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A New Family of Galeaspids (Jawless Stem‐Gnathostomata) from the Llandovery, Silurian of Chongqing, Southwestern China
Abstract and Figures
A new genus and species of agnathan Eugaleaspidiformes (Galeaspida), Yongdongaspis littoralis gen. et sp. nov., is described from the Llandovery (lower Silurian) Huixingshao Formation at Yongdong township, Xiushan County, Chongqing, southwestern China. The new taxon morphologically exhibits some transitional states between Sinogaleaspidae and a cluster of higher eugaleaspidiforms containing Tridensaspidae, Eugaleaspidae, Yunnanogaleaspis, and Nochelaspis, which we term here as the ‘eugaleaspid cluster’. Phylogenetic analysis of an extended character matrix of Galeaspida reveals Yongdongaspis, on which Yongdongaspidae fam. nov. is erected, as the sister taxon of this ‘eugaleaspid cluster’, supported by two synapomorphies, the presence of one median transverse canal, and two lateral transverse canals leaving from the infraorbital canal. As the first fish described from the Llandovery Huixingshao Formation in Chongqing, Yongdongaspis provides new fossil evidence to the subdivision and correlation of the Upper Red Beds in South China.
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... These recent cladistic analyses consistently suggest that Eugaleaspis, Dunyu, and Xitunaspis form a monophyletic group for Eugaleaspidae (Figure 7) with the synapomorphy of the loss of inner cornual processes (Sun et al., 2022). In contrast, Falxcornus, Pterogonaspis, and Tridensaspis form another monophyletic group for Tridensaspidae (Figure 7) characterized by synapomorphies of subacute rostral margin and sickle-like complex of cornual and inner cornual processes (Meng & Gai, 2021;Chen et al., 2022;Sun et al., 2022;Shan et al., 2022). The Tridensaspidae has a closer relationship to Eugaleaspidae than Yunnanogaleaspis and Nochelaspis by sharing the synapomorphies of the position of the posterior end of the median dorsal opening and the longer prepineal region. ...
... It is noteworthy that the canals for the dorsal aorta in galeaspids are paired (Gai et al., 2011(Gai et al., , 2019Gai, Zhu, et al., 2022) and display a central placement in the postbranchial region (Figures 8d,e). In contrast, the canal for the dorsal aorta is unpaired, displaced dorsally in lampreys F I G U R E 7 The cladogram of the Eugaleaspiformes projected against stratigraphy (based on Liu et al., 2021;Chen et al., 2022;Shan et al., 2022;Sun et al., 2022) ( Figure 8a) and osteostracans (Figures 8b,c); this is unique to lampreys and galeaspids, but probably homoplastic (Janvier, 2007). Further, in osteostracans, the esophagus passes through the postbranchial region through the same canal with the dorsal aorta. ...
New material of the tridensaspid Pterogonaspis yuhaii is described from the Xujiachong Formation in Qujing City, Yunnan Province, revealing the morphology of the ventral side of the headshield for the first time. Most significantly, the cranial anatomy of Pterogonaspis provides the first fossil evidence for the position of the esophagus in galeaspids. The esophagus and dorsal aortae display a central placement in the postbranchial region and do not share a common canal as in osteostracans. Moreover, the paired and symmetrically extending dorsal aortae in galeaspids strikingly resemble those of jawed vertebrates, probably representing a plesiomorphic condition for vertebrates because they are also present in amphioxus and hagfishes. In contrast, the unpaired and asymmetrically extending dorsal aorta in osteostracans is similar to that of lampreys, probably resulting from convergent evolution. In addition, our new data also exhibit some characters that galeaspids uniquely share with osteostracans, such as the complete endoskeletal postbranchial wall and the extensive lateral expansion of the headshield with the marginal arteries and veins.
