Awesome... Antennae? or Forks?

 Walliserops, a genus consisting of four recognized species, is a really interesting group of trilobites. Known from Devonian rocks of Morocco, there are a number of interesting anatomical features in these trilobites. All species of Walliserops exhibit some asymmetry, that is, the halves of their bodies are not identical on both sides, due to the curvature of the spine on the occipital lobe of the cephalon. Three spines in total originate from the cephalon. The occipital spine in the middle and farthest back (most caudal) and two more lateral spines located near or on the palpebral lobes, caudal to the compound eyes. Many trilobites have some kinds of spines on the cephalon or on the thorax (or both) and these are not what make this genus so interesting. What makes them truly interesting is the trident shaped fork protruding from the forward-most ridge of the cephalon. Each species has a distinctly shaped and different length trident. The exact purpose these tridents is not understood and, at one point, it was thought that they signalled differences between the sexes. This has been considered an interesting hypothesis, but is not considered a fact, as there is not enough evidence to support this claim. A plausible hypothesis states that the tridents were likely similar to the horns of the rhinoceros beetle, which are used for sparing against rivals during mating season and occasionally for digging. Of course, whatever the reason for the trident, it is a very interesting anatomical structure and makes the members of this genus appear very well protected (considering all of their spines as well).

Sources to Consider:

Brett, K. and Chatterton, N. (2001). Parabolops, a new asteropygine trilobite from southern Morocco with an unusual trident-like anterior cephalic frontal process. 3rd International Conference on Trilobites and their Relatives. University of Oxford.

Knell, R. J. and Fortey, R. A. (2005). "Trilobite spines and beetle horns: sexual selection in the Palaeozoic?". Biology Letters. 1: 196–199. doi:10.1098/rsbl.2005.0304. 

Whittington, H. B. (1997). "Mode of Life, Habits and Occurrence". In R. L. Kaesler (ed.). Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, revised. Volume 1: Introduction, Order Agnostida, Order Redlichiida. Boulder, Colorado & Lawrence, Kansas: The Geological Society of America, Inc. & The University of Kansas.

Triarthrus - Preserved Legs and Antennae

Often when we imagine a "typical" trilobite we picture an animal something like this genus, Triarthrus. Known from the Upper Ordivician soils of North America (midwestern states as well as New York and regions of Canada), China, and Scandinavia, Triarthrus is one of the final lineages of Olenid trilobites which was highly successful and very diverse during the Cambrian. Triarthrus is so well represented in the fossil record and considered so highly "typical" of trilobites that it is often used as the textbook example of what a trilobite looks like. One of the best preserved species within this genus is T. eatoni, is known from the state of New York and Canada (multiple sites across the provinces of Ontario and Quebec). Shale and iron pyrite deposits in these areas, especially the Franklin Shale in the state of New York, have produced specimens so exceptionally preserved that legs and associated appendages, gills, and antennae are perfectly retained in the fossils. A single location in New York, the Beecher's Trilobite  Bed, is world known; Triarthrus makes up approximately 85% of all of the material that has been recovered in that location. An entire community, including the shed and discarded remains of younger life stages, of T. eatoni are known from the Franklin Shale. 

This community graveyard of Triarthrus has allowed for a great deal of interpretation concerning the life cycle of these animals. The discarded exoskeletons of members that could float about with plankton were interspersed with the exoskeletons of 2mm sea floor dwelling individuals and, of course, a large number of larger exoskeletons of adults. Though 2mm may appear to be minuscule, adults of T. eatoni were not very large overall either, at approximately 5cm (50mm). Triarthrus individuals are preserved in a variety of configurations; lateral dorsal, and ventral views are all well represented. 

Other discoveries of T. eatoni have led to the discovery of trilobite eggs as well. Because of all of these exquisitely preserved Triarthrus specimens, we know much about its life from birth to death. The image below shows a ventral view of a well preserved T. eatoni with eggs preserved near the cephalon shield. The eggs were photographed in the study of this fossil by Thomas A. Hegna using a scanning electron microscope. 

