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Paleontological Society
Mazon Creek Cycloidea
Author(s): Frederick R. Schram, Ronald Vonk and Cees H. J. Hof
Source:
Journal of Paleontology,
Vol. 71, No. 2 (Mar., 1997), pp. 261-284
Published by: Paleontological Society
Stable URL: https://www.jstor.org/stable/1306460
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ADRAIN AND RAMSKOLD- SILURIAN TRILOBITES ADRAIN AND RAMSKOLD- SILURIAN TRILOBITES
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biostratigraphy of the central Arctic Islands: a preliminary report.
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PERRY, D. G., AND B. D. E. CHATTERTON. 1977. Silurian (Wenlockian)
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topleuracea nov. superfam. (trilobites). Rozpravy Ustredniho uistavu
Geologick6ho, 12:1-221.
RAMSKOLD, L. 1984. Silurian odontopleurid trilobites from Gotland.
Palaeontology, 27:239-264.
199 a. The perforated trilobite Laethoprusia gen. nov., and the
phylogeny of Koneprusia and Isoprusia (Odontopleuridae, Konepru-
DALMAN, J. W. 1828. Nya svenska palaeader. Kungliga Svenska Ve-
tenskaps-Akademiens Handlingar 1828:134-138.
EDGECOMBE, G. D., AND B. D. E. CHATTERTON. 1987. Heterochrony
in the Silurian radiation of encrinurine trilobites. Lethaia, 20:337-
351.
EMMRICH, H. F. 1839. De trilobitis. Dissertatio petrefactologica quam
consensu et auctoritate amplissimi philosophorum ordinis, etc., Ber-
lin, 56 p.
GOLDFUSS, A. 1843. Systematische iibersicht der Trilobiten und Bes-
chreibung einiger neue Arten derselben. Neues Jahrbuch fur Miner-
alogie, Geognosie, Geologie, und Petrefaktenkunde, for 1843:537-
567.
LENz, A. C. 1990. Ludlow and Pridoli (Upper Silurian) graptolite
biostratigraphy of the central Arctic Islands: a preliminary report.
Canadian Journal of Earth Sciences, 27:1074-1083.
-, AND M. J. MELCHIN. 1990. Wenlock graptolite biostratigraphy
of the Cape Phillips Formation, Canadian Arctic Islands. Canadian
Journal of Earth Sciences, 27:1-13.
, AND . 1991. Wenlock (Silurian) graptolites, Cape Phillips
Formation, Canadian Arctic Islands. Transactions of the Royal So-
ciety of Edinburgh: Earth Sciences, 82:211-237.
PERRY, D. G., AND B. D. E. CHATTERTON. 1977. Silurian (Wenlockian)
trilobites from Baillie-Hamilton Island, Canadian Arctic Archipel-
ago. Canadian Journal of Earth Sciences, 14:285-317.
PRANTL, F., AND A. PAIBYL. 1949. A study of the superfamily Odon-
topleuracea nov. superfam. (trilobites). Rozpravy Ustredniho uistavu
Geologick6ho, 12:1-221.
RAMSKOLD, L. 1984. Silurian odontopleurid trilobites from Gotland.
Palaeontology, 27:239-264.
199 a. The perforated trilobite Laethoprusia gen. nov., and the
phylogeny of Koneprusia and Isoprusia (Odontopleuridae, Konepru-
siinae). Transactions of the Royal Society of Edinburgh: Earth Sci-
ences, 82:125-141.
199 lb. Pattern and process in the evolution of the Odontopleu-
ridae (Trilobita). The Selenopeltinae and Ceratocephalinae. Trans-
actions of the Royal Society of Edinburgh: Earth Sciences, 82:143-
181.
- , AND B. D. E. CHATTERTON. 1991. Revision and subdivision of
the polyphyletic 'Leonaspis' (Trilobita). Transactions of the Royal
Society of Edinburgh: Earth Sciences, 82:333-371.
RICHTER, R., AND E. RicHTER. 1917. Uber die Einteilung der Familie
Acidaspidae und iiber einige ihrer devonische Vertreter. Zentralblatt
fir Mineralogie, Geologie und Palaontologie, for 1917:462-472.
SALTER, J. W. 1864. A monograph of the British trilobites from the
Cambrian, Silurian and Devonian formations. Palaeontographical So-
ciety Monographs, 80 p.
SWOFVFRD, D. L. 1993. Phylogenetic Analysis Using Parsimony Ver-
sion 3.1.1. Program distributed by the Illinois Natural History Surv-
ery, Champaign.
STEINMAN, G. 1912. In Steinmann, G., and Hoek, H., Das Silur und
Cambrium des Hochlandes von Bolivia und ihre Fauna. Neues Jahr-
buch fir Mineralogie, Geologie und Paliontologie, Beil 34:176-252.
WHITTINTON, H. B. 1956a. Silicified Middle Ordovician trilobites:
the Odontopleuridae. Bulletin of the Museum of Comparative Zo-
ology, Harvard, 114:155-288.
1956b. Type and other species of Odontopleuridae. Journal of
Paleontology, 30:504-520.
-, AND K. S. W. CAMPBELL. 1967. Silicified Silurian trilobites from
Maine. Bulletin of the Museum of Comparative Zoology, Harvard,
135:447-483.
AccETED 31 JULY 1996
siinae). Transactions of the Royal Society of Edinburgh: Earth Sci-
ences, 82:125-141.
199 lb. Pattern and process in the evolution of the Odontopleu-
ridae (Trilobita). The Selenopeltinae and Ceratocephalinae. Trans-
actions of the Royal Society of Edinburgh: Earth Sciences, 82:143-
181.
- , AND B. D. E. CHATTERTON. 1991. Revision and subdivision of
the polyphyletic 'Leonaspis' (Trilobita). Transactions of the Royal
Society of Edinburgh: Earth Sciences, 82:333-371.
RICHTER, R., AND E. RicHTER. 1917. Uber die Einteilung der Familie
Acidaspidae und iiber einige ihrer devonische Vertreter. Zentralblatt
fir Mineralogie, Geologie und Palaontologie, for 1917:462-472.
SALTER, J. W. 1864. A monograph of the British trilobites from the
Cambrian, Silurian and Devonian formations. Palaeontographical So-
ciety Monographs, 80 p.
SWOFVFRD, D. L. 1993. Phylogenetic Analysis Using Parsimony Ver-
sion 3.1.1. Program distributed by the Illinois Natural History Surv-
ery, Champaign.
STEINMAN, G. 1912. In Steinmann, G., and Hoek, H., Das Silur und
Cambrium des Hochlandes von Bolivia und ihre Fauna. Neues Jahr-
buch fir Mineralogie, Geologie und Paliontologie, Beil 34:176-252.
WHITTINTON, H. B. 1956a. Silicified Middle Ordovician trilobites:
the Odontopleuridae. Bulletin of the Museum of Comparative Zo-
ology, Harvard, 114:155-288.
1956b. Type and other species of Odontopleuridae. Journal of
Paleontology, 30:504-520.
-, AND K. S. W. CAMPBELL. 1967. Silicified Silurian trilobites from
Maine. Bulletin of the Museum of Comparative Zoology, Harvard,
135:447-483.
AccETED 31 JULY 1996
J. Paleont., 71(2), 1997, pp. 261-284
Copyright ? 1997, The Paleontological Society
0022-3360/97/0071-0261 $03.00
MAZON CREEK CYCLOIDEA
FREDERICK R. SCHRAM, RONALD VONK, AND CEES H. J. HOF
Institute for Systematics and Population Biology, University of Amsterdam,
Post Box 94766, 1090 GT Amsterdam, The Netherlands
ABsTRAcr-The Mazon Creek Cycloidea contain four taxa: Cyclus americanus Packard, 1885, Cyclus obesus, new species, Halicyne
max, new species, and Apionicon apioides, new genus, new species. We conclude, based on a cladistic analysis, that cycloids are
specialized maxillopodan crustaceans and a possible sister group to the Copepoda. They may have filled a niche similar to modern-
day crabs.
J. Paleont., 71(2), 1997, pp. 261-284
Copyright ? 1997, The Paleontological Society
0022-3360/97/0071-0261 $03.00
MAZON CREEK CYCLOIDEA
FREDERICK R. SCHRAM, RONALD VONK, AND CEES H. J. HOF
Institute for Systematics and Population Biology, University of Amsterdam,
Post Box 94766, 1090 GT Amsterdam, The Netherlands
ABsTRAcr-The Mazon Creek Cycloidea contain four taxa: Cyclus americanus Packard, 1885, Cyclus obesus, new species, Halicyne
max, new species, and Apionicon apioides, new genus, new species. We conclude, based on a cladistic analysis, that cycloids are
specialized maxillopodan crustaceans and a possible sister group to the Copepoda. They may have filled a niche similar to modern-
day crabs.
INTRODUCTION
CYCLUS AMERICANUS PACKARD, 1885, is among the most
common of Pennsylvanian arthropods from the Essex bi-
ota of the Mazon Creek area of northeastern Illinois. Packard's
original description employed only a single specimen from the
famous Lacoe Collection, now in the National Museum in
Washington. At that time, despite a lack of good illustrations
in the literature for the European species of Cyclus with which
to compare his fossil, Packard managed to relate those previ-
ously known species to his specimen, interpreting C. americanus
as a larva of some kind of horseshoe crab. However, Packard's
effort stands as only a single incident in a long history of con-
fusion and debate over the affinities of these enigmatic arthro-
pods.
Phillips (1835) described the first cycloid based on a single
example from the Carboniferous Limestone of Yorkshire, En-
gland, assigning his peculiar little nut-shaped species, Agnostus
INTRODUCTION
CYCLUS AMERICANUS PACKARD, 1885, is among the most
common of Pennsylvanian arthropods from the Essex bi-
ota of the Mazon Creek area of northeastern Illinois. Packard's
original description employed only a single specimen from the
famous Lacoe Collection, now in the National Museum in
Washington. At that time, despite a lack of good illustrations
in the literature for the European species of Cyclus with which
to compare his fossil, Packard managed to relate those previ-
ously known species to his specimen, interpreting C. americanus
as a larva of some kind of horseshoe crab. However, Packard's
effort stands as only a single incident in a long history of con-
fusion and debate over the affinities of these enigmatic arthro-
pods.
Phillips (1835) described the first cycloid based on a single
example from the Carboniferous Limestone of Yorkshire, En-
gland, assigning his peculiar little nut-shaped species, Agnostus
radialis, with radiating grooves and ridges, to the trilobites. Not
long afterward, de Koninck (1841) concluded that Phillips' spec-
imen was not a trilobite and created a new genus, Cyclus, for it
and other material of his own from the Carboniferous of Bel-
gium. To de Koninck, the genus Cyclus clearly possessed a sym-
metrical round to oval shell with depressed margins, anterior
paired ocular tubercles, and posterior longitudinal and radial
sinuous ridges. Nevertheless, de Koninck did not have a clear
understanding of Cyclus because later (de Koninck, 1842) he
erected a second species (C. brongniartianus) that Woodward
(1870) subsequently recognized as a trilobite hypostome.
