The Trilobite “Dalmanites” Maecurua Clarke, 1890 (Middle Devonian, Amazon Basin, Brazil) and the New Genus Amazonaspis (Synphoriidae)

2007·3.5 MB·English

by  Maria Da Gloria Pires De Carvalho

PUBLISHED BY THE AMERICAN MUSEUM OF NATURAL HISTORY
CENTRAL PARK WEST AT 79TH STREET, NEW YORK, NY 10024
Number 3591, 16 pp., 4 figures, 0 tables December 12, 2007
The Trilobite ‘‘Dalmanites’’ maecurua Clarke, 1890
(Middle Devonian, Amazon Basin, Brazil) and the
New Genus Amazonaspis (Synphoriidae)
MARIA DA GLORIA PIRES DE CARVALHO1 AND
VERA MARIA MEDINA DA FONSECA2
ABSTRACT
Therevisionof‘‘Dalmanites’’maecuruaClarke,1890,fromtheUpperLontraMember,Eifelian,
MaecuruFormation,Para´ State,AmazonBasin,Brazilispresented.ThenewgenusAmazonaspis
is assigned within the family Synphoriidae. Comparisons are made with other Silurian and
Devoniansynphoriids, andsome paleobiogeographic inferencesare presented.
RESUMO
E´ apresentadaarevisa˜ode‘‘Dalmanites’’maecuruaClarke,1890,procedentedapartesuperior
doMembroLontra,Eifeliano,daFormac¸a˜oMaecuru,noestadodoPara´,daBaciadoAmazonas,
Brasil. O novo geˆnero Amazonaspis e´ atribu´ıdo a` fam´ılia Synphoriidae. Sa˜o feitas comparac¸o˜es
comoutrossynfori´ıdeossilurianosedevonianos,eapresentadasalgumasinfereˆnciaspaleobiogeo-
gra´ficas.
INTRODUCTION the Maecuru and Erereˆ formations of the
Amazon Basin, with ages varying from late
Clarke (1890) originally described Dal- Eifelian to early Givetian. The material from
manitesmaecuruaamongothertrilobitesfrom the Maecuru Formation (late Eifelian) was
1DivisionofPaleontology,AmericanMuseumofNaturalHistory([email protected]).
2Museu Nacional/Universidade Federal do Rio de Janeiro, Departamento de Geologia e Paleontologia (vmedina@
acd.ufrj.br).
CopyrightEAmericanMuseumofNaturalHistory2007 ISSN0003-0082
2 AMERICAN MUSEUMNOVITATES NO. 3591
collected in 1876 by the Imperial Geological bordersanddoublures;thepresenceorabsence
Commission, from several localities along the of a genal spine and an epiborder furrow; the
Maecuru River, north of the Teaupixuna thoracic and pygidial architecture, especially
rapids, in the state of Para´. Additional themorphologyofthepleuralfurrowsandthe
material was collected in the same area, by tipsofthethoracicpleurae;andthepositionof
the Orville Adalbert Derby Expedition, con- the pygidial apodemes. Thus, according to
ducted by Petrobras in 1986. Campbell (1977), diagnostic features of the
Clarke (1900: 15) proposed Synphoria as Synphoriinaeare:gapbetweenS1andS2more
a subgenus of Dalmanites, for his new species than 1.5 times that between the occipital
Dalmanites (Synphoria) stemmatus from the apodeme and S1; S1 slightly oblique to the
Oriskany fauna, Lower Devonian of New sagittallineandS2tendstobeequidimensional
York State. He considered that the Brazilian indorsalview(theshapeoftheapodemeinS2
species Dalmanites maecurua was closely re- produces the transversally short furrow); ce-
lated to that form as he included it in the phalic border narrow, convex, and poorly
same subgenus as Dalmanites (Synphoria) defined; lateral parts of the cephalic doublure
maecurua though he did not comment on the correspondingly narrow and rather evenly
assignment (Clarke, 1900: 68). Delo (1935) rolled, or with a slight vincular furrow; genal
reviewed the phacopid trilobites and divided spine (if present) short, lacking an epiborder
the family Dalmanitidae into two subfamilies: furrow, tending to be oval in cross section;
Dalmanitinae Reed, 1905, and Synphoriinae thoracicpleuraehaveawide(exsag.)andwell-
Delo,1935.HeconsideredtheSynphoriinaeto roundedposteriorpleuralband,athinanterior
be characterized by more or less complete band, and pleural furrow not dominating;
distal fusion and elevation of L2 and L3 in pygidial pleurae have well-developed anterior
the glabella, the reduction of S1 and S2 to and posterior bands, and the posterior band
submesialpits,andthepresenceinsomeforms does not fade toward the border; pygidial
of spines, denticles, or crenulations on the apodemes discrete and positioned away from
cephalon and pygidium. He also elevated theaxialfurrow.