Image credit: Thomas A. Hegna et al, doi: 10.1130/G38773.1.

Short Time

Rather than rush a post today (the first day of the semester was rather busy), I want to encourage you all to listen to Dr. Melanie J. Hopkins discuss trilobite fossils. She is an authority on trilobite evolution and paleobiology and knows a lot of valuable information about these intriguing arthropods. Take a 20 minute break from whatever you might be doing and listen to someone that really knows their science share their knowledge with you!

General Anatomical Survey of Trilobites

Calling trilobite anatomy simple is not fair to these highly diverse creatures. Some of their fossils may make their anatomy appear to be highly simplified, but many of those fossils are lacking imprints and other evidence of the complex soft structures, fine details, and even fragile hard structures that also make up the bodies and appendages of trilobites. There are many great finds that do preserve these types of structures, so we do have information about them. These structures are variable across species, of course, and will be better described in individual circumstances. There are abundant excellently preserved core exoskeletons of these animals, and this generalized regional anatomy is our focus today. Discussing them in the simplest terms, however, we are able to break down trilobites into six general regions. 

 

We can break them down from one side to the other (4 - 6 below) and describe the right pleural, axial, and left pleural lobes. These three lobes are where the name trilobite originates from. Pleura is a word of medieval Latin and Greek origin that means "to the side of the body" and is often used in zoology to describe the sidewalls of arthropods. The pleural lobes are literally the "side lobes". The axial lobe, then, is the lobe that makes up the center of the body. 

We can also break down trilobite anatomy by discussing it from head to tail (1 - 3 below). The head region is known as the cephalon (1), the middle region is the thorax (2), and the tail region is the pygidium (3). The cephalon can be broken down into many different smaller regions based on facial sutures (natural fractures separating components of the head) that include preocular and postocular (before and after the eyes, respectively), the rostrum (the "nose" or front end part), and the hypostome ("mouth" part). The cephalon includes the mouth area of the trilobite, houses the compound eyes, and would have had attachments for antennae. The large lateral (side) flanges or fringes are also a part of the cephalon, regardless of how long they may have been; some trilobite species had lateral fringes that extended to being nearly the length of their body. 

 

The thorax is the middle region of the body and is made up of multiple articulated segments. The number was variable between species and could be as few as two and as many as 103. The thorax helped to protect vital organs of the trilobite, including the gills, and served as the attachment site for the limbs; the thorax  therefore protected the limbs as well. The articulation of these segments is such that they allow for "rolling up" as can be seen in modern pill bugs (I always called them "roly-pollies" when I was a kid). Fossils of this activity have been discovered and it is thought to have been a protective measure that trilobites employed against predators. The pygidium is the most posterior portion of the trilobite. It is formed by the fusing of a number of smaller segments, like those making up the thorax, and the most posterior portion of the animal, the telson.

 Sources to consider:

Bruton, D. L.; Nakrem, H. A. (2005), "Enrollment in a Middle Ordovician agnostoid trilobite", Acta Palaeontologica Polonica (3 ed.), 50: 441–448, retrieved June 22, 2009

Paterson, J.R.; Edgecombe, G.D. (2006). "The Early Cambrian trilobite Family Emuellidae Popock, 1970: Systematic position and revision of Australian Species". Journal of Paleontology. 85 (3): 496–513.

Whittington, H. B. (1997), "Morphology of the Exoskeleton", in Kaesler, R. L. (ed.), Treatise on Invertebrate Paleontology, Part O, Arthropoda 1, Trilobita, revised. Volume 1: Introduction, Order Agnostida, Order Redlichiida, Boulder, CO & Lawrence, KA: The Geological Society of America, Inc. & The University of Kansas, pp. 1–85.

