1
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Plateau O, Green TL, Gignac PM, Foth C. Comparative digital reconstruction of Pica pica and Struthio camelus and their cranial suture ontogenies. Anat Rec (Hoboken) 2024; 307:5-48. [PMID: 37338258 DOI: 10.1002/ar.25275] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2023] [Revised: 05/25/2023] [Accepted: 05/26/2023] [Indexed: 06/21/2023]
Abstract
To date, several studies describe post-hatching ontogenetic variation in birds; however, none of these studies document and compare ontogenetic variation of the entire skull in multiple avian species. Therefore, we studied ontogenetic skull variation of two bird species with very different ecologies, Pica pica, and Struthio camelus, using μCT based 3D reconstructions. For each specimen, we performed bone-by-bone segmentation in order to visualize and describe the morphological variation of each bone during ontogeny and estimated the average sutural closure of the skulls to identify different ontogenetic stages. Although bone fusion of P. pica occurs more rapidly than that of S. camelus the general sequence of bone fusion follows a similar trend from posterior to anterior, but a more detailed analysis reveals some interspecific variation in the fusion patterns. Although growth persists over a longer period in S. camelus than in P. pica and adults of the former species are significantly larger, the skull of the most mature S. camelus is still less fused than that of P. pica. Different growth and fusion patterns of the two species indicate that the interspecific ontogenetic variation could be related to heterochronic developments. Nevertheless, this hypothesis needs to be tested in a broader phylogenetic framework in order to detect the evolutionary direction of the potential heterochronic transformations.
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Affiliation(s)
- Olivia Plateau
- Department of Geosciences, University of Fribourg, Fribourg, Switzerland
- Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Todd L Green
- Department of Anatomy, New York Institute of Technology College of Osteopathic Medicine, Old Westbury, New York, USA
| | - Paul M Gignac
- Department of Cellular & Molecular Medicine, University of Arizona College of Medicine, Tucson, Arizona, USA
| | - Christian Foth
- Department of Geosciences, University of Fribourg, Fribourg, Switzerland
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2
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Clark AD, Hu H, Benson RBJ, O’Connor JK. Reconstructing the dietary habits and trophic positions of the Longipterygidae (Aves: Enantiornithes) using neontological and comparative morphological methods. PeerJ 2023; 11:e15139. [PMID: 37009163 PMCID: PMC10062354 DOI: 10.7717/peerj.15139] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/02/2022] [Accepted: 03/07/2023] [Indexed: 03/29/2023] Open
Abstract
The Longipterygidae are a unique clade among the enantiornithines in that they exhibit elongate rostra (≥60% total skull length) with dentition restricted to the distal tip of the rostrum, and pedal morphologies suited for an arboreal lifestyle (as in other enantiornithines). This suite of features has made interpretations of this group’s diet and ecology difficult to determine due to the lack of analogous taxa that exhibit similar morphologies together. Many extant bird groups exhibit rostral elongation, which is associated with several disparate ecologies and diets (e.g., aerial insectivory, piscivory, terrestrial carnivory). Thus, the presence of rostral elongation in the Longipterygidae only somewhat refines trophic predictions of this clade. Anatomical morphologies do not function singularly but as part of a whole and thus, any dietary or ecological hypothesis regarding this clade must also consider other features such as their unique dentition. The only extant group of dentulous volant tetrapods are the chiropterans, in which tooth morphology and enamel thickness vary depending upon food preference. Drawing inferences from both avian bill proportions and variations in the dental morphology of extinct and extant taxa, we provide quantitative data to support the hypothesis that the Longipterygidae were animalivorous, with greater support for insectivory.
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Affiliation(s)
- Alexander D. Clark
- Cincinnati Museum Center, Geier Collections & Research Center, Cincinnati, Ohio, United States
| | - Han Hu
- Department of Earth Sciences, University of Oxford, Oxford, United Kingdom
| | - Roger BJ Benson
- American Museum of Natural History, New York City, New York, United States
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3
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Yoshida J, Kobayashi Y, Fiorillo AR. Evolutionary insights from an anatomical network analysis of the hyolaryngeal apparatus in extant archosaurs (birds and crocodilians). Anat Rec (Hoboken) 2023. [PMID: 36594713 DOI: 10.1002/ar.25153] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/22/2022] [Revised: 12/04/2022] [Accepted: 12/20/2022] [Indexed: 01/04/2023]
Abstract
Adaptive radiation of archosaurs, represented by crocodilians, non-avian dinosaurs, and birds, since the Mesozoic has been studied mainly based on their major skeletal elements (skull, vertebrae, and limbs). However, little is known about the evolution of their hyolaryngeal apparatus, which is involved with feeding, respiration, and vocalization, because of poor fossil preservation and the difficulty in determining the musculoskeletal homology of the apparatus. Network analysis is a framework to quantitatively characterize the topological organization of anatomical structures for comparing structural integration and modularity regardless of ambiguous homology. Herein, we modeled the musculoskeletal system of hyolarynx in six species of extant archosaurs and its sister-taxon turtle, and conducted a network analysis using network parameters, modular partition, and bone centrality in a phylogenetic framework. The network parameters reveal that ancestral archosaurs have reduced the numbers of elements and links and acquired complex networks as a whole domain with strong modularity in the hyolarynx. Furthermore, the modular partition and centrality reveal that the hyoids are highly evolvable, while the larynx is constrained and less evolvable. The archosaur hyolarynx exhibits different evolutionary trends: crocodilians with the system integration, basihyal simplification, and ceratobranchial centralization; and birds with the simplicity, weak integration, and modularity of the hyolarynx, laryngeal integration with cricoid centrality, and tongue-module expansion with the acquisition of paraglossal. Four hyolaryngeal bones (ceratobranchial, basihyal, paraglossal, and cricoid) have played important roles in archosaur evolution, and their fossil records are keys to understanding the two major archosaur lineages toward crocodilians and birds.
