Avian brain evolution: new data from Palaeogene birds (Lower Eocene) from England. (original) (raw)

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;

Beyond Endocasts: Using Predicted Brain-Structure Volumes of Extinct Birds to Assess Neuroanatomical and Behavioral Inferences

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...

Novel insights into early neuroanatomical evolution in penguins from the oldest described penguin brain endocast

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).)

Opinion: Avian brains and a new understanding of vertebrate brain evolution

Nature Reviews Neuroscience, 2005

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 ...

Complete Ichthyornis skull illuminates mosaic assembly of the avian head

Nature, 2018

The skull of living birds is greatly modified from the condition found in their dinosaurian antecedents. Bird skulls have an enlarged, toothless premaxillary beak and an intricate kinetic system that includes a mobile palate and jaw suspensorium. The expanded avian neurocranium protects an enlarged brain and is flanked by reduced jaw adductor muscles. However, the order of appearance of these features and the nature of their earliest manifestations remain unknown. The Late Cretaceous toothed bird Ichthyornis dispar sits in a pivotal phylogenetic position outside living groups: it is close to the extant avian radiation but retains numerous ancestral characters1,2,3. Although its evolutionary importance continues to be affirmed3,4,5,6,7,8, no substantial new cranial material of I. dispar has been described beyond incomplete remains recovered in the 1870s. Jurassic and Cretaceous Lagerstätten have yielded important avialan fossils, but their skulls are typically crushed and distorted9. Here we report four three-dimensionally preserved specimens of I. dispar—including an unusually complete skull—as well as two previously overlooked elements from the Yale Peabody Museum holotype, YPM 1450. We used these specimens to generate a nearly complete three-dimensional reconstruction of the I. dispar skull using high-resolution computed tomography. Our study reveals that I. dispar had a transitional beak—small, lacking a palatal shelf and restricted to the tips of the jaws—coupled with a kinetic system similar to that of living birds. The feeding apparatus of extant birds therefore evolved earlier than previously thought and its components were functionally and developmentally coordinated. The brain was relatively modern, but the temporal region was unexpectedly dinosaurian: it retained a large adductor chamber bounded dorsally by substantial bony remnants of the ancestral reptilian upper temporal fenestra. This combination of features documents that important attributes of the avian brain and palate evolved before the reduction of jaw musculature and the full transformation of the beak.