Assembly of modern mammal community structure driven by Late Cretaceous dental evolution, rise of flowering plants, and dinosaur demise

Abstract

The long-standing view that Mesozoic mammaliaforms living in dinosaur-dominated ecosystems were ecologically constrained to small size and insectivory has been challenged by astonishing fossil discoveries over the last three decades. By studying these well-preserved early mammaliaform specimens, paleontologists now agree that mammaliaforms underwent ecomorphological diversification during the Mesozoic Era. This implies that Mesozoic mammaliaform communities had ecological structure and breadth that were comparable to today’s small-bodied mammalian communities. However, this hypothesis remains untested in part because the primary focus of most studies is on individual taxa. Here, we present a study quantifying the ecological structure of Mesozoic mammaliaform communities with the aim of identifying evolutionary and ecological drivers that influenced the deep-time assembly of small-bodied mammaliaform communities. We used body size, dietary preference, and locomotor mode to establish the ecospace occupation of 98 extant, small-bodied mammalian communities from diverse biomes around the world. We calculated ecological disparity and ecological richness to measure the magnitude of ecological differences among species in a community and the number of different eco-cells occupied by species of a community, respectively. This modern dataset served as a reference for analyzing five exceptionally preserved, extinct mammaliaform communities (two Jurassic, two Cretaceous, one Eocene) from Konservat-Lagerstätten. Our results indicate that the interplay of at least three factors, namely the evolution of the tribosphenic molar, the ecological rise of angiosperms, and potential competition with other vertebrates, may have been critical in shaping the ecological structure of small-bodied mammaliaform communities through time.

Feeding ecology has a stronger evolutionary influence on functional morphology than on body mass in mammals

“…; Chen et al. ). The jaw metrics identified here offer an additional ecomorphological correlate beyond those commonly found in the literature (e.g., dental metrics) that can be readily applied to extant and fossil mammals.…”

“…; Slater ; Grossnickle and Newham ; Chen et al. ). The jaw correlates of diet presented in this study, especially JAPr distance and JAPr angle, may offer new functional traits that can be easily applied to broad studies of extant and fossil mammals.…”

“…Conclusions about macroevolutionary patterns in therians are sensitive to the ecomorphological trait being examined, and I advocate using functionally relevant traits as ecomorphological correlates when possible (Slater ; Smits ; Santana and Cheung ; Chen et al. ; Slater and Friscia ). Evolutionary patterns for these functional traits provide direct evidence of selective pressures associated with specific ecological or biomechanical functions.…”

“…; Olsen ; Chen et al. ), examine macroevolutionary patterns in major clades (Grossnickle and Polly ; Mitchell and Makovicky ), and reconstruct paleoenvironments (Vermillion et al. ).…”

“…; Grossnickle and Newham ; Chen et al. ). Numerous therian subclades adaptively radiated in response to novel ecological opportunities, often resulting in convergent evolution of ecomorphotypes as lineages repeatedly invaded similar ecological niches or adaptive zones (Osborn ; Simpson ; Eisenberg ; Smith et al.…”