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Affiliation(s)
- Junki Yoshida
- Fukushima Museum, Aizu-wakamatsu, Fukushima, Japan.,Hokkaido University Museum, Sapporo, Hokkaido, Japan
| | | | - Anthony R Fiorillo
- The New Mexico Museum of Natural History & Science, Albuquerque, New Mexico, USA
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4
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Li Z, Wang M, Stidham TA, Zhou Z. Decoupling the skull and skeleton in a Cretaceous bird with unique appendicular morphologies. Nat Ecol Evol 2023; 7:20-31. [PMID: 36593291 DOI: 10.1038/s41559-022-01921-w] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/01/2022] [Accepted: 10/03/2022] [Indexed: 01/03/2023]
Abstract
The Cretaceous is a critical time interval that encompasses explosive diversifications of terrestrial vertebrates, particularly the period when the earliest-branching birds, after divergence from their theropod ancestors, evolved the characteristic avian Bauplan that led eventually to their global radiation. This early phylogenetic diversity is overwhelmed by the Ornithothoraces, consisting of the Enantiornithes and Ornithuromorpha, whose members evolved key derived features of crown birds. This disparity consequently circumscribes a large morphological gap between these derived clades and the oldest bird Archaeopteryx. The non-ornithothoracine pygostylians, with an intermediate phylogenetic position, are key to deciphering those evolutionary transformations, but progress in their study has been hampered by the limited diversity of known fossils. Here we report an Early Cetaceous non-ornithothoracine pygostylian, Cratonavis zhui gen. et sp. nov., that exhibits a unique combination of a non-avialan dinosaurian akinetic skull with an avialan post-cranial skeleton, revealing the key role of evolutionary mosaicism in early bird diversification. The unusually elongated scapular and metatarsal one preserved in Cratonavis highlights a breadth of skeletal plasticity, stemming from their distinct developmental modules and selection for possibly raptorial behaviour. Mapped changes in these two elements across theropod phylogeny demonstrate clade-specific evolutionary lability.
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Affiliation(s)
- Zhiheng Li
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.,Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
| | - Min Wang
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China. .,Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China.
| | - Thomas A Stidham
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.,Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China.,University of Chinese Academy of Sciences, Beijing, China
| | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.,Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
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5
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Wang M, Stidham TA, O'Connor JK, Zhou Z. Insight into the evolutionary assemblage of cranial kinesis from a Cretaceous bird. eLife 2022; 11:e81337. [PMID: 36469022 PMCID: PMC9721616 DOI: 10.7554/elife.81337] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2022] [Accepted: 11/28/2022] [Indexed: 12/07/2022] Open
Abstract
The independent movements and flexibility of various parts of the skull, called cranial kinesis, are an evolutionary innovation that is found in living vertebrates only in some squamates and crown birds and is considered to be a major factor underpinning much of the enormous phenotypic and ecological diversity of living birds, the most diverse group of extant amniotes. Compared to the postcranium, our understanding of the evolutionary assemblage of the characteristic modern bird skull has been hampered by sparse fossil records of early cranial materials, with competing hypotheses regarding the evolutionary development of cranial kinesis among early members of the avialans. Here, a detailed three-dimensional reconstruction of the skull of the Early Cretaceous enantiornithine Yuanchuavis kompsosoura allows for its in-depth description, including elements that are poorly known among early-diverging avialans but are central to deciphering the mosaic assembly of features required for modern avian cranial kinesis. Our reconstruction of the skull shows evolutionary and functional conservation of the temporal and palatal regions by retaining the ancestral theropod dinosaurian configuration within the skull of this otherwise derived and volant bird. Geometric morphometric analysis of the palatine suggests that loss of the jugal process represents the first step in the structural modifications of this element leading to the kinetic crown bird condition. The mixture of plesiomorphic temporal and palatal structures together with a derived avialan rostrum and postcranial skeleton encapsulated in Yuanchuavis manifests the key role of evolutionary mosaicism and experimentation in early bird diversification.
