Neurocranial anatomy of an enigmatic Early Devonian fish sheds light on early osteichthyan evolution.

The skull of 'Ligulalepis' from the Early Devonian of Australia (AM-F101607) has significantly expanded our knowledge of early osteichthyan anatomy, but its phylogenetic position has remained uncertain. We herein describe a second skull of 'Ligulalepis' and present micro-CT data on both specimens to reveal novel anatomical features, including cranial endocasts. Several features previously considered to link 'Ligulalepis' with actinopterygians are now considered generalized osteichthyan characters or of uncertain polarity. The presence of a lateral cranial canal is shown to be variable in its development between specimens. Other notable new features include the presence of a pineal foramen, the some detail of skull roof sutures, the shape of the nasal capsules, a placoderm-like hypophysial vein, and a chondrichthyan-like labyrinth system. New phylogenetic analyses place 'Ligulalepis' as a stem osteichthyan, specifically as the sister taxon to 'psarolepids' plus crown osteichthyans. The precise position of 'psarolepids' differs between parsimony and Bayesian analyses.

Live birth in the Devonian period.

The extinct placoderm fishes were the dominant group of vertebrates throughout the Middle Palaeozoic era, yet controversy about their relationships within the gnathostomes (jawed vertebrates) is partly due to different interpretations of their reproductive biology. Here we document the oldest record of a live-bearing vertebrate in a new ptyctodontid placoderm, Materpiscis attenboroughi gen. et sp. nov., from the Late Devonian Gogo Formation of Australia (approximately 380 million years ago). The new specimen, remarkably preserved in three dimensions, contains a single, intra-uterine embryo connected by a permineralized umbilical cord. An amorphous crystalline mass near the umbilical cord possibly represents the recrystallized yolk sac. Another ptyctodont from the Gogo Formation, Austroptyctodus gardineri, also shows three small embryos inside it in the same position. Ptyctodontids have already provided the oldest definite evidence for vertebrate copulation, and the new specimens confirm that some placoderms had a remarkably advanced reproductive biology, comparable to that of some modern sharks and rays. The new discovery points to internal fertilization and viviparity in vertebrates as originating earliest within placoderms.

An exceptional Devonian fish from Australia sheds light on tetrapod origins.

The transition from fishes to tetrapods was one of the most dramatic events in the evolution of vertebrates, but many pivotal fossils are incomplete, resulting in gaps in the data that are used for phylogenetic reconstruction. Here we present new observations from the most complete, acid-prepared Devonian tetrapodomorph fish yet discovered, Gogonasus, which was previously placed just crownward of Kenichthys and rhizodontids, the most primitive taxa on the tetrapod lineage. Unexpectedly, Gogonasus shows a mosaic of plesiomorphic and derived tetrapod-like features. Whereas the braincase and dermal cranial skeleton exhibit generalized morphologies with respect to Eusthenopteron or Panderichthys, taxa that are traditionally considered to be phyletically close to tetrapods, the presence of a deeply invaginated, wide spiracle, advanced internal spiracular architecture and near-horizontal hyomandibula are specialized features that are absent from Eusthenopteron. Furthermore, the pectoral fin skeleton of Gogonasus shares several features with that of Tiktaalik, the most tetrapod-like fish. A new phylogenetic analysis places Gogonasus crownward of Eusthenopteron as the sister taxon to the Elpistostegalia. Aspects of the basic tetrapod limb skeleton and middle ear architecture can now be traced further back within the tetrapodomorph radiation.