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Nekroplanktonic dispersal of echinoid tests
Palaeogeography, Palaeoclimatology, Palaeoecology, 52 (1986): 347--349 Elsevier Science Publishers B.V., Amsterdam -- Printed in The Netherlands
347
N E K R O P L A N K T O N I C D I S P E R S A L OF ECHINOID TESTS
RICHARD A. REYMENT Paleontologiska Institutionen, Uppsala Universitet, Box 558, $75122 Uppsala (Swedet~) (Received December 11, 1984; accepted June 10, 1985)
ABSTRACT Reyment, R. A., 1986. Nekroplanktonic dispersal of echinoid tests. Palaeogeogr., Palaeoclimatol., Palaeoecol., 52: 347--349. The find of an echinoid shell in the process of being nekroplanktonically transported is of significance for the interpretation of isolated occurrences of echinoids in the fossil record. INTRODUCTION The p o s t - m o r t e m dispersal o f c e p h a l o p o d shells is n o w a well established fact. B o t h direct observations on living Nautilus ( R e y m e n t , 1958, 1973; House, 1 9 7 3 ; J E C O L N , 1 9 8 0 ) and e x p e r i m e n t a l studies using exact m o d e l s o f c e p h a l o p o d shells ( R e y m e n t , 1980) provide o v e r w h e l m i n g evidence of the c o m m o n o c c u r r e n c e of drifted shells in the fossil record. (N.B. This is n o t m e a n t to imply t h a t all c e p h a l o p o d shells we find are drifts, nor t h a t all drifted shells have been t r a n s p o r t e d over great distances.) The o b j e c t o f the present n o t e is to bring to the a t t e n t i o n of palaeobiogeographers the fact t h a t e m p t y echinoid tests can be t r a n s p o r t e d nekrop l a n k t o n i c a l l y b y oceanic currents. THE MATERIAL During the s u m m e r o f 1 9 8 4 I was c o n c e r n e d with sampling the nearshore m a r i n e e n v i r o n m e n t o f s o u t h e r n Spain (Vdlez Mfilaga to Tarifa) for o s t r a c o d s . In J u n e , while w o r k i n g o f f E s t e p o n a , an e c h i n o i d was observed floating a b o u t 100 m f r o m the shore, a b o u t 1 k m E o f the t o w n . It was f o u n d to be a regular e c h i n o i d in a g o o d state o f p r e s e r v a t i o n (Plate I, 1, 2). The s p e c i m e n c o n t i n u e d to float in seawater for a m o n t h after c o l l e c t i o n (Plate I, 3, 4), after w h i c h o b s e r v a t i o n was d i s c o n t i n u e d . The sea u r c h i n seems to have u n d e r g o n e a p e r i o d o f dessication and " m u m m i f i c a t i o n " after death, to w h i c h attest the presence of a b u n d a n t fragm e n t s o f spines (Plate I, 2) c e m e n t e d to the surface of the test. The teeth are preserved in situ (Plate I, 1) and the oral region is intact. P r e s u m a b l y , after 0031-0182/86/$03.50
,<7 1986 Elsevier Science Publishers B.V.
348 PLATE I !i¸ ! ! ii
1. 2. 3. 4.
Oral aspect of the test of the regular sea urchin showing the teeth. Lateral view of the specimen ; note the cemented spine-fragments. Specimen floating in seawater after 28 days. Floating orientation of the test in seawater.
having been w a s h e d up and dried on the shore, the shell was carried o u t to sea d u r i n g a spate o f r o u g h weather. DISCUSSION The fact t h a t an e c h i n o i d test can, u n d e r certain c o n d i t i o n s of preservation, float and thus be t r a n s p o r t e d passively o p e n s i n t e r p r e t a t i o n a l possibilities for isolated o c c u r r e n c e s o f the shells o f sea urchins in the geological c o l u m n . S o m e w h a t analogous is the o b s e r v a t i o n o f K r e j c i - - G r a f ( 1 9 3 5 ) o n the floating p r o p e r t i e s o f e m p t y bivalve shells in w h i c h the l o o s e n e d p e r i o s t r a c u m m a y b e c o m e realigned in a m a n n e r such as to seal the valves. The n e k r o p l a n k t o n i c dispersal o f organisms w o u l d seem to be a palaeobiogeographical reality for m o r e g r o u p s o f invertebrates t h a n just the shellbearing c e p h a l o p o d s .
349 REFERENCES House~, M., 1973. An analysis of Devonian goniatite distributions. Palaeontology, Spec. Pap., 12: 305--317. JECOLN, 1980. Nautilus macromphalus in captivity. Tokai Univ. Press, Tokyo, 80 pp. Krejci-Graf, K., 1935. Beobachtungen am Tropenstrand I--IV. Senckenbergiana, 17: 21 -61. Reyment, R. A., 1958. Some factors in the distribution of fossil cephalopods. Stockholm Contrib. Geol., 1: 97--184. Reyment, R. A., 1973. Some factors in the distribution of fossil cephalopods: Part III. Experiments with exact models of certain shell types. Bull. Geol. Inst. Univ. Uppsala, N.S., 4: 7--41. Reyment, R. A., 1980. Floating orientations of cephalopod shell models. Palaeontology, 23: 931--936.
