No K grasslands (was RE: Cretaceous angiosperms)

["Thomas R. Holtz, Jr." <tholtz@geol.umd.edu>]

> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
>
> >> and may have preferred that milieu rather than grasslands (where the
> dromaeosaur packs ruled). <<
>
> I thought there was nothing like a grassland until the Oligocene? Has this
> changed?
> If so, what was growing there? There was no grass, after all?
>
No, this has not changed.  Grasses proper do not appear until the early
Cenozoic (pollen in the Paleocene, macrofossils in the Eocene; some possible
pollen from the sister groups to grasses are known in Maastrichtian). See
Kellog, E. A. 2000. The grasses: a case study in macroevolution.  Ann. Rev.
Ecol. System. 31:217-238
(http://ecolsys.annualreviews.org/cgi/content/full/31/1/217, if you have an
online access to it).  Also remember that bamboo, for example, is a grass:
evolution of the grasses per se occurs earlier in Earth history than
development of wide open grasslands.

The only places known where dromaeosaurids would have been the rulers of the
grasslands are Isla Sorna and Isla Nublar. :-)  Furthermore, three major
points to bring up:

1) The evidence for pack-hunting in dromaeosaurids is, at present,
restricted to the species _Deinonychus antirrhopus_.  Extrapolation of this
behavior to all members of this clade, regardless of size, environment, etc.
is as inappropriate as extrapolating pack hunting to all canids because of
dholes, wolves, and Cape hunting dogs; to all hyaenids because of the
spotted hyena; or to all felids becaues of lions.

2) Dromaeosaurids do not show a particularly strong environmental signal in
terms of where they are found, although truth to be told nobody has
conducted rigorous analyses of this yet.  However, they are found in very
dry (Djadokhta) to very wet (Dinosaur Park) environments, as well as more
moderate biomes in between (e.g., Cloverly).

3) The floral and zoological make up of "open land" in the Mesozoic is still
poorly understood, and an area of great potential work in the future.  I
would not be surprised if there weren't fern-savannas in the Cretaceous, for
example, with particular suites of dinosaurs adapted for such life.
However, a fernland would NOT be a grassland: there would be very different
plant productivities and very different seasonalities in the former vs. the
latter.

Related to the last, there is a tendancy on the part of a lot of people
(working from a 1970s paleobiological tradition) to "map" extinct animals
onto modern biomes; for example to regard the Morrison as the Serengeti
where the the giraffes are MUCH larger and the lions walk on two legs.
However, this is not the information that the fossil record yields.  Some
biomes do seem to have long histories; others are geologically very new.
Atmospheric composition has changed throughout the Phanerozoic: exactly how
this has affected physiologies of the breathers of that air is not yet
understood.  We already know that similar changes in ocean chemistry can
result in very different style of biomineralization, and hence different
sorts of communities ("calcite seas" vs. "aragonite seas").  Additionally,
new biochemical pathways have evolved in life history, and some of them are
post-Cretaceous and hence were not at play during the great Age of the
Dinosaurs.

Hope this helps.

                Thomas R. Holtz, Jr.
                Vertebrate Paleontologist
Department of Geology           Director, Earth, Life & Time Program
University of Maryland          College Park Scholars
                College Park, MD  20742
http://www.geol.umd.edu/~tholtz/tholtz.htm
http://www.geol.umd.edu/~jmerck/eltsite
Phone:  301-405-4084    Email:  tholtz@geol.umd.edu
Fax (Geol):  301-314-9661       Fax (CPS-ELT): 301-405-0796