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Affiliation(s)
- Min Wang
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of SciencesBeijingChina
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of SciencesBeijingChina
| | - Thomas A Stidham
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of SciencesBeijingChina
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of SciencesBeijingChina
- University of Chinese Academy of SciencesBeijingChina
| | | | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of SciencesBeijingChina
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of SciencesBeijingChina
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6
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Cretaceous ornithurine supports a neognathous crown bird ancestor. Nature 2022; 612:100-105. [PMID: 36450906 DOI: 10.1038/s41586-022-05445-y] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2022] [Accepted: 10/13/2022] [Indexed: 12/03/2022]
Abstract
The bony palate diagnoses the two deepest clades of extant birds: Neognathae and Palaeognathae1-5. Neognaths exhibit unfused palate bones and generally kinetic skulls, whereas palaeognaths possess comparatively rigid skulls with the pterygoid and palatine fused into a single element, a condition long considered ancestral for crown birds (Neornithes)3,5-8. However, fossil evidence of palatal remains from taxa close to the origin of Neornithes is scarce, hindering strong inferences regarding the ancestral condition of the neornithine palate. Here we report a new taxon of toothed Late Cretaceous ornithurine bearing a pterygoid that is remarkably similar to those of the extant neognath clade Galloanserae (waterfowl + landfowl). Janavis finalidens, gen. et sp. nov., is generally similar to the well-known Mesozoic ornithurine Ichthyornis in its overall morphology, although Janavis is much larger and exhibits a substantially greater degree of postcranial pneumaticity. We recovered Janavis as the first-known well-represented member of Ichthyornithes other than Ichthyornis, clearly substantiating the persistence of the clade into the latest Cretaceous9. Janavis confirms the presence of an anatomically neognathous palate in at least some Mesozoic non-crown ornithurines10-12, suggesting that pterygoids similar to those of extant Galloanserae may be plesiomorphic for crown birds. Our results, combined with recent evidence on the ichthyornithine palatine12, overturn longstanding assumptions about the ancestral crown bird palate, and should prompt reevaluation of the purported galloanseran affinities of several bizarre early Cenozoic groups such as the 'pseudotoothed birds' (Pelagornithidae)13-15.
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7
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Torres CR. Fossil find suggests ancestral bird beak was mobile. Nature 2022; 612:35-36. [DOI: 10.1038/d41586-022-03692-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/05/2022]
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8
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Hu H, Wang Y, Fabbri M, O’Connor JK, Mcdonald PG, Wroe S, Yin X, Zheng X, Zhou Z, Benson RBJ. Cranial osteology and palaeobiology of the Early Cretaceous bird Jeholornis prima (Aves: Jeholornithiformes). Zool J Linn Soc 2022. [DOI: 10.1093/zoolinnean/zlac089] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
Abstract
Abstract
Jeholornis is a representative of the earliest-diverging bird lineages, providing important evidence of anatomical transitions involved in bird origins. Although ~100 specimens have been reported, its cranial morphology remains poorly documented owing to poor two-dimensional preservation, limiting our understanding of the morphology and ecology of the key avian lineage Jeholornithiformes, in addition to cranial evolution during the origin and early evolution of birds. Here, we provide a detailed description of the cranial osteology of Jeholornis prima, based primarily on high-quality, three-dimensional data of a recently reported specimen. New anatomical information confirms the overall plesiomorphic morphology of the skull, with the exception of the more specialized rostrum. Data from a large sample size of specimens reveal the dental formula of J. prima to be 0–2–3 (premaxillary–maxillary–dentary tooth counts), contrary to previous suggestions that the presence of maxillary teeth is diagnostic of a separate species, Jeholornis palmapenis. We also present evidence of sensory adaptation, including relatively large olfactory bulbs in comparison to other known stem birds, suggesting that olfaction was an important aspect of Jeholornis ecology. The digitally reconstructed scleral ring suggests a strongly diurnal habit, supporting the hypothesis that early-diverging birds were predominantly active during the day.
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Affiliation(s)
- Han Hu
- Department of Earth Sciences, University of Oxford , Oxford OX1 3AN , UK
| | - Yan Wang
- Institute of Geology and Paleontology, Linyi University , Linyi, Shandong 276000 , China
| | - Matteo Fabbri
- Negaunee Integrative Research Center, Field Museum of Natural History , Chicago, IL 60605 , USA
| | - Jingmai K O’Connor
- Negaunee Integrative Research Center, Field Museum of Natural History , Chicago, IL 60605 , USA
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences , 100044 Beijing , China
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences , 100044 Beijing , China
| | - Paul G Mcdonald
- Zoology Division, School of Environmental and Rural Sciences, University of New England , Armidale, NSW 2351 , Australia
| | - Stephen Wroe
- Zoology Division, School of Environmental and Rural Sciences, University of New England , Armidale, NSW 2351 , Australia
| | - Xuwei Yin
- Shandong Tianyu Museum of Nature , Pingyi, Shandong, China
| | - Xiaoting Zheng
- Institute of Geology and Paleontology, Linyi University , Linyi, Shandong 276000 , China
- Shandong Tianyu Museum of Nature , Pingyi, Shandong, China
| | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences , 100044 Beijing , China
- Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences , 100044 Beijing , China
| | - Roger B J Benson
- Department of Earth Sciences, University of Oxford , Oxford OX1 3AN , UK
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9
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Navalón G, Chiappe LM, Martinelli AG, Nava W, Field DJ. Fossil basicranium clarifies the origin of the avian central nervous system and inner ear. Proc Biol Sci 2022; 289:20221398. [PMID: 36168759 PMCID: PMC9515635 DOI: 10.1098/rspb.2022.1398] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
Among terrestrial vertebrates, only crown birds (Neornithes) rival mammals in terms of relative brain size and behavioural complexity. Relatedly, the anatomy of the avian central nervous system and associated sensory structures, such as the vestibular system of the inner ear, are highly modified with respect to those of other extant reptile lineages. However, a dearth of three-dimensional Mesozoic fossils has limited our knowledge of the origins of the distinctive endocranial structures of crown birds. Traits such as an expanded, flexed brain, a ventral connection between the brain and spinal column, and a modified vestibular system have been regarded as exclusive to Neornithes. Here, we demonstrate all of these ‘advanced’ traits in an undistorted braincase from an Upper Cretaceous enantiornithine bonebed in southeastern Brazil. Our discovery suggests that these crown bird-like endocranial traits may have originated prior to the split between Enantiornithes and the more crownward portion of avian phylogeny over 140 Ma, while coexisting with a remarkably plesiomorphic cranial base and posterior palate region. Altogether, our results support the interpretation that the distinctive endocranial morphologies of crown birds and their Mesozoic relatives are affected by complex trade-offs between spatial constraints during development.
