Ontogenetic and life history trait changes associated with convergent ecological specializations in extinct ungulate mammals

Abstract

Investigating life history traits in mammals is crucial to understand their survival in changing environments. However, these parameters are hard to estimate in a macroevolutionary context. Here we show that the use of dental ontogenetic parameters can provide clues to better understand the adaptive nature of phenotypic traits in extinct species such as South American notoungulates. This recently extinct order of mammals evolved in a context of important geological, climatic, and environmental variations. Interestingly, notoungulates were mostly herbivorous and acquired highcrowned teeth very early in their evolutionary history. We focused on the variations in crown height, dental eruption pattern, and associated body mass of 69 notoungulate taxa, placed in their phylogenetic and geological contexts. We showed that notoungulates evolved higher crowns several times between 45 and 20 Ma, independently of the variation in body mass. Interestingly, the independent acquisitions of ever-growing teeth were systematically accompanied by eruption of molars faster than permanent premolars. These repeated associations of dental innovations have never been documented for other mammals and raise questions on their significance and causal relationships. We suggest that these correlated changes could originate from ontogenetic adjustments favored by structural constraints, and may indicate accelerated life histories. Complementarily, these more durable and efficient dentitions could be selected to cope with important ingestions of abrasive particles in the context of intensified volcanism and increasing aridity. This study demonstrates that assessing both life history and ecological traits allows a better knowledge of the specializations of extinct mammals that evolved under strong environmental constraints. dental ontogeny | hypsodonty | abrasion | notoungulates | South America

New remains of kollpaniine “condylarths” (Panameriungulata) from the early Palaeocene of Bolivia shed light on hypocone origins and molar proportions among ungulate-like placentals

“…The locality of Tiupampa (Cochabamba, Bolivia) has yielded the oldest mammalian assemblage of the Cenozoic of South America and is the type locality of the Tiupampan South America Land Mammal Age (SALMA), (Gelfo et al 2009). The only possibly older Cenozoic mammal of South America is an isolated lower molar of polydolopimorphian (Cocatherium lefipanum) from the Lefipan Formation at the Grenier farm (Chubut, Argentina) and discovered in beds located about 5 m above the K-T boundary (Goin et al 2006). A recent revision of Palaeogene SALMAs agreed with this view and considered a 64 Ma age for the Tiupampan (Woodburne et al 2014a).…”

Influences of Domestication and Island Evolution on Dental Growth in Sheep

“…Such variation of tooth eruption sequences between wild and domestic mammals has so far not been investigated. However, a similar process has been suggested for the evolutionary pattern of tooth eruption found in some notoungulates, in which earlier molar eruption might have evolved to acquire an efficient dentition more rapidly in a changing environment during the middle and late Paleogene of South America (Gomes Rodrigues et al 2017).…”

Tissue Mechanical Forces and Evolutionary Developmental Changes Act Through Space and Time to Shape Tooth Morphology and Function

“…There are nine extant mammalian orders in which all or some teeth have become hypselodont, from Glires (the clade of rodents and their relatives, the lagomorphs—rabbits, hares, and pikas), elephants, and walruses with hypselodont incisors to sloths with ever‐growth homodont dentitions . Extinct clades with ever‐growing teeth include the mysterious notoungulates of South America, some of which have superficially similar dentitions to those of rodents, featuring incisors and molars separated by a large diastema . Comparative analyses of high‐crowned and ever‐growing teeth in notoungulates and rodents suggested that the diastema and mesial drift of molars may be tied to morphological changes needed to accommodate these teeth .…”