User:Boor.17/sandbox

Elizabeth Boor (.17)

Topic: Evolution of tree sloths; particularly the relationship between two- and three-toed sloths

'''Nyakatura, J. A., A. Petrovitch, and M. S. Fischer. "Limb Kinematics during Locomotion in the Two-toed Sloth (Choloepus Didactylus, Xenarthra) and Its Implications for the Evolution of the Sloth Locomotor Apparatus." (2010): n. pag. PubMed. Web. 13 Sept. 2014.'''

This study was conducted in order to analyze the locomotion of the two-toed sloth. They examined gait, limb coordination and kinematics. It was determined that in order to move faster sloths would decrease contact time and increase the step length. They also analyzed the structure of the hands and feet and their effect on locomotion. They determined that the hands and feet were utilized to maintain grip and stability and not used to alter step length or speed. The implications of the study are that we know more about suspensory posture and movement in sloths.

'''Pujos, Francois, Timothy J. Gaudin, Gerardo De Iuliis, and Castor Cartelle. "Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths." Journal of Mammalian Evolution 19.3 (2012): 159-69. Web.'''

This article studies evidence of sloths in typically underexamined locations like the Andes and Pacific desert coast. Fossils of sloths were found that exhibit varying traits from the modern tree sloths such as bipedality, aquatic/semiaquatic lifestyle and semiarboreality. The use of a phylogenetic tree was utilized in order plot functional traits and determine/track evolutionary change in sloths. DNA analysis was also utilized.

'''Pant, Sara Raj, Anjali Goswami, and John A. Finarelli. "Complex Body Size Trends in the Evolution of Sloths (Xenarthra: Pilosa)." BMC Evolutionary Biology 14.2 (2014): n. pag. CrossRef. Web. 13 Sept. 2014.'''

This study consisted of analyzing 57 different species of living and fossil sloths focusing on changes in body mass and evolutionary variance. They resulted in 8 models which could potentially explain the extreme variance between sloth species. Species of sloths that exist today are believed to be separated by 30 million years of evolution. This study is useful in its stress of the use of fossil sloths since evolution is something that can only be accurately analyzed over an extensive period of time.

'''Billet, G., D. Germain, I. Ruf, and L. Hautier. "The Inner Ear of Megatherium and the Evolution of the Vestibular System in Sloths."Journal of Anatomy 223.6 (2013): 557-67. Elsevier B.V. Web. 13 Sept. 2014.'''

Like the “Complex body size in the evolution of sloths” article, this article also uses fossil sloths to gather information about the evolution of sloths, but instead of focusing on body mass it focuses on the structure of the inner ear in the fossil sloth, Megatherium americanum. The study found that the inner ear structure of Megatherium americanum suggests proximity to armadillos and anteaters.

'''Gaudin, Timothy J. "Phylogenetic Relationships among Sloths (Mammalia, Xenarthra, Tardigrada): The Craniodental Evidence." Zoological Journal of the Linnean Society 140.2 (2004): 255-305. Wiley Online Library. Web. 13 Sept. 2014.'''

This article evaluates relationships between extant and extinct sloths by analyzing bone structures such as that of the skull, jaw, and hyoid arch. The results suggest that the extant species of sloths, the two-toed sloths and three-toed sloths, split up to 40 million years ago. The author asserts that many of their adaptations such as suspensory locomotor habits are due to dramatic convergent evolution. By analyzing 286 characteristics in the bones the authors sought to create a phylogenetic tree with 33 different sloth species. Many of the relationships between clades are still unknown.



'''Part 2 (Oct 1) ''' https://en.wikipedia.org/wiki/Sloth#Evolution

Possible Improvements
 * 1) The Evolution portion states that two- and three-toed sloths are a great example of convergent or parallel evolution, but it doesn’t really describe any of the traits that make them appear similar. They share traits such as bipedalism, an arboreal lifestyle, and mode of locomotion.
 * 2) The Evolution portion states that two- and three-toed sloths are a great example of convergent or parallel evolution, but it doesn’t really describe any of the traits that indicate their separate paths of evolution. Physical qualities such as bone structures in the skull, jaw, and hyoid arch indicate that the extant species of sloths, the two-toed sloths and three-toed sloths, split up to 40 million years ago.
 * 3) Add a fact to convey how little is truly understood about the phylogenetic relationships between different types of extant and extinct sloths. Though data has been collected on over 33 different species of sloths just by analyzing bone structures, many of the relationships between clades on a phylogenetic tree are unknown

Edit was made to a different page due to the original page being locked. https://en.wikipedia.org/wiki/Two-toed_sloth

Added: “Though data has been collected on over 33 different species of sloths just by analyzing bone structures, many of the relationships between clades on a phylogenetic tree are unknown[7]”

