GeolCarp_Vol56_No4_317

GEOLOGICA CARPATHICA, AUGUST 2005, 56, 4, 317326

www.geologicacarpathica.sk

Geinitzaster gen. n. (Asteroidea, Echinodermata) from Upper

Cenomanian strata of the Bohemian Cretaceous Basin

JIØÍ ÍTT

Institute of Geology, Academy of Sciences of the Czech Republic, Rozvojová 135, 165 02 Praha 6, Czech Republic; zitt@gli.cas.cz

(Manuscript received February 25, 2004; accepted in revised form December 9, 2004)

Abstract: A new genus, Geinitzaster, is erected for Oreaster decoratus Geinitz, 1871, originally described from the

Upper Cenomanian of Saxony, Germany, and recently found also in the Upper Cenomanian of the Bohemian Cretaceous

Basin. This enigmatic asteroid species lived in nearshore environments and is now known from only four localities in

Bohemia: Pøedboj, Kuchyòka near Brázdim, Radim and Velim-Veronika. The morphology of the dissociated ossicles is

studied in detail and the function and position of individual ossicle types in the asteroid skeleton are discussed.

Key words: Cenomanian, Bohemian Cretaceous Basin, morphology, Echinodermata, Asteroidea, new genus.

Introduction

Isolated asteroid ossicles described as Oreaster decoratus by

Geinitz (1871) from the Upper Cenomanian of Saxony show a

peculiar morphology. Preliminary assignment to this species

of some Bohemian specimens have now been confirmed after

a recent study (2000) of Geinitzs originals in the Staatliches

Museum, Dresden. Additional material was subsequently ex-

tracted from the Bohemian samples of an asteroid project

(grant GACR 20012003). Renewed excavations at the locali-

ty of Kuchyòka near Brázdim have also yielded important new

material, including a set of asteroid ossicles. Some specimens

were also collected at Radim. Thus, the number of ossicles

known from Bohemia far exceeds the Saxonian material, pro-

viding a good basis for a more complete study of ossicle varia-

tion. From Bohemia, the species was first briefly mentioned

by ítt (in press a); in the present paper its morphology is de-

scribed in detail and the functional types of skeletal elements

are discussed.

Geographical and stratigraphic settings

The localities of Pøedboj, Kuchyòka, Radim and Velim-

Veronika (Fig. 1) are situated near the southern margin of the

Bohemian Cretaceous Basin in central Bohemia.

The most recent accounts of the geology and paleontology

of the Pøedboj site are those by ítt (1993) and ítt et al.

(1999a). The section, in a completely filled old quarry, was re-

constructed on the basis of field documentation and samples

supplied by O. Nekvasilová (ítt et al. 1999a) as well as on

published data (Svoboda 1986). The Proterozoic lydite bed-

rock is transgressively overlain by a relatively thin (about 2 m

thick) succession of conglomeratic rocks, upon which follow

siltstones. The asteroids come from the silty to carbonate ma-

trix of a coarse-grained conglomerate about 1.5 m above its

base. The age of this matrix is Late Cenomanian, more specifi-

cally, the boundary interval of the Rotalipora cushmani and

the overlying Praeactinocamax plenus Biozones.

The Kuchyòka section, situated in a quarry on the south-

westerly slope of Kuchyòka Hill near Brázdim, was described

by Záruba (1948) and ítt et al. (1999b, 2002). The asteroid

ossicles studied come from the top and median portions of the

coarse-grained lydite conglomerate, overlain by siltstones.

The conglomerate matrix is formed by yellowish to whitish

sand with a relatively rare macrofauna. The ossicles of Geinit-

zaster were collected by washing the sand. The asteroid ossi-

cles are associated with small gastropods, echinoids, rare bra-

Fig. 1. A sketch map of the BohemianSaxonian Cretaceous Basin

(shaded) showing localities of Geinitzaster decoratus (Geinitz).

1 Pøedboj, 2 Kuchyòka near Brázdim, 3 Radim, 4 Ve-

lim-Veronika.

318 ÍTT

chiopods, worms, bivalves, rudists (Araeopleura sp., Ichthy-

osarcolites sp.), amongst other faunal elements (see ítt et al.

