Trigonotarbus johnsoniPocock, 1911, revealed by Xray computed tomography, with a cladistic

22 Pages·2014·1.3 MB·English

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Zoological Journal of the Linnean Society, 2014, 172, 49–70. With 5 figures
Trigonotarbus johnsoni Pocock, 1911, revealed by X-ray
computed tomography, with a cladistic analysis of the
extinct trigonotarbid arachnids
FIONAM.JONES1*,JASONA.DUNLOP2,MATTFRIEDMAN3andRUSSELLJ.GARWOOD4* D
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1Department of Zoology, University of Oxford, South Parks Road, Oxford OX1 3PS, UK lo
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2Museum für Naturkunde, Leibniz Institute for Research on Evolution and Biodiversity at the e
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Humboldt University Berlin, D10115 Berlin, Germany fro
3Department of Earth Sciences, University of Oxford, South Parks Road, Oxford OX1 3AN, UK m
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4School of Earth, Atmospheric and Environmental Sciences and The Manchester X-ray Imaging ttp
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Facility, School of Materials, University of Manchester, Manchester M13 9PL, UK ://a
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Received11March2014;revised22April2014;acceptedforpublication30April2014 e
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Trigonotarbids are a group of Palaeozoic arachnids, best known from Coal Measures sites in Europe and North om
America.Here,wereviewpreviousworkontheirhighersystematicsandredescribeTrigonotarbusjohnsoniPocock, /z
o
1911, from the Coseley Lagerstätte, UK, on the basis of both hand specimens and X-ray microtomography recon- olin
struction. This is a historically important species – being the eponymous taxon for the entire order – but lacks n
e
recentorcomprehensivedescription.WealsopresentthefirstcladisticanalysisofTrigonotarbida,basedonanovel an
matrixof49characters,20trigonotarbids,andfouroutgroups.Twofamilies,ArchaeomartidaeandLissomartidae, /a
were only represented by a single exemplar.At least two exemplars were scored to test monophyly for other fami- rtic
le
lies.Anthracomartidae,Anthracosironidae,andEophrynidaewereallrecoveredasmonophyletic,butPalaeocharinidae, -a
b
Trigonotarbidae, Aphantomartidae, and Kreischeriidae were not. In a wider context, our data support a s
(Trigonotarbida+Ricinulei) clade; albeit based on a limited set of outgroups. Relationships within Trigonotarbida tra
c
were not so well resolved, although two previously anticipated clades were consistently recovered in the agree- t/1
7
mentsubtreeswithstrongsupport:(1)(Palaeocharinus(Archaeomartidae+Anthracomartidae))and(2)Lissomartus 2
/1
as sister group to a so-called ‘eophrynid assemblage’ (Aphantomartus (Alkenia (Pseudokreischeria (Kreischeria /4
9
(Eophrynus+Pleophrynus))))). /3
7
9
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70. 70
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doi: 10.1111/zoj.12167 4
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ADDITIONAL KEYWORDS: Arachnida – Carboniferous – microtomography – phylogeny – Trigonotarbida. g
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8
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INTRODUCTION 2011).Historicallytrigonotarbidgeneraandspecieswere p
often diagnosed on taphonomic features, sexual di- ril 2
Trigonotarbids(Arachnida:Trigonotarbida)areanextinct 0
morphism,and/ordifferentgrowthstages.Thishasled 19
order of arachnids that ranged from the late Silurian
to the creation of numerous synonyms, which revi-
(Prˇídolí; c.420Mya) through to the early Permian
sions are gradually starting to address (Rößler, 1998;
(Sakmarian; c.290Mya; Dunlop, 1996a; Dunlop &
Garwood & Dunlop, 2011).
Rößler, 2013). Sixty-seven species are currently rec-
Thegroupappearstohavepeakedinabundanceand
ognizedintheliterature,althoughthisisprobablyan
diversity during the late Carboniferous (c. 359–
overestimate (see comments in Garwood & Dunlop,
299Mya) with the majority of fossils deriving from
the Coal Measures of Europe and North America
(Dunlop&Rößler,2013).Indeedtrigonotarbidscanbe
amongstthemostabundantarachnidsinthesestrata
*Correspondingauthors.E-mail:fi[email protected];