Phillips' and de Koninck's confusion of their fossils with the
agnostid trilobites was not an isolated case. Quite independently,
von Meyer (1838) rather casually recognized a new species of
what he thought was a trilobite from the Triassic Muschelkalk,
naming it Limulus agnotus. He subsequently decided in 1844
that this species was neither a trilobite nor a Limulus and erected
radialis, with radiating grooves and ridges, to the trilobites. Not
long afterward, de Koninck (1841) concluded that Phillips' spec-
imen was not a trilobite and created a new genus, Cyclus, for it
and other material of his own from the Carboniferous of Bel-
gium. To de Koninck, the genus Cyclus clearly possessed a sym-
metrical round to oval shell with depressed margins, anterior
paired ocular tubercles, and posterior longitudinal and radial
sinuous ridges. Nevertheless, de Koninck did not have a clear
understanding of Cyclus because later (de Koninck, 1842) he
erected a second species (C. brongniartianus) that Woodward
(1870) subsequently recognized as a trilobite hypostome.
Phillips' and de Koninck's confusion of their fossils with the
agnostid trilobites was not an isolated case. Quite independently,
von Meyer (1838) rather casually recognized a new species of
what he thought was a trilobite from the Triassic Muschelkalk,
naming it Limulus agnotus. He subsequently decided in 1844
that this species was neither a trilobite nor a Limulus and erected
261 261
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
for it the genus Halicyne. However, this genus remained rather
vaguely diagnosed until von Meyer (1847) named a second,
somewhat smaller, sister species to H. agnota from the same
beds, H. laxa. Although these Halicyne occurred as steinkerns,
i.e., interior molds of the shell or carapace, the genus clearly
was about as wide as long, possessed a truncated front margin,
had a rather vaulted shell with its height being about 1/3 the
length, and displayed a wide, flat, posteriorly pointed margin.
So, by the middle of the 1800s two distinct cycloid morpho-
types occurred: a small, nut-like, ridged "skull cap," viz., Cyclus;
and a flattened "shield," viz., Halicyne. In 1857, von Seebach
collected three poorly preserved specimens from the Triassic
Lettenkohle of Thuringia near Weimar and named them Hal-
icyne plana. However, subsequent authors largely overlooked
this work. Schafhautl (1863, p. 423) recorded a form similar to
Halicyne, which he named Carcinaspis pustulosus, with a highly
papillose surface and sculpted margin from the Upper Triassic
of the Alps. Both H. plana and C. pustulosus broadly conformed
to the flattened shield morphotype.
In 1868 and 1870, Henry Woodward began to describe cy-
cloids in considerable numbers. Besides C. radialis, Woodward
recognized five species from the Carboniferous rocks of the
British Isles: C. harknessi, C. bilobatus, C. rankini, C. torosus,
C. wrightii and C. jonesianus, and these conformed in broad
outline to the morphotype of Phillips' C. radialis, i.e., small,
cap-like forms. All but the first of these, though, rather lacked
the distinctive radiating grooves and ridges, features which C.
radialis and C. harknessi shared. Because the non-radiating cap-
like forms resembled the shield-like genus Halicyne, Woodward
demoted Halicyne to a subgenus within the genus Cyclus. Wood-
ward thus began the confusion among cycloid genera that per-
sists to this day.
As we noted, Packard (1885, 1886) described the first Amer-
ican species of Cyclus, C. americanus, from the famous Penn-
sylvanian Mazon Creek deposits of Illinois. Packard compared
his little fossil to larval Limulus, but in this he merely followed
upon himself since his own earlier published commentary (Pack-
ard, 1872) treated Cyclus as a late larva of, or possibly an adult,
Limulus. The Mazon Creek fossil itself (see Figure 1.1, 1.2)
certainly preserved little that would have justified saying so.
Unwittingly, however, Packard introduced yet a third morpho-
type into the cycloid pantheon, not recognized as such at the
time. This morphotype possessed not only the flattened and
shield-like form evocative of Halicyne, but also had a rounded
or concave posterior margin and an anteriorly extended rostral
plate.
Woodward (1893) erected another species, Cyclus scotti, and
the first elucidation of the great array of preservational varia-
tions in Cyclus came from Woodward (1894). Peach (1883)
influenced Woodward in this regard, by first recognizing that C.
rankini preserved a ventral surface, and then describing a species
of his own from the Coal Measures of Scotland, C. testudo, that
supposedly had biramous limbs. From this work of Peach,
Woodward then recognized that 1) his species C. torosus in
reality preserved the ventral surface; 2) C. jonesianus had many
preservational variants; and 3) one preservational variant of C.
radialis displayed a broken carapace in such a way as to show
part of the radiating grooved and ridged dorsal surface of the
segments that lay beneath the shield. Woodward also speculated
for the first time on cycloid functional morphology, suggesting
that Cyclus had an enormously developed labrum with either
the mouth moved way posteriad and the leg bases serving as
jaws (as in Limulus), or the labrum developed as a sucking tube
(as in Argulus). Finally, Woodward's publication characterized
Cyclus for the first time as ". . . undoubtedly ... crustacean"
(Woodward, 1894, p. 534). Woodward also added two new
species to the growing list, C. scotti (1893) and C. johnsoni
(1894), which matched the general rounded shield-like form of
C. americanus and C. testudo.
Reed (1893) described another nut- or cap-like form with
radiating grooves and ridges, C. woodwardi. Thus by the turn
of the century, the British Cyclus assemblage exhibited great
diversity.
In parallel with this work on Coal Measure Cyclus and Triassic
Halicyne, descriptions of an enigmatic array of smaller, highly
vaulted cap-like species appeared. Von Schauroth (1854) pre-
sented a small granulate shell, Hemitrochiscus paradoxus, from
Upper Permian rocks in Germany. Gemmellaro (1890) dem-
onstrated a distinctly different, spinous form from the Permian
strata of Sicily, Oonocarcinus insignis, as well as a form more
akin to rounded shield-like Cyclus originally called Parapro-
sopon reussi. Stolley (1915) discovered in Triassic rocks of the
Alps and the Balkans a tiny, cap-like form, Cyclocarcinus ser-
ratus, and a very peculiar, possibly spinose species, Mesopro-
sopon triasinum.
Despite the fact that by this time three distinctively different
forms of cycloid occurred in rocks of either Carboniferous or
Triassic age, the general consensus viewed them as closely re-
lated species. As an example, Rogers (1902) described some
additional highly vaulted, cap-like, papillose forms from the
Pennsylvanian limestones of Missouri, Cyclus communis with
supposedly large compound eyes and C. permarginatus. Clearly,
Rogers attached no significance to the vaulting since he also
described some flattened Cyclus forms, C. packardi, C. limbatus
with distinctive spines on the margin, and C. minutus.
Woodward (1905) re-entered the field again with a short note
on C. johnsoni and C. rankini in which he asserted, with ap-
parently little basis except for Peach's earlier interpretation, that
all cycloids had biramous limbs; he also reiterated his view that
cycloids were limuloid-like crustaceans (not mutually exclusive
terms at that time in history because Limulus, and even trilo-
bites, were thought of as "crustaceous" in nature). Reed (1908)
described an Irish cycloid, C. simulans.
Bill (1914) noted specimens of Halicyne from the Alsatian
Buntsandstein, and Trauth (1918) also found Halicyne in Upper
Triassic rocks of the Alps. Neither of these authors formally
assigned their specimens to distinct species.
Hopwood (1925) finally tried to deal with the three distinct
morphotypes and re-separated Halicyne from Cyclus. However,
he focused on characters somewhat at odds with the original
diagnoses of the genera. Hopwood viewed Halicyne as a large
form with a bifurcate or bilobed posterior margin possessing
punctate ornament; whereas he perceived Cyclus as a small form
with a posterior median ridge that could bifurcate to enclose a
triangular area anteriorly and with lobate, ridged, nodular, or
papillose ornament. Hopwood sorted out all known species of
that time based on these characters. The genus Halicyne con-
tained the species agnota, americana, johnsoni, limbata, pack-
ardi, permarginata, and scotti. The genus Cyclus contained the
species radialis, bilobatus, communis, harknessi, woodwardi, jo-
nesianus, minutus, torosus and wrightii. Hopwood (1925, p. 308)
could not determine the affinities of H. laxa, and decided that
C. rankini was merely the ventral side of one of the other species.
He also believed that the affinities of the cycloids lay with Bran-
chiura, parasitic crustaceans also known as the fish lice.
Miiller (1955) clearly re-established the differences between
the two genera. Returning to the work of von Seebach (1857),
and prompted by some new material, Miiller identified the trun-
cated anterior margin and the pointed median, posterior margin
as the distinctive features of the genus Halicyne.
262
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
FIGURE 1 - Cyclus americanus Packard. 1,2, Part and counterpart of the holotype, USNMP 38863, x 4.3. 3, Note marapace shield showing anterior
lobe bearing antennules and antennae, posterior median notch, broad marginal sheltf median posterior ridge, lateral and posterior course
papillation, PE 22462, x 5. 4, Displaying trunk limbs impressed from below the carnpace, antenniules, geniculate maxillae, and caudal rami,
PE 31712, x 3. al = antennule, c = carapace, g = gut, mr = medial ridge, ms = marginal sheltf mx2 = maxilla, p = papillae, pn = posterior
notch, r = rostral lobe, s = sternites.
Triimpy (1957) promptly took up this definition when he
erected a species from the Muschelkalk, Halicyne ornata. Triim-
py also pointed out the great variation in shape within the genus
Cyclus and called attention to the difference between the flat-
tened species as opposed to highly vaulted taxa, suggesting that
separate generic names might eventually be necessary to distin-
guish these two morphotypes. Thus Triimpy recogni7ed as dis-
tinct the third cycloid morphotype introduced by Packard in
1885 when he described C. americanus.
Kramarenko (1961) extended the geographic range for Cyclus
when he described C. milaradovitchi from Lower Permian rocks
of the southern Urals.
Goldring (1967) introduced a new Cyclus species from Upper
Visean strata of FnEland, C. martinensis. He determined that
coral thickets formed probably the natural habitat of this species.
Meanwhile, Gall (Gall and Grauvogel, 1967; Gall, 1971) found
Halicyne ornata in the Buntsandstein (some specimens origi-
nally alluded to in Bill, 1914), a classic konservat lagerstatt. This
material occurred in greater abundance and with better pres-
ervation than that which Triimpy found in the Muschelkalk.
