Tuesday, September 5, 2017

[PaleoIchthyology • 2017] Hongyu chowi • A Devonian Tetrapod-like Fish Reveals Substantial Parallelism in Stem Tetrapod Evolution

Hongyu chowi 
Zhu, Ahlberg, Zhao & Jia, 2017  

The fossils assigned to the tetrapod stem group document the evolution of terrestrial vertebrates from lobe-finned fishes. During the past 18 years the phylogenetic structure of this stem group has remained remarkably stable, even when accommodating new discoveries such as the earliest known stem tetrapod Tungsenia and the elpistostegid (fish–tetrapod intermediate) Tiktaalik. Here we present a large lobe-finned fish from the Late Devonian period of China that disrupts this stability. It combines characteristics of rhizodont fishes (supposedly a basal branch in the stem group, distant from tetrapods) with derived elpistostegid-like and tetrapod-like characters. This mélange of characters may reflect either detailed convergence between rhizodonts and elpistostegids plus tetrapods, under a phylogenetic scenario deduced from Bayesian inference analysis, or a previously unrecognized close relationship between these groups, as supported by maximum parsimony analysis. In either case, the overall result reveals a substantial increase in homoplasy in the tetrapod stem group. It also suggests that ecological diversity and biogeographical provinciality in the tetrapod stem group have been underestimated.

Fig. 1 | V17681, holotype of Hongyu chowi gen. et sp. nov. ; Dorsal view. 

Systematic palaeontology. 
Osteichthyes Huxley, 1880
Sarcopterygii Romer, 1955
Tetrapodomorpha Ahlberg, 1991

Hongyu chowi gen. et sp. nov.

Etymology. The generic name derives from hong (Chinese Pinyin), which means large and yu (Chinese Pinyin), which means fish. The specific is in honor of Min-Chen Chow

Holotype. IVPP V17681, a three-dimensionally preserved and partially articulated specimen.

 Locality. A quarry at Shixiagou, Qingtongxia, Ningxia, China. Approximate coordinates: 37° 39′ 18.4″ N, 105° 59′ 34.2″ E. Horizon. Zhongning Formation, Famennian, Late Devonian period.

Fig. 4 | Life restoration. Hongyu chowi gen. et sp. nov. and associated antiarchs (Ningxialepis spinosa) from the Zhongning Formation (Famennian, Late Devonian period), Ningxia, China.
Illustration: B. Choo.

Min Zhu, Per E. Ahlberg, Wen-Jin Zhao and Lian-Tao Jia. 2017. A Devonian Tetrapod-like Fish Reveals Substantial Parallelism in Stem Tetrapod Evolution.
 Nature Ecology & Evolution. DOI: 10.1038/s41559-017-0293-5

Weird fish fossil changes the story of how we moved onto land

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