[email protected] (Garwood & Dunlop, 2010), with classic Westphalian
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70 49
50 F. JONES ETAL.
(315–304Mya;MoscoviantoKasimovian)localities,such (Buckland, 1837), pseudoscorpions (Woodward, 1871;
as the British Middle Coal Measures and the Saar- Geinitz,1882),andevencrabs(Woodward,1878).The
landofGermanybeingofparticularimportance.Many first author to recognize that they belonged to a dis-
exceptionallypreservedspecimensassignedtotheearly tinct–andextinct–arachnidorderwasKarsch(1882),
familyPalaeocharinidaehavebeenrecoveredfromDe- whoproposedthenameAnthracomartifortwogenera,
vonian localities. Perhaps the most famous of these plusanothergenusnowrecognizedasaphalangiotarbid
istheRhynieChertinScotland,datingto∼411.5Mya (another extinct order).An alternative ordinal name,
(Pragian; Parry etal., 2011), but valuable specimens Meridogastra, was proposed by Thorell & Lindström
havealsobeendiscoveredatBürdenbachinGermany (1885) and can occasionally be found in the older lit-
(Pragian/Emsian; Poschmann & Dunlop, 2011) and erature.Scudder(1884,1890)maintainedAnthracomarti
GilboainNewYork(Givetian;Shearetal.,1987).Gilboa asanorder,butincludedgeneraassignabletospiders D
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and Windyfield/Rhynie Chert fossils include both in- (Araneae) or ricinuleids (Ricinulei). Haase (1890) and n
dividualsandexuviae,andpreservetrigonotarbidmor- Fricˇ (1904) relegated trigonotarbids to a suborder of loa
d
phology in remarkable detail (including internal theharvestmen(Opiliones).Fricˇ’smonographwaspar- e
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anatomy), making them excellent tools for research. ticularlyproblematicinthatsometrigonotarbidgenera fro
m
Trigonotarbidsmayhavebeencursorialpredators,prob- were mistakenly assigned to the spiders (critiqued by
h
ablypreyingonsmallerarthropods(Garwood&Dunlop, Pocock, 1910). A degree of stability was imposed by ttp
s
2014).Furthermore,thepresenceofstiffsetaearound Pocock (1911), who restrictedAnthracomarti to those ://a
the mouth area, which probably acted as a filter, sug- genera that we would now recognize as core c
a
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geststhattheywereliquidfeedersthatdigestedtheir trigonotarbids. e
m
foodpre-orally(Garwood&Dunlop,2010).Anotherim- ic
portantfeatureobservedinthesespecimensisthepres- Anthracomartida and Trigonotarbida .ou
p
ence of book-lungs (Claridge & Lyon, 1961), which The name Trigonotarbida stems from Petrunkevitch .c
o
representtheoldestrecordoflungsinanyanimaltaxon. (1949) who split Anthracomarti into two, supposedly m
/z
Trabeculae and lamellar spines, which are found in unrelated,groups.HeretainedAnthracomartusKarsch, o
o
palaeocharinidbook-lungsbutareabsentfromthebook- 1882,withinAnthracomarti,alongwiththeothergenera lin
n
gills of the aquatic horseshoe crab, show that whoseopisthosomaltergitesweredividedintofivesepa- ea
n
trigonotarbids were air-breathing arachnids (Scholtz rate plates.Anthracomarti and another extinct order, /a
&Kamenz,2006;Kamenzetal.,2008).Thisprovesthat Haptopoda, were placed by Petrunkevitch in a sub- rtic
le
trigonotarbidswereunequivocallyterrestrialanimals, classStethostomata:definedasarachnidswithabroad -a
b
makingthemmembersoftheearliestknownlandfauna prosoma–opisthosomajunctionanddownward-hanging s
(Dunlop, 1996a). mouthparts. The remaining fossils – including trac
Trigonotarbids are similar in appearance to spiders Trigonotarbus Pocock, 1911 – with tergites divided t/1
7
2
but do not possess the key spider autapomorphies of intothreeplates,formedtheneworderTrigonotarbida. /1
spinnerets,silkglands,and,asfaraswecantell,ven- This was placed in its own suborder Soluta: defined /49
omous chelicerae. They also lack the naked cheliceral as arachnids with a prosoma–opisthosoma junction /37
9
fangthatunitesAraneaeandUraraneida.Despitetheir of variable width. This scheme was maintained 7
0
importance as a diverse radiation of early terrestrial by Petrunkevitch (1953), becoming the standard clas- 24
arachnids,noformalphylogenyforTrigonotarbidahas sification through its use in the Treatise on Inver- by
g
been published, and the evolutionary relationships tebrate Paleontology (Petrunkevitch, 1955a). Here the u
e
amongst the diverse families of the order remain un- order names were emended to Anthracomartida and st o
resolved. Trigonotarbid families vary widely in their Trigonotarbida to fit nomenclatural conventions. n
0
morphology(seeFig.1),withdifferencesincludingthe 8
A
structure of their carapace, degree of ornamentation, Cladistic placement p
and their opisthosomal segmentation. Trigonotarbids Little progress was made in the years subsequent to ril 2
0
also vary greatly in size, from only a few millimetres Petrunkevitch’swork,andmostauthorssimplymain- 1
9
toover50mminlength(Fig.1;Rößler&Dunlop,1997; tained his scheme (e.g. Savory, 1971). A key advance
Fayers, Dunlop & Trewin, 2005). It is this variation was the formal inclusion of at least the trigonotarbid
thatwillbeutilizedinthefirstformalcladisticanaly- arachnids in a cladistic analysis of arachnid relation-
sis of the group presented herein. shipsbyShear&Selden(1986)andShearetal.(1987).
