The Hell Creek Experience:
Discoveries and the Past
Michael Peirce
Geology (Earth Science)
Dr. Julia Sankey
16 May 2005
Abstract:
Hell Creek is the site where many fossils were found. There is an abundance of
them as many animals lived there during the Late Cretaceous era. Hell Creek also has a
border of evidence that an asteroid hit during the Late Cretaceous causing the K-T
extinction of many mammals and all dinosaurs. This conclusion can be either proven or
disproven from the fossils collected at Hell Creek. By examining these fossils it can be
determined what lived at Hell Creek during the Late Cretaceous and if in fact the
creatures all died around the same time supporting an asteroid impact.
Introduction:
The Hell Creek formation is mostly in Montana and the Dakotas. The age goes
all the way back to Cretaceous days. The rocks found there are mostly sandstones,
siltstones, and mudstones that have the formations to indicate a floodplain deposition
(Lofgren p. 302). Also judging from the fossils collected, Hell Creek must have been
under water at some point due to the massive amounts of marine fossils. Yet there were
quite a bit of terrestrial fossils found as well. Hell Creek is also known for its terrestrial
vertebrates which include the Triceratops zone (Johnson p. 300).
The impact theory holds water since the K-T boundary can be seen in the rock
and traces of iridium can be found right where the boundary is. This indicates that
something from outer space had plummeted toward the earth approximately 65 million
years ago.
Method:
Surface collecting was used to gather the fossils from Hell Creek. This means
that the fossils were gathered by volunteers who got down and dirty on all fours with
faces in the dirt looking for the small, fragile fossils. This method seems like it would
take a long time since glancing too quickly might give a fossil a chance to escape one’s
vision.
The method we used in class was similar in that we looked very closely at the
fossils. The difference is that we did not have to worry about getting dirty, nor glancing
around because the fossils were already found. Instruments such as rulers, microscopes,
and magnifying glasses were all used to help examine the fossils. As for the fossils
themselves we were looking for size, shape, color, angularity, fragments, holes, etc. Each
fossil was examined and then compared to those seen in Donald Brinkman’s An
Illustrated Guide to the Vertebrate Microfossils from the Dinosaur Park Formation.
Judging from fossils and findings found in that packet helped us to determine what it was
we were looking at.
Results:
Rocks: The Hell Creek rocks were all sedimentary, but began to vary in detail
upon looking at them more closely. The rock from locality V92002-JS was a sandstone
with fine grain size and well sorted. It was brownish tan on one side and sub angular.
There were leaves and other organic material in the rock and this rock had parallel
lamination. It consisted of stratified layers and had medium grit. The rock in locality
87012 was a mudstone with very fine grain size and was well sorted. There were a
number of colors in this rock consisting of reds, grays, with some black pieces scattered
throughout. It was sub rounded with medium grit and had organic plant material inside.
The rock in locality 88017-JS was a siltstone with very fine grain size and well sorted. It
was gray with some black pieces scattered around and the rock had rounded angularity
with organic plant material inside. Also this rock had brownish / orange layer visible.
The rock in locality 87012 screen sample was a silty mudstone with very fine grain and
medium grain size. It was poorly sorted and was not gritty. The color was a brownish
tan with black from the organic material inside. The rock was sub angular and had some
amber inside. This rock also had stratified layers. The rock in locality 88017 was a
siltstone with fine grain, medium sorting, and no grit. It had medium sorting and was tan
in color with the black organic material. It was sub rounded and contained small organic
material inside.
