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Modern Tapirs as Morphofunctional Analogues for Locomotion in Endemic Eocene European Perissodactyls

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Abstract

Tapirs have historically been considered as ecologically analogous to several groups of extinct perissodactyls based on dental and locomotor morphology. Here, we investigate comparative functional morphology between living tapirs and endemic Eocene European perissodactyls to ascertain whether tapirs represent viable analogues for locomotion in palaeotheres and lophiodontids. Forelimb bones from 20 species of Eocene European perissodactyls were laser scanned and compared to a forelimb dataset of extant Tapirus. Bone shape was quantified using 3D geometric morphometrics; coordinates were Procrustes aligned and compared using Principal Component Analysis and neighbor-joining trees. Functional traits included lever-arm ratios (LARs; proxy for joint angular velocity), long-bone proportions (speed proxy), and estimated body mass. Results suggest that Paralophiodon and Palaeotherium magnum resemble Neotropical tapirs in humeral morphology and LARs. Palaeotheres demonstrate extensive forelimb shape disparity. Despite previous assessments, metacarpal shape analyzes do not support a strong morphological similarity between palaeotheres and tapirs, with Tapirus pinchaque representing the closest analogue for Eocene European equoid manus morphology. Our analyses suggest lophiodontids were not capable of moving as swiftly as tapirs due to greater loading over the manus. We conclude that the variation within modern tapir forelimb morphology confounds the assignment of one living analogue within Tapirus for extinct European equoids, whereas tapirs adapted for greater loading over the manus (e.g., T. bairdii, T. indicus) represent viable locomotor analogues for lophiodontids. This study represents a valuable first step toward locomotor simulation and behavioral inference for both hippomorph and tapiromorph perissodactyls in Eocene faunal communities.

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References

  • Adams WHD, Meunier V (1872) The Pachydermata. In: Adams WHD, Meunier V (eds) Life in the Primeval World. T. Nelson and Sons, New York, pp 107–142

    Google Scholar 

  • Agusti J, Anton M (2004) The Eocene: Reaching the Climax. In: Mammoths, Sabertooths, and Hominids: 65 Million Years of Mammalian Evolution in Europe. Columbia University Press, New York, pp 23–66

    Google Scholar 

  • Alberdi MT, Rodriguez J (2012) Anchitherium Meyer, 1844 (Perissodactyla, Equidae) de Sansan. In: Peigné S, Sen S (eds) Mammiferes de Sansan. Publication Scientifiques du Museum, Paris, pp 487–533

    Google Scholar 

  • Bai B (2017) Eocene Pachynolophinae (Perissodactyla, Palaeotheriidae) from China, and their palaeobiogeographical implications. Palaeontology 60:837–852

    Article  Google Scholar 

  • Bai B, Meng J, Wang Y-Q, Wang H-B, Holbrook LT (2017) Osteology of the middle Eocene ceratomorph Hyrachyus modestus (Mammalia, Perissodactyla). Bull Am Mus Nat Hist 413:1–70

    Article  Google Scholar 

  • Barone R (2000) Muscles de la ceinture et du membre thoraciques. In: Anatomie Comparée Des Mammiferes Domestique. Editions Vigot, Paris, pp 719–842

    Google Scholar 

  • Biewener AA (2005) Biomechanical consequences of scaling. J Exp Biol 208:1665–1676

    Article  PubMed  Google Scholar 

  • Biewener AA, Patek SN (2018) Movement on land. In: Animal Locomotion. Oxford University Press, Oxford, pp 61–89

    Google Scholar 

  • Blondel C (2001) The Eocene-Oligocene ungulates from Western Europe and their environment. Palaeogeogr Palaeoclimatol Palaeoecol 168:125–139

    Article  Google Scholar 

  • Bodmer RE, Brooks DM (1997) Status and action plan of the lowland tapir (Tapirus terrestris). In: Brooks DM, Bodmer RE, Matola S (eds) Tapirs: Status Survey and Conservation Action Plan. IUCN/SSC Tapir Specialist Group, Cambridge, pp 46–56

