| Emausaurus | |
|---|---|
 | |
| Dentary bone ofEmausaurus ernsti | |
Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Class: | Reptilia |
| Clade: | Dinosauria |
| Clade: | †Ornithischia |
| Clade: | †Genasauria |
| Clade: | †Thyreophora |
| Genus: | †Emausaurus Haubold, 1990 |
| Species: | †E. ernsti |
| Binomial name | |
| †Emausaurus ernsti Haubold, 1990 | |
Emausaurus is agenus ofthyreophoran or armoreddinosaur from theEarly Jurassic (EarlyToarcian). Its fossils have been found in theLehmhagen Member, inMecklenburg-Vorpommern, northernGermany.Emausaurus is the only knownToarcian thyreophoran, as well as the only dinosaur from the zone of the same age with a formal name.[1]
Thetype and only species,E. ernsti, was named and described byHartmut Haubold in 1990.[2] Thegeneric name is composed of anacronym ofErnst Moritz Arndt University of Greifswald and theGreeksauros/σαυρος (lizard). Thespecific name is derived from the name of geologist Werner Ernst, who acquired theholotype specimen,SGWG 85, in the summer of 1963 from foreman Werner Wollin at a loam pit nearGrimmen, in strata dating from theToarcian. 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.[1]
Emausaurus was probably a semi-bipedal to quadrupedal animal, being covered in an armor ofosteoderms across the body. Like other thyreophorans, it probably was an herbivore, specifically a low dwelling one, with a diet associated with ground flora, such ascycads andBennettitales.[1] The body length of the holotype juvenile individual ofEmausaurus has been estimated at 2–2.5 m (6.6–8.2 ft), with a body mass of 50–90 kg (110–200 lb).[3][4][1] The adult length has been estimated at 3–4 m (9.8–13.1 ft), with a body mass up to 240 kg (530 lb).[1] Some recent data suggest the holotype may be from a subadult rather than a juvenile.[5] Most of the reconstruction has been based onScelidosaurus, although it is possible thatEmausaurus was a more bipedal animal, as some of the young specimens ofScelidosaurus were thought to be. Adult forms probably were more quadrupedal. Unfortunately, the type specimen is too incomplete to infer a mode of locomotion.[6] Armor includes three conical scutes and one tall, spiny element.[7] In 2019, David Norman examined the morphology ofScelidosaurus, comparing it withEmausaurus. InEmausaurus, the maxilla has, overall, a similar morphology to that seen inScelidosaurus. The disarticulated maxilla ofEmausaurus 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. InEmausaurus, the structure of the frontals is not well preserved. In outline, its proportions resemble those ofScelidosaurus, but the same is true of manyOrnithischia. The lacrimal bone ofEmausaurus is incomplete, but includes a long, curved jugal process that evidently wrapped itself around the anterior tip of the jugal.[8]Very little is known of the postcraniumEmausaurus, recovering parts like a multipartite odontoid (sutured to the axis centrum), similar to that ofScelidosaurus.[9]Emausaurus has a series of assigned osteoderms, but lacks likeScutellosaurus 'scapular osteoderms'. The major series of osteoderms found appear to come from the tail or the dorsal section.[10]
Cladistic analyses have shown thatEmausaurus was a basal member of theThyreophora, more derived thanScutellosaurus, but less thanScelidosaurus.[11]Scelidosaurus,Emausaurus, andScutellosaurus cluster at the base of most trees because they can be scored for only a restricted number of anatomical characters.[12]The cladistic status of the specimen is relatively controversial due to its young nature. It is clearly a member of the Thyreophora, but its position may be modified if an adult specimen is found.Emausaurus may be more derived thanScelidosaurus, or even be a sister taxon toStegosauria.[13] The general consensus has establishedEmausaurus as a non-eurypodan stem thyreophoran, along withScutellosaurus andScelidosaurus reinforced by almost all subsequent systematic reviews of ornithischian–thyreophoran relationships.[14] BeingEmausaurus andScutellosaurus more basal thanScelidosaurus.[14]Emausaurus has been put on an outgroup to Ankylosauria, withScelidosaurus and the basal stegosaurHuayangosaurus.[15] 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 holotypeLesothosaurus andHuayangosaurus as outgroups, ignoringScelidosaurus andEmausaurus.[14] In 2020, Norman found thatScelidosaurus, along withScutellosaurus andEmausaurus, are positioned on the stem ofAnkylosauria, rather than on the stem ofThyreophora, withEmausaurus as the basal sister-taxon toScelidosaurus.[16] This is becauseEmausaurus possesses a dorsal margin of the dentary sinuous in lateral view and neither elongated nor squat proportions of metacarpal 1 'medium'.[16] Alternatively,Emausaurus may be a basal sister-taxon toScutellosaurus, but taking the similarities betweenEmausaurus andScelidosaurus this is less likely.[16] Yet this was contested the same year with the description of +70 specimens ofScutellosaurus, whereEmausaurus was found as sister taxon of this last one and both with strong evidence for a phylogenetic placement within Thyreophora but outside ofThyreophoroidea.[6] A cladogram following the results of Norman (2020) is shown below:
Emausaurus has a sinuous jaw profile, more advanced in ankylosauromorphs, unlike the rectilinear morphology seen in the more basal genusScutellosaurus.[16] The changes to the jaw are considered a series of modifications reflecting changes in the diet and evolution of the food processing of this dinosaur compared to its ancestors. It seems to be adapted to eat Coriaceous flora, such as bennettites and cycads, abundant on the coevalSorthat Formation, where probably this taxon lived.[17] 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.[16] The animal was covered in osteoderms, although the few found give no indication of how extensively they were distributed across the torso.[16]Emausaurus, based on the proportions of the preserved metacarpals that the forelimb shows adaptations for weight support, rather than grasping, having ungual phalanges that are conical and only slightly decurved.[16]The partially known proximal pedal phalanges are short and block-like, with near the same proportions seen in the pes ofScelidosaurus.[16] A series of characters that together are suggestive of graviportality and quadrupedality, makingEmausaurus a low roaming herbivore. Pseudo-bipedality is not discarded, with the animal able to reach slightly taller flora.[16] Later works however have criticised this assumption given the relationships withScutellosaurus are more likely and recommend to not infer bipedality or quadrupedality as the taxon is incomplete.[6]
The holotype ofEmausaurus was found in the so-called "Emausaurus type site", which represents a shale ingression from theLehmhagen Member, dated from the Lower Toarcian.[18] The site is a boundary composed of bituminous shale,[2] representing an ancient seashore-influenced environment, probably lagoonal, and contemporaneous with theSorthat Formation of the same region. Fossil wood has been found in the same location, includingdriftwood and others related to theAraucariaceae, present in other European environments of Toarcian age.[2] The invertebrate fauna consists of insects, bivalves, sea snails and ammonites (Tiltoniceras,Eleganticeras andLobolytoceras).[2] The vertebrate fauna is also diverse, with fossils of the fish generaSaurorhynchus,[19]Grimmenichthys,[20] andGrimmenodon.[21] Reptile fossils include indeterminateichthyosaurs andplesiosaurs,rhomaleosaurid plesiosaurs, indeterminatemesoeucrocodylians (probably related toSichuanosuchus), indeterminatethalattosuchians,[22] a possiblepterosaur,[23] and theropod andgravisaurian sauropod material, the latter related to the north AfricanTazoudasaurus.[24] A later discovery includes a thyreophoran osteoderm, interpreted as representing a lateral of the neck or shoulder region.[5]
Winter 2011 Appendix
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