Squirrel Mocking

Photo by Ghedoghedo

2012 saw the official description of an informally announced coelurosaurian dinosaur with feathers preserved along its tail that were as bushy as the tail of squirrel. Adding further evidence to the feathering of the theropod dinosaurs, Sciurumimus albersdoerfi is one of the smallest and most primitive of the coelurosaurian dinosaurs. This proved a difficult distinction to make from the type fossil as it is a young juvenile animal; juvenile specimens always make definitive diagnosis difficult as their adult morphology may be exceedingly different from their fossilized state. This original type fossil is an exquisitely preserved relief fossil in a limestone slab from a formation in Bavaria that is chronologically similar to the Rögling Formation; this places it in the Upper Kimmeridgian immediately prior to the Solnhofen formation which contained Archaeopteryx.

Popular Tiny Dromaeosaurs

In 2007 Mahakala was popular for a brief time and heralded as a news story celebrating an interesting new building block of evolution. Mahakala was never popular as a dinosaur for being a dinosaur in the media, unlike animals like Tyrannosaurus and Triceratops. Measuring in at just over 2 ft of solid muscle and predatory fierceness, Mahakala was an interesting and tiny dinosaur that certainly warrants more attention than decade old news stories that amount to little more than two minutes of reading or air time. Its small size was, and still is, heralded as an evolutionary step in the direction of the miniaturization that preceded true birds within the paravian clade; another trait that warrants more popularity in the general knowledge of dinosaurs (and birds).

©Jaime Headden Creative Commons Attribution 3.0 Unported license

Of Flying Size

Dromaeosaurs are closely related to birds and research concerning dromaeosaurs and birds sometimes inform one another and other times are conducted in concert with one another. An interesting paper that crosses that boundary and discusses Mahakala and its implications on the evolutionary history of birds is Turner, et al. 2007. This paper describes and names the fossil remains of Mahakala omnogovae, previously known only as IGM 100/1033, and includes high resolution photographs of the known cranium and portions of the postcranial skeleton that contain important characters recognized as "paravian". The clade Paraves is defined by possessing characters typical of dinosaurs more closely related to birds than oviraptors, the theropod outgroup to Paraves. Possibly the most interesting aspect of this description paper is the portion of the paper following the description that discusses the diminutive size of Mahakala and the implications of the size and characters of the animal on the evolution of birds and avian dinosaurs before the evolution of powered flight.

A second paper worth reading today is the longer anatomical description of Mahakala published by Turner, et al. in 2011. This updated and more rigorous anatomical description does not single out novel characteristics of the animal like the first paper did; the shorter description is in part a victim of its appearance in the shorter format of a Science article. This longer version is 68 pages and uses every page to share high resolution images of single elements of the known skeleton one at a time as it describes each. More need not be said to describe the 2011 description of Mahakala because it delivers on exactly that; pure detailed description that vividly shows what this fossil looks like and its complete (as we know it) anatomy.

Mahakala Facts

First return on a search for Mahakala videos is the WizScience video that relays all of the facts that we know about the dinosaur. This video also contains a lot of different images of Mahakala. It is the perfect combination of facts and interpretations of this tiny dinosaur.

Newer Dromaeosaurs

©Nobu Tamura

It has long been hypothesized that the origin of dromaeosaurs was likely to be found in Asia where preservation is fairly good and basal characteristics of dromaeosaurs are found in a number of fossils. Mongolia and Northern China are prominent sites of these fossils, so it was not much of a surprise when Turner, et al. announced the description of what was called one of the most basal dromaeosaurs discovered to date in 2007, Mahakala omnogovae. Its name directly references the Tibetan Buddhist protector deity Mahakala and the southern province of Ömnögovi in Mongolia. The type specimen is a small adult, approximately the size of Archaeopteryx, consisting of portions of the cranium, limbs, vertebrae, pelvic, and shoulder girdles. Distinctively, Mahakala possessed a second toe on the hindlimb that was expanded and highly recurved. The small size of the dromaeosaur makes it a little less frightening than its larger descendants and cousins, but fear is relative when you are small enough to be the prey of this early diminutive dromaeosaur.

Looking Similar

Peteinosaurus illustrations are like many pterosaur illustrations in that they all look very similar and very often depict a flying reptile with wings spread and mouth open. The less popular version, which still turns up fairly often, depicts the pterosaur in question sitting on a branch or the ground ready to vault into the air. Somewhere in between there are hunting and swooping images. This image by Nobu Tamura captures the moment after swooping and chasing and the moments before our friendly Peteinosaurus would be ready to again launch (or fall) from the branch to take to the air once more.

