Species New to Science: Silurian

Showing posts with label Silurian. Show all posts

Tuesday, November 7, 2023

[Paleontology • 2023] Rotaciurca superbus • A Silurian pseudocolonial pterobranch

Rotaciurca superbus

Briggs & Koch, 2023

DOI: 10.1016/j.cub.2023.10.024

twitter.com/phyloprog

yale.edu

Summary

Pterobranchs, a major group of the phylum Hemichordata, first appear in the fossil record during the Cambrian, and there are more than 600 fossil genera dominated by the mainly planktic graptolites of the Paleozoic, which are widely used as zone fossils for correlating sedimentary rock sequences. Pterobranchs are rare today; they are sessile marine forms represented by Rhabdopleura, which is considered the only living graptolite, and Cephalodiscus. Unlike their sister taxon, the colonial graptolites, cephalodiscids are pseudocolonial. Here, we describe a problematic fossil from the Silurian (Pridoli) Bertie Group of Ontario (420 mya), a sequence of near-shore sediments well known for its remarkably preserved diversity of eurypterids (sea scorpions).5 The fossil, Rotaciurca superbus, a new genus and species, was familiarly known as Ezekiel’s Wheel,5 with reference to the unusual circular arrangement of the tubes that compose it. The structure and arrangement of the tubes identify Rotaciurca as a pterobranch, and phylogenetic analysis groups it with the cephalodiscids. We place it in a new family Ezekielidae to distinguish it from Cephalodiscidae. A large structure associated with the tubes is interpreted as a float, which would distinguish Rotaciurca as the only known planktic cephalodiscid—thus cephalodiscids, like the graptolites, invaded the water column. This mode of life reflects the rarity of pseudocolonial macroinvertebrates in planktic ocean communities, a role occupied by the tunicates (Chordata) known as salps today. Our estimates of divergence times, the first using relaxed total-evidence clocks, date the origins of both hemichordates and pterobranchs to the earliest Cambrian (Fortunian).

Derek E.G. Briggs and Nicolás Mongiardino Koch. 2023. A Silurian pseudocolonial pterobranch. Current Biology. In Press, DOI: 10.1016/j.cub.2023.10.024

twitter.com/phyloprog/status/1721620500244582805

The last turn of ‘Ezekiel’s Wheel’ honors a Yale-affiliated fossil hunter

Yale paleontologists have identified a “problematic” fossil as an ancient sea creature that lived in the plankton 420 million years ago.

news.yale.edu/2023/11/06/last-turn-ezekiels-wheel-honors-yale-affiliated-fossil-hunter

Sunday, October 16, 2022

[PaleoIchthyology • 2022] Tujiaaspis vividus • Galeaspid Anatomy and the Origin of Vertebrate Paired Appendages

Tujiaaspis vividus

Gai, Li, Ferrón, Keating, Wang, Donoghue & Zhu, 2022

DOI: 10.1038/s41586-022-04897-6

Abstract

Paired fins are a major innovation that evolved in the jawed vertebrate lineage after divergence from living jawless vertebrates. Extinct jawless armoured stem gnathostomes show a diversity of paired body-wall extensions, ranging from skeletal processes to simple flaps. By contrast, osteostracans (a sister group to jawed vertebrates) are interpreted to have the first true paired appendages in a pectoral position, with pelvic appendages evolving later in association with jaws. Here we show, on the basis of articulated remains of Tujiaaspis vividus from the Silurian period of China, that galeaspids (a sister group to both osteostracans and jawed vertebrates) possessed three unpaired dorsal fins, an approximately symmetrical hypochordal tail and a pair of continuous, branchial-to-caudal ventrolateral fins. The ventrolateral fins are similar to paired fin flaps in other stem gnathostomes, and specifically to the ventrolateral ridges of cephalaspid osteostracans that also possess differentiated pectoral fins. The ventrolateral fins are compatible with aspects of the fin-fold hypothesis for the origin of vertebrate paired appendages. Galeaspids have a precursor condition to osteostracans and jawed vertebrates in which paired fins arose initially as continuous pectoral–pelvic lateral fins that our computed fluid-dynamics experiments show passively generated lift. Only later in the stem lineage to osteostracans and jawed vertebrates did pectoral fins differentiate anteriorly. This later differentiation was followed by restriction of the remaining field of fin competence to a pelvic position, facilitating active propulsion and steering.

Systematic palaeontology

Class Galeaspida Tarlo, 1967

Order Eugaleaspidiformes Liu, 1980

Tujiaaspis vividus gen. et sp. nov.

Etymology. The genus name tujia, Pinyin for the Tujia people, a minority ethnic group in China, in reference to the two fossil sites located in Xiangxi Tujia, Miao Autonomous Prefecture, Hunan Province, and Xiushan Tujia, Miao Autonomous County, Chongqing Municipality; aspis (Gr.), shield; and species name vividus (L.), spirited, full of life.

Holotype. A nearly complete fish accessioned as Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) V26668 (Fig. 1).

Zhikun Gai, Qiang Li, Humberto G. Ferrón, Joseph N. Keating, Junqing Wang, Philip C. J. Donoghue and Min Zhu. 2022. Galeaspid Anatomy and the Origin of Vertebrate Paired Appendages. Nature. 609, 959–963. DOI: 10.1038/s41586-022-04897-6

bristol.ac.uk/biology/news/2022/dead-fish-breathes-new-life-into-the-evolutionary-origin-of-fins-and-limbs.html

Thursday, October 6, 2022

[PaleoIchthyology • 2022] Xiushanosteus mirabilis & Shenacanthus vermiformis • The Oldest Complete Jawed Vertebrates from the early Silurian of China

Xiushanosteus mirabilis Zhu, Li, Ahlberg & Zhu,

in Zhu, Li, Lu, Chen, ... Ahlberg et Zhu, 2022.

