Day #15 on our Christmas Countdown is…
ORNITHOSUCHUs!
Ornithosuchus: the “Bird Crocodile”
Ornithosuchus prowled the arid desert of Late Triassic Scotland. It was named in 1894, and is one of those odd critters that has some dinosaur-ish features, and some croc-ish features.
For example, it has a double row of armored plates, or osteoderms, along its back and five toes on each foot. Along with a number of other, far more technical details about its bones (more technical than I have the time or information to cover in this post) that make it more closely related to crocodilians.
On the other hand, it carried its legs underneath its body when it walked, could stand on its hind legs if it wanted to get anywhere in a hurry, and the shape of its head is much more dinosaur than crocodile in shape.
So what sort of critter is it?
Ornithosuchus is what is known as a pseudosuchian, which are archosaurs that are more closely related to crocodiles than to birds. Whereas dinosaurs are more closely related to birds than they are crocodiles.
If we were to break it down a bit more and start from the top, then it would go like this…Though take it with a bit of salt, since I’m grabbing this info from Wikipedia, and family trees of extinct animal groups are always being changed around and regrouped as more fossils are found or new papers come out with a convincing argument in support of change.
Archosaurs are the group of animals that includes the most recent common ancestor of living birds and crocodilians, and all the descendants of that ancient ancestor.
Archosaurs are then divided into two groups, or clades. These two clades are Pseudosuchia, which includes all crocodilians and their extinct relatives, and Avemetatarsalia, which includes birds and all of their extinct relatives. Flying pterosaurs and non-avian (as in, not a bird) dinosaurs are in this second group.
Zooming in on Pseudosuchians, this clade branches off into two families- Ornithosuchidae and Suchia.
Ornithosuchidae includes our friend Ornithosuchus and his closest relatives. In general they walked on four legs, but could walk on their hind legs for short periods of time if they wanted. They had downturned snouts that almost look like they hook over the lower jaw, ankle bones that are described as “crocodilian, but reversed”, a few other specific traits in the bones that a professional could point out, and there are also only four genera…
- Ornithosuchus: Late Triassic Scotland. The first critter named of this family, and considered the most “basal” or the oldest of the group.
- Venaticosuchus: Late Triassic Argentina. A study on jaw biomechanics done with this animal showed a very strong, but slow bite force, and relatively weak teeth.
- Dynamosuchus: Late Triassic Brazil. Like most of the others, it is only known from a single partial skeleton.
- Riojasuchus: Late Triassic Argentina. Known from nearly complete and partial skeletons of four individuals.
Suchia, on the other hand, includes just about every other croc-ish thing out there. Alligators, crocodiles, the marine Metriorhynchus we met the other day, the giant Deinosuchus, the cat-sized Fruitachampsa, and many other weird and wonderful croc-cousins.
Suchians were a very successful family of archosaurs, and critters like Ornithosuchus are an example of little off-shoot groups that just didn’t survive the many extinction events. This doesn’t make them any less successful in their own right and in their own habitats, it just means they weren’t as adaptable to rapid change as other groups. Or maybe they were just unlucky.
Overall I still think it is interesting to learn about these lesser known groups of animals. They help to fill in the picture of the environment in which they lived, and they give us a glimpse into what could have been.
In the end, they still survived long enough to leave fossils that let us know that they lived on this earth. That they were a part of the circle of life, however brief in the grand scale of time it might be.
What do you think success is for an animal? Continued existence of a family line that can be traced all the way to the present day? Surviving just long enough to leave fossil evidence? Thriving in one’s environment even though humans may never know of the animal’s existence? I’d love to hear from you in the comments!
See you tomorrow for day 16 of the Critter Christmas Countdown!
Pete's Paleo Petshop 
Finally glad to see something from the Triassic. You helped make Ornithosuchus interesting again. For me personally, I believe success for species tends to be longevity from prehistoric times to the more modern era. However, even now-extinct groups of organisms can still be successful as long as they show diverse differences and forms that fossil evidence points towards.
For the 15th, I want to bring up Sillosuchus, another bipedal non-dinosaur from the Triassic. It was a shuvosaurid, which were a strange group of pseudosuchians: they are more related to crocodiles than to dinosaurs but were bipedal, lightly armored, and had body plans and skull shapes more similar to theropod dinosaurs than to crocs. Based on the skull remains of Effigia, these archosaurs were further shown to be toothless and beaked, similar to ornithomimosaurs. Sillosuchus was found in the Ischigualasto Formation in Argentina, which preserved diverse assortment of Late Triassic synapsids, temnospondyls, and reptiles (including some of the earliest-known dinosaurs).
Initially, it was thought that the animal grew up to 9.8 feet (3 meters). However, other remains, including a giant neck vertebra initially mistaken to be from the quadrupedal Saurosuchus, could indicate a size of 30 to 33 feet (9-10 m). Unique features of it included neck and back vertebrae that had large excavations or pockets on the side, the left and right ischia (rear-pointing hip bones) being short and fused to each other and flattened in a top-to bottom direction. This is unlike in most other reptiles in which they were flattened in a side-to-side direction. Aside from this, the hip is basically identical to Effigia’s.
Names for each if I could decide:
Ornithosuchus: Orenthal
Sillosuchus: Selma
LikeLike