Contributions to Zoology, 72 (I) 1-16 (2003)
SPB Academic Publishing hv, The Hague
Paleozoic cumaceans (Crustacea, Malacostraca, Peracarida) from North America
² Frederick+R. Schram Cees+H.J. Hof Mapes³ & Snowdon² ¹, Royal+H. Polly 1 Institute for Biodiversity and Ecosystem Dynamics, University ofAmsterdam, Post Box 94766,
1090 GT 2 Amsterdam, Netherlands, [email protected]; Dept. ofEarth Sciences, University of Bristol, Bristol 3 BS8 IRJ, UK; Dept. of Geological Sciences, Ohio University, Athens, Ohio 45701, USA, e-mail: mapes@oak. cats, ohiou.edu
Keywords:: Cumacea, North America, Paleozoic, Peracarida
Abstract forms inhabit the fine sand and coarse silts perfect
for fossilization (Schram, 1986). Bachmayer, (1960) Thiee new species of are described from North malacostracans recorded a poorly preserved cumacean-like speci- America in the UpperMississippian Into Formation ofArkansas, men Palaeocuma hessi from the Callovian, Middle and the Pennsylvanian Eudora Shale of southeastern Kansas. of France’. These Jurassic, Subsequently, Malzahn (1972) appear to be the oldest fossils attributed to the Cumacea and studied two Permian are well-preserved species of the only the third collection of fossil cumaceansanywhere to be described. Permian genus O. and O. Previously depicted forms occur in the Opthalmdiastylis, inflata costata, and Jurassic of Europe. We herein double the numberof described from the marl beds ofZechstein I, Kamp-Lintfort, fossil cumacean species and suggest some adjustments necessary Germany. These latter taxa are noteworthy in that tothe higher ofthe accommodate taxonomy group to apomorphic they exhibit lobed as the features of distinctly eyes, generic the fossil and Recent forms. name implies.
This describes paper three new species of Car-
Contents boniferous cumaceans from the lino Formation (Up-
per Mississippian) of northwestern Arkansas, and
the Eudora Shale (Pennsylvanian) of southeastern Introduction 1
Localities and Kansas. our not methods I Although specimens are as com- Systematics 4 pletely preserved as the Jurassic and Permian ma- Neocumacea 4 theseCarboniferous terial, nonetheless, species are Ophthalrncumacea 4 related clearly to the younger specimens. We ef- Ophthaldiastylis parvulorostrum 5 extend the for the Cumacea fectively range into a Carbocuma imoensis 1 Securicaris time frame for which we also have the earliest fos- spinosus 9 Lhscussion sils for other 12 peracaridan groups, viz., the Isopoda, Acknowledgements 15 Tanaidacea, Pygocephalomorpha, Lophogastrida, References ] 5 and Spelaeogriphacea.
Introduction Localities and methods
e m°dern Cumacea are These specimens are in the fossil a very successful group invertebratecollections ofthe 0 P erac aridan San Diego Natural History Museum (SDSNH). Two localities malacostracan crustaceans with ‘Hound are involved (Fig, 1). 1215 species (Watling, pers. comm.). Never- 6 css unt 'l now ’ only three species of fossil cuma- SDNHM locality 3191:- Imo Formation, Upper °eans Mississippian; Jve t* een described, these despite the fact that Peyton Creek, Van Buren County, The Arkansas. outcrop is
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Fig. I. Geographic information for cumaceanlocalities. Site 1 (SDSNH locality 3191), Imo Formation., U. Miss; Peyton Creek, Van
Buren Co., Arkansas; outcrop just south ofthe northern border of Van Buren Co., on US Highway 65, about 6.4 km. southeast of
Leslie, Searcy Co. (NE 1/4, sec. 11, T13N; R15W; Leslie 7 1/2 quadrangle).Site 2 (SDSNH locality 3267), Eudora Shale, Penn; Tyro
Quarry, Montgomery Co., Kansas; 2.7 km. northeast of Tyro (NE 1/4, SE 1/4, sec. 30, T34S, RISE; Tyro 7 1/2 Quadrangle).