These early efforts were further refined by Selden,
Shear & Bonamo (1991). These authors questioned
PREVIOUS WORK
the wisdom of defining Soluta on a variable charac-
DISCOVERYANDAFFINITIES OF TRIGONOTARBIDA ter state, and recovered trigonotarbids at the base of
The first trigonotarbids to be discovered were invari- the so-called Tetrapulmonata group (cf. Shultz, 1990),
ablymisidentifiedasotherarthropods,includingbeetles which otherwise includes the spiders, whip spiders
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
CLADISTICS OF THE TRIGONOTARBID ARACHNIDS 51
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Figure1. Reconstructionsofrepresentativesofninetrigonotarbidfamilies,showntoscale.A,Palaeocharinusrhyniensis by
(Palaeocharinidae).B,Archaeomartuslevis(Archaeomartidae).C,Anthracomartushindi(Anthracomartidae).D,Anthracosiro gu
e
woodwardi(Anthracosironidae).E,Trigonotarbusjohnsoni(Trigonotarbidae).F,Lissomartusschucherti(Lissomartidae). s
G,Aphantomartuspustulatus(Aphantomartidae).H,Eophrynusprestvicii(Eophrynidae).I,Kreischeriawiedei(Kreischeriidae). t on
Scale bar=10mm. 08
A
p
(Amblypygi), whip scorpions (Thelyphonida), and Tetrapulmonata). Note that Shear etal. (1987) also ril 2
0
schizomids(Schizomida).Derivedcharactersinsupport questioned the distinction between anthracomartids 19
of this placement include the presence of two pairs and trigonotarbids and Dunlop (1996b) formally pro-
of book-lungs in trigonotarbids (cf. Claridge & Lyon, posed reuniting them under the now better-defined
1961) and chelicerae of the ‘pocket-knife’ form, in nameTrigonotarbida,whichhadbythenbecomemore
which a fang articulates against the basal segment. widespread in the literature.
Trigonotarbids as tetrapulmonate relatives had been
anticipated in some earlier, noncladistic, studies (e.g. Trigonotarbids and ricinuleids?
Van der Hammen, 1977: table3; Grasshoff, 1978: AfurtherhypothesisdatesbacktoKarsch(1892),who
fig. 1) that have largely been corroborated by modern essentiallyproposedthatricinuleidswerethelastliving
analyses, leading Shultz (2007) to formally introduce descendantsoftrigonotarbids.Althoughricinuleidshave
a clade Pantetrapulmonata for (Trigonotarbida + conventionallybeenresolvedasthesistergroupofthe
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
52 F. JONES ETAL.
mites(Acari)basedonthepresenceofsix-leggedlarvae, and Aphantomartus Pocock, 1911, assigned to
asuiteofpotentialsynapomorphiesunitingricinuleids Eophrynidae.Additionally,Haase’sKreischeriidae(1890)
andtrigonotarbidshavebeenidentified(Dunlop,1996c; was synonymized with Eophrynidae (but see below)
Dunlop, Kamenz & Talarico, 2009). These include: (1) andFricˇ’sPromygalidae(1904)wasformallysunkinto
thedividedopisthosomaltergites;(2)acurious‘locking- Anthracomartidae.Afewyearslater,Hirst(1923)intro-
ridge’,whichcouplestheprosomaandopisthosomato- duced the name Palaeocharinidae for the exception-
gether; and (3) a pedipalp ending in a small, chelate allypreservedRhynieChertfossilsfromtheDevonian
claw. To this list is added the observation of Talarico, of Scotland.
Lipke & Alberti (2011: fig. 1) that ricinuleids bear a
seriesofcuticularprojectionsinthemouthregionthat
Petrunkevitch
look remarkably similar to corresponding structures D
Petrunkevitch (1945) proposed Coryphomartidae and ow
intheRhynieCherttrigonotarbids(Dunlop,1994a:fig. n
4)andwereassumedtorepresentsomesortofpreoral Pleomartidae for the NorthAmerican Coal Measures loa
genera Coryphomartus Petrunkevitch, 1945, and d
filtering device. In light of this and other evidence, e
Giribetetal.(2002)recovered(Trigonotarbida+Ricinulei) PevleidomenatrlytuasnPtehtrraucnokmeavirttcihd,s1a9n4d5,threesspeecgteinveelrya.Bwoetrhearree- d from
to the exclusion ofAcari. If this hypothesis is correct,
centlysynonymizedwithAnthracomartusbyGarwood h
ricinuleidsmaybemorecloselyrelatedtospidersthan & Dunlop (2011). Even Petrunkevitch (1953: 59) later ttps
they are to mites. recognized that his 1945 families are junior syno- ://a
c
nyms of Anthracomartidae. In the 1945 monograph ad
e
FAMILIALGROUPS another new family, Aphantomartidae, was recog- m
ic
Nine trigonotarbid families are currently recognized nized for Pocock’s Aphantomartus (1911) and another .o
u
genus previously assigned to the eophrynids named p
in the literature (Fig.1); each represented by at least .c
Trigonomartus Petrunkevitch, 1913. Yet in a subse- o
one species in the present analysis (see below). The m
currentfamilialstructuredevelopedgraduallyoverthe quentstudyPetrunkevitch(1949)abandonedthename /zo
last130years;althoughasnotedbelowtherehavebeen AphantomartidaeandsubstitutedTrigonomartidaefor olin
essentiallythesameassemblageofgenera.Thismove n
remarkably few attempts to resolve relationships e
a
