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AMERICANt MUSEUM

NorntatesPUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORYCENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024

Number 3231, 16 pp., 28 figures, 1 table June 10, 1998

Centiped Legs (Arthropoda, Chilopoda,Scutigeromorpha) from the Silurian and Devonianof Britain and the Devonian of North America

WILLIAM A. SHEAR,1 ANDREW J. JERAM,2 AND PAUL A. SELDEN3

ABSTRACT

Remains of arthropod legs with a pentagonalcross section and serrate margins, found at threeSilurian and Devonian sites (Ludford Lane,Wales; Rhynie, Scotland; and Gilboa, New York,USA), are herein attributed to teffestrial scutig-eromorph centipeds. The Silurian and Devonianlegs are distinct from each other, from previouslydescribed Carboniferous remains, and from mod-em scutigeromorphs, but the general pattern andmany of the details of leg construction in these

centipeds seems to have been conserved over a415 million year history. The legs are attributedto a new scutigeromorph genus, Crussolum,placed in a new monobasic family Crussolidae;fairly complete remains from the Devonian of Gil-boa, New York, are assigned to the new speciesCrussolum crusserratum Shear. The Silurian(Ludford Lane) and Rhynie legs are too poorlyknown to be given a species epithet, but morethan one taxon may be present.

INTRODUCTION

One of the most distinctive isolated exo-skeletal elements found by hydrofluoric acidmaceration in the intensively studied MiddleDevonian (Givetian) Gilboa fauna of terres-trial arthropods is the "sawblade" or serratepodomere, initially attributed to a scutigero-

morph centiped (Shear et al., 1984). Thesepodomeres are characterized by a pentangu-lar cross section, with each of the anglesridged and set with distally pointing cuticularteeth, which on better preserved examplessubtend small setal sockets. Arthropod po-

I Research Associate, Department of Entomology, American Museum of Natural History; Professor, Departmentof Biology, Hampden-Sydney College, Hampden-Sydney, Virginia 23439.

2 Keeper of Palaeontology, Ulster Museum, Botanic Gardens, Belfast BT9 5AB, N. Ireland, UK.3Senior Lecturer, Department of Geology, University of Manchester, Manchester M13 9PL, UK.

Copyright C American Museum of Natural History 1998 ISSN 0003-0082 / Price $2.30

AMERICAN MUSEUM NOVITATES

TABLE 1Specimens Studied

BriefSlide no. Accession no.a Figure description

Crussolum crusserratum329/AR35 AMNH 43162 17 tibia334/1a/AR16 AMNH 43163 prefemur334/lb/ARI AMNH 43164 16 femur334/lb/AR78 AMNH 43165 11-13, 19 tarsus411/2/AR20a AMNH 43166 prefemur411/7/AR14b 18 tibia + tarsus41 1/7/AR44 AMNH 43167 tibia411/15/AR8 AMNH 43168 tibia411/15/AR15 AMNH 43169 tibia2002/12/AR12 AMNH 43170 8, 14 prefemur2002/12/AR15 AMNH 43171 prefemur2002/12/AR20 AMNH 43172 tibia2002/12/AR21 AMNH 43173 9 tibia

Crussolum sp. from Ludford LaneDE 1.4.2/50 UM K25082 21, 22 femur + tibiaDE 1.4.12/60 UM K25083 23 femurDE 3.1.1/88A UM K25084 femur + tibiaDE 3.1.18/105 UM K25085 tibiaDE 3.2.32.141 UM K25086 tibiaDE 4.1.9/48 UM K25087 25 tibiaDE M.2.8/181 UM K25088 tibiaLE 1.6/15/76 UM K25089 tibiaLL 1.6/15/76 UM K25090 tibiaLL/S10/1/6 UM K25091 tibiaLL Orig "cent tibia" UM K25092 tibia

Rhynie specimen UM K25093 tibiae?

a AMNH: American Museum of Natural History, UM: Ulster Museum.b Unfortunately this important slide was destroyed in a laboratory accident.

domeres have been recovered from the Up-per Silurian (Pridoli) Ludford Lane deposit(Jeram et al., 1990), characterized by the ser-rate margins of at least some of the podom-eres, strikingly similar to the Gilboa "saw-blade" leg segments. The best articulated ex-amples from Ludford Lane, however, cannotwith certainty be attributed to the same taxonas the serrate podomeres. Careful searchingof Rhynie Chert thin sections by one of us(AJJ) has revealed small sections of nearlyidentical podomeres.

All the fossils discussed here, with the ex-ception of the single Rhynie example, wereobtained by hydrofluoric acid maceration ofshales, mounted on microscope slides andstudied and photographed using NomarskiDifferential Interference contrast optics. The

Ludford Lane and Rhynie specimens are de-posited in the Ulster Museum, Belfast, andthe Gilboa specimens in the American Mu-seum of Natural History, New York. Table 1provides the slide numbers engraved on eachslide and the corresponding museum acces-sion number.