2002). A find of the belemnite Praeactinocamax plenus (Bla-

inville) was mentioned by Klein (1952). The overall character

of the macrofauna (including the asteroid ossicles studied

here) is partially or fully identical to that of the Pøedboj sec-

tion (see above) and confirms the Late Cenomanian age of

these sediments.

The Radim section has not been precisely described yet, al-

though it was mentioned by Ziegler (1982) and ítt (1992).

Rare asteroid material was found together with other macro-

fauna (e.g. the rudist species Radiolites undulatus) in reddish

siltstones to limestones with gneiss clasts filling the basal

parts of a depression several meters deep, eroded in the crys-

talline bedrock during the Cretaceous transgression. The mac-

rofaunal taphocoenosis is of the Pøedboj type, which may indi-

cate a similar age for this horizon.

The Velim-Veronika section is situated in the western part

of an abandoned quarry near Velim. This section is close to

the well-known Velim-Václav section (e.g. ítt & Nekvasi-

lová 1994, 1996; ítt et al. 1997; ítt in press b). The rather

complex filling of the deep depression is formed by Late Cen-

omanian, coarse-grained conglomerate overlain by claystone

passing upwards into siltstone with sponges. The basal parts

of the northern side of the conglomerate body have yielded

finds of Geinitzaster decoratus, occurring in a highly fossilif-

erous (large oysters, brachiopods, corals, echinoid remains,

worms, etc.) sandyclayey limestone matrix among large

boulders. The conglomerate was dated as Late Cenomanian

(ítt et al.1997) on the basis of foraminifers (a low-diversity

Fig. 2. Geinitzaster decoratus (Geinitz), ossicles of type A. ac No. O 6339, Kuchyòka near Brázdim; df No. O 6340, Pøedboj; g

j No. O 6341, Velim-Veronika; k, l No. O 6342, Kuchyòka near Brázdim; mo No. O 6343, Pøedboj. All specimens are housed

in the National Museum, Prague. Scale bars represent 1 mm.

GEINITZASTER FROM UPPER CENOMANIAN STRATA OF THE BOHEMIAN CRETACEOUS BASIN 319

association with Guembelitria cenomana Keller). This age is

also supported by finds of Praeactinocamax plenus and the

brachiopod Thecidiopsis bohemica Backhaus.

Material and preservation

The asteroid ossicles are very rare in all strata studied, and

the available material represents collecting efforts over a num-

ber of years. The Pøedboj specimens were collected by O.

Nekvasilová during her brachiopod studies in 19601970 be-

fore the quarry was infilled. The total number of ossicles is 30.

Sediments from Kuchyòka, Radim, and Velim-Veronika were

washed in large volumes mainly by the present author. From

Kuchyòka section, a total of 64 ossicles were collected by

washing of about 80 kg of the sandy conglomerate matrix.

Weathered portions of reddish to yellowish, relatively hard

silty limestone to siltstone (about 40 kg in total) from Radim

were washed between the 1980s and 2002 and have yielded

only 16 ossicles. Only two albeit highly typical Geinit-

zaster ossicles were found in old residues from Velim-Veroni-

ka carried out in collaboration with O. Nekvasilová in 1972.

No additional specimens were found at this site despite wash-

ing tens of kilogrammes of sediment (yellowish sandy bioclas-

tic conglomerate matrix) over several years.

The preservation of the ossicles is nearly identical at all lo-

calities. It is important to note that ossicles with high process-

es are mostly completely preserved, and that breakage of the

processes is rare (e.g. Fig. 4a,j). Primary fragmentation of part

of one ossicle was encountered in the Kuchyòka sands. How-

ever, secondary fragmentation occurred frequently during

Fig. 3. A sketch complementing Fig. 2 in showing simplified mor-

phology, location of articulation facets (shaded), position and ori-

entation of different views (arrow with the respective letter; letter

x placed inside some drawings). For data on specimens including

their dimensions, see Fig. 2.

washing of these sands, and several specimens were lost due

to dense fracturing and resultant fragility. In spite of the most-

ly complete preservation of individual ossicles, their surface

features often show a slight abrasion. Such cases can be attrib-

uted to the effect of slight otherwise non-destructive

mechanical wear (possibly by sand grains) in combination

with later diagenetic dissolution. As a result, some morpho-

logical details (e.g. articulation facets) are partly obscured

and, occasionally, the morpho-functional types of ossicles (see

below) are hardly determinable.

