Tyrannosaurus rex, Osborn, 1905
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https://doi.org/ 10.1126/science.1108397 |
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https://treatment.plazi.org/id/03E28E29-FFD6-190D-FC2E-F4006FE5F91E |
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Jeremy |
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Tyrannosaurus rex |
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A newly discovered specimen of Tyrannosaurus rex [ Museum of the Rockies (MOR) specimen 1125] was found at the base of the Hell Creek Formation, 8 m above the Fox Hills Sandstone , as an association of disarticulated elements. The specimen was incorporated within a soft, well-sorted sandstone that
was interpreted as estuarine in origin. Although some bones are slightly deformed or crushed, preservation is excellent. MOR
1125 represents a relatively small individual of T. rex , with a femoral length of 107 cm, as compared to the Field Museum (Chicago) specimen ( FMNH PR 2081 ) that has a femoral length of approximately 131 cm. On the basis of calculated lines of arrested growth (LAG), we estimated that this animal was 18 + 2 years old at death ( 7).
No preservatives were applied to interior fragments of the femur of MOR 1125 during preparation, and these fragments were reserved for chemical analyses. In addition to the dense compact bone typical of theropods, this specimen contained regions of unusual bone tissue on the endosteal surface (2). Cortical and endosteal bone tissues were demineralized (3), and after 7 days, several fragments of the lining tissue exhibited unusual characteristics not normally observed in fossil bone. Removal of the mineral phase left a flexible vascular tissue that demonstrated great elasticity and resilience upon manipulation. In some cases, repeated stretching was possible ( Fig. 1 A View Fig. 1 , arrow), and small pieces of this demineralized bone tissue could undergo repeated dehydrationrehydration cycles (Fig. IB) and still retain this elastic character. Demineralization also revealed that some regions of the bone were highly fibrous ( Fig. 1C View Fig. 1 , arrows).
Partial demineralization of the cortical bone revealed parallel-oriented vascular canals that were seen to bifurcate in some areas ( Fig. 2A View Fig. 2 , arrows). Occasional fenestrae (marked F) were observed on the surface of the vascular canals, possibly correlating with communicating Volkmann’s canals. Complete demineralization of the cortical bone released thin and transparent soft-tissue vessels from some regions of the matrix ( Fig. 2 View Fig. 2 , B and C), which floated freely in the demineralizing solution. Vessels similar in diameter and texture were recovered from extant ostrich bone, when demineralization was followed by digestion with collagenase enzyme (3) to remove densely fibrous collagen matrix ( Fig. 2D View Fig. 2 ). In both dinosaur ( Fig. 2C View Fig. 2 ) and ostrich ( Fig. 2D View Fig. 2 ), remnants of the original organic matrix in which the vessels were embedded can still be visualized under transmitted light microscopy. These vessels are flexible, pliable, and translucent ( Fig. 2E View Fig. 2 ). The vessels branch in a pattern consistent with extant vessels, and many bifurcation points are visible ( Fig. 2E View Fig. 2 , arrows). Many of the dinosaur vessels contain small round microstructures that vary from deep red to dark brown ( Fig. 2 View Fig. 2 , F and G). The vessels and contents are similar in all respects to blood vessels recovered from extant ostrich bone ( Fig. 2H View Fig. 2 ). Aldehyde-fixed (3) dinosaur vessels ( Fig. 2I View Fig. 2 ) are virtually identical in overall morphology to similarly prepared ostrich vessels ( Fig. 2J View Fig. 2 ), and structures consistent with remnants of nuclei from the original endothelial cells are visible on the exterior of both dinosaur and ostrich specimens ( Fig. 2 View Fig. 2 , I and J, arrows).
The fossil record is capable of exceptional preservation, including feathers ( 4 - 6), hair ( 7), color or color patterns ( 7, 8), embryonic soft tissues ( 9), muscle tissue and/or internal organs ( 10 - 13), and cellular structure ( 7, 14 - 16). These soft tissues are preserved as carbon films ( 4, 5, 10) or as permineralized threedimensional replications ( 9, 11, 13), but in none of these cases are they described as stillsoft, pliable tissues.
Mesozoic fossils, particularly dinosaur fossils, are known to be extremely well preserved histologically and occasionally retain molecular information ( 6, 17, 18), the presence of which is closely linked to morphological preservation ( 19). Vascular microstructures that may be derived from original blood materials of Cretaceous organisms have also been reported ( 14 - 16).
Pawlicki was able to demonstrate osteocytes and vessels obtained from dinosaur bone using an etching and replication technique (14,15). However, we demonstrate the retention of pliable soft-tissue blood vessels with contents that are capable of being liberated from the bone matrix, while still retaining their flexibility, resilience, original hollow nature, and three-dimensionality. Additionally, we can isolate three-dimensional osteocytes with internal cellular contents and intact, supple filipodia that float freely in solution. This T. rex also contains flexible and fibrillar bone matrices that retain elasticity. The unusual preservation of the originally organic matrix may be due in part to the dense mineralization of dinosaur bone, because a certain portion of the organic matrix within extant bone is intracrystalline and therefore extremely resistant to degradation ( 20, 21). These factors, combined with as yet undetermined geochemical and environmental factors, presumably also contribute to the preservation of soft-tissue vessels. Because they have not been embedded or subjected to other chemical treatments, the cells and vessels are capable of being analyzed further for the persistence of molecular or other chemical information (3).
Using the methodologies described here, we isolated translucent vessels from two other exceptionally well-preserved tyrannosaurs (figs. S1 and S2) (3), and we isolated microstructures consistent with osteocytes in at least three other dinosaurs: two tyrannosaurs and one hadrosaur (fig. S3). Vessels in these specimens exhibit highly variable preservation, from crystalline morphs to transparent and pliable soft tissues.
The elucidation and modeling of processes resulting in soft-tissue preservation may form the basis for an avenue of research into the recovery and characterization of similar structures in other specimens, paving the way for micro- and molecular taphonomic investigations. Whether preservation is strictly morphological and the result of some kind of unknown geochemical replacement process or whether it extends to the subcellular and molecular levels is uncertain. However, we have identified protein fragments in extracted bone samples, some of which retain slight antigenicity (3). These data indicate that exceptional morphological preservation in some dinosaurian specimens may extend to the cellular level or beyond. If so, in addition to providing independent means of testing phylogenetic hypotheses about dinosaurs, applying molecular and analytical methods to well-preserved dinosaur specimens has important implications for elucidating preservational microenvironments and will contribute to our understanding of biogeochemical interactions at the microscopic and molecular levels that lead to fossilization.
No known copyright restrictions apply. See Agosti, D., Egloff, W., 2009. Taxonomic information exchange and copyright: the Plazi approach. BMC Research Notes 2009, 2:53 for further explanation.
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