Diversity_and_Relationships_within_Crown_Mammalia
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Diversity_and_Relationships_within_Crown_Mammalia
Diversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliacrown group. Mammalia is defined by extinction, and comprises all descendants of the common ancestor shared by the three synapsid lineages that happen to exist today: monotremes, marsupials, and placentals. A more inclusive, apomorphy-defined synapsid clade is Mammaliaformes, composed of all descend Diversity_and_Relationships_within_Crown_Mammaliaants of the first synapsid to evolve a functional, squamosal-dentary jaw joint. In addition to Mammalia, Mammaliaformes includes Adelobasileus, SinocoDiversity_and_Relationships_within_Crown_Mammalia
nodon, morganucodonts, docodonts, and haramiyids (see chapters by Angielczyk & Kammerer and Manin, this volume).My goal in this chapter is to outline Diversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliace the early 20th century, and to summarize how certain fossil groups are related to extant, high-level clades, with an emphasis on Placentalia. Mammalian interrelationships are depicted in Fig. 1 based primarily on overlap across four phylogenetic studies using large samples of data and taxa: Mered Diversity_and_Relationships_within_Crown_Mammaliaith et al. (2011, 36 kilobases of nuclear DNA from 164 mammals), Mitchell et al. (2014, 44 kilobases of mitochondrial and nuclear DNA for 203 mammals)Diversity_and_Relationships_within_Crown_Mammalia
, Tarver et al. (2016, 32 megabases of nuclear DNA for 36 mammals, 15.6 kilobases of microRNA for 42 mammals, and reanalyses of datasets from HallstroDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammalias). These studies are not completely congruent; cases of disagreement (with exceptions detailed below) have been represented with polytomies. Nonetheless, given all of the ways in which these topologies could differ (e.g., 3.37X1049RJ Asher, "Diversity and Relationships of Crown Mammalia", Handbook Diversity_and_Relationships_within_Crown_Mammaliaof Zoology: MammaliaJhttps://khothuvien.cori!distinct, rooted, bifurcating trees for the 36 genomically sampled taxa in Tarver et al. 2016), they areDiversity_and_Relationships_within_Crown_Mammalia
very close in overall shape and, I predict, future discoveries will agree far more than disagree with the phylogenetic relationships shown in Fig. 1.IDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliacentury, but that interrelationships among orders have been well understood only since the late 1990s. 1 recognize the biological arbitrariness of Linnean ranks and therefore minimize their use. However, they do have some utility, as evident in the practical, legal framework articulated by the Inter Diversity_and_Relationships_within_Crown_Mammalianational Code of Zoological Nomenclature (ICZN, 1999). The fact that this code does not apply above the rank of family has led to inconsistency regardDiversity_and_Relationships_within_Crown_Mammalia
ing the use of some high level names. Here, I follow' Simpson (1945) in arbitrating among such names based on priority and stability, as summarized byDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliapitalize formal cladistic names (e.g., mammals in the genus Homo belong to the clade Primates) but do not capitalize adjectives or common nouns (e.g., the capybara is a hystricognath rodent). Quotes surrounding a high-level taxon indicate that it is not monophyletic (e.g., "Edentata").Another semant Diversity_and_Relationships_within_Crown_Mammaliaic but important point worth making concerns the use of adjectives like "molecular" and "morphological" to describe phylogenetic trees. One of the keyDiversity_and_Relationships_within_Crown_Mammalia
postulates of evolutionary theory is that living things share common ancestry. Tree-diagrams represent this common ancestry, and investigators have uDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammalia known since the early 20th century, and encompass immunochemical (Nuttall et al. 1904) and hybridization (Kirsch et al. 1991) techniques, as well as direct comparisons of protein (Zuckerkandl & Pauling 1965) and nucleotide (Irwin et al. 1991) sequences. The ease of applying quantitative methods to Diversity_and_Relationships_within_Crown_Mammaliacompare species, along with the massive quantities of genomic characters with readily defined states, has meant that whereRJ Asher, "Diversity and RelDiversity_and_Relationships_within_Crown_Mammalia
