Data from: Tactile bill-tip organs in seabirds suggests conservation of a deep avian symplesiomorphy

Birds’ bills are their main tactile interface with the outside world.
Tactile bill-tip organs associated with specialised foraging techniques
are present in several bird groups, yet remain understudied in most
clades. One example is Austrodyptornithes, the major seabird clade uniting
Procellariiformes (albatrosses and petrels) and Sphenisciformes
(penguins). Here, we describe the mechanoreceptor arrangement and
neurovascular anatomy in the premaxillae of Austrodyptornithes. Using a
wide phylogenetic sample of extant birds (361 species), we show that
albatrosses and penguins exhibit complex tactile bill-tip anatomies,
comparable to birds with known bill-tip organs, despite not being known to
use tactile foraging. Petrels (Procellariidae, Hydrobatidae and
Oceanitidae) lack these morphologies, indicating an evolutionary
transition in bill-tip mechanosensitivity within Procellariiformes. The
bill-tip organ in Austrodyptornithes may be functionally related to
nocturnal foraging and prey detection under water, or courtship displays
involving tactile stimulation of the bill. Alternatively, these organs may
be vestigial, as is likely the case in most palaeognaths (e.g., ostriches
and emu). Ancestral state reconstructions fail to reject the hypothesis
that the last common ancestor of Austrodyptornithes had a bill-tip organ;
thus, tactile-foraging may be ancestral for this major extant clade,
perhaps retained from a deeper point in crown bird evolutionary history.