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Theropod fractures

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Allosaurus fragilis was found to have the most stress fractures of any taxon examined in the study.

Bruce Rothschild and others published a study examining evidence for stress fractures and tendon avulsions in theropod dinosaurs and the implications for their behavior.[1] These pathologies provide evidence for very active predation-based rather than scavenging diets.[1] Stress fractures are caused by repeated trauma rather than singular events like acute fractures.[2] Since stress fractures are due to repeated events they are probably caused by expressions of behavior.[3] Activity-related fractures are also known from ceratopsians.[3] Pedal injuries could be caused by runnning or migration, but manual injuries would most likely be due to resistant prey items.[3] Stress fractures in dinosaur bones can be identified by studying the bones for diaphyseal surface bulges, usually facing anteriorly on the bone. When viewed under x-rays the fractures exhibit areas of reduced x-ray attenuation that appear as a clear zone angled through the diaphyseal bulge.[4] Usually this zone of attenuation is not visible on the surface of the bone.[4] Allosaurus had a significantly greater number of diaphyeal bumps than Albertosaurus, Ornithomimus or Archaeornithomimus.[5] The fractures "were distributed to the proximal phalanges" and occurred across all three major digits in "statistically indistinguishable" numbers.[5] Pathologies of the distal unguals were only noted among dromaeosaurids, where they represented 50% of manual lesions.[6] The authors refrained from performing a statistical analysis of these injuries in non-dromaeosaur theropods because they were so uncommon that such an analysis would be impossible for all intents and purposes.[6]

Avulsion injuries were only noted among Tyrannosaurus and Allosaurus.[7] Scars from these sorts of injuries were limited to the humerus and scapula.[7] A divot on the humerus of Sue the T. rex was one such avulsion.[7] The divot appears to be located at the origin of the deltoid or teres major.[7] The researchers described theropod phalanges as being pathognomonic for stress fractures, meaning they are "characteristic and unequivocal diagnostically."[7] Lesions left by stress fractures can be distinguished from osteomyelitis without difficulty because of a lack of bone destruction.[7] They can be distinguished from benign bone tumors like osteoid osteoma by the lack of a sclerotic perimeter.[7] No disturbance of the internal bony architecture of the sort caused by malignant bone tumors was encountered among the stress fracture candidates.[7] No evidence of metabolic disorders like hyperparathyroidism or hyperthyroidism was found in the specimens.[7] The thin shell caused by a subperiosteal hematoma was not seen and would have been easily identified under x-ray.[7] Since the lower end of the third metatarsal would contacted the ground first while a theropod was running it would have borne the most stress and should be most predisposed to suffer stress factors.[7] The lack of such a bias in the examined fossils indicates an origin for the stress fractures from a source other than running.[7] The authors conclude that these fractures occurred during interaction with prey.[7] They suggest that such injuries could occur as a result of the theropod trying to hold struggling prey with its feet.[7] The localization in theropod scapulae as evidenced by the tendon avulsion in Sue suggests that theropods may have had a musculature more complex and functionally different than those of birds.[8] The authors suggest that future workers compare the anatomy of a Komodo dragon and crocodile with that of Tyrannosaurus.[8]


Affected Taxon[9] Affected Pedes[9] Total Pedes Examined[9] Affected Manus[9] Total Manus Examined[9] Affected Specimen[9]

Ceratosaurus

1

1

0

0

Not listed.

Allosaurus

17

281

3

47

AMNH 324 and AMNH 6128

Albertosaurus

1

319

0

4

AMNH 5432

Tyrannosaurus

1

81

0

10

LACM 23844

Tyrannosauridae (indeterminate)

3

105

1

5

RTMP 81.16.328, RTMP 79.14.694, RTMP 89.36.343

Tarbosaurus

0

18

1

10

Blanding-II-2

Saurornitholestes

2

82

2

9

RTMP 89.172.32, RTMP 94.172.32, RTMP 81.19.97

Dromaeosauridae (indeterminate)

4

17

4

12

RTMP 79.14.900

Ornithomimidae (indeterminate)

1

15

0

8

Not listed.

Chirostenotes

1

17

1

17

RTMP 92.36.448. Note that the authors weren't sure if this was a pedal or manual specimen.

Theropoda (small, indeterminate)

1

4

0

0

Not listed.

The following taxa had no evidence of stress fractures or tendon avulsions among the examined specimens: Herrerasaurus, Coelophysis, Dilophosaurus, Carnosaur (indeterminate), Velocisaurus, Mononykus, Megalosaurus, Marshosaurus, Ornitholestes, Compsognathus, Alectrosaurus, Albertosaur, Gorgosaurus, Utahraptor, Deinonychus, Therizinosauridae (indeterminate), Struthiomimus, Ornithomimus, Archaeornithomimus, Dromiceiomimus, Elmisaurus, and Troodon.[9]

Footnotes

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  1. ^ a b "Abstract," in Rothschild, et al., et al. (2001); page 331.
  2. ^ "Introduction," in Rothschild, et al. (2001); pages 331-332.
  3. ^ a b c "Introduction," in Rothschild, et al. (2001); page 332.
  4. ^ a b "Methods," in Rothschild, et al. (2001); page 332.
  5. ^ a b "Results," in Rothschild, et al. (2001); page 332.
  6. ^ a b "Results," in Rothschild, et al. (2001); page 334.
  7. ^ a b c d e f g h i j k l m n "Discussion," in Rothschild, et al. (2001); page 334.
  8. ^ a b "Discussion," in Rothschild, et al. (2001); page 335.
  9. ^ a b c d e f g "Table 23.1," in Rothschild, et al. (2001); page 333.


Reference

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  • Rothschild, B., Tanke, D. H., and Ford, T. L., 2001, Theropod stress fractures and tendon avulsions as a clue to activity: In: Mesozoic Vertebrate Life, edited by Tanke, D. H., and Carpenter, K., Indiana University Press, p. 331-336.