amongst these different lineages or even to test the was criticized by Selden & Romano (1983), who re- n/a
monophyly of the family groups. The oldest available turned to the older name Aphantomartidae and also rtic
nthaemdeisitsinEctoipvheraynndidhaeea,viinlytroordnuacmeednbteydKgaernsucshE(1op8h8r2y)nfuors saylsnoonRyömßliezre(d19T9r8ig)ofnoormaarretvuissiownitohfAthpihsafnamtoimlya].rtFuisna[slelye, le-abs
Woodward, 1871. Note that Karsch originally placed in his 1949 monograph Petrunkevitch removed tra
c
hisnewgenusAnthracomartusinthephalangiotarbid Trigonotarbus from the anthracosironids and raised a t/1
fwaamsilfiyrAstrcrheictoagrnbiidzeade.bAyfaHmaialyseg(r1o8u9p0A),nwthhroacaolmsoarintitdraoe- ntheawtfhaemmilyi,ssTpreigltonthoteanrbaimdaee‘,Ttroicaocgcoonmotmaorbdiadtaeei’ti.nNtohtee 72/1/4
ducedKreischeriidaeforthegenusKreischeriaGeinitz, systematic heading on p. 250. This is presumably a 9/3
7
1882.ThenextoldestfamilynameisAnthracosironidae, lapsus calami as the name is spelt correctly in a pre- 97
ceding family key on p. 236. 0
raised by Pocock (1903) for the unusual looking 2
4
AnthracosiroPocock,1903,withitslarge,raptorialfore- b
y
legs.Fricˇ (1904)erectedthefamilynamesPromygalidae Further families gu
e
and Hemiphrynidae. However, both encompassed InrecentyearsDunlop(1995)addedLissomartidaefor st o
trigonotarbidfossils,whichhemisidentifiedasspiders the Mazon Creek genus Lissomartus Petrunkevitch, n
0
(see above). These names are now considered junior 1949, arguing that its unique character combination 8
A
synonyms of Anthracomartidae and Eophrynidae, of a weakly lobed carapace but little dorsal ornamen- p
respectively. tationmeritedaseparatefamily.Rößler&Dunlop(1997) ril 2
0
redescribed Kreischeria Geinitz, 1882, and, based on 1
9
Pocock and Hirst this, revalidated Haase’s Kreischeriidae (1890); dis-
Pocock’s (1911) monograph on the British Coal Meas- cussingtheminordifferencesinopisthosomalsegmen-
ures arachnids introduced Brachypygidae for two tationthatservetodistinguishkreischeriidsfromthe
anthracomartid genera with a scalloped (as opposed probably closely related eophrynids (see below). The
to a smooth) opisthosomal margin: Brachypyge most recent family to be proposed is Poschmann &
Woodward, 1878, and Maiocercus Pocock, 1911. Dunlop’s (2010) Archaeomartidae, which was recog-
This family is now regarded as a synonym of nizedfortheDevoniangenusArchaeomartusStørmer,
Anthracomartidae(seealsoGarwood&Dunlop,2011). 1970.Originallyonlyknownfromisolatedopisthosomas,
In the same monograph, Pocock established two new newmaterialallowedabetterappreciationofbothits
genera:Trigonotarbus,assignedtoAnthracosironidae, anatomy and possible affinities.
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
CLADISTICS OF THE TRIGONOTARBID ARACHNIDS 53
HIGHER SYSTEMATICS that these lines – which separate the ventral seg-
mentsintomedianandlateralplates–foreshadowthe
The relationships amongst the trigonotarbid families
continuous marginal ventral suture line seen in
are poorly understood, with the only cladistic analy-
anthracomartids. The recently recognized family
sis for internal phylogeny presented in the unpub-
Archaeomartidae (see above) possesses a number
lished thesis of Dunlop (1994b). Based in part on
of anthracomartid synapomorphies, and as a result
stratigraphical distribution, some possible evolution-
appears as a morphological intermediate between
arytrendshavebeenproposedwithcorrespondinglinks
Palaeocharinidae andAnthracomartidae.Accordingly
between certain taxa. For example, the presence of
this may be sister group to the Anthracomartidae to
multifacetted lateral eyes has been interpreted as the
theexclusionofPalaeocharinidae(Poschmann&Dunlop,
plesiomorphiccharacterstateforTrigonotarbidabased
2010: fig. 9). D
on outgroup comparison with eurypterids and horse- o
w
shoecrabs.ThistraitisobservedintheDevonianfamily n
lo
Palaeocharinidae(Hirst,1923;Shearetal.,1987;Fayers The eophrynid assemblage a
d
etal., 2005). The loss of the lateral eyes would there- ThreeCoalMeasuresfamilieswereproposedbyDunlop ed
fore represent an apomorphic state defining a more &Brauckmann(2006)asamonophyleticeophrynidas- fro
m
restricted clade of trigonotarbids. Some of these po- semblage. Here, there is a putative trend towards a h
tentiallyderivedtaxaalsoexpressamoresubtriangular structurallycomplexcarapacewithlaterallobespresent. ttp
s
carapace,asopposedtothesubrectangular,morebox- Furthermore,thesetrigonotarbidsaretypicallyhighly ://a
like carapace of palaeocharinids. Other potentially ornamented,oftenwithdensedorsaltuberculationand ca
d
apomorphictrendselucidatedbyDunlop(1994b)include posterior opisthosomal spines. Two of its constituent em
reduction of the locking-ridge between the two halves families,KreischeriidaeandEophrynidae,wereatone ic
.o
