Teeth and Fossils

Teeth in the fossil record are massively over-represented. However, as one of the hardest bits of the body and a portion that is replaced often and with some regularity, the discovery of teeth more than any other portion of a fossilized body is not at all surprising. Placodus teeth have been recovered for centuries in fossil deposits and at one point or another various species of the genus were identified mainly by teeth. A species named by Owen in 1858 (and another species given the same name in 1863 by Meyer) was described using teeth and partial cranial remains, but has since been reassigned to another genus of placodonts (Cyamodus). The cranium and skull (cranium plus mandible) have been described numerous times with different goals in mind. Sues (1987) described the phylogenetic relationships of the placodonts using a description of the skull of P. gigas. Fifteen years later the skull of P. gigas was again described, but with a more specific goal in mind. Neenan and Scheyer (2012) specifically described the anatomy of the inner ear and the braincase of a specimen of P. gigas using computed tomography (CT).

Not all of the studies conducted with Placodus are description based or anatomy centered of course. A number of studies such as Diedrich 2010 and Diedrich 2013 have assessed the paleoecology of Placodus. Diedrich 2013, specifically, describes the life of a Placodus as very "sea cow" like; in other words, Placodus was, as we mentioned on Saturday, very much like a Triassic manatee. Bone beds of "several thousand individual 'Triassic sea cows'" are used to describe the communal living of Placodus in the shallow seas covering an immense portion of what is now Europe. Diedrich 2013 was based partially off of the conclusions of Diedrich 2010 which discussed the paleocological role of Placodus using anatomical characteristics and laying the foundation of the "sea cow" - like analogy.

Facts and Movies

Movies featuring the stocky marine reptile Placodus are difficult to find because it is not an animal that routinely features as a main character in documentaries, films, or any other medium that incorporates fossil animals. I did not find much in the way of fact films or many new or interesting fact pages online yesterday. However, there is an application created by Corinth, a Czech educational company, that contains information on paleontology related topics, including this short clip featuring Placodus. There are a number of short videos that display animation models of Placodus, though they are short clips with very little contextual information. However, these clips have been informed by the skeletal biology of the animal and, we hope at least, some knowledge, or consultation with people who understand, biomechanical principles of locomotion. This does not apply to the model presentation clips, like this short spinning clip. A knowledge of biomechanical principles is helpful, and probably should be required for clips like this movement test of a Placodus on a rocky beach. Potentially, in the future, there will be more animated Placodus characters in games, movies, and other media.

Flat Teeth in the Ocean

Illustration by Zdenek Burian, 1962

 "Prehistoric Sea Monsters," 1964

In the Triassic a group of large lizards lived in the marine waters of what is now Central Europe and Asia, as far as we know currently from fossil remains found in Poland, France, Germany, and China. Possessing flattened teeth, stocky bodies, and long tails, Placodus gigas Agassiz, 1833 (type species) and Placodus inexpectatus Jiang et al., 2008 swam around the shallow waters and was related to the stem animals of the Sauropterygia, the group that includes plesiosaurs and nothosaurs. The skeletal remains of these animals show a squat animal that appears heavily armored and very "negatively buoyant". Essentially this means that Placodus was born ready to sink and may have either been a poor swimmer or was a very strong swimmer. After an initial look, it appears that Placodus was possibly very hippo-like, or perhaps even manatee-esque. The diet of Placodus was much closer to hippos and manatees than it was to its descendants, so these may not be terribly distant comparisons.

Bear Art

There are a quite a few interesting illustrations of Arctotherium. A healthy percentage of these illustrations show the size relationship of this bear with other bears or with human silhouettes. These are helpful for appreciating the size of the largest known bear and it is this claim, of course, that interests so many people. Despite having shared few illustrations showing the bear in any type of action this week, those kinds of illustrations do exist and they are of extremely high quality. Many of these illustrations are not released into the public domain; however, we can share links to these illustrations without effectively stealing from the artists. The most colorful action illustration shared via link here is Arthur J. Doretty's Arctotherium. This illustration shows the bear confronting a pair of Smilodon as they appear to protect a carcass. Scavenging the kills of other animals was probably a very viable source of food for Arctotherium. Another interpretation of this image is that the bear may have wandered away, for water or to sleep for example, and come back to find scavengers at its kill and this is an act of reclaiming a meal. This appears to be in contrast to a much clearer depiction of carcass stealing by Diego Barletta. Barletta's bear is highlighted by, from what I can tell, a very diagonally oriented series of digital pen strokes to accentuate the rainy scene of an Arctotherium attacking a group of canids and claiming their meal for its own. The heavy details of the rain make the whole scene appear to be slanted and adds in an aesthetic that probably has a term in the study of art that I do not know but very much enjoy and appreciate in appropriate scenarios, like this image.

