Pronunciation: PRO-pan-OP-lo-SOR-us
Meaning: Pre (before) Panoplosaurus
Author/s: Stanford et al. (2011)
Synonyms: None known
First Discovery: Maryland, USA
Discovery Chart Position: #783
Propanoplosaurus marylandicus
Dinosaur remains from the Cretaceous of eastern North America (Appalachia) are much rarer than those from the Cretaceous of western North America (Laramidia), with Priconodon crassus being their sole ankylosaur representative, and even that is known only from some teeth and a later-referred shin bone that it may or may not own. Although still hopelessly outnumbered by their western neighbours, Maryland's Propanoplosaurus doubled the eastern ranks in 2011 without contributing an actual body fossil to their cause, but at the same time... and this is the confusing part... it actually did.
Propanoplosaurus is known only from imprints and casts of where fossils used to be: a "negative fossil" of sorts. But they can't be classed as "ichnites" which are remnants of the actions of an organism, such as fossilised dung, so they have to be body fossils, because there's no other name for them. Being so tiny, they were initially interpreted as embryonic and identified as a nodosaurid ankylosaur based on the shape of the skull and arm bones compared to those of adult nodosaur specimens from elsewhere. But the level of bone development and presumed articulation capabilities, and the presence of equally tiny fossilised footprints in the vicinity, proved it was a hatchling that had perhaps wandered from the nesting area, toppled into a stream and drowned, and sank upside-down into sediment, where it lay for 112 million years.
Propanoplosaurus is known only from imprints and casts of where fossils used to be: a "negative fossil" of sorts. But they can't be classed as "ichnites" which are remnants of the actions of an organism, such as fossilised dung, so they have to be body fossils, because there's no other name for them. Being so tiny, they were initially interpreted as embryonic and identified as a nodosaurid ankylosaur based on the shape of the skull and arm bones compared to those of adult nodosaur specimens from elsewhere. But the level of bone development and presumed articulation capabilities, and the presence of equally tiny fossilised footprints in the vicinity, proved it was a hatchling that had perhaps wandered from the nesting area, toppled into a stream and drowned, and sank upside-down into sediment, where it lay for 112 million years.
(Maryland's pre-Panoplosaurus)Etymology
Propanoplosaurus combines the Latin "pro" (pre, before) with Panoplosaurus (a similar but younger species of nodosaurid ankylosaur). The species epithet, marylandicus, refers to its discovery in Maryland.
Discovery
The remains of Propanoplosaurus were discovered in the Arundel Clay Member of the Patuxent Formation at Langley Park, Prince Georges County, Maryland, USA, by Ray Stanford in 1997.
The holotype (USNM 540686) is a cast of the top parts of the skull, ribcage and some vertebrae, the right forelimb, the right thigh and a right foot. Discovered alongside the tiniest fossilised footprints and measuring just 13cm long, experts think Propanoplosaurus is a hatchling specimen that drowned in a stream and was buried in sediment, upside-down.
