September 29. Wingate Sandstone and phytosaurs

It isn’t directly related to today’s post, but I wanted to call your attention to a recent blog post by Brian Switek who blogs at phenomena.nationalgeographic.com as Laelaps. His post on September 23 is a great one about carnivores of the Triassic. If you are fascinated by dinosaurs, Brian’s blog is for you.

Now, it’s back to the southwestern United States for today’s episode.

Wingate Sandstone photo by Greg Willis from Denver, CO,
used under Creative Commons license.

The Wingate Sandstone is a light red to buff cross-bedded sandstone of Late Triassic age. Although it looks a lot like the later Jurassic Navajo and Entrada sandstones, it’s actually at least 30 million years older, deposited in wind-blown dunes in an extensive desert. It forms many of the massive cliff faces in Capitol Reef National Park, Utah, as well as many of the sculpted towers in Colorado National Monument, near Grand Junction, Colorado. Parts of the Wingate were river-laid, so its deposition included several environments from deserts to riparian wetlands. 

The Wingate actually spans the time from late Triassic into the early Jurassic, about 210 to 190 million years ago, similar to the late part of the Karoo rocks that we talked about yesterday. The Triassic part of the Wingate was dated on the basis of a phytosaur skull. Phytosaurs were widespread Triassic reptiles whose fossils have been found on every continent except Australia and Antarctica. Phytosaurs first came up in our calendar on September 18 when we talked about the Chinle Formation, which underlies the Wingate Sandstone in many places in the southwestern United States. Phytosaurs were crocodile-like animals that appeared in the Carnian age, about 228 million years ago, more or less at the start of the Carnian Pluvial Event that we discussed a few days ago.

Phytosaurs were predators, and seem to have occupied ecological niches similar to those where crocodiles live today. But despite a similar appearance, with long toothy snouts, they were probably not crocodile ancestors, but were rather a failed early reptilian branch that evolved before the primary split between crocodilians and the archosaurs that led to dinosaurs and birds. Their exact relations and ancestry are not clear, but they spanned only a relatively brief period of time, about 28 million years during the late Triassic. They appear to have gone extinct in the event at the end of the Triassic, although there are some disputed phytosaur fossils that are very early Jurassic in age.

Smilosuchus drawing by Dr. Jeff Martz/NPS via Wikimedia, used under Creative Commons license.

There were lots of varieties of phytosaur in the late Triassic world – at least 24 genera encompassing more than 50 species.  Some, like Smilosuchus, grew to lengths of 15 feet or more.

—Richard I. Gibson

Drawing by Dr. Jeff Martz/NPS via Wikimedia, used under Creative Commons license.
Wingate Sandstone photo by Greg Willis from Denver, CO, used under Creative Commons license.