Vrije Universiteit Brussel

Cases of pathological bone growth in Isanosaurus and Spinophorosaurus (Sauropoda)Jentgen, Benjamin Paul C; Stein, Koen; Fischer, Valentin

DOI:10.13140/RG.2.2.10914.27840

Publication date:2018

Document Version:Final published version

Link to publication

Citation for published version (APA):Jentgen, B. P. C., Stein, K., & Fischer, V. (2018). Cases of pathological bone growth in Isanosaurus andSpinophorosaurus (Sauropoda). Poster session presented at 5th International Palaeontological Congress, Paris,France. https://doi.org/10.13140/RG.2.2.10914.27840

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The histology of the long bone of sauropods appears uniform and conservative along the Sauropoda evolutionary tree. One of the main aspects of their bone histology is to exhibit a Fibrolamellar Complex (FLC) with circumferential vascularization in the cortex of their long bones. However, we report Radial Fibrolamellar bone (RFB) in the outer cortex of the humeri of a young adult Isanosaurus (Histological Ontogenetic Stage - HOS - 8) and an adult Spinophorosaurus (HOS 12). RFB is regarded as a fast-growing bone tissue and has been documented in a few dinosaurian taxa, but never

among Sauropoda. Its outermost position within the cortex raises questions, because such a rapidly apposited bone tissue would rather be expected in the inner cortex (corresponding to an early juvenile ontogenetic stage). Our thorough histological analysis of these specimens reveals some highly vascularized RFB yielding densely packed plump osteocyte lacunae that can even obscure the surrounding bone in both transverse and longitudinal sections. This osteocyte pattern is restricted to the RFB. Bone remodelling is more expressed in this cortical layer with denser secondary osteons than

more internally or externally. This contrasts with the other dinosaurian taxa affected by RFB which contains no secondary osteon in this bone tissue. The individual of Spinophorosaurus represents in Sauropoda the first occurrence of RFB buried in the outer cortex followed by a recovery of a ‘normal' FLC after this event meaning this individual survived for some time after its phase of accelerated growth. This sequence of widely distinct modes of bone apposition suggests that these specimens are pathological.

1. The RFB apposited in Isanosaurus and Spinophorosaurus humeri are the first cases reported within Sauropoda

2. The RFB apposition during slower growth stages and coinciding with precocious remodelling is probably pathological in nature. The humerus 2.38a of Spinophorosaurus is the first case of survival of a RFB growth impulse in Sauropoda

Abstract

Pathological Radial Fibrolamellar Bone (RFB): growth impulse and precocious remodelling

Jentgen-Ceschino B.1,*, Stein K.2 & Fischer V.1 *Corresponding author. e-mail : bjentgen@uliege.be 1: EDDyLab, University of Liège, Belgium 2: AMGC, Vrije Universiteit of Brussel, Belgium

Sampling by core drilling of 2 humeri: • CH8-66 (Isanosaurus, Nam Phong Fm., Late Triassic of Thailand[1]) • 2.38a (Spinophorosaurus, ‘Argiles de l’Irhazer’, Lower/Middle Jurassic of Niger[2])

Main histological features: • HOS 8 (young adult Isanosaurus) – 12 (adult Spinophorosaurus) • FLC in the inner to the outer cortex and RFB in the outer cortex: accelerated growing phase

during slowdown in growth. Spinophorosaurus recovers a ‘normal’ FLC after this event • Biomechanics: RFB triggers precocious remodelling

(microstructural weaknesses)

Conclusions Acknowledgements

‘Normal’ FLC

Outer RFB

Avascular ‘normal’ bone cap

[3]

Periosteal surface

RFB Cortex

Radial vascular canal

Weakness points: remodelling

[1] Buffetaut E. et al. (2000). Nature 407, 72-74. [2] Remes K. et al. (2009). PLoS ONE 4, e6924. doi: 10.1371/journal.pone.0006924 [3] de Margerie E. et al. (2004). The Journal of Experimental Biology 207, 869-879. doi: 10.1242/jeb.00841

Big, dense packs of plump

osteocyte lacunae

Some say growth’s painful Suddenly so fast, so odd That its nature’s doubtful When the pulse’s over There’s a spiny sauropod Whose bones are treasure to discover

1,0 mm

0,5 mm

0,5 mm

100,0 mm

CH8-66

0,5 mm

God dammit! I twisted my arm!

Again!

2.38a

1. Drill

2. Core

3. Thin sections