Headless Pterosaurs

Despite well preserved slab fossils, not a single specimen of Peteinosaurus possessed an intact skull or any skull actually. The teeth of Peteinosaurus are known somehow, though. Three types of conical teeth are associated with the pterosaur and their shape indicated an insect based diet. The teeth and diet of Peteinosaurus are not the most unique characteristics of the fossils though. The fifth toe on each foot was elongated and had lost its claw. The toe possessed a joint that was different from the other toes of the foot. This joint allowed the fifth two to move in ways that enabled movements of the cruropatagium, the skin between the ankles, that acts as an airfoil. In a way, this structure acts like the retrices, tail feathers, of birds allowing for more precise control of flight movements. Some birds, bats, and pterosaurs like Peteinosaurus need precise control of their flights capabilities for aerial hunting in order to maintain pursuits. This cruropatagium most likely worked very much like a Barn Swallow's tail, as can be seen here:

Flying Literature

The literature history of pterosaurs is quite extensive. Peteinosaurus is not neglected in that rich history either. The paper naming and describing Peteinosaurus is difficult to find online, but luckily I know where to find it. One of the most prolific pterosaur researchers of our time keeps an updated bibliography of all pterosaur research and an archive of available PDF files of the studies he has collected over the years. Rupert Wild's 1978 opus "Die Flugsaurier (Reptilia, Pterosauria) aus der Oberen Trias von Cene bei Bergamo, Italien" is only available in the original German, despite its publication in the Italian publication Bolletino della Societa Paleontologica Italiana. The study is a review of six fossil genera discovered in and around Bergamo, Italy and includes descriptive text alongside photographs of specimens and line drawings highlighting important structures from the fossils and their photographs. This is not the only review of Italian or Triassic pterosaurs featuring Peteinosaurus though. Fabio Dalla Vecchia's review of Italian pterosaurs is hosted in English and possesses a similar amount of detail, though not as much as Wild's review. However, if reading German is not something that one can do quickly or in their spare time in the near future, the descriptions of Dalla Vecchia are more than sufficient. Many of the other articles that are published which heavily feature Peteinosaurus are themselves reviews and new descriptions. Therefore, these two highly detailed descriptions of Peteinosaurus are more than enough to read today.

Supporting Character on Wings

First and foremost, here is a link to the episode of Dinosaur Train that introduced "Petey the Peteinosaurus" (there are a number of versions of this but this is the only full episode that is not flipped horizontally). The first episode of the original "Walking with..." series was about dinosaurs specifically and mentioned supporting characters like Peteinosaurus (and mammals and amphibians) in passing. Peteinosaurus, however, benefited, in terms of the show, by existing during the Triassic dawn of the dinosaurs. The first episode of Walking with Dinosaurs focuses extensively on the environment that fostered the rise of the dinosaurs. This environment was populated by various protomammals and archosaurs, one of which was the "exotic hunter... Peteinosaurus" as Kenneth Branagh describes it. The short blurb about the flying reptile is not an enormous portion of the episode, but we know that Peteinosaurus is an important member of its environment. Its hypothesized role can be seen clearly in the show, as can its acrobatic capabilities.

Two Movies

Peteinosaurus appears in a few television roles, but only one is relevant today. There is a second video that is relevant to today in that it relays facts and shows some relevant illustrations of the flying reptile. The cartoon that is relevant today is, as it usually is on a Sunday, a short clip from the PBS show Dinosaur Train. As usual, the alliterative name of the Peteinosaurus in this episode is Petey. The clip attached here, however, is just Dr. Scott talking about facts like height and weight of Peteinosaurus and not a portion from the actual episode with Petey in it.

The second video clip is from WizScience and is nothing but straight facts and a single view of one of the fossil slabs containing Peteinosaurus material.

