The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals

O’Leary, Maureen A.; Bloch, Jonathan I.; Flynn, John J.; Gaudin, Timothy J.; Giallombardo, Andres; Giannini, Norberto P.; Goldberg, Suzann L.; Kraatz, Brian P.; Luo, Zhe Xi; Meng, Jin; Ni, Xijun; Novacek, Michael J.; Perini, Fernando A.; Randall, Zachary S.; Rougier, Guillermo W.; Sargis, Eric J.; Silcox, Mary; Simmons, Nancy B.; Spaulding, Michelle; Velazco, Paúl M.; Weksler, Marcelo; Wible, John R.; Cirranello, Andrea L.

doi:10.1126/science.1229237

Cited by 1,019 publications

(1,137 citation statements)

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“…Features of physiology and soft tissue anatomy mostly play a minor role in reconstructing phylogenies but have sometimes been used in conjunction with molecular and skeletal data (e.g., O'Leary et al 2013, Clauss 2014. For mammals, detailed morphological soft tissue analyses, such as lung anatomy (Wallau et al 2000) or anatomy of the gastrointestinal tract (Langer 2001), can be used to derive phylogenies, but we are not aware of cases where such characteristics have been used to actually resolve a phylogenetic debate.…”

Section: Discussionmentioning

confidence: 99%

Comparative digesta retention patterns in ratites

Frei

Ortmann

Reutlinger³

et al. 2015

The Auk

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Ratites differ distinctively in the anatomy of their digestive tract. For example, Ostriches (Struthio camelus) have a particularly long, voluminous colon and long paired caeca, Rheas (Rhea spp.) are characterised by a short colon with particularly prominent paired caeca, and Emus (Dromaius novaehollandiae) -have neither very prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97-123kg), 5 Greater Rheas (R. americana, 22-27kg) and 2 Emus (32-34kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species ; Emu: 1.3-1.8h), but there were no differences between the retention of 2 mm or 8 mm particles or a solute marker within species. The shape of the marker excretion curves corresponded to digesta mixing in the digestive tract of Ostriches and Rheas but not Emus. The calculated dry matter gut fill (% of body mass) was significantly higher in Ostriches (1.6-1.8) than Rheas (0.3-1.0) and Emus (0.2). Ostriches had the highest, and Emus the lowest fecal dry matter concentration. These physiological findings match the differences in digestive anatomy and support the concept that in ratites, herbivory -and hence flightlessness -evolved repeatedly in different ways. ABSTRACT Ratites differ distinctively in the anatomy of their digestive tracts. For example, Common Ostriches (Struthio camelus, hereafter Ostriches) have a particularly long, voluminous colon and long, paired caeca; Rheas (Rhea spp.) are characterized by a short colon with particularly prominent paired caeca; and Emus (Dromaius novaehollandiae) have neither prominent caeca nor a prominent colon. We tested whether digesta excretion patterns corresponded to these differences in anatomy, expecting Ostriches to have the longest and Emus the shortest digesta retention times, and Rheas possibly showing a selective retention of fluids observed in other birds and mammals with prominent caeca. We used 6 Ostriches (97-123 kg), 5 Greater Rheas (R. americana, 22-27 kg), and 2 Emus (32-34 kg) fed a common diet of alfalfa pellets ad libitum in captivity. Intake per unit of metabolic body mass did not differ between Ostriches and Greater Rheas but was significantly higher in Emus, which also displayed higher defecation frequencies and lower fiber digestibility. Mean digesta retention time for small fiber particles (2 mm) differed significantly among species (Ostrich: 30-36 h; Greater Rhea: 7-19 h; Emu: 1.3-1.8 h), but there were no differences between the retention o...

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Section: Discussionmentioning

confidence: 99%

Comparative digesta retention patterns in ratites

Frei

Ortmann

Reutlinger³

et al. 2015

The Auk

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“…We follow a crown-clade definition for Placentalia, with Eutheria referring to the total clade of Placentalia [2]. In the context of our analyses, Placentalia is the least inclusive clade that includes all extant placentals present in our morphological character matrix, whereas Eutheria is the most inclusive clade that excludes our outgroup taxa, namely the metatherians (Deltatheridium, Mayulestes and Pucadelphys) and the non-therian cladotherians (Nanolestes, Peramus and Vincelestes).…”

Section: Materials and Methods (A) Phylogenetic Definitions And Assumpmentioning

confidence: 99%

“…Obviously, the discovery of a single unequivocal placental fossil prior to the K-Pg boundary would overturn the strict 'explosive' model. However, despite intensive collecting and enormous improvements in our knowledge of Mesozoic mammals in recent years [11][12][13], definitive pre-Palaeocene placentals have still not been identified [2,7,8,14]; a few putative Mesozoic records of placentals have been reported, but they are from the latest Cretaceous [15,16], and they remain controversial [2,16,17].…”