Synphoria to generic status. Holloway (1981) revised some Silurian
In the classification of Richter et al. (1959), dalmanitaceans from North America and
the subfamily Synphoriinae was not recog- also supported this concept of the family
nized as valid and Synphoria was placed Synphoriidae. His diagnosis of the sub-
in the subfamily Dalmanitinae. However, family Synphoriinae was adapted from
Lespe´rance and Bourque (1971) resurrected Campbell’s (1977) work with slight modifica-
the Synphoriinae and Lespe´rance (1975) sub- tions to accommodate stratigraphically earlier
sequently elevated it to family status (Silurian)taxa.Themodificationsincludedthe
(Synphoriidae), characterized inter alia by shape of the cephalic border (flattened dor-
the fusion of L2 and L3. Lespe´rance recog- sally but rolled downward and inward along
nized two subfamilies within Synphoriidae: theoutermargin)andtheshapeofthepleural
the Synphoriinae and the Trypaulitinae. tips on the thoracic segments (which can be
Campbell (1977) accepted Lespe´rance’s rounded, pointed, or deflected backward into
(1975) subdivision of the Synphoriidae into a spine).
the Synphoriinae and Trypaulitinae, but
modifiedhisconceptofthefamilybyrejecting MATERIAL AND METHODS
the distal coalescence of L3 and L2 as
diagnostic and arguing that this feature is Specimens studied and figured herein are
widespread throughout the Dalmanitoidea. housed in the Museu Nacional/UFRJ (MN),
New criteria proposed by Campbell for Rio de Janeiro and Universidade Federal of
recognizing the Dalmanitinae, Synphoriinae, Rio de Janeiro (UFRJ). For conservational
and Trypaulitinae included the spacing of the reasons it was not possible to coat these
cephalic apodemes (i.e., the gap between the specimens for photography.
occipital and S1 apodemes and between S1 Comparisons were made with another
and S2); the development of the cephalic Malvinokaffric synphoriinid, Dalmanitoides
2007 CARVALHO AND DA FONSECA: REVISION OFTRILOBITE SPECIES 3
Delo, 1935, from the Devonian of Argentina; SYSTEMATIC PALEONTOLOGY
Fenestraspis Branisˇa and Vaneˇk, 1973, from
the Devonian of Bolivia; the North American ORDERPHACOPIDASALTER,1864
Devonian synphoriinids Synphoria stemmata
SUBORDERPHACOPINASTRUVE,1959
(Clarke, 1900), Odontocephalus selenourus
(Eaton, 1832), Anchiops anchiopsis (Green, SUPERFAMILYDALMANITOIDEAVOGDES,
1832),andSynphoroidesbiardi(Clarke,1907); 1890
and with two Silurian synphoriinids, FAMILYSYNPHORIIDAELESPE´RANCE,1975
Lygdozoon collatum Holloway (1981) from
North America and Delops obtusicaudatus SUBFAMILYSYNPHORIINAEDELO,1935
(Salter 1849) from Britain. Terminology used
here for the descriptions follows Whittington Amazonaspis, new genus
and Kelly (1997).
