It's in the Name

It was mentioned earlier this week that Protarchaeopteryx, as a name, translates literally to "Before Archaeopteryx". This poses a small problem because Protarchaeopteryx is a Cretaceous archaeopterygian and Archaeopteryx itself is a Jurassic animal. Geologically speaking, Archaeopteryx predates Protarchaeopteryx by approximately 25MY; though it is important to note that the accepted span of existence for Archaeopteryx is 150MYA - 125.45MYA and Protarchaeopteryx shows up in the fossil record at 124.6MYA. This means that they are not, temporally, that distant from one another. This does not necessarily reflect their phylogenetic relationship to one another. Now, the reason that we brought up the names is that the implication of the name is not actually what the name means. What I mean, and what Ji and Ji meant by that in 1997, is that Protarchaeopteryx did not come before Archaeopteryx, but rather it possess characters which appear to place it in a phylogenetically primitive position in relation to Archaeopteryx. The justification for the name as assigned by Ji and Ji was that "...it [Protarchaeopteryx] is regarded as more primitive because it has a more elongated tail, more robust pelvic girdle, longer and larger hind limb, and unfused proximal metatarsals [than Archaeopteryx]." These characters, it may not require stipulating, are more derived in Archaeopteryx. To better understand the description and read the translated version of that 1997 paper, please see the reference presented below.

Reference:
Ji, Qiang, Shu’an Ji, and Translated By Will Downs. "A Chinese archaeopterygian, Protarchaeopteryx gen. nov." Geol Sci Tech 238 (1997): 38-41.

Caveats of the Internet

Any time that one searches for anything discussing birds, dinosaurs, and/or evolution, one must be aware of the confusing and argumentative cyclone of websites that are out there. Looking up an animal like Protarchaeopteryx is a part of that rule and certainly not an exception. A safe place to start is something like the WizScience video below that just presents facts that we know about this dinosaur without adding conjecture or argument to what is presented.

Of course, we cannot assume that all of the videos and websites are as neutral as those put forth by a group like the team behind WizScience. That being said, there are websites that do avoid the arguments on the internet by presenting information (and being fairly regularly updated to maintain that information) without allowing comments; it really can be as scary as I am making this sound when a website discusses the dinosaur-bird transition and key fossils and allows for commenting. Pages that are safe include:
Encyclopedia Britannica
The Natural History Museum of London
Age of Dinosaurs
Dinosaur Jungle
Enchanted Learning

Early Feathers

We always love a fossil that we haven't talked about or a fossil that has had a lengthy absence and we are talking about it for the first time in a really long time. This may or may not be one of those times; I feel like we have covered Protarchaeopteryx robusta before, but searches of the entries on the blog turned up nothing. That is almost 8 years worth of entries to search though, and considering that with this year as an exception of every day entries, that is a search of almost 2500 entries. Regardless, the small "Before Archaeopteryx" feathered theropod is an interesting dinosaur that was discovered in the Yixian Formation of China in rocks that belong to the Aptian age of the Early Cretaceous (approximately 124.6 MYA). There are questions about the validity of the animal; some discussion has involved its relationship to another small dinosaur, Incisivosaurus (we may visit this animal next week to follow up). However, with that relationship in question and not cemented or ignored, another relationship is still alternatively proposed for Protarchaeopteryx; that this animal represents a basal oviraptorosaurid. Despite this ancestral mystery, we do have some idea about what the animal ate (likely mostly herbivorous but sometimes supplementing this diet with meat) and what it was covered in (symmetrical, flightless feathers) and we can therefore form a few hypotheses about the way that Protarchaeopteryx lived in and interacted with its environment and other animals.

Protarchaeopteryx holotype at the Geological Museum of China
CC BY-SA 4.0

Two papers

There are two important papers that everyone interested in Rubeosaurus should take a moment to read today. These papers discuss, first, some interesting remains of "Styracosaurus" ovatus in which the authors, McDonald and Horner, introduce new remains attributed to this species and then analyze the characters and describe the phylogeny of the animal. This paper contains the naming of the new genus, Rubeosaurus, based on this material and is therefore important in knowing where the dinosaur came from and what was known about it previous to its naming in a new genus in 2010. The second paper is about a subadult specimen of the genus that was discovered somewhat recently and described by McDonald in 2017. This description is actually a revisiting of a previous description of another dinosaur (Brachyceratops) and places a young animal within the genus Rubeosaurus. Additionally, this description causes the name Brachyceratops to be considered invalid, or as we more commonly say in paleontology, it is a nomen dubium (a problem name).