The paucity of ossicles of G. decoratus in samples is strik-

ing, especially in comparison to abundant remains of other,

non-echinoderm macrofauna. However, if only asteroids are

considered, the scarcity of G. decoratus decreases significant-

ly. Ossicle numbers of other asteroid species (mainly Gonias-

teridae and Stauranderasteridae) in the samples studied range

mostly from tens to a few hundreds (Pøedboj) only. The over-

all rare occurrence of asteroids is obvious from all studied

Cenomanian samples, in contrast to those from some basal

Early Turonian deposits (ítt in press a).

Systematic description

Asteroidea de Blainville, 1830

Order: ?Valvatida Perrier, 1884

Family: unknown, probably new

Geinitzaster gen. n.

Derivation of name: After H.B. Geinitz, German pa-

leontologist and geologist, who first described the present

species.

Type species: Oreaster decoratus Geinitz, 1871, by

monotypy.

Type horizon and locality: Untere Pläner at Plauen,

Saxony, Germany. Upper Cenomanian.

Diagnosis: The unknown skeleton comprising large,

massive ossicles with one or more cylindrical projections on

their outer faces to which spines or tubercles articulated. Some

ossicles, probably from the disc or in dorsal, proximal arm

portions, are tall with outer faces around and distally articulat-

ed with similar elements terminated by spine bases. Probable

marginals are mostly elongated (i.e. wide). Probable supero-

marginals vary widely, some of them being tall, others rather

flat. Some superomarginal-like elements have wedge-like fac-

ets abradially. Adambulacral-like ossicle massive, with a sin-

gle spine base on the outer face. Probable abactinals are sim-

ple plates with mostly one spine base and small facets around.

Remarks: The species described as Oreaster decoratus

most probably has nothing in common with the genus Oreast-

er which comprises only Recent forms as does the family

Oreasteridae Fisher, 1911. In the past, this name was used for

species of unknown affinities; Geinitz had probably noted the

apparent similarities to Forbess (1848) species O. coronatus

(later Stauranderaster coronatus; see Spencer (1907)). Spen-

cer (1913) placed Geinitzs species tentatively as belonging in

Stauranderaster, noting that it could well be related to a num-

ber of Jurassic genera. The systematic position of Geinitzaster

GEINITZASTER FROM UPPER CENOMANIAN STRATA OF THE BOHEMIAN CRETACEOUS BASIN 321

Fig. 5. A sketch complementing Fig. 4 in showing simplified mor-

phology, location of articulation facets (shaded), position and ori-

entation of different views (arrow with the respective letter).

For data on specimens including their dimensions, see Fig. 4.

Material: Pøedboj 30, Kuchyòka near Brázdim 64,

Radim 16, Velim-Veronika 2 isolated ossicles.

Description: Ossicles are basically of eleven morpho-

logical types, designated herein as AK. All these, except for

types C and IK, may attain considerable sizes. Some termi-

nological problems in the descriptions arise from the impre-

cisely known position in the skeleton of the majority of ossi-

cles. The terms distal and proximal are used herein for each

ossicle as if growing from basal faces or facets (proximal part)

upwards or downwards to the outer face and tips of cylindrical

bases of spines (distal part). The term lateral facets is used

without stating which of these is distal and proximal. The term

subvertical refers to each lateral flat structure (e.g. facet) on

the ossicle oriented proximally downwards or upwards. The

term adradial(?) refers to parts of an ossicle to which some

smaller elements clearly articulated close to each other in the

way of articulation between, e.g. median superomarginals and

abactinals (Breton 1992; aborals by Gale 1987) in Metopaster-

like goniasterid.