DOI: 10.1038/s41586-022-05136-8

Abstract

Molecular studies suggest that the origin of jawed vertebrates was no later than the Late Ordovician period (around 450 million years ago (Ma)). Together with disarticulated micro-remains of putative chondrichthyans from the Ordovician and early Silurian period these analyses suggest an evolutionary proliferation of jawed vertebrates before, and immediately after, the end-Ordovician mass extinction. However, until now, the earliest complete fossils of jawed fishes for which a detailed reconstruction of their morphology was possible came from late Silurian assemblages (about 425 Ma). The dearth of articulated, whole-body fossils from before the late Silurian has long rendered the earliest history of jawed vertebrates obscure. Here we report a newly discovered Konservat-Lagerstätte, which is marked by the presence of diverse, well-preserved jawed fishes with complete bodies, from the early Silurian (Telychian age, around 436 Ma) of Chongqing, South China. The dominant species, a ‘placoderm’ or jawed stem gnathostome, which we name Xiushanosteus mirabilis gen. et sp. nov., combines characters from major placoderm subgroups and foreshadows the transformation of the skull roof pattern from the placoderm to the osteichthyan condition. The chondrichthyan Shenacanthus vermiformis gen. et sp. nov. exhibits extensive thoracic armour plates that were previously unknown in this lineage, and include a large median dorsal plate as in placoderms combined with a conventional chondrichthyan bauplan. Together, these species reveal a previously unseen diversification of jawed vertebrates in the early Silurian, and provide detailed insights into the whole-body morphology of the jawed vertebrates of this period.

Systematic palaeontology

Gnathostomata Gegenbaur, 1874

Xiushanosteus mirabilis Zhu, Li, Ahlberg and Zhu gen. et sp. nov.

Etymology. Xiushan county, where the fossils were discovered, and osteus (Latin), bone; mirabilis (Latin), miracle, referring to the miraculous discovery of complete jawed vertebrates from the early Silurian.

Holotype. Institute of Vertebrate Paleontology and Paleoanthropology (IVPP) V300001, part and counterpart of a complete fish.

Referred material. A total of 20 individuals, catalogued as IVPP V300002–V300021.

Locality and horizon. Yongdong, Xiushan county, Chongqing, China; Huixingshao Formation, middle-to-late Telychian, Llandovery, Silurian, about 436 Ma (Extended Data Figs. 1 and 2 and Supplementary Information). The horizon yields fossils of diverse jawless and jawed fishes (Extended Data Fig. 3a–d), including the two taxa described here. The Lagerstätte features many head-to-tail fishes with fine details such as the complete fin web and possible vertebral column cartilage (Extended Data Fig. 3e). Furthermore, fossils of eurypterids (Fig. 1c,d) and phyllocarid crustaceans (Extended Data Fig. 3f), as well as algal fragments were also discovered alongside the fish fauna.

Chondrichthyes Huxley, 1880

Shenacanthus vermiformis Zhu, Li, Ahlberg and Zhu gen. et sp. nov.

Etymology. In honour of Congwen Shen, a distinguished writer who located his most famous story Border Town (Biancheng) at Hong’an Biancheng, close to the fossil site. Greek akantha, a thorn. Species name, Latin vermiformis, referring to the worm-like ornament on the median dorsal plates.

Holotype. IVPP V300000, the only known specimen of the genus and species, part and counterpart of a near-complete fish.

Locality and horizon. The same as for X. mirabilis.

Diagnosis. Small chondrichthyan, approximately 22 mm from the rostrum to the anal fin. Fusiform body shape; small cranium (~3.5 mm from the rostrum to the shoulder girdle) with blunt rostrum; dentition absent; branchial region posteriorly positioned in relation to the cranium; branchiostegal and hyoidean plates absent, shoulder girdle covered in large dermal plates both dorsally and ventrally, two median dorsal plates, the anterior one smaller and oblate, the posterior one larger and teardrop-shaped, with vermiform ornament; paddle-like pectoral fins lacking fin spine; Anal fin also lacking fin spine. Small, diamond-shaped scales. Small scutes or dermal plates with linear ornament along the dorsal and ventral midlines.

You-an Zhu, Qiang Li, Jing Lu, Yang Chen, Jianhua Wang, Zhikun Gai, Wenjin Zhao, Guangbiao Wei, Yilun Yu, Per E. Ahlberg and Min Zhu. 2022. The Oldest Complete Jawed Vertebrates from the early Silurian of China. Nature. 609; 954–958. DOI: 10.1038/s41586-022-05136-8

https://phys.org/news/2022-09-fish-fossil-china-oldest-teeth.html

Sunday, April 3, 2022

[PaleoIchthyology • 2022] Qingshuiaspis junqingi & Anjiaspis ericius • The Oldest Eugaleaspiform Fishes from the Silurian Red Beds in Jiangxi, South China and Their Stratigraphic Significance

