[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

[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

[Paleontology • 2016] Aquilonifer spinosus • Tiny Iindividuals attached to A New Silurian Arthropod from Herefordshire Lagerstätte of England, Suggest A Unique Mode of Brood Care

Aquilonifer spinosus 

Briggs, Siveter, Siveter, Sutton & Legg, 2016  

  DOI:  10.1073/pnas.1600489113 

Significance

The paper reports a remarkable arthropod from the Silurian Herefordshire Lagerstätte of England. The fossil reveals a unique association in an early Paleozoic arthropod involving tethering of 10 tiny individuals each by a single thread to the tergites so that their appearance is reminiscent of kites. The evidence suggests that these are juveniles and that the specimen records a unique brooding strategy. This is part of a diversity of complex brooding behaviors in early arthropods heralding the variety that occurs today. The possibility that the small individuals represent a different arthropod, possibly parasitic, which colonized the larger individual, seems less likely.

Abstract

The ∼430-My-old Herefordshire, United Kingdom, Lagerstätte has yielded a diversity of remarkably preserved invertebrates, many of which provide fundamental insights into the evolutionary history and ecology of particular taxa. Here we report a new arthropod with 10 tiny arthropods tethered to its tergites by long individual threads. The head of the host, which is covered by a shield that projects anteriorly, bears a long stout uniramous antenna and a chelate limb followed by two biramous appendages. The trunk comprises 11 segments, all bearing limbs and covered by tergites with long slender lateral spines. A short telson bears long parallel cerci. Our phylogenetic analysis resolves the new arthropod as a stem-group mandibulate. The evidence suggests that the tethered individuals are juveniles and the association represents a complex brooding behavior. Alternative possibilities—that the tethered individuals represent a different epizoic or parasitic arthropod—appear less likely.

Keywords: Arthropod; Silurian; brood care; juvenile; Herefordshire Lagerstätte

Aquilonifer spinosus is a new genus and species of arthropod from the Herefordshire Lagerstätte, a late Wenlock (mid-Silurian) volcaniclastic deposit in Herefordshire, United Kingdom. It is preserved, as are the other fossils from this Lagerstätte, in three dimensions as a calcitic void fill in a carbonate concretion. The name of the new taxon refers to the fancied resemblance between the tethered individuals and kites, and echoes the title of the 2003 novel The Kite Runner by Khaled Hosseini (aquila, eagle or kite; -fer, suffix meaning carry; thus aquilonifer, kite bearer; spinosus, spiny, referring to the long lateral spines on the tergites). The material is a single specimen, the holotype OUMNH C.29695, registered at the Oxford University Museum of Natural History (Fig. 1 and Movie S1).

Diagnosis. Features include a head shield with rostrum-like anterior projection, large uniramous antenna, chelate limb, and two other biramous appendages in the head, the last similar to those of the trunk; an elongated trunk with long, slender lateral spines on the 11 tergites, with all trunk somites bearing limbs of which all but the last are biramous; and a short telson and long cerci.

......

Derek E. G. Briggs, Derek J. Siveter, David J. Siveter, Mark D. Sutton and David Legg. 2016. Tiny Iindividuals attached to A New Silurian Arthropod Suggest A Unique Mode of Brood Care.
Proceedings of the National Academy of Sciences. 113(16) DOI:  10.1073/pnas.1600489113

[PaleoIchthyology • 2015] Janusiscus schultzei • Osteichthyan-like Cranial Conditions in an Early Devonian stem Gnathostome

The 415-million-year-old fish fossil (Janusiscus schultzei) has a well-developed external skeleton (shown in blue), a feature that is seen in the common ancestor of bony fish and cartilaginous fishes, such as sharks.