A-type is based on five figured and six additional specimens

(2 Pøedboj, 2 Kuchyòka, 2 Radim). Ossicles are elon-

gated and more or less flattened, with well-defined proximal

and distal ends. The flattened sides (i.e. outer face) bear irreg-

ularly distributed cylindrical processes (Figs. 2, 3) serving as

bases for unknown spines. These bases, especially the longer

ones, are inclined so that they point obliquely upwards (distal-

ly) (Figs. 2a,g, 3a,g). Two articulation facets are present on

the proximal end of the ossicle. They are separated from each

other in the ossicle plane of symmetry and are arranged in a

roof-like manner, meeting under obtuse angles, with the ridge

oriented proximally (Fig. 2b,e,i). One suboval facet, some-

what smaller, lies on the distal end of the ossicle (Fig. 2c,d).

The distal elements articulated with this facet. These elements

can be elongated, ending distally in a bundle of cylindrical

bases of spines (Figs. 2l, 3l), or even flattened with another

small facet distally, to which an unknown, small end-element

undoubtedly articulated, possibly in the form of a large, spine-

like process (Figs. 2m,n, 3m,n). Proximal facets of these ele-

ments are figured in Figs. 2k,o and 3k,o.

B-type is based on one figured and one unfigured (Radim)

ossicle. High crown-like massive ossicles of circular outline in

distal view (Figs. 4b, 5b). The margin of the distal end bears

six cylindrical spine bases with central pores in their distal

facets. Subvertical articulation facets are visible in lateral and

proximal views, each composed of two parts: a shallow distal

one and a deeper proximal one (Figs. 4b, 5b). In total, 6 facets

are present (Fig. 5c).

C-type is based on two figured and two unfigured (Radim)

ossicles. Relatively small, bilaterally symmetrical ossicles

with mostly only one cylindrical spine base in the centre of the

outer surface (Figs. 4r,t,u, 5r,t,u). The ossicles are approxi-

mately quadrangular in proximal or distal views, with six

(Figs. 4r,t, 5r,t) or two (Figs. 4u, 5u) flat or slightly concave

lateral articulation facets. The proximal (internal) face is flat

or slightly concave, without any structure (Fig. 4s).

D-type is based on three figured and two unfigured (Pøed-

boj) ossicles. Large, massive, rather tall ossicles (Figs. 4d

g,hi, 5dg,hi, 6ac, 7ac). They are mostly bilaterally sym-

metrical. Several cylindrical spine bases on the outer face are

arranged in the plane of symmetry (Fig. 4d,h); this condition

may be only approximative in some specimens (Fig. 6a). The

inclined lateral parts of the outer face are convex (Fig. 4i) or

divided into two convex lobes (Figs. 4g, 5g). Two articulation

facets are possibly present, the first of them situated on the

slightly overhanging end of the ossicle (see the upper facet in

Fig. 5e,f) and slightly concave; the second, very extensive, flat

and indistinct, meets the first one under an obtuse angle (ossi-

cles in Fig.4d and 4i lie on this second facet). The first articu-

lation facet in another specimen (Figs. 6c, 7c) is divided into

two parts. This ossicle is positioned with this facet down in

Figs. 6b and 7b. The shallower second facet (face?) of this os-

sicle is divided into 23 parts as if articulated by several

smaller elements (Fig. 6c).

E-type is based on one figured and two unfigured (Pøedboj)

ossicles. Large and massive, bilaterally symmetrical ossicles

(Fig. 4j), to some extent similar to those of D-type. However,

the lateral subvertical articulation facets are developed

(Figs. 4k,l, 5k,l). The ossicle is wedge-shaped in aboral view.

Its wider end has three small subvertical facets (situated on

downwardly directed part in Fig. 4j). The most proximal part

is flat or slightly concave and probably represents another ar-

ticulation surface. This surface can be divided into two parts:

one flat and the other slightly concave (unfigured ossicles,

Pøedboj), similar to those in type F (Figs. 4p, 5p).

F-type is based on three figured ossicles. Ossicles with

mostly low cylindrical bases for spine articulation on outer

322 ÍTT

face (Figs. 4m, 6t). Some of these bases are, however, longer

(Fig. 6e). Ossicles bear partly lateral, partly adradial (?) and

partly proximal facets. Lateral subvertical facets are 13 in

number, situated on opposite ends of ossicles (Figs. 4n,o, 6e,u).

