Isaberrysaura
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''Isaberrysaura'' is a
genus Genus ( plural genera ) is a taxonomic rank used in the biological classification of extant taxon, living and fossil organisms as well as Virus classification#ICTV classification, viruses. In the hierarchy of biological classification, genus com ...
of
stegosauria Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...
n
ornithischian Ornithischia () is an extinct order of mainly herbivorous dinosaurs characterized by a pelvic structure superficially similar to that of birds. The name ''Ornithischia'', or "bird-hipped", reflects this similarity and is derived from the Greek st ...
dinosaur from the
Middle Jurassic The Middle Jurassic is the second epoch of the Jurassic Period. It lasted from about 174.1 to 163.5 million years ago. Fossils of land-dwelling animals, such as dinosaurs, from the Middle Jurassic are relatively rare, but geological formations co ...
Los Molles Formation The Los Molles Formation is a geologic formation of Early to Middle Jurassic age, located at northern and central part of Neuquén Basin at Mendoza Shelf in Argentina. It is overlain by the Niyeu–Lajas Formation.McIlroy et al., 2005 Descrip ...
of
Patagonia Patagonia () refers to a geographical region that encompasses the southern end of South America, governed by Argentina and Chile. The region comprises the southern section of the Andes Mountains with lakes, fjords, temperate rainforests, and gl ...
,
Argentina Argentina (), officially the Argentine Republic ( es, link=no, República Argentina), is a country in the southern half of South America. Argentina covers an area of , making it the second-largest country in South America after Brazil, th ...
. The genus contains a single species, ''I. mollensis'', described by Salgado ''et al.'' in 2017 from a single specimen. Although initially classified as a basal
neornithischia Neornithischia ("new ornithischians") is a clade of the dinosaur order Ornithischia. It is the sister group of the Thyreophora within the clade Genasauria. Neornithischians are united by having a thicker layer of asymmetrical enamel on the inside ...
n, subsequent analysis has allied it with the
Stegosauria Stegosauria is a group of herbivorous ornithischian dinosaurs that lived during the Jurassic and early Cretaceous periods. Stegosaurian fossils have been found mostly in the Northern Hemisphere, predominantly in what is now North America, Europe, ...
; the morphology of its skull resembles those of other members of the group.


Description

The teeth of ''Isaberrysaura'' are heterodont, with recurved premaxillary teeth and lanceolate maxillary and dentary teeth. In extant
iguanid The Iguanidae is a family of lizards composed of the iguanas, chuckwallas, and their prehistoric relatives, including the widespread green iguana. Taxonomy Iguanidae is thought to be the sister group to the collared lizards (family Crotaphy ...
lizard Lizards are a widespread group of squamate reptiles, with over 7,000 species, ranging across all continents except Antarctica, as well as most oceanic island chains. The group is paraphyletic since it excludes the snakes and Amphisbaenia alt ...
s, similar dentition is correlated with
omnivorous An omnivore () is an animal that has the ability to eat and survive on both plant and animal matter. Obtaining energy and nutrients from plant and animal matter, omnivores digest carbohydrates, protein, fat, and fiber, and metabolize the nutri ...
diets, indicating that ''Isaberrysaura'' might too have been omnivorous. ''Isaberrysaura'' is also estimated to have measured around long, making it of moderate size. The skull in particular is very unusual; it is estimated to be 52 cm long and 20 cm wide across the orbits, and it is almost as high as it is wide. The snout slopes anteroventrally from the posterodorsal corner of the infratemporal fenestra to what is seemingly the maxillary-premaxillary contact and the infratemporal fenestra is dorsoventrally deep. In contrast, the orbit is subcircular, not quite as dorsoventrally tall as anteroposteriorly long, smaller than the infratemporal fenestra, and only visible in lateral view. The anterolateral sector of the left supratemporal fenestra is relatively well preserved and it is visible only in dorsal view. The skull's antorbital fossa is roughly triangular, with its base longer than the other two sides. The jugal is triradiate and the anterior process of the jugal forms the posteroventral corner of the antorbital fossa and surpasses anteriorly the base of the lacrimal, a feature seen in basal
thyreophora Thyreophora ("shield bearers", often known simply as "armored dinosaurs") is a group of armored ornithischian dinosaurs that lived from the Early Jurassic until the end of the Cretaceous. Thyreophorans are characterized by the presence of body ...
ns and stegosaurs. The dorsal process of the jugal is proportionally long. The quadratojugal is very broad and the premaxilla is incompletely preserved while the post-cranial material is as-yet-undescribed at present. The dentition is heterodont, with six premaxillary teeth and thirty maxillary teeth. The genus' overall appearance is highly similar to that of stegosaurians, though lacking the characteristic plates and likely possessing a bipedal stance.


