Avian brain evolution: new data from Palaeogene birds (Lower Eocene) from England. (original) (raw)
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Avian palaeoneurology: Reflections on the eve of its 200th anniversary
Journal of Anatomy, 2020
Avian palaeoneurology has been a relatively neglected field of research (for earlier reviews that either centred on or included avian palaeoneurology see Walsh and Milner, 2011a; Walsh and Knoll; 2011; Walsh and Knoll, 2018). This is no doubt due to the fact that the skulls of birds are particularly fragile and, therefore, not commonly found in fossil sites (Gardner et al., 2016). Even when the skull is preserved, it may be crushed, limiting considerably its potential for palaeoneurological investigations. Thus, the vast majority of Early Cretaceous birds that could theoretically be studied from the viewpoint of palaeoneurology, such as those of the famous Jehol biota, have flattened skeletons (see Wang et al., 2016). Yet, despite these difficult circumstances, palaeoneurological investigations on birds have a long history (Figure 1). 2 | PI ONEERING DAYS The first mention of an avian fossil brain is to be found in a nota bene in the second edition of Cuvier's (1822: 328) Recherches sur les Ossemens fossiles, a seminal work in vertebrate palaeontology. The discreet text reads: 'Au moment où l'on achève l'impression de cette feuille, je reçois encore de Montmartre, un Ornitholithe, où la tête, le cou, l'aile, le croupion, la cuisse, et ce qui est plus extraordinaire, la trachée-artère, sont en place et bien conservés;
Diversity
The shape of the brain influences skull morphology in birds, and both traits are driven by phylogenetic and functional constraints. Studies on avian cranial and neuroanatomical evolution are strengthened by data on extinct birds, but complete, 3D-preserved vertebrate brains are not known from the fossil record, so brain endocasts often serve as proxies. Recent work on extant birds shows that the Wulst and optic lobe faithfully represent the size of their underlying brain structures, both of which are involved in avian visual pathways. The endocasts of seven extinct birds were generated from microCT scans of their skulls to add to an existing sample of endocasts of extant birds, and the surface areas of their Wulsts and optic lobes were measured. A phylogenetic prediction method based on Bayesian inference was used to calculate the volumes of the brain structures of these extinct birds based on the surface areas of their overlying endocast structures. This analysis resulted in hyperp...
Journal of Anatomy, 2016
Digital methodologies for rendering the gross morphology of the brain from X-ray computed tomography data have expanded our current understanding of the origin and evolution of avian neuroanatomy and provided new perspectives on the cognition and behavior of birds in deep time. However, fossil skulls germane to extracting digital endocasts from early stem members of extant avian lineages remain exceptionally rare. Data from earlydiverging species of major avian subclades provide key information on ancestral morphologies in Aves and shifts in gross neuroanatomical structure that have occurred within those groups. Here we describe data on the gross morphology of the brain from a mid-to-late Paleocene penguin fossil from New Zealand. This most basal and geochronologically earliest-described endocast from the penguin clade indicates that described neuroanatomical features of early stem penguins, such as lower telencephalic lateral expansion, a relatively wider cerebellum, and lack of cerebellar folding, were present far earlier in penguin history than previously inferred. Limited dorsal expansion of the wulst in the new fossil is a feature seen in outgroup waterbird taxa such as Gaviidae (Loons) and diving Procellariiformes (Shearwaters, Diving Petrels, and allies), indicating that loss of flight may not drastically affect neuroanatomy in diving taxa. Wulst enlargement in the penguin lineage is first seen in the late Eocene, at least 25 million years after loss of flight and cooption of the flight stroke for aquatic diving. Similar to the origin of avian flight, major shifts in gross brain morphology follow, but do not appear to evolve quickly after, acquisition of a novel locomotor mode. Enlargement of the wulst shows a complex pattern across waterbirds, and may be linked to sensory modifications related to prey choice and foraging strategy.