    Google Scholar 

  • Bronnert C, Gheerbrant E, Godinot M, Métais G (2017) A primitive perissodactyl (Mammalia) from the early Eocene of Le Quesnoy (MP7, France). Hist Biol 30:237–250

    Article  Google Scholar 

  • Buffetaut É (1986) Un Mésosuchien ziphodonte dans l’Éocène supérieurde La Livinière (Hérault, France). Geobios 19:101–113

    Article  Google Scholar 

  • Carrano MT (1998) Locomotion in non-avian dinosaurs: integrating data from hindlimb kinematics, in vivo strains, and bone morphology. Paleobiology 24:450–469

    Article  Google Scholar 

  • Carrano MT (1999) What, if anything, is a cursor? Categories versus continua for determining locomotor habit in mammals and dinosaurs. J Zool 247:29–42

    Article  Google Scholar 

  • Clarke KR (1993) Non-parametric multivariate analyzes of changes in community structure. Austral Ecol 18:117–143

    Article  Google Scholar 

  • Cozzuol MA, Clozato CL, Holanda EC, Rodrigues FHG, Nienow S, de Thoisy B, Redondo RAF, Santos FR (2013) A new species of tapir from the Amazon. J Mammal 94:1331–1345

    Article  Google Scholar 

  • Cuvier G (1812) Recherches sur les ossemens fossiles de quadrupèdes: Tome III. Chez Deterville Libraire, Paris

    Google Scholar 

  • Danilo L, Remy JA, Vianey-Liaud M, Marandat B, Sudre J, Lihoreau F (2013) A new Eocene locality in southern France sheds light on the basal radiation of Palaeotheriidae (Mammalia, Perissodactyla, Equoidea). J Vertebr Paleontol 33:195–215

    Article  Google Scholar 

  • Depéret MC (1907) Études des Membres du Lophiodon. In: Depéret MC (ed) Études Paléontologiques Sur Les Lophiodon Du Minervois: Structure Du Cran, Des Membres et Affinités Générales Des Lophiodon. A. Rey and Company, Lyon pp 34–40

    Google Scholar 

  • DeSantis LRG (2011) Stable isotope ecology of extant tapirs from the Americas. Biotropica 43:746–754

    Article  Google Scholar 

  • DeSantis LRG, Wallace SC (2008) Neogene forests from the Appalachians of Tennessee, USA: geochemical evidence from fossil mammal teeth. Palaeogeogr Palaeoclimatol Palaeoecol 266:59–68

    Article  Google Scholar 

  • Dumbá LCCS, Dutra RP, Cozzuol MA (2018) Cranial geometric morphometric analysis of the genus Tapirus (Mammalia, Perissodactyla). J Mammal Evol. https://doi.org/10.1007/s10914-018-9432-2

    Article  Google Scholar 

  • Earle C (1893) Some points in the comparative osteology of the tapir. Science 21:118

    Article  CAS  PubMed  Google Scholar 

  • Elissamburu A, Vizcaíno SF (2004) Limb proportions and adaptations in caviomorph rodents (Rodentia: Caviomorpha). J Zool 262:145–159

    Article  Google Scholar 

  • Fisher REK, Scott M, Naples VL (2007) Forelimb myology of the pygmy hippopotamus (Choeropsis liberiensis). Anat Rec 290:673–693

    Article  Google Scholar 

  • Franzen JL (1990) Hallensia (Mammalia, Perissodactyla) aus Messel und dem Pariser Becken sowie Nachtrage aus dem Geiseltal. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre 60:175–201

    Google Scholar 

  • Franzen JL (2006) Eurohippus n.g., a new genus of horses from the middle to late Eocene of Europe. Senckenbergiana Lethaea 86:97–102

    Article  Google Scholar 

  • Franzen JL (2010a) The dawn horses of the morning cloud. In: The Rise of Horses: 55 Million Years of Evolution. Johns Hopkins University Press, Baltimore, pp 45–76

    Google Scholar 

  • Franzen JL (2010b) Pseudo horses and relatives of horses. In: The Rise of Horses: 55 Million Years of Evolution. Johns Hopkins University Press, Baltimore, pp 145–164

