Prof. Nathan Aviezer wrote a book "בראשית ברא" answering questions about the creation in torah view.

There he claims the 6 days of creation to be 6 periods of time that didn't necessarily last 24 hours. Moreover - maybe it was one cycle of dark&light, but things happened at a quicker pace.

Take, for example, a person's growth. If you were to calculate the rate of growth during his first two years, you would conclude that at the age of 20 he'd be as tall as a skyscraper. Similarly, scientists calculate age of things according to he worlds' pace today, but things may have worked differently in the past.

Hence, dinosaurs might have lived and died prior to _Adam Harishon_. Maybe created on "day" 5 and extinct before 6.

(Somewhat related: https://judaism.stackexchange.com/questions/10079/what-is-the-meaning-of-yowm-in-bereshit?rq=1)

<hr>

The *Malbim* (on Noach [7:23][2]) addresses "large animals" that couldn't be "wiped out" by the flood, but were buried in depths of the earth following quakes the *Mabul* created. He is clearly addressing dinosaurs since he's talking about (my free translation): "... geologists who dig and find large animals who have become extinct, they use this to show earth existed long before *Bereshis* creation..."

Some attribute "התנינים הגדולים" (Bereshis 1:21) to the dinosaurs as a reference of their existing (not mentioned in *Malbim*).

[2]:http://hebrewbooks.org/pdfpager.aspx?req=40102&st=&pgnum=97
<hr>

Another opinion I've heard from reliable people (suggested by the Lubavitcher Rebbe in [this][1] letter) is that the world was created "old", such as _Adam Harishon_ was created as a man of 20 and not a newborn baby. Hence, dinosaurs could have either existed - or their remains and footprints were melded into the creation.


  [1]: http://books.google.com.au/books?id=FmabnhsgSVAC&lpg=PR1&pg=PA28#v=onepage&q&f=false