Axiopsis Eximia, a New Thalassinidean Shrimp (Crustacea, Decapoda, Axiidae) from the Middle Eocene of South Carolina Author(S): Brian Kensley and Austin B
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Axiopsis eximia, a New Thalassinidean Shrimp (Crustacea, Decapoda, Axiidae) from the Middle Eocene of South Carolina Author(s): Brian Kensley and Austin B. Williams Source: Journal of Paleontology, Vol. 64, No. 5, (Sep., 1990), pp. 798-802 Published by: Paleontological Society Stable URL: http://www.jstor.org/stable/1305715 Accessed: 25/07/2008 10:17 Your use of the JSTOR archive indicates your acceptance of JSTOR's Terms and Conditions of Use, available at http://www.jstor.org/page/info/about/policies/terms.jsp. JSTOR's Terms and Conditions of Use provides, in part, that unless you have obtained prior permission, you may not download an entire issue of a journal or multiple copies of articles, and you may use content in the JSTOR archive only for your personal, non-commercial use. Please contact the publisher regarding any further use of this work. Publisher contact information may be obtained at http://www.jstor.org/action/showPublisher?publisherCode=sepm and http://www.jstor.org/action/showPublisher?publisherCode=paleo. Each copy of any part of a JSTOR transmission must contain the same copyright notice that appears on the screen or printed page of such transmission. JSTOR is a not-for-profit organization founded in 1995 to build trusted digital archives for scholarship. We work with the scholarly community to preserve their work and the materials they rely upon, and to build a common research platform that promotes the discovery and use of these resources. For more information about JSTOR, please contact [email protected]. http://www.jstor.org J. Paleont.,64(5), 1990, pp. 798-802 Copyright? 1990, The PaleontologicalSociety 0022-3360/90/0064-0798503.00 AXIOPSIS EXIMIA, A NEW THALASSINIDEAN SHRIMP (CRUSTACEA, DECAPODA, AXIIDAE) FROM THE MIDDLE EOCENE OF SOUTH CAROLINA BRIAN KENSLEY1 ANDAUSTIN B. WILLIAMS2 'Departmentof InvertebrateZoology and 2National MarineFisheries Service SystematicsLaboratory, National Museum of NaturalHistory, SmithsonianInstitution, Washington, D.C. 20560 ABSTRACTr-Axiopsiseximia, a new species of thalassinideanshrimp, is describedfrom an exposureof the Middle Eocene Lower WarleyHill Formationof South Carolina,U.S.A. Fossil axiids are rare,but this unique specimenis remarkablypreserved as quartz free of envelopingmatrix, having a nearlycomplete though distortedcarapace, proximal parts of most thoracicappendages in situ but with distal articlesmissing, and extendedabdomen with segmentsalmost completeexcept for a few missingappendages. Presence of the bases of pleopods 1 and the elongateeyestalks surpassing the rostralapex, which it shareswith the extantAxiopsis caespitosa group, place it provisionallyin Axiopsis,which generallylacks first pleopods in males. INTRODUCTION with the specimen contained a single species each of the bivalve molluscs Cardita, Venericardia, and "Corbula," the gastropod FOSSILrecord of the Axiidae (summarized by Glaessner, Turritella, and the scaphopod Dentalium. THE sheds little on the of this 1969) very light understanding The cephalothorax and abdomen of the shrimp are closely diverse about 19 extant Of the six family containing genera. connected as in life, as are the mouthparts and proximal articles fossil one is genera, represented only by coprolites (Palaxius of the cephalic and thoracic appendages. It seems unlikely that Br6nnimann and Axius reticulatus Norton, 1960). Rathbun, the specimen is a molt, but it is likely that the animal was rapidly from the of is a 1919, Oligocene Panama, represented by single buried, perhaps during a storm, thereby preventing the disar- chela. Placement in the Axius in this case was incomplete genus ticulation usually accompanying decay of the fragile parts. The a matter of the chela obviously convenience, single providing high permeability of the matrix with its quartz content probably no indication of the true The specimen's systematic position. facilitated replacement with silica dioxide. In section, the exo- four Etallonia Pro- remaining genera, Oppel, Magila Miinster, skeletal material is replaced with a fine crystalline white quartz, taxius and Schlueteria are all from the Jurassic Beurlen, Fritsch, while the inner region is replaced with a more translucent aga- or Cretaceous of of these taxa are almost Europe. Specimens tized quartz. and the details of and always laterally compressed, carapace Measurements.