TYPE AND ONLY SPECIES: Dalmanites mae-
curua Clarke, 1890, from the Upper Lontra
GEOLOGICAL SETTING
Member, Eifelian, Maecuru Formation, Para´
State, Brazil.
The fossils described here were collected
from fossiliferous sandstones that belong to DIAGNOSIS: Glabella wide, with sculpture
of coarse tubercles. Frontal lobe rhombic in
the upper part of the Maecuru Formation
outline, moderately inflated, glabellar furrows
(Lontra Member). These sandstones crop out
reaching axial furrows; S1 very close to
along the Maecuru and Curua´ rivers, in the
occipital ring and oblique, S2 subparallel to
northern border region of the Amazon Basin
S1, inner ends of S3 and S1 joined by shallow
in Para´ State, Brazil (fig. 1), and are overlain
longitudinal depression separating inflated
by the Erereˆ Formation (Melo, 1988). The
L2 and L3 from depressed medial part of
Lontra Member consists mainly of fluvial
glabella. Anterior branch of facial suture
sandstones and conglomerates, but its upper-
runningoutsidefrontalglabellarlobe,parallel
most part includes shallowmarinetempestites
to preglabellar furrows. Anterior cephalic
with hummocky cross-stratified sandstones
border increasing slightly in length (sag.,
that contain an important Devonian inverte-
exsag.) medially, margin without spines or
brate fauna recorded by pioneer workers,
crenulations.Pygidiumwith16–17axialrings,
among whom were Rathbun (1879), Clarke
first three weakly convex (tr.); first four
(1890, 1899), and Katzer (1903). The un-
interpleural furrows weakly impressed, sub-
derlying Jatapu Member of the Maecuru
sequent ones line-like; 11 wide and well-
Formation consists of bioturbated silty/shaly
developed pleural furrows; narrow border;
layers and argillaceous sandstones with chit-
median keel or mucro absent.
inozoans and acritarchs, but does not contain
ETYMOLOGY: In reference to the Amazon
marine macrofossils.
Basin, where the type species occurs, together
There is some palynological evidence that with the feminine Greek word aspis, ‘‘shield’’.
the underlying fluvio-deltaic and neritic parts STRATIGRAPHIC RANGE: Eifelian, Middle
of the Lontra Member are of Emsian to Devonian.
Eifelian age, while the overlying Erereˆ REMARKS: Clarke (1890) did not provide
Formation is of Eifelian-Givetian ages (Melo a diagnosis for maecurua and his description
and Loboziak, 2003). Thus, the age of the was based upon a syntype series that consists
fossiliferous marine sandstones forming the only of a few disarticulated specimens.
uppermost part of the Lontra Member is Although the available material is fragmen-
constrained to the Eifelian (fig. 2). tary and many morphological details are not
The marine invertebrate fauna of the veryclear,somestatementsabouttheaffinities
Maecuru Formation is considerably more of the species can be made. Amazonaspis
diverse than other Devonian faunas from displays at least some of the cranidial char-
Brazil; besides trilobites, it includes brachio- acters of synphoriinids, which include: dis-
pods, bivalves, gastropods, bryozoans, corals, tance between the cephalic apodemes S1 and
crinoids, and tentaculitids. S2 more than 1.5 times the gap between the
4 AMERICAN MUSEUMNOVITATES NO. 3591
Fig. 1. Location map of the studied fossiliferous outcrops. 1. Probable collecting site of the Imperial
GeologicalCommission. 2. Collectingsite ofthe Orville A.DerbyExpedition.