Although the wealth of information available from the Bunt-
sandstein specimens allowed a detailed reconstruction of H.
ornata, Gall could say nothing about the higher level relation-
ships of these cycloids other than "Crustaces aux affinites in-
263
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
certaines" (Gall, 1971, p. 55). However, Gall and Grauvogel
did erect a subclass for cycloids, the Halicyna, and they clearly
believed in biramous trunk limbs.
Glaessner (1969) provided a summary review of the cycloids,
but their status within the Crustacea remained uncertain. He
also took the opportunity to correct some generic names.
Schafhiutl's Carcinaspis became Carcinaspides, and Stolley's
Cyclocarcinus changed to Cyclocarcinides. Glaessner also sorted
the genera known at that time into three families. The Cyclidae
contained the more or less flatter forms Cyclus, Halicyne, and
Carcinaspides; the Hemithrochiscidae included the small, high-
ly vaulted taxa Hemitrochiscus, Cyclocarcinides, and Oonocar-
cinus; and the peculiar Mesoprosodon earned its own family,
the Mesoprosopidae.
Clark (1989) conducted the most recent study of Cyclus based
on material from the Namurian shales of Scotland. He produced
a detailed reconstruction of C. rankini and, more importantly,
attempted the first rigorous character analysis of known Cyclus
in combination with various other crustaceans, concluding that
cycloids belong within the Copepoda.
In addition to the above problems engendered by over a cen-
tury of taxonomic confusion concerning cycloids among pro-
fessional paleontologists, confusion also occurs among moder
collectors of Mazon Creek fossils about what name to use when
referring to their cycloids. These collectors variously call these
fossils Cyclus, Halicyne, or "trilobitomorphs." Use of the term
trilobitomorph harkens to the vague similarity of cycloids (albeit
without tails) to forms like the Burgess Shale creatures Burgessia
or Waptia. As to the origin of the confusion among collectors
about generic names (though Packard placed his species amer-
icanus within the genus Cyclus), for some time the late Gene
Richardson and one of us (FRS) used the generic designation
of Halicyne for Mazon Creek cycloids. This usage developed
from some contacts we had in 1967 with Prof. H. K. Brooks,
who mistakenly equated the name Cyclus with Halicyne. Rich-
ardson, before his death, had begun a study of the Mazon Creek
cycloids. He recognized that the fauna contained at least three
species of cycloids, but remained confused as to their taxonomy
and mistaken as to certain details of their anatomy. In point of
fact, Halicyne differs significantly from Cyclus, and we now
realize that both genera occur in the Mazon Creek fauna in
addition to some previously unrecognized new species.
For this study, we used specimens in the fossil invertebrate
collections of the Field Museum of Natural History in Chicago
(PE), the Mazon Creek Project at Northeastern Illinois Uni-
versity in Chicago (MCP), the Natural History Museum of Los
Angeles County (LACM), the National Museum of Natural His-
tory in Washington (USNMP), and the Nationaal Natuurhis-
torische Museum, Leiden (St).
SYSTEMATIC PALEONTOLOGY
Class MAXILLOPODA Dahl, 1956
Diagnosis.--No more than 12 postcephalic trunk segments,
uniramous antennules, at most six thoracic segments, abdomen
lacking most or all limbs, heart small and bulbous, with "max-
illopodan" naupliar eye with tapetal cells.
Remarks.--This diagnosis comes from that provided for
Maxillopoda in Schram (1986), and a few items in the definition
(e.g., heart and naupliar eye) do not occur in any known fossils.
Many crustacean workers place the Maxillopoda among the
most derived of all the crustaceans. The maxillopodans exhibit
a clear trend to reduce various parts of the body, often linked
to repeated evolution of a parasitic life style. However, the
reader should realize that if the number of trunk and thoracic
segments in a crustacean does not exceed the respective numbers
specified above, then one almost automatically considers it a
maxillopodan by default-not a particularly desirable situation.
Subclass HALICYNA Gall and Grauvogel, 1967
Diagnosis. -With only one order recognized at present, the
subclass definition is the same as that of the order.
Order CYCLOIDEA Glaessner, 1928.
Diagnosis.-Maxillopodans with flattened bodies, carapace
oval to subcircular in outline and typically covering entire body,
uniramous antennules large, uniramous antennae reduced in
size, antennules and antennae laterally attached on the anteri-
ormost part of the head, abdomen reduced to no more than one
or two segments, maxilla and anterior thoracopod(s) developed
as geniculate claspers.
Family CYCLIDAE Packard, 1885.
Diagnosis. -Dorsal surface shield-like in appearance and of-
ten highly convex; carapace with margin entire or denticulate
and with central regions smooth, longitudinally keeled, or pa-
pillose; segments underlying carapace appear somewhat radially
arranged; abdomen bears terminal, blade-like caudal rami.
Remarks. -The above definition modifies that of Glaessner
(1969). The range of structural diversity in carapace form, as
well as in genicula number and their anatomical variations in
the Mazon Creek cycloids, may in fact be the basis some day
for splitting this single family into several. Future discoveries
about these features in other genera and species of the cycloids
will undoubtedly lead to complete taxonomic revision of the
group.
The preservation of these fossils can confuse the casual ob-
server. The carapace can occasionally appear intact (e.g., PE
22462, Figures 1.3, 2.2). More often one or more surfaces of
the original body can appear on the same specimen. The dorsal
surface of the carapace often breaks away in the central area,
displaying portions of the cephalothoracic segments underneath
(USNMP 38863, Figure 1.1). One can often see traces of the
cephalothoracic limbs impressed from below (e.g., PE 31712,
Figure 1.4; PE 22472, Figure 3.4). In some specimens, the lateral
portions of the carapace are missing to reveal the lateral portions
of the thoracic tergites and limbs PE 34759, Figure 5.4). The
ventral surface can also display variations in their preservation,
e.g., as a ventral view of the sterites without legs (PE 22478,
Figures 6.1,2) or as a ventral view of the legs lying over the
sternites (PE 34954, Figure 5.2). Preservation commonly occurs
in negative, i.e., a mold of the original (PE 21013, Figure 6.5).
Fossils may exhibit variations ranging from three-dimensional
preservation of the original form (e.g., PE 22495, Figure 6.3) to
mere color differences in the rock (e.g., the antennae on MCP
507, Figure 4.1), or retain a lot of clay mineral such as kaolinite
(PE 24959, Figure 3.1) or pyrite (PE 20601, Figure 6.4). Because
of the variations in preservation that one can find on these
fossils, no one specimen preserves all the anatomy in perfect
array. Thus, reconstructions offered by us are composites based
on examination of several specimens for each feature. Material
actually illustrated here represents only a small portion of what
one can see on the 876 specimens available for this study.
Genus CYCLUS de Koninck, 1841.
Diagnosis. -Carapace oval to subcircular except for a large
rectangular plate over a frontal extension of cephalon, not very
convex and somewhat flattened in lateral or cross-sectional view,
surface papillose or smooth, margin either smooth or decorated
with fine crenulations. Antennules and antennae attached lat-
erally to frontal extension. Mandibles small and serrate, max-
illules small and bearing reflexed palps. Maxillae as large gen-
264
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
FIURtE 2-Cyclus americanus Packard. 1, Close-up of the anterior half showing the rostral lobe, antennvle (segments numbered) and antennal
peduncles, crenulated carapace margin and the proximal segments of some of the trunk limbs, PE 20985, x 6.9. 2, Close-up under alcohol of
the antennule peduncle with the proximal portion of the flagellum and a small antenna, PE 22462, x 6. 3, Anterior part of the body displaying
the antennular peduncle segments and antennae, counterpart of PE 31712, x 3.2. al = antennule (peduncular segments numbered), a2 =
antenna, c = carapace, cn = crenulated edge of carapace, ms = marginal shelf, r = rostral lobe, t = thoracic limbs.
icula, commonly preserved outstretched beyond frontal or ros-
tral plate. First thoracopod as geniculate maxillipede, last five
thoracopods as robust walking legs.
Type species. -Agnostus radialis Phillips, 1835.
CYcLus AMERICANUS Packard, 1885
Figures 1-8.
Diagnosis. -Carapace subcircular; margins as a broad shelf,
postero-lateral edges of shelf crenulate, margin bearing postero-
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
5
L
FIGURE 3-Cyclus americanus Packard. 1, PE 24959 with antennular flagella and maxillary geniculum, x 4. 2, PE 22498, maxillulary palp, x
10.6. 3, PE 34763, close-up of anterior ventral area with labrum, x 7. 4, PE 22472, displaying a negative impression of the labrum, of the
maxillules, the proximal segments of the maxillary geniculum, the proximal segments of the maxillipedal geniculum, and the first walking legs,
x 6.4. 5, Line drawing of 4. al = antennule, g = gut, = labrum, m = mandible, mxl = maxillule, mx2 = maxilla, mxpd = maxillipede, t"n"
= thoracic limbs.
median semicircular notch that dorsally exposes part of abdo-
men; central region of carapace marked posteriorly with broad
median ridge and decorated postero-laterally with coarse pa-
pillae.
Description. -The body is roughly subcircular in outline. The
length/width ratio is 0.98 (see Table 1).
The carapace has the form of a circular shield except for an
anterior frontal extension, or shelf-like rostrum, that covers that
part of the head that bears the antennules and antennae (e.g.,
PE 22462, Figure 1.3; PE 31712, Figure 1.4) and a posterior,
broadly rounded, median notch (PE 22462, Figure 1.3). The
carapace margin forms a broad shelf (USNMP 38863, Figure
1.2; PE 22462, Figure 2.2) that laterally and posteriorly displays
crenulations, which resemble the scoring of a pie crust with a
fork (PE 31712, Figure 2.3). The surface of the central part of
the carapace shield has a broad, subtriangular ridge on its pos-
terior half, as well as fields of coarse papillae located laterally
and posteriorly (USNMP 38863, Figure 1.2; PE 22462, Figures
1.3, 2.2).
The large antennules extend laterally from the frontal exten-
266
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
1
L
FIGURE 4-1, 2, Cyclus americanus Packard, MCP 507, 1, Under alcohol , showing maxillae, maxillipedes, five thoracopods, caudal rami, and
gut cast, x 2.4; 2, under direct light, x 2.7. 3, Cyclus rostratus Phillips. St 39783, showing the characteristic highly-vaulted body with thoracic
segments visible, x 8.4. 4-6 Cyclus americanus Packard. 4, MCP 557 showing cephalic structures, x 5.0. 5,6, MCP 556, with antennular
flagellum segments, maxilla, and gut cast, 5, under alcohol, 6, under direct lighting, x 3. al = antennule, cr = caudal rami, g = gut, 1 = labrum,
mn = mandible, mxl = maxillule, mx2 = maxilla, mxpd = maxillipede, 2-6 = 2nd-6th thoracopods.
sion of the head (PE 20985, Fig 2.1). The basal segment of the
peduncle is roughly subquadrangular in outline (PE 20985). The
second peduncular segment, more than twice as long as the first,
distally bears another short segment subequal to the first (PE
20985, Figure 2.1; PE 31712, Figure 2.3). The distal portion of
the antennule possess numerous short segments (PE 24959, Fig-
ure 3.1). However, only a few specimens (PE 24959, Figure 3.1;
MCP 556, Figures 4.5,4.6) preserve these segments well enough
along the entire length of the appendage that we can attempt to
count them. It appears that this portion of the limb has 25-27
segments, which when added to the three peduncular segments
totals 28-30 for the whole appendage (Figure 8.1).
