| Symposium proposal | |
| Organizer: | Zhu Min (Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences) |
| Co-organizer: | Zhu You-an (Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences) |
| The proposed symposium centres on the early evolution of fishes, from the advent of jawed vertebrates, to the diversification of the hyper-successful teleosts. "Fish" is a general term of non-tetrapod vertebrates. Many, and arguably most of the key evolutionary breakthroughs in vertebrate history, which eventually assembled the body plan shared in human, frog and carp today, happened in the evolution of fishes. While recent progresses in molecular biology have shed much light on some aspect of the evolution of fishes, most part of the diversity of fishes in deep time is evidenced by paleontological data, the fossils. In this symposium we will invite leading paleontologists in this field. to report their recent advances on the key events in the evolution of fishes, such as the rise of jawed vertebrates, and the recovery of fish diversity from the End-Permian Extinction, These advances will surly provide inspiring insight for the interdisciplinary researchs in other branches of evolutionary biology. | |
S19-1
Early evolution of the vertebrate morphology: a view from evolutionary developmental biology
Tatsuya Hirasawa1
1The University of Tokyo
In vertebrate evolution, the major transitions that brought about morphological gaps in modern groups had mostly occurred by the end of the Devonian. Such transitions involved establishments of evolutionary novelties violating homology continuity, thus comparative analyses of modern taxa cannot reveal the evolutionary processes alone. The fossil record of stem group taxa provides pivotal evidence for the history of major morphological transitions, in light of evolutionary developmental biology. In particular, recent advances in developmental biology of key modern taxa including cyclostomes and sarcopterygian fishes have promoted our understanding on transitional morphologies of the stem group taxa. In this presentation, by introducing our study on the Middle Devonian Palaeospondylus, whose strange morphology has not been comparable with known vertebrate morphotype diversity, I will discuss how the integration of paleontology and evolutionary developmental biology can solve elusive problems of major morphological transitions in deep time.
S19-2
Adaptive radiation of early neopterygian fishes in the aftermath of end-Permian extinction: evidences of large durophagous predators from China and their implications
Guang-Hui Xu1
1Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences
The end-Permian mass extinction devastated the marine ecosystem (causing 90–95% of marine species to become extinct), with restructuring of communities in the Triassic. By the Middle Triassic, the Neopterygii (‘new fins’), the largest group of ray-finned fishes today, exhibited a high morphological diversity, probably adapted for different ecological niches in the marine ecosystems. The Colobodontidae is a stem group of neopterygian fishes in the Middle to Late Triassic marine ecosystems. Members of this family are generally durophagous predators with a large body size (up to 650 mm in total length), and consequently are important for understanding the trophic structure of Triassic marine ecosystems. Recently, two new colobodontids, Feroxichthys yunnanensis and F. panzhouensis are recovered from the early Middle Triassic (Pelsonian, Anisian, ~244 Ma) of Yunnan and Guizhou, China, respectively. They represent the earliest known members of this family, providing new evidences for understanding the adaptive radiation of early neopterygians during this age. The skull of Feroxichthys shows some peculiar features rarely known in other stem neopterygians, for example fusion of paired premaxillae, fusion of lacrimal with maxilla, and a fused parieto-dermopterotic with a strong posterior process. Specially, F. panzhouensis is unique among colobodontids in having a relatively short and deep body with a prominent postcranial hump. This body form implicates a morphological adaptation to structurally complex habitats. The feeding apparatus of Feroxichthys indicates a predominantly durophagous adaption, as in other colobodontids. However, the anterior peg-like teeth in the jaws of Feroxichthys are much longer and stronger than other colobodontids, enabling a more powerful initial prey capture before food was passed posteriorly to molariform teeth for crushing in the oral cavity. As two previously unknown large durophagous predators, the new findings add our understanding on the complex trophic structure of the Middle Triassic Yangtze Sea (a part of eastern Paleotethys Ocean), and render support that a stable, complex ecosystem has re-emerged in the early Middle Triassic, ~8 Myr after the end-Permian period mass extinction.
S19-3
Morphometric Analysis of Lungfish Endocasts Elucidates Early Dipnoan Palaeoneurological Evolution
Alice Clement1, T. J. Challands2, Richard Cloutier3, Laurent Houle3, John Long1
1Flinders University
2University of Edinburgh
3University of Quebec
2University of Edinburgh
3University of Quebec
Lungfish (Dipnoi) are a group of lobe-finned fish that first appeared during the Devonian Period some 400 million years ago. They are the extant sister group to tetrapods; and thus, have fascinated researchers for centuries for their ability to provide unique insight into the condition of the earliest tetrapods as well as their own exceptional history. While evolution of their dermal skull and dentition is relatively well understood, the evolution of their neurology is less so, likely limited by the fact that brains don’t typically fossilise. Instead, cranial endocasts are often used as proxies in palaeoneurological studies. Herein we morphometrically analyse 10 virtual lungfish cranial endocasts created from CT data. Bayesian principal component analysis and principal component analysis for incomplete data (InDaPCA) were used to decipher variation tendencies among 17 endocranial variables. We find that the olfactory region appears to be more highly plastic than the hindbrain, and undergoes significant elongation in several taxa. Further, while the semicircular canals covary as an integrated module, the utriculus and sacculus of the inner ear vary independently of each other. Both utriculus and sacculus have an auditory function, but are sensitive to movements in different planes (vertical and horizontal). The functional implications of our findings are discussed.