347
N E K R O P L A N K T O N I C D I S P E R S A L OF ECHINOID TESTS
RICHARD A. REYMENT Paleontologiska Institutionen, Uppsala Universitet, Box 558, $75122 Uppsala (Swedet~) (Received December 11, 1984; accepted June 10, 1985)
ABSTRACT Reyment, R. A., 1986. Nekroplanktonic dispersal of echinoid tests. Palaeogeogr., Palaeoclimatol., Palaeoecol., 52: 347--349. The find of an echinoid shell in the process of being nekroplanktonically transported is of significance for the interpretation of isolated occurrences of echinoids in the fossil record. INTRODUCTION The p o s t - m o r t e m dispersal o f c e p h a l o p o d shells is n o w a well established fact. B o t h direct observations on living Nautilus ( R e y m e n t , 1958, 1973; House, 1 9 7 3 ; J E C O L N , 1 9 8 0 ) and e x p e r i m e n t a l studies using exact m o d e l s o f c e p h a l o p o d shells ( R e y m e n t , 1980) provide o v e r w h e l m i n g evidence of the c o m m o n o c c u r r e n c e of drifted shells in the fossil record. (N.B. This is n o t m e a n t to imply t h a t all c e p h a l o p o d shells we find are drifts, nor t h a t all drifted shells have been t r a n s p o r t e d over great distances.) The o b j e c t o f the present n o t e is to bring to the a t t e n t i o n of palaeobiogeographers the fact t h a t e m p t y echinoid tests can be t r a n s p o r t e d nekrop l a n k t o n i c a l l y b y oceanic currents. THE MATERIAL During the s u m m e r o f 1 9 8 4 I was c o n c e r n e d with sampling the nearshore m a r i n e e n v i r o n m e n t o f s o u t h e r n Spain (Vdlez Mfilaga to Tarifa) for o s t r a c o d s . In J u n e , while w o r k i n g o f f E s t e p o n a , an e c h i n o i d was observed floating a b o u t 100 m f r o m the shore, a b o u t 1 k m E o f the t o w n . It was f o u n d to be a regular e c h i n o i d in a g o o d state o f p r e s e r v a t i o n (Plate I, 1, 2). The s p e c i m e n c o n t i n u e d to float in seawater for a m o n t h after c o l l e c t i o n (Plate I, 3, 4), after w h i c h o b s e r v a t i o n was d i s c o n t i n u e d . The sea u r c h i n seems to have u n d e r g o n e a p e r i o d o f dessication and " m u m m i f i c a t i o n " after death, to w h i c h attest the presence of a b u n d a n t fragm e n t s o f spines (Plate I, 2) c e m e n t e d to the surface of the test. The teeth are preserved in situ (Plate I, 1) and the oral region is intact. P r e s u m a b l y , after 0031-0182/86/$03.50
,<7 1986 Elsevier Science Publishers B.V.
348 PLATE I !i¸ ! ! ii
1. 2. 3. 4.
Oral aspect of the test of the regular sea urchin showing the teeth. Lateral view of the specimen ; note the cemented spine-fragments. Specimen floating in seawater after 28 days. Floating orientation of the test in seawater.
having been w a s h e d up and dried on the shore, the shell was carried o u t to sea d u r i n g a spate o f r o u g h weather. DISCUSSION The fact t h a t an e c h i n o i d test can, u n d e r certain c o n d i t i o n s of preservation, float and thus be t r a n s p o r t e d passively o p e n s i n t e r p r e t a t i o n a l possibilities for isolated o c c u r r e n c e s o f the shells o f sea urchins in the geological c o l u m n . S o m e w h a t analogous is the o b s e r v a t i o n o f K r e j c i - - G r a f ( 1 9 3 5 ) o n the floating p r o p e r t i e s o f e m p t y bivalve shells in w h i c h the l o o s e n e d p e r i o s t r a c u m m a y b e c o m e realigned in a m a n n e r such as to seal the valves. The n e k r o p l a n k t o n i c dispersal o f organisms w o u l d seem to be a palaeobiogeographical reality for m o r e g r o u p s o f invertebrates t h a n just the shellbearing c e p h a l o p o d s .
349 REFERENCES House~, M., 1973. An analysis of Devonian goniatite distributions. Palaeontology, Spec. Pap., 12: 305--317. JECOLN, 1980. Nautilus macromphalus in captivity. Tokai Univ. Press, Tokyo, 80 pp. Krejci-Graf, K., 1935. Beobachtungen am Tropenstrand I--IV. Senckenbergiana, 17: 21 -61. Reyment, R. A., 1958. Some factors in the distribution of fossil cephalopods. Stockholm Contrib. Geol., 1: 97--184. Reyment, R. A., 1973. Some factors in the distribution of fossil cephalopods: Part III. Experiments with exact models of certain shell types. Bull. Geol. Inst. Univ. Uppsala, N.S., 4: 7--41. Reyment, R. A., 1980. Floating orientations of cephalopod shell models. Palaeontology, 23: 931--936.