2007 CARVALHO AND DA FONSECA: REVISION OFTRILOBITE SPECIES 5
Fig. 2. The Devonian miospore zonation schemes of the Amazon Basin and its relationships with
regional rock units, the standard zonal schemes in Western Europe and Petrobras operational
palynozonation. A. Chronostratigraphy. B. Palynozonal scheme in Western Europe. C. Palynozonal
schemein Amazon Basin. D.Lithostratigraphy.
occipital and S1 apodemes (these apodemes Comparison of Amazonaspis with Syn-
are more nearly equidistant in dalmanitinids); phoria: As Clarke (1900) recognized, Amazo-
S1 directed obliquely forward adaxially; S2 naspis maecurua and Synphoria stemmata are
also oblique; L2 and L3 inflated above the very similar, particularly in the general shape
median part of the glabella adjacent to them; of the frontal glabellar lobe (with a large and
genal spine lacks a longitudinal furrow. In rounded anterior margin); the smooth curva-
addition, the pygidium of Amazonaspis lacks ture of the posterior cephalic border toward
a well-defined border; the apodemes are the blunt and rounded genal spines; the
discrete and isolated from the axial furrow; smooth occipital ring, without a central spine
and the pleural furrows are deep and wide or tubercles; and the third and second
(although it is not clear whether these are glabellar lobes, which have similar ornamen-
symmetrical in cross section). It is concluded tation. The pygidial margins are also similar,
that the Amazonian material can be placed with a slight outward curvature terminating
withinthefamilySynphoriidaeratherthanthe posteriorlyataroundedangle,whichdoesnot
Dalmanitidae. form a mucro or spine; furthermore, the axis
6 AMERICAN MUSEUMNOVITATES NO. 3591
does not reach the posterior margin of the convex (sag., tr.) with the highest point on
pygidium. theposteriorpartofthefrontalglabellarlobe.
Despite these similarities, these two species The anterior cephalic border has a rounded
differ in a number of characters: the axial andsmoothmargin.Theaxialfurrowisbroad
furrows are shallower in A. maecurua; glabel- and shallow. It diverges gently forward to
lar lobes L3 and L2 are not fused abaxially in about the middle (exsag.) of L3, thereafter
A. maecurua; S2 and S3 are wider (tr.) and converges to the outer end of S3, from where
touch the axial furrows in A. maecurua; the it becomes deeper and diverges again anteri-
occipital furrow is distinct in both species, orly. The lateral glabellar furrows are well
deep and almost transverse in Synphoria developed. S3 is broad, shallow, slightly
stemmata, but slightly convex forward medi- narrower and deeper proximally, lengthening
ally in A. maecurua; the central area of the (exsag.), and diverging forward abaxially. S2
glabella in A. maecurua bears tubercles but is is deeper than S3, directed slightly obliquely
smooth in S. stemmata; the anterior cephalic backward abaxially, shallowing as it reaches
margin of A. maecurua lacks crenulations like the axial furrow. S1 is situated very close to
those of S. stemmata, and the pygidium theoccipitalring,curvedinagentleforwardly
includes 10–11 axial rings and 10–11 pleural concave arc parallel to the occipital furrow
furrows in S. stemmata against 16–17 axial and becomes shallower distally where it meets
rings and 13 pleural furrows in A. maecurua. the axial furrow. The occipital furrow (S0) is
bowed slightly forward medially, becoming
Amazonaspis maecurua (Clarke, 1890) narrower and deeper as it approaches the
axial furrows. L3 and L2 are inflated above
figure 3A–H the median part of the glabella adjacent to
them.L3issubtriangularwithroundededges;
DalmanitesmaecuruaClarke;Clarke,1890:23–29,pl.II, L2 is roughly rectangular with the edges
figs.1–3;6–7;10;15. similarly rounded. L1 is shorter (sag., exsag.)
Dalmanites (Synphoria) maecurua Clarke; Clarke, 1900:
than the occipital ring and extends across the
68.
