A non-archaeopterygid avialan theropod from the Late Jurassic of southern Germany

The Late Jurassic ‘Solnhofen Limestones’ are famous for their exceptionally preserved fossils, including the urvogel Archaeopteryx, which has played a pivotal role in the discussion of bird origins. Here we describe a new, non-archaeopterygid avialan from the Lower Tithonian Mörnsheim Formation of the Solnhofen Archipelago, Alcmonavis poeschli gen. et sp. nov. Represented by a right wing, Alcmonavis shows several derived characters, including a pronounced attachment for the pectoralis muscle, a pronounced tuberculum bicipitale radii, and a robust second manual digit, indicating that it is a more derived avialan than Archaeopteryx. Several modifications, especially in muscle attachments of muscles that in modern birds are related to the downstroke of the wing, indicate an increased adaptation of the forelimb for active flapping flight in the early evolution of birds. This discovery indicates higher avialan diversity in the Late Jurassic than previously recognized.

Comparative digestive physiology of archosaurs with notes on bird origins

It is widely accepted that birds evolved from theropod dinosaurs, and few paleontologists disagree preferring a more ancient split of the avian and dinosaur lineages. The difference in digestive physiology between members of the theropod and crocodile lineages, documented by fossil feces and gut contents, offers an opportunity to test these phylogenetic hypotheses. Birds share with crocodiles the functional gizzard that contains swallowed stones and where gastric pellets are formed before regurgitation, as well as a mechanism that prevents the passage of indigestible residues into the intestine. Both these adaptations are missing in unquestionable theropod groups (compsognathids, tyrannosaurids, allosaurids, coelophysids). The theropod ancestry of birds implies reappearance and strong development of a specific stomach functionality that either had been already lost in the theropod dinosaurs or was never present in their lineage. Coprolites of early archosaurs contain undigested bones, which suggests a short digestion time and higher metabolic rates than in extant crocodiles. Early archosaurs were similar to birds, but not to dinosaurs, in all these aspects of physiology.

Comparative digestive physiology of archosaurs with notes on bird origins

It is widely accepted that birds evolved from theropod dinosaurs, and few paleontologists disagree preferring a more ancient split of the avian and dinosaur lineages. The difference in digestive physiology between members of the theropod and crocodile lineages, documented by fossil feces and gut contents, offers an opportunity to test these phylogenetic hypotheses. Birds share with crocodiles the functional gizzard that contains swallowed stones and where gastric pellets are formed before regurgitation, as well as a mechanism that prevents the passage of indigestible residues into the intestine. Both these adaptations are missing in unquestionable theropod groups (compsognathids, tyrannosaurids, allosaurids, coelophysids). The theropod ancestry of birds implies reappearance and strong development of a specific stomach functionality that either had been already lost in the theropod dinosaurs or was never present in their lineage. Coprolites of early archosaurs contain undigested bones, which suggests a short digestion time and higher metabolic rates than in extant crocodiles. Early archosaurs were similar to birds, but not to dinosaurs, in all these aspects of physiology.

Comparative digestive physiology of archosaurs with notes on bird origins

It is widely accepted that birds evolved from theropod dinosaurs, and few paleontologists disagree preferring a more ancient split of the avian and dinosaur lineages. The difference in digestive physiology between members of the theropod and crocodile lineages, documented by fossil feces and gut contents, offers an opportunity to test these phylogenetic hypotheses. Birds share with crocodiles the functional gizzard that contains swallowed stones and where gastric pellets are formed before regurgitation, as well as a mechanism that prevents the passage of indigestible residues into the intestine. Both these adaptations are missing in unquestionable theropod groups (compsognathids, tyrannosaurids, allosaurids, coelophysids). The theropod ancestry of birds implies reappearance and strong development of a specific stomach functionality that either had been already lost in the theropod dinosaurs or was never present in their lineage. Coprolites of early archosaurs contain undigested bones, which suggests a short digestion time and higher metabolic rates than in extant crocodiles. Early archosaurs were similar to birds, but not to dinosaurs, in all these aspects of physiology.

Cretaceous Reverie: Review of Birds of Stone: Chinese Avian Fossils from the Age of Dinosaurs by Luis M. Chiappe and Meng Qingjin1

Birds of Stone contains a portfolio of outstanding photographs of the spectacularly preserved Jehol bird fossils, from the Chinese Lower Cretaceous, and other pertinent vertebrate fossils of varying ages, along with comments on each fossil. The book nicely illustrates a range of species of the radiation of enantiornithines (opposite birds), the dominant Mesozoic landbirds, as well as the ornithuromorphs, the Mesozoic antecedents of the modern neornithine birds. Although the first section of the book is fairly straight forward, the second section, on bird origins and their early evolution is one-sided, presenting only the popular paleontological view and omits discussion of controversial subjects. Examples are the highly speculative presence of dinosaur protofeathers and improbable scenarios of flight origins. There are no citations of the numerous credible opposing views in the literature.

FANTASY VS REALITY: A Critique of Smith et al.'s Bird Origins

Adherents of the current orthodoxy of a derivation of birds from theropod dinosaurs, criticize the commentary by Feduccia (2013, Auk, 130) [1 - 12] entitled “Bird Origins Anew” as well as numerous papers by Lingham-Soliar on theropod dermal fibers, using numerous mischaracterizations and misstatements of content, and illustrate their own misconceptions of the nature of the debate, which are here clarified. While there is general agreement with the affinity of birds and maniraptorans, the widely accepted phylogeny, advocating derived earth-bound maniraptorans giving rise to more primitive avians (i.e. Archaeopteryx), may be “topsy-turvy.” The current primary debate concerns whether maniraptorans are ancestral or derived within the phylogeny, and whether many maniraptorans and birds form a clade distinct from true theropods. Corollaries of the current scheme show largely terrestrial maniraptoran theropods similar to the Late CretaceousVelociraptorgiving rise to avians, and flight originatingviaa terrestrial (cursorial) “gravity-resisted,” as opposed to an arboreal “gravity-assisted” model. The current dogma posits pennaceous flight remiges in earth-bound theropods having evolved in terrestrial theropods that never flew. As part of the orthodoxy, fully feathered maniraptorans such as the tetrapteryx glidersMicroraptorand allies, are incorrectly reconstructed as terrestrial cursors, when in reality their anatomy and elongate hindlimb feathers would be a hindrance to terrestrial locomotion.The same is true of many early birds, exemplified by reconstruction of the arboreally adaptedConfuciusornisas a terrestrial predator, part of the overall theropodan scheme of birds evolving from terrestrial dinosaurs, and flight from the ground up. Both sides of this contentious debate must be constantly aware that new fossil or even molecular discoveries on birds may change current conclusions.