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New Insights Into the Lifestyle of Allosaurus (Dinosauria: Theropoda) Based on Another Specimen With Multiple Pathologies

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New Insights Into the Lifestyle of Allosaurus (Dinosauria: Theropoda) Based on Another Specimen With Multiple Pathologies

Christian Foth et al. PeerJ.

Abstract

Adult large-bodied theropods are often found with numerous pathologies. A large, almost complete, probably adult Allosaurus specimen from the Howe Stephens Quarry, Morrison Formation (Late Kimmeridgian-Early Tithonian), Wyoming, exhibits multiple pathologies. Pathologic bones include the left dentary, two cervical vertebrae, one cervical and several dorsal ribs, the left scapula, the left humerus, the right ischium, and two left pedal phalanges. These pathologies can be classified as follows: the fifth cervical vertebra, the scapula, several ribs and the ischium are probably traumatic, and a callus on the shaft of the left pedal phalanx II-2 is probably traumatic-infectious. Traumatically fractured elements exposed to frequent movement (e.g., the scapula and the ribs) show a tendency to develop pseudarthroses instead of a callus. The pathologies in the lower jaw and a reduced extensor tubercle of the left pedal phalanx II-2 are most likely traumatic or developmental in origin. The pathologies on the fourth cervical are most likely developmental in origin or idiopathic, that on the left humerus could be traumatic, developmental, infectious or idiopathic, whereas the left pedal phalanx IV-1 is classified as idiopathic. With exception of the ischium, all as traumatic/traumatic-infectious classified pathologic elements show unambiguous evidences of healing, indicating that the respective pathologies did not cause the death of this individual. Alignment of the scapula and rib pathologies from the left side suggests that all may have been caused by a single traumatic event. The ischial fracture may have been fatal. The occurrence of multiple lesions interpreted as traumatic pathologies again underlines that large-bodied theropods experienced frequent injuries during life, indicating an active predatory lifestyle, and their survival perhaps supports a gregarious behavior for Allosaurus. Alternatively, the frequent survival of traumatic events could be also related to the presence of non-endothermic metabolic rates that allow survival based on sporadic food consumption or scavenging behavior. Signs of pathologies consistent with infections are scarce and locally restricted, indicating a successful prevention of the spread of pathogens, as it is the case in extant reptiles (including birds).

Keywords: Archosauria; Gregarious behavior; Jurassic; Osteomyelitis; Paleopathology; Pseudarthrosis; Theropoda.

Conflict of interest statement

The authors declare there are no competing interests.