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located south of the Van Buren border the U.S. just County on glomerate. Intermediate diversity between levels 1 Highway 65, about 6.4 km southeast of Leslie, Searcy County, and 3. Molluscs are less common than in level 1. Arkansas. Specimens were either collected on the surface or Level 3: From the concretionary shale. The higher obtained from bulk samples that were not in situ. diversity and abundance of palaeocopid ostracodes
indicates a shallow marine environment, somewhat The fauna is quite extensive. Schram and Mapes further offshore and with more normal than described salinity (1984) a single carapace of a new genus levels 1 and 2. Gastropods, bivalves, cephalopods and species of decapod crustacean, Imocaris tuber-
are but no echino- from this site (including goniatites) common, culata, associated with a molluscan derms. dominated fauna of ammonoids, gastropods and Level 4\ From limey shale above the limestone. Most bivalves. Hoare and Mapes (2000) recorded a total diverse fauna in this level, including the cumaceans of 49 taxa of ostracodes from the Imo Formation. in indicates normal marine Sohn question. Assemblage (1940) listed 364 species representing 82 salinity, deeper water, more calcareous sediment genera of Mississippian ostracodes. In addition, a
with less terrigenous clastic additions in an off- variety of molluscs are known (Hoare et ah, 1982, shore environment. Abundant bryozoans and echi- 1988, 1989; Hoare and Mapes, 1985; Jeffrey et ah, noderms, but few cephalopods. 1994; Malinky and Mapes, 1983; Mapes, 1987; Level 5: From just below the limestone in limey Mapes et ah, 1986). On the basis of ammonoids
shale. Diversity declines by more than 50% from (Saunders, 1973; Saunders and Work, 1999) the Level 4. Lower reflects the decline in formation diversity is dated to late Chesterian, Elviran Stage calcareous-deposition with an increase in terrig- (E2b to E2b-c), equivalent to the Arnsbergian Stage elastics. enous Assemblage represents a shallow in Europe. marine offshore environment. Salinity, water depth, The faunal composition of the Into formation substrate, depositional rate and temperature fluc- differs from that of the Chesterian faunas of the tuations all affected the faunal diversity. Appalachian and Eastern Interior. Webband Suther- land (1993) show the laterally varying lithologies
SDNHM 3267: - Eudora Shale, in locality Pennsylvanian; Tyro a short distance of the Imo Formation and dras- Quarry, Montgomery County, Kansas. Quarry is located 2.7 tically different local environments. The inverte- km northeast ofTyro, Montgomery County, Kansas. brate faunas previously described from the Peyton
Creek road section indicate The cut a general deepen- cumacean specimens came from the upper dark ■ng of in shore marine water a relatively near envi- gray shale facies, thought to represent somewhat
ronment. there fluctuations in the Also, were amount less oxygenated conditions than those of the un- of clastic At medium shales and terrigenous deposit being deposited. derlying gray (Malinky Mapes, least 3 storm have been observed in the The Eudora deposits 1982). Shale is very fossiliferous. There
section (Hoare and Mapes, 2000), and the diver- is a highly diverse molluscan fauna, though only a
shy of ostracodes varied between dif- few considerably genera are common, with 9 genera of bivalves, lerent levels within the formation, generally increas- and cephalopods, especially bactritoids (Mapes,
ing from 1 to 5. level level 1979), while gastropods are less common. Scapho-
pods, rostroconchs and hyoliths are found even less
Level /: black shale. Concretionary Assemblage frequently. For the most part the molluscs in their
dominated the dark shale by widespread platycopid ostracode, gray occur as pyritized internal moulds.
the dominance Cavellina, of which and the low Non-molluscan fossils are rare and include a few
indicates diversity an unstable, well-oxygenated, fragmentary sponges, bryozoa and brachiopods,
near-shore environment with much terrigenous clas- echinoid fragments, crinoid columnals and blastoids, tlc deposition. Common in this level are; articu- and lophophyllid corals. The microfauna includes lated echinoderms, bivalves, gastropods, orthoconic conodonts, ostracodes and agglutinated foramini-
eephalopods are ammonoids common yet goniatite fers. Vertebrates are diverse and abundant as frag- are rare. mented specimens in the phosphate nodule hori- Level 2: Just below a crinozoan storm con- zon at the base of the dark shale grain sequence, which
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probably represents a storm deposit. The faunal shelfcharacteristic of the Paleozoic taxa. Currently,
and 8 of Bodo- analysis of the facies by Malinky Mapes (1982) families living cumaceans are recognized:
indicates the upper dark shale bed was deposited triidae, Ceratocumatidae, Diastylidae, Gynodia-
in an oxygen-poor, normal marine, off-shore envi- stylidae, Lampropidae, Leuconidae, Nannastacidae,
ronment. The high organic contentand total pyritiza- and Pseudocumatidae.