Things We Do Not Talk About

There is an entire Class of animals that we have not really discussed. They are always right there when we look up fossils. We should take a closer look at these alien, but very familiar, animals. Appearing between 540 and 520 million years ago, the Class we know as the Trilobites, are ovoid, sometimes clearly showing appendages, arthropods that existed until shortly before the end Permian extinction. No existing direct descendants of trilobites exist today. However, in the age of the greatest diversity of trilobites, from the Early Cambrian to the end-Permian, there are 11 known orders of trilobites that includes more than 30 genera and many more species. Talking about "the trilobite" fossils is actually quite misleading. Usually when someone mentions trilobites they conjure up images of trilobites such as Ogygopsis, or Meroperix. Perhaps you might think of a less ovoid member of the group, one that has large head elements, like Paradoxides, or with long tail structures, like Cheirurus. We will look at general anatomy of trilobites tomorrow, then, during the rest of the week, we will discuss some specific examples of genera or species of iconic trilobites.

Freshwater Sharks

 Growing up we often kept Rainbow sharks in aquaria. These streamlined pets were fast when they wanted to be and were fairly aggressive. They often jumped from out of the tanks as well. We stopped keeping them after a while. However, these are not true sharks and freshwater sharks are globally rare in modern times.The most common are those of the genus Glyphis, commonly called "river sharks", and Carcharhinus leucas, commonly known as the bull shark. The bull shark is known worldwide (and by many names such as Zambezi shark, Lake Nicaragua shark, and freshwater whaler, to name a few), whereas the Glyphis sharks are less well known, by the general public, but they also enjoy a global distribution. Four extant Glyphis species inhabit mainly southeast Asian, Indian, and Australian rivers including the Ganges, Brahmaputra, and Adelaide Rivers (this is a small fraction of the rivers the extant species inhabit). Two extinct species, G. hastalis and G. pagoda are known from British and southern Asian fluvial fossil records respectively. The most important difference between Glyphis sharks and bull sharks is that the Glyphis sharks are true freshwater-only sharks, whereas the bull shark can adapt and survive in freshwater, but is more suited to marine environments. We could discuss the shallow, brackish water suitability and aggressive nature of bull sharks for days, but we are more interested in the history of freshwater sharks today. 

Glyphis sharks are more closely related to ocean-going tiger sharks and reef sharks than they are the original, well represented freshwater sharks. Many fossils from the Order Xenacanthida are known from the Carboniferous Period. The most well known are Xenacanthus and Orthacanthus. Xenacanthus may be the better known genus, on the internet at least, and consisted of many more species than Orthacanthus, even having some species survive the end Permian extinction event and last into the Triassic. Orthacanthus, however, appears to have been an older lineage and died out well before the end Permian extinction event. Both genera of freshwater shark were apex predators in freshwater environments and were likely in direct competition in freshwater environments throughout their existence. Orthacanthus, has a well documented predatory lifestyle. Coprolites (fossilized feces) from Orthacanthus have been discovered containing the remains (often teeth but also bones) of smaller Orthacanthus (cannibalism), other Xenacanthid, tetrapods, and various other fish. The coprolites are known to come from Orthacanthus because skin and other soft tissue impressions in fossils have allowed paleontologists to reconstruct rectal anatomy of Orthacanthus and match this anatomy to the shapes of coprolites.

The Cretaceous Sharp Nose

 During the Cretaceous, when the crushing Ptychodus sharks were breaking open shells, sharks were often not the greatest predators in the neighborhood. They competed with plesiosaurs, tylosaurs, and even Xiphactinus, a very large fish with impressive dental hardware. Despite being outclassed in many of the world's oceans, sharks were still capable of becoming apex predators and competing directly with their fish and marine reptile neighbors. One of the sharks most capable of direct competition in the Cretaceous seas and oceans was the rather large (up to 8 m, 26 ft, and 3400 kg, 3.3 tons) mackerel shark, Cretoxyrhina. Mackerel sharks are sharks in the Order Lamniformes and are fast, powerful, ocean swimming sharks. The most notable living member of this group is the Great White Shark, which grows to approximately the same size as Cretoxyrhina is thought to have grown to. The genus Cretoxyrhina consists of four recognized species with C. mantelli being the first described; initially teeth of the shark were described in 1822 by Gideon Mantell as a modern shark's teeth and a second formally published description, honoring Mantell, was written in 1835 by Louis Agassiz. These teeth were all collected from England, but a number of exceptionally well-preserved vertebral columns (and some associated other elements including teeth) are known from the work of George F. Sternberg, and his father Charles H. Sternberg, that was conducted in the state of Kansas in the mid-western United States of America. 