FINAL PAPER Evolution of Extant Tree Sloth Species It is a probable assertion to say that the majority of people believe that all species of sloths are close relatives of one another. This would mean that they are a monophyletic group with a common ancestor. However, despite this widely believed, preconceived notion, extant species of two- and three- toed sloths are in actuality a diphyletic group. This means that each type has a different ancestor and they are primarily similar due to factors involving convergent evolution. In fact, if the hypothesis of diphyletic sloth groups is accepted, they would be deemed “one of the most striking examples of convergent evolution known among mammals” (Gaudin et al., 2004). There are three species of three-toed sloths and two-species of two-toed sloths currently in existence- ‘extant’ (Gaudin et al., 2003). Each respective genera of sloth has a common ancestor, but what that ancestor was, when it existed, and many of its traits remain virtually unknown. There is relatively little evidence to support the hypothesis of diphyly and remarkably small amount of data to study overall. In fact, most of the evidence to support the hypothesis of diphyly is still heavily based in the same trait that cause the hypothesis to be suggested; the structure of the respective sloth genera’s inner ear (Patterson et al., 1992). One of the largest problems that exists when attempting to identify clades of modern extant tree sloths is the issue of missing links between surviving, living species and their unidentified common ancestors. There are a multitude of families of extinct sloths, about which we know very little. This missing information causes large holes in phylogenetic trees and makes tracing paths of evolution a daunting task. As a result, there are many, many versions of the phylogenetic tree that would describe the evolution and relationship between sloths, most of which conclude that convergent evolution is the likely mechanism that resulted in today’s genera of tree sloths. The first study to draw conclusions about the relationships between genera of extant tree sloths was by Patterson et al. in 1995. He focused on and compared the ear and the skull structures of 21 different species of sloth- both extant and extinct- to multiple outgroups, including species of anteaters and armadillos. Their study was noted for being one of the first studies to be so comprehensive, but more recent studies have contributed additional information that has altered the accepted structure for sloth evolution. A more recent study by one of the same authors, Timothy J. Gaudin, has taken a more extensive look at the osteological characteristics of the skull, jaw, hyoid, and teeth in a wide variety of extant and extinct sloth taxa to reinforce the phylogenetic understanding of sloth evolution. He analyzed 201 different characteristics and then joined the findings with 85 auditory region characters (Gaudin et al., 2004). Through analyzing even more osteological characteristics of the skull and auditory region, Gaudin concluded that Bradypus (two-toed sloths) were an isolated group whilst there is evidence that Choloepus (three-toed sloths) are closely related to megalonychids (Gaudin et al., 2004). This strongly supported the assertions made in Patterson’s earlier 1992 study. Similar studies seek not only to examine and test the validity of the diphyletic phylogenetic structure proposed to represent two- and three- toed sloths, but to also examine and identify the common ancestor and perhaps make links between them. One study isolated the majority of its efforts to the extinct species Megatherium, a giant ground sloth, and attempted to trace the evolution in respect to the vestibular system in particular. Findings indicate that the shape of the semicircular canal might have an effect on habitat preference because Megatherium’s inner ear structure is more similar to armadillos than to tree sloths (Billet et al., 2013). This makes sense since the equilibrium of a relatively small animal that lives upside down in a tree would likely need to differ greatly from a large mammal that lives upright on the ground. This might also suggest that Megatherium is not the most recent common ancestor of extant tree sloth genera. If however, Megatherium is a common ancestor, some morphological traits that would have needed to evolve through convergence are size and arboreality. Through the incorporation of a time-variable model Pant sought to construct multiple phylogenies that support the mode of convergence for size and arboreality in extant tree sloth species. By studying over 50 species, eight different possible trees were constructed, all of which were further complicated by the addition of modern genera (Pant et al., 2014). This study was particularly interesting because it was the only one found where initial thoughts were not as well supported or substantiated as the authors suggested they were seeking in their hypothesis. One study approached validating the hypothesis of diphyly in extant tree sloth species from a completely different vantage point; locomotion methodes. Nyakatura, Petrovich, and Fisher sought to analyze the structures, similarities, and differences of hindlimb muscles and locomotion techniques in two- and three-toed sloths. Through the study of these morph-functional traits, they found evidence to support convergent evolution from ground sloths to be the most likely mode of evolution for two- and three- toed sloths (Nyakatura et al., 2010). Locomotion is not the only morpho-functional adaptation studied when it comes to the evolution of extant sloth species. Stance and dental comparisons regarding recently discovered species of ground sloths in the Amazon, Andes, and northern South America are instigating massive contributions and alterations to the structure of the phylogenic tree that includes extant tree sloth clades (Pujos et al., 2012). Studying dentition has lead to an increase in knowledge regarding the species of extinct sloths that may be a link between ground and tree sloths. These newly discovered species found in the Amazon, Andes, and northern South America suggest that there were semiarboreal sloth species- or ground sloths with climbing adaptations (Pujos et al., 2012). The study of these extinct sloths’ dentition patterns and traits between clades has lead to insight regarding how diet might have been a driving force of convergent evolution between the two extant tree sloth species. Relatively recently, studies have been conducted that examine traits between species of sloths on the molecular level as opposed from a morphological or morpho-functional standpoint. Samples of preserved skin from species of extinct and extant sloths have been compared to one another as well as to species of armadillo and other species, both extinct and extant (Hoss et al., 1995). The results from comparing rDNA samples supported the relationships suggested by Gaudin in his 1995, even though they differed in the types of characteristics being studied. This is a positive indicator, because it is typical for molecular genetics to indicate things different than what traits that are visually observable may lead us to believe. An example of molecular genetics providing differing relationships to morphological is Hofreiter’s 2000 study of the rRNA at homologous locations. Hofreiter’s molecular study compared rRNA in a different group of species than those that were examined in Hoss’ study to extant sloth genera. This study disagreed with the findings of Gaudin’s 1995 study. Instead of finding two- and three- toed sloths to be a product of convergent evolution, it grouped some species that were formerly believed to be close relatives (some even sister taxa) to three- toed sloths to be related to one another (Hofreiter et al., 2000). This study even placed two- and three- toed sloths to be much more closely related than previous studies. Yet another molecular study agreed with pieces of Hoss’ study but disagreed with portions of Gaudin and Hofreiter. Greenwood’s study compared mitochondrial genes across another selection of sloth species. He agreed with Hoss’ conclusion of proximity three- toed sloths and Mylodon (an extinct giant ground sloth), but did not place two-toed sloths in a monophyletic group with Nothrotheriops (a type of ground sloth) which Gaudin had done with morphological analysis of the skull, jaw, and inner ear and Hofreiter had done with a comparison of rRNA sequences. Something important to take away from the contradictions among differing studies is that even conclusions in one study may be disproved or contradicted in the studies of another. Phylogenetic relationships and paths of evolution are highly subjective when there is little research and limited data to utilize. This is especially true since we are unaware of a large number of intermediate sloth species between extant tree sloths and a common ancestor. Despite a couple of discrepancies in DNA sequencing, it is largely accepted that extant tree sloth species Choloepus and Bradypus do not share a recent common ancestor making them diphyletic to one another and indicating similarities through convergent evolution. This means that the two extant species evolved analogous traits such as locomotion methods, size, habitat, and many other traits independently from one another as opposed to from their last common ancestor. If the theory of convergent evolution between the two species were accepted as true, that would make sloths “one of the most striking examples of convergent evolution known among mammals” (Gaudin et al., 2004). In order to further support this theory, there would need to be more information and data gathered about intermediate species between the extant species and the common ancestor, which is estimated to have gone extinct over 30 million years ago (Pant et al., 2014). More data would also need to be collected regarding the proximity to extant tree sloths to suspected (and not yet suspected) ground sloth relatives.

