Broome Dinosaur Tracks (Long)

[Tony Thulborn <paswamp@mailbox.uq.edu.au>]

In response to several requests, some news of recent dinosaur track
discoveries in the Broome Sandstone (Lower Cretaceous) of Western Australia.

Together with Giuseppe Leonardi (Naples) and Tim Hamley (my part-time
student-assistant) I made a trip to Broome in late June and early July,
combined with attendance at CAVEPS in Perth.  [CAVEPS = Conference on
Australasian Vertebrate Evolution, Palaeontology & Systematics.]  We were
accompanied by my son, Guy (10), and Tim's son, Angus (14).  These kids are
the best field-assistants of all time.  (Sometimes too good, as in September
1995, when they picked up the first Carboniferous tetrapods in the southern
hemisphere.)

Tim and I hadn't managed to visit Broome since 1995, owing to lack of funds.
So, this was our first chance to assess any damage resulting from
much-publicized disappearance (?theft) of footprints last year.  To provide
some perspective: the Brisbane-Broome trip is roughly comparable to New
York-Los Angeles, so we can't just jump into a vehicle and go for the
weekend.  And domestic air travel is so expensive that we can't manage more
than a single field-trip every 12-18 months.   

I'd been telling people for several years that the Broome tracks were
something special, though to little effect.  Paul Foulkes, our naturalist
colleague in Broome, had been saying the same thing for even longer, with
equal lack of response.  This time I invested the residue of our (alleged)
research budget in airfares, so that Giuseppe Leonardi could visit Australia
and give us an independent assessment.   He managed to get away from Italy
for a whole month, of which we spent 3 weeks in Western Australia and
another week looking at sites in Queensland.

A brief summary of the Broome tracks, with emphasis on sauropods, was
published in the 'Sauropod Paleobiology' issue of Gaia (vol. 10, 1994).
Some colleagues thought aspects of that account were exaggerated or
improbable - e.g. unusually big sauropod prints (pes prints reportedly up to
1.5 m long), the exceptional diversity (at least 10 different types of
track-makers), and the co-occurrence of sauropod and ornithopod tracks
(sometimes thought to be ecologically separated).

When we got to Broome, the coast (as usual) had altered somewhat from the
last time.  The annual cyclones tend to dump sand and rocks on some
exposures, whereas others may be swept clean.  We spent the first week
checking some easily accessible sites, where Giuseppe was suitably impressed
by the diversity and fine preservation of tracks.  In the second week we
camped at one remote site which, from experience, isn't particularly rich in
tracks - just a pleasant and convenient spot.  

On the first morning, we went down to the shore and waited for the tide to
fall (most of the sites emerge only briefly at low tide).  As the water
receded a whole new site came into view.  In previous years that stretch of
foreshore had been buried under rubble and sand, but it had been swept clean
by the last cyclone, and we may have been the first people ever to see it.
Certainly, none of the locals had seen it before.  Acres of freshly exposed
rock, along a couple of kilometres of coastline (at least), and in pristine
condition.  An Early Cretaceous land-surface emerging from the water
virtually intact, with the original topography, channels and hillocks,
tree-stumps and root systems in their position of growth... and footprints
everywhere.  Sauropods, ornithopods, theropods and some mystery items
including supposed ?stegosaur tracks.  All in perfect condition, looking as
if they'd been imprinted yesterday.  We took photos (inadequate), made latex
peels (hardly representative) and tried to map out a small selected area
(but were defeated by the rising tide).  By this time Giuseppe was stunned.
Despite his vast experience with fossil footprints, including 17 years work
in Brazil, I don't think he'd ever seen so many, so diverse, and so
magnificently preserved.  In the following days we went exploring along the
coast for a couple of kilometres, stumbling over more and more footprints
all the way - but we never reached the end before time, latex, film,
provisions and superlatives ran out. Then we had to get back to Broome, to
meet up with CAVEPS field-excursion.

Back in Broome we told Paul Foulkes, who promptly set off to see for
himself.  He came back slack-jawed, reporting that he'd gone a bit further
along the coast and found (you guessed it) even more newly-uncovered tracks.
Paul has been hunting dinosaur tracks in the Broome Sandstone for more than
12 years, and in all that time he'd never seen anything to match these
newly-exposed sites.  Tim made another flying visit, with last of the latex,
to snatch a couple more peels from exceptionally fine prints that Paul had
discovered.

