One of the, if not THE, classic US-produced prehistoric animal-related sets. The fronts of the cards are an odd combination of black & white vignettes with aquamarine-like highlights and borders. Another unique feature of this set is its attention to prehistoric non-reptilian animals. A quick survey of the set reveals that the subjects of the 80 cards are pretty much split 50/50 with approximately 40 cards featuring reptiles (e.g., dinosaurs, pterosaurs, plesiosauria, pterosauria) and approximately 40 cards featuring non-reptiles (e.g., mammals, fish, amphibians, therapsida).
The backs of the cards, which are plain and uninformative, are the subject of a couple of on-going controversies associated with the strange symbols & single letters that are printed on them. Under the Apatosaurus image on the back of each card is a seemingly meaningless symbol. There currently is no definitive explanation for these symbols however the leading theory suggests that these may have been identification codes for each print sheet (e.g., sheet "X", sheet "||", and sheet "O").
VARIATIONS (see section below)
The letters next to the "See wrapper for free album" box printed on some of the cards are slightly less of a mystery. The wrappers of this set contain an offer for a "free" album to anyone who (a) sends in eight cards with the letters on the back that spell the name of this set (i.e., D I N O S A U R) or (b) sends in one wrapper and $1.00. The catch was that Nu-Card short-printed cards with the letter "S" making it extremely difficult to obtain an album which incidentally may or may not account for the associated scarcity of the album itself.
To date, I am aware of the actual or rumored existence of the following cards which supposedly have the "S" back as listed below.
#2 (Prehistoric Man) - rumored to have been sold in a public auction in October 2000
#3 (Wooly Mammoth) - e-Bay auction #330651768557 (December 2011) - See image above
#6 (Dimetrodon) - a photocopy of this card is contained in The Wrapper (Issue #230, Page 13)
#9 (Hoplophoneus) - in my personal collection (see image above)
#12 (Allosaurus) - a photocopy of this card is contained in The Wrapper (Issue #80, Page 7)
#16 (Gorgosaurus & Scolosaurus) - according to an article written by Jeff & Bob Marks contained in The Wrapper (Issue #230, Page 12)
#65 (Agathaumas Monoclonium) - in my personal collection (see image above)