images: Sam Giles; Placoderm image: K. Trinajstic
DOI: 10.1038/nature14065

The phylogeny of Silurian and Devonian (443–358 million years (Myr) ago) fishes remains the foremost problem in the study of the origin of modern gnathostomes (jawed vertebrates). A central question concerns the morphology of the last common ancestor of living jawed vertebrates, with competing hypotheses advancing either a chondrichthyan- or osteichthyan-like model. Here we present Janusiscus schultzei gen. et sp. nov., an Early Devonian (approximately 415 Myr ago) gnathostome from Siberia previously interpreted as a ray-finned fish, which provides important new information about cranial anatomy near the last common ancestor of chondrichthyans and osteichthyans. The skull roof of Janusiscus resembles that of early osteichthyans, with large plates bearing vermiform ridges and partially enclosed sensory canals. High-resolution computed tomography (CT) reveals a braincase bearing characters typically associated with either chondrichthyans (large hypophyseal opening accommodating the internal carotid arteries) or osteichthyans (facial nerve exiting through jugular canal, endolymphatic ducts exiting posterior to the skull roof) but lacking a ventral cranial fissure, the presence of which is considered a derived feature of crown gnathostomes. A conjunction of well-developed cranial processes in Janusiscus helps unify the comparative anatomy of early jawed vertebrate neurocrania, clarifying primary homologies in ‘placoderms’, osteichthyans and chondrichthyans. Phylogenetic analysis further supports the chondrichthyan affinities of ‘acanthodians’, and places Janusiscus and the enigmatic Ramirosuarezia in a polytomy with crown gnathostomes. The close correspondence between the skull roof of Janusiscus and that of osteichthyans suggests that an extensive dermal skeleton was present in the last common ancestor of jawed vertebrates4, but ambiguities arise from uncertainties in the anatomy of Ramirosuarezia. The unexpected contrast between endoskeletal structure in Janusiscus and its superficially osteichthyan-like dermal skeleton highlights the potential importance of other incompletely known Siluro-Devonian ‘bony fishes’ for reconstructing patterns of trait evolution near the origin of modern gnathostomes.

Gnathostomata Gegenbaur, 1874

Janusiscus schultzei gen. et sp. nov.

Etymology. Generic name refers to double-sided nature of the specimen, with an osteichthyan-like dorsal skull roof, but a braincase that displays an array of plesiomorphic gnathostome characters (Latin Ianus, the god of doorways and transitions, often depicted as having two faces; [p]iscis, fish). Specific name in honour of Hans-Peter Schultze (University of Kansas), who first described these specimens.

Holotype. GIT (Institute of Geology, Talinn, Estonia) 496-6 (Pi.1384), skull roof and braincase, both missing anterior region 

 Giles, Sam; Friedman, Matt; Brazeau, Martin D. 2015. Osteichthyan-like Cranial Conditions in an Early Devonian stem Gnathostome. Nature. doi: 10.1038/nature14065L3

Ancient fossil may rewrite fish family tree http://news.sciencemag.org/paleontology/2015/01/ancient-fossil-may-rewrite-fish-family-tree

Birth of Jaws: Tiny Fish May Be Ancient Ancestor http://shar.es/1fHsYF via @LiveScience

[Paleontology • 2012] Dibasterium durgae • Silurian horseshoe crab illuminates the evolution of arthropod limbs

Dibasterium durgae gen. et sp. nov.

Abstract

The basic arrangement of limbs in euarthropods consists of a uniramous head appendage followed by a series of biramous appendages. The body is divided into functional units or tagmata which are usually distinguished by further differentiation of the limbs. The living horseshoe crabs are remnants of a much larger diversity of aquatic chelicerates. The limbs of the anterior and posterior divisions of the body of living horseshoe crabs differ in the loss of the outer and inner ramus, respectively, of an ancestral biramous limb. Here we report a new fossil horseshoe crab from the mid-Silurian Lagerstätte in Herefordshire, United Kingdom (approximately 425 Myr B.P.), a site that has yielded a remarkably preserved assemblage of soft-bodied fossils. The limbs of the new form can be homologized with those of living Limulus, but retain an ancestral biramous morphology. Remarkably, however, the two limb branches originate separately, providing fossil evidence to suggest that repression or loss of gene expression might have given rise to the appendage morphology of Limulus. Both branches of the prosomal limbs of this new fossil are robust and segmented in contrast to their morphology in Cambrian arthropods, revealing that a true biramous limb was once present in chelicerates as well as in the mandibulates.

Keywords: Xiphosurida, origin of limb, morphology, Herefordshire Lagerstätte

Holotype of Dibasterium durgae gen. et sp. nov.

Horseshoe crabs, including the iconic Limulus we know today, have existed for more than 450 million years. Over that long history, evolutionary change has particularly affected the nature of their legs.