Qingshuiaspis junqingi & Anjiaspis ericius

Shan, Gai, Lin, Chen, Zhu & Zhao, 2022

DOI: 10.1016/j.jseaes.2022.105187

Abstract

Two new species of Eugaleaspiformes, Qingshuiaspis junqingi gen. et sp. nov. and Anjiaspis ericius sp. nov., were described from the lower Telychian Qingshui Formation in Wuning, Jiangxi Province. Our phylogenetic analysis reveals that Qingshuiaspis clusters with Shuyu, Meishanaspis, and Jiangxialepis to form the clade Shuyuidae, which is the sister to all other Eugaleaspiformes. These represent the oldest and most primitive fossil occurrences of Eugaleaspiformes in the marine Lower Red Beds of Silurian in South China. The new fossil evidence indicates that the vertebrate assemblages consisting of Shuyu, Meishanaspis, and Anjiaspis from the Silurian marine red beds in northwestern Zhejiang are more comparable to that of the Qingshui Formation (Lower Red Beds) than that of the Xikeng Formation (Upper Red Beds) in Jiangxi Province. The fish-bearing marine red beds in northwestern Zhejiang probably belong to the Tangchiawu Formation rather than the Maoshan Formation, and its age should be modified as early Telychian, about 438 million years ago. The oldest eugaleaspiforms and polybranchiaspiforms from the marine Lower Red Beds of Silurian in South China demonstrate that the two major groups of galeaspids split no later than the early Telychian.

Qingshuiaspis junqingi gen. et sp. nov.

Anjiaspis ericius sp. nov.

Xianren Shan, Zhikun Gai, Xianghong Lin, Yang Chen, Min Zhu and Wenjin Zhao. 2022. The Oldest Eugaleaspiform Fishes from the Silurian Red Beds in Jiangxi, South China and Their Stratigraphic Significance. Journal of Asian Earth Sciences. 229, 105187. DOI: 10.1016/j.jseaes.2022.105187

Sunday, January 9, 2022

[Paleontology • 2022] Bryozoan-rich Stromatolites (Bryostromatolites) from the Silurian of Gotland, Sweden and their Relation to Climate-related Perturbations of the Global Carbon Cycle

Bryostromatolite Reef.
The front is showing the initial stage of the bryostromatolite, indicated by rugose corals, tabulates, sponges and stromatoporoids. Towards the background it is developing more and more into a bryostromatolite,

in Claussen, Munnecke & Ernst. 2022.

DOI: 10.1111/sed.12863

drawing by Anna Merkel.

twitter.com/JSedimentology

ABSTRACT

Bryozoan–stromatolite associations (bryostromatolites) formed conspicuous reef structures throughout the Sheinwoodian (Wenlock) to Ludfordian (Ludlow) stratigraphy on Gotland but have not been described so far. They are mainly composed of encrusting bryozoans forming a complex intergrowth with porostromate and spongiostromate microbes and are different from the abundant stromatoporoid–coral–algal reefs with respect to their composition. In the bryostromatolite different growth stages can be identified. The observed succession can be taken as evidence for cyclic environmental changes during reef formation. Stenohaline reef-dwelling organisms, such as echinoderms, sponges, corals and trilobites, indicate fully marine salinities. Ten localities exposing bryostromatolites were discovered. Individual bryostromatolites are small with few decimetres up to one metre in size, and occur solely in shallow marine areas. Common features of these reefs on Gotland are cauliflower-like growth, a high bryozoan diversity, a high abundance of phosphatic fossils and components such as bryozoan pearls and inarticulate phosphatic brachiopods, enhanced bioerosion, Palaeomicrocodium crusts, vadose silt and gypsum pseudomorphs. The high abundance of Palaeomicrocodium, as well as the alternation with other crust-forming contributors, suggest that it could have been formed directly at the palaeo-sea surface, probably in times of minor but high-frequency sea-level fluctuations. Vadose silt and pseudomorphs after gypsum in reef cavities indicate subaerial exposure shortly after reef growth. The high amount of phosphatic components indicates a high nutrient input, probably by dust. All bryostromatolites were formed in times of strongly elevated δ13C values. The unusual combination of sedimentological and palaeoecological features, as well as their occurrence exclusively during strong positive δ13C excursions, are evidence that the bryostromatolite development responded to climatic/oceanographic changes, which may have played an important role in reef control.

Keywords: Palaeomicrocodium, phosphate, reef, stable carbon isotopes, subaerial exposure

Artistic reconstruction of a bryostromatolite reef.
The front is showing the initial stage of the bryostromatolite, indicated by rugose corals, tabulates, sponges and stromatoporoids. Towards the background it is developing more and more into a bryostromatolite,

drawing by Anna Merkel.

CONCLUSIONS:

The conclusions of this study can be summarized as follows:

• For the first time bryostromatolite reefs are described from the Silurian of Gotland. They have a cauliflower-like appearance in the field and consist mostly of porostromate and spongiostromate microbial carbonates and bryozoans.

• On Gotland, bryostromatolites only occur in the Högklint and Tofta formations (Sheinwoodian) and in the Eke and Hamra formations (Ludfordian). They grew in fully marine conditions, and formed a rigid framework and a topographic relief of several decimetres up to about 1 m.

• The bryostromatolites show a relatively high diversity of bryozoans (with up to twenty species in a single reef), a high abundance of reef-building and reef-dwelling organisms, and a surprisingly high abundance of phosphatic constituents.

• Repeated alternations of distinct layers dominated by either porostromate microbes, spongiostromate microbial layers, or encrusting bryozoans indicate cyclic environmental changes.

• Reef growth took place in extremely shallow water. The occurrence of vadose silt and gypsum pseudomorphs in reef cavities indicate subaerial exposure shortly after reef growth.

