Data from: Patterns of ecological diversification in thelodonts

Here we explore the spatial, temporal and phylogenetic patterns of
ecological diversification for the entire clade of thelodonts, one of the
earliest groups of vertebrates and longest lasting of the Palaeozoic
agnathans in the fossil record. Parsimony and maximum-likelihood methods
are used to reconstruct ancestral states of their geographical
distributions, habitats and lifestyles. Our results support the concept
that thelodonts originated during the Middle?–Late Ordovician probably in
marine open waters of Laurasia, with a demersal lifestyle on hard
substrates being the ancestral condition for the whole clade. Later,
thelodonts underwent a complex ecological diversification and
palaeobiogeographical history, comparable in many aspects to those of some
major groups of living fishes. Different modes of life evolved repeatedly
and a wide range of habitats were colonized by distinct groups, including
deep waters and brackish marine and/or freshwater environments. Diadromous
strategies presumably appeared on nine different occasions. The
palaeobiogeographical history of thelodonts reveals significant
differences in the dispersal potential of some major groups. Dispersal of
thelodontiforms entailed displacements over long distances and the
crossing of deep-water biogeographical barriers, whereas those of
furcacaudiforms were always limited to areas interconnected by shallow
platforms. We propose that the evolution of pelagic larval stages in
thelodontiforms might explain this biogeographical pattern and could
satisfactorily account for the greater evolutionary success of this group.