tion of the diverse fauna also indicates the dark
gray facies was deposited under reduced oxygen
levels. The and dark shale facies of the Infraorder gray gray Ophthalmcumacea Malzahn, 1972
Eudora Shale, near Tyro, Kansas are similar to other
Shale in - from Eudora exposures the region as indicated Diagnosis. Distinctly lobed eyes, free cepha-
faunal by common elements including conodonts lothorax, bearing well-developed facets; carapace
and crinoids. lacking pseudorostra, but with anterolateral lappets
The materials were generally studied initially extending forward; large ventral branchiostegal shelf
underregular light microscopy. However, the small providing a partial floor to branchial chamber.
size of the specimens demanded SEM techniques
for finer analysis. Both regular SEM and images Remarks. - Malzahn (1972: 448) used this taxon
were made using a low vacuum (variable pressure) to accommodate cumaceans with lobed, well-fac-
SEM back scattered electron detector etted he did utilizing a eyes, but not place it in opposition to
(in our case a Robinson were other taxon. The characters used detector) employed. any diagnostic here,
In the and latter, uncoated material can be safely ex- viz., the lobed eyes lappets (which we believe
amined Burnstock and (see Jones, 2000). are precursors of the pseudorostrum), are perhaps
intermediate between generally plesiomorphic con-
ditions (stalked eyes, carapace without lappets or
Systematics pseudorostrum) and the states seen within the neo-
In cumaceans. this respect, as Malzahn (1972) first
Class Malacostraca Latreille, 1806 pointed out, the evolution of cumaceans would seem
Superorder Peracarida, Caiman, 1904 to parallel that of the tanaidaceans (Schram et al.,
Order Hemicaridea Schram, 1981 1986) wherein the Paleozoic infraorder Anthraco-
Suborder Cumacea Kroyer, 1846 caridomorpha is also predominantly characterized
Infraorder the of characters Ncocumacea, nov. by presence intermediate such as
lobed The ventral shelf of the eyes. branchiostegal
- Diagnosis, Eyes, when present at all, developed ophthalcumaceans, however, is a unique apomorphic
as an dorso-median fused shared all the unpaired organ to cepha- feature and apparently by Paleozoic
lothorax, generally without separate facets; pseudo- forms. rostra and siphons well developed; ventral margin of carapace without medially directed shelf.
Family Ophthalmdiastylidae Malzahn, 1972
Remarks. - The distinctly apomorphic condition of the and - As eyes the development of the distinctive Diagnosis. only one family is currently rec-
pseudorostrum and siphons, as opposed to what is ognized, the diagnosis of the family is the same as in seen the Paleozoic forms, we believe necessi- that of the infraorder.
tate the of creation a distinct infraorder to accom-
modate the living cumaceans. This infraordcr should Type genus. - Ophthalmdiastylis Malzahn, 1972.
contain all the living cumaceans and should also
include the Jurassic species Palaeocuma hessi Bach- Remarks. - Malzahn (1972) did not formally des-
meyer, I960. the but its im- Although preservation of this ignate or diagnose a family, status is
Mesozoic form leaves lot be a to desired, we can plicit in his description of the species and use of
see nothing that resembles the ventral branchiostegal the higher taxon name Ophthalmcumacea.
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Ophthalmdiastylis Malzahn, 1972 smoothly into the anterior lappets (Figs. 2.1, 2.5).
the Ventrally, carapace displays a narrow ventral
Diagnosis. — Rostrum wide and relatively long; ridge marking the bend that forms the branchiostegal
pseudorostra if The very weakly, at all, developed. shelf. anterior lappets display a slight, spatu- late form and extend anteriorly ventral and lateral
- to the Type species. Ophthalmcliastylis inflata Malzahn, compound eyes (Figs. 2.1, 2.2).