Dalmanites maecurua Clarke; Katzer, 1903: 212, pl. 15, entire width of the glabella, slightly curved
fig.12. forward medially. The occipital ring is longer
DalmanitesmaecuruaClarke;Lima,1989:12. than L1 (sag.) with a weakly concave anterior
DalmanitesmaecuruaClarke;SilvaandFonseca,2005:76, margin and convex posterior margin. The
fig.3C–D.
median area of the glabella is ornamented
TYPE MATERIAL: From Clarke’s syntypes, with tubercles. The frontal glabellar lobe is
MN 3383-I, internal mold of glabella plus relatively large, rhombic in outline, with its
small part of left fixigena (figured by Clarke, anterior margin broad and rounded, and its
1890:pl.II,fig. 2;refiguredhereasfig. 3C–E) posteromedian extremity forms a subacute
is here designated as lectotype; this designa- and prominent angle. There is a very faint
tion is made in order to establish a single elongate posteromedian depression on the
name-bearing type for the species. Paralecto- sagittal line and a circular pit near each of
typesare:MN3382-I,internalmoldofpartof the lateral angles. The frontal glabellar lobe,
the left librigena including genal spine; MN L3, and L2 are all covered withlow tubercles.
3384-I, incomplete internal mold of hypo- Those on the frontal glabellar lobe are
stome; MN 3385-I, internal mold of an approx. 1–1.5 mm across and scattered un-
incomplete thoracic segment; MN 3386-I and evenly (2–3 mm apart) over its surface.
MN 3387-I, external and internal molds Tubercles on L3 and L2 are slightly smaller
respectively of an almost complete pygidium. andclosertogether.Asmallportionoftheleft
OTHER MATERIAL: UFRJ-DG 115-Tr, in- fixigena is preserved, with a small and
ternal andexternalmolds ofacranidiumwith elevated palpebral lobe situated opposite the
cheeks missing. anterior half of L2 and the posterior half of
DESCRIPTION: The cephalon is represented L3. The anterior branch of the facial suture
only by two very incomplete specimens (MN delimits a very narrow strip of the gena
3383-I, UFRJ 115-Tr). It is moderately betweenthefacialsutureandtheaxialfurrow,
2007 CARVALHO AND DA FONSECA: REVISION OFTRILOBITE SPECIES 7
along of the frontal lobe, running close to the angle. The axial furrow is well developed,
glabella. The lateral border is beveled; the shallow,andnarrow.Theaxisisgentlyconvex
lateral and posterior furrows are broad and intransverseprofile,taperedevenlybackward,
quite deep. The posterior furrow curves anditsanteriorwidthisslightlylessthan30%
backwards and tapers distally toward the of the maximum pygidial width. The axis
genal spine but does not meet the lateral includes 16–17 axial rings plus a blunt termi-
cephalicfurrow(whichiswideandalsotapers nal piece that does not reach the posterior
posteriorly). The furrows are separated by margin of the pygidium. The first three axial
a small, narrow convex portion of the free rings are arched gently forward medially, but
gena. The genal spine is small, diverging subsequent ones are transverse. The pleurae
laterally, its internal margin forms a smooth are gently arched (tr.) and almost flat proxi-
concave curve. The hypostome is elongate- mally, but curve more conspicuously toward
linguiforme in outline, with a convex anterior the margin. There are 11 well-developed
margin. The lateral margins converge in pleural furrows plus an inconspicuous final
a gently concave curve from the anterior one. The first three pleural furrows curve
wings to the shoulder, situated opposite the smoothly to the margin, but subsequent
posterior lobe of the middle body; behind the furrows are almost straight and are directed
shoulder the posterior margin is parabolic in successivelymorestronglybackward,withthe
outline.Theanteriorlobeisconvex,separated last one running very close to the axis. The
from the posterior lobe by a well-developed pleural furrows are wide and deep, shallow
furrow that is deep and narrower abaxially distally, and probably symmetrical in cross
and very shallow medially. The macula is section, but this is not clear from the
located approximately midway between the specimen. The pleural ribs become obsolete
lateral margin and the midline. It is unknown before reaching the margin. Interpleural fur-
whether the posterior margin was spinose, rows are narrow and weakly defined, and the
although Clarke (1890: pl. II, fig. 3) restored subsequent ones are line-like. There are in-
its outline with three small spines. distinct nodes scattered over some ribs in an
The thorax is represented only by an apparentlyrandompattern.Themarginalarea
incomplete internal mold of a single segment is smooth, scarcely developed into a faint
lackingthepleuraltermination.Theaxialring border. Terminal spine or mucro is absent.
