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Emausaurus

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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, as well as the only dinosaur from the zone of the same age with a formal name.[1]

Emausaurus
Temporal range: Early Toarcian
~183–182 Ma
↓
Tenuicostatum
Restoration of Emausaurus being attacked by an unnamed theropod belonging to the Orionides
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Clade: Dinosauria
Clade: †Ornithischia
Clade: †Genasauria
Clade: †Thyreophora
Genus: †Emausaurus
Haubold, 1990
Species:
†E. ernsti
Binomial name
†Emausaurus ernsti
Haubold, 1990

Discovery and naming

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The type and only species, E. ernsti, was named and described by Hartmut Haubold in 1990.[2] The generic name is composed of an acronym of Ernst Moritz Arndt University of Greifswald and the Greek sauros/σαυρος (lizard). The specific name is derived from the name of geologist Werner Ernst, who acquired the holotype specimen, 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.[1]

Description

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Size compared to a human

Emausaurus was probably a semi-bipedal to quadrupedal animal, being covered in an armor of osteoderms across the body. Like other thyreophorans, it probably was an herbivore, specifically a low dwelling one, with a diet associated with ground flora, such as cycads and Bennettitales.[1] The body length of the holotype juvenile individual of Emausaurus 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 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. 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 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.[8] Very little is known of the postcranium Emausaurus, recovering parts like a multipartite odontoid (sutured to the axis centrum), similar to that of Scelidosaurus.[9] 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.[10]

Classification

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Cladistic analyses have shown that Emausaurus was a basal member of the Thyreophora, more derived than Scutellosaurus, but less than Scelidosaurus.[11] Scelidosaurus, Emausaurus, and Scutellosaurus 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 than Scelidosaurus, or even be a sister taxon to Stegosauria.[13] 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.[14] Being Emausaurus and Scutellosaurus more basal than Scelidosaurus.[14] Emausaurus has been put on an outgroup to Ankylosauria, with Scelidosaurus and the basal stegosaur Huayangosaurus.[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 holotype Lesothosaurus and Huayangosaurus as outgroups, ignoring Scelidosaurus and Emausaurus.[14] 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.[16] 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'.[16] Alternatively, Emausaurus may be a basal sister-taxon to Scutellosaurus, but taking the similarities between Emausaurus and Scelidosaurus this is less likely.[16] 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.[6] A cladogram following the results of Norman (2020) is shown below:

 Thyreophora 

Paleoecology

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Emausaurus has a sinuous jaw profile, more advanced in ankylosauromorphans, unlike the rectilinear morphology seen in the more basal genus Scutellosaurus.[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 bennetites and cycads, abundant on the coeval Sorthat 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 ungulal 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 of Scelidosaurus.[16] A series of characters that together are suggestive of graviportality and quadrupedality, making Emausaurus 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 with Scutellosaurus are more likely and recommend to not infer bipedality or quadrupedality as the taxon is incomplete.[6]

Paleoenvironment

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The holotype of Emausaurus was found in the so-called "Emausaurus type site", which represents a shale ingression from the Ciechocinek Formation, dated from the Lower Toarcian (Tenuicostatum).[18] The site is a boundary composed of bituminous shale,[2] representing an ancient seashore-influenced environment, probably lagoonal, and contemporaneous with the Posidonia Shale and specifically the Sorthat Formation of the same region. Fossil wood has been found in the same location, including driftwood and others related to the Araucariaceae, present in other European environments of Toarcian age.[2] The invertebrate fauna consists of insects, bivalves, sea snails and ammonites (Tiltoniceras, Eleganticeras and Lobolytoceras).[2] The vertebrate fauna is also diverse, with fossils of the fish genera Saurorhynchus,[19] Grimmenichthys,[20] and Grimmenodon.[21] Reptile fossils include indeterminate ichthyosaurs and plesiosaurs, rhomaleosaurid plesiosaurs, indeterminate mesoeucrocodylians (probably related to Sichuanosuchus), indeterminate thalattosuchians,[22] a possible pterosaur,[23] and theropod and gravisaurian sauropod material, the latter related to the north African Tazoudasaurus.[24] A later discovery includes a thyreophoran osteoderm, interpreted as representing a lateral of the neck or shoulder region.[5]

