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Publié par | friedrich-schiller-universitat_jena |
Publié le | 01 janvier 2011 |
Nombre de lectures | 39 |
Langue | English |
Poids de l'ouvrage | 11 Mo |
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On the functional morphology and locomotion
of the two‐toed sloth
(Choloepus didactylus, Xenarthra)
Dissertation zur Erlangung des akademischen Grades
Doctor rerum naturalium (Dr. rer. nat.)
Vorgelegt dem Rat der Biologisch‐Pharmazeutischen Fakultät der Friedrich‐Schiller‐ Universität Jena am 14.06.2010
von John A. Nyakatura (1. Staatsexamen für das Lehramt an Gymnasien) geboren am 19.09.1979 in Merseburg.
Gutachter:
Prof. Dr. Martin S. Fischer (Friedrich‐Schiller‐Universität Jena, Germany)
Prof. Dr. David R. Carrier (University of Utah, Salt Lake City, USA)
Prof. Dr. Sergio F. Vizcaìno (Universidad Nacional de La Plata, Argentina)
Datum der öffentlichen Disputation: 08.11.2010.
ACKNOWLEDGEMENTS
First and foremost I thank my supervisor Prof. Dr. M.S. Fischer for giving me the
opportunity to do research on these fascinating animals.
This dissertation would not have been possible without the constant help of my
colleagues. In particular I am indebted to my fellow PhD candidates, some of which ‐ of
course ‐ already earned their degrees. I am grateful for the many enlightening
discussions and practical support. I have listed the detailed acknowledgements at the
end of each chapter.
Last but not least I want to thank my family for the encouragement and support to
commence and finish this project.
“Of all mammals the sloths have probably the
strangest mode of progression.”
Ruth A. Miller, anatomist (1935)
CONTENTS
Chapter 1:
General Introduction 1
Overview of manuscripts 10
Chapter 2:
Limb kinematics during locomotion in the two‐toed sloth (Choloepus didactylus, 13
Xenarthra) and its implications for the evolution of the sloth locomotor
apparatus
Chapter 3:
Three‐dimensional kinematic analysis of the pectoral girdle during upside‐down 45
locomotion of two‐toed sloths (Choloepus didactylus, Xenarthra)
Chapter 4:
Functional morphology of the muscular sling at the pectoral girdle in tree sloths: 73
convergent morphological solutions to new functional demands?
Chapter 5:
Functional morphology and three‐dimensional kinematics of the thoraco‐lumbar 99
spine of the two‐toed sloth (Choloepus didactylus, Xenarthra)
Chapter 6:
Inverse dynamic analysis aids interpretation of functional limb morphology and 129
locomotor strategy of two toed sloths
Chapter 7:
Synopsis 149
Summary 159
Zusammenfassung 163
References 167
Appendix 177
Erklärungen (declarations) 183
‐ Chapter 1 ‐
1 ‐ Chapter 1 ‐
GENERAL INTRODUCTION
The new framework for the investigation of the evolution of quadrupedal
suspensory locomotion in sloths
Long before Ruth Miller stated “of all mammals the sloths probably have the strangest
mode of progression” in 1935, the quadrupedal suspensory locomotion of sloths drew
th ththe interest of anatomists of the 18P P and 19P P century. Georges Cuvier (1798) early
analyzed the anatomy of sloths in comparison to other mammals and grouped them
with anteaters, armadillos, pangolins and the aardvark. Drawing on Cuvier’s early
work, others soon followed (Humphry, 1869; Mackintosh, 1873, 1874; Flower, 1882;
Lucae, 1882; Windle and Parsons, 1899; Meincke, 1911).
Almost 30 years ago Frank Mendel published a series of papers that discuss different
aspects of the functional anatomy of sloths in the context of ‘upside down’ posture
and locomotion (Mendel, 1979, 1981a, 1981b, 1981c, 1985a, 1985b). Making use of
the classic morphological approach he mostly deduced function from morphology, but
also studied aspects of the locomotion of these American mammals in vivo. In his
published findings he exquisitely and aptly describes the functional anatomy of the
appendages (hands and feet) in two‐toed sloths and his publications will remain a key
reference for years to come.
It was a long held belief that there is a phylogenetic division between extant ‘tree
sloths’ and extinct ‘ground sloths’. After all, it was Sir Richard Owen himself who
coined the term Gravigrada for ‘ground sloths’ to clearly distinguish them from the
Tardigrada (‘tree sloths’) (Owen, 1842). But recent molecular phylogenetic studies that
also include ancient DNA from fossil skin and dung remnants (Höss et al., 1996;
Greenwood et al., 2001; Poinar et al., 2003) as well as phylogenetic studies based on
morphologic comparison of extinct and extant sloth species (Gaudin, 2004; Pujos et al.,
2007) suggest that modern sloths are only distantly related. It is thereby proposed that
the three‐toed sloth (Bradypus) is the sister taxon to all other known sloths (Gaudin,
2004; Fig. 1‐1) and is not closely related to two‐toed sloths (Choloepus). This
th
Phypothesis was first postulated by Patterson and Pascual at the 16P International
Zoological Congress in 1963 (cited in Webb, 1985). Taking into account that no known
fossil has been interpreted to have been suspensory (Webb, 1985;