Growth cycles in fossil pelecypod shells and relationship to tidal cycles in earth-moon syste

Berry, W. B. N.

English

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Space Sciences Laboratory 
University of California 
Berkeley, California 94720 
Semi -Annual Report on 
STUDY OF GROWTH 
IN RECENT AND FOSSIL INVERTEBRATE EXOSKELETONS 
AND ITS RELATIONSHIP TO TIDAL CYCLES 
I N  THE EARTH-MOON SYSTEM 
Supported b y  
NASA Grant 
NGR-05-003-067 
t 
For the period 
May 1 through October 31, 1966 
?rincipal Investigator: Professor  W. B. N. Be r ry  
M6? - (ACCESSION 13128 NUMBER1 (THRUI 
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(NASA CR OR TMXOR AD NUMBER) (CATEGORY) 
Apace Sciences Laboratory Ser ies  No. 7, Issue No. 45 
September 30, 1966 
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https://ntrs.nasa.gov/search.jsp?R=19670003799 2020-03-16T17:19:25+00:00Z
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STUDY OF GROWTH 
IN RECENT AND FOSSIL INVERTEBRATE EXOSKELETONS 
AND ITS RELATIONSHIP TO TIDAL CYCLES 
IN THE EARTH-MOON SYSTEM 
NASA Grant 
NGR - 0 5 - 0 0 3 - 0 67 
Introduction 
~ 
This study includes development of techniques for  discerning growth 
cycles in fossi l  pelecypod shells and a tentative morphogenetic classifica- 
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tion of those cycles. 
the length of the months and years  in the pre-h is tor ic  past  based on the 
relationship between environmental rhythms and the growth cycles. 
growth cycles, which a r e  reflected in the shell  as growth increments,  a r e  
closely related to tidal phenomena in many piesent-day pelecypods. 
increments  a r e  present  in  their fossil  ancestors ,  and a considerable body 
of evidence suggests that in the past these organisms added growth incre-  
ments  in the s a m e  relationship to environmental phenomena as in the 
modern seas .  
The recognition of the cycles leads to estimation of 
The 
The 
Technique 
Analysis of the shells commences with observation of untreated. 
specimens with the unaided eye and with the microscope using reflected 
light. 
surface,  but the t r aces  of finer growth l aye r s  either a re  generally 
obscured by pitting and smoothing of the shell  a s  a r e su l t  of abrasion 
o r  they a r e  too fine to be readily observed. 
The l a r g e r  growth increments a r e  commonly distinct on the shell  , 
' 
Feature less  and nearly-featureless surfaces  have been etched with 
acid i n  an  attempt to bring out the finer layers ,  but this technique has  
not been successful. 
especially prominent concentric ridges, the finer l aye r s  may be seen  on 
the flanks of such ridges only with great  difficulty. 
rep l icas  of these shells have been made, but they have proven to be of 
l i t t le  a id  in studying the fine layers .  
view the f iner  growth layers .  
Although certain growth layers  in some shells f o r m  
Flexible surface 
The shells mus t  be sectioned to 
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After the shells have been studied in ref lected light a t  magnifications 
up to X200 and, in many cases ,  photographed, the shells a r e  cut in thin 
sections in the directions that appear most  suitable fo r  the par t icular  
shell. 
factory resu l t s  because the molluscan shells tend to break apa r t  a s  they 
a r e  polished down to the desired thickness of 15 to  20 microns.  
breakage, which is commonly the result  of faulty adhesion of the shell  to 
the slide, may be  reduced by using a new epoxy r e s in  instead of the res ins  
most  commonly in use in cutting thin sections of rocks.  
been applied to decrease  breakage resulting f r o m  the flexible proteinous 
nature of pa r t s  of the shell. 
Conventional thin sectioning processes  do not yield entirely satis- 
This 
Oxidants have 
The thin sections a r e  examined in polarized light. They a r e  photo- 
graphed along a t r ave r se  connecting the dorsal  and ventral  shell  margins .  
Then the photographs (actually on the scale  of photomicrographs) a r e  
joined together to f o r m  a composite f igure of the shell  in thin section. 
These composites facilitate objective study; when the image of the shell  
thin section has  been projected to a ten by two foot a r e a ,  i t  is possible to 
place one's finger on the l ikeness of s t ruc tures  only a few microns in 
s ize .  The resolution quality is considerably superior  to that obtained 
f r o m  ordinary lantern slide projectors.  
The Growth Lavers - -A Tentative Classification 