is broad (tr.), rounded and thickened near the Comparison of A. maecurua with other
axialfurrow,whichisshallowandmoderately North American synphoriinids:
wide. Theposteriormarginoftheaxialringis Odontocephalus selenourus (Eaton, 1832),
gently convex posteriorly while its anterior from the Lower Devonian of New York
partisdepressedmediallyandmergeswiththe (OnandagaLimestone)isreadilydistinguished
articulation furrow. The depression expands from A. maecurua by having an anterior
toward the sagittal line, where it is approxi- cephalic border that bears a series of distally
mately equalinlengthtotheremainderofthe broadened and coalesced processes, and the
ring. The lateral part of the articulation pygidium bears a distinct pair of pointed or
furrow/apodemal pits has a markedly oblique blunt spines posteriorly (see Whiteley et al.,
orientation. The posterior edge of the articu- 2002: pl. 125).
lating half ring is transverse and sharply Anchiopsis anchiopsis (Green, 1832), from
definedoveritsmedialtwo-thirds.Thepleural Lower Devonian of New York (Schoharie
furrow is well developed, deep, wide, and Formation) differs from A. maecurua by
symmetrical in cross section. The anterior having L2 and L3 highly elevated and more
portionofthepleuraadjacenttotheaxialring or less completely fused; S1 and S2 with
is almost transverse, then deflected gently adaxial pits connected by transglabellar
backward and outward. furrows; the occipital ring bears a median
The pygidium is triangular in outline, spine; and the pygidium has a long posterior
approximately 125% as wide as long (sag.) process (see Lespe´rance and Bourque, 1971:
and moderately convex (tr.), with gently pl. 27, figs. 1–3, 10–11; Whiteley et al., 2002,
rounded margins and an obtuse posterior pl. 120).
8 AMERICAN MUSEUMNOVITATES NO. 3591
2007 CARVALHO AND DA FONSECA: REVISION OFTRILOBITE SPECIES 9
Synphoroides biardi (Clarke, 1907) from the formingsubovalimpressionsthatdonotreach
Lower Devonian of the Gaspe´ Peninsula, the axial furrows ( in A. maecurua S1 and S2
Canada, differs from Amazonaspis maecurua distinctly meet the axial furrow); the occipital
in possessing a trifid anterior cephalic process ring bears three spines in F. amauta, but is
and crenulated lateral cephalic margin. In smoothinA.maecurua;finallytheexoskeleton
addition, its pygidium ends in a blunt, tri- is densely and coarsely tuberculated in F.
angular, slightly upturned spine (see Clarke, amauta (the tubercles are not as coarse in A.
1907: pl. 6, figs. 1–12). maecurua). The pygidium of F. amauta has at
Comparison with Malvinokaffric synphor- least 20 rings and is extended posteriorly over
iinids from South America: thepygidialmargintoformastout,upwardly
These include Dalmanitoides drevermanni directed spine (A. maecurua has 16–17 rings
(Thomas, 1906) from the Lower Devonian of and the axis ends in front of the posterior
the Talacasto Formation, Ja´chal, Argentina margin,whichissmoothandlacksamucroor
and Fenestraspis amauta Branisˇa and Vaneˇk spine); there are stout, upwardly directed
(1973) from the Lower Bele´n Formation paired spines on several axial rings situated
(Lower Devonian), of Chacoma, Bolivia. towardoratthedistalendsofthepleuralribs
Dalmanitoides drevermanni (see Thomas, (such spines are absent in A. maecurua);
1906: pl. 11, figs. 1–3) is readily distinguished and the pygidial apodemes are deeply im-
from A. maecurua by having five very short pressed (exsag.) and connected with the axial
frontal processes on the cephalon; S1–S3 furrow (they are comparatively shallow and
connectedbyindistincttransglabellarfurrows; are not connected to the axial furrow in A.