Paul and I then had to lead a party of about 24 CAVEPS participants around
some track-sites near Broome, showing them a fairly small sample of
footprints and trackways.  These were examples that happened to be
accessible at convenient times and places - not the new sites (which we
didn't even know existed at the time the excursion was organised.)   Even
so, some of the prints and trackways were reasonably good examples...  if
not always outstanding.  I think that the people attending the excursion
formed some favourable opinions of the tracks - though, of course, you'd
have to ask them for their own opinions.

At the conference in Perth, the following week, we were thoughtless enough
to discuss some of this within earshot of a stray reporter.  And, of course,
all hell broke loose in the media, with journalistic imagination liberally
injected into the bare facts.   Let me straighten out the worst
misconception.  Yes, the footprint sites (plural) do extend over 80 to 100
km of coast.  No, it is NOT a single exposure, NOT one continuous trackway
surface.  It is a series of sites, many of them rather small, with stretches
of beach (and sometimes very long stretches of beach) intervening.  The
sites aren't all at the same stratigraphic level (so far as we can figure
out stratigraphy from disconnected exposures) and they represent a variety
of environments (forest, swamp, lagoon, fluviatile/deltaic)... each with its
own distinctive suite of dinosaur track types.  The newly-exposed sites seem
to represent fairly well-vegetated forest or swamp environments.  So,
despite newspaper reports, it's NOT a single dinosaur trackway, NOR an
unbroken dinosaur highway 80 km in length.  Even so, it's interesting enough.  

Here's a summary list of the track-types we've seen so far in the Broome
Sandstone:

Ornithopod tracks - large and small.  Some small ones resemble Wintonopus,
others don't.  The big ones are commonly 60-65 cm pes length, and Giuseppe
found one measuring 80 cm.

Theropod tracks - large and moderate in size.   Some are definitely
Megalosauropus (which is poorly - and misleadingly - illustrated in the
literature); some definitely aren't.  One of the biggest we found has pes
length of 51 cm.  There are some small tridactyl prints too (5-10 cm range),
but I haven't yet convinced myself that they're theropod.

Sauropod tracks - all over the place.  Some of moderate size, but plenty
with pes length greater than 60 cm.  Biggest we have to date is 1.7 m pes
length - discovered by Giuseppe (he seemed to get all the big ones).  Yes,
1.7 m, and that is NOT an exaggeration.  Some have manus prints, others
don't.  Some fit easily into ichnogenus Brontopodus, but there's a vast
range that doesn't - in all shapes and sizes, with and without indications
of digits.  At a conservative guess I'd say 3-4 different types, with
consistent morphological differences.   (Note, these are different types of
sauropod TRACKS - not necessarily different types of sauropods.)  There are
some nice trackway sequences, though none of them very lengthy, and at least
two 'stomping grounds' - one of which is so breath-taking that it deserves
to be lifted bodily (or replicated as high-fidelity cast) and put into a
museum.  By this point Giuseppe was nearly weeping - joy or frustration, I
don't know.  What I do know is that we were all getting heartily sick at the
sight of more and more - and yet more - footprints.

Lastly, there are at least three odd types of footprints - one with curious
rectangular outline, another including the so-called ?stegosaur tracks; and,
maybe, some swimming/paddling traces.  Overall the sauropod and
ornithischian tracks vastly outnumber theropod tracks, and at some sites
they are undeniably, and abundantly, jumbled up together.  In Giuseppe's
words, a "plant-eater's paradise".  

There is a lot more to the story - particularly concerning our past work and
future plans - but I hope this will suffice for now.  Giuseppe is now back
in Italy, trying to convince himself that it wasn't all a dream.  Although
he isn't accessible via e-mail, he will (I'm sure) confirm all these salient
facts about the Broome dinosaur tracks.

I'll take the opportunity to apologise to various colleagues who have (for
too long) been awaiting news or information on tracks and other items.  Yes,
I am the world's worst correspondent... but, believe me, this time I do have
some plausible excuses for delay.

Tony Thulborn