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constricting the terminal aperture. Others added apertural appendages. All of these
modifications in the last growth stage limited the mobility of the ammonoid by the
constricted or upward oriented aperture, complicated nourishment, and in some cases must
have resulted in death of starvation. These rather fatal modifications could not have been
intended to live further in a different way (Westermann, 1990) and were interpreted to have
served the last and most important biological duty of breeding by providing protected
brood chambers (Lewy, 1996). The female was situated beside numerous tiny eggs (detected
in fossil ammonites) being drifted by currents across the ocean while the eggs developed.
This drifting process is corroborated by the wide distribution of many of these non-
streamlined heteromorphy ammonite species along the Tethys Sea, which could not have
been explained by swimming. Such mode of breeding in cephalopods is known in extant
octopods which carry out two breeding strategies. The common one is laying large, yolk-
rich eggs in bundles attached to submarine substrates ('stationary' mode of breeding), in
which both parents care for the brood during several months without eating. They die of
starvation close to when the young hatch, each with some yolk for their nourishment during
the first hours of free swimming. In the single group of argonautids the female
Argonauta
(larger than the male) secrets from the expanded edge of two of its tentacles a thin calcitic,
widely-coiled shell. It situates itself in this boat-shaped shell and lays numerous tiny
spherical eggs about 1 mm in diameter, similar in shape and size to spheres detected in
fossil ammonites (Lewy, 1996). Together they drift over the sea while the eggs develop
('pelagic' mode of breeding) and the young are shed into the water to cope with life. The
shapes of all of the argonautid brood chambers (several fossil and extant species) are
identical to latest Cretaceous ammonites. This fragile conch cannot protect its content and
merely carries the female and the brood. For this purpose, a smooth boat-shaped shell
would be sufficient and the ammonite-like complex sculpture cannot be explained by
convergent evolution. Argonautid egg-cases occur since the Late Oligocene (Saul & Stadum,
2005). It is unlikely that only then the 'pelagic' mode of breeding was introduced into
octopod breeding strategy. It is more reasonable to explain the first occurrence in Late
Oligocene times of fossils of ammonite-like argonautids by the preservation of their calcitic
shell. This brood-case might have been made in earlier times of an organic substance
(conchiolin) which disintegrated close to after burial in the marine sediment. Octopods have
neither an external conch nor an internal hard feature, which renders their geological record
sparse. The earliest fossil octopod is an imprint from the Middle Jurassic, but the
development of these cephalopods must have been earlier. The few octopod fossils
preserved in restricted environments of unusual burial conditions resulted in the dispute
over their systematic position among cephalopods. The comparison between the anatomy
and physiology of extant octopods and the functional morphology of ammonites suggests
close genetic relationships between these two cephalopod groups, one of which survived the
end-Cretaceous biological crisis (Lewy, 1996, 2002).
The straight (orthocone) baculitids are heteromorph ammonites which did not modify the
last growth stage and probably had another breeding strategy. All baculitid species seem to
have formed local evolutionary lineages and were hence indigenous species like several
planispiral ammonites, which characterize biogeographic provinces in contrast to the
'cosmopolitan' distribution of most heteromorphs. The 'pelagic' mode of breeding resulted
in the wide distribution of these species, whereas in the 'stationary' mode of breeding the
hatchlings remained in the area where they hatched and formed indigenous species. This
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