Abstract
The 438–370-million-year-old galeaspids, diversified armoured jawless vertebrates (‘ostracoderms’) from China and northern Vietnam, were assumed to have a benthic feeding habit in a coastal, marine environment. Here, we describe two new genera of galeaspid fishes, Platylomaspis gen. nov. and Nanningaspis gen. nov. from the Middle Palaeozoic of China. The two new forms are characterized by a rostral process and strikingly broad ventral rim, and clustered with Gumuaspis to form a new family, Gumuaspidae, which represents the most primitive clade of Polybranchiaspiformes. They extend the earliest occurrence of Polybranchiaspiformes backward about 19 million years, and expand its geographical distribution from southern China and northern Vietnam to the Tarim Basin, northwestern China. The new taxa exhibit many morphological convergences with modern rays, and might specify a new kind of lifestyle of galeaspids, the half burrowing habit. Probably benefiting from the new lifestyle, the Gumuaspidae has become the longest lasting galeaspid family. The new findings demonstrated that the demersal galeaspids had developed three different kinds of lifestyles: semi-infaunal benthic (half buried), epibenthic, and suprabenthic (nektonic) habits to accommodate to differentiated ecological niches, and reached the peak of their diversity by the Pragian of the Early Devonian.
Highlights
The 438–370-million-year-old galeaspids are a diversified but endemic group of armoured jawless vertebrates (‘ostracoderms’) occurring only in China and northern Vietnam [1,2,3,4,5]
The material of Platylomaspis serratus gen. et sp. nov. was collected by Professor Shiben Zhang in 1990 and 1992 when he worked in Tarim Petroleum Exploration and Development Bureau, Korla, Xinjiang
Pseudolaxaspis was originally referred to Laxaspis as it resembles the type species of Laxaspis, L. qujingensis, in many respects such as the shape and position of the median dorsal opening and orbital opening, the ornamentation of the head-shield, and the end of sensory canals
Summary
The 438–370-million-year-old galeaspids are a diversified but endemic group of armoured jawless vertebrates (‘ostracoderms’) occurring only in China and northern Vietnam [1,2,3,4,5]. Galeaspids have no biting jaws, they are regarded as an important stem-group of gnathostomes that provides the crucial fossil evidence for the culmination of stepwise anatomical changes towards crown gnathostomes [6,7,8]. Galeaspids have a diagnostic large median dorsal opening for the common nostril of paired separated nasal sacs, which.
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