It Refers to Brambles

One might imagine that with a name like Rubeosaurus ovatus the person naming the dinosaur may have been poking fun at someone, but the name actually means "Bramble lizard" and references the appearance of the ceratopsian frill that makes up a good portion of the known skeletal elements. Originally named by Charles W. Gilmore in 1930 as a species of Styracosaurus, Rubeosaurus was split from that genus in 2010 by McDonald and Horner following a phylogenetic analysis conducted using new material attributed to what would be renamed Rubeosaurus. The ceratopsian dinosaur has a similar frill to its close relatives Styracosaurus and Einiosaurus. These frills all possess large parietal fenestrations and are bordered by large conical processes surrounding these cranial bones and highly ornamenting the skull. A singular and immense nasal horn is also present in Rubeosaurus, just as in its close relatives.

©Lukas Panzarin CC BY 2.5
From McDonald and Horner 2011

Papers of Many Measures

There are many Dimetrodon papers. A significant number of those papers are descriptions of different finds of Dimetrodon from various different places. The original naming papers would be most interesting, if we had them somewhere online. We do not, to my knowledge. However, we do have the first Dimetrodon species known from Europe, the first from outside of North America actually, which was found in the Bromacker assemblage. This is a Lower Permian formation in and around the Thuringian Forest of Central Germany.

There are other descriptions of Dimetrodon as well. Some of these regard the jaw muscles of the interestingly shaped skull of Dimetrodon. Other venture into describing how Dimetrodon may have regulated its temperature using its unique sail structure. The structure of the sail is, of course, a constant subject of study. Like any other body part, the sail could be subjected to injury as well, and studies have certainly been conducted that on said injuries.

Many of these studies together have led to phylogenetic studies of Dimetrodon. The pelycosaurs, in general, are in an interesting position in the evolutionary tree of synapsids. One of the papers I enjoyed reading when I first learned systematics and began dealing with trees is this paper by Ken Angielczyk which uses Dimetrodon as an example species in how to think about trees (otherwise discussed as "tree thinking") how to use them to understand relationships between taxa.

Not A Dinosaur

Pelycosaurs are not dinosaurs. As Dimetrodon is a pelycosaur, Dimetrodon is also not a dinosaur. This has mostly been eroded from the popular psyche, though there are still vestiges of Dimetrodon's inclusion in the world of dinosaurs out in the modern world. These videos will make sure that everyone knows what a Dimetrodon is and is not.

Emily Graslie (she is a professional science communicator, so expect a well delivered video) on Brain Scoop:

A top ten list of facts. This video again addresses the fact that Dimetrodon was not a dinosaur straight off the bat. It then lists some interesting facts about Dimetrodon. The video includes a lot of images and video game animations.

New Old Animals

Sphenacodontids ("Wedge point tooth") are a group of synapsids that are known from fossils found across Europe and North America from ages between from the Late Pennsylvanian to the Middle Permian. The most well-known examples of not only sphenacodontids but also pelycosaurs is the large headed apex predator known from Texas and Oklahoma (mostly), Dimetrodon ("Two measures of teeth"). The genus Dimetrodon actually consists of 13 recognized valid species; though we regularly hear Dimetrodon referenced as though it is a single species (generally the type species, D. limbatus Cope 1877). The general description of Dimetrodon species is a group of animals presenting with tall laterally compressed skulls, a large dorsal sail, and a tail composed of upwards of 50 caudal vertebrae, accounting for a significant portion of the total length of the animals. The sail is what most people think of when they think of Dimetrodon, but these pelycosaurs are actually named after their teeth, which consist of 1 - 2 pairs of large caniniform teeth and large incisors in the front of the mouth and smaller teeth caudally. Also intriguing in the skulls of Dimetrodon species are primitive nasal turbinates, appearing to indicate a capability of warming and cooling air as it was inhaled and exhaled and what appears to be a transitional morphology of the ear that would give rise to the mammalian ear. The story of the mammalian ear is far more complicated than the previous sentence makes it sound, but this intermediate ear morphology is important in overall ear evolution.

There are many reasons that Dimetrodon is an interesting animal to study and, given time this week, we can get into some of the studies that have been done with disparate species of the Dimetrodon genus. Dimetrodon will always stand out because of their importance in the evolutionary history of synapsids, their unique morphology, and, personally, because the first model I ever built was of a Dimetrodon standing on a rock. It is very possible that this was the model kit (I was young and it was forever ago, but this brings up the memory of building it).

 Also, here is a nice illustration of a few of the species of Dimetrodon scaled to one another by Dmitry Bogdanov.

©Dmitry Bogdanov