Geology Reference
In-Depth Information
Fig. 10.16.
Frequency of Jurassic to Cenozoic dasyclad genera
. New genera originated predominantly in the Late Jurassic
and Paleogene. Data after Bucur (1999). Extinction rates of species were high at the end of the Early and Middle Jurassic, in
the Late Aptian and near the Cretaceous-Tertiary boundary. Origination rates of Late Cretaceous species are somewhat
controversial in comparison to generic origination rates, as shown by the increase in the number of species in the Cenoma-
nian (Kuss 1994).
the main axis (endospore, e.g.
Diplopora
, Pl. 59/2),
within the laterals, predominantly of primary laterals
(cladospore), in cysts that are laterally or terminally
attached to the primary laterals (choristospore), and in
ray-shaped gametophors (umbrellospore;
Acetabularia
;
Acicularia,
Pl. 64/9).
In addition, up to 30 quantitative parameters are used
in discriminating species (e.g. exterior diameter, dia-
meter of the stem cell, height of a segment, number of
whorls per segment, distance between whorls, diam-
eter of branches and pores). The biometrical treatment
of these measurements assists in evaluating species-
specific variations.
systematic subunits (tribi). In this topic the term dasy-
clads is used as a name for the entire group.
Following Deloffre (1988) and Berger and Kaever
(1992) the dasyclads are now subdivided into six fami-
lies comprising the
•
Seletonellaceae (laterals aspondyl. Reproductive or-
gans endospore, seldom cladospore. Cambrian to
Early Cretaceous, predominantly Early Paleozoic.
7 subgroups),
•
Diploporaceae (metaspondyl, endospore, seldom
cladospore. Devonian to Early Cretaceous, predomi-
nantly Late Paleozoic and Triassic. 4 subgroups),
•
Triploporellaceae (euspondyl, cladospore. Devonian
to Early Tertiary. 7 subgroups),
Classification
: Modern dasyclads are represented by
only about 11 genera and 37 species (Berger and Kaever
1992), in contrast to ancient dasyclads comprising about
235 genera and up to 830 species (Bucur 1999). For a
long time dasyclads were considered as one family
(Dasycladaceae), and were promoted to the rank of an
order (Dasycladales) comprising several families and
•
Dasycladaceae (euspondyl, choristospore. Jurassic
to recent, predominantly Cretaceous and Early Ter-
tiary. 4 subgroups),
•
Acetabulariaceae (euspondyl, umbrellospore. Juras-
sic to recent. 3 subgroups).
•
Beresellaceae (Late Devonian to Early Permian).
Text continued on p. 438