ACKNOWLEDGMENTS

P. M. Bonamo, of SUNY Binghamton,oversaw the preparation of specimens fromGilboa, and was responsible, with the late J.D. Grierson, for the original discovery of thatfauna; the Hudwick Dingle slides were pre-pared in the Cardiff laboratory of D. Ed-wards, who also provided bulk samples forpreparation in Manchester. P. Manning gave

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SHEAR ET AL.: CENTIPED LEGS

technical assistance in Manchester. We alsothank J. Hannibal of the Cleveland Museumof Natural History and G. Buckley of theField Museum of Natural History, Chicago,for the loan of specimens of Latzelia primor-dialis, and Hannibal for the photograph of thatspecies. We wish to thank E. L. Smith, SanFrancisco, and the late R. Crabill for sugges-tions on the identity of the Gilboa specimens,early in the work on that fauna, and H. Bo-rucki, University of Hamburg, Germany, forhis comments at a later stage. This researchwas supported by National Science Founda-tion Grants BSR-8216410, DEB-9112487,and DEB-9508573 to W. A. Shear, and NERCGrant GR3/7882 to P. A. Selden.

ATELOCERATE LEGS

We briefly considered an arachnid identityfor the legs discussed here, but the presenceof prefemora and the single claw of the tar-sus do not support this hypothesis, and leavethe various classes of Atelocerata for consid-eration.

Homologies of leg podomeres among theArthropoda have been the subject of exten-sive debate. Difficulties have arisen in partbecause the same names have been used forpodomeres that may not be homologous,and different names have been used forclearly homologous podomeres, even withintaxa that are relatively uniform in leg struc-ture. Kukalova-Peck (1978, 1983, 1986,1990) has attempted to integrate informationobtained by careful study of fossil insectswith the results of modem insect morphol-ogy. The details of her work are beyond thescope of this article, but fundamentally shesuggests that the primitive arthropod legwas multiramous (neither biramous nor uni-ramous) and that its "stem" consisted of 11segments. In the course of evolution, thenumber of stem segments and rami has beenreduced in all extant arthropod groups. (Inthe following discussion, the podomerenames sensu Kukalova-Peck are precededby the letters KP.) In the Atelocerata (Chil-opoda, Hexapoda, Symphyla, Diplopoda,and Pauropoda), according to Kukalova-Peck (1978, 1990) the two basal podomeres,epicoxa and subcoxa, have been subsumedinto the lateral body wall. The coxae of all

Atelocerata are evidently homologous assuch. However, the trochanter is hypothe-sized to be a synthetic podomere resultingfrom the fusion of the KPtrochanter and theKPprefemur; in some Paleozoic insects, andpossibly in the extinct Euphoberiida, theline of fusion can still be detected (Kuka-lova-Peck, 1978). Thus the KPfemur is theinsect femur, but is called the prefemur inmyriapodous atelocerates. The KPpatellahas fused to the KPtibia in all living insects(but remains partially free in some Paleo-zoic ones), while in the myriapodous class-es, the KPpatella is called the femur and re-mains a distinct segment. For both insectsand myriapodous classes the KPtibia is thesame as the tibia sensu auctorum. TheKPbasitarsus and KPdistitarsus are regardedas distinct segments, and may be subject toeither extensive fusion or subdivision; someauthors recognize a basitarsus in hexapods,but in such groups as Diplura the tarsus isunitary and evidently a fused basitarsus +distitarsus. Among myriapods, millipedshave a unitary tarsus (where a divided tarsusoccurs, as in some species of the order Cal-lipodida, it is clearly secondary) and centi-peds frequently retain the distinction be-tween basitarsus and distitarsus. The postar-sus is uniformly recognized in all groups,but is often simply called a claw in myria-pods. Thus the fundamental difference be-tween the insect leg and the myriapod leg isthe plesiomorphic presence of two segments(femur [KPpatella] and tibia) between theprefemur (KPfemur) and the tarsus in thelatter; only the tibia and tarsus are distal tothe knee in hexapod legs. Additionally, allpterygote insect thoracic legs bear two ar-ticulated claws on the tarsus, while those ofmyriapodous arthropods have at most a sin-gle accessory claw, the functional claw be-ing the postarsus.The presence of a free prefemur and a sin-

gle tarsal claw strongly indicates that the legsdiscussed below are not from insects, and asimilar argument, based on the presence oftwo articles preceding the "knee" podomere,excludes arachnids. No known fossil or ex-tant diplopods have multiarticulate tarsi. Thestrongly apomorphic legs of symphylans andpauropods have reduced numbers of podo-meres, with strikingly different proportions;

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symphyla have two tarsal claws. Thus wehave concluded that the legs are from a chi-lopod. Among chilopods, only scutigero-morphs have legs pentagonal in cross sectionand having marginal spines on the anglessubtending small setae. Likewise, multiarti-culate tarsi are found only in this group. Theevidence therefore strongly points to a scu-tigeromorph centiped identity for these iso-lated legs.The following section demonstrates even

more detailed similarities between the legs ofextant scutigeromorphs and the fossil legs.

SCUTIGEROMORPH CENTIPEDS

Scutigeromorph centipeds are perhaps themost familiar members of the Class Chilo-poda because of the frequent occurrence ofScutigera coleoptrata L., the House Centi-ped, in centrally heated homes of the northtemperate zone. Its original habitat is theMediterranean region, where it occurs out ofdoors in sunny places, hiding under stones.This large, fleet centiped often elicits fearwhen it makes an appearance in a home inEurope or America, but is probably quite ef-fective in helping to control household in-sects. The order Scutigeromorpha is of lowdiversity worldwide compared to other or-ders of centipeds; recent systematic treat-ments have significantly reduced the num-bers of species recognized (Wurmli, 1973a,1973b, 1974a, 1974b, 1975, 1977; Wurmliand Negrea, 1977). Scutigeromorph speciestend to resemble one another closely, varyingin size and in details of the mouthparts, cu-ticular microsculpture, and genitalia. Mostspecies are tropical in distribution. Generalinformation on scutigeromorph anatomy andbiology is summarized in Lewis (1981).