The very small antennae appear just dorsal and posterior to
the antennules (PE 20985, Figure 2.1). The peduncles possess
267
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
FiGou 5-Cyclus americanus Packard. 1, PE 22421 with maxillary geniculum extended to display scimitar-like terminal segment, blade-like
penultimate segment, and caudal rami, x 5. 2,3, PE 34954 (part and counterpart) x 4.8, 2, Medial-most maxillary genicula and maxillipede
distal segment. 3, Clear view of teeth on penultimate blade of maxillipedal genicula. 4 ,5, PE 34759, 4, Showing general body form and
placement of thoracic legs, x 4.3. 5, Close-up revealing leg segments distal to knee, x 7.8. al = antennule, cr = caudal rami, ms = marginal
shelf of carapace, mx2 = maxillae, te = teeth, t "n" = thoracopods, 1-5 segments on third thoracopod.
~~~~Ce~LEs I |
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I _ [ '~~~~~~~~~~~~~~~~~~~~~~~P~
I ;._~~~~~~~~~~
I _ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~jl
~ad ,al qpl- ~~;,~~;~8pRl~Oi__i;;lW ~ ~pl~frY
_IUR _-CcU mrcnsPcad ,P 22 ihmxlaygnclmetne odslysiia-ietria emn,baelk
pnI mt 1emn,adcua ai .23 E394(atadcutrpr)x48 ,Mda-otmxlay gncl n ailpd
268
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
FIGURE 6-Cyclus americanus Packard. 1,2, PE 22478, part and counterpart with associated plant remains and displaying ventral surface, note
long proximal leg segments and apparent basal-most ring segments (arrow heads), x 5. 3, PE 22495, posterior portion of body with abdomen,
caudal rami and portions of posterior thoracic limbs, x 6. 4, PE20601, under alcohol, with foregut, pyritized gut dilator muscles (arrow heads),
midgut, x 5.7. 5, PE 21013, ventral surface, printed reversed to heighten relief, x 4.7. cr = caudal rami, fg = foregut, mg = midgut, mx2 =
maxilla, mxpd = maxillipede, pl = plant material, pp = "genital" posterior papillae, t "n" = thoracopods, 1-2 = abdominal segments.
269
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JOURNAL OF PALEONTOLOGY. V. 71. NO. 2. 1997
_1
7
FIGURE 7-Cyclus americanus Packard. Reconstruction of dorsal sur-
face. Scale = 2 mm.
3 segments: a short basal one and two longer more distal articles.
The last of these carry a short flagellum (PE 20985, Figure 2.1;
Figure 8.2).
The small and delicate mouth parts occur on only a few spec-
imens. The small labrum displays a somewhat triangular struc-
ture (PE 34763, Figure 3.3; Figure 8.3). Just posterior to these,
the mandibles (Figure 8.4) appear as blades (PE 22472, Figure
3.4; MCP 557, Figure 4.4). Whether these bore palps can not
be determined.
What appears as the small maxillules (Figure 8.5), lie just
posterior to the mandibles, and each bear a pronounced, reflexed
palp. The small basal segment (PE 22498, Figure 3.2) carries a
long article, which in turn distally connects to another long
segment directed medially and posterior, effectively bending
back on the proximal segment (MCP 557, Figure 4.4).
The large, robust maxillae (Figure 8.6) apparently could col-
lapse on themselves, like multiple-jointed jackknives, but they
frequently extend beyond the anterior edge of the rostral plate
(PE 24959, Figure 3.1; MCP 507, Figures 4.1, 4.2). The terminal
segment, shaped like a scimitar (PE 22421, Figure 5.1, PE 31713,
and PE 15167), apparently bears robust setae on its medial
terminus and flexes against a large, blade-like, penultimate seg-
ment with large setae on its medial margin (PE 34940, PE 34954,
Figure 5.2) to form a geniculate claw or clasper. Proximal to
the claw, two short segments connect to a very long segment
(PE 22421, Figure 5.1) that in turn may articulate with a short
basal-most segment.
The first pair of thoracopods, or maxillipedes (Figure 8.7),
greatly resemble the geniculate maxillae (PE 34954, Figure 5.2).
The maxillipedes, like the maxillae, also were capable of ex-
tending anteriorly beyond the edge of the front of the head. The
geniculate claw is somewhat larger than that seen on the maxilla
(PE 34954, Figure 5.3) and bears more robust setae on the
penultimate blade-like segment. Two intermediate segments
connect the geniculum to a long proximal segment (PE 1280,
TABLE I-Size in cm of a representative array of 55 well-preserved
specimens Cyclus americanus in the collections of the Field Museum
of Natural History.
Carapace
Length Width Length: width
Range 0.96-2.02 0.90-2.0
Av. length 1.40 1.43 0.98
St. dev. 0.23 0.27
St. error 0.03 0.04
270
2
9
8
4
o
3
a
5
FIGURE 8--Cyclus americanus Packard. Reconstruction of appendages
and associated structures: 1, antennule; 2, antenna; 3, labrum; 4,
mandible; 5, maxillule; 6, maxilla; 7, maxillipede; 8, thoracic walking
leg; 9, caudal ramus. Scale = 2 mm.
PE 22472, Figure 3.4), which in turn seems to attach proximally
to a very short, ring-like segment.
Thoracopods two through six, virtually identical, tend to be-
come somewhat shorter posteriorly in the series. Although we
examined almost 900 specimens from several museum collec-
tions in this study, of these we found that very few preserve the
thoracopods adequately (e.g., PE 22495, Figure 6.3; PE 34759,
Figures 5.4, 5.5; PE 34954, Figure 5.2). These limbs apparently
all articulate on the margin of the thoracic sternites. It is not
clear whether a very long, often medially directed, proximal
segment attaches directly to the sternites. Some evidence seems
to indicate in this regard that a small ring-like article (PE 22478,
Figures 6.1, 6.2) connects this long segment to the sternite.
(Indeed, the dynamics of movement possible around the thor-
acopod/sternite joint would seem to require a small "coxal"
segment.) The distal end of the long segment marks a knee in
the thoracopods (Figure 8.8), and five moderate to short seg-
ments compose the distal aspect of the thoracopod (Figures 5.4,
5.5).
The abdomen possesses two segments, a short anterior one,
which bears a pair of large papillae laterally (PE 22495, Figure
6.3), and a somewhat larger posterior segment exposed dorsally
by the median posterior carapace notch. This last segment bears
the anus as well as the marginally serrate (PE 22421, Figure 5.1)
caudal rami (PE 22495, Figure 6.3).
Occurrence. -Francis Creek Shale, Desmoinsean, Middle
Pennsylvanian.
Material examined. -USNMP 38863. Some 876 specimens
in the fossil invertebrate collections of the Field Museum of
Natural History, but especially PE 15167, 15191,20601,20616,
20985, 21013, 22421, 22444, 22462, 22472, 22478, 22495,
22498, 23397, 24949, 24959, 31712, 31713, 32159, 32173,
34940, 34759, 34763, 34791, 34797, 34822, 34842, 34925,
34935, 34954. MCP 452, 507, 554, 555, 556, 557, 558.
Holotype.-USNMP 38863 (Figures 1.1, 1.2) ; from along
Mazon Creek, Grundy County, Illinois.
Remarks.--We offer a reconstruction of the dorsal aspect of
C. americana in Figure 7 and our interpretation of the append-
ages in Figure 8.
A problem exists regarding the identity of the antennules and
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
antennae. Although the large size of the anterior-most limbs
might suggest antennae, we denoted these long limbs as the
antennules, initially only because of their location. We thus
identified the much shorter and somewhat more posterior limbs
as the antennae. Clark (1989), however, believed that the op-
posite was true based on his work with Cyclus rankini, viewing
the large limbs as the antennae and the smaller ones as the
antennules. Although antennules generally occur as the smaller
of the two limbs in crustaceans, in many groups just the opposite
prevails. This in fact commonly happens within the Maxillo-
poda, as within many copepod orders, the branchiurans, and
the mystacocarids. Huys and Boxshall (1991) have advanced a
new interpretation of copepod evolution in which they hypoth-
esized that antennules had in their most plesiomorphic state 28
segments-virtually identical to what we found on those limbs
we identify as the antennules of Cyclus. So, Clark not withstand-
ing, we hold to our original designation.
These fossils can preserve internal soft-part anatomy. The gut
often occurs as a detritus-filled cast (e.g., see Figures 1.2, 1.4,
3.1, 4.5, 4.6). Occasionally, one can discern a somewhat wider
anterior region of the gut. In one particular specimen (PE 20601,
Figure 6.4), this transition appears not only as a change in gut
diameter, but also as a difference in gut content. The foregut in
this specimen (the anterior, wider region) contains slightly coars-
er sediment than the midgut (the posterior, narrow region) and,
when examined under alcohol, this specimen appears to pre-
serve pyritized remnants of the foregut dilator muscles associ-
ated with that region. Cyclus americanus is the most common
of the cycloids in the Mazon Creek biotas. Of the 876 specimens
in the collections of the Field Museum examined for this study,
all of them came from the Peabody Coal Company, Pit 11 mine,
in Will and Kankakee counties, northeastern Illinois. This is the
principle collecting site for the marine-like Essex fauna. The
holotype specimen that Packard described from the Lacoe Col-
lection had to have come from the fresh- to brackish-water
Braidwood fauna localities along Mazon Creek itself, the prin-
cipal source of classic Mazon Creek specimens in the last cen-
tury. However, one hardly ever sees examples of Cyclus in any
of the Braidwood fauna collections examined by many research-
ers over the years. This would indicate that, although Cyclus
could have occurred in the Braidwood habitat, in life Cyclus
americanus preferred more marine conditions.