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Affiliation(s)
- Guillermo Navalón
- Unidad de Paleontología, Departamento de Biología, Universidad Autónoma de Madrid, Madrid, Spain.,Department of Earth Sciences, University of Cambridge, Cambridge, UK
| | - Luis M Chiappe
- Dinosaur Institute, Natural History Museum of Los Angeles, 900 Exposition Boulevard, Los Angeles, CA 90007, USA
| | - Agustín G Martinelli
- Sección Paleontología de Vertebrados, CONICET-Museo Argentino de Ciencias Naturales 'Bernardino Rivadavia', Buenos Aires, Argentina
| | - William Nava
- Museu de Paleontologia de Marília, Marília, São Paulo, Brazil
| | - Daniel J Field
- Department of Earth Sciences, University of Cambridge, Cambridge, UK.,Museum of Zoology, University of Cambridge, Cambridge, UK
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10
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Hu H, Wang Y, McDonald PG, Wroe S, O'Connor JK, Bjarnason A, Bevitt JJ, Yin X, Zheng X, Zhou Z, Benson RBJ. Earliest evidence for fruit consumption and potential seed dispersal by birds. eLife 2022; 11:74751. [PMID: 35971758 PMCID: PMC9381037 DOI: 10.7554/elife.74751] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/15/2021] [Accepted: 07/08/2022] [Indexed: 12/24/2022] Open
Abstract
The Early Cretaceous diversification of birds was a major event in the history of terrestrial ecosystems, occurring during the earliest phase of the Cretaceous Terrestrial Revolution, long before the origin of the bird crown-group. Frugivorous birds play an important role in seed dispersal today. However, evidence of fruit consumption in early birds from outside the crown-group has been lacking. Jeholornis is one of the earliest-diverging birds, only slightly more crownward than Archaeopteryx, but its cranial anatomy has been poorly understood, limiting trophic information which may be gleaned from the skull. Originally hypothesised to be granivorous based on seeds preserved as gut contents, this interpretation has become controversial. We conducted high-resolution synchrotron tomography on an exquisitely preserved new skull of Jeholornis, revealing remarkable cranial plesiomorphies combined with a specialised rostrum. We use this to provide a near-complete cranial reconstruction of Jeholornis, and exclude the possibility that Jeholornis was granivorous, based on morphometric analyses of the mandible (3D) and cranium (2D), and comparisons with the 3D alimentary contents of extant birds. We show that Jeholornis provides the earliest evidence for fruit consumption in birds, and indicates that birds may have been recruited for seed dispersal during the earliest stages of the avian radiation. As mobile seed dispersers, early frugivorous birds could have expanded the scope for biotic dispersal in plants, and might therefore explain, at least in part, the subsequent evolutionary expansion of fruits, indicating a potential role of bird–plant interactions in the Cretaceous Terrestrial Revolution. Birds and plants have a close relationship that has developed over millions of years. Birds became diverse and abundant around 135 million years ago. Shortly after, plants started developing new and different kinds of fruits. Today, fruit-eating birds help plants to reproduce by spreading seeds in their droppings. This suggests that birds and plants have coevolved, changing together over time. But it is not clear exactly how their relationship started. One species that might hold the answers is an early bird species known as Jeholornis. It lived in China in the Early Cretaceous, around 120 million years ago. Palaeontologists have discovered preserved seeds inside its fossilised remains. The question is, how did they get there? Some birds eat seeds directly, cracking them open or grinding them up in the stomach to extract the nutrients inside. Other birds swallow seeds when they are eating fruit. If Jeholornis belonged to this second group, it could represent one of the early steps in plant-bird coevolution. Hu et al. scanned and reconstructed a preserved Jeholornis skull and compared it to the skulls, especially the mandibles, of modern birds, including species that grind seeds, species that crack seeds and species that eat fruits, leaving the seeds whole. The analyses ruled out seed cracking. But it could not distinguish between seed grinding and fruit eating. Hu et al. therefore compared the seed remains found inside Jeholornis fossils to seeds eaten by modern birds. The fossilised seeds were intact and showed no evidence of grinding. This suggests that Jeholornis ate whole fruits for at least part of the year. At around the time Jeholornis was alive, the world was entering a phase called the Cretaceous Terrestrial Revolution, which was characterized by an explosion of new species and an expansion of both flowering plants and birds. This finding opens new avenues for scientists to explore how plant and birds might have evolved together. Similar analyses could unlock new information about how other species interacted with their environments.