Scutigeromorphs are now generally rec-ognized as the earliest surviving offshoot ofthe atelocerate line and the sister group to allother centipeds. However, with their manyspecializations for a cursorial life, they areprobably far from the ground plan of the an-cestral centiped (Dohle, 1980, 1985; Krausand Kraus, 1994; Borucki, 1996).A single Paleozoic fossil species is known,

Latzelia primordialis Scudder, 1890, of theWestphalian D Francis Creek Shale at MazonCreek, Illinois, USA (Scudder, 1890a, 1890b;

Mundel, 1979). Although more detailedwork on this fossil is required, its generalappearance is remarkably similar to that ofliving scutigeromorphs.The scutigeromorphs are recognized as

primitive centipeds (Dohle 1980, 1985) andas such are the most primitive living atelo-cerates. Thus the extension of their fossil rec-ord back to the Devonian and Silurian, dem-onstrated below, is of considerable evolution-ary significance.

For purposes of comparison, we examinedthe legs of a range of taxa of living scutig-eromorphs, including the species Scutigeracoleoptrata L., S. rugosa Newport, S. ni-grovittata Pocock, Thereuonema tuberculata(Wood), Parascutigera mjoebergi (Verhoeff),and Thereuopodina queenslandica (Ver-hoeff). The legs of all these species are re-markably similar and thus the following de-scription was prepared, based primarily onthe fifth leg of Scutigera coleoptrata, the bestknown species.The leg (fig. 27) consists of seven podo-

meres: coxa, trochanter (KPtrochanter +KPprefemur), prefemur (KPfemur), femur(KPpatella), tibia, tarsus, and postarsus(claw). The coxae and trochanters are notpreserved in our fossil material and so willnot be described. The prefemur (fig. 1) is thebulkiest of the podomeres and generallyabout three times as long as wide. Seen inlateral view, the proximal end is obliquelytruncate, with the ventral margin somewhatswollen. The distal articulation with the fe-mur is likewise oblique, with the dorsal sur-face more extended distally. Two large ma-crosetae are present dorsally at the articula-tion; ventrally a single large macroseta, pro-jecting straight downward, is inserted abouta fourth of the podomere's length back fromthe distal articulation. These macrosetae havea distinctive scaly microsculpture. Though theprefemur is somewhat oval (anteroposteriorlycompressed) in cross section, there are alsofive to seven distinct angles, each of which ismarked by a row of small setae, and ventrallywith cuticular teeth in more posterior legs.The femur (fig. 2) is more slender, four to

five times as wide as long, but its generalshape is similar to that of the prefemur. Dis-tally there is a single large dorsal macrosetaand two ventrolateral macrosetae. The five-

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Figs. 1-6. Podomeres of scutigeromorph cen-

tipeds. Figs. 1-3. Scutigera coleoptrata, leg 11. 1.Prefemur. 2. Femur. 3. Tibia. Figs. 4-6. Latzeliaprimordialis. The exact identity of these legs isnot clear; compare fig. 7. 4. Left leg 14(?), coxa,

trochanter, prefemur, femur and proximal part oftibia. Femur is narrowed distally by obscuring ma-

trix. 5. Right leg 13(?), distal part of prefemur, fe-mur, proximal part of tibia. Note broken ventro-distal spine on prefemur; compare with fig. 1. 6.Right leg 1 1(?), joint between prefemur and femur.

angled appearance of the prefemur is accen-

tuated on the femur, and unarticulated spines(teeth) appear on the dorsal setal rows thatmark the angles; they are formed from ex-

tensions of the proximal side of the setalsockets and point distally at a low angle, giv-ing a serrate appearance. On the anterior andposterior surfaces, scattered setae also ap-pear. In cross section, the femur resembles a

pentagon with three angles dorsally and twoventrally. The distodorsal macroseta is at theend of the dorsalmost row of teeth, the twolaterodorsal rows lack a terminal macroseta,and the ventrodistal macrosetae are set at theends of the two ventral rows. We refer to theangles that end with a macroseta as majorangles, and those that lack a macroseta as

minor angles. There is some variation in an-

gulation. In the giant scutigeromorph Ther-euonema tuberculata (Wood), two additionalminor angles appear vaguely on the prefemur

and more distinctly on the femur, for a totalof seven. These additional angles never haveterminating macrosetae.The knee-joint of the leg, the point where