They are sometimes indistinct and obscured (Fig. 6e,u). The

most proximal facets are well defined and concave (positioned

downwards in Figs. 4p, 5p, 6f, 7f). The adradial (?) facet is in

fact formed by 23 smaller facets which resemble those on,

Fig. 6. Geinitzaster decoratus (Geinitz). ac ossicle of type D, No. O 6351 (a distal view), Pøedboj; df ossicle of type F,

No. O 6352 (d distal view), Pøedboj; gi ossicle of type H, No. O 6353 (g outer view), Pøedboj; jl ossicle of type H, No.

O 6354 (j outer view), Kuchyòka near Brázdim; mo ossicle of type I, No. O 6355xxx (m outer view), Pøedboj; ps ossicle of

type I, No. O 6356 (p outer view), Pøedboj; t, u ossicle of type F(?), No. O 6357 (t outer view), Pøedboj. All specimens are

housed in the National Museum, Prague. Scale bars represent 1 mm.

e.g. the adradial part of median marginals in Metopaster

(Figs. 4p, 6f).

G-type is based on one figured ossicle. Massive, bilaterally

symmetrical ossicle with the outer surface bearing one large

and one small side bases for spines. Four large lateral facets,

two lying on opposite sides, are oriented obliquely down-

wards (Figs. 8b, 9b) but do not intersect. The remaining two

facets are smaller and subvertical (Figs. 8a, 9a).

GEINITZASTER FROM UPPER CENOMANIAN STRATA OF THE BOHEMIAN CRETACEOUS BASIN 323

Fig. 7. A sketch complementing Fig. 6 in showing simplified mor-

phology, location of articulation facets (shaded), position and ori-

entation of different views (arrow with the respective letter; x

placed inside some drawings). For data on specimens including

their dimensions, see Fig. 6.

H-type is based on two figured and two unfigured (Pøedboj)

ossicles. Elongated ossicles with very low bases for spine artic-

ulation. The narrower end is cut in a wedge-like manner (much

like in A-type ossicles), with two facets (Figs. 6g,h,j,k, 7g,h,j,k).

I-type is based on 2 figured ossicles. They have only an out-

er surface on their narrower end, with bases for spines. This

surface passes up to the opposite side of this ossicle part. The

ossicle extremity thus bears no articulations with other ossi-

cles (Fig. 6n,o,r,s).

All ossicles of H and I-types bear long subvertical facets lat-

erally, with distinct articulation structures (tubercles, gran-

ules). Several (possibly 56) smaller facets are situated above

one long facet (Fig. 7k,n; unclear situation in Fig. 7g,h

probable facet outlines are dashed). The obliquely oriented

adradial (?) surface bears one (Fig. 6i) to three facets, which

are obliquely orientated with respect to the outer ossicle faces

(Fig. 6l,o,s). The proximal facet is flat and lies on a socket-

like elevation, thus separated from the adradial (?) facet

(Figs. 6l,o,s,u, 7l,o,s,u).

J-type is based on one figured and one unfigured (Radim)

ossicles. Small ossicles of irregular shape with outer face bear-

ing several small and low bases for spines (Fig. 8f,h). The ar-

ticulation facets are not clearly developed but at least one

small facet seems to be present. Large basal face (marked by

grey fill together with a small facet separated by a dashed line

in Fig. 9g) may in fact be an inwardly directed ossicle face

without articulatory function.

K-type is based on one figured and one very poorly pre-

served unfigured ossicle (Kuchyòka). Enigmatic, small but

massive ossicles, preserved fragmentarily. One low cylindrical

base for a spine occurs on the small outer face (directed down-

wards and to the right in Fig. 8e). The element is elongated

(viewed axially in Fig. 8e), bounded by poorly defined faces,

bearing depressed articular facet-like areas on the extremities

(see Fig. 8e for one of them).

