Reconstructing an incomparable organism: the Chalicothere in nineteenth and early-twentieth century palaeontology

Abstract

Palaeontology developed as a field dependent upon comparison. Not only did reconstructing the fragmentary records of fossil organisms and placing them within taxonomic systems and evolutionary lineages require detailed anatomical comparisons with living and fossil animals, but the field also required thinking in terms of behavioural, biological and ecological analogies with modern organisms to understand how prehistoric animals lived and behaved. Yet palaeontological material often worked against making easy linkages, bringing a sense of mystery and doubt. This paper will look at an animal whose study exemplified these problems: the Chalicothere. Increasingly (although not unproblematically) recognized as a specific type from finds across North America and Eurasia from the early nineteenth century onwards, these prehistoric mammals showed short back legs terminating in pawed feet, long front limbs ending in sharp claws, a long flexible neck, and herbivorous grinding teeth. The Chalicothere became a significant organism within palaeontological studies, as the unexpected mix of characters made it a textbook example against the Cuvierian notion of "correlation of parts," while explaining how the animal moved, fed and behaved became puzzling. However, rather than prevent comparisons, these actually led to comparative analogies becoming flexible and varied, with different forms of comparison being made with varying methods and degrees of confidence, and with the anatomy, movement and behaviour of giraffes, bears, horses, anteaters, primates and other organisms all serving at various points as potential models for different aspects of the animal. This paper will examine some of the attempts to reconstruct and define the Chalicotheres across a long timescale, using this to show how multiple comparisons and analogies could be deployed in a reconstructive and evolutionary science like palaeontology, and illustrate some of the limits and tensions in comparative methods, as they were used to reconstruct organisms which were thought to be incomparable to any modern animal.

Introduction to “Working Across Species”

“…In using comparison to consider relationships between different species, Liddell made explicit the link between the tangible and intangible, writing, “homology need not be limited to structures,” and could, in fact, be extended to behaviour. 6 Similarly, Manias ( 2018 ) describes how palaeontologists’ comparisons between anatomical features of extinct and extant animal species were extended into comparisons of feeding behaviours, allowing the inference of ecologically adaptive behaviours in extinct animals, as well as their particular ecological environments, both long disappeared from the planet.…”

“…Manias’s ( 2018 ) account of an enigmatic and even “aberrant” family of extinct mammals, the Chalicotheres, plays upon a similar tension, considering how comparisons of anatomical features were supplanted or enhanced by comparisons of inferred ecological behaviours. Spanning a century, from initial fossil discoveries in the 1800s to the unearthing of more complete skeletons in the early twentieth century, Manias uses the Chalicothere to trace paleontological practices from earlier anatomical methods, such as Georges Cuvier’s “correlation of parts,” to later methods “reconstructing fossil animals as living, breathing animals within past ecological communities.” The Chalicothere’s “chimeric” anatomy seemed nonsensical and “incomparable” when considered through Cuvier’s lens; however, comparisons between the extinct organism’s hypothetical ecological behaviours and those of contemporary living animals, such as bears and okapi, made its otherwise disharmonious amalgamation of claws and hooves suddenly comprehensible.…”