Re: Geographic Distribution of Deinonychosauria

[tholtz@geol.umd.edu]

>>  Myr, not Ma. Ma is for dates, not durations.
>
> No. Contrary to what some journals believe, "Ma" is not short for
> "million years ago". It's the symbol for "megayear": the SI prefix
> _mega-_ and the almost-SI symbol _a_ for "year" (Latin _annus_).

Sorry, but nearly all stratigraphic codes highly recommend this distinction:

Article 13c of the North American Stratigraphic Code:
c) Convention and abbreviations. -The age of a stratigraphic unit or the
time of a geologic event, as commonly determined by numerical dating or by
reference to a calibrated time-scale, may be expressed in years before the
present. The unit of time is the modern year as presently recognized
worldwide. Recommended (but not mandatory) abbreviations for such ages are
SI (International System of Units) multipliers coupled with "a" for annum:
ka, Ma, and Ga5 for kilo-annum (103 years), Mega-annum (106 years), and
Giga-annum (109 years), respectively. Use of these terms after the age
value follows the convention established in the field of C-14 dating. The
"present" refers to 1950 AD, and such qualifiers as "ago" or "before the
present" are omitted after the value because measurement of the duration
from the present to the past is implicit in the designation. In contrast,
the duration of a remote interval of geologic time, as a number of years,
should not be expressed by the same symbols. Abbreviations for numbers of
years, without reference to the present, are informal (e.g., y or yr for
years; my, m.y., or m.yr. for millions of years; and so forth, as
preference dictates). For example, boundaries of the Late Cretaceous Epoch
currently are calibrated at 63 Ma and 96 Ma, but the interval of time
represented by this epoch is 33 m.y.

See also: http://www.agiweb.org/nacsn/40890_articles_article_file_1641.pdf

And specifically:
"The International Stratigraphic Guide (Salvador, ed., 1994, p. 16), North
American Stratigraphic Code (NACSN 2005, Article 13 (c), p. 30-31), and
Glossary of Geology (cf. Neuendorfer, et al., 2009, p. 259, 386, 347) all
recommend the use of ?ka?, ?Ma? and ?Ga? for dates in years before
present."