Dr%20Duncan%20Murdock: List of publications

Conodonts were the first vertebrates to develop mineralized dental tools, known as elements. Recent research suggests that conodonts were macrophagous predators and/or scavengers but we do not know how this feeding habit emerged in the earliest coniform conodonts, since most studies focus on the derived, 'complex' conodonts. Previous modelling of element position and mechanical properties indicate they were capable of food processing. A direct test would be provided through evidence of <i>in vivo</i> element crown tissue damage or through <i>in vivo</i> incorporated chemical proxies for a shift in their trophic position during ontogeny. Here we focus on coniform elements from two conodont taxa, the phylogenetically primitive <i>Proconodontus muelleri</i> Miller, 1969 from the late Cambrian and the more derived <i>Panderodus equicostatus</i> Rhodes, 1954 from the Silurian. Proposing that this extremely small sample is, however, representative for these taxa, we aim to describe in detail the growth of an element from each of these taxa in order to the test the following hypotheses: (1) <i>Panderodus</i> and <i>Proconodontus</i> processed hard food, which led to damage of their elements consistent with prey capture function; and (2) both genera shifted towards higher trophic levels during ontogeny. We employed backscatter electron (BSE) imaging, energy-dispersive X-ray spectroscopy (EDX) and synchrotron radiation X-ray tomographic microscopy (SRXTM) to identify growth increments, wear and damage surfaces, and the Sr/Ca ratio in bioapatite as a proxy for the trophic position. Using these data, we can identify whether they exhibit determinate or indeterminate growth and whether both species followed linear or allometric growth dynamics. Growth increments (27 in <i>Pa. equicostatus</i> and 58 in <i>Pr. muelleri</i>) were formed in bundles of 4-7 increments in <i>Pa. equicostatus</i> and 7-9 in <i>Pr. muelleri</i>. We interpret the bundles as analogous to Retzius periodicity in vertebrate teeth. Based on applied optimal resource allocation models, internal periodicity might explain indeterminate growth in both species. They also allow us to interpret the almost linear growth of both individuals as an indicator that there was no size-dependent increase in mortality in the ecosystems where they lived <i>e.g</i>., as would be the case in the presence of larger predators. Our findings show that periodic growth was present in early conodonts and preceded tissue repair in response to wear and damage. We found no microwear and the Sr/Ca ratio, and therefore the trophic position, did not change substantially during the lifetimes of either individual. Trophic ecology of coniform conodonts differed from the predatory and/or scavenger lifestyle documented for "complex" conodonts. We propose that conodonts adapted their life histories to top-down controlled ecosystems during the Nekton Revolution.

Predation is potentially one of the most impactful evolutionary traits to have ever developed. Conodonts, an extinct group of early vertebrates, developed the first phosphatic dental tools, known as elements. Elements ranged from simple coniform types to more complex morphologies, predominantly in more derived species. Unlike the teeth of other vertebrates, these continuously grew throughout their lifetime by the periodic accretion of new lamellar tissues. This unique growth process continuously records chemical and physical characteristics throughout its lifespan which, when accessed, gives direct insight into the animal’s ecology and mode of life. Multiple lines of evidence, such as microwear studies and growth allometry, indicate that adult conodonts fed as predators and/or scavengers. There is little direct independent evidence for feeding ecologies in the earliest conodonts with coniform elements apparatuses, although previous modelling of element position and mechanical properties indicate these were capable of processing or manipulation of food. A direct test would be provided through evidence of tissue damage and its chemical composition. Our research focuses on samples of the coniform genus Panderodus (Family: Panderodontidae) from the Silurian of Poland and Ukraine. Panderodus has the best constrained apparatus reconstruction of any coniform conodont. Here we employ Backscatter electron (BSE) imaging and Energy-dispersive X-Ray spectroscopy (EDX) to identify growth dynamics, microwear, and chemical sclerochronology recorded within this unique mode of growth. Our results have direct implications not just for understanding the feeding mode of Panderodus, but also the origination of predation in the earliest vertebrates in the fossil record.

In a world where an increasing number of resources are hidden behind paywalls and monthly subscriptions, it is becoming crucial for the scientific community to invest energy into freely available, community-maintained systems. Open-source software projects offer a solution, with freely available code which users can utilise and modify, under an open source licence. In addition to software accessibility and methodological repeatability, this also enables and encourages the development of new tools. As palaeontology moves towards data driven methodologies, it is becoming more important to acquire and provide high quality data through reproducible systematic procedures. Within the field of morphometrics, it is vital to adopt digital methods that help mitigate human bias from data collection. In addition, mathematically founded approaches can reduce subjective decisions which plague classical data. This can be further developed through automation, which increases the efficiency of data collection and analysis. With these concepts in mind, we introduce two open-source shape analysis software, that arose from projects within the medical imaging field. These are ImageJ, an image processing program with batch processing features, and 3D Slicer which focuses on 3D informatics and visualisation. They are easily extensible using common programming languages, with 3D Slicer containing an internal python interactor, and ImageJ allowing the incorporation of several programming languages within its interface alongside its own simplified macro language. Additional features created by other users are readily available, on GitHub or through the software itself. In the examples presented, an ImageJ plugin “FossilJ” has been developed which provides semi-automated morphometric bivalve data collection. 3D Slicer is used with the extension SPHARM-PDM, applied to synchrotron scans of coniform conodonts for comparative morphometrics, for which small assistant tools have been created in Python.