maximum flexion occurs, is between the fe-mur and the tibia. The tibia (fig. 3) is a long,slender podomere typically ten times or morelonger than wide and only about half the di-ameter of the femur. The pentangular crosssection is so pronounced that the surfaces ofthe podomere between the angles may actu-ally be slightly concave. The angles are re-inforced with stronger cuticle and markedwith rows of setae, each subtended proximallyby a prominent acute tooth usually about thesame length at the seta itself. On the ventralangles, these spines may be somewhat sepa-rated from the setal base and there are oftentwo or three of them per seta, large singlespines separating linear series of smaller ones.On some legs, the two ventral rows are rep-resented only by the setae. The "sawblade"appearance is most distinctive in the tibia. Atthe distal end of the tibia, close to the artic-ulation with the tarsus, there are three macro-setae terminating the major angles, as de-scribed for the femur. Again, some variationin angulation occurs in larger species; in The-reuonema tuberculata, the posteriolateral mi-nor angle is suppressed in the midlength ofthe segment and the others are accentuated togive the segment an almost rectangular crosssection. The suppressed angles appear againdistally, near the articulation.The tarsus is clearly divided into two

parts, a basitarsus and telotarsus. The telo-tarsus is further subdivided into pseudoseg-ments (so called because they are not inde-pendently musculated). In Scutigera coleop-trata, the basitarsus begins with a long seg-ment and up to nine short segments follow;the last of these segments bears a pair ofstrong lateral macrosetae, and thus marks thedivision between the basitarsus and telotar-sus. The distitarsus may have 25 or morepseudosegments; the last one is the longestand bears the postarsus or claw. The setationand sculpture of the tarsal pseudosegmentsare complex. The basitarsal segments have adense cover of microspinules, with a fewshort, small setae. Distoventrally there aretwo large spines, and the ventral surface isset with fine hairs and setae, some of which

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Fig. 7. Latzelia primordialis, CMNH 008672, Cleveland Museum of Natural History. Photographcourtesy of Dr. J. Hannibal.

are bent proximally and some of which ex-tend straight ventrally. The distitarsal seg-ments are separated by poorly sclerotized cu-ticle ventrally but overlap dorsally, and arewell covered in spinules. There is a largedorsal seta subtended by a spine on each seg-ment. Ventrally, there are three socketed se-tae, one of them sharply bent and pointingdistally, or modified to a clublike shape. In-terestingly, these two types of modificationsoccur on alternating pseudosegments. On thelast segment, the postarsal claw is subtendedby a small, blunt, clawlike seta.

All of the 15 pairs of legs follow this basicpattern of segmentation and ornament, dif-fering in a single animal mostly in length(the length difference has the functional sig-nificance of overlap in stride, thus allowing

greater stride length and running speed);much of this length difference is made up insomewhat longer tibiae and much longer tar-si with more pseudosegments; the last pair oflegs is extremely long and antenniform andis used as a sense organ.

In addition to the socketed setae and thestrong spines referred to above as teeth, finehairlike spines also occur on the legs. Whilethese superficially resemble setae, they arenot socketed. These were described byWurmli (1974a, 1974b) as spiculae (Haar-spitzen). The spines of the tarsi verge on thistype, but are often rather flattened and broad-er.The fact that such a detailed composite de-

scription could be made up provides someclear guidelines in recognizing isolated po-

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Figs. 8-11. Podomeres of Crussolum crusserratum. 8. Specimen 2002.12.AR12 (see also fig. 14),prefemur; ventral surface missing. 40X. 9. Specimen 2002.12.AR12, distal end of tibia. lOOX. 10.Specimen 2002.9.AR15, showing marginal serrations subtending setal sockets. 400X. 11. Specimen334.1b.AR78, tarsus, probably incomplete proximally and lacking claw (see also fig. 19). lOOX.

'w12 13Figs. 12, 13. Specimen 334.1b.AR78, tarsus of C. crusserratum. 12. Segments from midregion;

large, dark, oval object is a plant spore. 13. More distal segments, showing spinules and setae.

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Figs. 14-16. Podomeres of Crussolum crusserratum. Distal to the left in all figures. 14. Specimen2002/12/AR12, prefemur (see also fig. 8; orientation reversed in drawing). 15. Specimen 2002/9/AR15,prefemur. 16. Specimen 334/lb/AR1, femur. Scale line = 0.43 mm.

domeres, which make up the bulk of our fos-sil material.We also studied specimens of the Carbon-

iferous fossil species Latzelia primordialisScudder, but because of the means of pres-ervation (in siderite nodules) no legs werepreserved distal to the basal half of the tibia.Only a small number of specimens wereavailable; most of those referred to by Mun-del (1979) can no longer be located in theField Museum (Chicago) collections. Thebest available specimen for legs thereforecame from the Cleveland Museum of NaturalHistory, Cleveland, Ohio (CMNH 8672; fig.7). As with all known specimens, it camefrom the Westphalian D Francis Creek Shaleof the Mazon Creek, Illinois, area. No furtherdata were available. The specimen consistsof part and counterpart of an ironstone nod-ule, showing the dorsal surface of a more orless complete individual (head and eight ter-gites). Two or three of the legs are reason-ably well preserved. Figure 4 shows a prob-ably penultimate leg (leg 14), and includes

part of the coxa, trochanter, prefemur, femur,and the basal section of the tibia. While nomacrosetae are visible on this leg, it is clearthat the podomeres in life had an angularcross section and that along the edges of theangles were small protuberances, probablylike the small spines found in living scutig-eromorphs. Another leg from the other sideof the body (fig. 5), which appears to be leg13, has the distal part of the prefemur, theentire femur, and the basal part of the tibiapreserved. The prefemur clearly shows an in-dication of the single large ventrodistal mac-roseta found in Scutigera legs, and the an-gular cross section with acute projections canbe seen on the femur. In both of these legs,the proportions are similar to those of extantforms. Only one major difference betweenthe legs of this Carboniferous scutigero-morph and the living species could be found.On the illustrated 13th leg, a series of large,well-defined quadrangular to oval depres-sions occurs in a row along one of the legangles on both the prefemur and femur. The