ofthebodyandtheseparationofopisthosomaltergites stage treated as synonyms (see above). The third pu- up
twoandthree,whichinmosttrigonotarbidsarefused tative member isAphantomartidae. This family com- .co
m
together into a single diplotergite. In a wider context, prisesindividualswithdeeplylobedcarapacesandheavy /z
andinanefforttominimizethenumberofmonotypic tuberculation,andthussharessomefeatureswithboth oo
higher taxa, species such as Namurotarbus roessleri KreischeriidaeandEophrynidae.Thesepatternsofchar- linn
e
(Dunlop & Brauckmann, 2006) were deliberately not acter distribution make it difficult to determine rela- a
n
assignedtoafamilyand/orreferredtoTrigonotarbida tionshipsbetweenthethreeputativeassemblagesand /a
incertae sedis (see also comments in Poschmann & theirproposedmembers(seealsoMiller&Forbes,2001). rticle
Dunlop, 2010); it may prove necessary to create new -a
b
families to accommodate them. This study will test TRIGONOTARBUS JOHNSONI stra
(where possible) the monophyly of the classic fami- c
lies, investigate the placement of species whose fa- Trigonotarbusjohnsoniisakeyspecies,beingthename- t/17
2
milial affinity is equivocal, and test proposals already giving taxon for the order Trigonotarbida. Further- /1
in the literature such as the two hypotheses outlined more,itrepresentsawell-preservedspeciessuperficially /49
below. similarinappearancetotheearliestknownbutpoorly /37
9
preservedtrigonotarbidPalaeotarbusjerami,andisnot 7
0
an overt member of either the eophrynid assemblage 24
Palaeocharinds and anthracomartids northePalaeocharinus/anthracomartidgroup.Indeed, by
g
BothPalaeocharinidaeandAnthracomartidaepossess both of these groupings have been recently restudied u
e
lateral eyes, have comparable carapace shapes, and with the aid of X-ray microtomography (micro-CT; st o
similarlimbproportions.Indeedthesesimilaritieswere Garwood,Dunlop&Sutton,2009;Garwood&Dunlop, n
0
one of the principal arguments for recombining 2011; Dunlop & Garwood, 2014). For this reason we 8
A
TrigonotarbidaandAnthracomartida(cf.Dunlop,1996b). includedaredescriptionofTr.johnsonibasedonrestudy p
A recent study has provided a further possible of the original material and a micro-CT scan in the ril 2
0
synapomorphy in the form of endites projecting from present study. 19
the coxae (Garwood & Dunlop, 2011). Further evi- TrigonotarbusjohnsoniwaserectedbyPocock(1911)
dencelinkingPalaeocharinidaeandAnthracomartidae basedonaseriesoffossilsfromthefamousCoalMeas-
isthepresenceofpseudodivisionsinthedorsallateral ures site of Coseley near Dudley in the English West
platesofPalaeocharinustuberculatusFayersetal.,2005. Midlands (see Material and methods). These speci-
These could be considered a precursor to the formal mens originated from the Egginton, Johnson, and
divisionsseenintheanthracomartids,whichgiverise Madeleycollections.HenryJohnson(1823–1885),after
to their characteristic five plates per opisthosomal whom the species is named, was a civil and mining
segment.Similarly,divisionscanbeseenonthefourth engineer and a Fellow of the Geological Society who
sternite and posterior operculum of Palaeocharinus lived in Dudley and was noted as an avid fossil col-
tuberculatus (Fayers etal., 2005). It could be argued lector (Jones 1885). Trigonotarbus johnsoni is one of
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
54 F. JONES ETAL.
the smaller Coal Measures trigonotarbids, typically SPIERS software suite (Sutton etal., 2012). Inverse
about5–6mminbodylength,andhasarathersimple linearthresholdimagesweregenerated,masksapplied,
body plan without strong ornamentation of the body. and isosurfaces created, following the protocol out-
The carapace is notably triangular and is presum- linedbyGarwoodetal.(2012).Publicationfiguresand
ably the source of the genus name: a combination of animations were rendered with the aid of the open
theancientGreektrigono (τρ(cid:2)γωνo=triangle) andthe sourceraytracerBLENDER(Garwood&Dunlop,2014).
suffix tarbos (τ(cid:3)ρβoς=terror). The carapace has a Missing elements of the anatomy (e.g. the limbs are
raisedcentralridgebearingapairofmedianeyes.The obscuredinplacesbythecrackalongwhichthenodule
legsarefairlyshortandstubby.Asnotedabove,Pocock wassplit)weremanuallymodelledinBLENDERbased
(1911) originally allied this species with Anthracosiro on more complete elements of the model. These are
in Anthracosironidae, before Petrunkevitch (1949) rendered transparent in both Figure3 and video. The D
o
w
placed it as the type and only genus of a new family animationsareprovidedasSupportingInformation(File n
Trigonotarbidae. S2), as is a VAXMLdata set of the virtual fossil (File loa
d
S3; Sutton etal., 2012).Acombination of this and the e
d
handspecimensthemselveswereusedtocreateanideal- fro
MATERIALAND METHODS m
ized reconstruction of the species (Fig.4).