1972. SDSNF1 26273 shows a pair of large, well-pre-
served eyes protruding from beneath the frontal lobe
Remarks. - Malzahn (1972) did not clearly diag- and separated by a small rostrum (Figs. 2.2, 2.3,
The nose the From the lobed are with genus. descriptions and illustra- 2.4). eyes equipped distally a tions it of facets rounded would appear that for both species of this well-developed set to hexagonal in outline genus a short, but true, rostrum characterizes O. (Figs. 2.3, 2.4). The lobes themselves
with inflata and are decorated a faint scale-like O. costata. O. inflata appears distin- sculpturing guished (Figs. 2.3, 2.4). by the smooth yet slightly papillose cara-
while Portions of endopods of thoracic limbs are pace, O. costata is characterized by distinct pre-
served on SDSNH 26279 The details longitudinal carinae on the carapace. (Fig. 3.1). are obscure since the distal portions of the limbs
limbs are not preserved. The individual are arranged
and parallel appear to be remains of pereiopods, Ophthalmdiastylis parvulorostrum new species if be made and tentative comparison can to mod- Figs. 2, 3.1, 3.2, 5.1, 5.2 ern forms the appendages bore rather elongate bases
(Fig. 3.2). Diagnosis. - Slender, somewhat laterally compressed carapace. Anteriorly serrate dorsal ridge extend- Etymology. - A reference to the tiny rostrum. ing in longitudinally, terminating anteriorly a slight frontal trough. Anterior lappets marked, extending Holotype. - SDSNH 26273 (Fig. 2.1 - 2.4). San slightly anteriad from the anterolateral edge of cara- Diego Natural History Museum. pace lateral of the lobed eyes.
Other material. - One fairly complete carapace
Description. - is about 1.3 in The carapace mm paratype (SDSNH 29305); another partial speci- length. In dorsal view, the carapace is elongate and men (SDSNH 26279); and a fragmentary and poorly is somewhat pointed posteriorly. In lateral view, preserved specimen (SDSNH 29309) the tentatively is carapace ovoid, more constricted anteriorly. assigned to this species as well. The height of the carapace is over 1/2 the length and the transverse width is under 1/2 that of the Occurrence. - The holotype specimen and the ques- length. A reticulate sculpturing (Fig. 2.1) covers tionablefragmentary specimen were collected from the carapace which is characterized ir- surface, by SDNF1M 3191 in Arkansas. locality The paratypes regular raised areas separated by narrow grooves. (SDSNH 26279, 29305) was collected from local- A mid-dorsal is and this bears a set ridge present, ity SDNHM 3267 in Kansas. ot 3 serrate teeth directed anteriorly (Figs. 2.1,2.2). The tip of the short rostrum was with 3 equipped Remarks. - The carapace of O. parvulorostrum is small spines (Figs. 2.3, 2.4); one can see their bases much more slender, elongated and laterally flat- though the have broken off. is tips One spine ter- tened than that of C. imoensis n. sp., another cuma- minal while the other are located two just posterior cean same from these localities. O. parvulorostrum to it, one slightly in front of the other on the O. edges differs from inflata Malzahn, 1972 in its smooth of the optic notches. A broad, ventral, branchiostegal carapace surface and smaller rostrum, and from O. shelf is present that extends the length of the cara- costata Malzahn, 1972 by its lack of longitudinal pace (29305, Fig. 2.5), There are no anterolateral carinae the A on carapace. reconstruction of O. spines, but the ventral shelf appears to merge parvulorostrum is offered in Figs. 5.1 and 5.2
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Carbocuma new genus almost scale-like in places (Fig. 3.4,3.5). The height
of the is 4/5 of the is carapace roughly length, as
Diagnosis. - Carapace highly vaulted and barrel- the transverse width. A deep median trough marks
almost dorsal like, bulbous in lateral view. A deep mid- the surface of the carapace (Fig. 3.3) and is
dorsal and flanked that bear trough runs longitudinally, anteriorly by large, parallel ridges less pro- expands to form a well-developed frontal lobe. A nounced troughs on their crests. Wide mid-dorsal small rostrum is present. Small, sinuous lappets indentations extend from below the smaller troughs, developed laterally. Well-developed lateral bran- anteriorly to spread around the frontal lobe, and
shelf ventral of the mid-lower of the chiostegal on aspect carapace. Large, ventrally to region carapace. faceted, paired eyes. . The frontal lobe itself is well developed and dis-
what plays appears to have been a small rostrum
- Carbocuma imoensis A Type species. n. sp. by mono- (Figs. 3.3, 3.4). prominent ventral branchiostegal
shelf extends the of typy. length the carapace and is dev-
eloped as a spine anteriorly, only the stump of which
Etymology. - Named after the Carboniferous pe- is typically preserved (Fig. 3.5). A distinct keel riod in which the fossils and the marks the which the shelf are found, genus point at branchiostegal
Cuma, which erected H. Milne Edwards the side of the and similar was by meets carapace, narrow and from which the of the Cumacea mark the interior of the name group longitudinal ridges edges arises (Schram, 1986). shelf (Fig. 3.5). The ridges and lateral keels con-
and verge posteriorly, anteriorly as well but to a
Remarks. - The size of the lesser The ventral of the relatively large species extent. margins carapace
along with the globose form and distinctive mid- floor a large branchiostegal chamber and extend dorsal ridges and grooves justify a separate genus toward a mid ventral gap, with two smaller ridges for this taxon. along the margins adjacent to the gap (Fig. 3.5).