Remarks and relations: The ossicles described by

Geinitz as Oreaster decoratus and restudied by the present au-

thor at the Staatliches Museum, Dresden, belong to two of the

ossicle types defined herein. The lectotype (SAK 6454) in the

Dresden collection, is of H-type but is very large (length

10.6 mm, width 6.8 mm, height 5.6 mm) and differs in having

ridge-like articulation structures on the abradial part of the

proximal facet. Paralectotype SAK 6455 is similar to the lec-

totype but somewhat smaller (length 9.6 mm, width 6.8 mm,

height 4.3 mm). Paralectotypes SAK 64566458 are of C-type

with several lateral subvertical facets around. The paralecto-

types are, however, larger (6456 length 9 mm, width

7.3 mm, height 3.5 mm; 6457 length 6.2 mm, width

6.2 mm, height 2.3 mm; 6458 length 6.2 mm, width

6.2 mm, height 2.4 mm; compare with Fig. 4r,s,t,u here) than

the Bohemian specimens.

The ossicles figured by Friè (1911, p. 76, Fig. 320) coming

from his locality Kamýk and referred to as Oreaster decoratus

could not be traced in the collections of the National Museum,

Prague. Because of the poor quality of the illustrations, their

systematic affinity remains questionable.

Although not described in detail, Jagt (2000, p. 489, Pl. 20,

Figs. 21,22) illustrated two dissociated ?marginals from the

lower Upper Campanian of Benzenrade-de Wingerd (the

Netherlands) that bear a certain resemblance to the Bohemian

material. Closer comparisons are, however, needed.

Notes on skeletal structure

Ossicles of A-type articulated to unknown ossicles along

their paired facets. Because all the lateral portions of these

ossicles are formed by outer structures, that is by outer sur-

face with cylindrical bases for spines, the ossicles must have

been oriented from the body outwards. This orientation is

confirmed by the slightly oblique (as if directed slightly up-

wards) position of bases for spines. Ossicles of A-type were

occasionally tall, also comprising some additional, yet more

distally articulated ossicles. Ossicles of A-type probably

formed part of the dorsal skeleton of the disc or proximal

arm portions.

Ossicles of B-type, which have lateral facets around the

whole base, must have been surrounded by smaller plates all

around. This is possible only on the aboral disc surface (pri-

mary plates?) or in aboral (upper) arms. If the asteroid had

more heavily plated arms, these ossicles could have been lo-

cated even in their more distal parts. The more or less well-de-

veloped radial symmetry of the ossicle shows a central posi-

tion (i.e. in the plane of arm symmetry).

Ossicles of C-type are rather small and flat and may repre-

sent a type of abactinal. The position and orientation of the

324 ÍTT

facets is, however, close to that of B-type, which indicates

possibly a similar position in the skeleton.

Ossicles of D-type, as indicated by the type of their two fac-

ets and bilateral symmetry, could have belonged to the mar-

ginal disc structure.

Ossicles of E-type, as indicated by their large lateral facets

and their wedge-like shape, could have formed part of the

marginal structure probably lying interradially in a superomar-

ginal position. They probably occurred as solitary elements

between the laterally positioned smaller elements of variable

size. The narrowed part of the ossicle onto which the outer os-

sicle face continues was directed outwards, because the wider

side bears facets for articulation with some small elements

(another type of abactinals?).

Ossicles of F-type formed part of the marginal frame, most

probably superomarginal, of the arms. Their clearly defined

adradial (?) facets probably articulated with small abactinals

in the arms. The facet referred to as proximal in this paper may

in fact be the intermarginal facet, to which the inferomarginal

articulated. The lateral small facets of one ossicle (Fig. 4n,o),

however, show that the lateral contact between these large su-

peromarginals was only weak and that additional small plates

were present here. The other ossicle of F-type laterally has

only one large, albeit indistinct, facet (Fig. 6e). Nevertheless,

the orientation of the bases for spines (obliquely upwards)

seems to confirm the superomarginal position of this element

(the orientation of ossicle in Fig. 6e corresponds to this posi-

tion in the skeleton).

