HOME | DD

Description

In the wake of the Cretaceous-Paleogene (K-Pg) mass extinction, neornithean birds were the only dinosaurs to have survived the devastation. It has been inferred that neornitheans were ancestrally ground-dwelling animals, which may have increased their chances of survival when widespread fires during the K-Pg burned down forest environments. As the forests recovered, however, neornitheans quickly diversified into the vacant arboreal niches that opened up. Arboreal lifestyles independently evolved in pigeons, cuckoos, turacos, and strisoreans , but by far the biggest radiation of arboreal birds has been the clade Telluraves.

Telluravians include the groups Accipitriformes (hawks, eagles, etc.), Strigiformes (owls), Coliiformes (mousebirds), Leptosomiformes (courols), Trogoniformes (trogons), Bucerotiformes (hornbills, hoopoes, etc.), Coraciiformes (rollers, kingfishers, etc.), Piciformes (woodpeckers, barbets, etc.), Cariamiformes (seriemas), Falconiformes (falcons), Psittaciformes (parrots), and Passeriformes (songbirds, etc.). Remarkably, early members of nearly all of these lineages have been discovered as fossils in the Messel Shale of Germany, dating to the Eocene about 47 million years ago. In fact, the only telluravian group that has definitely not yet been found in the Messel is Accipitriformes. Fossil birds from Messel are often discovered as complete skeletons with even their feathering still preserved, and I have selected a few representative taxa to illustrate here. (Note that I have not restored the only known Messel owl, Palaeoglaux, as its skull is still unknown.)

However, it should be said that the phylogenetic affinities of many fossil birds has not yet been rigorously tested, and even those that have are often still subject to debate. For example, two groups of extinct telluravians, the messelasturids and halcyornithids, have been widely considered stem-parrots in the literature, but several recent studies have cast doubt on this identification, with halcyornithids in particular now thought to have been equally closely related to parrots and passerines. Nonetheless, the Messel fossils provide an insightful glimpse into how quickly arboreal birds diversified into numerous species and ecologies.

As adaptations for climbing and clinging, telluravians evolved a diversity of foot morphologies. Zygodactyl feet (backward-pointing first and fourth toes) independently evolved in at least piciforms, the courol, and the group uniting parrots and passerines (then later lost in true passerines). Semizygodactyl feet (in which the fourth toe can be reversed by choice) evolved in owls, mousebirds, and the osprey. Trogons uniquely evolved the heterodactyl condition, in which the first and second toes point backwards.

That being said, not all telluravians took to a life in the trees. The cariamiforms notably spawned a radiation of mainly terrestrial birds, including the flightless phorusrhacids (terror birds) that would go on to become apex predators in the Americas.

Description

In the wake of the Cretaceous-Paleogene (K-Pg) mass extinction, neornithean birds were the only dinosaurs to have survived the devastation. It has been inferred that neornitheans were ancestrally ground-dwelling animals, which may have increased their chances of survival when widespread fires during the K-Pg burned down forest environments. As the forests recovered, however, neornitheans quickly diversified into the vacant arboreal niches that opened up. Arboreal lifestyles independently evolved in pigeons, cuckoos, turacos, and strisoreans , but by far the biggest radiation of arboreal birds has been the clade Telluraves.

Telluravians include the groups Accipitriformes (hawks, eagles, etc.), Strigiformes (owls), Coliiformes (mousebirds), Leptosomiformes (courols), Trogoniformes (trogons), Bucerotiformes (hornbills, hoopoes, etc.), Coraciiformes (rollers, kingfishers, etc.), Piciformes (woodpeckers, barbets, etc.), Cariamiformes (seriemas), Falconiformes (falcons), Psittaciformes (parrots), and Passeriformes (songbirds, etc.). Remarkably, early members of nearly all of these lineages have been discovered as fossils in the Messel Shale of Germany, dating to the Eocene about 47 million years ago. In fact, the only telluravian group that has definitely not yet been found in the Messel is Accipitriformes. Fossil birds from Messel are often discovered as complete skeletons with even their feathering still preserved, and I have selected a few representative taxa to illustrate here. (Note that I have not restored the only known Messel owl, Palaeoglaux, as its skull is still unknown.)

However, it should be said that the phylogenetic affinities of many fossil birds has not yet been rigorously tested, and even those that have are often still subject to debate. For example, two groups of extinct telluravians, the messelasturids and halcyornithids, have been widely considered stem-parrots in the literature, but several recent studies have cast doubt on this identification, with halcyornithids in particular now thought to have been equally closely related to parrots and passerines. Nonetheless, the Messel fossils provide an insightful glimpse into how quickly arboreal birds diversified into numerous species and ecologies.

As adaptations for climbing and clinging, telluravians evolved a diversity of foot morphologies. Zygodactyl feet (backward-pointing first and fourth toes) independently evolved in at least piciforms, the courol, and the group uniting parrots and passerines (then later lost in true passerines). Semizygodactyl feet (in which the fourth toe can be reversed by choice) evolved in owls, mousebirds, and the osprey. Trogons uniquely evolved the heterodactyl condition, in which the first and second toes point backwards.

That being said, not all telluravians took to a life in the trees. The cariamiforms notably spawned a radiation of mainly terrestrial birds, including the flightless phorusrhacids (terror birds) that would go on to become apex predators in the Americas.