Some question has arisen in the literature as to what Cyclus
fed upon. The loosely stated consensus of past workers has more
or less opted for some kind of parasitic mode, based mostly on
the gross similarity of cycloids to branchiuran fish lice. However,
the relatively large size of Cyclus argues against a parasitic habit
(at 1 cm in diameter these purported parasites match in size
many of the fish in the fauna they supposedly would have fed
upon). On the other hand, the only consistent association within
the Mazon Creek concretions of Cyclus, other than with other
examples of itself, occurs with plant material (e.g., see Figures
6.1, 6.2). Such associations inevitably have the plant material
lying close to or attached to the head. The geniculate claws and
slicing mouth parts not only could have served a parasite, but
also could have provided equally good service to a plant or
detritus eater. We believe this latter possibility much more likely
than parasitism.
CYCLUS OBESUS new species
Figures 9, 10
Diagnosis. -Carapace oval in outline, much wider than long,
surface smooth bearing no decoration, margin demarcated by
a narrow shelf, edges smooth and entire (no posterior notch),
central region of carapace shield elevated as a plateau and de-
lineated by a pronounced circular ridge.
Description. - C. obesus possesses a strikingly wide carapace
(see Table 2), with a surface not marked with any textured
decoration (PE 30630, Figure 9.2), but with a margin set off by
a narrow brim or shelf. The central area is flattened, higher than
the margin and set off by a distinct circular ridge (PE 23041,
Figure 9.3). The cephalon has a very wide frontal extension or
rostral plate, and the area of the carapace just posterior to the
antennular bases bears a slight, raised, ocular ridge (PE 23041,
PE 30630 , Figure 9.1, 9.3). The carapace displays neither pos-
terior median nor anterolateral ocular notches.
The large and very long antennules (PE 34834; PE 34880,
Figure 9.5) possess a basal peduncular segment of moderate
length, slightly longer than wide. The second peducular segment
appears shorter than the first. Presently we have little knowledge
concerning the rest of the limb.
We known nothing about the labrum, mandibles, or maxil-
lules. The geniculate maxillae have a robust, club-like, terminal
segment that folded back onto a rather wide penultimate seg-
ment (PE 39056, Figure 9.4). We have no knowledge about the
rest of the limbs.
The caudal rami appear as long blade-like processes on only
a single specimen (PE 34834, not illustrated).
The thoracic tergites have a subparallel, largely laterally di-
rected, linear arrangement and express only a slight posteriad
orientation (PE 34880, Figure 9.5).
Occurrence. -Francis Creek Shale, Desmoinsean, Middle
Pennsylvanian.
Material examined. -PE 23041, 24975, 30630, 34834, 34880,
39056.
Holotype and locality. -PE 30630 (Figure 9.1, 9.2), Peabody
Coal Co. Pit 11, Will and Kankakee counties, Illinois.
Remarks. -We present a reconstruction of the dorsal aspect
of C. obesus in Figure 10.
A few specimens of C. obesus (notably PE 39056, Figure 9.4,
PE 34880, Figure 9.5) preserve gut casts. However, the gut
appears to terminate in a position relatively more anterior to
that seen for the position of the anus of C. americanus.
The arrangement of the thoracic segments differs from that
of C. americanus. Rather than "radiating" out from an area
somewhat posterior to the center of the cephalothorax, they have
a somewhat more linear and subparallel array, with the posterior
deflection not nearly as pronounced as that seen in C. ameri-
canus. Thus, the thorax, wide like the carapace, may accom-
modate the short abdomen such that the terminus of the ab-
domen may lie well beneath the carapace.
The lack of a posterior median notch on the carapace shield
distinguishes C. obesus from what is known of other species of
Cyclus. However, the relatively flattened shape of the body, the
character of the geniculate maxillae, the prominence of the fron-
tal extension, and the nature and orientation of the antennules,
resemble the better known C. americanus and C. rankini. The
above features would seem perhaps more diagnostic at a family
rather than a generic level, and some future revision of the
cycloids may place C. obesus into a separate genus.
Genus HALICYNE von Meyer, 1844.
Diagnosis. -Carapace with moderately convex and shield-
like outline distinctly truncated anteriorly and either slightly
acute or distinctly pointed posteriorly, with distinct optic notch-
es, anteriorly articulated to a separate rostral plate; geniculate
maxillae modest to small in size; first two thoracopods at least
modified as maxillipedes; post-maxillipedal thoracic legs di-
rected laterally and anteriorly; underside of carapace in the tho-
racic region marked by densely packed transverse rugae or la-
mellae.
Type of genus. -Limulus agnotus von Meyer, 1838.
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
FIGoRE 9-Cyclus obesus new species. 1,2, PE 30630, holotype, 1, Under direct lighting, x 4.3; 2, Under alcohol, x 4.5. 3, PE 23041, note
circular central ridge and lack of a median 'posterior notch', x 4. 4, PE 39056, with distal elements of maxillary genicula and gut trace, x 5.
5, PE 34880, displaying proximal portion of the antennule and body segments (arrows), x 4. al = antennule, g = gut, or = orbital ridge, ms
= marginal shelf, r = rostral plate, rc = circular ridge, mxl = maxilla.
Remarks. - One can recognize members of the genus Halicyne
by their moderately convex yet distinctly shield-like carapace
that bears a clearly delineated margin, a rather truncated an-
terior aspect, and an articulated or hinged rostral plate. In ad-
dition, the posterior margin of the carapace shield can display
a somewhat pointed apex at the midline. The carapace surface
may or may not possess any decoration; H. max, H. ornata,
and H. plana do exhibit such decoration, whereas H. agnota
and H. laxa do not. All the thoracic legs may have a somewhat
geniculate character (not at present clear), but at the very least
the more anterior of the post-maxillipedal limbs have a distinct
lateral and anterior orientation.
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
TABLE 2-Measurements in cm of specimens of Cyclus obesus; * indi-
cates holotype.
Carapace
Specimen Length Width Length: width
PE 23041 1.22 1.70 0.72
PE 24975 1.32 1.70 0.78
PE 30630* 1.20 1.44 0.83
PE 34834 1.05 1.45 0.72
PE 34880 1.33 1.67 0.80
PE 39056 1.35 1.74 0.78
Average 1.24 1.62 0.76
FIGURE 10-Cyclus obesus new species. Reconstruction of the dorsal
surface. Scale = 2 mm.
Another fossil species should probably figure into these com-
parisons, the poorly known taxon Carcinaspides pustulosus
Schafhautl, 1863. This species more than likely seems related
to Halicyne, because it shares with that genus a truncated an-
terior area and lobate decoration on the anterior and median
areas of the carapace. The Carcinaspides fossils, however, ap-
pear to lack a clearly defined optic notch and a rostral plate.
Nevertheless, they display a distinct, dense, and robust array of
papillations on the carapace surface and a highly scalloped mar-
gin. Although Carcinaspides pustulosus should remain a distinct
species for now, one might make a convincing argument for
placing it within the genus Halicyne if the holotype ever becomes
available for study.
HALCYNE MAX new species
Figures 11-16
Diagnosis. -Carapace shield almost circular in outline, slight-
ly vaulted in cross section, bearing distinct papillose decoration
(especially on antero-medial parts), with distinctly thickened
submarginal rim bearing thin, scalloped, serrate, shelf-like edge;
underside of carapace with lamellae; distinct optic notches an-
tero-laterally with small stalked compound eyes; rostral plate
well developed with a distinct ventrally directed anterior-most
portion bearing a pair of rounded knobs or bosses; terminal
segments of all geniculate claws long and thin, two sets of max-
illipedes, maxillepedal genicula distinctly larger than those of
the maxillae.
Description.-The almost completely circular and vaulted
carapace appears about as long as wide (see Table 3) and bears
a distinctly papillose surface (e.g., PE 13445, Figure 11.2; PE
34772, Figure 11.1; PE 34772, Figure 12.3). The quite complex
margin of the carapace folds to form a distinct submarginal rim
(PE 15233, Figure 11.3, PE 34772, Figure 11.1) that bears a
thin, shelf-like, scalloped, and robustly spinose edge (e.g., PE
22453, Figure 13.1; PE 24954, Figure 13.2; PE 24061, Figures
13.3 and 13.4). The distinct optic notches occupy places at the
anterior ends of the submarginal rim and anteriorly bear a lat-
erally directed process (PE 15233, Figures 11.3 and 11.4; PE
34772, Figure 11.1). Stalked compound eyes lie in these notches
(PE 34772, Figure 14.1). A wide, papillose rostral plate extends
forward from the anterior margin of the carapace shield (PE
34772, Figure 12.3; PE 22453, Figure 13.1). Composed of two
portions, the dorsal part of the rostral plate bends ventrally to
form a separate "bumper" along the anterior-most facade of the
head (PE 15233, Figures 11.3, 11.4; PE 22552, Figure 15.1).
We cannot determine exactly whether this ventrally directed
portion forms a solid part of the rostral plate or movably artic-
ulates with the basal portion. This ventrally directed plate bears
distinct paired bosses (Figures 11.4, 12.3) and a median raised
area that has a finely reticulated, reflective surface similar to
that seen on the optic areas of the compound eyes (Figure 14.1).
The underside of the carapace in the region of the thorax has
a dense arrangement of subparallel lamellae or rugae (Figure
11.1; PE 25662, Figure 12.1, Figure 15.1; Figures 14.1, 14.2,
14.3). These occur as thin double-walled plates (PE 22552, Fig-
ure 14.3). These plates appear to arise as a series of folds or
flaps from the underside of the carapace proper rather than
growing out from the lateral thoracic body wall. The preser-
vation of these fossils precludes definitive conclusions, but it
appears that these plates lie in a U-shaped chamber formed by
the body wall and carapace and possibly partially enclosed by
a flange from the posterior and postero-lateral sternites and the
edge of the carapace (PE 22552, Figure 14.2, 14.3).
None of the specimens we have seen preserve much of the
antennules and antennae. We know only the geniculate limbs
completely. The maxillae have a short delicate terminal segment
(PE 28958, Figure 15.2) and serrations on the medial edge of
the moderately long penultimate segment (PE 13445; PE 34772,
Figure 12.3). Although well developed and directed distinctly
anteriad, the maxillae appear smaller than the maxillipedes (Fig-
ures 15.1-15.3).
The very large first maxillipede has a long and delicate ter-
minal segment, subequal to the single-segmented, somewhat
more robust, penultimate segment (PE 25662, Figure 12.2; PE
28958 Figure 15.2). These seem to have a distinct anterior ori-
entation extending out in front of the head. The second max-
illipede has a more antero-lateral orientation of its subchelate
geniculum (PE 13445, Figure 11.2; PE 11451, Figure 15.3). The
second maxillipede appears as somewhat shorter than the first
but still longer than the maxillae (PE 34772, Figure 11.1).
The well-developed walking legs extend laterally from the
body but are concentrated in the anterior portion of the thorax
(PE 34772, Figure 11.1). Furthermore, at least the anterior-most
of these have their distal segments directed anteriad (PE 25662,
Figure 12.1). Thus the posterior thoracopods appear to be some-
what geniculate.
We know nothing concerning the abdomen or caudal rami of
this species.
