Research Article: Pathological survey on Temnodontosaurus from the Early Jurassic of southern Germany

Date Published: October 24, 2018

Publisher: Public Library of Science

Author(s): Judith M. Pardo-Pérez, Benjamin P. Kear, Heinrich Mallison, Marcelo Gómez, Manuel Moroni, Erin E. Maxwell, Ulrich Joger.

http://doi.org/10.1371/journal.pone.0204951

Abstract

Paleopathologies document skeletal damage in extinct organisms and can be used to infer the causes of injury, as well as aspects of related biology, ecology and behavior. To date, few studies have been undertaken on Jurassic marine reptiles, while ichthyosaur pathologies in particular have never been systematically evaluated. Here we survey 41 specimens of the apex predator ichthyosaur Temnodontosaurus from the Early Jurassic of southern Germany in order to document the range and absolute frequency of pathologies observed in this taxon as a function of the number of specimens examined. According to our analysis, most observed pathologies in Temnodontosaurus are force-induced traumas with signs of healing, possibly inflicted during aggressive interactions with conspecifics. When the material is preserved, broken ribs are correlated in most of the cases with traumas elsewhere in the skeleton such as cranial injuries. The range of cranial pathologies in Temnodontosaurus is similar to those reported for extinct cetaceans and mosasaurs, which were interpreted as traces of aggressive encounters. Nevertheless, Temnodontosaurus differs from these other marine amniotes in the absence of pathologies in the vertebral column, consistent with the pattern previously documented in ichthyosaurs. We did not detect any instances of avascular necrosis in Temnodontosaurus from southern Germany, which may reflect a shallow diving life style. This study is intended to provide baseline data for the various types of observed pathologies in large ichthyosaurs occupying the ‘apex predator’ niche, and potentially clarifies aspects of species-specific behavior relative to other ichthyosaurs and marine amniotes.

Partial Text

Ichthyosaurs a group of highly specialized Mesozoic were marine reptiles that ranged from the Early Triassic to the early Late Cretaceous (250–90 Ma) [1]. Large-bodied macrophagous forms appeared early in the evolutionary history of the group (Middle Triassic: [2], and ichthyosaurs continued to occupy apex predator niches until the end of the Early Jurassic [3]; in later time periods this niche was occupied by large pliosaurids. Temnodontosaurus is a classic example of a large-bodied predatory ichthyosaur from the Early Jurassic [1]. The genus included some macrophagous species [4], characterized by skulls and jaws over 1 m in length, with the largest being over 1.9 m long [5]. The total body length of the largest Temnodontosaurus is estimated at up to 15 m (reviewed by [5]). Gastric contents indicate predation on marine reptiles, including other ichthyosaurs and cephalopods [6].

We surveyed 39 specimens of Temnodontosaurus from six collections (S1 Table), spanning the Pliensbachian to Toarcian of southwestern Germany. Each specimen was macroscopically examined in detail using a magnifying lens. We measured the total length of premaxilla, dentary, humerus, and femur to obtain an approximate size estimate for individuals and indirectly control for ontogenetic effects. We also recorded the state of preservation and preparation for each specimen. In the cases where pathologies where observed, we documented and described them according to it appearance, texture, dimensions and anatomical location.

Most of the specimens from the collections are strongly taphonomically compressed. They are typically prepared as flat panel mounts with large sections of the skeleton still embedded in matrix. The only exception are remains recovered from the Jurensismergel Formation, housed at the Urwelt-Museum Oberfranken, which are preserved in three dimensions. We provide a detailed description of the three-dimensionally preserved and recently collected and prepared U-MO no. 14 [14], to illustrate the range of pathologies observed as well as post-mortem artifacts. We also provide information on other pathological specimens, focusing only on unambiguous pathological structures.

We noted perimortem scratches possibly attributable to scavenging by sharks, discolorations caused by postmortem epibiont encrustation, depressions attributed to deformation and compression, and tool marks caused during excavation and preparation. However, we also note a wide range of traumatic injuries to the skeleton in Temnodontosaurus, concentrated in the skull, ribs and pectoral girdle/forefins. This detailed atlas and analysis of the types of pathologies observed in the Early Jurassic apex predator Temnodontosaurus will provide a guide with which to distinguish pathologies from peri- or postmortem skeletal damage.

 

Source:

http://doi.org/10.1371/journal.pone.0204951

 

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