Dinosaurian Soft Tissues Interpreted as Bacterial Biofilms

A scanning electron microscope survey was initiated to determine if the previously reported findings of “dinosaurian soft tissues” could be identified in situ within the bones. The results obtained allowed a reinterpretation of the formation and preservation of several types of these “tissues” and their content. Mineralized and non-mineralized coatings were found extensively in the porous trabecular bone of a variety of dinosaur and mammal species across time. They represent bacterial biofilms common throughout nature. Biofilms form endocasts and once dissolved out of the bone, mimic real blood vessels and osteocytes. Bridged trails observed in biofilms indicate that a previously viscous film was populated with swimming bacteria. Carbon dating of the film points to its relatively modern origin. A comparison of infrared spectra of modern biofilms with modern collagen and fossil bone coatings suggests that modern biofilms share a closer molecular make-up than modern collagen to the coatings from fossil bones. Blood cell size iron-oxygen spheres found in the vessels were identified as an oxidized form of formerly pyritic framboids. Our observations appeal to a more conservative explanation for the structures found preserved in fossil bone

Well preserved complete bone used in initial investigation.

<p>Exceptionally well preserved small phalange from the Lance formation used for initial survey. No cracks or deformities present. Specimen was pressure fractured and directly examined under the SEM. UWBM 89327 Scale bar, 10 mm.</p

EDS spectrum of framboid.

<p>EDS spectrum of framboid showing an iron-oxygen signature. Pt is from coating for SEM. Area in red box was scanned for elements.</p

Specimens examined in survey.

<p>Specimens examined in survey.</p

Iron mineralization in vascular canal.

<p>SEM image of fractured bone surface across canal. Bottom half is EDS overlay with red representing a mineralized iron coating and green, calcium from the original bone. The transition from bone to coating is not immediately apparent without elemental analysis. UWBM 89326 Scale bar, 10 µm.</p

Bubble structures.

<p>(A) Bubble-like structures are found throughout some vascular canals. (B) Similar bubble-like structures found on framboids demonstrating that the coatings are undifferentiated between framboids, crystals and canal walls. (C) Framboid on left shows a heavy coating of biofilm that completely obscures the framboidal structure that is still evident on the right specimen UWBM 89322, UWBM 89328 Scale bars, 2 µm.</p

Infrared spectral comparison.

<p>Infrared spectra showing similarity of modern biofilms and modern collagen compared to fossil coatings. Cross correlation shows that the fossil material more closely resembles the modern biofilm than the modern collagen.</p

Iron oxide framboids.

<p>An iron oxide framboid cluster in dinosaur trabecular bone found commonly throughout time and taxa. At approximately 10 microns in diameter they are closely matched in size to red blood cells and typical pyrite framboids. UWBM 89327 Scale bar, 3 µm.</p

Osteocytes and lacunae.

<p>(A and B) Osteocytes found floating free in acid baths with fillapodia. (C,D,E) Fractured lacunae examined with SEM show filaments and spheres consistent with bacterial forms. UWBM 89325, UWBM 89322 Scale bars, A,B 10 µm, C–E 1 µm.</p