Discovery

The holotype specimen of ''Isaberrysaura'' was discovered in the marine to
deltaic A river delta is a landform shaped like a triangle, created by deposition of sediment that is carried by a river and enters slower-moving or stagnant water. This occurs where a river enters an ocean, sea, estuary, lake, reservoir, or (more rarel ...
sediments of the
Los Molles Formation The Los Molles Formation is a geologic formation of Early to Middle Jurassic age, located at northern and central part of Neuquén Basin at Mendoza Shelf in Argentina. It is overlain by the Niyeu–Lajas Formation.McIlroy et al., 2005 Descrip ...
, which is of
Bajocian In the geologic timescale, the Bajocian is an age and stage in the Middle Jurassic. It lasted from approximately 170.3 Ma to around 168.3 Ma (million years ago). The Bajocian Age succeeds the Aalenian Age and precedes the Bathonian Age. Stra ...
age, by Isabel Valdivia Berry, who is honoured in the generic name. The holotype, known as MOZ-Pv 6459 consists of a partial skeleton with a nearly complete skull (the post-cranial material of which is still unprepared), six cervical vertebrae, fifteen dorsal vertebrae, a
sacrum The sacrum (plural: ''sacra'' or ''sacrums''), in human anatomy, is a large, triangular bone at the base of the spine that forms by the fusing of the sacral vertebrae (S1S5) between ages 18 and 30. The sacrum situates at the upper, back part ...
with a partial ilium and an apparently complete pubis, nine
caudal vertebra The spinal column, a defining synapomorphy shared by nearly all vertebrates,Hagfish are believed to have secondarily lost their spinal column is a moderately flexible series of vertebrae (singular vertebra), each constituting a characteristic ...
e, part of a
scapula The scapula (plural scapulae or scapulas), also known as the shoulder blade, is the bone that connects the humerus (upper arm bone) with the clavicle (collar bone). Like their connected bones, the scapulae are paired, with each scapula on eithe ...
, ribs, with the addition of unidentifiable fragments.


Classification

''Isaberrysaura's'' classification is problematic at best; the holotype specimen shares traits with both thyreophorans and neornithischians. For this reason, it has been placed in the
Genasauria Genasauria is a clade of extinct beaked, primarily herbivorous dinosaurs. Paleontologist Paul Sereno first named Genasauria in 1986. The name Genasauria is derived from the Latin word ''gena'' meaning ‘cheek’ and the Greek word ''saúra'' (Ï ...
. Three datasets within the same study by Salgado ''et al'' indicated that while it possessed the characteristics of the neornithischians and thyreophorans, it did not fit within either of those groups, representing a previously unknown morphotype within the Ornithischia as a whole. Subsequently, the phylogenetic analysis conducted by Han ''et al.'' (2018) recovered ''Isaberrysaura'' as one of the basalmost known stegosaurs.


Paleobiology

The holotype specimen of ''Isaberrysaura'' has been preserved with fossilized stomach contents. Within the rib cage, a mass of fossilized seeds was discovered; the first preserved meal uncovered in a basal ornithischian. Two types of seeds were recovered close to the posterior ribs of ''Isaberrysaura'', distinguished according to their size. The largest seeds preserved three layers: an outer fleshy sarcotesta, the sclerotesta, and the inner layer (possibly corresponding to the nucellus). These seeds are cycadales of the family Zamiineae on the basis of a well-defined coronula in the micropylar region, whereas the smaller, platyspermic seeds are still indeterminate. The intact nature of the sarcotesta in the largest seeds suggests that ''Isaberrysaura'' swallowed the seeds whole without chewing and that they were in the first stages of digestion based on their position in the gut. Based on its teeth, it is possible that the dinosaur had an omnivorous diet, but as no trace of animal remains have been found alongside the seeds, this remains speculative at best. It also remains possible that there were enzyme-producing bacteria present in the dinosaur's gut to aid in digesting tougher plant material as seeds.


See also

*
2017 in archosaur paleontology The year 2017 in archosaur paleontology was eventful. Archosaurs include the only living dinosaur group — birds — and the reptile crocodilians, plus all extinct dinosaurs, extinct crocodilian relatives, and pterosaurs. Archosaur palaeontology ...


References

{{Taxonbar, from=Q28791257 Thyreophorans Ornithischian genera Bajocian life Middle Jurassic dinosaurs of South America Jurassic Argentina Fossils of Argentina Neuquén Basin Fossil taxa described in 2017 â€