-Total length from tip of rostrum to base of needed for and accurate appendages comparison placement telson, 46.0 mm; length of rostrum, 3.0 mm; estimated carapace within the are The taxonomic family rarely preserved. position length including rostrum, 19.0 mm; abdomen, length in mid- of the fossil been established present specimen has, therefore, dorsal line from anterior exposed part of segment one to pos- with extant forms. by comparison terior margin of segment six, 27.0 m, maximum width, 8.0 mm, SYSTEMATIC PALEONTOLOGY length of segment one, 2.4 mm, two, 4.2 mm, three, 5.1 mm (est.), four, 4.7 mm (est.), five, 4.6 mm, six, 6.0 mm. Order DECAPODA 1803 Latreille, Diagnosis. -Rostrum narrowly elongate triangular, dorsally Suborder 1963 PLEOCYEMATA Burkenroad, concave, lateral margins bearing six well-developed teeth; gas- Infraorder THALASSINIDEA 1831 Latreille, tric region bearing central elongate oval field of scattered sharp THALASSINOIDEA 1831 Superfamily Latreille, tubercles, median carina at base of rostrum crested with six AXIIDAE 1879 Family Huxley, spines anteriorly; postorbital margin bearing three tiny acute Genus Axiomsis 1903 Borradaile, spines and at its lower limit a larger buttressed antennal spine; EXIMIA n. AXIOPSIS sp. eyestalk exceeding rostrum by half its length; antennular pe- 4 Figures 3, duncle with stout basal article tapering distally and bearing slen- Collection. - Holotype, USNM 219431. One specimen from der distolateral spine; second article subcylindrical, bearing slen- road cut on South Carolina route 261, 1.7 mi south of U.S. der distolateral spine; antennal peduncle with short basal article route 76, about 2 mi north ofWedgefield, Sumter County, South bearing ventral tubercles and spines, stout second article much Carolina (Figure 1). Collected by F. S. MacNeil, U.S. Geological longer and third article more slender, each bearing mesial and Survey Locality No. 25750, August 1950. lateral spines. The locality was revisited by W. Blow (Smithsonian Insti- collapsed posterior to region of cer- tution) almost 30 years later. The small exposure (maximum vicalDescription.--Carapace groove; left branchiostegite collapsed but surface tubercles vertical height about 2 m), cut into a low hill, yielded matrix visible; proximal parts of most cephalothoracic appendages containing molluscs, but no further crustacean fossils. present, arranged in normal position of repose but with distal This exposure was determined to be an outlier of the Lower articles missing; abdomen extended, segments almost complete, Warley Hill Marl (Figure 2). Definitions of the Warley Hill Marl proximal articles of two pleopods present, uropods and posterior and description of its type locality were reviewed by Siple (1959). part of telson missing. The Warley Hill Marl is regarded as of middle Eocene age in Rostrum narrowly elongate triangular, dorsally concave, acute western and central South Carolina (Keroher et al., 1966). tip reaching to distal third of second article in antennular pe- Preservation.- The specimen was taken from an iron-stained duncle; thin raised lateral margins with six well-developed teeth, argillaceous, calcareous, medium-to-coarse quartz sandstone distal teeth somewhat eroded, proximal teeth acute, erect; dorsal containing a roughly layered coquina, and is remarkably com- surface moderately troughlike, with transversely rounded con- plete and free of matrix. The small sample of matrix collected cavity gradually broadening to juncture with gastric region; latter 798 KENSLEY AND WILLIAMS-NEW EOCENE SHRIMP 799 0 5 10 15 20 Series Group Formation KMK Jackson Barnwell 261 15 521 Castle 76-378 E Upper Hayne limestone Sumter 76-378 Wedgefield 15 0 521 261 a 0 8100 C K M McBean Santee Middle limestone E b 0 FIGUREI1-Location of typelocality of Axiopsiseximia n. sp. in South N Carolina. r WarleyHill marl En with central elongate oval field of scattered sharp tubercles; median carinaat base of rostrum to development rising greatest e Lower Congaree crestedwith six well-developedspines on anteriorgastric region, becoming obsolete in tuberculategastric field; latter flankedby submarginalspineless tract, crescentic row of spine-tippedgran- broadercrescentic concave tract confluent with ules, spineless FIGURE2-Stratigraphic position of Axiopsiseximia n. sp. in Eocene dorsal surface of rostrum, and prominent lateral spiny ridge rocksof SouthCarolina. confluentwith rostralmargin. Each of these tractstrend slightly towardmidline posteriorly,but collapseof carapacebeyond that point prevents description. Postorbital margin confluent with lateral edge of rostrum at level of juncture with lateral gastric tral tip by nearlyone-third length, not includingmissing corneal ridge, with three tiny acute postorbitalspines, largerbuttressed bulb evidently at least one-fourthwider than shaft of stalk. marginal antennal spine at lower limit; anterolateral angle Antennularpeduncle with stout basalarticle tapering abruptly rounded;cervical groove missing, except possibly for obscure in distal fourth of length, exceedinglyslender distolateral spine sector on right side, but lateral surfaceanterior to it granulate; on shoulderof taperingbasal