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Chapter 23. Evolution of Amphicostella from the Middle Devonian in Europe (Metacopa, Ostracoda)

Chapter 23. Evolution of Amphicostella from the Middle Devonian in Europe (Metacopa, Ostracoda)

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276 F.J. ADAMCZAK



analogous strategies in reduction of meshes and distribute the rest of them in long and regular

rows. Although it is assumed that the decrease in number of meshes has been without any prearrangement in the different taxa, the site where this process took place was not coincidental. The

change in number of meshes within a species occurs mainly in the posterior sector of the carapace.

It is also responsible for the most important variation, which may be as high as 80%. Another

aspect of this phenomenon seems to be related to the enlargement of meshes. Judging from the

areal size of the reticulum, it seems that natural selection favoured individuals with large reticular

elements. The arrangement of meshes in regular rows could have affected (1) the calcium carbonate

economy of the animal and (2) reinforcement of the carapace wall.

STRATIGRAPHIC OCCURRENCE OF



Amphicostella IN THE



HOLY

CROSS

MOUNTAINS

The representatives of Amphicostella appear in calcareous clay rocks together with trilobites,

brachiopods, small rugose corals and bryozoans. They are not numerous and make up less than

one per cent of all ostracode forms in a sample. They have been found in three localities. At the

first locality (Wydryszow), besides the type species, there are two other forms, designated as

Amphicostella sp. 1 and Amphicostella sp. 2. At the second locality, there occurs Amphicostella

sp. 3, which seems to be quite closely related to A. prima Adamczak. Amphicostella sp. 3 has been

identified in only one sample (Text-fig. 1).

Although the four species appear suddenly in the Middle Devonian, it cannot be determined

whether they originated in this region or migrated to it during the latter part of the Early Devonian

transgression. The species mentioned above are presumably the earliest Amphicostella known

from Europe. The fifth species, A. sculpturata (Pokorn?), is represented in the Holy Cross Mountains

by one specimen, which occurs in the lower Givetian.

HOLY CROSS MOUNTAINS

EPOCH



AGE



M

I



G

I

V

E

T

I

A

N



D

D

L

E

D

E

V

0

N

I

A

N



1



I



FORMATION



I



LOCALITIES



NIECZULICE

BEDS

SWIETOMARZ

BEDS

SKALY



---E

I

F

E

L

I

A

N



BIOZONE



H. ANTRI- P. RETICULATA

HOWICE FM.

P. ABNORMIS ( X I

1



A. MAGNA ( 0 )



GRZEGORZOWICE FM.



GRZEGORZOWICE ( X I

WYDRYSZOW

(XI,

(0).



TEXT-no.I-Stratigraphicand sampling localities of the Middle Devonian in the Holy Cross Mountains where

Amphicostella has been found.



AmphicosteIIa from MiddEe Devonian in Europe 277



ORNAMENTAL

PATTERN

IN Amphicostella

The diagrams of Amphicostella forms shown in Text-figs. 2 and 3 indicate the presence of

several sectors (outer, anterior, adductorial, posterior and caudal) which are parts of the ornamental pattern (meshes, carinae and the adductor muscle rosette) of the carapace and which have

been examined in left aspect. From the sectors mentioned, anterior, adductorial and posterior have

also been studied by pattern analysis (Pokorn9, 1969; Liebau, 1969; Benson, 1972). The remaining

sectors, because of the preservational state of the fossil material and the complexity of the valve

ornamentation, have not been studied by this method.

The meshes of the analysed sectors have been coded in Arabic and Roman numerals and

small and capital letters which are written below the reticular silhouette drawings of the different

species in a characteristicrecord (Text-figs. 3,5,7,8,9 and 10). The records simplify the analysis of

the reticulum and allow a particular pattern of meshes to be easily compared with the record of

another individual of the same or different taxon. In other words, they are homologized.

It seems logical to begin the analysis of the various ornamental details with the more stable sculptural elements of the carapace, i.e. the rosette of the adductors and the major carinal (ridge) system.

The rosette. The rosette of the adductors is situated in the central part of the carapace. It consists of six “petals” which are presumably impressions of the adductors (Text-figs. 2,4 and 6). Although the dimensions of the rosette are above the average, this does not mean that the adductors

were abnormally large. The rosette seems to be a very stable feature in Amphicostella. It has greatly

aided in the identificationof most individuals of this genus and is suggested to be an important

generic character.

Amphicosteila sp. 3



A NTERl OR

ADDUCTORIAL

VERTICAL

,POSTERIOR



MUSCLE SCARS



I



CARINAE



VENTRAL CARINA



TEXT-FIG.

