[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: Ocean EcoSystems Unexpectedly Stable



----- Original Message -----
From: "John Bois" <jbois@umd5.umd.edu>
Sent: Wednesday, May 15, 2002 3:27 AM
Subject: Re: Ocean EcoSystems Unexpectedly Stable

> I wonder what it was that departed as a result of the event that so
> "emptied the world"?  After all, rudists were gone before,

Is that "still true"?

> ammonites had suffered a Cretaceous-long decline.

A decline throughout the K? Which strange sort of competition or whatever
could cause that? I mean, the K was longer than the time that has passed
since! -- In some places ammonites do appear to die out gradually, but in
others in the vicinity they last to the very end. I'll look for the refs.
Recently a pdf was mentioned onlist that reports the last ammonite of South
Dakota -- _within the last 10 cm_ below the boundary layer.

> Mosasaurs and other big reptillian
> marine animals had all but gone before.

That's apparently "no longer true":

Eric W. A. Mulder, Nathalie Bardet, Pascal Godefroit & John W. M. Jagt [and
no Scully...]: Elasmosaur Remains from the Maastrichtian type area, and a
Review of latest Cretaceous Elasmosaurs (Reptilia, Plesiosauroidea),
Bulletin de l'Institut Royal des Sciences Naturelles de Belgique -- Sciences
de la Terre = Bulletin van het Koninklijk Belgisch Instituut voor
Natuurwetenschappen -- Aardwetenschappen 70, 161 -- 178 (2000)

"Abstract

Isolated skeletal remains of elasmosaurid plesiosaurs are described from the
upper Upper [no typo] Maastrichtian of the type area of that stage and
compared with material from the Maastrichtian of southern Belgium (Mons
Basin) and Morocco. An overview of Maastricthian elasmosaurids worldwide is
presented. The rarity of elasmosaurids in the latest Cretaceous marginal
seas of the type Maastrichtian as compared with their common occurrence in
the oceanic waters near California and Morocco of that age may be related to
food abundance in upwelling areas along the margins of continental plates."

"Ever since the first unabiguous record by von Meyer (1860), it has become
apparent that, amongst remains of larger vertebrates in the uppermost
Maastrichtian strata of the type area of that stage [...], those of
plesiosaurs are very rare in comparison with mosasaurs and turtles. So far,
only a handful of isolated elasmosaur teeth and vertebrae are on record;
remains of hadrosaurid dinosaurs are even commoner, although these strata
are marine [...]."

"An overview of Maastrichtian elasmosaurids worldwide

During the latest Cretaceous, plesiosaurs were represented by both groups of
Plesiosauroidea, i.e. the long-necked elasmosaurids and the short-necked
polycotylids [...] and by rare Pliosauroidea [...]. They were distributed
worldwide [...] [long, impressive list].
    [...] In Antarctica, and more precisely in Vicecomodoro Marambio Island
(Seymour Island), the Lopez de Bertodano Formation represents a continuous
sequence form the Upper Campanian to the Palaeocene [...]. The fauna
includes indeterminate elasmosaurs [...], some of which were collected from
very close to the K/T boundary [...].
    In New Zealand, the Laidmore Formation on South Island, [w]hich is dated
as Late to latest Maastrichtian [...], has yielded plesiosaur remains [...]
*Mauisaurus haasti* [...].
    In recent years, the similarities in fossil faunas between the
Maastrichtian marine deposits of the east coast of the United States on the
one hand and those of the type area on the other have received ample
attention [...]. These areas have also in common the extreme rarity of
plesiosaur remains [...]. Parris (1974, p. 32) noted that in New Jersey
[...] Plesiosauria declined markedly prior to the deposition of the late
Maastrichtian basal Hornerstown Formation. As stated above, elasmosaurids
have not been found in the latest Maastrichtian *Belemnella kazimirovensis*
Zone (= upper half of Meerssen Member, Maastricht Formation) in the type
area.

Discussion

When reviewing the latest Cretaceous marine fossils of the northern
hemisphere, a striking contrast between New Jersey and the Maastrichtian
type area on one hand, and California and Morocco on the other, with regard
to plesiosaur abundance, is noted. [...] Bakker (1993 [...]) suggested that
the absence of fast-swimming plesiosaurs could be explained by the presence
of an exceptionally dense algal forest. Only the California coast had an
abrupt continental slope, wiht a narrower zone of shallow water where an
algal forest could grow. The relative abundance of elasmosaurs there could
be explained by the wide expanses of open water. However, we consider that
the presence of an abrupt continental slope also coincided with the
upwelling of nutrient-enriched water, which favoured the presence of a high
biomass, being an ideal condition for open-water predators such as
elasmosaurids.
    In the North Atlantic basin, the Upper or uppermost Maastrichtian
phosphatic deposits in Morocco are the only strata of that age which have
yielded plesiosaur remains (teeth and vertebrae in such abundance, that
[...] [it's possible to do some _stratigraphy_ with them].
    The fossils from Belgium and the Netherlands come from epicontinental
shallow seas. In the Maastrichtian type area the first appearance datum
[...] of elasmosaurids appears to coincide with a major Tethyan incursion
[...], an observation which allows elasmosaurids to be regarded as a
southerly Tethys/north African faunal element, in view of their abundance in
the Maastrichtian of Morocco. The paucity of plesiosaur remains in the
Maastrichtian type area would seem to match to Bakker's (1993) observation
to some extent; [...] have yielded common to locally abundant remains of
seagrass (an angiosperm), [...]
    From the distribution of Maastrichtian elasmosaurids worldwide it may be
concluded that, like mosasaurs, elasmosaurids were still widespread and
diversified during the late(st) Maastrichtian [...]. Even if precise
stratigraphical extensions are often difficult to obtain for large
vertebrate remains, the extinction of elasmosaurids at the K/T boundary thus
appears to be sudden rather than gradual."

Sorry for the long post. Hope that helps. :-)