Inferences on the lifestyle of fossil xenarthrans based on limb long bone inner structure
Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia)
Bone inner structure bears a strong functional signal and can be used in paleontology to make inferences about the ecology of fossil forms. The increasing use of microtomography enables to analyze both cortical and trabecular features in three dimensions, and thus in long bones to investigate the diaphyseal and epiphyseal structures. Moreover, this can now be done through quantitative, and not only qualitative analyses. Studies focusing on the diaphyseal inner structure (cortical bone and sometimes also spongious bone) of long bones are rather numerous, but essentially based on 2D sections. It is only recently that analyses of the whole diaphyseal structure have been investigated. Studies on the trabecular architecture are much rarer.
Amson & Nyakatura (2018) propose a comparative quantitative analysis combining parameters of the epiphyseal trabecular architecture and of the diaphyseal structure, using phylogenetically informed discriminant analyses, and with the aim of inferring the lifestyle of extinct taxa. The group of interest is xenarthrans, one of the four major extant clades of placental mammals. Xenarthrans exhibit different lifestyles, from fully terrestrial to arboreal, and show various degrees of fossoriality. The authors analyzed forelimb long bones of some fossil sloths and made comparisons with several species of extant xenarthrans. The aim was notably to discuss the degree of arboreality and fossoriality of these fossil forms.
This study is among the first ones to conjointly analyze both diaphyseal and trabecular parameters to characterize lifestyles, and the first one outside of primates. No fossil form could undoubtedly be assigned to one lifestyle exhibited by extant xenarthrans, though some previous ecological hypotheses could be corroborated. This study also raised some technical challenges, linked to the sample and to the parameters studied, and thus constitutes a great step, from which to go further.
Amson, E., & Nyakatura, J. A. (2018). Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia). bioRxiv, 318121, ver. 5 peer-reviewed and recommended by PCI Paleo. doi: 10.1101/318121
Alexandra Houssaye (2018) Inferences on the lifestyle of fossil xenarthrans based on limb long bone inner structure. Peer Community in Paleontology, 100001. 10.24072/pci.paleo.100001
Revision round #22018-09-11
Decision round #2
Thank you for submitting a revised version of your manuscript entitled “Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia)“. You made significant changes to your manuscript, in order to address the points raised by the reviewers. I checked the whole manuscript and I have only a few comments that I wrote directly in the manuscript before to recommend it. I will send it to you by email because we can not send it via the website yet. Could you please consider the remarks and submit a new version accordingly. Best wishes,
Revision round #12018-09-04
Decision round #1
I have agreed to handle the evaluation of a preprint entitled "Palaeobiological inferences based on long bone epiphyseal and diaphyseal structure - the forelimb of xenarthrans (Mammalia)", for potential recommendation by Peer Community in Paleontology (PCI Paleontology).
The preprint was sent to two reviewers. If they both highlight the interest and quality of the preprint, they also suggest moderate/major revision. Their comments, which should enable you to greatly improve the preprint, are attached. Below, you will also find additional comments provided by a PCI Paleo recommender.
Thank you again for submitting your interesting work to PCI Paleo. I look forward to receive your revision.
Additional comments from a PCI Paleo recommender:
- Suggestion to use Folivora rather than Tardigrada
- l. 111. Suggestion to cite Pujos et al. 2012 Figure 4 Pujos, F., Gaudin, T. J., De Iuliis, G., & Cartelle, C. (2012). Recent advances on variability, morpho-functional adaptations, dental terminology, and evolution of sloths. Journal of Mammalian Evolution, 19(3), 159-169.
- l. 236. Suggestion to compare with the two last molecular publications for the age of the split between Bradypus & Choloepus (Slater et al. 2016; Delsuc et al. 2018) Slater, G. J., Cui, P., Forasiepi, A. M., Lenz, D., Tsangaras, K., Voirin, B., ... & Greenwood, A. D. (2016). Evolutionary relationships among extinct and extant sloths: the evidence of mitogenomes and retroviruses. Genome biology and evolution, 8(3), 607-621. Delsuc, F., Philippe, H., Tsagkogeorga, G., Simion, P., Tilak, M. K., Turon, X., ... & Douzery, E. J. (2018). A phylogenomic framework and timescale for comparative studies of tunicates. BMC biology, 16(1), 39. -l.419. Considering the strong uncertainties relative to the position of Hapalops (notably linked to strong changes in sloth phylogeny with the new results coming from aDNA), you should say on world on this as well, to moderate your results based on phylogenetically informed analysis. If you change the position of Hapalops (for example closer to Bradypus), dies it change the result?
- l. 462. You cite a manuscript under review.
- l. 489. It is not only argued that Xenarthra would be one of the major clades of placental mammals; it is one of the 4 early diverging clades of extant placentals; you might cite molecular analyses for that as well.