    Google Scholar 

  • Franzen JL, Haupzeter J (2017) Complete skeleton of Eurohippus messelensis (Mammalia, Perissodactyla, Equoidea) from the early middle Eocene of Grube Messel (Germany). Palaeobio Palaeoenv 97:807–832

    Article  Google Scholar 

  • Froehlich DJ (1999) Phylogenetic systematics of basal perissodactyls. J Vertebr Paleontol 19:140–159

    Article  Google Scholar 

  • Froehlich DJ (2002) Quo vadis eohippus? The systematics and taxonomy of the early Eocene equids (Perissodactyla). Zool J Linn Soc 134:141–256

    Article  Google Scholar 

  • Gewaily MS, Fayed MH, Farrag FA (2017) Architectural and functional specifications of the intrinsic muscles of the forelimb of the Egyptian Baladi goats (Capra hircus). Alexandria J Vet Sci 55:110–124

    Article  Google Scholar 

  • Gregory WK (1929) Mechanics of locomotion in the evolution of limb structure as bearing on the form and habits of the titanotheres and the related odd-toed ungulates. In: Osborn HF (ed) The Titanotheres of Ancient Wyoming, Dakota and Nebraska. United States Government Printing Office, Washington D.C., pp 727–756

    Google Scholar 

  • Hammer Ø, Harper DAT, Ryan PD (2001) PAST: paleontological statistics software package for education and data analysis. Palaeontol Electron 4:9

    Google Scholar 

  • Heissig K (2012) Les Rhinocerotidae (Perissodactyla) de Sansan. In: Peigné S, Sen S (eds) Mammiferes de Sansan. Publication Scientifiques du Museum, Paris, pp 317–486

    Google Scholar 

  • Hildebrand M (1985) Walking and running. In: Hildebrand DB, Bramble M, Liem DM, Wake KF (eds) Functional Vertebrate Morphology. Harvard University Press, Cambridge, pp 38–57

    Chapter  Google Scholar 

  • Holanda EC, Ferrero BS (2013) Reappraisal of the genus Tapirus (Perissodactyla, Tapiridae): systematics and phylogenetic affinities of the South American tapirs. J Mammal Evol 20:33–44

    Article  Google Scholar 

  • Holbrook LT (2001) Comparative osteology of early Tertiary tapiromorphs (Mammalia, Perissodactyla). Zool J Linn Soc 132:1–54

    Article  Google Scholar 

  • Holbrook LT (2009) Osteology of Lophiodon Cuvier, 1822 (Mammalia, Perissodactyla) and its phylogenetic implications. J Vertebr Paleontol 29:212–230

    Article  Google Scholar 

  • Holbrook LT, Lucas SG (1997) A new genus of rhinocerotoid from the Eocene of Utah and the status of North American “Forstercooperia”. J Vertebr Paleontol 17:384–396

    Article  Google Scholar 

  • Hooker JJ (2010a) The mammal fauna of the early Eocene Blackheath Formation of Abbey Wood, London. Monograph of the Palaeontographical Society 624:1–162

    Google Scholar 

  • Hooker JJ (2010b) The “Grande Coupure” in the Hampshire Basin, UK: taxonomy and stratigraphy of the mammals on either side of this major Paleogene faunal turnover. In: Whittaker JE, Hart MB (eds) Micropalaeontology, Sedimentary Environments and Stratigraphy: A Tribute to Dennis Curry (1912–2001). The Geological Society Publishing House, Bath, pp 147–215

    Chapter  Google Scholar 

  • Hulbert RC (2005) Late Miocene Tapirus (Mammalia, Perissodactyla) from Florida, with description of a new species, Tapirus webbi. Bull Florida Mus Nat Hist 45:465–494

    Google Scholar 

  • Hulbert RC, Wallace SC, Klippel WE, Parmalee PW (2009) Cranial morphology and systematics of an extraordinary sample of the late Neogene dwarf tapir, Tapirus polkensis (Olsen). J Paleontol 83:238–262