A new fossil discovery in Britain captures a previously unseen stage in the evolution of these ancient arthropods — the transformation of two-branched legs into nearly identical but separately attached limbs, one of which was destined to disappear.

“This fossil provides remarkable confirmation of the loss of a limb branch during horseshoe crab evolution, a change predicted by the common presence of two branches in the arthropods that appeared earlier, during the Cambrian explosion,” said Derek E. G. Briggs, director of the Yale Peabody Museum of Natural History and lead author of a paper to be published online the week of Sept. 10 in the journal PNAS.

The fossil dates from the Silurian period, about 425 million years ago.

Modern horseshoe crabs (Limulus) have segmented legs at the front, which they use for walking and feeding. Their rear legs form flattened gills for breathing. In their ancestors, scientists believe, these functions were combined in limbs with two branches — one limb for walking and eating, one for breathing.

Scholars have long assumed that modern horseshoe crabs had lost the extra limb branch as its function was assumed by the limbs at the rear, which form book-like gills. The newly discovered fossil, a 23 mm specimen representing a new genus and species called Dibasterium durgae, shows 4 two-branched limbs, with an important distinction: The extra branch is not attached to the primary limb, but instead originates independently on the body like an extra leg. It appears that the branches first separated before the outer one was lost.

Combined with genetic analysis, the new fossil evidence suggests that repression or loss of gene expression might have yielded the modern horseshoe crab’s appendage structure. “This discovery should prompt further investigation of the genes that control limb development in living horseshoe crabs, as the process is not fully understood,” said Briggs.

The name of the new fossil, Dibasterium durgae, refers to the double limbs and to Durga, the Hindu goddess with many arms. It was reconstructed in three dimensions by stacking digital images of physical surfaces exposed by grinding away layers in tiny increments. The fossil was found in the mid-Siluran Lagerstaette, on the English-Welsh border, a site rich in well preserved, soft-bodied fossils.

The other authors of the paper are Derek Siveter (University of Oxford), David Siveter (University of Leicester), Mark Sutton and David Legg (Imperial College, London), and Russell Garwood (University of Manchester).

Support for the research was provided by the Natural Environmental Research Council.

Author: Eric Gershon | Source: Yale University [September 10, 2012]

In horseshoe crab history, legs come and go

http://archaeologynewsnetwork.blogspot.com/2012/09/in-horseshoe-crab-history-legs-come-and.html

Silurian horseshoe crab illuminates the evolution of arthropod limbs

http://dx.doi.org/10.1073/pnas.1205875109

[Palaeontology • 2011] Shuyu zhejiangensis • Fossil jawless fish from China foreshadows early jawed vertebrate anatomy

Most living vertebrates are jawed vertebrates (gnathostomes), and the living jawless vertebrates (cyclostomes), hagfishes and lampreys, provide scarce information about the profound reorganization of the vertebrate skull during the evolutionary origin of jaws. The origin of a mouthful of jaws and teeth is one of the biggest steps in our evolutionary history but fossils have not provided any insights. Scientists from the Institute of Vertebrate Palaeontology and Palaeoanthropology (IVPP), Chinese Academy of Sciences, the University of Bristol (UK), Museum national d'Histoire naturelle (Paris, France) and the Paul Scherrer Institut (Switzerland) collaborated to study the structure of the head of a primitive fossil jawless fish called a galeaspid, Shuyu zhejiangensis, claims to have solved this scientific riddle by studying the brain of a 400 million year old fossilized jawless fish – an evolutionary intermediate between the living jawless and jawed vertebrates, according to a paper published in the journal Nature on August 18, 2011.

The extinct bony jawless vertebrates, or “ostracoderms”, are regarded as precursors of jawed vertebrates and provide insight into this formative episode in vertebrate evolution. Scientists, using synchrotron radiation X-ray tomography, describe the cranial anatomy of galeaspids, a 435–370-million-year-old “ostracoderm” group from China and Vietnam. They found the paired nasal sacs of galeaspids are located anterolaterally in the braincase, and the hypophyseal duct opens anteriorly towards the oral cavity. These three structures (the paired nasal sacs and the hypophyseal duct) were thus already independent of each other, like in gnathostomes and unlike in cyclostomes and osteostracans (another “ostracoderm” group), and therefore have the condition that current developmental models regard as prerequisites for the development of jaws. This indicates that the reorganization of vertebrate cranial anatomy was not driven deterministically by the evolutionary origin of jaws but occurred stepwise, ultimately allowing the rostral growth of ectomesenchyme that now characterizes gnathostome head development.

