Hi list members,
For several of you, I'd have been back in touch sooner, but have been doing a lot of field work here in the Early Cretaceous of Maryland. And, WOW!, has it paid off greatly. I will describe one of the nicest recent finds.
On Sunday afternoon, September 2, I found a wonderful piece of substrate with a maximum dimensions of only 45 X 33 cm, which contains a total of 24.5 small, tridactyl, seemingly non-avian (no sign of a digit I impression on any of the tracks, either) dinosaur tracks, including four trackways and, additionally, four possibly unassociated tracks. Each of the four trackways appear to be of theropod origin. [If anyone cares to know why I say this, just ask me for an off-list explanation.]
One trackway consists of 4 tracks, each 7 cm long -- the longest pes lengths on the slab. 3 successive tracks, quite narrow with an exceptionally long digit III (central toe), each only 1.85 cm length, form another trackway. 6.5 tracks of about 1.7 cm length comprise another trackway. The fourth trackway consists of 6 tracks of only 1.5 cm length.
Two isolated tracks are each of approximately 2.5 cm length, although they appear to have been made by different dinosaur types. Another two are tridactyl tracks only 1.0 cm long (if one measures the thickness of the push up ridge, 1.3 cm long) with relatively 'fat' toes, but one track is so immediately in front of the other that it is difficult to conceive of the two as successive tracks.
Because of distinct differences in pes shape on a substrate of consistent type, we may -- surprisingly -- have five different types of trackmakers on the one slab. I presume that all but the largest track maker may have been babies, or even hatchlings, but only because it is hard to conceive of adult dinosaurs approximately the size of sparrows.
One area of the thin, primary track surface is missing for two of the small track trackways, and in each instance we see the trackway continuing as under-prints. This shows us something about depth of sub-surface penetration and other things, as well.
Print number 1 of the trackway of 7 cm tracks is on primary surface, but the foot sank deep and there is wonderful 'pull up' rim as high as 2.4 cm around that track. I can almost hear the "ssllloooppp", as the foot pulled out of the muck. :) The successive three tracks of that trackway are under-prints because the primary surface has been broken off, possibly when this piece of substrate was broken out of context years ago during a stream deepening operation using heavy equipment.
That 1.5 cm pes length may seem small, but on another multi-trackway slab (found a few years ago) there is a 6-track trackway wherein the pes length is 1.0 cm, right beside another trackway of similar length with 1.3 cm pes length, plus several other tracks (one of much larger size).
On the slab under discussion, all the tracks except those of 7 cm length are progressing in roughly the same direction. The larger tracks are proceeding at roughly 90 degrees from the course of the little ones. There is really no way to determine for sure the temporal disposition of all four trackways, except that the largest trackmaker stepped into and evidently obliterated a couple of the tracks that we would otherwise see in one of the small trackways.
"You know my method. It is founded upon the observance of trifles." -- Sherlock Holmes in The Boscombe Valley Mystery