References

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  1. ^ a b c d e Haubold, H. (1991). "Der Greifswalder Dinosaurier Emausaurus". Fundgrube. 27 (2): 51–60.
  2. ^ a b c d Haubold, H. (1990). "Ein neuer Dinosaurier (Ornithischia, Thyreophora) aus dem Unteren Jura des nördlichen Mitteleuropa". Revue de Paléobiologie. 9 (1): 149–177. Retrieved 24 October 2021.
  3. ^ Holtz, Thomas R. Jr. (2012). Dinosaurs: The Most Complete, Up-to-Date Encyclopedia for Dinosaur Lovers of All Ages (PDF). Winter 2011 Appendix
  4. ^ Paul, Gregory S. (2016). The Princeton Field Guide to Dinosaurs. Princeton University Press. p. 242. ISBN 978-1-78684-190-2. OCLC 985402380.
  5. ^ a b Schade, Marco; Ansorge, Jörg (2022). "New thyreophoran dinosaur material from the Early Jurassic of northeastern Germany". Paläontologische Zeitschrift. 96 (1–14): 303–311. Bibcode:2022PalZ...96..303S. doi:10.1007/s12542-022-00605-x. S2CID 246040635.
  6. ^ a b c Breeden III, B. T; Raven, T. J; Butler, R. J.; Rowe, T. B.; Maidment, S. C. (2021). "The anatomy and palaeobiology of the early armoured dinosaur Scutellosaurus lawleri (Ornithischia: Thyreophora) from the Kayenta Formation (Lower Jurassic) of Arizona". Royal Society Open Science. 8 (7): 201676. Bibcode:2021RSOS....801676B. doi:10.1098/rsos.201676. PMC 8292774. PMID 34295511.
  7. ^ Norman, D.B.; Witmer, L.M. & Weishampel, D.B. (2004). "Basal Thyreophora". In Weishampel, D.B.; Dodson, P. & Osmólska, H. (eds.). The Dinosauria, 2nd Edition. University of Californian Press. pp. 335–342. ISBN 0-520-24209-2.
  8. ^ Norman, D. B. (2019). "Scelidosaurus harrisonii from the Early Jurassic of Dorset, England: cranial anatomy". Zoological Journal of the Linnean Society. 188 (1): 1–81. doi:10.1093/zoolinnean/zlz074. Retrieved 17 November 2021.
  9. ^ Norman, D. B. (2019). "Scelidosaurus harrisonii from the Early Jurassic of Dorset, England: postcranial skeleton". Zoological Journal of the Linnean Society. 189 (1): 47–157. doi:10.1093/zoolinnean/zlz078. Retrieved 17 November 2021.
  10. ^ Norman, D. B. (2020). "Scelidosaurus harrisonii from the Early Jurassic of Dorset, England: the dermal skeleton". Zoological Journal of the Linnean Society. 190 (1): 1–53. doi:10.1093/zoolinnean/zlz085. Retrieved 17 November 2021.
  11. ^ Sereno, P. C. (1997). "The origin and evolution of dinosaurs" (PDF). Annual Review of Earth and Planetary Sciences. 25 (1): 435–489. Bibcode:1997AREPS..25..435S. doi:10.1146/annurev.earth.25.1.435.
  12. ^ Butler, R.J.; Upchurch, P.; Norman, D.B. (2008). "The phylogeny of the ornithischian dinosaurs". Journal of Systematic Palaeontology. 6 (1): 1–40. Bibcode:2008JSPal...6....1B. doi:10.1017/S1477201907002271. S2CID 86728076.
  13. ^ Stumpf, S.; Meng, S. (2013). "Dinosaurier aus Nordostdeutschland: Verschleppt". Biologie in unserer Zeit. 43 (6): 362–368. doi:10.1002/biuz.201310521. S2CID 83200480. Retrieved 24 October 2021.