• The problematicum Palaeomicrocodium indicates an extreme environment and, according to Antoskhina (2006), even subaerial exposure. The high abundance and alternation with crust-forming reef-building organisms suggest short phases of subaerial exposure even during reef growth and, therefore, reef growth in extremely shallow water.

• The high abundance of phosphatic components (for example, inarticulate brachiopods, bryozoan pearls and linings) indicates a high input of phosphorous by either rivers or wind. For bryozoan pearls and linings, this hypothesis is supported by several literature studies (e.g. Oakley, 1934; Conti & Serpagli, 1988; Ma et al., 2014b). According to the studies of Kozłowski (2015) in the Baltic area, an aeolian input seems more plausible. This fits the fact that so far, no bryostromatolites have been discovered from the humid equatorial belt.

• Both the bryostromatolites on Gotland and bryostromatolites in the Silurian and Ordovician of other areas occur only in times of elevated δ13C values, indicating a close link of local bryostromatolite growth and global perturbations of the carbon cycle.

Anna Lene Claussen, Axel Munnecke and Andrej Ernst. 2022. Bryozoan-rich Stromatolites (bryostromatolites) from the Silurian of Gotland and their Relation to Climate-related Perturbations of the Global Carbon Cycle. Sedimentology. 69(1) Special Issue: Understanding carbonate factories through palaeoecological and sedimentological signals – Tribute to Luis Pomar; 162-198. DOI: 10.1111/sed.12863

twitter.com/JSedimentology/status/1479030480594944003

Tuesday, May 18, 2021

[Paleontology • 2021] Parioscorpio venator • Stranger than A Scorpion: A Reassessment of A problematic Arthropod from the Llandoverian Waukesha Lagerstätte, Wisconsin, USA

Parioscorpio venator Wendruff, Babcock, Wirkner, Kluessendorf & Mikulic, 2020

in Anderson, Schiffbauer, Jacquet, ... et Mikulic, 2021.

DOI: 10.1111/pala.12534

twitter.com/FossilDetective

2020. DOI: 10.1038/s41598-019-56010-z

Abstract

A relatively uncommon arthropod of the Waukesha lagerstätte, Parioscorpio venator, is redescribed as an arthropod bearing a combination of characters that defy ready classification. Diagnostic features include sub‐chelate ‘great appendages’, a lack of antennae, multiramous anterior trunk appendages, filamentous fan‐like rear trunk appendages, and apparently thin and poorly preserved pleural fields. Phylogenetic analysis resolves this organism as basal to crown‐group Mandibulata and Chelicerata, but its exact placement is inconclusive. Thus, we compare its morphology to several stem groups of arthropods in a discussion of its plausible taxonomic affinities. The examined specimens are probably carcasses and preserve a variety of soft‐tissue details, including muscle blocks in the head, eyes and eye facets, likely ventral nerve cords, a central gut tract and trunk legs with multiple filamentous elements organized into stiff bundles. The preservation habits of P. venator are characterized and compared to previous assessments of Waukesha lagerstätte taxa. Four preservation habits are observed: a phosphatized habit showing flattened to partly three‐dimensional mineralization in francolite; a mouldic habit largely left behind by removed francolite that shows no carbon enrichment despite a darkened colour; sheet‐like or speckled carbonaceous compressions; and scattered pyrite crystals. This redescription highlights both the palaeobiological value of ‘small’ lagerstätten typical of the middle Palaeozoic and the caution that must be taken when interpreting their more enigmatic constituents.

Keywords: stem‐group Arthropoda, taphonomy, phosphatization, nerve cord, appendage, morphology, tagma

Specimens upon which the rediagnosis and redescription of Parioscorpio venator Wendruff et al., 2020 are primarily based.
A, UWGM2793, a nearly complete specimen with an entire left great appendage. B, UWGM2785, a specimen with all cephalic appendages intact, including both great appendages, which are nearly complete; note that the posterior portion of the body is still buried beneath the matrix. C, UWGM2764, paratype and counterpart to UWGM2163, preserved as a thin film with the right great appendage barely visible on the upper right; no trunk appendages are preserved, which makes the posterior constriction of the axial trunk easy to see compared to other specimens. D–E, part and counterpart of UWGM2857, a nearly complete specimen with numerous head and trunk details.

F–G, part and counterpart of UWGM2854, which preserves many three‐dimensional limbs, but whose head is cut off by the border of the matrix. H, UWGM2798, a largely mouldic specimen showing excellent preservation of the cephalic appendages, including two complete great appendages. I–J, part and counterpart of UWGM2885, a nearly complete specimen which shows limited three‐dimensional preservation, but preserves many walking legs as dark compressions. All scale bars represent 5 mm.

Reconstructions of the morphology of Parioscorpio venator.
A, whole body, from a three‐quarters dorsal view; note that the limbs can be seen through the thin, translucent tergopleural cuticle; the tentative preservation of the tergopleurae in most specimens raises this possibility. B, focus on the great appendage and second cephalic appendage and their attachment to the head; the reconstruction shows slight lateral displacement of the limbs to better envision their bases; note that the sclerotized portion of the first article of the great appendage is contained within a translucent membrane. C, illustration showing our reconstruction of a standard trunk limb; limb rami are labelled in roman (with alternative interpretations in smaller font), while individual filamentous bundles on the endopod and endopodal exite/exopod are labelled in italics; the exact proportions of the limb components vary based on the limb's placement on the body; this illustrated limb, with the racemose filamentous bundle considerably longer than the exopod/epipod or the walking portion of the endopod, is from the middle of the trunk.

twitter.com/FossilDetective

Evan P. Anderson, James D. Schiffbauer, Sarah M. Jacquet, James C. Lamsdell, Joanne Kluessendorf and Donald G. Mikulic. 2021. Stranger than A Scorpion: A Reassessment of Parioscorpio venator, A problematic Arthropod from the Llandoverian Waukesha Lagerstätte. Palaeontology. DOI: 10.1111/pala.12534

twitter.com/FossilDetective/status/1384488772331573249

Genus Parioscorpio gen. nov.