ationships of Crown Mammalia", Handbook of Zoology: Mammalia9available, molecular data have become crucial in establishing the topology and confidenceDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammalia to build them. However, describing a given tree as "molecular" is slightly misleading. It implies that there are multiple phylogenetic trees out there according to data type; indeed, genetic loci often do have different gene trees that explain their history, distinct from the species trees of their Diversity_and_Relationships_within_Crown_Mammalia host taxa. However, the existence of a single, historical tree (with qualifications about hard polytomies and population-level reticulations) joiningDiversity_and_Relationships_within_Crown_Mammalia
all species is not only a key postulate of evolutionary theory, but comprises a prediction that enables evolution to be tested given the expectation Diversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammalia; Asher this volume). Thus, when authors have the concept of a species tree in mind, the phrase "molecular tree" obscures the expectation of a single, historical pattern. The tree of life is neither ' molecular" nor "morphological", although the data used to reconstruct it can be one or both. Stated Diversity_and_Relationships_within_Crown_Mammalia differently, a phylogenetic species tree is no more "molecular" than a genome is "morphological" when its size is inferred using the morphology of boDiversity_and_Relationships_within_Crown_Mammalia
ne cells (Organ et al. 2012). Inferences of tree shape or genome size are biological hypotheses, whatever sources of data are used to make or test theDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliahind such hypotheses.Finally, I would also like to clarify the terms "basal" and "nested" when describing phylogenetic trees (see also discussion in Bronzati 2017). Specifically, taxa used in a phylogenetic analysis are connected via branches to nodes. Nodes (i.e., bifurcations that connect two bran Diversity_and_Relationships_within_Crown_Mammaliaches) may vary in their distance to the root due to branch length and the number of other, intervening nodes. A taxon may be nested, or connected to aDiversity_and_Relationships_within_Crown_Mammalia
node that is separated from the root by many other nodes; another taxon may be basal, or connected to aRJ Asher, "Diversit)' and Relationships of CroDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliaa given taxon as "basal", one necessarily implies that it is somehow less evolved and/or more primitive than other taxa. While this may be true for some taxa (e.g., a fossil perissodactyl that existed within one or few generations of the clade’s origin), this is difficult to test in most cases. More Diversity_and_Relationships_within_Crown_Mammaliaover, and for extant taxa, all branches lead to the present, and regardless of the position of an extant taxon on a phylogenetic tree, it is no less "Diversity_and_Relationships_within_Crown_Mammalia
evolved" than other extant taxa. It is also true that the number of nodes between a given taxon and the root is dependent on sampling, and future discDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliaid points do not change the meaning I intend, namely, that "basal" and "nested" are convenient ways of describing the number of nodes separating a taxon from the root of a given phylogenetic tree.For example, within Xenarthra. cingulates (armadillos and glyptodonts) comprise the sister taxon of pilo Diversity_and_Relationships_within_Crown_Mammaliasans (sloths and anteaters). The genus Dasypus comprises the sister taxon of other cingulates. Based on the phylogenetic hypothesis of Delsuc et al. (Diversity_and_Relationships_within_Crown_Mammalia
2016: fig. 1), there is one node separating the common ancestor of Dasypus from the xenarthran root, and at least two separating other cingulate generDiversity and Relationships within Crown MammaliaRobert J. AsherDepartment of Zoology. University of Cambridge, Cambridge. UKIntroductionAs with any c Diversity_and_Relationships_within_Crown_Mammaliale) more extinct taxa on the branch leading to Dasypus. Nonetheless, the terms "basal" and "nested" still convey useful information about distance to the root as measured by nodes on a given phylogenetic tree.To begin this survey I first outline who the major mammalian clades are and present current Diversity_and_Relationships_within_Crown_Mammalialy well-corroborated hypotheses on their interrelationships. Three papers from 2001 (Murphy et al. 2001a, b; Madsen et al. 2001) demarcate an importanDiversity_and_Relationships_within_Crown_Mammalia
t shift in the consensus regarding the shape of this tree, in particular regarding its most diverse clade, Placentalia. I describe a number of pre-200Gọi ngay
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