Anatomy of the Bear

From Soibelzon and Schubert, 2011

The anatomy of Arctotherium is, at least superficially, almost the same as that of extant bears. There are differences in bone size and morphology from extant bears. The body plan has not changed in a very long time for bears because it is a very successful body plan. During the species exchange of the Great American Interchange the ancestors of Arctotherium and their competitors such as Smilodon were very successful in their invasion of South America. The portions of the anatomy that ultimately made Arctotherium successful, within the ursine body plan, were the robust limbs and strong but versatile cranium and teeth. As with extant bears, Arctotherium likely, as we have seen in papers, had an omnivorous diet. An omnivorous diet allows an animal like Arctotherium maintain the high caloric intake that a body of its size would require during times when either vegetation or prey animals might be scarce. A flexible diet is a winning characteristic in an invasive species as it allows it to expand into any niche that it can muscle itself into. Not having any natural predators or being a nearly 2 tonne bear certainly helps as well.

Bears On Paper

The makings of a giant bear are of great interest to many paleontologists, and therefore papers describing their size as well as their diet and how they got to be their giant size are common topics of study. In 2011, when the largest Arctotherium was discovered and made a great deal of news, Soibelzon and Schubert 2011 described that enormous specimen and inferred from the fossil the age as well as the diet of both Arctotherium and bears as an entire group; the more recent Soibelzon, et al., 2014 further details diet using isotope analysis and pathological evidence from fossils. Only a few years before the description of this enormous specimen Soibelzon, et al., 2009 had described an Arctotherium den and the inferences made from the den and the items found within greatly influenced the inferences that were then made on diet and size in the 2011 paper. The den also provided the first evidence of familial behaviors in Arctotherium. These two papers possess a lot of knowledge about these bears, their anatomy, and their behaviors. As such, we actually have a very large amount of data on Arctotherium behaviors and ecology. The many descriptions of fossil remains provide us with a great deal of anatomical information as well. However, many of the original descriptions are not hosted online, making Soibelzon and Schubert 2011 a good quality anatomical description of Arctotherium to consult for today.

Always Short Faced Bears

In general a lot of the pages and videos relating facts about extinct giant bears very vaguely name those bears "short-faced bears". Commonly, this is the name that is associated with the genus Arctodus, though the common name is often applied to Arctotherium as well. The name, when specifically referring to Arctotherium is typically amended to include the continent as well; South American Short-faced Bear. This article on LiveScience follows this trend as well, but does draw a very clear line by only discussing Arctotherium within the article. Many fact page online do not host pages for Arctotherium specifically, or do not add much information beyond what is available on Wikipedia. Interestingly, there is a very useful image that contains a lot of facts about the bear (specifically A. angustidens) shown as a layout in an issue of Epoca, a Brazilian magazine, from 2011. You may need a translator to find it useful. Also, feel free to correct this; there are three Epoca Magazines globally and the archives are not searchable for any of them.

The Biggest Bear

There is a plush Wookie on my table where I was trying to think of what animal we should focus on this week. The animals I decided to discuss this week, after staring at the plush toy for a few minutes, constitute the largest genera of bears that ever walked the planet. Consisting of 5 recognized species, the genus Arctotherium is a group of bears estimated to weigh in at a range from 1,588 to 1,749 kg (3,501 to 3,856 lb), though its height is similar to its ancestors, the bears of Arctodus. Most closely related to the extant Spectacled Bear (Tremarctos ornatus) of South America, Arctotherium represents one of the many animals that moved from North America to South America in the midst of the Great American Interchange. The largest specimen of the genus is an animal representing A. angustidens Gervais and Ameghino, 1880 recovered from Argentina. The other four species (A. vetustum Ameghino, 1885; A. wingei Ameghino, 1902; A. bonariense Gervais, 1852, type; A. tarijense Ameghino, 1902).

Shrimp in Action

We have shown many different illustrations, models, robots, and 3D models this week. Instead of a big long post about illustrations and all kinds of discussion about art, here is my favorite interpretation:

©Andrey Atuchin

The Popular Shrimp

In case anyone did not realize how popular Anomalocaris is, after all of the documentaries (minor and major) and different books, texts, robots, and multiple illustrations and photos of the Cambrian's largest predator, here is a picture I took Monday afternoon at Michael's, a hobby and craft store:

Though the eyes were not colored in like compound eyes, we can see that they do still feature prominently on this version of Anomalocaris. Toys are not the ultimate models of fossil animals, though this toy Anomalocaris does look a lot like a number of the good museum models that exist across the world. As an example, here are models from the National Dinosaur Museum in Canberra, Australia (left) and the Houston Museum of Natural Science (right).