2-Basic morphological features in Amphicostelfashowing the mura1 and carinae systems as seen in the

left valve ( X 140). Holy Cross Mountains, Grzegorzowice; Middle Devonian, Grzegorzowice Formation.



218 F.J. ADAMCZAK



The carinal system. The major ridge (carinal) system, considered as an enlargement of the muri

(Benson, 1977), consists of five carinae in the Eifelian forms (Text-fig. 2) and six ridges (carinae)

in the Givetian species. From the five ridges identifiable in the Eifelian forms, the ventral, outer and

adductorial ridges are less massive in Amphicostella sp. 1 and Amphicostella sp. 2 (Text-figs. 4, 6).

The remaining ridge elements, i.e. the posterior and anterior carinae seem to be much more stable.

Being massive and long, they connect the dorsal margin with the ventral carina. The sixth of the

major ridges is present in the posterior sector of A. sculpturata (Text-figs. 9,lO). It is long and stable

whereas its equivalents in the Eifelian forms are considered to be minor elements, which are less

firm and one or two in number. They appear in A. prima and Amphicostella. sp. 3.

The reticulum. Although the pattern of meshes of a particular species of Amphicostella is quite

distinct, the number of meshes, especially in the posterior sector, is considerably variable. A review

of the different parts (sectors) of the valve given below begins with the anterior sector, which may

be divided into dorsal and ventral sections. The dorsal part starts at the level of mesh I of the adductorial sector (Text-fig. 3). It may be biserial, coded: A], B1; Az, B2, etc., which means that the

meshes are arranged in two rows, as for example in A. prima (Text-fig. 8) or three rows (Al, B1, C1;

Amphicostella sp. 3



ADDUCTOR I A L

SECTOR



ANTE R IOR

SECTOR



POSTER IOR

SECTOR



I

I

6



7



LB5



1

c5 85 As



m



CI, 01, A 4

C3 83 A 3

C2 B2 A2

CI 81 A I



a



1 I f



b



I



C



e



d



13 12 1 1



F"



23 22 21

33 32 31



F'

F E



1 3 42



5h

59

51

5e

5d



3

1



B" A"



D'



C' 6' A'



D



C



B



A



Lh 3h 2h lh



4 39 29 19

L f 3f 2f I f



Le 3e 2e le

Ld 3d 2d Id

5c Lc 3c 2c 1c

5b L b 3 b 2 b Ib

5a La 3a 20 la

D C B A



B EXTRA MESH



41



TEXT-no.34chematic drawing of reticulation patterns traced from a SEM micrograph and record of meshes

( x 160). Holy Cross Mountah, Grzegorzowice; Middle Devonian, Grzegoaowice Formation.



279



Taxr-pro. QSEM micrographs. 1. Left lateral view of carapace( x 155). 2. Fragment of reticulationwith adductor



muscle rosette (to the left) and mural system. 3. Inside view of a mesh showing a surface of sieve-type pores(?)

Holy ,Cross Mountains, Wydryszow; Middle Devonian, Grzegorzowice Formation.



280 F.J. ADAMCZAK



Az, Bz,Cz; A3, etc.) as in Amphicostella sp. 2, Amphicostella sp. 3 and A . sculpturata (Text-figs. 3,

7 , 9). Often the triserial arrangement of meshes can dorsally pass into a biserial one, similar to

that visible in A. prima. In Amphicostella sp. 1 (Text-figs. 4 and 5), this part of the sector shows an

intermediate character indicating that it starts at the height of mesh I with three meshes (A1, B1,

C,) and passes into a biserial design (Az,Cz;A3,C3),and again demonstrates a triserial arrangement

with the reticular elements coded &, B,, C,; AS,etc. The ventral part of the anterior sector of the

Amphicostella sp. 1



M



I



ADDUCTORIAL

SECTOR



ANTERIOR

SECTOR



*



6



7



4



5



2



3

1



a



F



E



D



C



B



A



POSTER IOR

SECTOR



.A

I

I



5 i @ Li 3 i 2 i

5h

L h 3 h 2h

Lg 3 9 2 9

5g

5 f Ig 4 f 3 f 2 f

5e

Le 3 e 2 e

5d

Ld 3d 2d

M 5c

Lc 3 c 2c

@ 5b

L b 3 b 2b

5a

La 3 a 2a

F E

D C B



a



a



E

l



li



a



Id



a lh

a lg

a If

IEl l e

I C



lb

la

A



1



r-i



~ - j DIMINISHED MESH



0 REDUCED MESH

EXTRA MESH



TEXT-FIG.