Fossils:
Locality: V-00006 (Surface)
Gar Scales (33)
Centra of Primitive Telosts (2)
Turtle Carapace (181)
Crocodile Scute (1)
Gar Tooth (1)
Unidentifiable Bone Fragments (105)
End of Bone With Socket Joint (1)
Hadrosaur Tooth Fragments (11)
Finger or Toe Bone (1)
? Mammal bone (1)
Tyrannosaurid Tooth Fragment(2)
Theropod Claw Fragment (1)
Turtle Bone Fragment (1)
Ossified Hadrosaur Tendons (1)
Unidentified Long Teeth (1)
Turtle Scute (5)
Amiidae Fish Jaw Fragment (1)
Crocodile Teeth (4)
Locality: V-89004 - Surface
Amiidae Fish Tooth (1)
Gar Vertebrae (1)
Turtle Carapace (7)
Champsosaurus Vertebrae (1)
? Sturgeon Scale (1)
Crocodile Teeth (3)
Crocodile Scute (4)
Unidentifiable Bone Fragments (246)
Salamander Vertebrae (3)
Hybodus Shark Tooth (1)
Myledaphus Teeth (2)
Gar Teeth (9)
Gar Vertebrae (2)
Gar Scales (10)
Amiidae Vertebrae (1)
Myledaphus Vertebrae (2)
Hadrosaur Teeth (5)
Fish Vertebrae (3)
Crocodile Vertebrae (1)
Fish Teeth (9)
Fish Jaw Fragment (1)
Turtle Scute (1)
Locality: 88017 - Surface
Gar Scales (26)
Gar Teeth (8)
Complete Fish Vertebrae (1)
Fish Vertebrae Fragment (5)
Gar Vertebrae-Anterior Dorsal Centrum (1)
Salamander Vertebrae (3)
Crocodile Scute (9)
Tooth Fragments (12)
Crocodile Tooth (14)
Fossilized Wood (13)
Fish Jaw Fragment (1)
Turtle Carapace (20)
Turtle Scute (400)
Hadrosaur Teeth (32)
Coprolite (4)
Fish Costal (4)
Myledaphus Tooth (1)
Lizard Scute (3)
Unidentifiable Bone Fragments (12)
Clam (1)
Locality: 88017 Restricted
Hadrosaur Tooth Fragments (7)
Long Bone Fragments (4)
Unidentifiable Bones (3)
Turtle Carapace (1)
Crocodile Teeth (2)
Locality: V-92002-JS - Surface
Ossified Hadrosaur Tendons (3)
Hadrosaur Tooth Fragments (18)
Therapod Tooth Fragment (1)
Hollow Long Bone (1)
Miscellaneous Bone Fragments (32)
Champsosaurus Limb Fragment (1)
Champsosaurus Vertebrae (1)
Crocodile Scute (51)
Unidentifiable Hollow Bone Fragments (3)
Finger or Toe Bone (1)
Small Amphibian Humerus (1)
? Turtle Bone (1)
Salamander Vertebrae (1)
Turtle Carapace (89)
Myledaphus Tooth (2)
Salamander Limb Bone (1)
Fossilized Wood (13)
Gar Scales (62)
Gar Vertebrae (5)
Seed Fossils (2)
Gar Tooth Bearing Bone (2)
Gar Teeth (10)
Locality: 87012 - Surface
Crocodile Teeth (4)
Myledaphus Tooth (4)
Crocodile Scute (6)
Possible Dinosaur Claw Fragments (4)
Richardoestesia isosceles Teeth (2)
? Mammal Bone (1)
Gar Tooth (5)
Hollow Bird Bones (2)
Gar Scales (42)
Scapherpeton Vertebrae (Salamander) (1)
Fish Vertebrae (9)
? Mammal or Lizard Vertebrae (1)
Unidentifiable Bones (446)
Turtle Carapace (107)
? Turtle Limb Bone (1)
Gar Tooth Bearing Bone (1)
Shark Tooth (1)
Gar Vertebrae (9)
Amphibian Vertebrae (3)
Ossified Hadrosaur Tendons (3)
Petrified Wood (1)
Ceratopsian Tooth Fragment (1)
Turtle Scute (264)
Salamander Vertebrae (1)
Amber (1)
Fish:
In locality 88017 – Surface I found one fish jaw and three gar teeth. They were
very small and shiny. There were triangular in shape and ranged in sizes. The biggest
gar tooth in the bag was 0.8 cm long and was black with a
light top. There were ridges that went down the tooth all the
way to the point as seen in the picture to the left. When
compared to those in Brinkman’s packet it was nearly
identical. The gar scales were similar in size but had a
different shape to them. They have a diamond shape to them and look like those found
on page 19 of Brinkman’s packet. Despite having the packet it was too difficult to
determine which exactly it was in the packet because there was so many. The gar scales
were shiny and ranged from 0.4 cm being the smallest to 1.3 cm being the biggest. The
gar vertebrate was very small and round. It was light in color and had a small hole in the
middle.
Amphibians and Lizards:
At locality 87012 – Surface I found a frog vertebrate that was light in color, had
few marks on it, and was circular. It was 0.7 cm across and had a sort of a gash in the
side of it. A salamander vertebrate was also found, but it was in locality 88017. It was
curvy and was missing a part of the top. It was circular with rough ends and was fairly
smooth. It was 0.9 cm tall and 0.5 cm across. There could have possibly been others, but
fragments were unidentifiable even using Brinkman’s packet.