Flying Fun

Aerial acrobatics in the days of the dinosaurs were not conducted by birds or bats, not early on at least. During the Triassic there were a number of small reptiles capable of flight, the pterosaurs. One of the smallest, oldest, pterosaurs of the Triassic was Peteinosaurus zambelli. This small pterosaur had a wingspan of approximately 60 cm (24 in), one of the smallest known for pterosaurs, and weighed about the same as a Common Blackbird (or American Robin for North American readers). Known from fossils from northern Italy, Peteinosaurus has been well preserved mainly on three slabs of material that house very flat and fragile specimens. This is not abnormal for pterosaurs as they possessed very strong but light bones. Peteinosaurus is slightly abnormal for pterosaurs in that it is known to have possessed three different types of teeth (called tridontomorphy). These teeth were used for catching insects and hypothesized features of the manus and wing may have been highly suited to permit precision aerodynamic control of the pterosaur in flight, meaning that at least some of the insects Peteinosaurus hunted may have been flying meals.

A Furry Star

Whenever any fossil is found in a level of completeness like that of Castorocauda it becomes a little bit more famous than other fossil animals. Sometimes this popular knowledge of a taxon remains and continues onward for centuries (T. rex, etc.) and sometimes it lasts mere moments (Morganucodon, perhaps, for the non-professional readers). Castorocauda appears to have retained some of its initial popularity, but has generally been mostly lost to the public over the past decade. In that time, however, Dinosaur Revolution and Dinosaur Train both capitalized on the discovery and description of this small swimming mammal. Arguably, Dinosaur Train did a much better job of describing and showing the features of Castorocauda, as we can see in the clip below. Dinosaur Revolution mentioned some of the characteristics of Castorocauda, but these were largely ignored in its animation. The tail and overall body shape can be seen clearly, but the show depicts Castorocauda running through a forest and into a hollow tree whereas the Dinosaur Train scene below takes place at the edge of a marshy lake possibly like the area from which the nearly complete Castorocauda fossil was recovered. Granted Dinosaur Train is much more educational and thoroughly proves it by comparing mammals against mammals and mammals against dinosaurs and pterosaurs as well as describing the characteristics of Castorocauda in great detail (for a kid's show).

Fur Anatomy

The fur of Castorocauda has been described as consisting of two kinds of mammalian fur: guard hairs and underfur. These two kinds of fur seen in the fossil of Castorocauda provided some of the first very solid evidence of a furry mammal in the Jurassic; evidence of mammalian traits and some samples of fur and hair have been seen prior to this, but, as with feathers, this was one of the first truly wonderful collections of soft tissue that is generally lost to fossilization processes. It is also one of the earliest mammals recognized to have possessed the modern mammalian fur arrangement and follicle structure. The first kind of fur that was definitively recognize in the fossil is what is known as underfur or undercoat. This fur is short, flat, curly, and dense. It is this hair that keeps mammals dry in water and warm in winter. These rather different capabilities of this layer of fur are similarly achieved through the trapping of dry air against the skin which both repels water and maintains a buffer of warmth against the cold of the environment. Underfur serves as a thermoregulatory buffer for the skin and, overall, whole organisms like us and Castorocauda from the temperatures outside our bodies.

This is in contrast to the role of the second layer of fur recognized in Castorocauda: guard hairs. Also colloquially referred to as the coat, guard hairs are the main centers of pigmentation in fur. Display patterns, camouflage, and the shininess of a mammal's fur are reliant on the pigments collected in the guard hairs; these are of course regulated by other factors such as genetics and diet as well. Guard hairs are typically long straight hairs that come to a point and, in some mammals, can be fairly coarse. It is these hairs that we notice in threat displays, when frightened, and in other moments of agitation or excitement. Guard hairs also, as the name implies, guard the body. They do not trap warmth or repel water as well as underfur (though they are capable of doing so). However, guard hairs can significantly block harmful ultraviolet radiation from reaching the skin, something that the underfur does not do as much of (possibly because of the presence of guard hair of course).

What does all of this fur mean to Castorocauda? Thermoregulation, as a small mammal, and thermal insulation, as an aquatic mammal, created enormous metabolic requirements for Castorocauda. Out of the water, seasonal shifts in temperature would have caused the animal to need more or less of a coat of fur, but may not have been so demanding that Castorocauda possessed seasonally variable coats. We can remain open to this possibility as we do not know exactly how much of a temperature shift between seasons mammals were readily tolerant of during the Mesozoic, but it may be that the shifts did not cause radical changes in coat length or color (see #7 on this list specifically). In the water, coat length changes the dynamics of locomotion and, if we consider mammals that we know to be semiaquatic, we can make inferences on whether or not Castorocauda would have benefited from having a long coat; color changes based on season may not have affected the animal at all. Most semiaquatic mammals possess short, coarse guard hairs with a few exceptions, river otters and beaver, for example, possess long guard hairs. The unique mammalian hairs of Castorocauda, regardless of their seasonal changes, pigmentation, or general coarseness, were and remain an important feature of the mammalian body plan. The fur allowed Castorocauda to stay warm all year long and to dive into waters both warm and cold to chase fish and crustaceans (or other invertebrates). Weighing in at up to 800 g (about 2 lbs), Castorocauda would have gotten a great deal of help in maintaining its body temperature in colder waters from a thick coat of fur.