Figures

Figure 1
Figure 1. Overview of pathologies in SMA 0005.
Skeletal reconstruction of SMA 0005, showing all pathologic bones. Pathologic elements from the left side are shown in red, while respective elements from the right side are marked in blue. Unpaired pathologic bones are colored in cyan. Green ribs represent ribs from the left, for which a pathologic condition is uncertain. Abbreviations: c, cervical; cr, cervical rib; de, dentary; dr, dorsal rib; hu, humerus; is, ischium; p, pedal phalanx; sc, scapula. Skeletal reconstruction of SMA 0005 with courtesy from the Sauriermuseum Aathal.
Figure 2
Figure 2. The dentaries of SMA 0005.
(A) Left dentary with pathologic anterior end in lateral view. (B) Medial side of the left dentary with pathologic anterior end in mirrored view. (C) Right dentary in mirrored view, showing the normal condition for Allosaurus. The differences in the shape of the alveolar margin in both dentaries (A, C) are shown with a dashed line. Note that most teeth in both dentaries are not original, but glued to the internal margin of the dentaries. Abbreviations: dep, depression; idp, interdental plates; mg, Meckelian groove. Scale bar = 5 cm.
Figure 3
Figure 3. Surface model of the left dentary of SMA 0005 with anterior and posterior CT sections.
(A) Posterior end of the left dentary in lateral view, showing signs of alveoli of dentary teeth. (B) Anterior end of the left dentary in mirrored medial view, showing dense bone matrix with no sign of alveoli. Abbreviations: adt, artificial dentary tooth with an internal wire; alv, alveoli; db, dense bone. Scale bar = 5 cm.
Figure 4
Figure 4. Fourth cervical of SMA 0005.
(A) Fourth cervical in dorsal view, showing a pathologic exostosis (possible osteochondroma) between the prezygapophyses. (B) Possible osteochondroma from anterior view marked by a dotted line. (C) Fourth cervical in posterior view, showing another exostosis (possible inflammatory ossification) above the neural canel. (D) Possible inflammatory ossification (dotted line) in close-view. (E) Possible inflammatory ossification (dotted line) in posterolateral view. Abbreviations: ep, epipophysis; ex, exostosis; nc, neural canal; ns, neural spine; poz, postzygapophysis; prz, prezygapophysis; tp, transverse process. Scale bar = 5 cm.
Figure 5
Figure 5. Fifth cervical of SMA 0005.
(A) Fifth cervical in left lateral view, showing the callus and the fracture (dotted line) at the base of the left postzygapophysis. (B) Fifth cervical in lateral view in posterolateral view. (C) Callus (dashed line) and fracture (dotted line) in laterodorsal view. (D) Callus (dashed line) and fracture (dotted line) in lateroventral view. (E) Callus (dashed line) and fracture (dotted line) in oblique posterolateral view. Structures of minor interest in the neural arch are colored transparently for cover. Abbreviations: ca, callus; ep, epipophysis; ns, neural spine; poz, postzygapophysis; pp, parapophysis; prz, prezygapophysis; tp, transverse process. Scale bar = 5 cm.
Figure 6
Figure 6. CT section through the callus of the fifth cervical of SMA 0005.
(A) Fifth cervical in left lateral view, showing the progression of the CT section through the callus. (B1) Surface model of the fifth cervical in posterior view, showing the section through the neural arch at the anterior level of the callus. (B2) Tomogram of the anterior section. (C1) Surface model of the fifth cervical in posterior view, showing the section through the neural arch at the posterior level of the callus. (C2) Tomogram of the posterior section. The CT data show that the callus at the left postzygapophysis is made of dense bone, while the right postzygapophysis is pneumatised by a large internal cavity. Abbreviations: ca, callus; L, left side; ns, neural spine; poz, postzygapophysis; pn, pneumatization; prz, prezygapophysis. Scale bar = 5 cm.
Figure 7
Figure 7. Pathologic ribs and cortical traces in SMA 0005.
(A) Fourth cervical rib from the right side with fracture (dotted line). (B) Seventh dorsal rib from the left side with fracture (dotted line). (C) Cortical traces in the right ischium. (D) Cortical traces in the left scapula. Abbreviations: ca, callus. Scale bar = 2 cm.
Figure 8
Figure 8. Pathologic scapula of SMA 0005.
(A) Left scapula in anterolateral view, showing the fractured area of the scapula blade (dashed line). (B) Fracture (dotted line) in dorsal view. (C) Fracture (dotted line) in ventral view. (D) Tomogram of the scapula, showing that only the fracture ends constitute a fused bridge between the fracture elements (arrows), which is consistent with a pseudarthrosis. Abbreviations: co, coracoid; cf, coracoid foramen; fr, fracture; gl, glenoid facet; sc, scapula blade. Scale bar = 5 cm.
Figure 9
Figure 9. Left and right humerus of SMA 0005.
(A) Distal portion of the left humerus in anteromedial view, showing idiopathic pathologies. The pathologies contain an irregular cortical texture with numerous depressions (arrows), a deep oblique groove toward the anterior aspect of the medial side (dotted lines), and two sharp, trough-like marks on the ventral surface of the ulnar condyle (dashed lines). (B) Distal portion of the right humerus in anterior view. Abbreviations: epc, epicondyle; hu, humerus; ul, ulna; uc, ulnar condyle. Scale bar = 5 cm.
Figure 10
Figure 10. Ischium of SMA 0005.
(A) Both Ischia in anterolateral view, showing the oblique fracture at the shaft of the right ischium. (B) Interfragmentary gap (arrow) of the right ischium in anterior view. (C) Fracture (dotted line) of the right ischium in anterolateral view. (D) Fracture (dotted line) of the right ischium in lateral view. (E) Fracture (dotted line) of the right ischium in posterior view. Abbreviations: fr, fracture; ib, ischial boot; ip, ischial peduncle; op, obturator process; pp, pubic peduncle. Scale bar = 5 cm.
Figure 11
Figure 11. Pathologic phalanges in SMA 0005.
(A) Left pedal phalanx II-2 from lateral view, showing the callus and the reduced extensor tubercle. (B) Left pedal phalanx II-2 from ventral view, showing the callus and multiple small depressions (arrows). (C) Left pedal phalanx II-2 from medial view, showing the callus and two large depressions (arrows), possibly indicating a secondary infection of the bone. (D) Left pedal phalanx II-2 from dorsal view, showing the callus and one of the two large depressions on the medial side. (E) Right pedal phalanx II-2 from mediodorsal view, showing the normal condition and size of the extensor tubercle. (F) Left pedal phalanx IV-1 in lateral view, showing two idiopathic bulbous swellings (dotted lines). Abbreviations: ca, callus; et, extensor tubercle. Scale bar = 5 cm.

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Grant support

This study was supported by the Volkswagen Foundation under grant I/84 640 (to Oliver W.M. Rauhut). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.

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