The holotype specimen, SDSNF126275, preserves
one short lobe large eye (Fig. 3.4). Its apparently Carbocuma imoensis new species bears a densely facetted field of ommatidia. Just F 'gs. 3.3-3.6, 5.3-5.5. ventral to the eyes, between them and the antero-
ventral the of is devel- spine, margin the carapace
Diagnosis. - As this taxon is monotypic, the diag- oped as a somewhat sinuous, weakly developed set
nosis of the species is that same as that for the genus. of lappets (Fig. 3.3, 3.4).
Specimen SDSNF129308 illustrates preservation
Description. - The approximate length of the cara- of pereiopods (Fig. 3.6). These are incomplete, but
pace is 1.75 is the basis in mm. In dorsal view, the carapace elongate is virtually tact and is marked ovoid in and cuticular outline, though complete posterior by a scale-like decoration, not uncommon anterior margins are not preserved together on the in living cumaceans too. Specimen SDSNH 29310
same In specimen on of the material at hand. shows of and a faceted any preservation pereiopods eye lateral view, the dorsal is carapace more rounded, fragment. although the ventral aspect is slightly flatter and
has a bulbous into - The imoensis from mid-region that dips anteriorly Etymology. name is the type the frontal lobe the (Fig. 3.3). The surface of the cara- locality of specimen. is pace rather lightly textured with faint papillae,
Fig. 2. Ophthalmdiastylis 1-4, SDSNH I. dorsal of note parvulorostrum. holotype, 26273, general aspect specimen, sculpturing on 2. carapace, intermediateview of anterior views ofleft and end, 3-4, close-up right eye lobes, respectively, note scale-like ornament on lobes, 5, SDSNH26279, = ventral folded itself, mr = median + = showing aspect, specimen on c carapace, ridge, r rostrum, rs rostral spines, vs = ventral shelf.
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- SDSNH 26275 San Securicaris Holotype. (Figs. 3.2, 3.4). spinosus new species
Diego Natural History Museum. Figs 4.1, 4.2, 5.6, 5.7
- - there Additional specimens. SDSNH 26274, 26277, Diagnosis. Since is but a single specimen,
and 29308. the of 26278, 29307, Another partial speci- diagnosis of the species is the same as that
SDSNH men, 29310 is also tentative assigned to the genus. this species.
- The is Description. fairly complete carapace 1.5
Occurrence. - SDSNH 26275 (the holotype) and mm in length. It is slender and elongate (Fig. 4.1).
SDSNH lateral view 26274, 26277, and 29308 come from lo- In the dorsal ridge is rather concave, cality SDNHM 3191 in Arkansas. SDSNH 26278, more so than the ventral edge which is flatter. The
and 29307, 29310 come from locality SDNHM 3267 height of the carapace is roughly 1/2 that of the in Kansas. length, and the transverse width is just 1/3 of the
length. There is a sharp, narrow mid-dorsal ridge
Remarks. - This constitutes the most numerous and or crest, which flattens out anteriorly to form a distinctive of cumacean species in these two lo- triangular frontal lobe, widest at its most anterior calities. views end. A Reconstructions of the various of well-defined lateral ridge is present on the the in 5.3 5.5. side and marks transition cephalothorax are provided Figs. to right-hand the to a ven-
tral branchiostegal shelf. This lateral ridge extends
anteriorly to form a rather delicate, well-developed,
Securicaris new anterolateral the is absent. genus spine, though tip Ridge
and spine are not preserved on the left-hand side.
Diagnosis. - Slender, laterally compressed cara- In ventral view, the ventral aspect of the left valve pace. dorsal of the is folded under the Sharp ridge, anteriorly giving way to carapace branchiostegal a relatively elongate and narrow frontal lobe al- shelf of the right side, a vagary of the preservation most 1/3 the The length of the carapace. Ventro-lateral of this specimen. surface of the carapace be- ndge extends anteriorly to form large spine. Cara- tween the mid-dorsal ridge and ventral keels is pace decorated with a scale-like terracing. curved and decoratedwith a distinct scale-like sculp-
ture creating the effect of overlapping terraces.
Type - species. Securicaris spinosus n. sp. by mono- typy. Etymology. - A reference to the delicate anterolat-
eral spine of the carapace.