Instead of breaking the fossil up, they studied it using high energy X-rays at the Swiss Light Source in Switzerland, revealing the shape of the animal's brain and sense organs.

Lead author, GAI Zhi-kun, a Ph. D Student co-sponsored by the University of Bristol and the IVPP, China, said "We were able to see the paths of all the veins, nerves and arteries that plumbed the brain of these amazing fossils. They had brains much like living sharks – but no jaws", "We've been able to show that the brain of vertebrates was reorganised before the evolutionary origin of jaws."

Co-author and project designer, Professor Philip Donoghue of the University of Bristol's School of Earth Sciences said: "In the embryology of living vertebrates, jaws develop from stem cells that migrate forwards from the hindbrain, and down between the developing nostrils. This does not and cannot happen in living jawless vertebrates because they have a single nasal organ that simply gets in the way."

Professor Min Zhu of IVPP, coauthor and research designer, continued: "This is the first real evidence for the steps that led to the evolutionary origin of jawed vertebrates, and the fossil provides us with rock solid proof."

"This research has been held back for decades, waiting for a technology that will allow us to see inside the fossil without damaging it. We could not have done this work without this crazy collaboration between palaeontologists and physicists" , said Professor Philippe Janvier of the Museum national d'Histoire naturelle, Paris.

"We used a particle accelerator called synchrotron as X-ray source for performing non destructive 3D microscopy of the sample. It allowed us to make a perfect computer model of the fossil that we could cut up in any way that we wanted, but without damaging the fossil in any way. We would never have got permission to study the fossil otherwise", said Professor Marco Stampanoni of the Paul Scherrer Insitut, the location of the Swiss Light Source.

This work was supported by the Chinese Academy of Sciences, the Chinese Foundation of Natural Sciences, the Major Basic Research Projects of MST of China, the Paul Scherrer Institut, European Union FP6, the Leverhulme Trust, the Natural Environmental Research Council, the SYNTHESYS Project and a Dorothy Hodgkin studentship from the Royal Society.

Etymology. Shu (Chinese Pinyin): dawn; yu (Chinese Pinyin): fish. But essentially ‘jawed fish’; thus, Shuyu here means ‘dawn of gnathostomes’. The new genus is erected for ‘Sinogaleaspis’ zhejiangensis Pan, 1986, from the Maoshan Formation (late Llandovery epoch to early Wenlock epoch, Silurian period, ~430 million years ago) of Zhejiang, China.

Fig.1: Natural endocast of Shuyu zhejiangensis, Silurian of Zhejiang, China (IVPP V14334.5). (Image by Gai Zhi-kun)

Figure 1: Shuyu zhejiangensis, Silurian of Zhejiang, China.

a, b, Two natural endocast specimens: V14334.1 (a); V14334.5 (b). c, d, Structure of nasal and hypophyseal region magnified from the boxed region of V14334.5: digital picture (c); three-dimensional (3D) reconstruction (d). e, Virtual endocast (V14334.3). f, Restoration of external morphology. g, Synthetic restoration.

Figure 3: The nasohypophyseal complex in craniates.

Left, oblique view; right, sagittal section. The disassociation of the nasohypophyseal complex, an evolutionary prerequisite for the origin of jaws, happened at least in the common ancestor of galeaspids, osteostracans and gnathostomes (arrow). The condition of osteostracans probably converged with that of lampreys. ade, adenohypophysis; br, branchial duct or slit; eso, oesophagus; m, mouth; nc, neural cord; nt, notochord; pha, pharynx. See Figs 1 and 2 for other notation.

Shuyu -- Fossil jawless fish from China foreshadows early jawed vertebrate anatomy http://go.nature.com/NvO4yv

Fossil Jawless Fish from China Provides Evidence for the Origin of Jaws

http://english.ivpp.cas.cn/rh/rp/201108/t20110819_73948.html