well-developed longitudinal glabellar furrow; maecurua.)
a slender pygidial axis reaching the posterior Lespe´rance (1975) excluded Fenestraspis
end and extending into a short, slightly from the Synphoriidae despite the fact that it
upturned point, as well as a higher number possesses at least one of the characters he
of pygopleurae (14). regardedasdiagnosticofthefamily(fusionof
Branisa and Vanek (1973) suggested that L2 and L3). Significantly, it also has S2
Dalmanitesmaecuruamaybelongtotheirnew reduced in width (tr.) and forming a suboval
genus Fenestraspis, but Eldredge and impression; the distance between cephalic
Ormiston (1979) considered the Brazilian apodemes S1 and S2 is more than 1.5 times
species to be distinct and referred it to a new that between the occipital and S1 apodemes;
genus aff. Fenestraspis. We are in agreement andthegenalspinedoesnothavealongitudi-
with Eldredge and Ormiston (1979) that the nal furrow, all features now considered di-
Brazilian and Bolivian species deserve separa- agnosticoftheSynphoriidae(Campbell,1977;
tion at genus level. Holloway, 1981).
Fenestraspis amauta (interpreted here large- Comparison with Silurian synphoriinids:
ly on the basis of specimens in the AMNH Additionally, two Silurian synphoriinid
collections) differs from Amazonaspis maecur- taxa were compared with A. maecurua,
uainthepresenceofsmallcrenulationsonthe Lygdozoon collatum Holloway, 1981, and
anterior cephalic margin (the anterior margin Delops obtusicaudatus (Salter, 1849). Like A.
issmoothinA.maecurua);theshapeofS1and maecurua, these forms have a rounded anteri-
S2, which in F. amauta are deeper adaxially or cephalic margin, a smooth, entire pygidial
r
Fig. 3. A–H. Amazonaspis maecurua (Clarke, 1890), Upper Lontra Member, Eifelian, Maecuru
Formation, Para´ State, Brazil. A. Paralectotype, MN 3387-I, internal mold of pygidium, dorsal view; B.
Latex cast of external mold of an incomplete cephalon, UFRJ 115-Tr, dorsal view. C–E. Lectotype, MN
3383-I, internal mold of an incomplete cephalon; C, dorsal view; D, lateral view; E, frontal view. F.
Paralectotype,MN3384-I,internalmoldofanalmostcompletehypostome,ventralview.G.Paralectotype,
MN3382-I,internalmoldofpartoftheleftlibrigenaincludinggenalspine,dorsalview.H.Paralectotype,
MN3385-I,internal moldof anincomplete thoracicsegment, dorsalview.
10 AMERICAN MUSEUMNOVITATES NO. 3591
margin, and the pygidium is not mucronate. family Synphoriidae) into the Silurian, by
However,bothformsdifferfromA.maecurua including Lygdozoon and Delops. Here we
in certain features. propose geographical extension of the family
L. collatum from the St. Clair Limestone Synphoriidae into South America, including
(Wenlock) of Arkansas differs from A. mae- species from Argentina, Bolivia and Brazil
curua in having a longer, more slender genal (Amazon Basin).