Ossicles of G-type have features of A-type (two obliquely

oriented facets lying on opposite sides) but there are two other

smaller facets in 90

position relative to the above ones. The

Fig. 8. Geinitzaster decoratus (Geinitz), ossicles from Kuchyòka. a, b ossicle of type G, No. O 6358 (lateral views); c, d fragmen-

tary ossicle of indeterminate type, No. O 6359 (c distal view); e ossicle of type K, No. O 6360; fh ossicle of type J,

No. O 6361 (f distal view). All specimens are housed in the National Museum, Prague. Scale bars represents 1 mm.

Fig. 9. A sketch complementing Fig. 8 in showing simplified mor-

phology, location of articulation facets (shaded), position and ori-

entation of different views (arrow with the respective letter; letter

x placed inside some drawings). For data on specimens including

their dimensions, see Fig. 8.

facets all around the base thus indicate a position among sev-

eral other ossicles, similar to the ossicles of B and C-types.

Ossicles of H-type are somewhat enigmatic because the

wedge-like lateral and the adradial (?) facets are both devel-

oped (see e.g. Fig. 7jl). This ossicle may be tentatively inter-

preted as a special type of superomarginal, which adradially

articulated with smaller, possibly abactinal plates, and was di-

rected abradially (to the margin of the disc or arm) with the

wedge-like articulation of opposite ossicle side. If two such el-

ements were present next to each other, a small (unknown) ad-

jacent superomarginal or other plate could have articulated in

a triangular wedge-shaped gap. The ossicle in Fig. 6tu slight-

ly differs in having one larger facet abradially and one smaller

asymmetrically positioned facet.

GEINITZASTER FROM UPPER CENOMANIAN STRATA OF THE BOHEMIAN CRETACEOUS BASIN 325

Ossicles of I-type, similar to H-type but having an outer sur-

face instead of roof-like articulation (Fig. 7ps), could well

represent a type of marginal element (possibly inferomargin-

al). The adradial facet articulated with actinolaterals and that

designated here as proximal may in fact be the intermarginal

one. Low bases for spines indicate a possible ventral (adoral)

position for this ossicle type. Up- and outwardly directed

bases for spines (see Fig. 7r, the element is inversely oriented

here) on the free end of the ossicle could have served for de-

fence of lateral portions of the marginal frame.

The small ossicles of J-type probably functioned as plates

filling irregular spaces between larger ossicles.

Ossicles of K-type are poorly preserved but their function as

adambulacrals should be considered. A large, probably short

tubercle articulated on the oral side of the element.

Conclusion

On the basis of study of rich Bohemian material (Upper

Cenomanian) and in part on Geinitzs original type series of

Oreaster decoratus (Upper Cenomanian, Germany), the new

genus Geinitzaster gen. n. is erected. In spite of detailed mor-

phological study, there are many uncertainties regarding ossi-

cle types and their position in the skeleton. The immense mor-

phological variability of these ossicles (i.e. practically no

element is exactly identical with any other, in contrast to the

pronounced and clearly differrentiated ossicle types in the ma-

jority of, e.g. goniasterids), points to rather wide variation in

the skeleton composition if viewed in detail (irregularities in

the size and shape of plates and their mutual articulations)

while the body appearance was generally identical. The body

could have possessed massive arms with small ossicles irregu-

larly filling the gaps between the large ones. The high tufts of

spines dispersed on the body gave the asteroid the appearance

of a rough and uneven object. The overall aspect could well

have served for protection against predation and for masking

on the uneven rocky bottom or on coarse-grained clastic

stretches.

The results of the present study of Geinitzaster ossicles

call for future comparative studies of all materials known in

the world. The author hopes that the illustrations and de-

scriptions of the Bohemian material will be of use for such

future revisions.

Acknowledgments: The author is indebted mainly to Loïc

Villier (Marseille) for ideas on the species studied. Hannes

Löser (Dresden, presently in Mexico) is thanked for his help

during visits to the Staatliches Museum, Dresden. The author

is also grateful to O. Nekvasilová (Prague) for providing the

Pøedboj specimens from her collection and to È. Nekovaøík

(Prague) for his assistance during excavations at Kuchyòka

near Brázdim. The Geinitzaster study is a substantial part of

the Project No. 206/01/1580 supported by the Grant Agency

of the Czech Republic and within the Research Programme Z3

013 912 of the Institute of Geology AS CR, Prague.

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