Photo by Yinan Chen; CC0 1.0 Universal (CC0 1.0)

Photo by Photnart; CC0 1.0 Universal (CC0 1.0)

Perhaps, however, the ultimate popular culture manifestation of the admiration and love of Anomalocaris might just be this plush version of our favorite ocean going arthropod. I have to say that it honestly looks a little bit more fluffy and adorable than it does frightening and carnivorous.

Mouths and Arms

James St. John - (Burgess Shale Formation, Middle Cambrian;
Walcott Quarry, above Field, British Columbia, Canada)

The grasping appendage, sometimes called an arm, of Anomalocaris was approximately 45.72 cm (18 in) long and covered in spiky barbs. The arms and the spiky barbs would have served two important uses in the feeding behavior of the Cambrian predator: 1) to grasp and hold prey items and 2) to move the food near and into the mouth of Anomalocaris. These long grasping appendages, in coordination, with the large compound eyes made Anomalocaris an accurate predator, though of course we do not have any way to gauge its actual capture rate. Dragonflies, in the world of extent arthropods, are the most successful hunters with a prey capture rate that is approximately 95%. The current apex predators of the ocean, Great White Sharks and Orcas, have widely variable hunting success rates that are reported between 48% (for Great White Sharks) and 95% (for Orcas). Anomalocaris could have fallen anywhere in this range, but was most likely fairly successful given its high mobility, articulate (appearing) arms, and compound eyes. The mouth, of course, had quite an impact on the feeding capabilities of Anomalocaris as well.

James St. John - Anomalocaris canadensis mouthpiece
(~5.25 x ~4.25 cm) from the Walcott Quarry, Burgess Shale

The mouth of Anomalocaris consisted of 32 oral plates that have, multiple times, been compared to pineapple rings. The plates were constituted of 4 large and 28 small interlocking plates that were ringed internally by denticulate prongs that, thanks to multiple specimens, have been observed stretching down the entire gullet of the animal. This ring, save where the denticulate prongs would meet or occlude, was capable of closing and crushing, effectively biting in a circular motion, the trilobites that it shared the Cambrian waters with.

A Few Good Papers

There are numerous papers on trilobite wounds and feeding in the Cambrian sea as inferred from ichnofossils and taphonomic studies (as a singular example consider Selly, et al. 2015). Many of these address the mouth and feeding appendages of Anomalocaris; however, before considering how the animal was capable of biting and wounding prey or grasping its prey and pulling it toward its mouth, one needs to understand how all of the elements of Anomalocaris anatomy come together. Descriptions of the animal can be found in many different places, but one of the more intense versions of a description of Anomalocaris is Whittington and Briggs, 1985. The authors describe not only the genus Anomalocaris in great detail, but also the general stratigraphic surroundings of all known (at the time) specimens of Anomalocaris and each species in greater detail including the holotypes and any referred material then known. As a comprehensive description for understanding the species this paper is a must read. However, it is a highly detailed scientific paper, and it can therefore be a difficult read as well. One of the first portions of the 40 page article is a terminology section which should help non-scientist readers, arguably. If reading through an article of this length is not for you today, though, popular science articles like Briggs 1994 (includes discussion of a robotic model used to analyze swimming in Anomalocaris), Patterson, et al., 2011 (previously mentioned discussing compound eyes), and Nedin 1999 (for more discussion about the mouth and feeding in Anomalocaris).

Anomalocaris on Tape

The way of the on-tape documentary has gone, so saying that Anomalocaris is more well known from its appearance on a taped documentary is not entirely correct, though it is certainly where most know the name and general shape of the Cambrian animal Anomalocaris. Despite existing entirely as a 3D digital model in underwater scenes of the first episode of the Walking with Series in which it appears, Anomalocaris has made a lasting impression in the minds of paleontologists, people afraid of creepy sea creatures, and most likely some impressionable youngsters that just like documentaries about odd creatures. Anomalocaris has appeared in other documentaries as well, but its general model is the same. Regardless of which documentary we watch, Anomalocaris is depicted as a very active predatory arthropod. Anomalocaris was capable of breaking into the hardened shells protecting the bodies of its prey items, such as the trilobites shown in this documentary clip. A general overview of Anomalocaris is also available, in a separate and previously unknown, to me, documentary that lasts approximately 11 minutes. This is the direct link shared below:

Largest Facts of the Burgess Shale

The largest known animal of the Burgess Shale is Anomalocaris and this undisputed fact is often the first fact mentioned on any site that discusses the facts we know about this (as the Smithsonian calls it) proto-arthropod. The scale shared yesterday considers the largest known specimens of the genus; however, related and possible members of the genus recovered from China approach 1.8 m (6 ft) long. The scale on Prehistoric Wildlife's page detailing Anomalocaris does show what a nearly 6 foot animal would look like compared to an average human. The page also has a rather extensive list of suggested reading; this constitutes a good source of papers for getting ahead of those papers that will be shared on Tuesday. The page also contains a rather extensive description of the history of the animal's discovery and description of Anomalocaris.

