The Last North American Pliosaur:
Remains from the Blue Hill Shale
(Middle Turonian) of Kansas
Copyright © 2012-2013 by Mike Everhart
Page created 01/02/2012 Last updated 05/07/2013
LEFT: Encounter over Kansas - One of the last pliosaurs (Megacephalosaurus eulerti) takes out an early mosasaur. Painting by Dan Varner - Copyright © Dan Varner.
On April 3, 2010, Bruce Schumacher and I had the opportunity to search
(and literally walk right to) the long lost site of a Kansas pliosaur specimen
that was discovered in the early 1990s. The specimen was first mentioned in
Schwimmer et al. 1997. Although the landowner had intended for
the specimen (FHSM VP-17469) to be donated to the Sternberg Museum of Natural History, it ended
up, un-curated, in a Los Angeles museum, and has since been
"misplaced." We are currently seeking it's return.
The specimen was originally discovered in a large septarian concretion by amateur rock collectors. Judging from the abundance of large bone fragments that we found in the debris yesterday, the concretion was broken apart haphazardly in an attempt to recover the remains, which reportedly included a partial skull, limb bones and ribs.
Although we able to salvage some meaningful fragments, including large (5 in /13 cm) teeth and jaw fragments, we will have to return to the site at a later date and do an additional excavation. The site is fairly unique in that the only exposed rocks are a very few septarian concretions. Everything else is rolling hills and grassland. Fortunately, the concretions stand out in the grass because of their yellow-orange color. The first concretion that Bruce flipped over contained most of a Collignoniceras hyatti ammonite (below).
This is the first known pliosaur from Blue Hills Shale Member of the Carlile Shale (late middle Turonian) and thus it is the youngest pliosaur specimen known from North America....(never mind that represents the largest vertebrate specimen EVER collected from the Blue Hill Shale). Our previous upper record (Brachauchenius lucasi - FHSM VP-321) was collected from the lower (older) Fairport Chalk Member.
Note that I did report (2009) on a probable rib of a large plesiosaur (FHSM VP-17299) from the Blue Hill Shale, and have since found fragments of a plesiosaur propodial (FHSM VP-17596) at a nearby locality.
Below are some pictures from our Saturday adventure..... A rolling grassland is a bit of an unusual place to find a big pliosaur... We have since learned that the big propodial was laying on the surface when the site was initially discovered.... otherwise, there is nothing but grass and a few concretions.
When we started out from the van, we only knew that the site was located on the side of a hill in the southeast quarter section.... we walked to the highest spot we could find and looked around... nothing there, so we decided to go further east to the next largest hill... as we went up a small rise,
|LEFT: Bruce spotted a small concretion ... flipped it over and found a nearly complete ammonite...
Collignoniceras hyatti ... a good omen to start the day. (Rock
hammer is 16 inches - 41 cm in length)
RIGHT: Leaving the ammonite for later pick up, we headed up the next rise and immediate saw fragments of a large septarian concretion... The first large fragment we looked at had lots of bone in it... Here Bruce is surveying the busted concretion that we saw as we walked up the hill. The hill in the background is capped by the Fort Hays Limestone.
|LEFT: We sorted through the broken septarian concretion and picked out those chunks that contained bone
fragments. According to our records, the skull was contained in the large concretion... and most of the fragments of large bones are probably from the skull... Not as big as Predator X.. but certainly a large pliosaur.
RIGHT: One of the larger pieces of the concretion with showing bone
fragments. (Rock hammer is 16 inches - 41 cm in length)
|LEFT: One of the larger pieces of the concretion still in
the soil, showing bone fragments. (Rock hammer is 16 inches - 41 cm in
RIGHT: Another piece of the concretion. This original was a huge skull, probably close to 2 m in length, from an animal that would have been 5 to 6 m overall.
|LEFT: One of the best finds of the day was a nearly complete tooth, or at least the core of a tooth... being enclosed in a septarian concretion does strange things to vertebrate bones and teeth... none of them good. This is a field photo of the tooth.
RIGHT: We recovered a number of bone fragments that were most likely cross sections of the dentarys or maxillae.... hard to tell at this point... but they definitely revealed some teeth in cross section.. judging from the surrounding bone, these may have been pre-emergent, replacement teeth. I suspect both of the teeth shown below are from the maxillae. (Scale = cm).
|LEFT: Although most of the teeth were in pretty bad shape, we did find enamel preserved on some of them, complete with nice striations.... more to come on that
subject. (Scale = cm).
RIGHT: A close up view of some of the remaining enamel. (Scale = mm).
|LEFT: After exploring the site as much as possible given that the soil was very wet, we did a 'walk-about' to see what else we could find.... Aside from a very few concretions containing shattered ammonites, there wasn't much else visible on the prairie.... so we loaded up and carried a few selected fragments (and the ammonite) over two hills and up to the van. This is a distant view of the site, looking to the east.... The fence posts are along an abandoned road that would have made this dig much easier....
RIGHT: A week later, Bruce collected a series of fairly large mosasaur caudal vertebrae in the Fairport Chalk (lower Middle Turonian)..... so it appears that the two groups over lapped by at least a million years (see Schumacher 2011). There are several other fragmentary mosasaur specimens from the Fairport Chalk...I have no doubt that a pliosaur would have preyed on mosasaurs, given the opportunity.
It's now been over a year since we visited the site... Hopefully we'll find the time in 2012.
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