page_title: Polacanthus
section_title: Description
hierarchical_section_title: Polacanthus / Description
caption_attribution_description: Hypothetical Polacanthus foxii restoration, based mostly on Gastonia.
context_page_description: Polacanthus, deriving its name from the Ancient Greek polys-/πολύς- "many" and akantha/ἄκανθα "thorn" or "prickle", is an early armoured, spiked, plant-eating ankylosaurian dinosaur from the early Cretaceous period of England.
  In the genus Polacanthus several species have been named but only the type species Polacanthus foxii is today seen as valid.
  Polacanthus was a quadrupedal ornithischian or "bird-hipped" dinosaur. It lived 130 to 125 million years ago in what is now western Europe. Polacanthus foxii was named after a find on the Isle of Wight in 1865. There are not many fossil remains of this creature, and some important anatomical features, such as its skull, are poorly known. Early depictions often gave it a very generic head as it was only known from the rear half of the creature. It grew to about 5 metres long. Its body was covered with armour plates and spikes. It possibly was a basal member of the Nodosauridae.
context_section_description: Polacanthus was a medium-sized ankylosaur. In 2010, Gregory S. Paul estimated its length at 5 meters (16 ft), its weight at 2 tonnes (2.2 short tons). Thomas Holtz gave a lower estimation of 4 meters (13 ft) and 227-454 kg (500-1.000 lbs) in 2012. Its hindlimbs are relatively long for an ankylosaur, with a right femur length of 555 millimetres with the holotype.
  In 2011 Barrett e.a. indicated two possible unique traits, autapomorphies: the floor of the neural canal is deeply cut by a groove with a V-shaped transverse profile; the caudal spikes have triangular bases in side view and narrow points.
   
  The subsequent describers have always dedicated much effort at restoring the armour configuration. Hulke understood that Polacanthus had a large "pelvic shield" or "sacral shield", a single fused sheet of dermal bone over its hips (sacral area) which perhaps was not attached to the underlying bone and decorated with tubercles. This feature is shared with other "polacanthine" (basal nodosaurids) dinosaurs such as Gastonia and Mymoorapelta. With the holotype, this shield is 108 centimetres wide and 90 centimetres long. It features four horizontal rows of larger keeled osteoderms per side, surrounded by smaller ossicles. These latter are sometimes completely fused to form flat armour plates. Hulke thought that on the tail there were two rows of keeled osteoderms per side. Of a set of spikes found with the fossil, he assumed they had adorned the sides of the rump. A different arrangement was hypothesised by Nopcsa. He thought that both the tail and the front of the body including the neck featured two parallel rows of spikes, one per side. On the front body each row would have consisted of five spikes and he claimed that seven of these had been conserved with the fossil, five of the right side and two of the left. The tail rows would have consisted of twenty-two shorter pairs, fifteen spikes being still extant, eight of the left side and seven of the right. As the spikes are asymmetrical their position can more or less be deduced. Blows in 1987 basically agreed with Nopcsa but also distinguished three spike types, a Type A, B and C, allowing him to classify additional fossil finds, which often differed from the holotype spikes in several details.
caption: Hypothetical P. foxii restoration, based mostly on Gastonia
exif: {"Image Orientation": "Horizontal (normal)", "Image XResolution": "200", "Image YResolution": "200", "Image ResolutionUnit": "Pixels/Inch", "Image Software": "Adobe Photoshop CS3 Windows", "Image DateTime": "2011:03:20 13:42:24", "Image ExifOffset": "164", "Thumbnail Compression": "JPEG (old-style)", "Thumbnail XResolution": "72", "Thumbnail YResolution": "72", "Thumbnail ResolutionUnit": "Pixels/Inch", "Thumbnail JPEGInterchangeFormat": "302", "Thumbnail JPEGInterchangeFormatLength": "3130", "EXIF ColorSpace": "sRGB", "EXIF ExifImageWidth": "2077", "EXIF ExifImageLength": "890"}