Etymology. - From the Latin, securis (f.), mean-
ing - axe-like. Holotype. The single known specimen, SDSNH
26276 (Fig. 4.1). Remarks. - The rarest of the cumaceans reported
herein, known the Occurrence. - from a single specimen. Though The specimen was collected from specimen is SDNHM incomplete, the sum of what is pre- locality 3191 in Arkansas. served seems to indicate that it is probably a cuma- cean. The - general habitus accords with the other Remarks. Though ofsimilar size to Ophthalmdia- species described here, it is unfortunate the S. although stylus parvulorostrum,, carapace of spinosus that only one specimen is at hand for study. appears to be more laterally flattened. The frontal
F‘S■ 3. 1,2, Ophthalmdiastylis parvulorostrum, SDSNH 26279, 1, general ventral aspect, 2, close-up ofpereiopods; 3-6, Carbocuma imoensis ,3,4, holotype, SDSNH 26275, note SDSNH ventral , papillate sculpturing.on carapace, 5, 29307, aspect showing ventral s elf and mid-ventral into SDSNH note on gap chamber, 6, 2903, sculpturing basis of = branchiostegal long pereiopod. c carapace, r - dorsal = ridges, fl frontal 1 = = = = lobe, mt vas = lappets, median trough, p pereiopod, ventro-anterior spine, vk ventral keel vs = ventral shelf
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Fig. 4. 1,2, Securicaris SDSNH lateral of spinosus, holotype 26276; 1, general view, 2, close-up carapace cuticle; 3-5, SDSNH 29306, 3, dorsal aspect of one ofthree detached pleons referable to Cumacea, 4 and 5 key to the close-ups, 4-5, patches ofthe pleonal
cuticle of 3 = fig, the and = anterior vk = ventral displaying papillate (4) scale-like(S) ornament, as spine, c carapace, keel,
4 = areas with designates cuticle ornament as illustrated in = areas with cuticle ornament illustrated in fig. 4.4, 5 designates as fig. 4.5.
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Fig- 5. lateral and Reconstructions of Paleozoic cumacean cephalothoraxes. 1-2, Ophthalmdiastylis parvulorostrum, (1) dorsal (2)
views, scale and views, scale b; 6-7, Securicaris lateral a; 3-5, Carbocuma imoensis, lateral (3), dorsal (4), ventral (5) spinosus, (6) and dorsal (7) views, scale c.
lobe is narrower and than of the other Cumacea longer any sp. lossil cumaceans described herein, and there is a (Figs. 4.3-4.5)
clear set of in anterolateral spines that are lacking
- the Ophthalmdiastylus. The posterior dorsal area of the Remarks. In addition to cephalothoracic ma-
carapace on SDSNH 26276 does not seem to be terial described and named above, the specimens complete, so the lateral outline as reconstructed (Fig. at hand include three pleonal fragments (SDSNH
5-6) is a referable surmise of the original form. Neverthe- 29310) that seem to the Cumacea (Fig. less, despite the singular and fragmentary nature 4.3). These specimens are narrow and elongate of the 3 4 specimen, all the features noted above jus- consisting of to articulated segments and are tify the erection of a separate taxon. virtually identical to the long, narrow pleons char-
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acteristic for Cumacea. From their size and preser- into a pseudorostrum. Though the anterior lappets
vation, these pleons might be those of Carbocuma (“pre-pseudorostral lobes”), as exhibited in Oph-
but without their attached and imoensis, being to a cepha- thalmdiastylis C. imoensis, might appear to be
be lothorax there is no way to certain. a precursor to the pseudorbstrum, such lappets are
The specimens are highly sculptured (Fig. 4.3) prevented from meeting their counterpart dorso-
with mid-dorsal The cuticle is marked in the Paleozoic forms the paired ridges. anteriorly by presence
with distinct different textured deco- of the and Of areas bearing large paired eyes true rostrum. course,
rations. These range from papillose (Fig. 4.4) to one could postulate that as the eyes reduced and
scale-likc (Fig. 4.5) in form. These cuticular deco- repositioned themselves onto the frontal lobe, the
rations similar what could haveextend are again very to occurs on lappets to meet dorso-anteriorly
and The living cumaceans. form a pseudorostrum. formation of the
pseudorostrum apparently aided in channeling water
out of the branchial chamber, but these conclusions
Discussion are speculation. The discovery of evolutionary in-
termediates between the large paired-eyed Paleo-
and Most of the species of these Paleozoic cumaceans zoic forms modern reduced or eyeless species
apparently share basic characteristic features such could possibly confirm this transition scenario, and
ornamented with and functional and TEM studies of as a carapace spines lappets, morphologic living
forms could cast this well. How- pairs of large lobed eyes, and a ventral lateral shelf more light on as
alternative be that the on the carapace. These features stand in opposi- ever, an hypothesis might
inde- tion to those foundin modern Modern forms and the anterior are groups. pseudorostrum lappets
display a pseudorostrum (Fig. 6.1,6.2), a fused and pendent solutions to the problem of channeling
central ocular and reduced lobe (Fig. 6.2), no ven- respiratory currents.