Turtles:
Turtle scutes were found in localities 87012 – surface. There were nine pieces of
turtle scute that ranged from 0.9 cm long and 0.4 cm thick to 1.9 cm long and 0.4 cm
thick. These scutes had shallow holes on one side
while the other side was smooth and the overall scute
was relatively thick as seen in Brinkman’s packet on
page 79 and the picture to the left. There were 39
pieces of turtle shells recovered in this locality, but
none of them really of great size. A random piece of shell picked from the pile was 1.9
cm across and was smooth on one side with ridges on the other.
Crocodilians:
In locality 87012 there was one crocodile tooth observed. This was not a
complete tooth as some of it was broken off exposing a hollow inside. It was 1.5 cm tall
and 0.7 cm at the base. The crocodile tooth was coned
in shape and has ridges going down the entire tooth as
seen in Brinkman’s packet on page 87 and the picture to
the left. The crocodile scutes looked very similar to
those of turtles save a few exceptions. The crocodile
scutes have bigger and deeper holes than those of turtles and the holes are spread out
further rather than bunched together. Just like the turtle, the crocodile scutes only have
the holes on one side while the other side is smooth. The crocodile scute examined in
locality 87012 was 1.2 cm across and was relatively thick.
Dinosaurs:
Clearly the most abundant dinosaur fossil that kept appearing were hadrasaur
teeth. The hadrasaur tooth I examined in locality 88017 was 0.7 cm tall and 0.6 cm
across. It had a triangular shape to it and looking from
above I could see a cross pattern in the tooth as seen in
Brinkman’s packet on page 103. Hadrasaur teeth had
lines going all the way down the chewing surface was
flat since they were herbivores as seen in the picture to
the left. In locality 87012 two hadrasaur tendons were found. The tendons have tiny
holes on the top to one side when looking at the tendon from above. The bigger of the
two tendons was 0.7 cm tall and 0.7 cm wide. They are long and cylinder in shape and
could almost be mistaken for a salamander tendon. Another tooth that was examined was
the dromaeosaurs. This fossil was 1.1 cm long and the ridges were not as noticeable as
those on the hadrosaur. This tooth had a J-shape to it and had a hollow center.
Mammals:
I did not find any mammal fossils in the bags I examined.
Discussion:
1)
At all of the fossil localities save a few restricted 88017 ones turtles
and fish were dominant. The number of scutes was simply astonishing,
but I think most of that has to do with a lot of the scutes are simply
broken off from the larger piece making it seem like there is more than
there really should be. The number of fish teeth and scales were
abundant as well in localities 87012 as Hell Creek was underwater at
some point in time in the past. Hadrasaur teeth ran rampant in locality
88017 – Surface but not many whole teeth specimens were left.
2)
The rocks were all sedimentary rocks and each one differed. The
sandstone in locality V92002-JS was fine grain and well sorted where
as the silty mudstone in locality 87012 was fine to medium grain and
poorly sorted. Some rocks had stratified layers and some did not. Also
some rocks had different colors and fossils within them. Some fossils
contained leaves that were preserved in them whereas others had black
organic material and one rock even had amber. The grittiness differed
in some as well where some rocks had no grit and others had very find
to medium grit.
3)
As the localities get closer to the K-T boundary there becomes more
and more fossils found. This suggests that there was indeed some sort
of impact or weather change that occurred to disrupt the Hell Creek
habitat sending not just dinosaurs; but fish, amphibians, crocodilians,
and turtles to their dooms. Surely the number of animals and lives of
them go up and down, but as the K-T boundary approaches it’s clear
that more of them died due to all the fossil finds.
4)
Since there are both marine and land fossils found at the localities it’s
easy to conclude that at one point in time Hell Creek was under water.
The hard part is to decide when Hell Creek started drying up to make
way for the terrestrial animals. From the fish fossils collected Hell
Creek was either under an ocean, run by rivers and streams, or all of
the above. Yet there was also terrestrial fossils found in those of
hadrasaurs. This means that land was exposed at one point to allow the
herbivores to flourish on land until the K-T extinction. Some of their
fossils may have been found in a different location to that of their
deaths because a steam or river could have carried their fossils
downstream until found by the volunteers of Hell Creek.
References:
“Hell Creek Flora.” Johnson, K.R.
“Hell Creek Formation.” Lofgren, D. F.
An Illustrated Guide to the Vertebrate Microfossils from the Dinosaur Park Formation .
Brinkman, Donald. 2002.
CD pictures. Dr. Julia Sankey.