Occurrence. -Francis Creek Shale, Desmoinsean, Middle
Pennsylvanian.
Material examined.-PE 11451, 13445, 15233,20613,21610,
22464, 22552, 22471, 24061, 24954, 25662, 28958, 34764,
34772.
Holotype and locality. -PE 34772 (Figures 11.1, 12.3), Pea-
body Coal Company Pit 11, Will and Kankakee counties, Illi-
nois.
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JOURNAL OF PALEONTOLOG Y, V. 71, NO. 2, 1997
FIGURE 11 -Halicyne max new species. 1, PE 34772, holotype, x 4.6.2, PE13445, clearly preserving the carapace in one plane and in a different
plane portions of the thoracic limbs, x 4.8. 3,4, PE 15233, 3, Part, with optic notch and inflated rim, papillated dorsal surface of carapace
missing, x 4; 4, Counterpart, under alcohol, canted with posterior edge higher than anterior so that the rostral plate, at an angle to plane of
carapace, can be more fully seen, x 6. ms = marginal shelf, mx2 = maxillae, mxpdl, 2 = first and second maxillipedes, on = optic notch, r =
rostral plate, ru = gill lamellae or rugae.
Remarks.--We offer in Figure 16 a dorsal and anterior re- information available for Cyclus americanus. Even so, the van-
constructions of this species. ations in preservation between the various known Halicyne taxa
Halicyne max takes its place as one of the better known species make it difficult to compare species, especially those for which
of the genus. Yet it pales in comparison with the amount of we know so little. H. agnota and H. laxa have smooth surfaces
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
FIGURE 12-Halicyne max new species. 1, PE 25662, counterpart, with maxillae and maxillipedal genicula and laterally/anteriorly oriented
thoracopod, x 5.2. 2, PE 25662, with fully extended maxilla and first maxillipede genicula and showing rugae or lamellae in carapace chamber,
x 3.8. 3, PE 34772, close-up of Figure 11.1 printed in reverse to better illustrate surface popillation, rostral plate, optic notch, and genicula,
x 8.3. mx2 = maxillae, mxpdl,2 = maxillipedes, r = rostral plate, ru = gill rugae or lamellae.
on the carapace, and the anterior and median portions of the
carapace shield possess prominently inflated bumps and folds.
All other species of Halicyne have papillated carapace surfaces.
H. plana possesses a body more narrow than long, inflated areas
on the anterior part of the carapace, and a postero-medial dis-
tinctly pointed margin. H. ornata may resemble H. max most
closely in that it has an almost circular outline; but it exhibits
large optic notches and a pointed postero-medial margin, and
the ventral part of the rostral plate appears to lack bosses on
the surface.
The lamellae under the carapace of Halicyne pose problems
for interpretation. These structures may constitute a diagnostic
feature for this genus. We do not notice lamellae such as these
on any other cycloids. Aside from H. max, similar lamellae also
occur in H. ornata. The thin, double-walled nature of the plates
possibly suggests an interpretation of these as "gills." One might
275
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
FIGURE 13-Halicyne max new species. 1, PE 22453, with sculpted ring-like marginal shelf, x 6. 2, PE 24954, note plant material adjacent to
rostral plate and sculpted margin, x 8. 3,4, PE 24061, 3, with extended maxillipede, x 5.4; 4, Close-up showing sculpted margin, x9.3. ms
= marginal shelf, mxpd = maxillipede, pl = plant material, r = rostral plate, ru = gill rugae or lamellae.
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
FIGURE 14-Halicyne max new species, latex molds. 1, PE 34772, displaying the extended genicula, the rounded bosses on the rostral plate, and
the stalked eyes in the optic notches, x 5.7; 2,3, PE 22552, 2, Featuring the underside of the body and the opening to the "gill chamber," note
also serrated marginal shelf, x 4.0; 3, Counterpart of 2 with the underside of the carapace and the gill lamellae, note that the lamellae are
paired (arrows) which we believe indicates they were folded each member of a pair forming a wall of the fold, x 4.0. 4, PE 20812, clearly
showing the paired nature of these lamellae, x 4.0. b = bosses on rostral plate, ce = stalked compound eye, eg = edge of gill chamber, mx2 =
maxillae, mxpdl = maxillipede, ru = gill lamellae or rugae.
look for parallels in the densely packed thoracopodal epipodites
seen among many branchiopods or the lamellae of phyllobran-
chiate gills in eucarid malacostracans.
The reflective bosses on the anterior bumper raise questions.
As noted above, upon close examination they appear similar to
sessile eyes. However, we hesitate to call them so because we
note a perfectly good set of stalked compound eyes located in
the antero-lateral optic notches of the carapace. More and better
preserved material may subsequently confirm these bosses as
eyes. If that occurs, the only parallel we can draw upon comes
from the unusually large ocelli of naupliar eyes seen in pontellid
copepods (Park, 1966), so large in fact that at one time Parker
(1891) mistakenly reported them as compound eyes.
Genus APONICON new genus
Diagnosis. -Carapace distinctly oval and anteroposteriorly
elongate, with no well-developed marginal shelf; small rostral
plate extending from anterior portion of carapace; antennules
directed laterally.
Type of genus. -Apionicon apioides new species
APIONICON APIOIDES new species
Figures 15.4, 17, 18.
Diagnosis. -Carapace marked by median and lateral longi-
tudinal ribs and furrows, posterolaterally lightly decorated with
papillae, margin slightly crenulate.
Description. -The carapace envelops the body, and displays
an elongate, oval form with a medial and some paired longi-
tudinal ribs flanked by slight furrows and a posterolateral field
of papillate ornament (PE 22464, Figure 15.4). The anterior
part of the carapace has a rounded rostral extension from which
a well-developed set of antennules and smaller antennae extend
laterally (PE 22471; PE 34764, Figure 17.1). The margin of the
carapace exhibits some faint crenulation (PE 22464, PE 34764).
The specimens studied preserve few of the remaining ap-
pendages. PE 20613 may preserve some remnants of one of the
geniculate limbs, whereas LACM 1052 preserves some faint
outlines of long thin caudal rami (Figure 17.2).
Occurrence. -Francis Creek Shale, Desmoinsean, Middle
Pennsylvanian.
Material examined.-PE 20613, 22464, 22471, 34764.
Holotype and locality. -PE 22464 (Figure 15.4); Peabody Coal
Company Pit 11, Will and Kankakee counties, Illinois.
Remarks. -With only five poorly preserved specimens of this
species available for study, the species description must remain
minimal for now. However, one should not conclude that this
scarcity indicates any unimportance for this species in the orig-
inal Late Pennsylvanian Mazon Creek biotas. Amateur and pro-
fessional collectors through the years have tended to keep only
better preserved specimens gathered from Mazon Creek local-
ities. The generally poor preservation of A. apiodes may have
produced a bias against this species in museum and private
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
FIoURE 15-1-3, Halicyne max new species. 1, PE 22552, note gill rugae on posterior and lateral areas of carapace underside, x 4.8; 2, PE 28958,
with well-preserved maxilla and first maxillipede, x 6.4; 3, PE 11451, close-up showing portion of maxillae, first and second maxillipedes, x
6. 4, Apionicon apioides new genus, new species, PE 22464, holotype, x 8.4. al = antennule, mx2 = maxilla, mxpdl = maxillipedes, p =
papillations, r = rostral plate, ru = gill rugae or lamellae.
._ _. _
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
TABLE 3-Measurements in cm of specimens of Halicyne max; * in-
dicates the holotype.
Carapace
Specimen Length Width Length: width
PE 11451 - 1.35 -
PE 15233 1.30 1.23 1.06
PE 22552 1.45 1.43 1.01
PE 24954 -0.84 0.80 1.05
PE 24061 1.05 1.00 1.05
PE 25662 1.24 -1.10 1.13
PE 34772* 1.13 1.10 1.03
Average 1.17 1.14 1.03
FIGURE 16-Halicyne max new species. Reconstruction of dorsal (1)
and anterior views (2). Scale = 2.5 mm.
collections. As a typically structureless, color-fossil, A. apiodes
displays the kind of preservation generally discarded in the field
by collectors and which can cause casual sorters of Mazon Creek
collections to misidentify these fossils as belonging to some other
group, e.g., jellyfish. This kind of preservation in other Mazon
Creek fossils more often than not occurs in groups that were
highly calcified in life, such as molluscs, and this may indicate
that A. apioides also may have had a high degree of cuticular
mineralization.
DISCUSSION
Earlier workers on cycloids were obviously uncertain about
the taxonomic affinities of the group. As we have seen above,
within the first 16 years of work on the group, various workers
had suggested every major higher category of arthropods as a
repository for cycloids. This confusion has continued down to
the present.
The reason for so much disagreement regarding not only high-
er taxonomic placement, but also the generic affinities of the
species described, centers on problems with taphonomy. The
forms found in limestone appear as small, highly convex fossils
with little or no information concerning appendages, whereas
those collected from shales appear generally flatter and often
preserve additional information concerning limbs and internal
anatomy. The question then becomes whether these differences
arise from varying modes of preservation, or do they reflect
some real structural variants. Triimpy (1957) believed them
real, although Clark (1989) thought them to be taphonomic. We
believe that proper consideration of both taphonomy and real
morphology will play equal roles in any future revision of the
cycloids.
However, we see clearly distinct body types within the genus
Cyclus alone. Many species of Cyclus at least superficially more
closely resemble species in other cycloid genera than they do
each other (Figure 19). We can distinguish at least three body
types within Cyclus: 1) a form characterized by C. radialis (the
"type" form; see also Figure 4.3), a highly vaulted cap-like body
and including C. bilobatus, C. communis, C. harkensii, C. jo-
nesianus, C. martinensis, C. milaradovitchi, C. minutus, C. per-
marginatus, C. simulans, C. torosus, C. woodwardi, and C.
wrighti; 2) a form represented by C. rankini, very flat, wide,
with a weakly developed rostral plate, and a distinctly raised
margin on the carapace including C. johnsoni, C. scotti, and C.
testudo; and 3) the form characterized by C. americanus with
moderate vaulting and a well-developed rostral plate and that
also includes C. obesus. The affinities of C. limbatus and C.
packardi may actually lie with the Halicyne/Caracinaspides
complex, but the type specimens of these species, as well those
as of C. communis, C. minutus, and C. permarginatus appear
to be lost.
The issue of taphonomy cannot be ignored in all of the above.
The radialis cluster of species occurs in limestones, whereas the
rankini and americanus clusters occur in shales and coal-mea-
sure deposits. Without examining all the material available for
all species, clearly beyond the scope of this paper, we cannot
hope to make any reasonable judgements as to the status of
these groups. Consequently, rather than erect new genera, we
believe it more prudent for now to refer to these clusters of taxa
within Cyclus as species groups.
