Osteocyte Density in Fossil Vertebrates
Ethan H. Smith, Edwin A. Cadena
Wake Tech MEAS Program, NCSU Department of Marine, Earth, and Atmospheric Sciences
Introduction
In bone, osteocytes are the most abundant cells making up 95
percent of all the cells . They have an important role in bone
formation, function, maintenance, and pathology(Cadena
Schweitzer 2012; Reference therin). Osteocytes contain branches
called canaliculi from which they communicate and exchange
nutrients and waste. The purpose of this work is to understand the
patterns of preservation of ancient osteocytes and to interpret their
paleophysiological implications such as: metabolism, body size, and
genomics.
Species
Cetacean (marine
mammal) Toe Bone
Trachemys scripta (turtle)
Peripheral bone
Objectives
• To prepare thin sections from turtle (Florida, 5 mya),
dinosaur(Hell Creek, SD, Cretaceous Era), and cetacean (Aurora,
NC, Pliocene Epoch) fossils
• To calculate the density of osteocytes from the thin sections
Discussion
Results
Ornithischian (dinosaur)
Rib Section
Osteocytes/mm2
1148.42-CB
1206.2-CB
802.58-CC
671.25-CC
642.63-CB
659.85-CB
959.93-EC
767.57-EC
1068.71-IC
890.13-IC
340.81-CB
831.67-CC
Osteocytes/mm3
5468.65-CB
5433.34-CB
4137.01-CC
3460.05-CC
3991.47-CB
3881.50-CB
5188.81-EC
4104.63-EC
6003.99-IC
4564.76-IC
3786.81-CB
7295.4-CC
*Bone Type: CC-Cortical Bone, CB-Cancellous Bone, EC-External Cortex, IC-Internal Cortex
Based on the data, the cetacean fossil has a higher
density of osteocytes compared to the turtle and
dinosaur. According to Cullinane (2002), mammals have
a higher metabolic demand, which explains why the
cetacean fossil has more osteocytes per bone volume.
The turtle and dinosaur fossils show similar values of
osteocyte density per volume, because they are reptiles
and have a lower metabolic demand (Cullinane, 2002).
Fig. 5. Shows the
types of tissue in
turtle bone.
(Cadena and
Schweitzer, Bone
(2012): 45, 215225)
Methods & Materials
1) First, the fossils were cleaned and cut. Then embedded in Silmar,
which is a clear resin.
2) After the Silmar was solid, I
removed the excess Silmar using a
saw.
3) Then the fossils were cut into
1.5 mm sections using a
mechanical diamond tip saw.
4) Next I ground down the
fossils to .5-.15 mm.
5) Then viewed the slides
under a microscope and took
pictures of the different parts
of bone.
7) Osteocyte density was calculated using the program ImageJ,
which measures the area based on how many pixels is equal to a
millimeter. Bone porosity was calculated and subtracted from the
total area. Then the osteocytes were counted using the cell counter
tool (Fig. 5) and finally we measured the thickness of the thin
sections to calculate the volume.
Osteocyte density in the fossilized turtle bone,
Trachemys scripta, showed variation according to the
type of bone tissue. The highest values of osteocyte
density is found in the internal cortex, and the lowest is
found in the cancellous bone (Fig. 5). A similar pattern is
also present in the ornithischian bone tissue where
cancellous bone has lower osteocyte density values
compared to the cortical bone.
Fig. 1. Picture taken at 20x magnification of
the cortical bone of the cetacean toe bone.
Fig. 2. Same picture as Fig 1. with all the
osteocytes counted using ImageJ.
Acknowledgements
I would like to thank Edwin Cadena for being a helpful
mentor and for all the time he put into this internship. I
would also like to thank Gretchen L. Miller for informing
me of this internship, Dr. Mary Schweitzer for allowing
me to use the labs, and Dr. John Fountain for organizing
this internship.
Works Cited
Fig. 3. Osteocyte preservation in the
Fig 4. Two isolated osteocytes at 63x
cancellous tissue of the peripheral turtle bone magnification. The branches coming out of the
at 20x magnification .
cell body are the canaliculi.
Cullinane, D.M. (2002). The role of Osteocytes in Bone
Regulation: Mineral Homeostasis vs
Mechanoreception. Journal of Musculoskel Neuron
Interaction, Boston, MA. 242-244.
Bonewald, Lynda F. (2011).The Amazing Osteocyte.
Journal of Bone and Mineral Research, 229-238.