''Pawpawsaurus'', meaning "Pawpaw Lizard", is a nodosaurid

ankylosaur Ankylosauria is a group of herbivorous dinosaurs of the order Ornithischia. It includes the great majority of dinosaurs with armor in the form of bony osteoderms, similar to turtles. Ankylosaurs were bulky quadrupeds, with short, powerful limbs. ...

from the Cretaceous (late Albian) of Tarrant County, Texas, discovered in May 1992. The only species yet assigned to this taxon, ''Pawpawsaurus campbelli,'' is based on a complete skull (lacking mandibles) from the

marine Marine is an adjective meaning of or pertaining to the sea or ocean. Marine or marines may refer to: Ocean * Maritime (disambiguation) * Marine art * Marine biology * Marine debris * Marine habitats * Marine life * Marine pollution Military * ...

Paw Paw Formation The Paw Paw Formation is a geological formation in Texas whose strata date back to the late Albian stage of the Early Cretaceous. Dinosaur remains are among the fossils that have been recovered from the formation.Weishampel, David B; et al. (200 ...

(Wachita Group).

Discovery

''Pawpawsaurus'' was found in the

in Tarrant County, Texas, in May 1992, by Cameron Campbell. A complete skull is the only specimen, from which the binomial was named ''Pawpawsaurus campbelli''. The Paw Paw Formation has produced another nodosaurid, '' Texasetes pleurohalio'' (Coombs, 1995), which may prove to be a senior synonym of ''Pawpawsaurus''. This is the only nodosaurid known to have possessed the bony eyelids commonly found in ankylosaurids. The skull of ''Pawpawsaurus'' bears some notable similarities to that of '' Silvisaurus'', such as the presence of teeth in the premaxilla and the restriction of the

osseous A bone is a rigid organ that constitutes part of the skeleton in most vertebrate animals. Bones protect the various other organs of the body, produce red and white blood cells, store minerals, provide structure and support for the body, and e ...

secondary palate to the

rostral Rostral may refer to: Anatomy * Rostral (anatomical term), situated toward the oral or nasal region * Rostral bone, in ceratopsian dinosaurs * Rostral organ, of certain fish * Rostral scale, in snakes and scaled reptiles Other uses * Rostral colu ...

portion of the palatal region.

Description

''Pawpawsaurus'' is known from a relatively well preserved and complete skull. The skull is complete enough for a 2016 study to be able to identify and reconstruct the brain, nasal cavities and

inner ear The inner ear (internal ear, auris interna) is the innermost part of the vertebrate ear. In vertebrates, the inner ear is mainly responsible for sound detection and balance. In mammals, it consists of the bony labyrinth, a hollow cavity in the ...

of the specimen, and

CT scan A computed tomography scan (CT scan; formerly called computed axial tomography scan or CAT scan) is a medical imaging technique used to obtain detailed internal images of the body. The personnel that perform CT scans are called radiographers ...

it to find new anatomical features. The brain of ''Pawpawsaurus'' is very similar to other ankylosaurians, but along with more derived taxa it is most different from '' Kunbarrasaurus''. The brain is 30% of the skull length, very similar to '' Panoplosaurus'', higher than '' Euoplocephalus'', and lower than ''Kunbarrasaurus''. The brain of ''Pawpawsaurus'' is long and wide. The inner ear is also similar to ankylosaurians to the exclusion of ''Kunbarrasaurus'', being tall and wide at the level of the semicircular canals. The nasal cavities of ''Pawpawsaurus'' resemble that of ''Panoplosaurus'' and ''Euoplocephalus'', although the thin dividing medians are not preserved as they were likely cartilaginous.

Classification

Based on the dimensions of the skull, ''Pawpawsaurus'' is believed to have been approximately 4.5 meters in length. Vickaryous et al. (2004) have stated that "'' Sauropelta edwardsorum'', '' Silvisaurus condrayi'', and ''Pawpawsaurus campbelli'' form a basal polytomy nested deep to ''

Cedarpelta ''Cedarpelta'' is a extinct genus of basal ankylosaurid dinosaur from Utah that lived during the Late Cretaceous period (Cenomanian to lower Turonian stage, 98.2 to 93 Ma) in what is now the Mussentuchit Member of the Cedar Mountain Formation. Th ...

''." Alternatively, ''Pawpawsaurus'' has been identified as a relative of ''

Struthiosaurus ''Struthiosaurus'' (Latin ''struthio'' = ostrich + Greek ''sauros'' = lizard) is a genus of nodosaurid dinosaurs, from the Late Cretaceous period (Santonian-Maastrichtian) of Austria, Romania, France and Hungary in Europe.

'', with cladogram below showing the results of the

2018 File:2018 Events Collage.png, From top left, clockwise: The 2018 Winter Olympics opening ceremony in PyeongChang, South Korea; Protests erupt following the Assassination of Jamal Khashoggi; March for Our Lives protests take place across the United ...

phylogenetic analysis of Rivera-Sylva and colleagues, resolving ''Pawpawsaurus'' within the clade

Struthiosaurini Struthiosaurini (derived from ''Struthiosaurus'', "ostrich reptile") is a clade of nodosauridae, nodosaurid ankylosaurs from the Cretaceous of Europe and North America. The group is defined as the largest clade containing ''Struthiosaurus austriacu ...

as labelled by Madzia ''et al.'', with relationships outside Struthiosaurini excluded for simplicity.

Palaeobiology

''Pawpawsaurus'' was primitive in regards to its sensory abilities when compared to later ankylosaurs. CT scans of its skull and brain by Paulina-Carabajal and Louis Jacobs et al. revealed that ''Pawpawsaurus hearing was on par with that of modern crocodilians, indicating that its hearing was relatively poor. Its sense of smell meanwhile, while not as advanced as that of later ankylosaurs, was still more powerful and acute than many of the theropods existent at the time thanks to its large nasal cavities. The enlarged nasal cavities of ''Pawpawsaurus'' would also likely have been useful for cooling blood that was entering the brain, finding food and potential mates, or alerting it to danger.

References

External links