 Charles Sternberg found a skeleton and 250 teeth in 1890 that were sold to a German museum (it was destroyed during WWII), but George Sternberg found many skeletons of Cretoxyrhina. The first (1891) contained portions of the jaw as well as a last meal of Xiphactinus and 150 teeth. In 1950 and 1965 he found even more of the shark, including specimens with preserved gills, portions of the skull, complete jaws, and pectoral fins. These are exceptional discoveries because, as many of us may know, sharks are cartilaginous fish, and much of their skeleton is difficult to preserve. Teeth are typical remains that we possess for sharks because of their durability, continuous replacement (allowing for many more teeth to be potentially preserved compared to whole individuals), and the number each animal possesses; remember that Charles Sternberg found 250 teeth in his 1890 fossil.

These large sharks, and their teeth, are associated with numerous other fossils, indicating what kinds of animals they fed on regularly. These include fish like, and including, Xiphactinus, plesiosaurs, mosasaurs, turtles, other sharks, and even pterosaurs and dinosaurs. Pterosaurs are thought to have sometimes fished over ocean waters, and it is thought, as shown in the Mark P. Witton illustration below, taht the sharks may have actively hunted low flying pterosaurs such as Pteranodon. Dinosaurs are often considered a scavanged meal in relation to Cretoxyrhina, showing that the shark was an opportunistic hunter as well. One hypothesis, involving a Claosaurus (shown below also), is that dinosaurs sometimes died on the shore, during a flooding event, or in some other way that enabled their bodies to float out into the ocean where they were eaten by sea creatures of all sorts. Evidence for Cretoxyrhina feeding on dinosaurs includes not only the hadrosaur Claosaurus, but also the nodosaurian Niobrarasaurus. The evidence for larger prey (fish have been found in the stomach areas of Cretoxyrhina) such as plesiosaurs, pterosaurs, and the dinosaur mentioned is mostly based on Cretoxyrhina teeth embedded in bones, where they were broken off during biting and feeding. Finding shark teeth in bone is very interesting. A plesiosaur vertebral column I worked with had shark teeth embedded. I did not diagnose the teeth, but the animal was from a time and area populated by Cretoxyrhina, so it is a likely culprit to include in the list of suspects.

Crushing it in the Cretaceous

Yesterday we went over a bit of the development of sharks and discussed an early group of sharks that has persisted since the dawn of recognizable sharks and their jaw arrangements. Today we are going to look at a Cretaceous era group of sharks in the genus Ptychodus. These sharks possessed interesting teeth that would not be recognizable as shark teeth but were efficient and crushing and smashing food items, specifically large bivalves and crustaceans. Large numbers of the fossils of Ptychodus are known from the middle of North America in what was, during the Cretaceous, the Western Interior Seaway, but the distribution of Ptychodus species (22 species overall) is truly global. Part of the reason that large numbers of these fossils are known from the Western Interior Seaway is that this area, encompassing what is now the dry land stretching from the Gulf of Mexico to the Arctic Circle, is thought to be the last "stronghold" of Ptychodus sharks before their extinction around 85 million years ago.

The teeth of the Ptychodus sharks are peculiar, for a shark, as I noted above. Rather than individual conical, spiny, or serrated wedge shaped teeth, Ptychodus sharks possessed large crushing plates. These plates were known as early as 1822 from the Mantell illustrations by Mary Ann Mantell and likely could have been known earlier than this, but without published scientific scrutiny. The plates consist of multiple lobed projections and would have been used to crunch down on the shells of the sharks food items. In any kind of territorial battles it could have been used to bite down and crush other Ptychodus fins and bodies as well. My hypothesis is that being bitten by this shark would feel something like slamming one's hand in a car door. Or possibly more like being hit by a meat tenderizer. Regardless, it would likely hurt.