Etymology. From Latin, pario, progenitor, and scorpio, scorpion.

Parioscorpio venator gen. et sp. nov.

Etymology. From Latin, venator, hunter.

Types. Holotype, University of Wisconsin Geology Museum, Madison, Wisconsin, UWGM 2162. Paratype, UWGM 2163. Location. Waukesha Lime and Stone Company west quarry, north of State Highway 164, Waukesha, Wisconsin, USA.

Horizon. Lower part of the Brandon Bridge Formation (Silurian: Llandovery, Telychian).

Andrew J. Wendruff, Loren E. Babcock, Christian S. Wirkner, Joanne Kluessendorf and Donald G. Mikulic. 2020. A Silurian ancestral scorpion with fossilised internal anatomy illustrating a pathway to arachnid terrestrialisation. Scientific Reports. 10: 14. DOI: 10.1038/s41598-019-56010-z

Sunday, May 17, 2020

[PaleoIchthyology • 2020] Rumporostralis gen. nov. • A New Genus of Sinogaleaspids (stem-Gnathostomata: Galeaspida) from the Silurian Period in Jiangxi, China

Rumporostralis xikengensis (Pan & Wang, 1980)

in Shan, Zhu, Zhao, et al., 2020

DOI: 10.7717/peerj.9008

Artwork: Xiaocong Guo.

Abstract

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.

Systematic paleontology

Subclass Galeaspida Tarlo, 1967
Order Eugaleaspiformes (Liu, 1965) Liu, 1980

Family Shuyuidae fam. nov.

Differential diagnosis. Shuyuidae differs from other families of Eugaleaspiformes in the splayed posterior supraorbital canals and absence of U-shaped median dorsal canals.

Type genus. Shuyu Gai et al., 2011

Referred genera. Meishanaspis

Remarks. Newly discovered sinogaleaspid material provides a wealth of data and reliable diagnostic features to erect the new genus Rumporostralis gen. nov. for ‘Sinogaleaspis’ xikengensis. Our phylogenetic analysis of Galeaspida shows that Shuyu and Meishanaspis are not included in Sinogaleaspidae and form another monophyletic group. A new family, Shuyuidae fam. nov., was created for Shuyu and Meishanaspis. Shuyuidae is positioned in the new cladogram as the sister to all other Eugaleaspididiformes with synapomorphies including a subtriangular head-shield and longitudinal oval or wedge-shaped median dorsal opening.

Family Sinogaleaspidae Pan & Wang, 1980

Differential diagnosis. Sinogaleaspidae differs from other families of Eugaleaspiformes in the V-shaped posterior supraorbital canals and more than 2 pairs of median transverse canals (autapomorphy).

Type genus. Sinogaleaspis. Pan & Wang, 1980

Referred genera. Rumporostralis gen. nov., Anjiaspis

Remarks. The amended Sinogaleaspidae, including Sinogaleaspis shankouensis, Rumporostralis xikengensis, (Figs. 3, 4) R. shipanensis (Fig. 5), and Anjiaspis reticularis is monophyletic with synapomorphy (U-shaped median dorsal canals) and autapomorphy (more than 2 pairs of median transverse canals).

Genus Rumporostralis gen. nov.

Etymology. Rumpo latin, state of being dehiscent or split; rostralis, Latin, snout, in referring to the rostral margin of the head-shield split by the anterior end of median dorsal opening.

Type species. Rumporostralis xikengensis (Pan & Wang, 1980)

Referred species. Rumporostralis shipanensis gen. et sp. nov.

Differential diagnosis. Rumporostralis differs from other Eugaleaspiformes by an unclosed rostral margin of the head-shield, indicating autapomorphy.

Remarks. The genus including R. xikengensis and R. shipanensis is uniquely characterized by the unclosed rostral margin.

Holotype. A nearly complete head-shield GMC V1753A, B

Referred specimens. A nearly complete head-shield IVPP V25136.1, three incomplete head-shields IVPP V25136.2–4.

Type locality and horizon. Xikeng village and Shipan reservoir, Taiyangsheng Town, Xiushui County, Jiangxi Province, China; Xikeng formation, Telychian, Llandovery, Silurian.

Differential diagnosis. R. xikengensis differs from the other species R. shipanensis in the small size of the head-shield.

Rumporostralis shipanensis gen. et sp. nov.

Holotype. An incomplete head-shield IVPP V26114.1a, b

Type locality and horizon. Shipan reservoir, Taiyangsheng Town, Xiushui County, Jiangxi Province, China; Xikeng formation, Telychian, Llandovery, Silurian.

Differential diagnosis. R. shipanensis differs from the type species R. xikengensis by the large size of the head-shield.

Figure 7: Life restoration of Sinogaleaspis shankouensis (left) and Rumporostralis xikengensis (right) in a fresh river.

Artwork: Xiaocong Guo.