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Av, IFigs. 17-20. Podomeres of Crussolum crusserratum and Ludford Lane specimen. Figs. 17-19. Po-

domeres of C. crusserratum. 17. Specimen 329/AR35, tibia, distal above, distal part incomplete; prox-imal end possibly present; dashed sections obscured by overlying material. 18. Specimen 411n/AR14,distal end of tibia and complete tarsus; dark object is overlying piece of coalified plant material; ti,tibia; ta, tarsus; m, macroseta displaced from distal end of tarsus. 19. Specimen 334/lb/AR78, partialtarsus (see also figs. 11-13); proximal end incomplete, missing at least 10 segments. 20. SpecimenDE.3.1.18/105, distal end of tibia of Ludford Lane Crussolum with preserved articulating surface. Scaleline = 0.43 mm for fig. 17, 0.3 mm for figs. 19, 20, 0.6 mm for fig. 18.

same situation occurs on the prefemur andfemur of another leg on the counterpart (fig.6). These depressions would have appearedon the leg as rounded bosses, if they are notartifacts of preservation. We were not able toverify the appearance of this detail on thethree available Field Museum specimens be-cause they were not as well preserved.

DESCRIPTIONS OF FOSSILSThe serrate edges, pentagonal cross sec-

tion, subsegmented tarsi with characteristic

ventral ornamentation including spiculae,knee articulation between femur and tibia,and single claws of the fossil podomeres de-scribed below, by comparison with livingand already-known fossil forms, support thehypothesis that they belonged to scutigero-morph centipeds. In addition, the single ar-ticulated example from Ludford Lane ap-pears to preserve the femuro-tibial joint asthe knee, or point of maximum flexion of theleg, typical of scutigeromorph centipeds. Bymeans of this comparison, it has been pos-

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sible to tenatively identify isolated podo-meres, and these have then been observed tocarry features, such as macrosetal sockets,consistent with a scutigeromorph identity.

THE GILBOA LEGS

LOCALITY AND HORIZON: Near Gilboa,Schoharie County, New York State, in theupper part of the Panther Mountain Forma-tion on the west flank of Brown Mountain.The Panther Mountain Formation belongs tothe Tioughniogan Stage of the Erian Seriesand has been thought to be roughly equiva-lent in age to the middle Givetian of Europe(Shear et al., 1984; where more details onstratigraphy can be found). Richardson et al.(1993) considered the formation to be pos-sibly older, based on palynological evidence.Spores from the deposit conform to thosehigh in the devonicus-naumovae Zone, sug-gesting an age no older than late Eifelian, butmore likely early to middle Givetian.

PRESERVATION: The fossils are preservedas small fragments of more or less unalteredcuticle, with infrequent articulated speci-mens. The level of preservation is uniformlymuch higher than at the earlier Ludford Lanelocality. For further details on preservation,see Shear et al. (1987). The appearance ofthe cuticle of the "sawblade" legs from thisdeposit, as well as the presence of fragmentsin organic connection, suggest that only asingle species of scutigeromorph centipedwas present. Therefore, we will discuss thematerial not specimen by specimen, but bypodomere, and provide a formal name for thespecies.

CHILOPODA LATREILLE, 1802ORDER SCUTIGEROMORPHA LEACH, 1814

FAMILY CRUSSOLIDAE SHEAR, NEW FAMILY

TYPE GENUS: Monobasic on CrussolumShear, new genus.

DIAGNOSIS: as for Crussolum, new genus(see below).

Genus Crussolum Shear, new genusTYPE SPECIES: Crussolum crusserratum

Shear, new species.ETYMOLOGY: From the Latin crus, a leg,

and solum, only; neuter. "Only legs," andrefers to the fact that no other body parts canunequivocably be attributed to this species.

DIAGNOSIS: A genus of scutigeromorphcentiped in which the leg tarsi are not clearlydivided into basitarsi and distitarsi and havea characteristic pattern of ventral spinationand setation (see below, and figs. 11-13, 19and 26; these characters are not known forLatzelia, which preserves only the body andthe proximal portions of the legs). Presentlyknown only from the Silurian and Devonianof Britain and the United States.

Crussolum crusseratum Shear,new species

Figures 8-19, 26, 28

TYPES: Holotype, specimen 334/lb/AR78,deposited in the American Museum of Nat-ural History. The other specimens named anddiscussed below and listed in table 1 areparatypes.

DIAGNOSIS: as for the genus (see above).DESCRIPTION: Prefemur: Based on size,

general shape, and the presence of macrose-tal sockets in one case, specimens 2002/12/AR12 (figs. 8, 14), 2002/9/AR15 (fig. 10,15), 334/la/AR16, and 411/2/AR20A areprefemora. This podomere is characterizedby two dorsal rows of small serrations, scat-tered spinules on the lateral surface (411/1/AR20A), and two dorsal macrosetae (2002/12/AR12; figs. 8, 14). The largest specimen,2002/9/AR15 (fig. 15), seems relatively com-plete except for the ventral surface and is2.56 mm long. As in this specimen, 334/la/AR16 shows small spinules on the lateralsurface, below the dorsal serrated ridges.