References Billet, G., D. Germain, I. Ruf, and L. Hautier. "The Inner Ear of Megatherium and the Evolution of the Vestibular System in Sloths."Journal of Anatomy 223.6 (2013): 557-67. Elsevier B.V. Web. 13 Sept. 2014. Gaudin, Timothy J. "Phylogenetic Relationships among Sloths (Mammalia, Xenarthra, Tardigrada): The Craniodental Evidence." Zoological Journal of the Linnean Society 140.2 (2004): 255-305. Wiley Online Library. Web. 13 Sept. 2014. Hofreiter, M., H. N. Poinar, W. G. Spaulding, K. Bauer, P. S. Martin, G. Possnert, and S. Paabo. "Lackwell Science, Ltd A Molecular Analysis of Ground Sloth Diet through the Last Glaciation." Lackwell Science, Ltd A Molecular Analysis of Ground Sloth Diet through the Last Glaciation (2000): 1975-984. Web. 14 Oct. 2014. Hoss, Matt, Amrei Dilling, Andrew Currant, and Svante Pabo. "Molecular Phylogeny of the Extinct Ground Sloth Mylodon Darwinii." The Natural History Museum, 1995. Web. 14 Oct. 2014. Nyakatura, J. A., A. Petrovitch, and M. S. Fischer. "Limb Kinematics during Locomotion in the Two-toed Sloth (Choloepus Didactylus, Xenarthra) and Its Implications for the Evolution of the Sloth Locomotor Apparatus." (2010): n. pag. PubMed. Web. 13 Sept. 2014. Pant, Sara Raj, Anjali Goswami, and John A. Finarelli. "Complex Body Size Trends in the Evolution of Sloths (Xenarthra: Pilosa)." BMC Evolutionary Biology 14.2 (2014): n. pag. CrossRef. Web. 13 Sept. 2014. Patterson, Bryan, Walter Segall, William D. Turnbull, and Timothy J. Gaudin. "The Ear Region in Xenarthrans ( = Edentata: Mammalia)."The Ear Region in Xenarthrans ( = Edentata: Mammalia). Field Museum of Natural History, 30 Sept. 1992. Web. 14 Oct. 2014. Pujos, Francois, Timothy J. Gaudin, Gerardo De Iuliis, and Castor Cartelle. "Recent Advances on Variability, Morpho-Functional Adaptations, Dental Terminology, and Evolution of Sloths." Journal of Mammalian Evolution 19.3 (2012): 159-69. Web.

Edits Made To https://en.wikipedia.org/wiki/Two-toed_sloth