spine; an ornamented occipital ring (with Since the pioneering work of Katzer (1897)
a small tubercle medially and weak nodes the affinities of the invertebrate fauna of the
distally); a smaller pygidium (9–11 axial rings Maecuru Formation to both austral (Mal-
and9pleuralfurrows);andthehypostomehas vinokkafric) and boreal (Appalachian/Old
a deeper posterior border furrow. World) faunas has become well-known
Delops Rickards 1965 was originally as- (Loczy, 1966; Harrington, 1967; Boucot,
signed to the subfamily Zeliskellinae within 1975, 1988; Carvalho, 1975; Machado, 1990;
the Dalmanitidae, but Holloway (1981) con- Melo, 1988). In the Maecuru Formation this
sidered it to be a synphoriinid. The type ‘‘mixed’’ faunal composition is particularly
species Delops obtusicaudatus (Salter, 1849) is evident among the bivalves (e.g. Ptychopteria,
readily distinguished from Amazonaspis mae- Leptodesma, and Pseudaviculopecten) and bra-
curua by several features; the frontal glabellar chiopods (e.g., orthids including Platyorthis,
lobe protrudes in front of the outline of the Discomyorthis,andTropidoleptus;thestropho-
cheeks; the genal spine is slender; L2 and L3 menids Megastrophia and Protoleptostro-
arefusedabaxially;S2doesnotreachtheaxial phia; the chonetids ‘‘Chonetes’’ freitasi and
furrows; the pygidium is smaller (11–13 axial Montsenets; the spiriferids Patriaspirifer,
ringsand9pleuralfurrows),andtheposterior Mucrospirifer and Plicoplasia; and terebratu-
extremity of the pygidial axis reaches the lids such as Amphigenia, Derbyina, and
posterior margin of the pygidium. Paranaia). The high number of Appalachian
Three other Devonian species, Gamone- genera among the brachiopods led Boucot
daspis scutata, from the Devonian of Bolivia, (1975) and Boucot et al. (1969) to consider
Gamonedaspis accola (Clarke, 1913) from the theAmazonBasinasouthernpaleogeographi-
PontaGrossaFormationoftheParana´ Basin, c extension of the Eastern Americas Realm,
Brazil, and Gamonedaspis boehmi (Knod, designated the Amazon-Colombian Subpro-
1908) from the Voorstehoek Formation of vince. This faunal ‘‘mixing’’ is not as strongly
South Africa were previously assigned to the expressed among the trilobites from the
Subfamily Synphoriinae. However, Gamone- Maecuru Formation, since the majority of
daspis Branisa and Vanek. 1963, is now theseshowgreateraffinitywithMalvinokaffric
considered a dalmanitinid rather than a syn- forms (Eldredge and Ormiston, 1979), espe-
phoriinid (Edgecombe, 1993). cially with Bolivian calmoniids. Nevertheless,
certain trilobites show some affinity to
Appalachian and Old World forms (e.g.,
BIOGEOGRAPHIC CONSIDERATIONS
homalonotidsandsynphoriinids).
Lespe´rance (1975) suggested that the These Devonian Appalachian immigrants
Family Synphoriidae was exclusively Devo- into the Amazon Basin (in the uppermost
nian and almost restricted to cratonic North Maecuru Formation) may have migrated
America and the Appalachian Region; how- during a widespread Eifelian transgression
ever, he also included in the family specimens from the northeast (formerly regarded as late
assigned by Haas (1969: pl. 83, figs. 5–8) Emsian-EifelianbyMelo,1988;Carozzietal.,
to Synphoroides biardi (Clarke, 1907), from 1973),mostprobablyrelatedtotransgression-
the upper Pragian of Central Chihuahua, regression cycle Id of Johnson et al. (1985),
Northern Mexico, a region related to the which thoroughly flooded this basin. In
Appalachian geosyncline. He excluded Fene- addition, a marine connection between Brazil
straspis from this family. and Bolivia may have developed at that time
Holloway (1981) extended the stratigraphic (Loczy, 1966; Melo, 1988; Isaacson and
range of the synphoriinids (and thus the Sablock, 1990), as suggested by the presence