    Article  Google Scholar 

  • Hutchinson JR, Gatesy SM (2006) Beyond the bones. Nature 440:292–294

    Article  CAS  PubMed  Google Scholar 

  • IBM Corp. (2017) IBM SPSS statistics for windows, version 25.0. IBM Corp., Armonk, NY

  • Joomun SC, Hooker JJ, Collinson ME (2008) Dental wear variation and implications for diet: an example from Eocene perissodactyls (Mammalia). Palaeogeogr Palaeoclimatol Palaeoecol 263:92–106

    Article  Google Scholar 

  • Klingenberg CP (2016) Size, shape, and form: concepts of allometry in geometric morphometrics. Development Genes and Evolution 226:113–137

    Article  PubMed  PubMed Central  Google Scholar 

  • Liebich H-G, Konig HE, Maierl J (2007) Forelimb or thoracic limb (membra thoracica). In: Konig HE, Liebich H-G (eds) Veterinary Anatomy of Domestic Animals: Textbook and Color Atlas. Schlutersche, Stuttgart, pp 145–214

    Google Scholar 

  • MacFadden BJ (1992) What’s the use? Functional morphology of feeding and locomotion. In: Fossil Horses: Systematics, Paleobiology, and Evolution of the Family Equidae. Cambridge University Press, Cambridge, pp 229–262

    Google Scholar 

  • MacFadden BJ (2005) Fossil horses – evidence for evolution. Science 307:1728–1730

    Article  CAS  PubMed  Google Scholar 

  • MacFadden BJ, Hulbert RC (1990) Body size estimates and size distribution of ungulate mammals from the late Miocene Love Bone Bed of Florida. In: Damuth J, MacFadden BJ (eds) Body Size in Mammalian Paleobiology: Estimation and Biological Implications. Cambridge University Press, Cambridge, pp 337–363

    Google Scholar 

  • MacLaren JA, Hulbert RC, Wallace SC, Nauwelaerts S (2018) A morphometric analysis of the forelimb in the genus Tapirus (Perissodactyla: Tapiridae) reveals influences of habitat, phylogeny and size through time and across geographical space. Zool J Linn Soc. 184:499–515

    Article  Google Scholar 

  • MacLaren JA, Nauwelaerts S (2016) A three-dimensional morphometric analysis of upper forelimb morphology in the enigmatic tapir (Perissodactyla: Tapirus) hints at subtle variations in locomotor ecology. J Morphol 277:1469–1485

    Article  PubMed  Google Scholar 

  • MacLaren JA, Nauwelaerts S (2017) Interspecific variation in the tetradactyl manus of modern tapirs (Perissodactyla: Tapirus ) exposed using geometric morphometrics. J Morphol 278:1515–1535

    Article  Google Scholar 

  • Martin JE (2014) A sebecosuchian in a middle Eocene karst with comments on the dorsal shield in Crocodylomorpha. Acta Palaeontol Pol 60:673–680

    Google Scholar 

  • Matola S, Cuarón AD, Rubio-Torgler H (1997) Status and action plan of the Baird’s tapir (Tapirus bairdii). In: Brooks DM, Bodmer RE, Matola S (eds) Tapirs: Status Survey and Conservation Action Plan. IUCN/SSC Tapir Specialist Group, Cambridge, pp 29–45

    Google Scholar 

  • Mead AJ (2000) Sexual dimorphism and paleoecology in Teleoceras, a North American Miocene rhinoceros. Paleobiology 26:689–706

    Article  Google Scholar 

  • Mihlbachler MC, Rivals F, Solounias N, Semprebon GM (2011) Dietary change and evolution of horses in North America. Science 331:1178–1181

    Article  CAS  PubMed  Google Scholar 

  • O’Higgins P, Jones N (1999) Morphologika. Tools for Shape Analysis. University College London, London.