Conclusion:

The newly discovered sinogaleaspids from the Lower Silurian in Jiangxi, China provides a wealth of new data and reliable diagnostic features to assign the new genus, Rumporostralis gen. nov., to ‘Sinogaleaspis’ xikengensis. This in-depth morphological study determined that the sensory canal system of sinogaleaspids exhibits the mosaic features of three known galeaspid patterns. The presence of 3-8 pairs of transverse canals in Sinogaleaspidae suggests that the sensory canal system of galeaspids probably displayed a grid distribution with transverse canals arranged throughout the cephalic division. An extended phylogenetic analysis of Galeaspida corroborates the monophyly of Sinogaleaspidae, which consists of Sinogaleaspis, Rumporostralis, and Anjiaspis. Shuyu and Meishanaspis were excluded from Sinogaleaspidae to form the monophyletic group Shuyuidae fam. nov., which is the sister of all other Eugaleaspididiformes. We propose a cladistically-based classification of the Galeaspida.

Xianren Shan, Min Zhu, Wenjin Zhao, Zhaohui Pan, Pingli Wang and Zhikun Gai. 2020. A New Genus of Sinogaleaspids (Galeaspida, stem-Gnathostomata) from the Silurian Period in Jiangxi, China. PeerJ. 8:e9008. DOI: 10.7717/peerj.9008

Friday, April 3, 2020

[Paleontology • 2020] New Rhenopyrgid Edrioasteroids (Echinodermata) and Their Implications for Taxonomy, Functional Morphology, and Paleoecology

Rhenopyrgus viviani Ewin, Martin, Isotalo & Zamora, 2020

Silurian (lower Telychian), Jupiter Formation, Anticosti Island, Canada.

(1, 2) Rhenopyrgus grayae (Bather, 1915), Upper Ordovician, Ayrshire, Scotland
(holotype E23470); (6–7) Rhenopyrgus indet. 3; (9) Rhenopyrgus coronaeformis Rievers, 1961, Lower Devonian, Bavaria, Germany
(holotype SNSB-BSPG 1958 XV 50)

DOI: 10.1017/jpa.2019.65

Illustration: Virgil Tanasa NHM.ac.uk

Abstract

Rhenopyrgids are rare, turreted edrioasterid edrioasteroids from the lower Paleozoic with a distinctive and apparently conservative morphology. However, new, well-preserved rhenopyrgid edrioasteroid material from Canada, along with a review of described taxa, has revealed broader structural diversity in the oral surface and enabled a re-evaluation of rhenopyrgid functional morphology and paleoecology.

The floor plates in Rhenopyrgus viviani n. sp., R. coronaeformis Rievers, 1961 and, R. flos Klug et al., 2008 are well fused to each other and the interradial oral plate and lack obvious sutures, thereby forming a single compound interradial plate. This differs from other rhenopyrgids where sutures are more apparent. Such fused oral surface construction is only otherwise seen in some derived edrioblastoids and in the cyathocystids, suggesting homoplasy.

Our analysis further suggests that the suboral constriction could contract but the flexible pyrgate zone could not. Thus, specimens apparently lacking a sub-oral constriction should not necessarily be placed in separate genera within the Rhenopyrgidae. It also supports rhenopyrgids as epifaunal mud-stickers with only the bulbous, textured, entire holdfasts (coriaceous sacs) anchored within the substrate rather than as burrow dwellers or encrusters.

Rhenopyrgus viviani n. sp. is described from the Telychian (lower Silurian) Jupiter Formation of Anticosti Island, Québec, Canada and is differentiated by a high degree of morphological variability of pedunculate plates, broader oral plates, and narrower distal ambulacral zones. Specimens lacking or with obscured diagnostic plates from the Ordovician of Montagne Noire, France, and the Ordovician and Silurian of Girvan, Scotland are also described.

Systematic paleontology

Phylum Echinodermata de Bruguière, 1791 (ex. Klein, 1734)

Class Edrioasteroidea Billings, 1858

Order Edrioasterida Bell, 1976

Suborder Edrioblastoidina Fay, 1962

Family Rhenopyrgidae Holloway and Jell, 1983

Genera included.— Rhenopyrgus Dehm, 1961; Heropyrgus Briggs et al., 2017.

Figure 3. Rhenopyrgidae; all whitened with ammonium chloride.
(1, 2) Rhenopyrgus grayae, Upper Ordovician, Lady Burn Starfish Bed, Girvan, Ayrshire, Scotland (holotype E23470): (1) details of oral surface with prominent collar plates and no suboral constriction apparent; black arrows highlight exposed floor plates in distal ambulacra; white arrow points to a small, exposed part of a plate of the suboral constriction, suggesting that suboral constriction could be contracted behind collar plates; (2) lateral view.
(3, 4) Rhenopyrgus indet. 1, Silurian, Newland Formation, Newlands, Ayrshire, Scotland (E 62753): (3) lateral view of pyrgate zone, arrow points to enlarged plates interpreted here as collar plates; (4) oral view, black arrow highlights disarticulated large D-shaped oral ossicle.
(5) Rhenopyrgus indet. 2, Ordovician, Drummuck Series, Ardmillan, Girvan District, Ayrshire, Scotland (EE 16254); lateral view of pyrgate zone; note difference in size and morphology of the pyrgate ossicles suggesting it is different than R. grayae, which is found in similar age rocks that are geographically close; also note disarticulated ridged deltoidshaped plate closely associated with articulated pyrgate plates.
(6–8) Rhenopyrgus indet. 3: (6, 7) Foulon Formation (middle Floian), La Croix de Roquebrun, Saint-Nazaire-de-Ladarez, Hérault, France (UCBL-FSL 713312); (6) lateral view of whole specimen; (7) enlargement of the oral surface, showing confused plate articulation of this region; black arrow highlights possible oral ossicle; white arrows highlight collar plate series; (8) late Tremadocian, beneath Saint-Chinian Formation, Saint-Chinian, SW of Donnadieu, Babeau-Bouldoux, Hérault, France (UCBL-FSL 713316), lateral view.
(9–11) Rhenopyrgus coronaeformis Rievers, 1961, Lower Devonian, Emsian, Hunsrück Slate, Bavaria, Germany (holotype SNSB-BSPG 1958 XV 50): (9) detail of oral surface and proximal structures; (10) detail of oral surface; note complicated cover plate articulation surfaces; black arrow highlights grooved adambulacral margin of oral plate; (11) detail of coriaceous sac.

