‘the answer’?

Left: A side view of the right leg of an adult Tyrannosaurus rex, represented as a 3D musculoskeletal biomechanical model. What are the inputs and assumptions for such an analysis, and what can they reliably tell us?