Specimens of Halicyne max also demonstrate the clear as-
sociation of cycloids with plant remains. Figure 13.2 illustrates
one such specimen with the cycloid clearly attached by the head
to a plant. When we build on this association to indicate a diet
of herbivory, or possibly scavenging, and combine this with
general features of the cycloid habitus (viz., broad, round, flat
bodies; small antennae and possibly small antennules; laterally
placed, stalked, compound eyes; claws; laterally located, robust,
uniramous, walking limbs; broad sternites; and greatly reduced
abdomen), we come to a startling conclusion. Cycloids bear
striking, convergent similarities to the body plan of crabs! The
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JOURNAL OF PALEONTOLOG Y, V. 71, NO. 2, 1997
FIGURE 17-1,2, Apionicon apioides new species. 1, PE 34764, with antennules from rostral extension, x 6; 2, LACM 1052, with antennules and
faint remnants of caudal rami, x 3. al = antennule, cr = caudal rami, r = rostral plate.
only true crab from the Paleozoic, Imocaris tuberculata Schram
and Mapes, 1984, apparently has affinities to the dromiaceans.
In light of well-developed lobsters appearing in Late Devonian
time (e.g., Schram et al., 1978), paleocarcinologists have had
problems explaining why crabs came into full development rel-
atively late (from Jurassic and Cretaceous onward). The answer
1, d.c f
:. - .: -: -. .
? ; *?: ' i ? ;.:' ?
?: t'pli'
dorsal surface. Scale = 2 mm.
may lie in the fact that cycloids occupied the niche, and crabs
could not really begin to radiate until cycloids became extinct
after the Triassic-an interesting speculation.
The above taxonomic issues notwithstanding, we can advance
a clear hypothesis about the higher taxonomic affinities of Cy-
cloidea. First, there now appears little doubt that the Cycloidea
belong among the crustaceans. The possession of two sets of
antennae, mandibles, and two sets of maxillae with maxillipedes
clearly places at least the genus Cyclus squarely within the Crus-
tacea. This would strongly infer that genera such as Halicyne
1 2
f--
3
()'4 X
FIGURE 19-Outline diagrams of generalized dorsal (anterior towards
the top) and lateral (anterior to the right) body forms in the currently
recognized species groups in the genus Cyclus and the genus Halicyne.
1, The highly vaulted, button-like C. retractata species group; 2, The
flattened, bilobed C. rankini species group; 3, The flattened, shield-
like C. americanus species group; 4, The highly vaulted, shield-like,
anteriorly blunted Halicyne.
280
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
TABLE 4-Measurements in cm of specimens of Apionicon apioides; *
indicates the holotype.
Carapace
Specimen Length Width Length: width
PE 20613 1.45 -
PE 22464* 1.29 ~0.90 1.43
PE 22471 1.46 1.17 1.25
PE 34764 1.27 1.57 0.81
and Apionicon belong there as well, even though currently known
specimens of these and other genera do not always preserve
pertinent information concerning the antennae, mandibles, and
maxillules. Nevertheless, the form of the maxillae in these more
poorly known species, with two sets of maxillipedes and caudal
rami, agrees with what we now known about Cyclus americanus.
In addition, a combination of other features discernible on
these fossils places them squarely inside the Class Maxillopoda.
These include uniramous antennules and, most importantly, the
body tagmosis pattern in accord with that seen in maxillopo-
dans, viz., a classic 5-6-5 (head, thorax, and abdomen) segment
pattern. The maxillopodans often reduce the abdomen (and in
some cases the posterior thorax). Cyclus clearly has a 5-6-2
pattern, and thus falls within a maxillopodan bauplan. In ad-
dition, the anterior abdomen segment may bear some repro-
ductive structures. Clark (1989) reported apparently paired pe-
nes extending forward from the abdomen in Cyclus rankini, and
we have noted possible genital papillae similar to those seen in
female branchiurans (see above) on the first abdominal segment
in C. americanus, another common feature of maxillopodans.
We disagree, however, with the opinions of previous authors
about where the cycloids belong within the array of the various
Maxillopoda. Though cycloids have a large, shield-like carapace
and apparently serrate mandibles like branchiurans, they lack
other apomorphic features of the branchiuran fish lice. First,
cycloids do not bear antennules and antennae modified for at-
tachment to a host. Cycloid antennules, at least for Cyclus prop-
er, are actually rather plesiomorphic, albeit large; and the an-
tennae, while uniramous, are well within what one would expect
for a basically sensory appendage. Second, cycloids do not bear
sucker-like or hook-laden maxillules modified for attachment
to the host. Cycloid maxillules appear to be typical crustacean
mouthparts. Third, cycloids do not have maxillae that would
have functioned strictly as grooming structures, although
grooming could have been another function of the geniculate
cycloid maxillae and maxillipedes. And fourth, cycloids do not
have the abdomen reduced to a single, unsegmented lobe. At
least some cycloids, although having a reduced abdomen, still
display segmentation in that region. Thus, chances of bran-
chiuran affinities for the cycloids appear negligible.
Although cycloids share with copepods several features, such
as fusion of the first thoracic segment into the head, develop-
ment of the first thoracopod as a maxillipede, and specialization
of the maxillipede as a uniramous limb, these two groups bear
distinct differences. Cycloids posses several unique characters
that include: the presence of the carapace and its apparent fusion
to all the thoracic segments, the uniramous antennae, the large
geniculate maxillae and maxillipedes (this latter in some forms
also including the second thoracopods as maxillipedes), the pos-
terior thoracopods as robust and uniramous "walking" limbs,
an abdomen reduced to two segments, and the development of
wide sternal plates in the cephalothorax. Cycloids also lack the
intercoxal sclerites used as couplers on the thoracic limbs (an
important apomorphy of copepods).
We can now assess cladistically where the Cycloidea fit with
the Maxillopoda. Schram (1986, p. 538) made the first attempt
at a cladistic analysis of the class Maxillopoda and felt, given
TABLE 5-Characters used in the cladistic analysis of maxillopodan taxa. Multistate characters denoted with variations. Plesiomorphic state
essentially represented by those characters found in the Malacostraca as the outgroup.
Character Plesiomorphic state Apomorphic state(s)
1. Antennule biramous uniramous
2. Trunk-limb number 14 (1) = 7, (2) = 6, (3) = 5, (4) = 4, (5) = 2, (6)1
3. Trunk somite number 15 (1) = 12, (2) = 11, (3) = 8, (4) = 5
4. Male pore location thoracomere 8 (1) tmere 7, (2) tmere 4 or 5
5. Naupliar eye without tap. cells with tapetal cells
6. 1st thoracopod unmodified as a maxillipede
7. Maxillipedes biramous uniramous
8. Carapace present absent
9. Compound eye present absent
10. Male trunk limb 7 not as a penis (1) paired penes, (2) median penes
11. Female trunk limb 7 present absent
12. Thoracopodal endite absent present
13. Thoracopodal exopod 3 segments or more (1) 1-2 segs., (2) absent
14. Thoracopod number 2-6 present (1) 5-6 absent, (2) 2-6 absent
15. Caudal rami single segment three segs.
16. Antennal exopod at least 14 segs. (1) <9, (2) absent
17. Mandibular exopod at least 11 (1) <7, (23) absent
18. Antennule segments 9 or more eight or less
19. Thoracopods 2-5 biramous (1) uniramous, (2) buds, (3) absent
20. Intercoxal sclerites none sclerites as couplers
21. 1st thoracomere free fused to head
22. Cephalic appendages present absent
23. Oral disc none present
24. Bipartite pigment cells none in cmpd. eyes present in compound eyes
25. Naupliar carapace none present
26. Carapace gut caeca none present
27. Al attachment organ none present
28. Poison spine none present
29. Naupliar postmaxillary limb buds present absent
30. Frontal filaments not with cmpd. eye associated with cmpd. eye
31. Lattice organ none present
32. Female pore location thoracomere 6 (1) tmere = 7, (2) tmere = 4 or 5, (3) tmere = 1
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JOURNAL OF PALEONTOLOGY, V. 71, NO. 2, 1997
Malacostraca
Bredocaris
Skara
Tantulocarida
85
Ostracoda
Branchiura
85
Thecostraca
Mystacocarida
55 I Copepoda
100 l- Cyclus
FIGURE 20-A 50% majority-rule consensus obtained from 20 equally
parsimonious trees from the cladistic analysis of the data matrix in
Table 6; characters as in Table 5. Numbers represent the percentage
of times a particular bifurcation appeared. Analysis of data ran unor-
dered, unweighted, and with the uninformative characters
(1,2,5,15,19,20,22-24,27-31) deleted.
the limited data base available to him then, that there was much
irresolution at the base of the tree. Grygier (1987), in trying to
clarify the position of the Facetotecta (= y-larvae forms), de-
veloped a data base utilizing 20 features focusing on larval max-
illopodans. Grygier excluded from consideration the mystaco-
carids, tantulocarids, and ostracodes. Boxshall and Huys (1989),
building on both Schram and Grygier, produced another ar-
rangement using some 35 characters identifiable in adult forms,
and as a result they had to exclude the facetotectans. Abele et
al. (1992), using 18S ribosomal RNA, concluded that the bran-
chiurans and their sister group the Pentastomida (Abele et al.,
1989) may have sister-group affinities outside the maxillopo-
dans (Walossek and Miiller [1994], however, advocated a stem-
group crustacean position for the Pentastomida). We cannot
resolve in this paper issues of larval affinities or evaluate the
role of molecular sequencing. We only wish to assess the affin-
ities of Cycloidea.
To this end we modified slightly the data base of Boxshall
and Huys (1989) by reconfiguring some features into multistate
characters and incorporating some more recent knowledge con-
cerning fossil and Recent forms uncovered in the last few years
(e.g., Huys et al., 1993). The list of these characters appears in
Table 5. We used the taxa essentially as Boxshall and Huys
presented them, adding of course Cyclus. Thus we included the
branchiurans, and our scoring of ostracodes continues to con-
sider the phosphatocopines as part of that group. This does not
necessarily reject other options concerning the affinities of these
groups (e.g., see Boxshall, 1992), but these issues do not concern
the immediate matter at hand. Finally, we have also included
into the data base the Cambrian Bredocaris (Miiller and Wal-
ossek, 1988) to offer a complete cladistic analysis of all the
potential maxillopodan forms.
Figure 20 presents the results of this analysis, based on the
matrix of Table 6. The analysis utilized malacostracans as an
outgroup, unordered all the data so as not to inject preconceived
TABLE 6-Character matrix used in the cladistic analysis of maxillo-
podans, based on the character list of Table 5.