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Affiliation(s)
- Han Hu
- Department of Earth Sciences, University of Oxford
- Zoology Division, School of Environmental and Rural Sciences, University of New England
| | - Yan Wang
- Institute of Geology and Paleontology, Linyi University
| | - Paul G McDonald
- Zoology Division, School of Environmental and Rural Sciences, University of New England
| | - Stephen Wroe
- Zoology Division, School of Environmental and Rural Sciences, University of New England
| | - Jingmai K O'Connor
- Field Museum of Natural History
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
- Chinese Academy of Sciences Center for Excellence in Life and Paleoenvironment
| | | | - Joseph J Bevitt
- Australian Centre for Neutron Scattering, Australian Nuclear Science and Technology Organisation
| | | | - Xiaoting Zheng
- Institute of Geology and Paleontology, Linyi University
- Shandong Tianyu Museum of Nature
| | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
- Chinese Academy of Sciences Center for Excellence in Life and Paleoenvironment
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11
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Wang M, O'Connor JK, Zhao T, Pan Y, Zheng X, Wang X, Zhou Z. An Early Cretaceous enantiornithine bird with a pintail. Curr Biol 2021; 31:4845-4852.e2. [PMID: 34534442 DOI: 10.1016/j.cub.2021.08.044] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/18/2021] [Revised: 07/18/2021] [Accepted: 08/16/2021] [Indexed: 11/18/2022]
Abstract
Enantiornithes are the most successful group of Mesozoic birds, arguably representing the first global avian radiation,1-4 and commonly resolved as the sister to the Ornithuromorpha, the clade within which all living birds are nested.1,3 The wealth of fossils makes it feasible to comparatively test evolutionary hypotheses about the pattern and mode of eco-morphological diversity of these sister clades that co-existed for approximately 65 Ma. Here, we report a new Early Cretaceous enantiornithine, Yuanchuavis kompsosoura gen. et. sp. nov., with a rectricial fan combined with an elongate central pair of fully pennaceous rachis-dominated plumes, constituting a new tail plumage previously unknown among nonavialan dinosaurs and Mesozoic birds but which strongly resembles the pintail in many neornithines. The extravagant but aerodynamically costly long central plumes, as an honest signal of quality, likely evolved in enantiornithines through the handicap process of sexual selection. The contrasting tail morphotypes observed between enantiornithines and early ornithuromorphs reflect the complex interplay between sexual and natural selections and indicate that each lineage experienced unique pressures reflecting ecological differences. As in neornithines, early avialans repeatedly evolved extravagant structures highlighting the importance of sexual selection in shaping the plumage of feathered dinosaurs, even early in their evolutionary history.
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Affiliation(s)
- Min Wang
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing 100044, China.
| | | | - Tao Zhao
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
| | - Yanhong Pan
- State Key Laboratory for Mineral Deposits Research, School of Earth Sciences and Engineering, Nanjing University, Nanjing 210023, China
| | - Xiaoting Zheng
- Institute of Geology and Paleontology, Linyi University, Linyi, 276000 Shandong, China; Shandong Tianyu Museum of Nature, Pingyi, 273300 Shandong, China
| | - Xiaoli Wang
- Institute of Geology and Paleontology, Linyi University, Linyi, 276000 Shandong, China; Shandong Tianyu Museum of Nature, Pingyi, 273300 Shandong, China
| | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China; Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing 100044, China
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12
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Miller CV, Pittman M. The diet of early birds based on modern and fossil evidence and a new framework for its reconstruction. Biol Rev Camb Philos Soc 2021; 96:2058-2112. [PMID: 34240530 PMCID: PMC8519158 DOI: 10.1111/brv.12743] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2020] [Revised: 05/07/2021] [Accepted: 05/10/2021] [Indexed: 12/14/2022]
Abstract
Birds are some of the most diverse organisms on Earth, with species inhabiting a wide variety of niches across every major biome. As such, birds are vital to our understanding of modern ecosystems. Unfortunately, our understanding of the evolutionary history of modern ecosystems is hampered by knowledge gaps in the origin of modern bird diversity and ecosystem ecology. A crucial part of addressing these shortcomings is improving our understanding of the earliest birds, the non-avian avialans (i.e. non-crown birds), particularly of their diet. The diet of non-avian avialans has been a matter of debate, in large part because of the ambiguous qualitative approaches that have been used to reconstruct it. Here we review methods for determining diet in modern and fossil avians (i.e. crown birds) as well as non-avian theropods, and comment on their usefulness when applied to non-avian avialans. We use this to propose a set of comparable, quantitative approaches to ascertain fossil bird diet and on this basis provide a consensus of what we currently know about fossil bird diet. While no single approach can precisely predict diet in birds, each can exclude some diets and narrow the dietary possibilities. We recommend combining (i) dental microwear, (ii) landmark-based muscular reconstruction, (iii) stable isotope geochemistry, (iv) body mass estimations, (v) traditional and/or geometric morphometric analysis, (vi) lever modelling, and (vii) finite element analysis to reconstruct fossil bird diet accurately. Our review provides specific methodologies to implement each approach and discusses complications future researchers should keep in mind. We note that current forms of assessment of dental mesowear, skull traditional morphometrics, geometric morphometrics, and certain stable isotope systems have yet to be proven effective at discerning fossil bird diet. On this basis we report the current state of knowledge of non-avian avialan diet which remains very incomplete. The ancestral dietary condition in non-avian avialans remains unclear due to scarce data and contradictory evidence in Archaeopteryx. Among early non-avian pygostylians, Confuciusornis has finite element analysis and mechanical advantage evidence pointing to herbivory, whilst Sapeornis only has mechanical advantage evidence indicating granivory, agreeing with fossilised ingested material known for this taxon. The enantiornithine ornithothoracine Shenqiornis has mechanical advantage and pedal morphometric evidence pointing to carnivory. In the hongshanornithid ornithuromorph Hongshanornis only mechanical advantage evidence indicates granivory, but this agrees with evidence of gastrolith ingestion in this taxon. Mechanical advantage and ingested fish support carnivory in the songlingornithid ornithuromorph Yanornis. Due to the sparsity of robust dietary assignments, no clear trends in non-avian avialan dietary evolution have yet emerged. Dietary diversity seems to increase through time, but this is a preservational bias associated with a predominance of data from the Early Cretaceous Jehol Lagerstätte. With this new framework and our synthesis of the current knowledge of non-avian avialan diet, we expect dietary knowledge and evolutionary trends to become much clearer in the coming years, especially as fossils from other locations and climates are found. This will allow for a deeper and more robust understanding of the role birds played in Mesozoic ecosystems and how this developed into their pivotal role in modern ecosystems.