~~ 
The following growth layers  have been observed in the shells of both 
fossi l  and modern pelecypods: 
1) Elemental l ayers ,  o r  the smallest  growth layers  visible through 
the l ight microscope. 
opaque substance, and (c)  conchiolin dispersed in an  aggregate of microerystal-  
line Ca  C 0 3  (in the formof aragonite). 
amined are arranged in the following sequence, which may be repeated thousands 
oftimes during the formation of a single shell: a ,  b, c ,  b, c, b ,  c ,  b, ; 
a, b, c, b, . . , . . etc. This bundle of eight elemental l ayers  often is 
visible as a single striation on the shell surface.  
p e r  annual layer  suggests diurnal origin. Some species,  however, lack 
such a n  order ly  grouping of elemental l ayers ,  the smallest  cyclic layer  
consisting of an  alternation of a with either b or c. In these forms ,  the 
number of smal les t  cyclic layers  per annual layer  is often m o r e  o r  l e s s  
than 365. 
These a re  (a) cryptocrystall ine CaC03, (b) an  
The l aye r s  in  most  of the species ex- 
The number of s t r ia t ions 
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2)  Ridge- troughs, o r  cyclic alternations of concentric ridges and 
troughs. The component growth layers  of the ridges a r e  relatively thin 
and therefore must  resul t  f r o m  relatively slow shell growth during t ime 
of ridge formation. 
to 24, or  12 per  annual layer ,  and the number of component layers  pe r  
ridge-trough is either close to 15 or in the vicinity of 30 .  
that the ridge-troughs may be formed monthly or  bimonthly with the 
ridges recording slow growth phases of the tidal cycles. There  a r e ,  
however, a t  l eas t  two species that form concentric ridge-troughs in a 
manner which obviates environmental connections. 
Ridge-trough cycles have been found to number close 
Thus, it s eems  
3) Node-troughs. These a r e  similar to concentric ridge-troughs 
Despite the fact  that some species have but a r e  confined to radial  r ibs .  
uniquely distributed nodes, many others feature  a remarkable  coincidence 
of nodes f rom one radial  r ib  to another. 
a r e  thinnest within the nodes. 
in Trigonia. 
The component growth s t r i ae  
They number close to 30 per  node cycle 
4) Annual bands. These  a r e  alternations of relatively thin portions 
Trans-  of translucent shell, with thicker portions of dark- colored shell. 
lucent shell consists chiefly of CaC03 crys ta l s  oriented with a high degree 
of optical parallelism, whereas  the dark- colored shell is composed of 
m o r e  i r regular ly-  oriented crystals,  mixed with a relatively l a rge  amount 
of brownish conchiolin. 
thickest  in the dark-colored portion, and as indicated by study of summer  
samples  of living pelecypods, a r e  deposited during summer  seasons of 
rapid shell growth. Thus, the band cycle has  diagnostic microtextural  
c r i t e r i a  and it is known to be of annual significance. 
The component growth l aye r s  of these bands a r e  
5) Variation of the shape of the whole shell. Specimens of Myalina 
(Carboniferous) a r e  constricted periodically five to six t imes along the 
dorso-ventral  axis. On the average, thirteen ridge-troughs a r e  comprised 
by a constriction cycle. 
sion of annual environmental variation may be strengthened by the fac t  
that  similar constrictions a r e  known to be formed annually in certain 
l iving Japanese pelecypods. 
Interpretation of this growth cycle as an  expres-  
6)  Disturbance rings.  These a r e  units of translucent shell which 
2 s  Si2Zi-i wit2 ttiz -Giiaided eye B O ~ 2 ' ; l r k t  si=.il=r ts the \\+Iter i n c r e m e n t s .  
They tend to Occur e r ra t ica l ly  with respect  to the annual band cycle and 
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their  number per  shell  var ies  greatly with environment and species .  
can be observed in thin section that the disturbance rings a r e  not on ly  
thinner than the winter growth units but have crinkled contacts with the 
normal  shell  growth units. 
when they occur in the midst  of the winter phase of the annual band 
cycle. 
turbance rings.  
turbance rings a r e  reflective of s torms.  
It 
Disturbance rings can be  recognized even 
Occasionally, some detri tal  quartz  sand is found within the dis- 
These observations lead to the conclusion that dis-  
Some Re c ent Determinations 
The techniques for  study of growth increments in foss i l  pelecypod 
shells and the classification of the shell growth l aye r s  discussed above 