Taxa
Malacostraca
Bredocaris
Skara
Mystacocarida
Copepoda
Cyclus
Tantulocarida
Ostracoda
Branchiura
Thecostraca
11111111112222222222333
12345678901234567890123456789012
000000000000000??000000000000000
11???000000110?00000000?1?000???
161??001101012100030000???00????
1322?101101021011120000000000002
12211111100000011001100000000001
123??110??1020022010100???00????
1231?0011211100???00111000000003
15211000011012010100000110000001
14421000001011012100000001010002
12211000011000021100000001101113
ideas about polarity, and deleted the uninformative characters.
Twenty equally parsimonious trees resulted using the exhaustive
search option of PAUP 3.1.1, length = 48, consistency index =
0.604, homoplasy index = 0.396, retention index = 0.441, and
rescaled consistency index = 0.267. The fifty-percent, majority-
rule, consensus tree reveals a high degree of certainty about the
copepod/cycloid clade.
The examination of the data with MacClade 3.0 revealed
some interesting issues. The location of Bredocaris (even to
outside the Maxillopoda) does not effect the length of the tree,
as might be expected in an animal that appears to exhibit a great
many plesiomorphic features. This proved true to a large extent
with the other Cambrian taxon in the analysis, Skara. However,
every alternative analysis we performed, whether it included the
fossils or not, or whether we used the data matrix exactly as
Boxshall and Huys (1989) had outlined it, always placed Cyclus
as a sister group to the Copepoda.
Despite the analysis above, which focuses solely on maxil-
lopodans, different data bases could come up with alternative
schemes. Schram and Hof (in press) used a much larger data
base for all fossil and Recent "crustaceoids" and noted two
things of relevance. First, that data base indicated a possibility
that the maxillopodans could occupy a paraphyletic position on
a cladogram of all crustaceoids. Second, under those circum-
stances cycloids may yet prove to bear some affinity to bran-
chiurans. The results from any analysis of such a larger data
base, however, should not necessarily negate the results of the
analysis here. Such results merely indicate that there still exists
a fair amount of uncertainty about the sister-group relationships
of extinct groups, such as cycloids.
Many aspects of the anatomy of the cycloids remain unclear.
We need more comparative information about the head ap-
pendages in all the cycloid genera. We still need to resolve in-
terpretations ofbiramous limbs in some cycloid species such as
Halicyne ornata and Cyclus torosus, and we need reliable in-
formation concerning the abdomen in all genera and the struc-
ture of possible penes. New information concerning these char-
acters could effect the location of cycloids within a crustacean
cladogram. Although our understanding of these peculiar fossil
arthropods has taken a giant step forward, we still have much
more to discover about these creatures.
ACKNOWLEDGEMENTS
The Field Museum of Natural History Visiting Scientists Pro-
gram supported this work in part under a grant in 1989. N.
Clark, Hunterian Museum, Glasgow, provided some useful views
concerning the anatomy and preservation of cycloids during a
visit to the Natural History Museum of Los Angeles County in
1991, and A. Kemp, of the Los Angeles Museum provided
insights into issues of siderite mineralization. Photographic as-
282
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SCHRAM ET AL. -MAZON CREEK CYCLOIDEA
sistance came over a period of years from C. P. Majors, formerly
of the San Diego Natural History Museum; R. Meirs, Natural
History Museum of Los Angeles Co.; and L. A. van der Laan,
photographic department of the Faculty of Biology, University
of Amsterdam. We also want to acknowledge the late J. Simpson
for his help in producing Figure 7. The senior author wishes to
express special gratitude to G.A. Boxshall, British Natural His-
tory Museum, and W. A. Newman, Scripps Institution of Ocean-
ography, for the many discussions over the years concerning
maxillopodan anatomy and phylogeny.
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ACCEPTED 22 JULY 1996
J. Paleont., 71(2), 1997, pp. 284-287
Copyright ? 1997, The Paleontological Society
0022-3360/97/0071-0284$03.00
ON THE RARE OCCURRENCE OF EOCENE
CALLIANASSID DECAPODS (ARTHROPODA) PRESERVED IN
THEIR BURROWS, MOUNT DISCOVERY, EAST ANTARCTICA
JEFFREY D. STILWELL,1 RICHARD H. LEVY,2 RODNEY M. FELDMANN,3 AND
DAVID M. HARWOOD2
tDepartment of Earth Sciences, James Cook University of North Queensland, Townsville, Q 4811, Australia,
2Department of Geology, 214 Bessey Hall, University of Nebraska-Lincoln, Lincoln, 68588-0340, and
3Department of Geology, Kent State University, Kent, Ohio 44242
ABsTRATr-Callianassid fossils, preserved within their burrows, collected from Mount Discovery, East Antarctica, provide the first
such occurrence in Antarctica as well as evidence for deposition in a shallow marine environment distal to a deltaic system. The
age of the specimens, based upon associated dinoflagellate cysts, is late early to middle Eocene.
J. Paleont., 71(2), 1997, pp. 284-287
Copyright ? 1997, The Paleontological Society
0022-3360/97/0071-0284$03.00
ON THE RARE OCCURRENCE OF EOCENE
CALLIANASSID DECAPODS (ARTHROPODA) PRESERVED IN
THEIR BURROWS, MOUNT DISCOVERY, EAST ANTARCTICA
JEFFREY D. STILWELL,1 RICHARD H. LEVY,2 RODNEY M. FELDMANN,3 AND
DAVID M. HARWOOD2
tDepartment of Earth Sciences, James Cook University of North Queensland, Townsville, Q 4811, Australia,
2Department of Geology, 214 Bessey Hall, University of Nebraska-Lincoln, Lincoln, 68588-0340, and
3Department of Geology, Kent State University, Kent, Ohio 44242
ABsTRATr-Callianassid fossils, preserved within their burrows, collected from Mount Discovery, East Antarctica, provide the first
such occurrence in Antarctica as well as evidence for deposition in a shallow marine environment distal to a deltaic system. The
age of the specimens, based upon associated dinoflagellate cysts, is late early to middle Eocene.
INTRODUCTION
THE RARITY of fossil Callianassidae (ghost shrimps) in their
burrows reflects the apparent exceptional conditions re-
quired for their preservation (e.g., Waage, 1968; Beikirch and
Feldmann, 1980; Hasiotis and Mitchell, 1989). More often, cal-
lianassids and their burrows (the ichnogenera Ophiomorpha
Lundgren, Spongeliomorpha de Saporta, and Thalassinoides Eh-
renberg) are encountered separately. Because callianassids do
not exit their burrows often (Pohl, 1946; Weimer and Hoyt,
1964), it is surprising that so few examples of fossil callianassids
in their burrows have been recorded.
During the 1993-1994 austral summer, several callianassids,
preserved in their burrows, were discovered in fossiliferous er-
ratics in moraine flanking Mt. Discovery in the McMurdo Sound
area of East Antarctica (Figure 1). The specimens (Figure 2)
comprise mainly major cheliped elements and were identified
as Callianassa symmetrica Feldmann and Zinsmeister, 1984.
However, recent systematic work on extant callianassids (Man-
ning and Felder, 1991) suggests that these specimens might bet-
ter be tentatively assigned to Callichirus Stimpson.
Feldmann and Zinsmeister (1984, p. 1041) stated that the
most abundant source of these fossiliferous erratics is along the
northeast coast of Mount Discovery. Far richer deposits con-
taining fossiliferous erratics with decapod and other macroin-
vertebrate and vertebrate fossils were discovered at that locality
and on Minna Bluff during 1991-1994 expeditions. In total,
approximately 60 macroinvertebrate and four vertebrate species
have been recovered to date from the erratics. Only two taxa
have been described previously, making these rocks the primary
source of data on Eocene macroinvertebrate and vertebrate ma-
rine life from East Antarctica. Feldmann and Zinsmeister (1984,
p. 1041) emphasized the importance of the McMurdo Sound
INTRODUCTION
THE RARITY of fossil Callianassidae (ghost shrimps) in their
burrows reflects the apparent exceptional conditions re-
quired for their preservation (e.g., Waage, 1968; Beikirch and
Feldmann, 1980; Hasiotis and Mitchell, 1989). More often, cal-
lianassids and their burrows (the ichnogenera Ophiomorpha
Lundgren, Spongeliomorpha de Saporta, and Thalassinoides Eh-
renberg) are encountered separately. Because callianassids do
not exit their burrows often (Pohl, 1946; Weimer and Hoyt,
1964), it is surprising that so few examples of fossil callianassids
in their burrows have been recorded.
During the 1993-1994 austral summer, several callianassids,
preserved in their burrows, were discovered in fossiliferous er-
ratics in moraine flanking Mt. Discovery in the McMurdo Sound
area of East Antarctica (Figure 1). The specimens (Figure 2)
comprise mainly major cheliped elements and were identified
as Callianassa symmetrica Feldmann and Zinsmeister, 1984.
However, recent systematic work on extant callianassids (Man-
ning and Felder, 1991) suggests that these specimens might bet-
ter be tentatively assigned to Callichirus Stimpson.
Feldmann and Zinsmeister (1984, p. 1041) stated that the
most abundant source of these fossiliferous erratics is along the
northeast coast of Mount Discovery. Far richer deposits con-
taining fossiliferous erratics with decapod and other macroin-
vertebrate and vertebrate fossils were discovered at that locality
and on Minna Bluff during 1991-1994 expeditions. In total,
approximately 60 macroinvertebrate and four vertebrate species
have been recovered to date from the erratics. Only two taxa
have been described previously, making these rocks the primary
source of data on Eocene macroinvertebrate and vertebrate ma-
rine life from East Antarctica. Feldmann and Zinsmeister (1984,
p. 1041) emphasized the importance of the McMurdo Sound
erratics by stating that, "Unfortunately, the organisms identified
from the erratics have generated little interest even though they
provide one of the few sources of data about conditions in the
Ross Sea area during this time." Preliminary paleobiological
investigations of these erratics have been presented recently by
Stilwell et al. (1993) and Levy et al. (1995). The present paper
records the first account of decapods preserved in their burrows
from Antarctica, more tightly constrains the age of the fossils,
and suggests a depositional setting distal to a deltaic system.
erratics by stating that, "Unfortunately, the organisms identified
from the erratics have generated little interest even though they
provide one of the few sources of data about conditions in the
Ross Sea area during this time." Preliminary paleobiological
investigations of these erratics have been presented recently by
Stilwell et al. (1993) and Levy et al. (1995). The present paper
records the first account of decapods preserved in their burrows
from Antarctica, more tightly constrains the age of the fossils,
and suggests a depositional setting distal to a deltaic system.
FIGURE 1-Location map of Mount Discovery, Minna Bluff, and "Dis-
covery Deep", McMurdo Sound, East Antarctica.
FIGURE 1-Location map of Mount Discovery, Minna Bluff, and "Dis-
covery Deep", McMurdo Sound, East Antarctica.
284 284
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