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Affiliation(s)
- Case Vincent Miller
- Vertebrate Palaeontology Laboratory, Research Division for Earth and Planetary ScienceThe University of Hong KongPokfulamHong Kong SARChina
| | - Michael Pittman
- Vertebrate Palaeontology Laboratory, Research Division for Earth and Planetary ScienceThe University of Hong KongPokfulamHong Kong SARChina
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Abstract
Reconstructing the history of biodiversity has been hindered by often-separate analyses of stem and crown groups of the clades in question that are not easily understood within the same unified evolutionary framework. Here, we investigate the evolutionary history of birds by analyzing three supertrees that combine published phylogenies of both stem and crown birds. Our analyses reveal three distinct large-scale increases in the diversification rate across bird evolutionary history. The first increase, which began between 160 and 170 Ma and reached its peak between 130 and 135 Ma, corresponds to an accelerated morphological evolutionary rate associated with the locomotory systems among early stem birds. This radiation resulted in morphospace occupation that is larger and different from their close dinosaurian relatives, demonstrating the occurrence of a radiation among early stem birds. The second increase, which started ∼90 Ma and reached its peak between 65 and 55 Ma, is associated with rapid evolution of the cranial skeleton among early crown birds, driven differently from the first radiation. The third increase, which occurred after ∼40 to 45 Ma, has yet to be supported by quantitative morphological data but gains some support from the fossil record. Our analyses indicate that the bird biodiversity evolution was influenced mainly by long-term climatic changes and also by major paleobiological events such as the Cretaceous-Paleogene (K-Pg) extinction.
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Torres CR, Norell MA, Clarke JA. Bird neurocranial and body mass evolution across the end-Cretaceous mass extinction: The avian brain shape left other dinosaurs behind. SCIENCE ADVANCES 2021; 7:eabg7099. [PMID: 34330706 PMCID: PMC8324052 DOI: 10.1126/sciadv.abg7099] [Citation(s) in RCA: 15] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/22/2021] [Accepted: 06/15/2021] [Indexed: 05/30/2023]
Abstract
Birds today are the most diverse clade of terrestrial vertebrates, and understanding why extant birds (Aves) alone among dinosaurs survived the Cretaceous-Paleogene mass extinction is crucial to reconstructing the history of life. Hypotheses proposed to explain this pattern demand identification of traits unique to Aves. However, this identification is complicated by a lack of data from non-avian birds. Here, we interrogate survivorship hypotheses using data from a new, nearly complete skull of Late Cretaceous (~70 million years) bird Ichthyornis and reassess shifts in bird body size across the Cretaceous-Paleogene boundary. Ichthyornis exhibited a wulst and segmented palate, previously proposed to have arisen within extant birds. The origin of Aves is marked by larger, reshaped brains indicating selection for relatively large telencephala and eyes but not by uniquely small body size. Sensory system differences, potentially linked to these shifts, may help explain avian survivorship relative to other dinosaurs.
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Affiliation(s)
- Christopher R Torres
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA.
- Jackson School of Geoscience, University of Texas at Austin, Austin, TX, USA
- Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, USA
| | - Mark A Norell
- Richard Gilder Graduate School, American Museum of Natural History, New York, NY, USA
- Division of Paleontology, American Museum of Natural History, New York, NY, USA
| | - Julia A Clarke
- Department of Integrative Biology, University of Texas at Austin, Austin, TX, USA.
- Jackson School of Geoscience, University of Texas at Austin, Austin, TX, USA
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15
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Wang M, Stidham TA, Li Z, Xu X, Zhou Z. Cretaceous bird with dinosaur skull sheds light on avian cranial evolution. Nat Commun 2021; 12:3890. [PMID: 34162868 PMCID: PMC8222284 DOI: 10.1038/s41467-021-24147-z] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2021] [Accepted: 06/03/2021] [Indexed: 02/05/2023] Open
Abstract
The transformation of the bird skull from an ancestral akinetic, heavy, and toothed dinosaurian morphology to a highly derived, lightweight, edentulous, and kinetic skull is an innovation as significant as powered flight and feathers. Our understanding of evolutionary assembly of the modern form and function of avian cranium has been impeded by the rarity of early bird fossils with well-preserved skulls. Here, we describe a new enantiornithine bird from the Early Cretaceous of China that preserves a nearly complete skull including the palatal elements, exposing the components of cranial kinesis. Our three-dimensional reconstruction of the entire enantiornithine skull demonstrates that this bird has an akinetic skull indicated by the unexpected retention of the plesiomorphic dinosaurian palate and diapsid temporal configurations, capped with a derived avialan rostrum and cranial roof, highlighting the highly modular and mosaic evolution of the avialan skull.
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Affiliation(s)
- Min Wang
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China.
