The conquest of spaces: Exploring drivers of morphological shifts through phylogenetic palaeoecology

Abstract

Much of the focus of palaeobiological studies in the last century can be summarized as seeking to understand how evolutionary lineages occupy new regions of morphological, ecological, and geographic space, or are excluded from those spaces. A desire to understand the processes that lead to morphological change unites a variety of biological disciplines focusing on topics ranging from studies of organism genomics to broad scale macroevolutionary analyses. There is increasing recognition that a hierarchical approach, incorporating both intrinsic genealogical processes and external ecological factors, is necessary to understand the mechanisms behind the drivers of phenotypic change. One of the most important issues that remains to be resolved regards the generation and fixation of morphological changes within evolutionary lineages, including whether the evolution of novel morphologies facilitates expansion to previously unoccupied environments (a developmental push mechanism) or whether a shift in ecological occupation results in subsequent morphologic change (an ecological pull mechanism). The geological record affords a unique perspective on morphological change, preserving both evidence of environmental change through shifts in sedimentology and the changing morphology of evolutionary lineages; as such, palaeontology provides a long-term view of the relationship between ecological and morphological shifts. This review focuses on the ways that phylogenetic palaeoecology, which utilizes phylogenetic frameworks in concert with palaeoecological data, can be leveraged to explore these questions. It begins by reviewing the literature on novelty and innovation – the origination of new morphologies and their proliferation within ecosystems – within a hierarchical framework and the role of heterochrony as the primary mechanism by which phenotypic change occurs before exploring evidence for developmental push and ecological pull as competing drivers of morphological shifts. Drivers of morphological shifts are examined through analysis of heterochronic trends in horseshoe crab evolution and comparison with case studies on angiosperm plants, giant ground sloths, and megatooth sharks. • Phenotypic changes occur through either a developmental push or ecological pull. • Heterochrony is the mechanism by which most morphological evolution occurs. • A hierarchical approach is needed to understand the causes behind phenotypic change. • Palaeontology provides a deep time perspective on ecological and morphological shifts. • Phylogenetic palaeoecology can be leveraged to explore morphological change.