h
FOSSILSPECIMENS ttp
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Tmreignosn(osteaerbSuysstjeomhnastoicnipaislakenoonwtonlofgroym;Faigt.l2ea),satl1l3hosupesecid- CLADISTICANALYSIS ://aca
in the Natural History Museum London (NHMUK). Character coding and taxon selection de
m
The fossils are from the Late Carboniferous, similis– Forthisnovelanalysismorphologicalcharacterstate- ic
mentswerederivedfromboththeliteratureanddirect .o
pulchra zone of the Clay Croft open-cast works at u
p
Coseley near Dudley, Staffordshire, UK. observationoftrigonotarbidtaxaintheformofvirtual .c
o
fossilsofAnthracomartushindiandMaiocercuscelticus m
sibTleh,isiswpealrl-tkonfotwhneBlorciatilsithy,MwidhdiclheCisoanloMloenagseurreasccaensd- (Garwood&Dunlop,2011),Eophrynusprestvicii(Dunlop /zoo
isconventionallyassignedtotheDuckmantianregion- & Garwood, 2014), and the model of Tr.johnsoni pre- lin
n
sented herein. Forty-nine discrete characters (Appen- e
al stage (c.313Mya; Pointon etal., 2012). This corre- a
spondstoWestphalianBintheEuropeanstratigraphical dix 1) were coded for 20 taxa (Appendix 2) and three n/a
scheme, and Moscovian in the ICS International outgroups.ThematrixisavailableasFileS1.Thetwo rtic
Chronostratigraphic Chart. The rich fossil biota morphologicallybest-knownspecieswereselectedfrom le-a
foundhereincludesferns,wingedinsects,xiphosurans, efrigomhtftahmeilmieosntoottyepsticmfoanmopilhyylLyi,swshomeraeratsidthaeesaolnedsptehcrieees bstra
arachnidsincludingscorpionsandtrigonotarbids,and c
crustaceans.Specimensareusuallypreservedinclay- species of unknown familial affinity were also coded. t/17
ironstone(siderite)nodulesandthereforeoftenretain The palpigrade Eukoenenia mirabilis (Grassi & 2/1
Calandruccio, 1885), amblypygid Phrynus longipes /4
adegreeofthree-dimensionalityandremarkabledetail 9
(Pocock,1894),ricinuleidRicinoideskarschii(Hansen /3
(Fig.2).Thetechniquesofvirtualpalaeontology(Sutton, 7
Rahman&Garwood,2014)areanexcellentwayofvisu- andSørensen,1904),andmesothelespiderHeptathela 970
bristowei(Gertsch,1967)wereusedasoutgroups.The 2
alizingthevoidleftbythefossilinthematrix(Garwood 4
firstwaschosenasagroupofunresolvedaffinities,but b
etal.,2009;Garwood&Sutton,2010,2012;Leggetal., y
2012). Hand specimens were studied and photo- whichretainsanumberofseeminglyplesiomorphicarach- gu
e
nid characters (Dunlop, 2010), whereas amblypygids s
graphed using a Leica MZ16A stereomicroscope. In- t o
cident lighting was used, and photographs taken at andspidersaretetrapulmonatesandthusmembersof n 0
multiple focal depths were combined using the soft- thepositedsistertaxontotrigonotarbids(e.g.Shultz, 8 A
wINaKreSCCAomPEbi0n.e4Z8M. before plates were assembled in 2of00a7s)i.sRteicri-ngruolueipdsrewlaetrieoninschliupdweditthottheestttrhigeopnoostsairbbiilditsy. pril 2
0
1
9
Analysis
TOMOGRAPHIC RECONSTRUCTION AnalyseswereperformedinthesoftwarepackageTNT
NHMUK I. 15860 was selected to scan because it dis- v. 1.1. (Goloboff, Farris & Nixon, 2008; made avail-
played the greatest three-dimensionality of the avail- ablewiththesponsorshipoftheWilliHennigSociety)
able specimens. The scan was conducted on a Nikon using traditional search options: tree bisection-
HMX-ST225attheNaturalHistoryMuseum,London, reconnectionwith1000replicates,saving100treesper
with a tungsten reflection target at 165kV/205μA, cycle. Multistate characters were unordered. Equal
0.1mm copper filter, and 3142 projections. CT PRO weighting resulted in 76 most parsimonious trees
wasusedtocreateatomographicdatasetwithavoxel of 116 steps, with a strict consensus showing limited
sizeof11.2μm.Reconstructionswerecreatedusingthe resolution.TNTwasusedtocreatebothconsensusand
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
CLADISTICS OF THE TRIGONOTARBID ARACHNIDS 55
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Figure2. Hand specimens of Trigonotarbus johnsoni from the NHMUK collections. Scale bars=1mm.
