Evidence of Spondyloarthropathy in the Spine of a Phytosaur (Reptilia: Archosauriformes) from the Late Triassic of Halberstadt, Germany

Abstract

Pathologies in the skeleton of phytosaurs, extinct archosauriform reptiles restricted to the Late Triassic, have only been rarely described. The only known postcranial pathologies of a phytosaur are two pairs of fused vertebrae of “Angistorhinopsis ruetimeyeri” from Halberstadt, Germany, as initially described by the paleontologist Friedrich von Huene. These pathologic vertebrae are redescribed in more detail in this study in the light of modern paleopathologic methods. Four different pathologic observations can be made in the vertebral column of this individual: 1) fusion of two thoracic vertebral bodies by new bone formation within the synovial membrane and articular capsule of the intervertebral joint; 2) fusion and conspicuous antero-posterior shortening of last presacral and first sacral vertebral bodies; 3) destruction and erosion of the anterior articular surface of the last presacral vertebra; and 4) a smooth depression on the ventral surface of the fused last presacral and first sacral vertebral bodies. Observations 1–3 can most plausibly and parsimoniously be attributed to one disease: spondyloarthropathy, an aseptic inflammatory process in which affected vertebrae show typical types of reactive new bone formation and erosion of subchondral bone. The kind of vertebral shortening present in the fused lumbosacral vertebrae suggests that the phytosaur acquired this disease in its early life. Observation 4, the smooth ventral depression in the fused lumbosacral vertebrae, is most probably not connected to the spondyloarthropathy, and can be regarded as a separate abnormality. It remains of uncertain origin, but may be the result of pressure, perhaps caused by a benign mass such as an aneurysm or cyst of unknown type. Reports of spondyloarthropathy in Paleozoic and Mesozoic reptiles are still exceptional, and our report of spondyloarthropathy in fossil material from Halberstadt is the first unequivocal occurrence of this disease in a Triassic tetrapod and in a phytosaur.

Sacral anatomy of the phytosaur Smilosuchus adamanensis, with implications for pelvic girdle evolution among Archosauriformes

“…), and that the faceted morphology of the dorsosacral is not the result of a pathological fusion similar to that reported by Witzmann et al. ().…”

“…The last presacral and first primordial sacral of a specimen of ‘Angistorhinopsis ruetimeyeri’ with spondyloarthropathy show fusion to such a high degree that the contact between these two elements was obliterated, though no fusion is present between the first and second primordial sacrals (Witzmann et al. ). It is clear from the CT scan of PEFO 34852 that the two primordial sacrals of this specimen are unfused (Fig.…”

“…; Witzmann et al. ) and is almost exclusively from the Late Triassic (but see Li et al. and Stocker et al.…”

Neural and endocranial anatomy of Triassic phytosaurian reptiles and convergence with fossil and modern crocodylians

“…Evidence from taphonomy and ichnofossils suggests that, similar to crocodylians, phytosaurs were generally aquatic or semi-aquatic (Buffetaut, 1993; Renesto & Lombardo, 1999), but were also capable of terrestrial locomotion (Parrish, 1986). Although phytosaurs and the earliest fossil crocodylians are significantly separated temporally (by about 100 million years) and phylogenetically, gross morphological similarities between the two groups have often been cited as evidence for ecological and behavioural convergence (Camp, 1930; Anderson, 1936; Hunt, 1989; Hungerbühler, 2002; Witzmann et al, 2014). However, phytosaurs are defined by a number of osteological characters that differentiate them from crocodylians, such as an elongate premaxilla, the caudal position of the external nares (which is placed close to the orbit in phytosaurs, rather than at the tip of the rostrum), and the absence of a secondary palate.…”

Pathology in a Permian parareptile: congenital malformation of sacral vertebrae

“…While detailed morphological descriptions of ankylosed vertebrae in pareiasaurs are lacking, the presence of a distinctly swollen bulge on the ventral surface between the centra of S1 and S2 in NHCC LB337 suggests a pathology beyond typical ankylosis. This ventral bulge is reminiscent of reports of pathological spondyloarthropathy in extant and extinct reptiles like lizards, crocodiles, and dinosaurs (Rothschild, ; Witzmann et al ., ; Rothschild & Everhart, ; Xing et al ., ). Given the frequency of spondyloarthropathy in reptiles, Witzmann et al .…”