... They are diversified with about 100 species, but only endemic in Silurian-Devonian strata of China and North Vietnam (Janvier, 1996;Liu et al., 2015). Phylogenetic analysis consistently indicates that Galeaspida has diversified into three plesiomorphic clades Xiushuiaspidae, Hanyangaspidae, and Dayongaspidae, and three major derived clades Eugaleaspiformes, Polybranchiaspiformes, and Huananaspiformes Chen et al., 2022;Meng and Gai, 2022;Shan et al., 2022a). The widely distributed fossil records and advances in the systematic taxonomy make them play a more and more important role in the biostratigraphic correlation of Silurian shallow marine red beds of South China and Tarim blocks Shan et al., 2022a;Shan et al., 2022b;Shan et al., 2023a). ...
... Differential diagnosis. Medium-sized jawless fish up to 100 mm in length, which can be referred to Duyunolepididae of Polybranchiaspidiformes by its diagnostic ovalshaped headshield lacking cornual and inner cornual processes [12][13][14][15]. It differs from Duyunolepis, Paraduyunaspis, and Lopadaspis in its serrated margin of the headshield, differs from Neoduyunaspis in its much larger size and more lateral position of the orbital opening; ventral rim is thin, but nearly aequilate with a width of 4.0 mm, which is similar to that of Lopadaspis, but clearly differs from that of Duyunolepis; at least 25 pairs of branchial fossae [16]; ornamentation of the headshield composed of tiny granular tubercles; an elongate trunk with a length of 49.0 mm that comprised about half of its total length; the trunk is covered with minute square-shaped scales; the caudal fin is laterally compressed and obviously forkshaped,which composed of a ventral chordal lobe and nine dorsal digitations; the caudal fin is clearly hypocercal in which the ventral chordal lobe is inclined downwards and much longer than the nine dorsal digitations; each digitation consists of lepidotrich-like rows of small elongate scales. ...
Galeaspids are extinct jawless relatives of living jawed vertebrates whose contribution to understanding the evolutionary assembly of the gnathostome bodyplan has been limited by absence of postcranial remains. Here, we describe Foxaspis novemura gen. et sp. nov., based on complete articulated remains from a newly discovered Konservat-Lagerstätte in the Early Devonian (Pragian, ∼410 Ma) of Guangxi, South China. F. novemura had a broad, circular dorso-ventrally compressed headshield, slender trunk and strongly asymmetrical hypochordal tail fin comprised of nine ray-like scale-covered digitations. This tail morphology contrasts with the symmetrical hypochordal tail fin of Tujiaaspis vividus, evidencing disparity in galeaspid post cranial anatomy. Analysis of swimming speed reveals galeaspids as moderately fast swimmers, capable of achieving greater cruising swimming speeds than their more derived jawless and jawed relatives. Our analyses reject the hypothesis of a driven trend towards increasingly active food acquisition which has been invoked to characterize early vertebrate evolution.
A new species of Shuyuidae (Eugaleaspiformes, Galeaspida), Jiangxialepis jiujiangensis sp. nov., is described from the lower Telychian (Llandovery, Silurian) Qingshui Formation in Jiujiang, Jiangxi Province, China. The new species differs from the type species J. retrospina from Wuhan, Hubei Province in its sharp and posteriorly positioned median dorsal spine and narrow spine‐shaped inner cornual processes. The Silurian strata in Xiushui–Wuning area has provided a standard framework for the correlation of Silurian shallow marine red beds in South China. Thus, the finding of J. jiujiangensis from the Silurian Lower Red Beds (LRBs) in Jiangxi Province bears very important biostratigraphic significance. It can directly compare to Jiangxialepis retrospina from the Fentou Formation in Wuhan, Hubei Province in the genus level. This indicates that the age of the fish‐bearing strata in Wuhan is most likely to be the early Telychian rather than middle Telychian as previously assumed.