The Literary Accomplishments of Small Mammals

Castorocauda is one of the better preserved mammalian specimens of the fossil record. Not simply of the Jurassic fossil record, but the entire mammalian fossil record. There are a number of younger finds that are wonderfully preserved for various reasons that include age, lagerstätten preservation (tar pits and tundra finds included), and occasionally luck. Regardless, the 2004 fossil find of Castorocauda has given mammalian paleontologists a lot to study and that has given us a lot that we are able to read. Ji, et al. 2006 introduces the approximately 425 mm mammal to the world and is openly published on Science's website, allowing everyone to read it without downloading a PDF or paying for the full article. Pictures of the fossil show that the mammal was preserved in a slab of rock with only small portions of the hindlimb, torso, and neck absent from the fossil. Science also hosts an article on mammalian brains (Rowe, et al. 2011) that mentions Castorocauda and discusses the animal's integument and subsequent meaning of these hairs in relation to brain development and sensory inputs. The majority of other papers that mention Castorocauda are likewise filled with very short single paragraph or less mentions of the animal to show one point or a snapshot in the development of a system. The major paper that we have for Castorocauda, however, is extensive and describes the animal and its functional morphology in high levels of detail.

Supposed Jurassic Beaver

Dinosaur Revolution was a Discovery Channel documentary that aired in 2011and consisted of four episodes that explored topics from evolution to defensive and offensive tactics of different dinosaurs. The third episode specifically examined how dinosaurs and their contemporaries hunted one another or defended themselves from predation. That episode included what some refer to as a "Jurassic Beaver", though we know better that Castorocauda was not related to beavers at all. The episode is available (for the moment) online and you can get to it below:

Information In Motion

Castorocauda has few informational websites. Instead of sending people to multiple sites to learn some quick facts about this Jurassic mammal today, here is the WizScience video that contains pretty much all the information that can be found on a myriad of sites.

The Not-A-Beaver Family Tree

©Nobu Tamura

In the past, at least once, we have discussed the rodent family Castoridae which includes the two extant members of beaver (North American and Eurasian Beaver both). This week we will be discussing a beaver-like animal from the Jurassic that, despite appearing to look very much like an extant beaver, was highly specialized for a semi-aquatic lifestyle similar to that of a beaver. There is also a great deal of similarity between river otters and our animal this week, which earned this cynodont mammal its specific epithet. The only animal that this animal convergently shares traits with, but not a name reference, is the platypus. The animal in question, Castorocauda lutrasimilis, actually translates to "Beaver Tail, Otter-like" and therefore directly references both similar extant animals. This animal, as stated, is actually a cynodont, a group of therapsids that appeared during the Permian and includes modern mammals as well. The closest family members of Castorocauda, other docodonts, are also extinct, with the family completely disappearing from the fossil record in the late Mesozoic. Castorocauda itself is found in 164 MA Jurassic rocks from Inner Mongolian fossil lakebed sediments. A wonderfully preserved fossil of Castorocauda was recovered in 2004 that possessed hair, including an undercoat of fur. Another difficult to preserve portion of mammal anatomy that was wonderfully preserved in Castorocauda is the delicate and tiny middle ear including the ossicles.

Lacking in Illustrations

The exquisite preservation of Heliobatis is often all anyone needs to imagine this animal punting along (that is correct verb to describe ray swimming) the bottom of the freshwater habitats they called home. Few illustrations, paintings, or other media have been carried out to depict Heliobatis in action within its habitat. Another, potential, reason that there is not a high demand for illustrations of the ray is that it appears to have been quite similar to extant rays, making illustrated representations of the ray appear less fantastic and awe inspiring than many other paleo art; this is not a reason to not create art of course. It is hard to pick a single image of Heliobatis to share as a wonderful depiction of the animal today because of all of the good photos of the well preserved fossils. Regardless, if I was forced to choose one single specimen to hang on my wall (Heliobatis fossils are for sale all over the internet, by the way), I would go with the image shown here. The detail is wonderful, as usual, but in a different way than the majority of other fossils. The slab is darker, and therefore the fossil details are also darker. The higher contrast makes thee anatomical details pop out a bit more and the contrasting elements of relieved and elevated portions of stone in the slab have a more natural look to them.

