Bone disease found in an early amniote from the Permian

Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniote
Yara Haridy, Florian Witzmann, Patrick Asbach, Robert R. Reisz
Summarized by Time Scavenger collaborator Jen Bauer

Brief Summary: This study examined bone remodeling (how the bone fixes itself after disease or other events) in an amniote (animals such as birds, reptiles, and mammals) from the early Permian (289 million years ago). Through detailed measurements and 3D internal and external modeling of the bone the authors determined that this animal suffered from a metabolic bone disease similar to Paget’s disease in humans. This is the oldest evidence of  viral infection in the fossil record!

What data were used? The authors were exploring two fused (pathological or abnormal) and one normal vertebra. Vertebrae are the interlocking bones that make up your spinal column. They were able to identify both specimens as being caudal vertebraes (vertebrae of the tail area) of a varanopid animal. For comparison, the authors also examined several other non-pathological caudal vertebrae of a similar animal for comparison to this abnormal specimen. 

Varanopids are an extinct group of amniotes (animals that have a membrane around their embryos) that looked similar to extant (still alive) monitor lizards. The veranopids were alive from the late Carboniferous to the late Middle Permian (~300-260 million years ago). 

Figure 1. External feature of the diseased varanopid vertebrae (specimen number MB.R.5931). (a) Generalized diagram with normal vertebrae in blue and the pathological (diseased) vertebrae in orange. (b-f) different views of the specimen. Abbreviations: as, articular surface; fz, fusion zone; gn, growth nodule; hp, haemapophyses; irg, irregular groove; ivf, intervertebral foramen; na, neural arch; nc, neural canal; ntc, notochordal canal; poz, postzygapophysis fused; vph, ventral processes of haemapophyses. Refer to Figure 2 in paper as this is a direct capture but with a more technical caption. Scale bar = 5 mm.

Methods: Measurements of the specimens were done using ImageJ, a freely available imaging editing program that can be used for a variety of projects. The idea was to measure different thickness of the bones. There is bone repair due to the disease and the author’s were quantifying the difference in the diseased bone compared to the thicknesses of normal (non-diseased) bones. Specimens were also CT scanned at the Museum für Naturkunde Berlin and the models were visualized and analyzed in Volume Graphics Studio MAX 2.2. Computed Tomography (CT) allows for scientists to look inside the bones without cutting them into pieces, making it a non-destructive visualization technique. This is particularly helpful for looking at any internal bone structure and any possible abnormalities in the external or internal structure. 

Results: The pathological (diseased) specimen is two vertebral centra completely fused together, with no trace of a previous suture between the bones. The internal bone structure is slightly different. The notochordal canal (where the notochord resides) is uniform where there is some tapering the non-pathological specimens. The micro-CT scans reveal the outer cortex of the vertebrae has been dramatically altered through bone remodeling and growth causing features to be thickened and misshapen.

Why is this study important? The oldest recorded case of Paget disease of bone (PBD)-like alteration was in a Late Jurassic (~150 million years ago) vertebrate of a dinosaur, so this new find pushes the interpretation back to the Permian (~290 million years ago) – a shift of 140 million years back! The other major finding is about how this disease affects animals. Certain organisms are susceptible to certain diseases more than others. This bone disease has been found in primates (including humans), extant (living) dogs, lizards and snakes, and a dinosaur. The new finding in a varanopid furthers the spread across the tree of life, meaning that the disease must have evolved in early amniotes before the split between the split of synapsids (mammals) and diapsids (reptiles and birds). 

Evolutionary history of groups that have recorded evidence of the disease. Modified from figure 5 of the paper.

Citation: Haridy Y, Witzmann F, Asbach P, Reisz RR (2019) Permian metabolic bone disease revealed by microCT: Paget’s disease-like pathology in vertebrae of an early amniote. PLoS ONE 14(8): e0219662.

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