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
56 F. JONES ETAL.
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Figure3. Tomographic reconstruction of Trigonotarbus johnsoni based on specimen NHMUK I. 15860.A, dorsal view. n
/a
B, fourth right leg, podomeres labelled. C, ventral view. D, ventrolateral view of the coxo-sternal region.Abbreviations: rtic
1–12,segmentnumber;CE1−2,coxalendites1–2;CH,chelicerae;CL,clypeus;FE,femur;L1−L4,legs1–4;ME,median le
eyetubercle;MT,metatarsus;PA,patella;PP,pedipalp;PR,projection;TA,tarsus;TI,tibia;TR,trochanter.Scalebars: -ab
s
A, C=2mm, B=1mm, D=0.5mm. tra
c
t/1
7
calculated for the agreement subtree by manually 2
/1
pruningwildcardtaxa.Jack-knifeandbootstrapnodal /4
9
support included as group present/contradicted fre- /3
7
quencydifferences.Analyseswerealsoconductedwith 9
7
implied weighting (Goloboff, 1993) using a variety of 02
4
concavity constants (k=1/4, 1, 3, and 10). Different b
y
k-values provided slight changes in the trees; accord- g
u
ingly we present a consensus, and agreement subtree es
of analyses at different concavity constants (Fig.5). t o
n
0
8
A
p
SYSTEMATIC PALAEONTOLOGY ril 2
0
TRIGONOTARBIDAPETRUNKEVITCH, 1949 1
9
TRIGONOTARBIDAE PETRUNKEVITCH, 1949
Figure4. An idealized reconstruction of Trigonotarbus
johnsonibasedonthecomputedtomographyscanofNHMUK TRIGONOTARBUS POCOCK, 1911
I.15860andadditionalhandspecimens.Scalebar=2mm. Type species
Trigonotarbus johnsoni Pocock, 1911, by original
designation.
agreementsubtrees,andprovidejack-knife(Farrisetal.,
1996; 33% removal probability, 1000 replicates), boot- Included species
strap(Felsenstein,1985;1000replicates),andBremer Trigonotarbus arnoldi Petrunkevitch, 1955b;
support (Bremer, 1994) values. Bremer support was Trigonotarbus stoermeri Schultka, 1991.
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
CLADISTICS OF THE TRIGONOTARBID ARACHNIDS 57
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Figure5. The results of the cladistic analysis. The four trees show, as labelled, the agreement subtree and strict con- /3
7
sensus of both the equally weighted analysis and implied weights analyses with concavity constants (k) of 0.25, 1, 3, 9
7
and 10. 02
4
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TRIGONOTARBUS JOHNSONI POCOCK, 1911 1996a Trigonotarbus johnsoni Pocock; Dunlop, t on
1911TrigonotarbusjohnsoniPocock,pp.74–75,fig.38, pp. 611–612, text-fig. 4. 08
A
pl. 3, fig. 4. p
1913TrigonotarbusjohnsoniPocock;Petrunkevitch, ril 2
Holotype 0
p. 98. NHMUK In 31239. From Coseley near Dudley, Staf- 19
1949TrigonotarbusjohnsoniPocock;Petrunkevitch,
fordshire,UK.LateCarboniferous(similis–pulchrazone,
pp. 250–255, figs 104–109, 111, 250–257.
WestphalianBintheEuropeanstratigraphicalscheme
1953 Trigonotarbus johnsoni Pocock; Petrunkevitch
andMoscovianinaninternationalstratigraphicalframe-
89–90, fig. 165.
work; Wilson, 2005).
1955aTrigonotarbusjohnsoniPocock;Petrunkevitch
p. 112, figs 77(2), 79(1–2).
1955bTrigonotarbusjohnsoniPocock;Petrunkevitch Additional material
p. 475. NHMUKI.7895,I.13911,I.13919,I.13921,I.15859,
1991 Trigonotarbus johnsoni Pocock; Schultka, I.15860,I.15897,In31240–41,In31243,andIn31254–
pp. 377, 381. 55. All from the same locality as the holotype.
