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Terrestrial vertebrates and the evolutionary origins of morphological diversity

Periodic Reporting for period 3 - TEMPO (Terrestrial vertebrates and the evolutionary origins of morphological diversity)

Reporting period: 2019-05-01 to 2020-10-31

The TEMPO project aims to address central hypotheses in evolutionary research, and in doing to shed light on a single core question in biology: How did the vast diversity of animals and their morphologies come of be? This question is important to society because it enhances human knowledge of the deep evolution and origins of biological organisms on Earth today. The project focusses on birds, mammals, and thier extinct relatives such as dinosaurs and mammal-like reptiles.

The approach of the project is to address three central questions:

(1) How have rates and constraints of phenotypic evolution varied through geological time? This is a quantitative statistical question. By quantifying the structure of the skeleton in many species, including both living and fossil animals, we hope to characterise how patterns of evolution vary among groups and through time. Understanding *how* they vary is the first step in answering *why* they vary.
(2) Are these patterns consistent with the occurrence of global niche-filling? This relates to the hypothesis of adaptive radiations, that evolution of organisms is a response to the distribution of ecological opportunities on Earth through time.
(3) Can evolutionary versatility enabled by key innovations explain these patterns? This relates to the hypothesis that some groups of animals are simply more versatile than others, due to features of their body plan, structure, or development.
So far, the project has assembled an unprecedented database of 3D digital skeletons of birds, mammals and their extinct relatives, which include dinosaurs and mammal-like reptiles (therapsids). This work is currently in-progress and so far spans more than 800 living and 1200 extinct species. This database allows us to address many questions about the evolution of these groups in a quantitative framework, which is not readily possible in the absence of such data. The data are central to the aims of the TEMPO project. They also allow many other types of questions to be answered in biological sciences, including many that are most likely not yet anticipated. To facilitate this they will be made freely available online. SWe ahve produced several scientific publications so far. For example, we have piloted some of the approaches of the wider project in a study of the evolution of body size in dinosaurs. This work unravels the patterns of evolution that gave rise to enormous disparity in that group, ranging from tiny birds (weighing as little as 2 grams), up to giant sauropods weighing in excess of 70 tonnes (https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12329).

We also have started to address questions of ecomorphology and evolution within groups such as marsupials, birds and dinosaurs. Ecomorphology is the study of relationships between the structure of organisms and their ecology. It is central to core macroevolutionary hypotheses such as the idea of adaptive radiation (that evolution is driven by availabilities of novel ecological opportunities) and also to interpreting the ecologies of extinct species known only from fossils (including dinosaurs). Among other findings made so far, the quantitative approaches of the project have uncovered new indicators of stance in extinct animals, allowing us to determine which dinosaurs were quadrupeds, and which were bipeds. We have also investigated links between the vestibule (organ of balance) in birds and their locomotion.

Becuase our data collection has now reached its critical phase, the second phase of the project has begun. In this second phase we will investigate wider patterns of evolution of the skeleton, how and why they vary among groups such as mammals and birds, and through time.
The project goes far beyond the state of the art by generating high-throughput methods to generate high resolution digital skeletons of living and extinct animals ranging in size from tiny hummingbirds and mice to dinosaurs and other extinct species that were larger than elephants. To the best of our knowledge, this database represents substantively the largest digital comparative anatomy dataset of its kind. Our project differs from other work in the field of skeletal evolution because it includes data from both living and fossil species within a single analytical framework, and includes data from all major parts of the skeleton, instead of analysing just parts (e.g. skulls) or small an groups of animals alone.

By the end of the project we expect to have synthesised and compared patterns of skeletal evolution from across birds, mammals, and their extinct relatives (dinosaurs mammal-like reptiles, and others). By doing so we hope to understand how patterns of the rate of evolution, and constraints on its outcomes, vary among groups and through time. This will shed light on the factors (e.g. evolutionary versatility, ecological opportunity) underlying the large-scale patterns of evolutionary history.