Background: The origin of the body plan of modern velvet worms (Onychophora) lies in the extinct lobopodians of the Palaeozoic. Helenodora inopinata, from the Mazon Creek Lagerstätte of Illinois (Francis Creek Shale, Carbondale Formation, Middle Pennsylvanian), has been proposed as an intermediate between the “weird wonders” of the Cambrian seas and modern terrestrial predatory onychophorans. The type material of H. inopinata, however, leaves much of the crucial anatomy unknown. Results: Here we present a redescription of this taxon based on more complete material, including new details of the head and posterior portion of the trunk, informed by the results of experimental decay of extant onychophorans. H. inopinata is indeed best resolved as a stem-onychophoran, but lacks several key features of modern velvet worms including, crucially, those that would suggest a terrestrial mode of life. Conclusions: The presence of H. inopinata in the Carboniferous demonstrates the survival of a Cambrian marine morphotype, and a likely post-Carboniferous origin of crown-Onychophora. Our analysis also demonstrates that taphonomically informed tests of character interpretations have the potential to improve phylogenetic resolution.

Conodonts are the first vertebrates to bear a mineralized skeleton, restricted to an array of tooth‐like feeding elements. The functional implications for the development of tooth‐like elements differentiated into two tissues is tested using 2D finite element modeling, mapping the patterns of stress and strain that elements with differing material properties exhibited during function. Addition of a stiff crown does not change the patterns of stress, rather it reduces the deformation of the element under the same force regime, and distributes stress more evenly across the element. The euconodont crown, like vertebrate dental enamel, serves to stiffen the element and protect the underlying dentine. Stiffness of the crown may be a contributing factor to the subsequent diversity of euconodont form, and logically function, by allowing a greater range of feeding strategies to be employed. The euconodont crown also serves as an analogue to enamel and enameloid, demonstrating that enamel‐like tissues have evolved multiple times in independent vertebrate lineages, likely as a response to similar selective pressures. Conodonts can, therefore, serve as an independent test on hypotheses of the effect of ecology on the development of the vertebrate skeleton.

Conodonts are an extinct group of jawless vertebrates whose tooth-like elements are the earliest instance of a mineralized skeleton in the vertebrate lineage1,2, inspiring the ‘inside-out’ hypothesis that teeth evolved independently of the vertebrate dermal skeleton and before the origin of jaws3,4,5,6. However, these propositions have been based on evidence from derived euconodonts. Here we test hypotheses of a paraconodont ancestry of euconodonts7,8,9,10,11 using synchrotron radiation X-ray tomographic microscopy to characterize and compare the microstructure of morphologically similar euconodont and paraconodont elements. Paraconodonts exhibit a range of grades of structural differentiation, including tissues and a pattern of growth common to euconodont basal bodies. The different grades of structural differentiation exhibited by paraconodonts demonstrate the stepwise acquisition of euconodont characters, resolving debate over the relationship between these two groups. By implication, the putative homology of euconodont crown tissue and vertebrate enamel must be rejected as these tissues have evolved independently and convergently. Thus, the precise ontogenetic, structural and topological similarities between conodont elements and vertebrate odontodes appear to be a remarkable instance of convergence. The last common ancestor of conodonts and jawed vertebrates probably lacked mineralized skeletal tissues. The hypothesis that teeth evolved before jaws and the inside-out hypothesis of dental evolution must be rejected; teeth seem to have evolved through the extension of odontogenic competence from the external dermis to internal epithelium soon after the origin of jaws.

Natural assemblages of a new conodont taxon, Notiodella keblon, from the Upper Ordovician Soom Shale Lagerstätte of South Africa contain 17 elements. This is the first time that a 17‐element apparatus plan has been unequivocally demonstrated in conodonts. The apparatus comprises paired P1, P2, P3, M, S1, S2, S3 and S4 elements and an unpaired, axial S0 element and provides a new template for use in the reconstruction of apparatuses from the collections of dispersed elements, particularly for those with icrion‐bearing P1 elements and perhaps for other balognathids.

The evolutionary history of biomineralization in animals is crucial to our understanding of modern mineralized tissues. Traditional methods of unravelling this history have aimed to derive a theory of the development of biomineralization through evolution by the comparison of mineralized systems in model organisms. This has led to the recognition of the ‘biomineralization toolkit’ and raised the question of the homology of mineralized tissues versus convergent or parallel evolution. The ‘new animal phylogeny’ reveals that many of the groups known to biomineralize sit among close relatives that do not, and it favours an interpretation of convergent or parallel evolution for biomineralization in animals. In addition, the fossil record of the earliest mineralized skeletons presents a rapid proliferation of biomineralization across a range of animal phyla with fossil representatives of many modern biomineralizing phyla. A synthesis of molecular, developmental, phylogenetic and fossil evidence demonstrates the convergent or parallel evolution of biomineralization in animals at the phylum level. The fossil record of the Cambrian explosion not only provides vital evidence for the evolution of animal mineralized tissues but also suggests a mechanism for its rapid and synchronous convergent origin.