  14. ^ a b c Coombs, W.P.; Maryańska, T. (1990). "Ankylosauria". The Dinosauria. 1 (1): 456–483.
  15. ^ Witmer, Hill R.V.; Norell, L.M. (2003). "A new specimen of Pinacosaurus grangeri (Dinosauria: Ornithischia) from the Late Cretaceous of Mongolia: ontogeny and phylogeny of ankylosaurs". American Museum Novitates (1): 1–29.
  16. ^ a b c d e f g h i Norman, D. B. (2020). "Scelidosaurus harrisonii (Dinosauria: Ornithischia) from the Early Jurassic of Dorset, England: biology and phylogenetic relationships". Zoological Journal of the Linnean Society. 192 (1): 1–86. Retrieved 17 November 2021.
  17. ^ McElwain, J. C.; Wade-Murphy, J.; Hesselbo, S. P. (2005). "Changes in carbon dioxide during an oceanic anoxic event linked to intrusion into Gondwana coals". Nature. 435 (7041): 479–482. Bibcode:2005Natur.435..479M. doi:10.1038/nature03618. PMID 15917805. S2CID 4339259. Retrieved 8 September 2021.
  18. ^ Ernst, W. (1967). "Die Liastongrube Grimmen. Sediment, Makrofauna und Stratigraphie". Ein Überblick Geologie. 16 (1): 550–569.
  19. ^ Maxwell, E. E.; Stumpf, S. (2017). "Revision of Saurorhynchus (Actinopterygii: Saurichthyidae) from the Early Jurassic of England and Germany". European Journal of Taxonomy (321): 1–29. doi:10.5852/ejt.2017.321. Retrieved 24 October 2021.
  20. ^ Konwert, M.; Hörnig, M. (2018). "Grimmenichthys ansorgei, gen. et sp. nov. (Teleostei, "Pholidophoriformes"), and other "pholidophoriform" fishes from the early Toarcian of Grimmen (Mecklenburg-Western Pomerania, Germany)". Journal of Vertebrate Paleontology. 38 (3): 1–16. doi:10.1080/02724634.2018.1451872. hdl:11336/84457. S2CID 90344418. Retrieved 24 October 2021.
  21. ^ Stumpf, S.; Ansorge, J.; Pfaff, C; Kriwet, J. (2017). "Early Jurassic diversification of pycnodontiform fishes (Actinopterygii, Neopterygii) after the end-Triassic extinction event: evidence from a new genus and species, Grimmenodon aureum". Journal of Vertebrate Paleontology. 37 (4): e1344679. Bibcode:2017JVPal..37E4679S. doi:10.1080/02724634.2017.1344679. PMC 5646184. PMID 29170576.
  22. ^ Stumpf, Sebastian (2017). A synoptic review of the vertebrate fauna from the "Green Series"(Toarcian) of northeastern Germany with descriptions of new taxa: A contribution to the knowledge of Early Jurassic vertebrate palaeobiodiversity patterns (PDF) (PhD Thesis). Greifswald University. pp. 1–47. Retrieved 9 September 2021.
  23. ^ Schade, Marco; Ansorge, Jörg (2024). "Enigmatic fragment possibly marks the first pterosaur record from the Lower Toarcian of Grimmen, NE Germany". PalZ. doi:10.1007/s12542-024-00698-6.
  24. ^ Stumpf, Sebastian; Ansorge, Jörg; Krempien, Wilfried (2015). "Gravisaurian sauropod remains from the marine late Early Jurassic (Lower Toarcian) of North-Eastern Germany". Geobios. 48 (3): 271–279. Bibcode:2015Geobi..48..271S. doi:10.1016/j.geobios.2015.04.001. Retrieved 30 July 2021.
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