The Silurian-Devonian interval is an essential period in Earth history for witnessing the rise of sarcopterygian fishes and terrestrial vascular plants. In addition to its implication in global stratigraphic correlation, the precise location of the Silurian-Devonian boundary (SDB) in East Yunnan closely relates to the minimal and maximal estimated dates for the lungfish-tetrapod split. Several geochemical indicators including the values and curves of δ 13 C org , δ 13 C carb and TOC are obtained from the continuous SDB sequence in Dahe, Yiliang County, East Yunnan. The results reveal the significant positive δ 13 C org shifts in the upper part of the Yulungssu Formation and the lower part of the Xishancun Formation, and the peak value (−20.0‰) in the sample YD-25 from the lowermost of the Xishancun Formation, replicating the δ 13 C org variation trend from the uppermost Silurian to the lowermost Devonian worldwide. The δ 13 C org variation across the SDB at the Dahe Section resembles the SDB curve from the borehole Klonk-1 drilled at the top of the Klonk GSSP in the Prague Basin, Czech Republic. As such, we place the SDB in the Dahe Area between the samples of YD-17 and YD-18 from the lowermost part of the Xishancun Formation. This SDB assignment is corroborated by new findings of Early Devonian thelodont Parathelodus from the lower part of the Xishancun Formation in Qujing Area. The resolution of the SDB in Dahe, coupled with available paleontological data and the biostratigraphic zonation in East Yunnan, has provided vital data for the geological ages of the fish-bearing strata in East Yunnan. The earliest rhipidistian Youngolepis from the Xishancun Formation (Lochkovian, Devonian) and earliest stem-sarcopterygian Psarolepis from the Kuanti Formation (Ludfordian, Silurian) in East Yunnan indicate that the split between lungfish and tetrapods occurred between 426.5 and 416.0 Ma.
A new genus and species of the Galeaspida Qushiaspis elaia gen. et sp. nov. is described from the Lower Devonian Xujiachong Formation of Qujing, Yunnan Province, southwestern China. The new genus displays the diagnostic characters of Huananaspidiformes including a large oval-shaped median dorsal opening, a slender rostral process, lateral positioned orbital opening, and posteriorly projecting cornual and inner cornual processes. It bears a closer resemblance to Gantarostrataspidae than to Sanchaspidae and Huananaspidae in lacking the laterally projecting cornual processes, than to Sanqiaspidae in lacking the crescent-shaped median dorsal opening. Unlike all other galeaspids, the dermal ornamentation of Qushiaspis exhibits numerous tessera-like units composed of a central large olive-shaped tubercle surrounded by 1–2 rings of much smaller tubercles. An extended phylogenetic analysis of Galeaspida indicates that Qushiaspis, Gantarostrataspis, Wumengshanaspis, and Rhegmaspis form a monophyletic group, the family Gantarostrataspidae, and Qushiaspis is the sister taxon of all other gantarostrataspids. As a less derived gantarostrataspid, Qushiaspis sheds new light on the plesiomorphic condition of the family Gantarostrataspidae, and demonstrates the high diversity of Devonian galeaspids during the Pragian in the Qujing Basin.
Galeaspids are an endemic clade of jawless stem-gnathostomes known as ostracoderms. Their existence illuminates how specific characteristics developed in jawed vertebrates. Sinogaleaspids are of particular interest among the galeaspids but their monophyly is controversial because little is known about Sinogaleaspis xikengensis . Newly discovered sinogaleaspids from the Lower Silurian of Jiangxi, China provide a wealth of data and diagnostic features used to establish the new genus, Rumporostralis gen. nov., for Sinogaleaspis xikengensis . A morphological study showed that the sensory canal system of sinogaleaspids had mosaic features similar to those of three known galeaspids. There are 3–8 pairs of transverse canals in the Sinogaleaspidae, which suggests that the sensory canal system of galeaspid probably had a grid distribution with transverse canals arranged throughout the cephalic division. Phylogenetic analysis of Galeaspida supports the monophyly of the Sinogaleaspidae, consisting of Sinogaleaspis , Rumporostralis, and Anjiaspis . However, Shuyu and Meishanaspis form another monophyletic group, Shuyuidae fam. nov., which is outside all other eugaleaspidiforms. We propose a cladistically-based classification of Galeaspida based on our analysis.