5-Schematic drawing of reticulation patterns traced from a SEM micrograph and record of meshes

( x 185). Holy Cross Mountains, Wyoryszow; Middle Devonian, Grzegorzowice Formation.



281



TEXT-FIG.

-EM



micrographs of Amphicoe

tella as seen in left lateral view ( ~ 1 5 5 ) .

Holy Cross Mountains, Wydryszow; (Amphicostelfa sp. 2. A . prima), GRegorzQwi~

(Amphicostelfu sp. 3); Middle Devonian,

Grzegorzowice Formation.



282 F.J. h m c z m



Eifelian forms is as a rule triserial(11, 12, 13; 21, 2,, &; 31, 3,, etc.), whereas in the Givetian species it

begins biserially and terminates with one mesh. In Amphicostella sp. 2 the lower part of the anterior

sector shows a Iarge and united mesh coded in 1 1, Z1, X* and the presence of another mesh of X

situated between the meshes, 41 and 4, (Text-fig. 7).

Although the adductorial sector may show a quite differentiated pattern of meshes, the number

of meshes remains quite stable within species. In the dorsal part of this sector, i.e. above the

adductor muscle rosette which has been coded with small letters (a, byc, d, e, f), there are 1-9 or

Amphicostella sp. 2

L



ANTERIOR

SECTOR



ADDUCTORIAL

SECTOR



,



POSTERIOR

SECTOR



I



5i m

6041

. 31. 2i l i



I 5h



QB



A5

G3 84 A4

GI 8 3 A3

Ci 8 2 A2



33 32



mU



f



I



e



I

a



Lh 3h 2h l h



5 9 m 9 39 29 1g

5f



b

C



d



F"

D"

8" A"

F ' E' D' C' 8' A'

F E D C B A



A t 3tmZf 11



ie 4e j e - i e le

M Ld 3d Zdmld

5c Lc 3c 2 c a c

605b L b 3b 2 M b

5aPoLa 3a 2a la

F E D C B AA,



4; 4; Po 4;



e



EXTRA'MESH



UNITED MESHES



TEXT-FIG.

74khematic drawing of reticulation patterns traced from a SEM micrograph and record of meshes

( x 190). The same specimen is pictured in Text-@. 6.



*



Mesh X, as interpretedin the present paper, is an element which docs not fit very well in therecord in question.



Amphicostella from Midde Devonian in Europe 283



more meshes. They are biserially arranged with distinct horizontal muri and less massive vertical

elements. Occasionally, a mesh X may appear in this part of the valve (Amphicostella sp. 3, Textfig. 3). In front of the adductor muscle rosette there are two (I, 111) or three (I, 11, 111) meshes.

Mesh I1 is often smaller, or very small.

The ventral part of the adductorial sector is coded with capital letters from A, A', A" to F".

It has a maximum of seventeen (Amphicostella sp. 1, Text-fig. 5 ) and a minimum of twelve meshes

(A. sculpturata, Text-fig. 10). In the latter species, which comes from Czechoslovakia and shows

the right valve, reticular elements A', B, D", E' and E" have disappeared. The posterior sector demonstrates not only the largest diversity in the pattern of meshes, their number, dimensions

Amphicostellaprima Adamczak



n



ADOUCTORIAL SECTOR



ADDUCTORIAL

SECTOR



6



ANTERIOR SECTOR



POSTERIOR

SECTOR



7



5h Lh 3h 2h lh

59;g

39 29 lg



4 5

J

l2 3

1



B5 A 5



8 3 A3

0 2 A2



13



B12

1



Al

11



2s 2? 21

$ 3; 3;

0



W



m



f



a



D P



b

c



I



d



F.*

F'

F E



D' C'

D C



8" A '

B

B



A'

A



51 Lf

0

5e Le

0 Ld

5c 4c

5b 4b

5a 4a



3f 21 If

3e

3d

3c

3b

30



E D



2e Ie

2d Id

2c 1c

2b lb

20 la



C B A



REDUCED MESH

EXTRA M E S H



TEXT-FIG.

8sChematic drawing of reticulation patterns traced from a SEM micrograph and record of meshes

( X 190). The same specimen is pictured in Text-fig. 6.