The skull roof tracks the brain during the evolution and development of reptiles including birds
Nature Ecology & Evolution
Major transformations in brain size and proportions, such as the enlargement of the brain during the evolution of birds, are accompanied by profound modifications to the skull roof. However, the hypothesis of concerted evolution of shape between brain and skull roof over major phylogenetic transitions, and in particular of an ontogenetic relationship between specific regions of the brain and the skull roof, has never been formally tested. We performed 3D 2 morphometric analyses to examine the deep history of brain and skull-roof morphology in Reptilia, focusing on changes during the well-documented transition from early reptiles through archosauromorphs including nonavian dinosaurs to birds. Non-avialan taxa cluster tightly together in morphospace, whereas Archaeopteryx and crown birds occupy a separate region. There is a one-to-one correspondence between the forebrain and frontal and the midbrain and parietal. Furthermore, the position of the forebrain-midbrain boundary correlates significantly with the position of the frontoparietal suture in across the phylogenetic breadth of Reptilia and during the ontogeny of individual taxa. Conservation of position and identity in the skull roof is apparent, and there is no support for prior hypotheses that the avian parietal is a transformed postparietal. The correlation and apparent developmental link between regions of the brain and bony skull elements are likely ancestral to Tetrapoda and may be fundamental to all of Osteichthyes, coeval with the origin of the dermatocranium.
Avian brains and a new understanding of vertebrate brain evolution
Nature Reviews …, 2005
Authors are ordered alphabetically in two groups: the first group, along with the first two and last two authors, are the core Avian Brain Nomenclature Forum Thinktank group; the second group are professors, postdoctoral fellows and students who also participated in the Avian Brain Nomenclature Forum. (For author affiliations see online supplementary information S1 (box).)
Integrative and comparative biology, 2016
The avian skull is distinctive in its construction and in its function. Much of bird anatomical variety is expressed in the beak; but the beak itself, largely formed of the premaxillary bone, is set upon a shortened face and a bulbous, enlarged braincase. Here, we use original anatomical observations and reconstructions to describe the overall form of the avian skull in a larger context and to provide a general account of the evolutionary transformation from the early dinosaur skull-the skull of an archosaurian macropredator-to that of modern birds. Facial shortening, the enlargement of the braincase around an enlarged brain (with consequential reduction of circumorbital elements and the adductor chamber), and general thinning and looser articulation of bones are trends. Many of these owe to juvenilization or paedomorphosis, something that is abundantly evident from comparison of a juvenile early theropod (Coelophysis) to early avialans like Archaeopteryx Near the avian crown, the p...
Opinion: Avian brains and a new understanding of vertebrate brain evolution
Nature Reviews Neuroscience, 2005
Authors are ordered alphabetically in two groups: the first group, along with the first two and last two authors, are the core Avian Brain Nomenclature Forum Thinktank group; the second group are professors, postdoctoral fellows and students who also participated in the Avian Brain Nomenclature Forum. (For author affiliations see online supplementary information S1 (box).)
Multiphase progenetic development shaped the brain of flying archosaurs
Scientific Reports, 2019
The growing availability of virtual cranial endocasts of extinct and extant vertebrates has fueled the quest for endocranial characters that discriminate between phylogenetic groups and resolve their neural significances. We used geometric morphometrics to compare a phylogenetically and ecologically comprehensive data set of archosaurian endocasts along the deep evolutionary history of modern birds and found that this lineage experienced progressive elevation of encephalisation through several chapters of increased endocranial doming that we demonstrate to result from progenetic developments. Elevated encephalisation associated with progressive size reduction within Maniraptoriformes was secondarily exapted for flight by stem avialans. Within Mesozoic Avialae, endocranial doming increased in at least some Ornithurae, yet remained relatively modest in early Neornithes. During the Paleogene, volant non-neoavian birds retained ancestral levels of endocast doming where a broad neoavian ...