- CAS Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China.
| | - Thomas A Stidham
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China
- CAS Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
- University of Chinese Academy of Sciences, Beijing, China
| | - Zhiheng Li
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China
- CAS Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
| | - Xing Xu
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China
- CAS Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
| | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing, China
- CAS Center for Excellence in Life and Paleoenvironment, Chinese Academy of Sciences, Beijing, China
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16
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17
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O'Connor PM, Turner AH, Groenke JR, Felice RN, Rogers RR, Krause DW, Rahantarisoa LJ. Late Cretaceous bird from Madagascar reveals unique development of beaks. Nature 2020; 588:272-276. [PMID: 33239782 DOI: 10.1038/s41586-020-2945-x] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2020] [Accepted: 09/14/2020] [Indexed: 11/09/2022]
Abstract
Mesozoic birds display considerable diversity in size, flight adaptations and feather organization1-4, but exhibit relatively conserved patterns of beak shape and development5-7. Although Neornithine (that is, crown group) birds also exhibit constraint on facial development8,9, they have comparatively diverse beak morphologies associated with a range of feeding and behavioural ecologies, in contrast to Mesozoic birds. Here we describe a crow-sized stem bird, Falcatakely forsterae gen. et sp. nov., from the Late Cretaceous epoch of Madagascar that possesses a long and deep rostrum, an expression of beak morphology that was previously unknown among Mesozoic birds and is superficially similar to that of a variety of crown-group birds (for example, toucans). The rostrum of Falcatakely is composed of an expansive edentulous maxilla and a small tooth-bearing premaxilla. Morphometric analyses of individual bony elements and three-dimensional rostrum shape reveal the development of a neornithine-like facial anatomy despite the retention of a maxilla-premaxilla organization that is similar to that of nonavialan theropods. The patterning and increased height of the rostrum in Falcatakely reveals a degree of developmental lability and increased morphological disparity that was previously unknown in early branching avialans. Expression of this phenotype (and presumed ecology) in a stem bird underscores that consolidation to the neornithine-like, premaxilla-dominated rostrum was not an evolutionary prerequisite for beak enlargement.
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Affiliation(s)
- Patrick M O'Connor
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, USA. .,Ohio Center for Ecological and Evolutionary Studies, Ohio University, Athens, OH, USA. .,Department of Earth Sciences, Denver Museum of Nature & Science, Denver, CO, USA.
| | - Alan H Turner
- Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY, USA
| | - Joseph R Groenke
- Department of Biomedical Sciences, Heritage College of Osteopathic Medicine, Ohio University, Athens, OH, USA
| | - Ryan N Felice
- Centre for Integrative Anatomy, Department of Cell and Developmental Biology, University College London, London, UK
| | - Raymond R Rogers
- Department of Earth Sciences, Denver Museum of Nature & Science, Denver, CO, USA.,Geology Department, Macalester College, St Paul, MN, USA
| | - David W Krause
- Department of Earth Sciences, Denver Museum of Nature & Science, Denver, CO, USA.,Department of Anatomical Sciences, Stony Brook University, Stony Brook, NY, USA
| | - Lydia J Rahantarisoa
- Département de Sciences de la Terre et de l'Environnement, Université d'Antananarivo, Antananarivo, Madagascar
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18
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Plateau O, Foth C. Birds have peramorphic skulls, too: anatomical network analyses reveal oppositional heterochronies in avian skull evolution. Commun Biol 2020; 3:195. [PMID: 32332847 PMCID: PMC7181600 DOI: 10.1038/s42003-020-0914-4] [Citation(s) in RCA: 22] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Accepted: 03/25/2020] [Indexed: 12/14/2022] Open
Abstract
In contrast to the vast majority of reptiles, the skulls of adult crown birds are characterized by a high degree of integration due to bone fusion, e.g., an ontogenetic event generating a net reduction in the number of bones. To understand this process in an evolutionary context, we investigate postnatal ontogenetic changes in the skulls of crown bird and non-avian theropods using anatomical network analysis (AnNA). Due to the greater number of bones and bone contacts, early juvenile crown birds have less integrated skulls, resembling their non-avian theropod ancestors, including Archaeopteryx lithographica and Ichthyornis dispars. Phylogenetic comparisons indicate that skull bone fusion and the resulting modular integration represent a peramorphosis (developmental exaggeration of the ancestral adult trait) that evolved late during avialan evolution, at the origin of crown-birds. Succeeding the general paedomorphic shape trend, the occurrence of an additional peramorphosis reflects the mosaic complexity of the avian skull evolution. Plateau and Foth use anatomical network analysis to study the evolution of avian skull anatomy. They report that the ontogenetic changes in the morphology and modularity of the avian skulls is comparable to evolutionary transformations from non-avian theropods to modern birds. Their work highlights the complexity of avian skull evolution.
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Affiliation(s)
- Olivia Plateau
- Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700, Fribourg, Switzerland
| | - Christian Foth
- Department of Geosciences, University of Fribourg, Chemin du Musée 6, CH-1700, Fribourg, Switzerland.
