Understanding past changes in biodiversity is a fundamental part of predicting the future of the Earth's ecosystems [1
]. Phylogenies and the fossil record provide two complementary windows on temporal variation in biodiversity. The most traditional, palaeontological approach is to document the gain and loss of taxa in the fossil record without recourse to phylogenetic information [3
]. Although the fossil record provides a direct timescale for observations and contains explicit information about extinction, it is incomplete, and more robust at higher taxonomic levels. A more recent, neontological approach is to analyse the shape of phylogenetic trees of extant taxa, revealing heterogeneity in the net rate of cladogenesis across taxa or through time [7
]. This allows researchers to compare like with like through identifying sister taxa, but relies on the fossil record to provide a direct timescale, and does not contain explicit information about extinction. Combining fossil with phylogenetic information provides the potential therefore to combine the advantages of both to make more robust inferences about macroevolution [9
]. In this paper we first summarise phylogenetic information for a long-lived clade of insects, the Odonatoidea (dragonflies and their relatives) and then combine it with fossil information to infer temporal changes in their diversification.
Identifying changes in the rate of diversification is central to understanding macroevolutionary processes. The simplest model of clade growth is an exponential one, where the rate of increase of taxa is constant through time [11
]. The next simplest alternative is logistic growth, an equilibrium model with the growth of the clade declining as richness rises, through competition. Establishing whether or not clade growth follows expansionist or equilibrial models can therefore contribute towards establishing whether biotic interactions are important in macroevolution, as implied by the Red Queen paradigm [1
]. Rates of speciation and extinction are also commonly variable across clades [7
]. Identifying which evolutionary branches have experienced shifts in their macroevolutionary rates is therefore a first step towards establishing which evolutionary or ecological events might be responsible.
The insects comprise the majority of extant described species. Previous work on insect macroevolution [14
] began with the traditional taxic approach from palaeontology [4
], to which was added the neontological phylogenetic approach [16
] which has identified a number of evolutionary and ecological processes that have shaped insect diversity [14
]. Data have suggested that overall rise in taxonomic richness may be declining modestly towards the present [4
], although not strongly so [15
], and not in many recent radiations [14
]. This is consistent with the generally exponential increase in taxa in the terrestrial fossil record [5
] in comparison to the marine record [6
]. However the relative incompleteness of the insect record may provide a source of bias, because the true originations of clades likely occurred prior to their first appearance in the fossil record. Using phylogenies to infer ghost ranges, Davis et al. [19
] showed that a number of insect orders likely originated prior to their first fossil appearance, making the increase in orders through time look more logistic. The analysis of order-level trends however raises problems; there is a greater risk of paraphyly, complicating the estimation of ghost ranges, and changes in order richness do not necessarily reflect changes at lower taxonomic levels [20
]. It would therefore be useful to examine patterns of diversification at a lower taxonomic level, in a clade of insects of equivalent age to the whole class, which previous studies have only achieved using the traditional taxic palaeontological approach.
Despite being less speciose than many other insect orders, the Odonatoidea (Odonata plus the extinct Protodonata) (= Holodonata [21
], = Neodonatoptera [22
]) are among the most ancient of all living continental fauna, with a fossil record extending back 320 million years, surviving several mass-extinction events [21
]. Their accessibility as study systems has informed on many questions in ecology, evolution, and conservation biology [23
]. This study aims to summarise existing phylogenetic information on the Odonatoidea by constructing a supertree at the family level. We first apply a neontological approach to the tree to detect where shifts in the net rate of diversification have occurred, and then combine the phylogenetic information with fossil record data to observe patterns of family-lineage richness over time.