have been used as the basis for recognition of annual, monthly, bi- 
monthly, and diurnal growth cycles in such shells.  
fossil  specimens examined have been preserved in such a manner that 
only single cycles o r  par t s  of cycles may be studied. 
shel ls  must  be examined carefully before finding shells in which an  un- 
broken succession of the several  component layers  that comprise  the 
l a rge r - sca l e  l aye r s  may be observed and counted. 
in Table 1 fo r  the mater ia l s  studied in the past  semi-annual period that 
have proven well-enough preserved to obtain counts of shell growth 
increments  over severa l  cycles. 
The majority of the 
Numbers of 
Data a r e  tabulated 
Myalina subundata appears  to be especially promising as an  index 
to the number of months p e r  year during the Carboniferous. 
periodicity observed in the samples of Astartella concentrica may not be 
a t rue  reflection of days pe r  month in the Carboniferous. 
r idge-troughs observed in its shells probably cor re la te  with rhythms of 
l e s s  than annual magnitude. 
fortnightly, o r  not controlled by the environment, can only be conjectured. 
The 19. 5 
The forty 
Whether the rhythms w e r e  monthly o r  
As figures given in ear l ie r  reports  on the project have indicated, 
the yea r  in the Cretaceous was apparently composed of 12. 5 lunar months 
and this  period is probably equivalent to 401 synodic days. 
data ( s e e  Table 1) continue to support the ear l ie r  conclusions concerning 
months pe r  year  and days per  month during the Cretaceous. At present,  
tLt: sileiis examined. suggest a n  average of 51. 8 - + 1. 35 synodic days for 
the Cretaceous lunar month. 
The present  
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Questions for fur ther  r e sea rch  
The observed range in possible number of days per  months a s  de te r -  
mined f r o m  the study of growth layers  in fossi l  pelecypod shells does 
r a i s e  some questions of interpretation. F o r  example, a r e  anomalous 
layers  present  that a r e  being counted as normal growth layers  ? Such 
layers  could resu l t  in the relatively high count seen in Crassatell i tes 
vadosus No. 3. 
in the 7-elatively low count observed in Trigonia thoracia ? 
anomalies and omissions simply the resul t  of some activity in the speci-  
f ic organism studied and not generally present  throughout whole popu- 
lations ? May these anomalous numbers be reflective of some special 
environmental phenomenon ? 
anomalous numbers of small-scale  layers  be averaged in a count to 
ascer ta in  an a r i thmet r ic  mean number of days ? 
be pursued as the study of the fossi l  mater ia l s  continues. 
Are there  omissions of diurnal layers  that a r e  expressed 
Are  these 
May the foss i l  f o r m s  exhibiting such 
These questions will 
Growth Experiments 
Growth experiments a r e  proceeding a s  planned and outlined in 
ea r l i e r  reports .  
total of fifty aquarium tanks, supplied with water  f r o m  the nearby ocean 
continuously pumped through the tank system. 
kept under a var ie ty  of light-dark and simulated tidal cycles. Juveniles 
of some other species-- those m o r e  closely related to the fossil  species 
being examined in this study--are to be included in the growth experi- 
ments.  
Juveniles of local pelecypod species a r e  living in a 
The tanks a r e  being 
Conclusions 
In conclusion, the examination of the foss i l  shells indicates a slow 
and continual decrease  in number of months per  year,  f r o m  13 in the 
Carboniferous (approximately 300 million years  ago), to 12. 5 in the 
Cretaceous (approximately 100 million years  ago), to 12 a t  the present  
t ime.  Fur ther ,  there  appear to have been somewhat m o r e  synodic 
days p e r  month in the Cretaceous than a t  present .  
ges t s  that  changes in distribution of angular momentum have taken 
place within the earth-moon system. 
This evidence sug- 
Personnel :  P r o f e s s o r  W. B. N. Be r ry  - Principal Investigator; 
Richard Barker  - Post  Graduate Research Paleontologist. 
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Study of Growth in Recent and Fossil Invertebrate Exoskeletons and Its Relationship to Tidal Cycles in the Earth-moon System Semiannual Report, May 1 - Oct. 31, 1966

Study of Growth in Recent and Fossil Invertebrate Exoskeletons and Its Relationship to Tidal Cycles in the Earth-moon System Semiannual Report, May 1 - Oct. 31, 1966

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