Tag: pachyrhinosaurini

Ceratopsian Month #17 – Pachyrhinosaurus canadensis

Pachyrhinosaurus (“thick-nosed lizard”) has become one of the more recognizable ceratopsian names in the last couple of decades, but its remains have actually been known for over 70 years, first discovered in the mid-1940s.

Three different species have been named within the genus, all living about 74-69 million years ago in Alberta, Canada, and Alaska, USA. The type species P. canadensis dates to roughly the middle of that time span, at an age of around 71 million years.

It was one of the largest of the centrosaurs, with the biggest specimens estimated to have measured up to 8m long (26′). Thousands of fossils have been found in a bone bed that seems to represent a mass mortality event – possibly a herd caught in a flash flood – with ages ranging from juveniles to adults.

Rather than horns, Pachyrhinosaurus had huge flattened bosses on its skull, which nearly grew together into a single large mass in both P. canandensis and the younger species P. perotorum. The older species P. lakustai instead had more separated bosses and a “unicorn horn” on its forehead.

(I’m also hardly the first person to speculate about fluffy pachyrhinosaurs, but since they lived in a chilly Arctic environment it’s certainly an interesting possibility.)

Ceratopsian Month #16 – Achelousaurus horneri

Achelousaurus (“Achelous lizard”) seems to have been a transitional form among the Pachyrhinosaurini. While slightly more basal members like Einiosaurus had well-developed nose horns, and the later Pachyrhinosaurus had enormous flattened nasal bosses, Achelousaurus was somewhere in-between.

Living in Montana, USA, about 74 million years ago, it reached sizes of about 6m long (19′8″). Instead of horns, rough patches of bone on its skull supported bosses over its snout and eyes, which in life would have been covered by thick layers of keratinous skin.

Unlike adults, juveniles had small brow horns with bony cores which gradually developed into full bosses as they grew. It’s possible that the bosses of mature individuals were used for headbutting or ramming behaviors.

Ceratopsian Month #15 – Einiosaurus procurvicornis

Einiosaurus (“buffalo lizard”) was part of a branch of the centrosaurs known as the Pachyrhinosaurini, a group with especially elaborate nose ornamentation.

Living about 74 million years ago in Montana, USA, it’s known from hundreds of bones representing over fifteen different individuals of varying ages. It had little-to-no brow horns, and two long spikes at the top of its frill – but also one of the most unusual-looking nose horns of all the ceratopsids, curving strongly forward and downward into a large hooked shape.

The juvenile remains show evidence of very rapid growth during their first few years of life, only starting to slow down around age 3-5, suggesting that was the point they began to reach reproductive maturity. The largest specimens are estimated to have measured about 4.5m long (14′9″), although they appear to have been subadults who still hadn’t quite reached their full size.