Phylogenetic signal of body size in sloths and anteaters (Xenarthra, Pilosa)

TOLEDO, N.; BARGO, M. S.; VIZCAÍNO, S. F.; PUJOS, F.; DE IULIIS, G.

Mendoza

Congreso; 4th International Palaeontological Congress; 2014

IPA

Pilosa xenarthrans includes sloths (Folivora) and anteaters (Vermilingua). Modern tree sloths are represented by two genera, Bradypus and Choloepus (less than 10 kg), while the fossil record is very diverse and rich (~ 80 genera) ranging from the Oligocene to the Early Holocene periods. The fossil group includes four main clades, Megalonychidae, Megatheriidae, Nothrotheriidae, and Mylodontidae, with body sizes from tens of kg to several tons. Vermilinguans are represented today by three genera, Cyclopes, Tamandua, and Myrmecophaga (from 0.5 to about 35 kg), and their fossil record is quite scarce and fragmentary but maybe similarly in size. we analyzed in this contribution the dependency of the body size from the phylogenetical pattern of Pilosa, following the current cladistic hypotheses using previously published body size estimates for 35 taxa (extant and extinct). An orthonormal decomposition analysis of the variance of body size is also performed. The observed distribution of this variable in the cladograms is compared using four statistical parameters, with a theoretical random distribution as null-hypothesis. Three of the four parameters were significantly different from the null-hypothesis, supporting the possibility that body size variation correlates with the cladograms topologies and, hence, with the phylogenetical pattern. This dependence is not restricted to a single node, but it is that was called diffuse phylogenetic signal.Inthefirstcladogram,mostofthephylogeneticsignalisconcentratedwithinVermilingua,andmuchlesswithinMylodontidae,MegatheriidaeandNothrotheriidae.Inthesecondcladogram,agreatproportionofphylogeneticalsignalisconcentratedinMegatheria,andlessinMegalonychidae.Inanteaters,arelationshipbetweendietand phylogeneticconstraintstobodysize'sdiversification is proposed;theirspecialized,strictinsectivorymayhaveplayedaleadrolerestrainingtheevolutionofbodysize.Concerningsloths,thetrendisnotclearlyrelatedtoasinglefactor.Mylodontidsandmegatheriansshowatendencytoincreasebodysizethroughtime,whileMegalonychidaeretainawiderdiversityinbodysizeuntiltheearlyHolocene.Biologicalattributessuchasdietaryhabits(herbivorousbulkfeedingvs.selectivefeeding)andpaleoenvironmentalfactorssuchasclimatechangesthroughouttheCenozoicaredoubtlesslyinvolvedintheevolutionof sloth's bodysize.Nextstepswillbetousealternativemethodstoassessphylogeneticdependencyandmoreaccuratebodysizeestimates.Whenavailable,moreinclusivephylogeneticalproposalscouldbenecessary,allowingexpandingtheanalysistoagreaterdiversity.