    Google Scholar 

  • Oksanen J, Blanchet FG, Friendly M, Kindt R, Legendre P, McGlinn D, Minchin PR, O’Hara RB, Simpson GL, Solymos P, Stevens MHH, Szoecs E, Wagner H (2018) vegan: Community Ecology Package. R package vers 2.5–3

  • Paradis E, Claude J, Strimmer K (2004) APE: analyzes of phylogenetics and evolution in R language. Bioinformatics 20:289–290

    Article  CAS  PubMed  Google Scholar 

  • Prothero DR (2005) Postcranial osteology. In: The Evolution of North American Rhinoceroses. Cambridge University Press, Cambridge, pp 146–181

    Google Scholar 

  • Prothero DR (2016) Perissodactyla. In: Prothero DR (ed) The Princeton Guide to Prehistoric Mammals. Princeton University Press, Oxford, pp 186–202

    Google Scholar 

  • Radinsky LB (1965) Evolution of the tapiroid skeleton from Heptodon to Tapirus. Bull Mus Comp Zool 134:69–106

    Google Scholar 

  • Radinsky LB (1967) Hyrachyus, Chasmotherium, and the early evolution of helaletid tapiroids. Am Mus Novitates 2313:1–23

    Google Scholar 

  • Remy JA (1992) Observations sur l’anatomie cranienne du genre Palaeotherium (Perissodactyla, Mammalia); mise en evidence d’un nouveu sous-genre, Franzenitherium. Palaeovertebrata 21:105–221

    Google Scholar 

  • Remy JA (2015) Les Périssodactyles (Mammalia) du gisement Bartonien supérieur de Robiac (Éocène moyen du Gard, Sud de la France). Palaeovertebrata 39:1–99

    Article  Google Scholar 

  • Robinet C, Remy JA, Laurent Y, Danilo L, Lihoreau F (2015) A new genus of Lophiodontidae (Perissodactyla, Mammalia) from the early Eocene of La Borie (southern France) and the origin of the genus Lophiodon Cuvier, 1822. Geobios 48:25–38

    Article  Google Scholar 

  • Rohlf FJ, Slice D (1990) Extensions of the Procrustes method for the optimal superimposition of landmarks. Syst Zool 39:40–59

    Article  Google Scholar 

  • Rose KD, Holbrook LT, Rana RS, Kumar K, Jones KE, Ahrens HE, Missiaen PE, Sahni A, Smith T (2014) Early Eocene fossils suggest that the mammalian order Perissodactyla originated in India. Nat Comm 5:5570

    Article  CAS  Google Scholar 

  • RStudioTeam (2016) RStudio: Integrated Development for R

  • Rudwick MJS (2008) The animals from the Gypsum Beds around Paris. In: Rudwick MJS (ed) George Cuvier, Fossil Bones and Geological Catastrophes: New Translations and Interpretations of the Primary Texts. University of Chicago Press, Chicago, pp 59–67

    Google Scholar 

  • Ryder OA (2009) Rhinoceroses, tapirs, and horses (Perissodactyla). In: Hedges SB, Kumar S (eds) The Timetree of Life. Oxford University Press, Oxford, pp 508–510

    Google Scholar 

  • Samuels JX, Van Valkenburgh B (2008) Skeletal indicators of locomotor adaptations in living and extinct rodents. J Morphol 269:1387–1411

    Article  PubMed  Google Scholar 

  • Scott WB (1941) The mammalian fauna of the White River Oligocene: Part V. Perissodactyla. Trans Am Philos Soc New Ser 28:747–964

    Article  Google Scholar 

  • Scott KM (1990) Postcranial dimensions of ungulates as predictors of body size. In: Damuth J, MacFadden BJ (eds) Body Size in Mammalian Paleobiology: Estimation and Biological Implications. Cambridge University Press, Cambridge, pp 301–335

    Google Scholar 

  • Secord R, Wing SL, Chew A (2008) Stable isotopes in early Eocene mammals as indicators of forest canopy structure and resource partitioning. Paleobiology 27:539–563

    Google Scholar 

  • Simpson GG (1945) Notes on Pleistocene and recent tapirs. Bull Am Mus Nat Hist 86:33–82

    Google Scholar 

  • Smith T, De Wilde B, Steurbaut E (2004) Primitive equoid and tapiroid mammals: keys for interpreting the Ypresian-Lutetian transition in Belgium. Bulletin de l’Institut Royal des Sciences Naturelles de Belgique, Sciences de la Terre 74:165–175

