Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic (Early Toarcian). Its fossils have been found in Mecklenburg-Vorpommern, northern Germany. Emausaurus is the only known Toarcian thyreophoran and it is also the only dinosaur from the zone of the same age with a formal name.
Discovery and naming[]
The type and only species, E. ernsti, was named and described by Harmut Haubold in 1990. The generic name is composed of an acronym of Ernst Moritz Arndt University of Greifswald and Greek sauros/σαυρος (lizard). The specific name is derived from the name of geologist Werner Ernst, who acquired the fossil, holotype SGWG 85, in the summer of 1963 from foreman Werner Wollin at a loampit near Grimmen, in strata dating from the Toarcian. It is known by the right side of the skull, the right lower jaw, caudal vertebrae, neural arches, a radius, a metatarsal, a claw, fragments of ribs, scutes and plates, known as EMAU SGWG 85.
Description[]
Emausaurus was probably a semibipedal to quadrupedal animal, being covered in an armor of osteoderms across the body. Like other thyreorphora, it probably was an herbivore, specifically a low dwelling one, with a diet associated with ground flora, such as Cycads and Bennnetitales. The body length of the holotype of Emausaurus has been estimated at around 2.5 m, with a weight of 70–90 kg. This was based on a juvenile individual though; adult length has been estimated at three to four metres, with a weight up to 240 kg. Most of the reconstruction has been based on Scelidosaurus, although it is possible that Emausaurus was a more bipedal animal, as some of the young specimens of Scelidosaurus were thought to be. Adult forms probably were more quadrupedal, hovewer, the type specimen is too incomplete to infer a mode of locomotion. Armor includes three conical scutes and one tall, spiny element. David Norman in 2019 examined the morphology of Scelidosaurus, comparing it with Emausaurus. In Emausaurus the maxilla has, overall, a similar morphology to that seen in Scelidosaurus. The disarticulated maxilla of Emausaurus exhibits an anteromedially directed robust process with which it met its counterpart in the midline, creating a wedge-like structure, with no obvious offset between the alveolar margins. In Emausaurus the structure of the frontals is not well preserved. In outline, its proportions resemble those of Scelidosaurus, but the same is true of many Ornithischia. The lacrimal bone of Emausaurus is incomplete, but includes a long, curved jugal process that evidently wrapped itself around the anterior tip of the jugal. So little is known of the postcranium Emausaurus, recovering parts like a multipartite odontoid (sutured to the axis centrum), similar to that of Scelidosaurus. Emausaurus has a series of assigned Osteoderms, but lacks like Scutellosaurus ‘scapular osteoderms’. The major series of osteoderms found appear to come from the tail or the dorsal section.
Classification[]
Cladistic analyses have shown that Emausaurus was a basal member of the Thyreophora, more derived than Scutellosaurus, but less than Scelidosaurus. Scelidosaurus, Emausaurus and Scutellosaurus cluster at the base of most trees because they can be scored for only a restricted number of anatomical characters. The cladistic status of the specimen is relatively controversial due to its young nature. Clearly it is a member of the Thyreophora, but its position may be modified if an adult specimen is found. Emausaurus may be more derived than Scelidosaurus, or even be a sister taxon to Stegosauria. The general consensus has established Emausaurus as a non-eurypodan stem thyreophoran, along with Scutellosaurus and Scelidosaurus reinforced by almost all subsequent systematic reviews of ornithischian–thyreophoran relationships. Being Emausaurus and Scutellosaurus more basal than Scelidosaurus. Emausaurus has been put on an outgroup to Ankylosauria, with Scelidosaurus and the basal stegosaur Huayangosaurus. Vickaryous et al. (2004), did the default phylogenetic analysis for ingroup ankylosaurs, due to including cranial and postcranial characters, a wide range of taxa and made no in-group relationships, although this analysis used the holotype Lesothosaurus and Huayangosaurus as outgroups, ignoring Scelidosaurus and Emausaurus. In 2020, Norman found that Scelidosaurus, along with Scutellosaurus and Emausaurus, are positioned on the stem of Ankylosauria, rather than on the stem of Thyreophora, with Emausaurus as the basal sister-taxon to Scelidosaurus. This is because Emausaurus possesses a dorsal margin of the dentary sinuous in lateral view and neither elongated nor squat proportions of metacarpal 1 ‘medium’. Alternatively, Emausaurus may be a basal sister-taxon to Scutellosaurus, but taking the similarities between Emausaurus and Scelidosaurus this is less likely. Yet this was contested the same year with the description of +70 specimens of Scutellosaurus, where Emausaurus was found as sister taxon of this last one and both with strong evidence for a phylogenetic placement within Thyreophora but outside of Thyreophoroidea.
Norman's cladogram is:
Thyreophora |
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