Femur: Only a single specimen, 334/lb/ARI (fig. 16), can unequivocally be assignedto this podomere. This specimen preservesthe distal one-half to two-thirds of the seg-ment; the proximal articulation is missing.Five longitudinal angles, each bearing typicalserrations (spines) subtending setae can bedetected. At the distal end are three macro-setal sockets, as in Scutigera coleoptrata.

Tibia: Tibiae may be recognized by theirnarrowness and long rows of well preservedserrations, five rows on more completely pre-served specimens. Two macrosetae occur atthe distal end near the articulation with thetarsus. The longest specimen is 329/AR35(fig. 17), about 3.63 mm long and 0.35 mmwide. Five angular ridges with serrations can

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Figs. 21-26. Podomeres of Ludford Lane Crussolum, Hudwick Dingle specimen, and partial reconstruction of C. crusserratum. 21. Specimen DE 1.4.2150, femur and tibia in articulation. 22. Same, reverse (drawn from other side of slide). 23. Specimen DE 1.4.12160, probable femur. 24. Specimen HD21211, example of Hudwick Dingle type of serrate fragment; specimen completely opaque and codified. 25. Specimen DE 4.1.9148, fragment of tibia from Ludford Lane. 26. Diagrammatic reconstruction of tarsal subsegments of C. crusserratum, ventral view; compare fig. 19. Scale line = 0.3 mrn; fig. 26 not to scale.

be seen; the distal end is broken but the proximal end may be present, though obscured by overlying pieces of cuticle. This specimen is associated with an unusual type of cuticle ornamented with elongated setal sockets in short, arcuate rows. This cuticle is found in living archaeognath insects, where the sockets bear broad scales. The cuticle and the serrate tibia are not in organic connnection and

their association on this slide is taken as for- tuitous; the legs of living archaeognaths do not resemble those of scutigeromorph centipeds. Isolated distal ends of tibiae are found on 2002112lAR21, marked by two large macrosetal sockets (fig. 9). Specimen 20021121 AR20 preserves the proximal end of a tibia, perhaps the same tibia as the distal end of 200211 2lAR2 1, since the slides are sequen-


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28

ti

Figs. 27, 28. Legs of scutigeromorph centipeds. 27. Leg 10 of Scutigera coleoptrata. 28. Recon-struction of generalized leg of Crussolum crusserratum. pf, prefemur; f, femur; ti, tibia; ta, tarsus.

tial. Specimen 411/15/AR15 is a fragment ofa large tibia in which the setal sockets distalto each spine of the serrate ridges can be eas-ily seen. Specimen 411/7/AR14 preservesthe distal end of a tibia in connection with atarsus (fig. 18). Specimen 411/20/AR22 isthe distal end of a tibia.

Tarsus: Two specimens preserve tarsi:334/lb/AR78 (figs. 11-13, 19) consists of 12pseudosegments from near the end of a tar-sus, and 411/7/AR44 (fig. 18) preserves anentire tarsus and postarsal claw in connectionwith the distal end of a tibia. Unfortunatelythis specimen was subsequently destroyed ina laboratory accident. There appear to beabout 25 pseudosegments in the completetarsus. Specimen 334/lb/AR78 is mountedventral side up on the slide and has the se-tation and spination of each pseudosegmentnearly perfectly preserved, and allows a ten-tative reconstruction (fig. 26). Each pseudo-segment is cylindrical, about one-fourth aslong as wide; There are four major spicules,two lateral and two more closely set near themidline. Between the lateral spicule of eachside and the central pair occur single, thinminor spicules. Spines subtend setal sockets;

about half of these contain long, thin, pre-sumably tactile setae. Near the distal end ofthe tarsus this pattern becomes congested andconfused and the pseudosegments loose theirdistinctiveness. The distal taper of the lastpseudosegment suggests that it is indeed themost distal and that only the claw is missing.This pseudospination is exactly matched onspecimen 411/7/AR14, the complete tarsus.In this specimen there is no indication ofsubdivision of the tarsus into basitarsus andtelotarsus (though part of the tarsus is foldedover and concealed by a bit of coalified plantmaterial) and all of the pseudosegments arevery similar. The claw is about three timeslonger than broad, very slightly curved, andacutely pointed.

DISCUSSION: Although a complete leg is notknown from this deposit, the shape and cutic-ular ornamentation of the fragments availablesuggest that they come from a single species.Based on the serrate angular ridges of the fe-mur and tibia, with the spines subtending se-tae, the macrosetation at the distal end of theprefemur, the pseudosegmentation of the tarsi,and the single claw, we interpret these legs ascoming from a scutigeromorph centiped. It is

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also possible that isolated segments from asingle sample of matrix (for example, 334/lbor 2002/12) are from the same individual an-imal or even the same leg, but this cannot bedefinitively established.OTHER GILBOA SPECIMENS: Scutigero-

morph centipeds have enormous eyes thatappear compound but are actually of thepseudofacetted type (Paulus, 1979). Thistype of eye, while appearing compound, is infact built up again from the remains of a de-generate compound eye and has a very dif-ferent microstructure. A large, many-facetedeye is known from Gilboa (Shear et al. 1984)from at least two specimens. We re-examineda large, complete eye (specimen 329-AR4)and a smaller, fragmentary one (411-20-AR1) for this study. The lenses of both eyesare obviously hexagonal, while those of scu-tigeromorph centiped eyes are round. The cu-ticle to which the eye of 329-AR4 is attachedbears sculpture which is unlike that of theGilboa "sawblade legs" as well as livingscutigeromorph centipeds. In our judgment itis not assignable to the Gilboa scutigero-morph, nor are other specimens of collec-tions of ringlike segments at Gilboa, basedon the characteristic complicated setation ofthe tarsal pseudosegments of the scutigero-morph.

