Pawpawsaurus, meaning "Pawpaw Lizard", is a nodosaurid ankylosaur 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 Paw Paw Formation (Wachita Group).
Discovery
Pawpawsaurus was found in the Paw Paw Formation 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 secondary palate to the rostral portion of the palatal region.
Description
Pawpawsaurus was a medium-sized nodosaur measuring long.
[ Genus List for Holtz 2012 Weight Information ] It 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 of the specimen, and
CT scan it to find new anatomical features.
The brain of Pawpawsaurus is very similar to other ankylosaurians, but along with more derived trait 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 cartilage.
Classification
Vickaryous
et al. (2004) have stated that "
Sauropelta edwardsorum,
Silvisaurus condrayi, and
Pawpawsaurus campbelli form a basal
polytomy nested deep to
Cedarpelta."
Alternatively,
Pawpawsaurus has been identified as a relative of
Struthiosaurus, with cladogram below showing the results of the 2018 phylogenetic analysis of Rivera-Sylva and colleagues, resolving
Pawpawsaurus within the clade
Struthiosaurini as labelled by Madzia
et al., with relationships outside Struthiosaurini excluded for simplicity.
However, the strict consensus tree of a phylogenetic analysis performed by Brown et al. (2017) placed Pawpawsaurus in a clade with Borealopelta markmitchelli and Europelta carbonensis. The results of the strict consensus are displayed in the phylogeny below, with taxa outside Nodosauridae being excluded.
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.
See also
-
Timeline of ankylosaur research
External links