    Google Scholar 

  • Sokal RR, Rohlf FJ (2012) Biometry: The Principles and Practice of Statistics in Biological Research. W. H. Freeman and Co., New York

    Google Scholar 

  • Steiner CC, Ryder OA (2011) Molecular phylogeny and evolution of the Perissodactyla. Zool J Linn Soc 163:1289–1303

    Article  Google Scholar 

  • Thewissen JGM, Fish FE (1997) Locomotor evolution in the earliest cetaceans: functional model, modern analogues, and paleontological evidence. Paleobiology 23:482–490

    Article  Google Scholar 

  • Van Valkenburgh B (1987) Skeletal indicators of locomotor behavior in living and extinct carnivores. J Vertebr Paleontol 7:162–182

    Article  Google Scholar 

  • Van Valkenburgh B, Koepfli K (1993) Cranial and dental adaptations to predation in canids. Symp Zool Soc Lond 65:15–37

    Google Scholar 

  • Warton DI, Wright ST, Wang Y (2012) Distance-based multivariate analyzes confound location and dispersion effects. Methods Ecol Evol 3:89–101

    Article  Google Scholar 

  • Wickham H (2009) Ggplot2: Elegant Graphics for Data Analysis. Springer, New York

    Book  Google Scholar 

  • Wiley DF, Amenta N, Alcantara DA, Ghosh D, Kil YJ, Delson E, Harcourt-Smith W, Rohlf FJ, St. John K, Hamann B, Motani R, Frost S, Rosenberger AL, Tallman L, Disotell T, O’Neill R (2006) Landmark Editor 3.0. Institute for Data Analysis and Visualization (IDAV) and the University of California, Davis

  • Wood AR, Bebej RM, Manz CL, Begun DL, Gingerich PD (2011) Postcranial functional morphology of Hyracotherium (Equidae, Perissodactyla) and locomotion in the earliest horses. J Mammal Evol 18:1–32

    Article  Google Scholar 

  • Zanazzi A, Kohn MJ (2008) Ecology and physiology of White River mammals based on stable isotope ratios of teeth. Palaeogeogr Palaeoclimatol Palaeoecol 257:22–37

    Article  Google Scholar 

  • Zelditch ML, Swiderski DL, Sheets HD (2012) Geometric Morphometrics for Biologists: A Primer. Elsevier Academic Press, New York

    Google Scholar 

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Acknowledgements

The authors wish to thank the following: M. Stache, F. Steinheimer and O. Wings (GMH), T. Schossleitner (MfN), G. Billet (MNHN), P. Brewer, J. Hooker, and S. Pappa (NHMUK), A. Folie and T. Smith (RBINS), E. Frey (SMNK), and E. Robert (FSL) for access to Eocene European perissodactyl specimens; all curatorial staff at the AMNH, ETMNH, MfN, MNHN, MVZ, NMW, and RMNH for access to tapir specimens; J. Mertens, J. Meany-Ward, and J. Scholliers for logistical support; H. Hanegraef, P. Indekeu, and C. Mallet for scanning assistance; and L. Holbrook, J. Hooker, and P. Aerts for guidance on interpretations and manuscript writing. This work was funded by an FWO doctoral scholarship and EAVP Travel Grant (JM) and a BOF-UA grant (SN).

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  1. Department of Biology, Universiteit Antwerpen, Gebouw D, Campus Drie Eiken, Universiteitsplein, Wilrijk, 2610, Antwerp, Belgium

    Jamie A. MacLaren & Sandra Nauwelaerts

  2. Center for Research and Conservation, Koninklijke Maatschappij voor Dierkunde (KMDA), Koningin Astridplein 26, 2018, Antwerp, Belgium

    Sandra Nauwelaerts

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MacLaren, J.A., Nauwelaerts, S. Modern Tapirs as Morphofunctional Analogues for Locomotion in Endemic Eocene European Perissodactyls. J Mammal Evol 27, 245–263 (2020). https://doi.org/10.1007/s10914-019-09460-1

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