Section: Introductionmentioning

confidence: 99%

Ancient dates or accelerated rates? Morphological clocks and the antiquity of placental mammals

2014

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Analyses of a comprehensive morphological character matrix of mammals using 'relaxed' clock models (which simultaneously estimate topology, divergence dates and evolutionary rates), either alone or in combination with an 8.5 kb nuclear sequence dataset, retrieve implausibly ancient, Late JurassicEarly Cretaceous estimates for the initial diversification of Placentalia (crown-group Eutheria). These dates are much older than all recent molecular and palaeontological estimates. They are recovered using two very different clock models, and regardless of whether the tree topology is freely estimated or constrained using scaffolds to match the current consensus placental phylogeny. This raises the possibility that divergence dates have been overestimated in previous analyses that have applied such clock models to morphological and total evidence datasets. Enforcing additional age constraints on selected internal divergences results in only a slight reduction of the age of Placentalia. Constraining Placentalia to less than 93.8 Ma, congruent with recent molecular estimates, does not require major changes in morphological or molecular evolutionary rates. Even constraining Placentalia to less than 66 Ma to match the 'explosive' palaeontological model results in only a 10-to 20-fold increase in maximum evolutionary rate for morphology, and fivefold for molecules. The large discrepancies between clock-and fossil-based estimates for divergence dates might therefore be attributable to relatively small changes in evolutionary rates through time, although other explanations (such as overly simplistic models of morphological evolution) need to be investigated. Conversely, dates inferred using relaxed clock models (especially with discrete morphological data and MRBAYES) should be treated cautiously, as relatively minor deviations in rate patterns can generate large effects on estimated divergence dates.

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“…He interpreted the enlargement as a derived haplorhine feature. Other pieces of evidence suggesting that a reduced ICA is primitive for Euprimates include 1) the frequent reduction in this canal exhibited by plesiadapiform stemprimates (Gingerich, 1976;MacPhee et al, 1983;Kay et al, 1992;Boyer et al, 2012) and 2) the reduction exhibited by cynocephalid dermopterans (Table 1) (Wible, 1993) that some analyses suggest are more closely related to Euprimates than are treeshrews (Beard, 1993;Bloch et al, 2007;Janecka et al, 2007;O'Leary et al, 2013).…”

Section: What Was the Pattern Of Ica Evolution In Early Primates?mentioning

confidence: 99%

Internal carotid arterial canal size and scaling in Euarchonta: Re-assessing implications for arterial patency and phylogenetic relationships in early fossil primates

Boyer

Kirk

Silcox

et al. 2016

Journal of Human Evolution

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a b s t r a c tPrimate species typically differ from other mammals in having bony canals that enclose the branches of the internal carotid artery (ICA) as they pass through the middle ear. The presence and relative size of these canals varies among major primate clades. As a result, differences in the anatomy of the canals for the promontorial and stapedial branches of the ICA have been cited as evidence of either haplorhine or strepsirrhine affinities among otherwise enigmatic early fossil euprimates. Here we use micro X-ray computed tomography to compile the largest quantitative dataset on ICA canal sizes. The data suggest greater variation of the ICA canals within some groups than has been previously appreciated. For example, Lepilemur and Avahi differ from most other lemuriforms in having a larger promontorial canal than stapedial canal. Furthermore, various lemurids are intraspecifically variable in relative canal size, with the promontorial canal being larger than the stapedial canal in some individuals but not others. In species where the promontorial artery supplies the brain with blood, the size of the promontorial canal is significantly correlated with endocranial volume (ECV). Among species with alternate routes of encephalic blood supply, the promontorial canal is highly reduced relative to ECV, and correlated with both ECV and cranium size. Ancestral state reconstructions incorporating data from fossils suggest that the last common ancestor of living primates had promontorial and stapedial canals that were similar to each other in size and large relative to ECV. We conclude that the plesiomorphic condition for crown primates is to have a patent promontorial artery supplying the brain and a patent stapedial artery for various nonencephalic structures. This inferred ancestral condition is exhibited by treeshrews and most early fossil euprimates, while extant primates exhibit reduction in one canal or another. The only early fossils deviating from this plesiomorphic condition are Adapis parisiensis with a reduced promontorial canal, and Rooneyia and Mahgarita with reduced stapedial canals.

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The Placental Mammal Ancestor and the Post–K-Pg Radiation of Placentals

Cited by 1,019 publications

References 218 publications

Comparative digesta retention patterns in ratites

Comparative digesta retention patterns in ratites

Ancient dates or accelerated rates? Morphological clocks and the antiquity of placental mammals

Internal carotid arterial canal size and scaling in Euarchonta: Re-assessing implications for arterial patency and phylogenetic relationships in early fossil primates

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