ScienceDaily (Nov. 27, 2009) — A new study pitting academic expertise against a computer in recreating a 425 million-year old jigsaw puzzle has discovered that there is no substitute for wisdom born out of experience.
The research tested the reliability of expert identification versus computer analysis in reconstructing fossils. The investigation, based on fossil teeth from extinct vertebrates, found that the most specialized experts provided the most reliable identifications.
These are four different types of conodont teeth from different species -- pieces from different puzzles -- mounted on a pinhead. (Credit: University of Leicester)
University of Leicester researcher Dr Mark Purnell said: "Being a palaeontologist can be fun, but sometimes it isn't easy. Take vertebrates, the group to which we belong. When a vertebrate animal dies, whether it's a fish, a sabre-tooth cat or a dinosaur, the flesh rots away and the bones of the skeleton are usually scattered before being fossilised. In order to interpret them correctly, the palaeontologist must piece them back together, or at least work out which bits are which.
"This is difficult enough when you have modern relatives for comparison; but what if there's nothing alive today that's remotely like the extinct animal you need to analyse? It's exactly like doing a jigsaw puzzle without a picture."
This is what faces palaeontologists who study conodonts. Lead author David Jones, who carried out the study while at the University of Leicester, explains: "Earth's oceans teemed with conodonts for 300 million years; they were the most common vertebrates around, and they were the first to evolve teeth. In fact the conodont skeleton was all teeth: a basket of hacksaw-shaped blades which was extended out of the mouth to grab prey, behind which lay pairs of slicing blades and crushing teeth -- a set of gnashers straight out of Alien."
Ancient marine rocks are often packed with hundreds or thousands of scattered conodont teeth, with many species jumbled up together.
"To make matters worse, within any one animal, teeth from different parts of the skeleton looked almost identical! Now we have a jigsaw puzzle with no picture, where each piece could go in different places. But just so it's not too easy, conodont teeth are also microscopic, "said Dr Purnell, of the Department of Geology.
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Journal Reference:
Jones et al. Morphological criteria for recognising homology in isolated skeletal elements: comparison of traditional and morphometric approaches in conodonts. Palaeontology, 2009; 52 (6): 1243 DOI: 10.1111/j.1475-4983.2009.00915.x
Morphological criteria for recognising homology in isolated skeletal elements: comparison of traditional and morphometric approaches in conodonts
by DAVID JONES*,‡, MARK A. PURNELL* and PETER H. von BITTER†
*Department of Geology, University of Leicester, Leicester LE1 7RH, UK; e-mails david.jones@bristol.ac.uk; map2@le.ac.uk
†Palaeobiology Division, Department of Natural History, Royal Ontario Museum, and Department of Geology, University of Toronto, Toronto, ON, Canada M5S 2C6; e-mail peterv@rom.on.ca
‡Current address: School of Biological Sciences, Monash University, Melbourne, VIC 3800, Australia
KEYWORDS
homology • morphometrics • skeleton • conodont • Wurmiella excavata
ABSTRACT
Abstract: Accurate hypotheses of primary homology are fundamental to many aspects of the systematics and palaeobiology of fossils. They are particularly critical for conodonts: virtually all areas of conodont research are underpinned by homology, yet the majority of conodont taxa are found only as disarticulated skeletal elements, and hypotheses of element homology are inferred from morphological comparisons with complete skeletons. This can cause problems in taxa where more than one location within the conodont skeleton is occupied by elements with similar morphology. In such cases, morphological comparisons can yield equivocal or erroneous hypotheses of homology of isolated elements. The Eramosa Lagerstätte of Ontario (Silurian, Wenlock) preserves both isolated skeletal elements and articulated conodont skeletons. The latter provide a topological context within which to test hypotheses of element homology and allow blind testing of qualitative discrimination of elements. When applied to P1 and P2 elements of Wurmiella excavata, this revealed inaccuracy and inconsistency in distinguishing these P element types. Standardised morphometric protocols were used to further test the efficacy of those characters used in traditional qualitative identification of P element homology, revealing that, individually, none of these characters provides an effective discriminator between P element types. Principal components and discriminant function analyses of ten 'traditional' morphological variables combined can distinguish P1 from P2 elements with a similar success rate to expert identification. Eigenshape and elliptic Fourier analyses of element outlines proved less effective at capturing shape differences that allowed for discrimination between P1 and P2 elements. Analysis of both traditional and outline data demonstrates that in some individuals P1 and P2 elements are morphologically distinct from one another, while in others they are almost indistinguishable. These results demonstrate that although qualitative assessments of homology can be prone to error, especially when undertaken by inexperienced researchers, the morphometric and analytical protocols used here provide effective additional tool for discriminating morphologically similar but non-homologous elements. These methods thus hold promise of broad application to other conodont taxa where identification of element homology in collections of isolated specimens is problematic.
Typescript received 9 April 2008; accepted in revised form 15 March 2009
DIGITAL OBJECT IDENTIFIER (DOI)
10.1111/j.1475-4983.2009.00915.x About DOI
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