THE LUDFORD LANE LEGS

LOCALITY AND HORIZON: The LudfordLane site comprises the Ludlow Bone BedMember of Downton Castle Sandstone For-mation, 0.15 to 0.20 m above the LudlowBone Bed, Ludford Lane, Ludlow, Shrop-shire, England (National Grid Reference SO5116 7413). The Ludlow Bone Bed marksthe base of the Pridoli Series of the SilurianSystem and has an approximate age of 414million years. Further details are given inJeram et al. (1990).

PRESERVATION: The preservation quality ofthe Ludford Lane terrestrial arthropod cutic-ular fragments is quite variable, but nowhereequal to that at the later Gilboa site. In con-trast, associated eurypterid and scorpion cu-ticle is much better preserved. Most centipedspecimens are very small fragments, flat-tened, often coalified to opacity, and badlyeroded. The erosion and reduction to small

size probably occurred during transport andbefore fossilization. Subsequently, crackingof the matrix may further have reduced thesize of the pieces, and the impressions of ma-trix grains further obscured detail. Thus thespecimens are best studied under both inci-dent and transmitted light.

Jeram et al. (1990) illustrated three legfragments (DE 3.1.2.87, figs. 1J, 1K;DE.1.2.16/47, figs. 1H, 11; DE M.2.11/185,figs. 1M, 10) which they attributed to a scu-tigeromorph centiped and restored as part ofa whole leg, along with DE 1.4.2.50. As de-tailed below, only this latter specimen andsome others subsequently obtained are in-deed scutigeromorph, but the three formerspecimens are not. The discovery of the ar-thropleurid Eoarthropleura at Ludford Lane(Shear and Selden 1995), and the additionalfinding of beautifully preserved legs of thisanimal from a Frasnian site in New York,have combined to convince us that thesethree fragments are in fact Eoarthropleuralegs. These, and the Eoarthropleura legsfrom New York, will be treated separately ina later publication.

Scraps and fragments of cuticle, includingmultiarticulate structures, probable tergitesand coxae, and other structures, may also beattributable to centipeds, but are too frag-mentary and too poorly preserved to be cer-tain.

SYSTEMATIC ASSIGNMENT: Because of theirsimilarity to the legs described above asCrussolum crusserratum, the following spec-imens are referred to Crussolum spp. Wehave no evidence that all the fragments camefrom the legs of a single species, and eventhe generic assignment may have to be re-vised later.

Specimen DE 1.4.2/50Figures 21, 22

Illustrated in Jeram et al. (1990), p. 660,fig. 1N.

DESCRIPTION: This specimen, less coalifiedthan the others but with considerably erodedcuticle, consists of the distal end of a femurand the proximal end of a tibia in articula-tion. It is referred to hereafter as LL50. Littledetail can be seen of the cuticle of the femur,which is 0.63 mm wide and bears a row of

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serrations on the dorsal edge. Laterally, nearthe articulation, there is a large round holewhich is likely to be a macrosetal socket. Aheavily sclerotized triangular process pro-jects from the rim just dorsal to the hole, andbelow it part of the rim margin has peeledoff and has been displaced proximally. Theshort piece of tibia is 0.24 mm wide. Thereare indications of three or four angular mar-gins, two of them preserving serrations.

INTERPRETATION: This is the prefemur andtibia of a scutigeromorph centiped, based onthe marginal serrations of both segments andthe shape of the tibia. The broken tibia maybe assumed to have been significantly longer(see below).

Specimen DE 3.1.1/88

Illustrated in Jeram et al. (1990), p. 660,fig. iP

DESCRIPTION: This poorly preserved spec-imen (hereafter called LL88A and LL88B)consists of two pieces originally in organicconnection but broken apart during mount-ing. Part A is a badly folded fragment of thedistal end of a femur; part B is a mostly com-plete tibia. The tibia has a single distal mac-roseta and preserves a few marginal serra-tions. Based on the curvature of the pre-served dorsal surface of the femur, the tibiawas about three times longer than the femur,and about ten times as wide as long.

INTERPRETATION: The femur and tibia of ascutigeromorph centiped, probably the samespecies as LL50, discussed above.

ADDITIONAL SPECIMENSFROM LUDFORD LANE

The following specimens are very small,fragmentary remains, all probably part of in-dividuals of the same scutigeromorph speciesfrom which the last two specimens came.DE 3.1.18/105 is a proximal end of a tibia,

with an articulating surface preserved.DE 1.4.12/60 (fig. 23), poorly preserved,

is nonetheless clearly a femur.LL 1.6/10/2 is a long, isolated angular

ridge with many serrations. It is one-thirdagain as long as the complete tibia of DE3.1.1/88 and thus came from a much largerleg.