Abbreviations, O = oral plate. All scale bars represent 1 mm.

Genus Rhenopyrgus Dehm, 1961

Type species.— Pyrgocystis (Rhenopyrgus) coronaeformis Rievers, 1961; Hunsrück Slate, Lower Devonian, (Emsian) of Germany.

Other species.— Rhenopyrgus coronaeformis Rievers, 1961; R. flos Klug et al., 2008; R. viviani n. sp.; R. sp. indet.1, formerly Pyrgocystis procera (Aurivillius) Bather, 1915; R. sp. indet. 2, R. sp. indet. 3, R. sp. indet. 4.; R. grayae (Bather, 1915); R. whitei Holloway and Jell, 1983; and R. piojoensis Sumrall et al., 2013.

Figure 5. Idealized reconstruction of Rhenopyrgus viviani n. sp. Silurian (lower Telychian), Jupiter Formation, Jupiter River, Anticosti Island, Canada. Note individuals with extended and contracted suboral constrictions and with only the coriaceous sac and very distal part of the pyrgate zone buried in the substrate.

Illustration: Virgil Tanasa

Rhenopyrgus viviani new species

Occurrence.— Cybèle Member to Pavillon Member, Jupiter Formation, Telychian, upper Llandovery, lower Silurian, Anticosti Island, Québec, Canada.

Etymology.— Named for the initial discoverer Mr. Travis Vivian.

Timothy A. M. Ewin, Markus Martin, Phillip Isotalo and Samuel Zamora. 2020. New Rhenopyrgid Edrioasteroids (Echinodermata) and Their Implications for Taxonomy, Functional Morphology, and Paleoecology. Journal of Paleontology. 94(1); 115-130. DOI: 10.1017/jpa.2019.65

Newest member of echinoderm family revealed

nhm.ac.uk/press-office/press-releases/newest-member-of-echinoderm-family-revealed.html

nhm.ac.uk/discover/news/2019/september/unusual-fossil-worms-surprise-scientists.html

Saturday, March 25, 2017

[Paleontology • 2017] Cascolus ravitis • A New Crustacean from the Herefordshire (Silurian) Lagerstätte, UK , and Its Significance in Malacostracan Evolution

Cascolus ravitis

Siveter, Briggs, Siveter, Sutton & Legg, 2017

DOI: 10.1098/rspb.2017.0279

Abstract

Cascolus ravitis gen. et sp. nov. is a three-dimensionally preserved fossil crustacean with soft parts from the Herefordshire (Silurian) Lagerstätte, UK. It is characterized by a head with a head shield and five limb pairs, and a thorax (pereon) with nine appendage-bearing segments followed by an apodous abdomen (pleon). All the appendages except the first are biramous and have a gnathobase. The post-mandibular appendages are similar one to another, and bear petal-shaped epipods that probably functioned as a part of the respiratory–circulatory system. Cladistic analysis resolves the new taxon as a stem-group leptostracan (Malacostraca). This well-preserved arthropod provides novel insights into the evolution of appendage morphology, tagmosis and the possible respiratory–circulatory physiology of a basal malacostracan.

An international team of scientists led by the University of Leicester has discovered a new 430 million-year-old fossil and has named it in honour of Sir David Attenborough - who grew up on the University campus.

Systematic palaeontology

Phylum Arthropoda
Subphylum Crustacea

Class Malacostraca
Subclass Phyllocarida

Order Leptostraca

Genus Cascolus gen. nov.

Type species: Cascolus ravitis sp. nov.

Etymology: The new crustacean is named in honour of the naturalist and broadcaster Sir David Attenborough, who grew up on University College Leicester campus, in celebration of his 90th birthday. Latin castrum ‘stronghold’ and colus ‘dwelling in’; alluding to the Middle/Old English source for the surname ‘Attenborough, derived from atten ‘at the’ and burgh ‘a fortified place’. Latin Ratae, the Roman name for Leicester, vita ‘life’ and commeatis ‘a messenger’.

Diagnosis of genus (monotypic) and species: An elongate body comprising a head with a head shield, pedunculate eyes and five limb pairs; and a trunk consisting of a thorax (pereon) with nine limb-bearing segments and an apodous abdomen (pleon). The first appendage is uniramous and has three slender flagella longer than the body. All other appendages are biramous and have a gnathobase. The post-mandibular appendages are similar to one another, except that the fourth head appendage bears a single petal-shaped epipod, and the fifth head appendage and each trunk appendage bear two petal-shaped epipods.