S19-4
New material of Youngolepis reveals the early evolution of lungfish durophagy
Xindong Cui1,2,3, Matt Friedman4, Tuo Qiao1,2, Yilun Yu1,2,3, Min Zhu1,2,3
1CAS Key Laboratory of Vertebrate Evolution and Human Origins, Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing 100044, China.
2CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China
3University of Chinese Academy of Sciences, Beijing 100049, China.
4Museum of Paleontology and Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
2CAS Center for Excellence in Life and Paleoenvironment, Beijing 100044, China
3University of Chinese Academy of Sciences, Beijing 100049, China.
4Museum of Paleontology and Department of Earth and Environmental Sciences, University of Michigan, Ann Arbor, MI 48109, USA.
Major paleobiological hypotheses implicate innovations in durophagy, the consumption of prey items protected by hard shells or exoskeletons, driving major ecological and evolutionary shifts in marine settings over the Phanerozoic. The first definitive support for major structural innovations associated with the consumption of hard prey by vertebrates appears with Diabolepis from the Early Devonian (late Lochkovian, ~415 Ma). However, the order in which these and critical features of dipnoan feeding anatomy remain unclear due to a lack of information in closest relatives of lungfishes.
Youngolepis praecursor is a key member of the diverse sarcopterygian assemblage from the Lower Devonian of Yunnan, China. Current consensus places Youngolepis at the base of the lungfish lineage, between the porolepiforms and Diabolepis. Therefore, Youngolepis is a pivotal taxon for investigating the origin of lungfish anatomical specializations. Its major changes in cranial mobility and mechanics foreshadow conditions in lungfishes, and suggest Youngolepis likely had a distinctive mode of feeding. However, major anatomical systems particularly relevant to the acquisition and processing of prey—the palate, hyoid arch, and branchial skeleton—remain unknown in Youngolepis.
Two articulated specimens of Youngolepis from the type locality preserve these critical aspects of morphology. Micro-computed tomography (µCT) reveals that Youngolepis is substantially more lungfish-like than previously anticipated, with substantially reorganized of palatal dentition, geometry, and suspension relative to primitive rhipidistian conditions. The postorbital region of the palatoquadrate is short and deep, and is buttressed by a stocky, vertically oriented hyomandibular. The entopterygoid is thickened, appears to be oriented horizontally, and bears patterned, radial rows of teeth like the tooth plates of Diabolepis and other primitive lungfishes. These attributes, which are further amplified in more crownward lungfishes, reflect biomechanical changes consistent with the processing of hard prey. Youngolepis captures the earliest stages in the development of a trophic strategy that has characterized the lungfishes for over 400 million years, the first and longest-lived lineage of durophagous gnathostomes.
S19-5
The Cenozoic Fish Fauna of the Tibetan Plateau
Feixiang Wu1, Dekui He2, Mee-mann Chang1,3, Gengyu Fang3
1Institute of Vertebrate Paleontology and Paleoanthropology, Chinese Academy of Sciences, Beijing
2Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan
3College of Earth Sciences, University of Chinese Academy of Sciences, Beijing
2Institute of Hydrobiology, Chinese Academy of Sciences, Wuhan
3College of Earth Sciences, University of Chinese Academy of Sciences, Beijing
The past two decades have witnessed a renewed vigor in research on geological history of the Tibetan Plateau and the newly emerged paleontological evidence has added a crucial, biological dimension to the scientific quest. Here we review an important part of that paleontological evidence, from fossil fishes, and its implications for interpreting the evolutionary history of the plateau during the Cenozoic era.
The present fish fauna on the Tibetan Plateau is dominated by the cold and high altitude adapted fishes, e.g., the snow carps (Schizothoracinae, Cyprinidae) and plateau loaches (Triplophysa, Nemacheilidae), a natural consequence of the stepwise uplift of the plateau. Based on new discoveries of fossil fishes from the Eocene to Pliocene, we have more details of the evolution of the fish fauna in Tibetan region. We have found that immediately after the hard collision between the Indian and Asian plates in the early Cenozoic, some freshwater fishes (e.g., the air-breathing climbing perch) that probably originated in Southeast Asia might have followed an “Into Africa via the Docked India” routine to set the stage for their modern African-Asian disjunct distribution. We have collected an assemblage of tropical and subtropical fishes (climbing perch, silurid catfish and some small barbine carps) from the late Eocene of northern Tibet, which suggests that the hinterland of todays’ Tibetan Plateau was low and humid then and is incompatible with some tectonic models for the uplift of the plateau. According to the fossil records of some highly specialized snow carps, we believe that the modernization of the fish diversity on the Tibetan Plateau occurred no earlier than the Pliocene. Admittedly, the results we have presented so far are preliminary, and the vast uninvestigated Cenozoic fluvial and lacustrine deposits on the Tibetan Plateau promise more fossil findings and greater research opportunities ahead.
