RE: [paleo_bio_dinosaur_ontology] dinosaur skeletal anatomy

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

> -----Original Message-----
> From: owner-dinosaur@usc.edu [mailto:owner-dinosaur@usc.edu]On Behalf Of
> David Marjanovic
> Sent: Tuesday, October 28, 2003 11:28 AM
> To: DML; paleo_bio_dinosaur_ontology@yahoogroups.com
> Subject: Re: [paleo_bio_dinosaur_ontology] dinosaur skeletal anatomy
>
>
> > Quick correction: Ma is for date (million years ago); Myr is
> for duration
> > (millions of years).
>
> Oh, need not be. a is for year (annum), and one can put M (mega-)
> in front.

Need not be, but is.

Ma is a time measurement from the present, as in the North American
Stratigraphic Code or the "Stratigraphic Nomenclature and Description" of
the USGS.  From the latter (p. 45 in the 7th edition, 1991):
"Units of time may be expressed in years (y or yr) as my, m.y., m.yr. for
millions of years and as by, b.y., b.yr. for billions of years for an
interval of time; or in annum as ka for kilo-annum, Ma for mega-annum, Ga
for giga-annum for ages. For example, boundaries of the Late Cretaceous
Epoch currently are calibrated at 66 Ma and 96 Ma, but the interval of time
represented by this epoch is 30 m.y."

I know that a lot of people are sloppy in misusing Ma for myr and vice
versa, but that is sloppiness and not correct.  This is comparable to not
italicizing a genus name, or using a lowercase "P" in "Cretaceous period".

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