STL Science Center

STL Science Center

20 January 2018

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).

19 January 2018

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

18 January 2018

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.

17 January 2018

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.

16 January 2018

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).

15 January 2018

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:

14 January 2018

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.