Small pieces of serrate tibiae are found on

slides DE 3.2.32/141, DE M.2.8/181, LL 1.6/15/76, LL Orig "cent tibia," DE 4.1.9/48(fig. 25), and LL/S10/1/6. Tibial fragmentson DEF 1.5.5/61 show an unusual form ofsculpture between the angular ridges, withscattered nodules of thicker cuticle. This maybe caused by real sculpture or random dif-ferential erosion. Such sculpture does not oc-cur on modem scutigeromorph legs.

SPECIMENS FROM HUDWICK DINGLE

Specimens HD 2/2/1 (fig. 24) and HD 0/0/1 were obtained from a different location,Hudwick Dingle, about 20 km northeast ofLudlow, Shropshire, from the Lower Devo-nian (Gedinnian) Ditton Series (see Dineley,1978, for details). They are serrated podo-mere margins, entirely opaque, significantlylarger than the Ludford Lane specimens, andwith much stouter serrations. They may ormay not be pieces of "sawblade" legs.

THE RHYNIE FRAGMENT

A sawed slab of Siegenian age RhynieChert (see Trewin, 1994, for a review of theRhynie paleoenvironment and depositionalconditions) from the Ulster Museum wasfound to contain a small fragment of "saw-blade" leg, probably part of a tibia of a Crus-solum. Impossible to photograph, the speci-men adds only an earlier Devonian occur-rence to the record, but also represents thefirst new animal to be discovered in the Rhy-nie Chert since the 1920s.

COMPARISONSAs is obvious from an examination of the

photographs and drawings, the leg of Crus-solum crusserratum bears a strong resem-blance to that of modern scutigeromorphcentipeds. A tenative reconstruction of theleg of C. crusserratum is presented in figure28. This reconstruction is admittedly highlyspeculative, since it is not known if the avail-able specimens represent parts of the same oreven similar legs; the legs of living scutig-eromorphs are known to vary along thelength of the body. There is also the possi-bility that more than one species is repre-sented, or even that we are in error is as-signing these fragments to the Scutigeromor-pha.

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Points of similarity with Scutigera coleop-trata (fig. 27) include the tibia, strongly pen-tangular in cross section, bearing prominentserrations on the angles, each of which prob-ably subtends a seta, and the multiarticulatetarsus with complex ventral setation and spi-nation, including spiculae. Details, however,differ. The ventral surface of the prefemur ismissing in all specimens. Thus the typicalmacrosetation pattern on that podomere ofmodern scutigeromorphs cannot be verifiedfor this species, but at the end of the prefe-mur and tibia we can clearly see three ma-crosetal sockets, as in the living forms. Al-though most of the legs of Scutigera coleop-trata have three apical tibial macrosetae, twosetae occur on some anterior legs, and spec-imen 411.7.AR14 has only two visible socketson the distal end of the tibia. However, theapex of the tibia is poorly oriented and partlyconcealed by an opaque fragment of plantmaterial; it is possible that three sockets arepresent. While both C. crusseratum and theliving species have multiarticulate tarsi,modern scutigeromorph centipeds have thetarsus divided into basitarsal and telotarsalregions, and have a different (and more com-plex) ventral spination of the tarsal pseudo-segments. The undivided tarsus would haveto be regarded as an autapomorphy of Crus-solum crusserratum.The Ludford legs represented by LL50 and

LL88 are also likely to be from a scutigero-morph centiped similar (at least in leg de-sign) to the Gilboa form and to modern scu-tigeromorph centipeds. The evidence, how-ever, is scanty: the tibiae are ten times longerthan broad and have serrate angles. Tarsi arenot known, so we cannot say if they were

subsegmented. Multisegmented structureshave been found in Ludford Lane residues,but are poorly preserved and cannot with cer-tainty be assigned to a taxon.None of the leg types described here can

be closely compared to the legs of the otherknown Gilboa centiped, Devonobius deltaShear and Bonamo. Entire legs are wellknown for that animal, and the differentlyshaped podomeres lack macrosetae, having amoderate vestiture of ordinary setae (Shearand Bonamo, 1988).

Nonetheless an important point is sup-ported by this fragmentary material: scutig-eromorph centipeds, with their distinctivelegs, may have already evolved by the LateSilurian, and by the Middle Devonian mayhave been approaching their modern form,which was obviously fully achieved by theUpper Pennsylvanian, attested to by the fos-sils of Latzelia primordialis. The discoveryof an extinct order of centipeds, Devono-biomorpha (Shear and Bonamo, 1988), atGilboa, indicates that there may have been agreater diversity of centipeds at the ordinallevel in the middle Paleozoic than exists to-day.4 As yet we know very little about Car-boniferous centipeds, with two Mazon Creekspecies, L. primordialis, and a scolopendro-morph, being the only adequately describedforms (Mundel, 1979).

4Borucki (1996), in a detailed and exemplary reviewof centiped phylogeny, has placed Devonobius in theorder Craterostigmatomorpha (recte pro 'Craterostig-momorpha'), but by implication as a plesion within thattaxon. Additional fossil evidence bearing on this ques-tion has recently been discovered and will be reportedon by one of us (WS) in a later publication.

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