tral shelf the addi- The in modern of neocumaceans on carapace (Fig. 6.6.5, 6.6). In eyes species
when fused and lo- tion, the presence of a well-developed rostrum in (Fig. 6-2), present, are small,
O. and cated on the anterior lobe parvulorostrum C. imoensis is not gener- dorso-medially (Schram,
In be in ally seen in extant taxa (Fig. Fig. 6.1). 1986). contrast, the eyes that can seen the
One feature that is absent in all Paleozoic of C. O. O. groups specimens imoensis, parvulorostrum,
O. and in all modern is the and are well yet present groups pseudorostrum costata, inflata large, paired
the (Fig. 6.1,6.2). The pseudorostrum is a specialized facetted, and arise from anterior part of the
and underneath the frontal lobe. This latter development of the anterior carapace, we be- ccphalon lieve could be indicative of that it was most likely formed by the medial arrangement a more primi-
tive state for cumaceans. it is extension of the anterior lappets seen in the Paleo- However, possible
of zoic species (Fig. 6.1, 6.2); it covers the anteriori that the reduced eyes modern forms also could extension have from the stalked of the branchial cavity (McLaughlin, developed independently eyes
in other Whether anterior observed in these common malacostracans. In that the 1980). the lappets case,
lobes is an actual to the in the fossils an inde- species evolutionary precursor eye might represent
pseudorostrum, or merely an analogous structure pendently derived character state from the fused condition in cannot be definitively determined at this point. seen living cumaceans. Nevertheless, this Assuming they are homologous, it is difficult to reduction of either stalked or
speculate about what might have encouraged the lobed eyes leading to the modern cumacean forms
of the anterior ofthe what is known in the Tanaidacea, another development lappets carapace parallels
Pig-6. cf. rathkei. left of of ventral of Diastylis I, lateral view carapace; 2, dorsal view pseudorostrum and optic lobe; 3, view
cephalothorax; 4, view of thorax of ventro-oblique posterior showing relationship pereiopods to posterior carapace margin, note long bases; 5, ventro-oblique view of with sideremoved to the ventral cephalothorax posterior maxillipeds on right clearly display carapace lack note of = = margin, a distinct ventral coxal of b = basis ol = shelf, c carapace, co openings pereiopods, ofpereiopods, optic lobe,
pr = pseudorostrum.
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whose Paleozoic forms also have lobed ber. Modern have cham- group large cumaceans a respiratory
from the eyes protruding underneath the anterior cara- ber that is dorso-lateral to thoracic segments
of pace, while modern tanaidaceans possess much proper, the bulging upward the carapace pro-
reduced Malzahn noted the eyes (Schram, 1986). (1972) viding a space “above” thorax, and movement
the Zechstein cumaceans had around 100 facets on of water within the chamber is facilitated by the
each eye, and this number is approximately matched beating of the epipodial bailers of the first maxil-
in the newly described forms O. parvulorostrum lipeds. These in combination with the siphons that
and C. imoensis. Modern species typically exhibit extend forward towards the pseudorostrum direct
3-4 facets, up to a maximum of 11. Gaten (1998) the flow of water out of the branchial chamber
commented on the diversity of optical arrangements forward under the pseudorostrum. In the fossils,
the in within Crustacea, which display nine out of the specimens like that seen Fig. 3.6 would seem to
ten types of described compound eye. The com- indicate that the branchial chamber of the Paleo-
of the Gaten zoic more lateral and ventral in loca- plexity compound eye brought (1998) species was
the conclusion that tion vis-a-vis the thorax is difficult to once an optical arrangement proper. It to
how have had evolved it would not be replaced by another conceive one arrangement could lead to
arrangement unless it provided a significant opti- the other. Consequently, it is a viable alternative
cal fossil advantage. The response of the eye, however, hypothesis that rather than the condition serv-
to such in conditions branchial adaptive pressures as those ing as a precursor to the arrangement seen
that reduce the effectiveness of the in in modern these conditions eye, e.g., forms, two represent
burrowing, cave-dwelling or deep-sea crustaceans, fundamentally different solutions to the functional
results in evolutionary convergence. Interpreting constraints of respiratory currents in Cumacea.
