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

Re: A few questions:Maastrichtian deposits & relative decline rates for dinos nearing the Maastrichtian - Danian deposits.



At 03:26 PM 5/11/98 -0700, Landry wrote:
>
>
>Anyone out there have any data on Maastrichtian age mariene deposits and
>thier relative proximity to those of extensive dinosaur bearing deposits.    

Could you be more specific? As in, what part of the world?  In general, the
better known the Maastrichtian marine deposits, the more poorly known the
terrestrial.  For example, southern Spain and Antarctica have FANTASTIC
records of the latest Maastrichtian/ earliest Danian marine, but neither
localities are immediately adjacent to  good diverse dinosaur bearing units.

In western North America, though, Maastrichtian marine units of the western
interior seaway are pretty well understood, at least until they drain away.
Even then, there is marine material preserved in the Gulf Coast.

The type Maastrichtian deposits contain, among other forms, the original
specimen of Mosasaurus.

>What are the major differances in fauna between the Maas. and Danian
>deposits other than the Danian being void of Dinosaur remains.  

Not sure how to answer this one: try finding faunal (& floral) lists for
typical Maastrichtian and Danian formations, and compare.  Basically, Danian
deposits contain all the survivors of the K-T impact, and show the beginning
of the adaptive radiations of typical lower Tertiary lineages of
vertebrates, plants, etc.

>Also I am having a hard time locating any information on Maas.
>and Danian statigraphy of the Gobi Desert with respect to dinosaurian
>fossil remains.  

Yeah, you are, as is everyone else.  The stratigraphy of the Late Cretaceous
Gobi is VERY poorly worked out at present (one of the main goals of several
of the different teams working there is trying to tie it in to global
stratigraphy).

The Nemegt Formation of Mongolia is typically considered early
Maastrichtian.  No late Maastrichtian deposits in Mongolia bearing dinosaur
fossils have been reported.  The Nanxiong (sp?) Basin of China DOES contain
latest Maastrichtian fossils, but most of these are not diagnostic beyond
"family" or "subfamily" rank.

However, to answer the question in your subject line ("A few
questions:Maastrichtian deposits & relative decline rates for dinos nearing
the Maastrichtian - Danian deposits"): no one has demonstrated at the limits
of resolution for terrestrial sediments a true decline *within* late
Maastrichtian dinosaur communities.

The decline that is supported by fossil evidence is longer scale: lineages
well documented in the late Campanian of western North America
(centrosaurines, lambeosaurines, maiasaurin and gryposaurin hadrosaurines)
are reduced in diversity or absent in Edmontonian and Lancian deposits,
especially when compared to their sister taxa (ceratopsines, hadrosaurines
as a whole, saurlophin and edmontosaurin hadrosaurines, respectively).

Declines in numbers of species are much less significant than claimed by
some workers: the fact that Judithian deposits have produced about twice the
number of non-avian dinosaur species as either Edmontonian or Lancian
deposits *might* be a real phenomenon, or it might be sampling due to
greater area of exposure, greater manpower in the field per season, longer
total manhours in the field, etc.  To my knowledge, no one has plotted such up.

(An additional test for enterprising grad students with nothing better to do
with their time: see if similar ratios (~2:1 for upper Campanian species
numbers compared to early Maastrichtian or to late Maastrichtian species
numbers) hold for other taxa, such as squamates, multituberculates,
crocodyliforms, etc.  If it is relatively constant across taxa, this might
support the idea that it is a sampling phenomenon rather than a biological one).

Thomas R. Holtz, Jr.
Vertebrate Paleontologist     Webpage: http://www.geol.umd.edu
Dept. of Geology              Email:th81@umail.umd.edu
University of Maryland        Phone:301-405-4084
College Park, MD  20742       Fax:  301-314-9661