Material: Only known from the holotype OUMNH C.29698 (figure 1v), a specimen with soft parts reconstructed in three dimensions (figure 1a–u).

Locality and horizon: Herefordshire, England, UK; Wenlock Series, Silurian.

David J. Siveter, Derek E. G. Briggs, Derek J. Siveter, Mark D. Sutton and David Legg. 2017. A New Crustacean from the Herefordshire (Silurian) Lagerstätte, UK, and Its Significance in Malacostracan Evolution. Proceedings of the Royal Society B. DOI: 10.1098/rspb.2017.0279

430 million-year-old fossil named in honor of Sir David Attenborough
http://phy.so/409322871 @physorg_com

Friday, March 17, 2017

[PaleoIchthyology • 2017] Sparalepis tingi • A New Osteichthyan from the late Silurian of Yunnan, China

Sparalepis tingi

Choo, Zhu, Qu, Yu, Jia & Zhao, 2017

DOI: 10.1371/journal.pone.0170929

Illustration by B. Choo blogs.plos.org/PaleoComm

Abstract

Our understanding of early gnathostome evolution has been hampered by a generally scant fossil record beyond the Devonian. Recent discoveries from the late Silurian Xiaoxiang Fauna of Yunnan, China, have yielded significant new information, including the earliest articulated osteichthyan fossils from the Ludlow-aged Kuanti Formation. Here we describe the partial postcranium of a new primitive bony fish from the Kuanti Formation that represents the second known taxon of pre-Devonian osteichthyan revealing articulated remains. The new form, Sparalepis tingi gen. et sp. nov., displays similarities with Guiyu and Psarolepis, including a spine-bearing pectoral girdle and a placoderm-like dermal pelvic girdle, a structure only recently identified in early osteichthyans. The squamation with particularly thick rhombic scales shares an overall morphological similarity to that of Psarolepis. However, the anterior flank scales of Sparalepis possess an unusual interlocking system of ventral bulges embraced by dorsal concavities on the outer surfaces. A phylogenetic analysis resolves Sparalepis within a previously recovered cluster of stem-sarcopterygians including Guiyu, Psarolepis and Achoania. The high diversity of osteichthyans from the Ludlow of Yunnan strongly contrasts with other Silurian vertebrate assemblages, suggesting that the South China block may have been an early center of diversification for early gnathostomes, well before the advent of the Devonian “Age of Fishes”.

Fig 9. Life restoration of Sparalepis tingi (foreground) and other fauna from the Kuanti Formation. Also in the scene are numerous conodont animals, a pair of the maxillate placoderm Entelognathus (middle distance) and two examples of the osteichthyan Megamastax (background), the largest known Silurian vertebrate.

Illustration by Brian Choo blogs.plos.org/PaleoComm DOI: 10.1371/journal.pone.0170929

Holotype and only specimen: V17915, a partial postcranium (Fig 2), with associated cleithrum, interclavicle and pelvic girdle. Institute of Vertebrate Paleontology and Paleoanthropology (IVPP), Beijing.

Diagnosis: Bony fish with spine-bearing dermal pectoral and pelvic girdles. Large median dorsal plates, with those immediately anterior to each the two dorsal fins bearing a large spine. Dermal surfaces of the scales and bony plates composed of glossy enamel ornamented with coarse sub-parallel ridges. Large surface pore openings within inter-ridge furrows on the appendicular girdles, gulars and median dorsal plates, but absent on the scales. Thick rhombic scales with a distinct neck separating the crown and the base. Anterior flank scales with a dermal interlocking mechanism of ventral bulges embraced by dorsal concavities on the ventrally adjacent scales. About 30 scale columns in front of the first dorsal fin base.

Etymology: Generic name from the Persian spara (shield) and the ancient Greek lepis (scale), in reference to the resemblance of the scales of the fish to depictions of rectangular wicker shields carried by the Achaemenid Sparabara infantry. Specific name after V. K. Ting (1887–1936) for his pioneering work on the geology of Yunnan.

Notes: The presence of spine-bearing dermal pectoral and pelvic girdles separates Sparalepis from all other known osteichthyans except for Guiyu and Psarolepis. The combination of prominent linear ridges and pore openings on the dermal surfaces of all the larger bones and ridge scutes distinguishes Sparalepis from Guiyu which possesses ridges only. The scale ornament, consisting of linear ridges and devoid of pores, is similar to that of Guiyu and many early actinopterygians, but distinct from the porous cosmine-like surface on the scales of Psarolepis. The scales of Sparalepis are smaller than those of Guiyu, with about 30 scale rows anterior to the first dorsal fin against 15 in Guiyu. As with Psarolepis, the flank scales lack extensive depressed fields and possess necks which separate the crowns from the bases. The ventral bulges and dorsal concavities on the outer surfaces of the anterior flank scales of Sparalepis form a unique interlocking system among early osteichthyans.

Brian Choo, Min Zhu, Qingming Qu, Xiaobo Yu, Liantao Jia and Wenjin Zhao. 2017. A New Osteichthyan from the late Silurian of Yunnan, China. PLoS ONE. 12(3): e0170929.

DOI: 10.1371/journal.pone.0170929

The (Now Older) Age of Fishes: New bony fish from the Silurian of China
http://blogs.plos.org/paleocomm/2017/03/08/the-now-older-age-of-fishes-new-bony-fish-from-the-silurian-of-china/

Ancient southern China fish may have evolved prior to the 'Age of Fish'
http://phy.so/408198292 @physorg_com