the reduction loss of in such The secondary or eyes evolutionary history of the Cumacea is little
be and limits of species can misleading the use eye understood, and the lack of preservation on these
of structure in systematics (Gaten, 1998). fossils important characters such as mouthparts,
The tanaidaceans and cumaceans are sister groups attached pleonal regions, and details of the pereio-
within the Peracarida (Schram, 1986), and there- pods makes the higher taxonomy of this group dif-
fore it is not surprising that during peracaridan ficult. Nevertheless, it would seem clear that there evolution the followed evolution- clades be within the groups parallel are two major to recognized
with to the reduction of the The Carboniferous ary paths respect eye. group (Fig. 7). ophthalmcuma-
Recent cumaceans are largely infaunal, and gener- ceans may have formed in an intermediate stage to
live it ally just at or slightly below the surface of the the living neocumaceans. However, is equally
with the and frontal lobe that of features in sediment, pseudorostrum likely many the seen the fossil
The need for is low in this could inde- exposed. large eyes ophthalmcumaceans equally represent
environment. The large eyes of the Paleozoic forms pendent solutions to the problems of the evolving
would have served well in a near-shore, marine cumacean life style.
environment with much available light. It might Assemblage information from the Imo Forma- also be suggested that perhaps these Paleozoic forms tion suggests that the Paleozoic cumaceans were had a more extended, pelagic aspect to their life living in a normal marine environment, slightly
and their cycles, larger eyes could have facilitated offshore and therefore deeper than the shallow ma-
active swimming, and enhanced the visual detec- rine fauna, with more calcareous sediment. The dark
tion of as well Details facies from the Eudora Shale in which predators as mates. concerning gray the
the and of the Paleozoic were found is also perciopods pleons species remaining specimens a very
are needed for this hypothesis to be evaluated. fossiliferous unit, and it is thought these cumaceans
Thc ventral shelf the on carapace appears to be were also deposited in a off-shore, normal marine,
a structure. Modern environment. unique cumaceans lack such yet very oxygen poor These environ-
an This difference have arrangement (Figs. 6.4, 6.5). may ments appearto relatively good preservational
different bespeak arrangements of water currents potentials, possibly due to pyritization as a result
through and around the branchial cham- ofreduced conditions. It is there- carapace oxygen very likely
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Fig- 7. Alternative phylograms of the Cumacea. Cumacea characterized by a core set of features (1), viz., posteriorly shortened carapace exposing 3-5 thoracic segments, 3 sets of maxillipeds, first maxilliped with multi-lobate epipodite, attenuated pleonal
of and reduced segments, and reduced or absent pleopods. 1, phylogram with independent development lobed (Ophthalmcumacea), and sessile and of either eyes (Neocumacea ) from a plesiomorphic stalked condition, a separate evolution lateral lappets (Oph-
from without anterior extensions thalmcumacea), or dorsal pseudorostrum (Neocumacea ) a plesiomorphic carapace any laterally or
2, with lobed the reduced sessile the dorsally. phylogram eyes (within Cumacea) as an intermediatecondition leading to and eyes on frontal lobe the formation (Neocumacea), and the development of lateral lappets (within the Cumacea) as a first stage towards ofa pseudorostrum the ventral shelf is for the and the loss (Neocumacea). In both, options, carapace an autapomorphy Ophthalmcumacea, of a true rostrum is an autapomorphy for the Neocumacea.
Tore that Union Marie Curie nr. ERBFMBICT many more fossil cumacean specimens Fellowship (Contract
thanks to Dr. Chris G. Jones, Head of could be found in these and similar localities of 983257). Special go Electron Microscope Unit, Natural History Museum London, normal marine, offshore environments, though their for providing the low vacuum SEM facilities and assistance. small size inhibits their inevitably recognition. Dr, John and the metric Malinky helped process sort two tons This collection of North American fossil cuma- from of Eudora Shale locality SDNHM 3267, and numerous
ceans doubles students in the the number of previously known taxa at Ohio University assisted collecting and pro- and cessing of the more than four metric tons ofthe lino shale; we provides and extension of knowledge of this thank these people for their assistance. group from the Permian back into the Carbonifer-
ous.
References
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