Blood Clots in Dinosaur Bones
reach other cells. Tere they connect using gap junctions. Workers note that in humans “the average cumulated length of a single cell process projecting from an osteocyte cell body including all its sub-branches is 47 μm” [23]. Tey also estimate that osteo- cytes have upwards of 89 dendritic processes per cell. Dinosaur osteocytes show similar numbers of extensions protruding from the cell membrane (Figure 7), but lengths over 18 µm have not been reported. Attention has been drawn to “extended”
dinosaur filipodial length [5–8]. Descrip- tions such as “long filipodia,” “long exten- sive filipodia,” “long flexible filipodia,” “very long extensive filipodia,”
and “extensive
Figure 1: Venule valves from HCTH-02 (see Methods) liberated with EDTA. Valves are stained with acridine orange for nucleic acid detection. Scale bar, 50 μm.
three-dimensional filipodial network” are used to describe intact filipodia [5–7]. In some instances, where dinosaur osteocytes
have been reported, image scale bars are not present or are obscured [8,24], but for the most part scales are supplied. Most cells feature non-cumulated filipodia lengths under 15–16 µm. One notable exception is that cells recovered from B. canadensis filipodia show filipodia lengths up to 18 µm [8,22], but lengths of 47 µm are unreported for dinosaur bone cell dendrites. Nev- ertheless, it is clear that many dST osteocytes characterized to date (especially those liberated from bone matrix) are marked by truncated or completely missing filipodia [5,7,8,21]. Dino- saur osteocytes with filipodia longer than 18 µm seem rare. Tis rarity might result from any number of variables,
Figure 2: Valve with folded leaflets visible (differential interference contrast [DIC] microscopy). Scale bar, 50 µm.
including initial degradation of cells within bone before pro- cessing, attachment of filipodia to inner canaliculi walls, rough handling during processing, lengthy exposure to decalcifica- tion reagents, and desiccation or improper dehydration. In other words, processing artifacts and unforeseen degradation prior to processing can disrupt cellular architecture. Addition- ally, prior to processing environmental extremes such as freeze/ thaw cycles, heat and desiccation exposure, exposure to natu- rally occurring radioactive decay, water or mud infiltration, ingress of soil microbes, bacteria, worms, insects, plant roots, fungal hyphae, and the like all result in cell degradation. More- over, natural events that occur within cells immediately post- mortem would certainly affect dendritic length. Schweitzer has remarked, “Te preservation of cells is difficult to account for in the fossil record, as autolytic destruction of cells and intracel- lular contents may begin within seconds aſter death” [22]. Widths of osteocyte filipodia are noted at 200 nm in humans
Figure 3: Valve with leaflets heavily stained with toluidine blue tissue stain. Scale bar, 50 µm.
their processes throughout bone tunnels known as canaliculi. Dendritic processes travel from bone lacunae (the indenta- tions that cells lie within) through fluid-filled canaliculi to
32
[25], but widths of dinosaur osteocytes are rarely reported [1]. Human canaliculi width radii have been estimated at 157.5 nm [23], thus the filipodia traversing these tunnels would be thinner to fit comfortably. Tis conforms to measurements on dinosaur osteocyte filopodia in this study. With lengths extending some 125 times their diminutive widths, they might well be charac- terized as the most delicate among soſt tissue elements found within dinosaur bones. Terefore, it is reasonable to expect that they would be susceptible to degradation as a result of any for- eign intrusions into the lacuno-canalicular network. Fossil osteocytes of Triceratops horn from Hell Creek, Montana (HCTH-02) show filipodia of 25 µm in length under
www.microscopy-today.com • 2020 September
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