Anatomy For All

©Brian Greenstone

Heliobatis fossils from the Green River Formation are very nearly the epitome of lagerstätten fossils. Because the preservation is so exceptional, there is a lot known about Heliobatis and its anatomy. The life history of these freshwater rays is well known because of this as well. We know that Heliobatis most likely ate small crustaceans, fish, and mollusks because we have found teeth in the fossils. Those teeth are small triangular biting teeth that are oriented very closely together.  These teeth could have been used defensively, however; like extant rays Heliobatis had a barbed stinger on their tails. Their stingers consisted of approximately three modified placoid scales (also called dermal denticles). The placoid scales were also found on the skin of these prehistoric rays and are very similar to the dermal denticles that are found attached to the skin of extant rays, skates, and sharks. One of the other very important characteristics of that we know of from the exquisite preservation of these animals is that they were sexually dimorphic. Male chondrichthyians, including Heliobatis, possessed clasping organs that are used to fertilize the female's eggs. More can be read about this topic in various places; the shortest version can be found here.

Written Rays

Many of the papers that appear in preliminary searches concerning Heliobatis either use the ray for comparison or note a collection of fauna from a given locality. These are of great worth to us in that they both require descriptive text about Heliobatis and both types of writing tend to provide or ascribe behaviors or habitat information to the sun ray. These are, in turn, both useful for understanding the organism and its environment and generating more hypotheses about the animal and its life history. As mentioned previously, the teeth of this ray are typically well preserved and they have been studied frequently in conjunction with the teeth of other fossil rays to discuss phylogeny, differences in environment, and in the context of dental evolution. In some instances, all three of these topics are discussed, to a point of course; that is a lot of information to attempt to shoehorn into a single paper. There are papers that discuss locomotion of skates and rays as well, using Heliobatis and other rays pelvic girdles to predict what their swimming will look like.

Zooming In

Heliobatis, despite being well known for a very long time, is not really a charismatic animal that has garnered a lot of demand in the documentary, cartoon, or feature movies of the world. As a somewhat stereotypical looking ray, it did not really possess any anatomy that would have stood out enough to garner special attention. There are very few videos in general that have anything to do with Heliobatis. We shared some of them yesterday. The only remaining video that definitely features Heliobatis is an eighteen second video zooming in and out of one of the fossils. That video can be seen here.

Skate Video

For those that lie to read their videos, there is a really informative video posted by the user Gemini Bull. The video is really a compilation of information found on all kinds of different sites online. The video and information on the video show a lot of images of Heliobatis and actually make it such that many different links would not be required to learn from this week, for the sake of keeping the post free from redundancy. One of the better sources online, that is not a video, to learn from is the virtual fossil museum. Prehistoric Wildlife also has some information though it is almost entirely taken from Wikipedia. It does have the only size comparison with a person shown online; that makes it worth a view as well.

Rays and Skates

© Didier Descouens

Rays and skates are members of the Chondrichthyes, a class of animals that first abundantly populated the oceans during the middle of the Devonian period and has persisted into the modern age. Other members of the class include sharks, chimaeras, and sawfish; sharks representing the best known members of the group. The rays that we are interested in this week are some of the most well known fossil chondrichthyians from the Eocene known as Heliobatis radians (Sun skate/ray). The ray Heliobatis was originally described in 1877 by O. C. Marsh (simply as Heliobatis) and has since had four genera synonymized under the name Heliobatis. Particularly well-known from the Green River Formation, Heliobatis is best known specifically from the Fossil Lake sediments of Wyoming; many of these are housed or on display in either Fossil Butte National Monument ("America's Stone Aquarium") or the Yale Peabody Museum. The known fossils housed and displayed in those two locations are highly detailed. The details are so well defined actually the sexually dimorphic characters, defensive characters, and the feeding apparatus have all been described. Teeth are observable in many of the specimens and based on the triangular shapes of the teeth, the diet that has been hypothesized for Heliobatis is largely based on small fish, crustaceans (there are numerous crayfish and prawn fossils associated with the same formations as Heliobatis), and mollusks.