Emausaurus is a genus of thyreophoran or armored dinosaur from the Early Jurassic (Toarcian). Its fossils have been found in Mecklenburg-Vorpommern, northern Germany. Emausaurus is the only known Toarcian thyreorphoran 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 on a armor of osteoderms across the body. Like other thyreorphora, probably was hervivore, concretely a low dwelling one, with a diet more related 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 where more quadrupedal. 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 foun appear to come from the tail or the dorsal section.
Classification[]
Cladistic analyses showed 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 can change by the time, if an adult specimen is found. Emausaurus can be more derived than Scelidosaurus, or even be a sister taxon to Stegosauria. The major consensus has put 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. 7. 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. On 2020, Norman et al. by studying Scelidosaurus found that along Scutellosaurus and Emausaurus both 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 can be basal sister-taxon to Scutellosaurus, but taking the similarities between Emausaurus and Scelidosaurus is more unlikely. The Norman study is resumed on:
Paleoecology[]
Emausaurus has a sinuous jaw profile, more advanced in ankylosauromorphans, unlike the rectilinear morphology seen in the more basal genus Scutellosaurus. The changes on the jaw is considered a series of modifications due to changes on the Diet and evolution of the food procesation of this dinosaurs, where it seems to be adapted to eat Coriaceous flora, such as Bennetites and Cycads, abundant on the coeval Ciechocinek Formation Lublin Coal Basin and specially on the Sorthat Formation. The rest of the skeleton of this genus is poorly presented, with for example the vertebrae showing no evidence of the proportional changes in the height of the neural arches and spines seen on stegosaurs. The animal was covered on Osteoderms, altrougth the few found give no indication of how extensively they were distributed across the torso. Emausaurus, based on the proportions of the preserved metacarpals that the forelimb shows adaptations for weight support, rather than grasping, having ungulal phalanges that are conical and only slightly decurved. The partial known proximal pedal phalanges are short and block-like, with near the same proportions seen in the pes of Scelidosaurus. A series of characters that together are suggestive of graviportality and quadrupedality, maling Emausaurus a low roaming herbivore. Pseudo-Bipedality isn't discarded, with the genus able to reach slightly taller flora.
Paleoenvironment[]
The holotype of Emausaurus was found on the so-called "Emausaurus type site", that represents a shale ingression from the Posidonia Shale, dated from the Lower Toarcian (Tenuicostatum). Is is a boundary composed by bituminous shale, It represents an ancient seashore-influenced environment, probably lagoonal, and it is contemporaneous of the Ciechocinek Formation of the same region. Fossil wood has been found on the same location, including driftwood and other related to the Araucariaceae, present in other European environments of Toarcian age. Of the invertebrate fauna insects, bivalves, sea snails and ammonites (Genus Tiltoniceras, Eleganticeras and Lobolytoceras) have been found. The vertebrate fauna is also varied, with fossils of the fish genus Saurorhynchus, and the new genus Grimmenichthys and Grimmenodon. Reptile fossils include Ichthyosauria indet., indeterminate Plesiosauria, rhomaleosaurid plesiosaurs, indeterminate Mesoeucrocodylia (probably Goniopholididae), indeterminate Thalattosuchia and at least two gravisaurian sauropods.
Gallery[]