The best image of Anomalocaris on a fact page is probably the illustration on DKfindout's encyclopedia page, though the page itself does not share as much detailed information as either the Smithsonian or Prehistoric Wildlife pages. This illustration makes the eyes of Anomalocaris very obvious, though the page does not directly address the interesting optic organs. Luckily, though, scientists have noticed that this Cambrian predator (or potential filter feeder) has well developed eyes. Discover Magazine's Ed Yong authored an article just over 6 years ago wrote a scientific journalism article detailing the first detailed discovery and description of Anomalocaris eyes by John Paterson of the University of New England (in Australia, not the northeastern United States). Doctor Paterson discovered, in a massive number of Anomalocaris fossils from southern Australia's Emu Bay Shale deposits, a pair of sophisticated compound eyes containing an estimated 16,700 lenses on the best preserved surface; estimations of total eye coverage may be discussed later this week providing I can find such information.

Welcome Back to Crazy Animals

©Dinoguy2 CC BY-SA 3.0

Coming back from a short hiatus and a very long Twitter feed at a scientific conference, this blog is ready to talk fossils and extinct animals again. We are going to go back pretty far into the fossil record for this first week back too. As I stated in the name change post, we are expanding our view beyond dinosaurs alone and even further than we ever have in the past (such as mammals and amphibians). To start looking at how massive the fossil record truly is, we will relaunch this week looking at one of the earliest known large sea creatures, an arthropod genus known as the "Abnormal Shrimp"; Anomalocaris. Some may recognize the name from the documentary series Walking with Prehistoric Monsters, the final series in the Walking with series of documentaries. Known largely from deposits of the Burgess Shale and other shales such as the Ogygopsis Shale (a subseries of the Burgess Shale), Anomalocaris consists of two accepted species and a third more contentious species. The original fossils, dating from 1892, consisted of a deceptively separated "arm", now known to be an individual portion of the feeding appendages encased in Middle Cambrian (508 MA) shales. The fragmentary nature of many specimens of Anomalocaris have, in the past, led to this single type of animal being labeled as many different animals and different types of animals. The body consists of many lobes and, as with all arthropods, these lobes are covered in a mineralized shell. The frightening look of this multi-lobed, shelled animal may be more a remnant of its alien (to us) body plan than it was an actually frightening carnivorous animal. One of the three species appears to have possessed robust feeding appendages capable of piercing the shells of other animals of the Cambrian sea; however, the other two species do not possess these and the diet of these other two species has been hypothesized to have been filter feeding rather than carnivory. Multiple dietary preferences in this genus point to a much more diverse group than has been portrayed in common accounts and means that the animal we are going to discuss this week is much more complex than originally thought as well.

SICB Twitter Feed

Dear readers, I apologize for not having written earlier, but I've been far busier than I assumed I would be. Below find the Twitter feed of SICB material I promised. I may need to edit the code later, but that's easier on a laptop, and I am on my phone right now! Tweets by DinootWeek_INC

Small Change of Name

I promised a small change of name around the time of the new year, but I have to admit that coming up with a new name was not all that easy. We wanted something that was all encompassing, still short, but did not look like we were specifically going to discuss only dinosaurs all the time. The truth of the matter is that there are a lot of different kinds of fossils out there still and only talking about dinosaurs limits the scope of the entries here and the whole of life's difficult history on Earth. We are going to continue discussing all extinct animals but with this small change of name there will no longer be any question about whether or not we are going to talk about birds or mice or dinosaurs or even human ancestors. Additionally, we will continue to discuss life from all eras, including extinct animals that went extinct due to human caused circumstances.

This week, however, we are not going to have an individual taxon to discuss. Instead I will be posting some short daily recaps of free-to-release information from the Society for Integrative and Comparative Biology meeting in San Francisco (so long as my flights stop getting cancelled). Whenever I can manage and am allowed, I will post interesting pictures and snippets of the conference as well on Twitter (here) and Facebook (here).