A key tenant of palaeontology is that soft tissue and DNA cannot be preserved in fossil bones; they’re much too old, and any soft tissue that survived microbial decay (the skin of mummies, for example) would have been mineralised. This is why, sadly, we cannot ever clone a dinosaur. But how long does it take soft tissue to decay? And more specifically, how long does blood last in the bones of a dead animal?
A new paper has just been published on the taphonomy of blood in decomposing human bones (Cappella et al., 2015). In it, the authors collected human bone samples from ‘fresh’ cadavers (no more than 24 hrs post-mortem), from those same cadavers each week for the next 7 weeks, from a ’putrified’ carcass (48-72 hours post-mortem), from 20 year old bones, and one sample from a 400 year old bone. One ‘fresh’ cadaver also had bone samples taken and frozen, boiled, or macerated (placed in fresh water). These bone samples were then examined in thin section under a microscope to see if any trace of blood could be found.
The authors found that they could identify blood in the ‘fresh’ bone, but it was nearly impossible to identify red blood cells in bones older than 2 weeks post-mortem. They confirmed that boiling and macerating bone is a very efficient ‘cleaning’ method with very little blood remaining, whereas blood was preserved well and easy to observe in frozen bone. Some more refined analysis (using immunohistochemistry) made it possible to identify red blood cells older bone samples (up to 15-20 years post-mortem), yet the amounts present were very small - found in only 10% of the bone pore space. However, no red blood cells could be detected in the 400 year old bone either by microscopy or immunohistochemistry.
A new paper has just been published on the taphonomy of blood in decomposing human bones (Cappella et al., 2015). In it, the authors collected human bone samples from ‘fresh’ cadavers (no more than 24 hrs post-mortem), from those same cadavers each week for the next 7 weeks, from a ’putrified’ carcass (48-72 hours post-mortem), from 20 year old bones, and one sample from a 400 year old bone. One ‘fresh’ cadaver also had bone samples taken and frozen, boiled, or macerated (placed in fresh water). These bone samples were then examined in thin section under a microscope to see if any trace of blood could be found.
The authors found that they could identify blood in the ‘fresh’ bone, but it was nearly impossible to identify red blood cells in bones older than 2 weeks post-mortem. They confirmed that boiling and macerating bone is a very efficient ‘cleaning’ method with very little blood remaining, whereas blood was preserved well and easy to observe in frozen bone. Some more refined analysis (using immunohistochemistry) made it possible to identify red blood cells older bone samples (up to 15-20 years post-mortem), yet the amounts present were very small - found in only 10% of the bone pore space. However, no red blood cells could be detected in the 400 year old bone either by microscopy or immunohistochemistry.
Graph showing the percentage of red blood cells and other blood components seen in frozen, boiled, macerated, putrefied, modern and ancient skeleton bone samples. The blue line indicates blood seen in thin section, the red line indicates blood seen using immunohistochemistry. From Cappella et al (2015).
The authors suggest that those who have reported seeing soft tissue in fossil bones are most likely mistaken in their interpretation. This finding is especially pertinent to palaeontology, as Schweitzer et al (2007) claimed to have found soft tissue preserved in 65 mya Triceratops horridus bone (MOR 699), 68-65 mya Tyrannosaurus rex bone (MOR 1125, MOR 555, FMNH-PR-2081), and 78 mya Brachylophosaurus canadensis bone (MOR 794). Given the results of this latest study by Cappella et al. (2015), these interpretations of dinosaur soft tissue preservation appear to be highly unlikely.
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| Top and centre images: 2 week old human bone in thin section, with blood preserved in cells (see arrows). Bottom image: 24 hr old bone with well defined red blood cells. From Cappella et al (2015). | Top image: 15 year old human bone in thin section, with no blood cells visible. Bottom image: the same 15 year old bone, viewed using immunohistochemical analysis. Minor red blood cells marked by black arrows. From Cappella et al (2015). |
References
Cappella, A., Bertoglio, B., Castoldi, E., Maderna, E., Di Giancamillo, A., Domeneghini, C., Andreola, S., Cattaneo, C. 2015. The taphonomy of blood components in decomposing bone and its relevance to physical anthropology. American Journal of Physical Anthropology, doi: 10.1002/ajpa.22830.
Schweitzer, M. H., Wittmeyer, J. L., Horner, J. R. 2007. Soft tissue and cellular preservation in vertebrate skeletal elements from the Cretaceous to the present. Proceedings of the Royal Society B: Biological Sciences. 274 (1607):183-197. doi:10.1098/rspb.2006.3705. 274:183–197.
Cappella, A., Bertoglio, B., Castoldi, E., Maderna, E., Di Giancamillo, A., Domeneghini, C., Andreola, S., Cattaneo, C. 2015. The taphonomy of blood components in decomposing bone and its relevance to physical anthropology. American Journal of Physical Anthropology, doi: 10.1002/ajpa.22830.
Schweitzer, M. H., Wittmeyer, J. L., Horner, J. R. 2007. Soft tissue and cellular preservation in vertebrate skeletal elements from the Cretaceous to the present. Proceedings of the Royal Society B: Biological Sciences. 274 (1607):183-197. doi:10.1098/rspb.2006.3705. 274:183–197.