Sinogaleaspis shankouensis is redescribed based on 11 new specimens collected from the type locality of the Xikeng Formation in Xiushui county, Jiangxi Province. The in-depth morphological study indicates that the sensory canal system of S. shankouensis exhibits a mélange of characters of plesiomorphic galeaspid taxa, Eugaleaspiformes, Polybranchiaspiformes and Huananaspiformes. The grid distribution of the sensory canal system on the dorsal side of the head-shield, which comprises four longitudinal canals intercrossed with six pairs of transverse canals in S. shankouensis, probably represents a plesiomorphic condition of vertebrates. Sinogaleaspis shankouensis belongs to the Sinogaleaspis-Xiushuiaspis Fauna or the Maoshan Assemblage which represents the first diversification of galeaspids in the Telychian, Llandovery of the Silurian period. The sedimentary paleoenvironment of the Xikeng Formation in Xiushui, Jiangxi Province is suggestive of a brackish water environment, whereas a large sum of muddy gravels in fish-bearing sandstone beds point to a short distance of potamic transportation. This indicates that the Sinogaleaspis-Xiushuiaspis Fauna may live in a fresh water environment in the river rather than their burial area in the sea.
Micro-CT provides a means of nondestructively investigating the internal structure of organisms with high spatial resolution and it has been applied to address a number of palaeontological problems that would be undesirable by destructive means. This approach has been applied successfully to characterize the cranial anatomy of Shuyu, a 428 million-year-old galeaspid (jawless stem-gnathostome) from the Silurian of Changxing, Zhejiang Province, China. Here, we use the synchrotron X-ray tomographic microscopy (SRXTM) to further describe the circulatory system of the head of Shuyu. Our results indicate that the circulatory system of galeaspids exhibits a mosaic of primitive vertebrate and derived gnathostome characters, including a number of derived gnathostome characters that are absent from osteostracans — the group conventionally interpreted as the sister lineage of jawed vertebrates. Our study provides a rich source of information that can be used to infer and reconstruct the early evolutionary history of the vertebrate cardiovascular system.
Silurian is a period with the shortest duration in Phanerozoic except for the Neogene and Quaternary. It represents an important and unique interval when the biotic diversity recovered quickly after the end-Ordovician mass extinction, different paleoplates or terranes conjoined, big oceans disappeared or narrowed, climate and sea level changed frequently, global biotic provincialism became weaker, some primitive plants started to occupy the land. Silurian is also the first system of which all the chronostratigraphic stratotypes (i.e. the GSSPs) including four series and seven stages were established by the International Subcommission on Silurian Stratigraphy (ISSS). Nonetheless, during the post-GSSP studies conducted by ISSS in the middle 1980s, some Silurian GSSPs were found to have some congenital defects such as no index fossils available that hinder the high resolution subdivision and correlation on a regional or global scale. In this paper, based on the latest development of Silurian study in China, the progress in biostratigraphy, chronostratigraphy, event stratigraphy (such as facies differentiation, heterochrony of black shales, marine red beds, carbonate rocks and reefs), chemostratigraphy, and tectonic stratigraphy (e.g., widespread of the late Silurian rocks in South China and its tectonic implication) are systematically summarized. Some existing problems and the areas to be focused in future work are also discussed. It is suitable for chronostratigraphic study to concentrate not only on the boundary but also doing multidisciplinary analysis on the biotic, chemical, magnetic, environmental, and chronologic aspects, in order to enhance the reliability and the potential for regional and global correlation of a certain GSSP. Some important achievements are expected in these areas in the Silurian study in China: (1) ecostratigraphy and basin analysis of the Llandovery, and the correlation of integrative stratigraphy with a high resolution; (2) establishment of the Wenlock to Pridoli chronostratigraphic framework; (3) the chemo- and magnetic stratigraphy and the age of some key intervals and horizons; (4) further investigation on paleogeography and plate tectonics; and (5) origin and early evolution of the terrestrial ecosystem. Some new breakthroughs might occur in the restudy on some of those problematic GSSPs of some particular series and stages.