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Li Z, Wang CC, Wang M, Chiang CC, Wang Y, Zheng X, Huang EW, Hsiao K, Zhou Z. Ultramicrostructural reductions in teeth: implications for dietary transition from non-avian dinosaurs to birds. BMC Evol Biol 2020; 20:46. [PMID: 32316913 PMCID: PMC7171806 DOI: 10.1186/s12862-020-01611-w] [Citation(s) in RCA: 8] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2019] [Accepted: 04/06/2020] [Indexed: 12/31/2022] Open
Abstract
Background Tooth morphology within theropod dinosaurs has been extensively investigated and shows high disparity throughout the Cretaceous. Changes or diversification in feeding ecology, i.e., adoption of an herbivorous diet (e.g., granivorous), is proposed as a major driver of tooth evolution in Paraves (e.g., Microraptor, troodontids and avialans). Here, we studied the microscopic features of paravian non-avian theropod and avialan teeth using high-spatial-resolution synchrotron transmission X-ray microscopy and scanning electron microscopy. Results We show that avialan teeth are characterized by the presence of simple enamel structures and a lack of porous mantle dentin between the enamel and orthodentin. Reduced internal structures of teeth took place independently in Early Cretaceous birds and a Microraptor specimen, implying that shifts in diet in avialans from that of closely related dinosaurs may correlate with a shift in feeding ecology during the transition from non-avian dinosaurs to birds. Conclusion Different lines of evidence all suggest a large reduction in biting force affecting the evolution of teeth in the dinosaur-bird transition. Changes in teeth microstructure and associated dietary shift may have contributed to the early evolutionary success of stemward birds in the shadow of other non-avian theropods.
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Affiliation(s)
- Zhiheng Li
- Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xizhimenwai Street, Beijing, 100044, China. .,CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China.
| | - Chun-Chieh Wang
- National Synchrotron Radiation Research Center, Hsinchu, 30076, Taiwan.
| | - Min Wang
- Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xizhimenwai Street, Beijing, 100044, China.,CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China
| | | | - Yan Wang
- Institute of Geology and Paleontology, Linyi University, Linyi, 276000, Shandong, China
| | - Xiaoting Zheng
- Tianyu Natural History Museum of Shandong, Pingyi, 273300, Shandong, China
| | - E-Wen Huang
- Department of Materials Science and Engineering, National Chiao Tung University, Hsinchu, 30010, Taiwan
| | - Kiko Hsiao
- Mr. Fossil Institute, New Taipei City, 23673, Taiwan
| | - Zhonghe Zhou
- Key Laboratory of Vertebrate Evolution and Human Origins of Chinese Academy of Sciences, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, 142 Xizhimenwai Street, Beijing, 100044, China.,CAS Center for Excellence in Life and Paleoenvironment, Beijing, 100044, China
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20
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Hummingbird-sized dinosaur from the Cretaceous period of Myanmar. Nature 2020; 579:245-249. [PMID: 32161388 DOI: 10.1038/s41586-020-2068-4] [Citation(s) in RCA: 19] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/12/2019] [Accepted: 01/22/2020] [Indexed: 11/08/2022]
Abstract
Skeletal inclusions in approximately 99-million-year-old amber from northern Myanmar provide unprecedented insights into the soft tissue and skeletal anatomy of minute fauna, which are not typically preserved in other depositional environments1-3. Among a diversity of vertebrates, seven specimens that preserve the skeletal remains of enantiornithine birds have previously been described1,4-8, all of which (including at least one seemingly mature specimen) are smaller than specimens recovered from lithic materials. Here we describe an exceptionally well-preserved and diminutive bird-like skull that documents a new species, which we name Oculudentavis khaungraae gen. et sp. nov. The find appears to represent the smallest known dinosaur of the Mesozoic era, rivalling the bee hummingbird (Mellisuga helenae)-the smallest living bird-in size. The O. khaungraae specimen preserves features that hint at miniaturization constraints, including a unique pattern of cranial fusion and an autapomorphic ocular morphology9 that resembles the eyes of lizards. The conically arranged scleral ossicles define a small pupil, indicative of diurnal activity. Miniaturization most commonly arises in isolated environments, and the diminutive size of Oculudentavis is therefore consistent with previous suggestions that this amber formed on an island within the Trans-Tethyan arc10. The size and morphology of this species suggest a previously unknown bauplan, and a previously undetected ecology. This discovery highlights the potential of amber deposits to reveal the lowest limits of vertebrate body size.
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Origin of the avian predentary and evidence of a unique form of cranial kinesis in Cretaceous ornithuromorphs. Proc Natl Acad Sci U S A 2019; 116:24696-24706. [PMID: 31740590 DOI: 10.1073/pnas.1911820116] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
The avian predentary is a small skeletal structure located rostral to the paired dentaries found only in Mesozoic ornithuromorphs. The evolution and function of this enigmatic element is unknown. Skeletal tissues forming the predentary and the lower jaws in the basal ornithuromorph Yanornis martini are identified using computed-tomography, scanning electron microscopy, and histology. On the basis of these data, we propose hypotheses for the development, structure, and function of this element. The predentary is composed of trabecular bone. The convex caudal surface articulates with rostromedial concavities on the dentaries. These articular surfaces are covered by cartilage, which on the dentaries is divided into 3 discrete patches: 1 rostral articular cartilage and 2 symphyseal cartilages. The mechanobiology of avian cartilage suggests both compression and kinesis were present at the predentary-dentary joint, therefore suggesting a yet unknown form of avian cranial kinesis. Ontogenetic processes of skeletal formation occurring within extant taxa do not suggest the predentary originates within the dentaries, nor Meckel's cartilage. We hypothesize that the predentary is a biomechanically induced sesamoid that arose within the soft connective tissues located rostral to the dentaries. The mandibular canal hosting the alveolar nerve suggests that the dentary teeth and predentary of Yanornis were proprioceptive. This whole system may have increased foraging efficiency. The Mesozoic avian predentary apparently coevolved with an edentulous portion of the premaxilla, representing a unique kinetic morphotype that combined teeth with a small functional beak and persisted successfully for ∼60 million years.
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