Skeletal marine animal biodiversity is built by families with long macroevolutionary lag times.

The clade dynamics of marine animals have changed markedly over the Phanerozoic. Long-term diversification is associated with decreasing origination and extinction rates, and with increasing taxon longevity. Here we use the diversification trajectories of skeletal non-colonial marine families to infer the mechanisms that generated these trends. Suggested mechanisms behind these trends include stochastic extinction of taxa with high evolutionary volatility and selection for traits that buffer against extinction. We find an increasing predominance of Phanerozoic families with long lag times between first appearance and peak diversity, over those with 'early burst' diversification trajectories. Long-lag families persisted for longer and had lower evolutionary volatilities, higher genus-level occupancies and genera with larger niche breadths than early burst families. However, they do not preferentially show ecological modes known to protect against extinction. We interpret the rise of the long-lag families as reflecting an intensification of ecosystem-level mechanisms supporting both long-term coexistence and transient dynamics, which increased the capacity of marine ecosystems to accommodate highly diverse communities.