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70
58 F. JONES ETAL.
Emended diagnosis narrow.Ventrally,smallanteriorandposterioroperculae
Small, stubby-limbed trigonotarbids with triangular abut coxae of leg 4. Sternites strongly posteriorly
carapace,lackinglaterallobes,butwitharaisedmedian recurved, especially towards the back, but sternite 4
ridge bearing the eyes and a deep, inverted T-shaped expressed as straight transverse ridge, visible in both
depressionbehindtheeyes.Roundedopisthosomahas tomographic reconstruction and in NHMUK In 31241
laterallyundividedtergitenine,apparentlywithfused and In 31240. Sternites 9+10 apparently fused (but
sternites9and10bearingthepygidiumattheirante- see Discussion). Pygidium towards anterior rounded
rior. (Emended from Petrunkevitch, 1955b.) marginofsternites9+10.Noevidenceofventralsacs
on underside of opisthosoma. Generally, no visible or-
Description namentation(spines,pustules,tubercles,etc.)oneither
Trigonotarbus johnsoni was described in some detail prosoma or opisthosoma. D
o
w
by Pocock (1911) and Petrunkevitch (1949). Here, we n
redescribeitfromrestudyofthehandspecimens(Fig.2) loa
d
and tomographic reconstruction of NHMUK I. 15860 e
RESULTS d
(Fig.3, Files S2, S3). Except where noted, measure- fro
ments derive from the latter. Small trigonotarbid; CLADISTIC RESULTS m
h
holotype 4.8mm long (carapace 2.0mm in length, Wepresentourresultsinfourtrees(Fig.5):thestrict ttp
s
opisthosoma 2.8mm long by 2.5mm wide); scanned consensus and agreement subtrees for both equally ://a
specimen6.3mminlength(carapace2.8mminlength, weighted (EW) and implied weighting analyses (IW, c
a
d
opisthosoma 3.5mm long by 3.6mm wide). Carapace the latter combining concavity constants of 1/4, 1, 3, e
m
triangularwithraisedmedianarea,increasinginwidth and 10; individual trees reported in Supporting Infor- ic
posteriorly (Fig.3A). Raised median area drawn into mation File S4). The spider (H. bristowei) and .ou
p
anteriorly pointing, rounded clypeus, surrounded by amblypygid(Phrynuslongipes)arerecoveredeitheras .c
o
zones of lower relief. Carapace with smooth lateral apolytomyintheEWstrictconsensus,oras(Phrynus m
/z
margins (see, e.g. NHMUK In 32139), i.e. no division longipes (H.bristowei (Trigonotarbida+Ricinulei))) in o
o
into lobes, posteriorly demarcated by strong trans- the IW analyses. The ricinuleid (R.karschi) is in a lin
n
versegroove;somespecimens(e.g.NHMUKIn31241) polytomy with the trigonotarbids in the EW consen- ea
n
revealdepressiononmedianridgebehindtheeyesand sus as a result of synapomorphies shared with the /a
shaped like an inverted T that effectively merges into trigonotarbids, such as a broad prosoma/opisthosoma rtic
le
this groove. Closely spaced median eyes situated on boundary, terminal palpal chela, and divided -a
b
median ridge, towards front of carapace (NHMUK In opisthosomal tergites. IW analyses recover the s
31239; Fig.2; NHMUK I. 15860, Fig.3). relationship(Phrynuslongipes(H.bristowei(R.karschi trac
Ventral prosoma comprising triangular coxae, in- (Trigonotarbida)))), whereby trigonotarbid t/1
7
2
creasing in size posteriorly (e.g. NHMUK I. 13239, synapomorphiesincludethepresenceofaclypeus,the /1
I.15897,In31241,Fig.3;1.1–1.3mm),truncateagainst median eye position, the absence of a sternite belong- /49
a central sternum. Sternum itself four-sided, ing to the first opisthosomal segment, the curvature /37
9
almost diamond shaped. NHMUK In 31240 suggests ofthesternites,andthepresenceofapygidiumformed 7
0
a pointed anterior sternal margin. Tomographic re- fromtworing-likesegments.Thereisalargepolytomy 24
construction reveals a dorsoposteriorly angled, trans- at the base of the trigonotarbids in the EW consen- by
g
verse groove between pedipalp coxae, and those of sustree(whichincludesthericinuleidR.karschi),and u
e
leg 1 (Fig. 3D). Medial boundary of leg 1 coxae thusthisanalysisisrelativelyuninformative.Wenote st o
developed into small, lip-like endites, with median that equal weighting may not be the most appropri- n
0
anteriorly pointing projection between (Fig.3D, PR). ate scheme for an analysis of this kind (see, e.g. com- 8
A
Small,palaeognath(i.e.downward-hanging)chelicerae ments in Legg, Sutton & Edgecombe, 2013). p
ventral to clypeus (Fig.3C). Legs short and stubby, DespitetheEWconsensustreehavinglimitedreso- ril 2
0
without strong ornament; 2–4 on right well pre- lution, some clades are common to all of the analy- 1
9
served (L4 shown in Fig.3B): small, bulbous tro- ses:AnthracosirowoodwardiandArianrhodabennetti
chanter(0.8mmonleg4R,chosenasbestpreserved), are consistently recovered as sister groups, sharing
femur (1.1mm), patella (0.8mm), and tibia (0.9mm) a rounded carapace shape, and an opisthosoma dis-
of similar length, short metatarsus (0.3mm), longer tinctly longer than wide with subparallel lateral
tarsus (0.8mm). margins. A clade comprising (Archaeomartus levis
Opisthosoma rounded; dorsal segmentation clear in (M.celticus+Anthracomartushindi))isdefinedbythe
modelandNHMUKIn31243.Tergite1apparentlyex- median axis of the carapace possessing a depression,
pressed as anterior ridge on tergite 2; itself partially opisthosomal median sclerites less than half of body
tuckedunderthecarapace(Fig.3A).Noapparentfusion width,andagranulardorsalcuticle(althoughnotethis
of tergites 2 and 3 into a diplotergite. Tergite nine character is also found in Tynecotarbus tichaveki).
© 2014 The Linnean Society of London, Zoological Journal of the Linnean Society, 2014, 172, 49–70