The Silurian fishes from north-western Hunan, China are characterised by the earliest known galeaspids Dayongaspis Pan and Zeng, 1985 and Konoceraspis Pan, 1992, and the earliest known antiarch Shimenolepis Wang J.-Q., 1991, as well as rich sinacanth fin spines. Shimenolepis from Lixian County in north-western Hunan, which was dated as the Telychian (late Llandovery), has long been regarded as the oldest representative of the placoderms in the world. As such, in addition to eastern Yunnan and the Lower Yangtze Region, north-western Hunan represents another important area in South China that yields important fossil material for the research of early vertebrates and related stratigraphy. Here we summarise the Silurian fishes known in north-western Hunan so far, and classify them into three vertebrate assemblages (i.e., the Wentang, Maoshan, and Yangtze assemblages). Based on the updated Silurian vertebrate and stratigraphic databases, the Silurian fish-bearing strata in north-western Hunan can be subdivided into the Rongxi, Huixingshao, and Xiaoxi formations in ascending chronological order, which can be correlated with the Lower Red Beds, the Upper Red Beds, and the Ludlow Red Beds in South China, respectively. A new look at the Silurian strata in Lixian suggests that the age of Shimenolepis is late Ludlow rather than late Llandovery as previously suggested. The research on Silurian fishes and biostratigraphy in north-western Hunan not only provides morphological data of early vertebrates, but also offers new palaeoichthyological evidence for the subdivision, correlation, and age assignment of the Silurian marine red beds in South China. The establishment of a related high-precision Silurian stratigraphic framework in north-western Hunan will help to elucidate the temporal and spatial distribution of Silurian fossil fishes, deepen the understanding of the evolution of early vertebrates, and unravel the coevolution between Silurian vertebrates and the palaeoenvironment.
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.
Synchrotron Radiation X-ray Tomographic Microscopy (SRXTM) is a powerful non-destructive method in paleontology, providing ultra-high-resolution 3D insights into the internal structure of fossils. Employing SRXTM, the skull specimens of Shuyu zhejiangensis, a 428 million-year-old galeaspid from the Silurian of Changxing, Zhejiang Province, are investigated. The subsequent analyses indicate that the endoskeletal skull of S. zhejiangensis is composed wholly of cartilage without convincing evidence for the presence of perichondral bone. The cranial anatomy of S. zhejiangensis are unusually preserved in three dimensions largely due to the non-random decay of the cartilaginous braincase and its connecting 'soft' tissues. Using AMIRA or AVIZO software, seven virtual 3D endocasts of the skull of S. zhejiangensis were created revealing the gross internal cranial anatomy of galeaspids in great detail for the first time. The preliminary results indicate that during evolution the galeaspid head experienced a fundamental reorganization resulting in the development of jaws.
The Silurian Period occupies a pivotal stage in the unfolding of key evolutionary events, including the rise of jawed vertebrates. However, the understanding of this early diversification is often hampered by the patchy nature of the Silurian fossil record, with the articulated specimens of jawed vertebrates only known in isolated localities, most notably Qujing, Yunnan, China. Here, we report a new Silurian maxillate placoderm, Bianchengichthys micros, from the Ludlow of Chongqing, with a near-complete dermatoskeleton preserved in articulation. Although geographically separated, the new taxon resembles the previously reported Qilinyu in possessing a unique combination of dermatoskeletal characters. However, the dermal bone of the mandible in Bianchengichthys unexpectedly differs from those in both Qilinyu and Entelognathus and displays a broad oral lamina carrying a line of tooth-like denticles, in addition to the marginal toothless flange. The external morphology of the pectoral fin is preserved and reveals an extensively scale-covered lobate part, flanked by a fringe of lepidotrichia-like aligned scales. The phylogenetic analysis reveals that Bianchengichthys is positioned immediately below Entelognathus plus modern gnathostomes. The discovery significantly widens the distribution of Silurian placoderm-grade gnathostomes in South China and provides a range of morphological disparity for the outgroup comparison to the earliest evolution of jaws, dentitions, and pectoral fins in modern gnathostomes. We also demonstrate that the previously reported Silurian placoderms from central Vietnam are maxillate placoderms close to Qilinyu, Silurolepis, and Bianchengichthys, corroborating the paleogeographic proximity between the Indochina and South China blocks during the Middle Paleozoic.