284 F.J. ADAMCZAK



and size among the different species of Amphicostella, but it also reveals an immense individual

variability. There are, at the base of this sector, just above the ventral carina, up to seven meshes

coded A,, A, ByC,D, E, F, as in Amphicostella sp. 2 (Text-fig. 7) or six meshes A, ByC, D, E, F, as in

Amphicostella sp. 1 (Text-fig. 5). In A . prima four meshes occur, coded: A, ByC, D, whereas Amphicostella sp. 3 and A . sculpturata (Text- figs. 9,lO) have five meshes (A, €3, C, D, E) in this part of the

valve. Besides the mentioned reticular elements, the majority of species of Amphicostella have five,

more or less vertically arranged, rows of meshes which are, beginning from behind, coded: la, lb,

lc, Id, le, lf, etc. to Say5b, 512, etc. In Amphicostella sp. 1 and Amphicostella sp. 2 there occur some

additional but incomplete rows of meshes coded as X-es. These are situated between rows 1 and 2,4

and 5, and in front of row 5. The mentioned species have as many as over ten X meshes present

in the posterior sector of the carapace (Text-figs. 5, 7). Furthermore, in A . prima the number of

X meshes is also important though not to such a degree as in the previous species. The largest

number of X meshes found in the form mentioned is five. Generally, A . prima, Amphicostella sp. 3

and A. sculpturata have only one X mesh, which may be situated any place in the posterior sector

of the valve, or none. Moreover, specimens provided with several X meshes frequently show that

Amphicostella sculpturata (Pokorn9)



POSTERIOR

SECTOR



+



ADDUCT, SECT



t



3+L

1 2



RECONSTRUCTED



3f

I l e 2e13e

; I d 2d13d

IIc 2 ~ 1

I l b 2bI3b

[ l a 2a13a

LA_+-!( C



Lfm5f

Le 5 e

Ld 5d

Lc

3 ~ Sc

Lb 5b

La So

D E



b



A4



e



III

II



E



F"

F'

F



f



C



I



d



A s 0"



0 8'

A 0



C' D'

C D



ANT.

SECT



A



a



v'.



p7-27:



'



5*6



A3 6 3 c3

0 B2 Cz

A1 61

11



12



EXTRA MESH



0



REDUCED MESH



TEXT-FIG.9-Schematic drawing of reticulation patterns traced from a SEM micrograph and record of meshes

( x 190). Holy Cross Mountains, Skaly; Middle Devonian, Skaly Formation.



Amphicostellafrom Midde Devonian in Europe 285



rows, 2, 3 and 4 are slightly curved anteriorly (Text-figs. 5, 7) whereas forms lacking such meshes

are straighter (cf. Text-fig. 8).

Another aspect of the appearance of meshes in the posterior sector is the occurrence, particularly

in row 5 and between rows 5 and 4, of increased muri. Often, these acquire the shape and size of

a mesh and are interpreted here as vestiges to them (Text-fig. 8).

A further set of features, which are worthy of mention, concern the size of meshes. These disclose a wide spectrum of dimensions among species and important variability on an intra-species

level in space and time (Text-fig. 11). They are round to polygonal in shape. Their shape is also a

function of size. It seems that it is the size of meshes which has had a significant selective value, as

indicated in the diagram of Text-fig. 11. On the other hand, changes in mesh size also influence the

size of the reticulum, which has been analysed with help of a bild analyser. The reticulum becomes

smaller (Text-fig. 12). This probably resulted in a more economical management of calcium carbonate for the animal and, perhaps, some behavioral advantage in which the valve wall becomes

strengthened, i.e. more resistant to wave action.

Amphicostella sculpturata (Pokornjr)



ADDUCT. SECT.

ANT. SECT.



5f



4-l

c4



8, A,



C3 8 3 A3

C2 8 2 A2



2



3

1



a



JU

0



b



f



e



C



I



d

.



F"

F'



F



0



POST. SECTOR



D'

E,D



B" A"

C' 8' A '

C OA



5e

Sd

5c

5b

Sa



E



'



L f 31

Le 3e ~e le

Ld 3d 2d Id

LC 3c 2c l c

L b 3b Zb l b



La 30 2 0



la



D



A



C



B



REDUCED MESH

EXTRA M E S H



TEXT-FIG.

1O-Schematic drawing of reticulation patterns traced from a SEM micrograph and record of meshes

(X



160). Czechoslovakia; Middle Devonian.



286



AMPHICOSTELLA SP. 1



TEXT-FIG.

11-Diagram



A. PRIMA

(SAMPLE 11



A. PRIMA AMPHICOSTELLA SP. 3

(SAMPLE 21



A. SCULPTURATA



of mesh indices (mesh diameterlvalve length X 100) in Amphicostelk.



AMPHICOSTELLA SP. 1



A. PRIMA



AMPHICOSTELLA SP. 3



A. SCULPTURATA



TEXT-FIG.

12-Dimensions of reticulation area in % in adductorial and posterior sectors in Amphicostella.



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