The Gilded Age of Hexanchus

 The Devonian Era saw sharks developing and diversifying under the "rule" of larger armored fish like Dunkleosteus. Sharks diverged from their cousins, the Chimaeriformes, somewhere around the time of yesterday's animal, Cladoselache; this branching is not completely understood, even leading to some discussion, but nothing definitive, about placing Cladoselache in the Chimaeriformes group. As the Devonian Era came to a close (also the start of the Carboniferous Era, approximately 359 million years ago) approximately three quarters of all species on the planet became extinct, including many of the larger fish. This left an apex predator role open and sharks and chimaera expertly filled that role, continuing to diversify and increase their overall size. Many of the best known of the Carboniferous sharks are actually members of the Chimaera branch of the family tree. These include the anvil finned Stethacanthus and the wheel-mouthed Helicoprion. Despite being outshined by their Chimaera cousins during the Carboniferous, the sharks began to develop the characteristic jaws full of teeth that we now associate with sharks. The end Permian extinction (252 million years ago), which caused the extinction of approximately 96% of all marine, was significant for the shark species that survived. With their mouths full of teeth and few rivals (including their Chimaera cousins), sharks truly became masters of the ocean for some time; as marine reptiles evolved the balance of power would shift again. During the Jurassic Period (195 million years ago) the first modern sharks began to appear. These include the genus Hexanchus, which includes one of the oldest surviving lineages of shark: Hexanchus griseus, commonly called the Bluntnose sixgill shark.

Bluntnose sharks would fall into the common misnomer of "living fossil" as evidence of their existence is extensive in the form of fossilized teeth from the Mesozoic Era. The fact that more of its relatives are extinct than living and that this shark has a primitive body plan with a single dorsal fin, broad rounded pectoral fins, and a number of gills (six) that is between the more primitive sharks (possessing seven) and the more derived sharks (possessing five). The Bluntnose sixgill shark, one may complain, is not a fossil animal and therefore has "no place" on a fossil animal discussion platform. However, as a shark with more extinct relatives than living relatives, the living Bluntnose sixgill sharks is a living breathing representation of Hexanchus sharks that came before it. Not much has changed in this genus either; hence the "living fossil" misnomer. Hexanchus sharks (collectively known as "Cow Sharks" within the family Hexanchidae) belong to the order Hexanchiformes and are described as the most primitive group of sharks. To compare the living and the fossil is not always easy with these sharks, as many of the fossils are teeth and very little else (skin impressions do exist but are a bit more rare than teeth).

Dawn of Sharks

 Regarded as the first genus of shark, Cladoselache is a group of 8 recognized species, all from North America. These sharks are commonly called "scaleless sharks". They retain many ancestral characteristics including very fish-like heads and more than five gills (most modern sharks have five gills). The fins of these sharks possessed spines consisting of dentine and enamel, making them on of the strongest portions of the external surface of the body. The skin itself was almost entirely scaleless, possessing scales only near the eyes, mouth, fins, and portions of the tail. We know this because there are numerous exceptionally well-preserved members of the genus; so well preserved that we have internal organs such as the kidneys in the Cladoselache fossil record. Smaller muscles, a semi-scaled tail, and a semi-lunate shape that was nearly symmetrical all came together to form a lightweight, lower (than modern sharks) powered shark that was considered capable bursts of speed rather than maintained high speeds. 

 

Those short bursts of speed would have been immensely important to these small ~ 1.8 m (5.9 ft) long sharks. They are known from the oceans that covered modern North America approximately 380 million years ago during the Devonian time period. At this time, the apex predator of these oceans was the giant placoderm (armored) fish Dunkleosteus. These first scaleless sharks were were on the menu for most of the time that Dunkleosteus ruled the oceans. However, the scaleless sharks diversified during this time and their descendants outlived Dunkleosteus and eventually became the apex predators we know today from these fairly humble fishy origins.

Hammerhead Body

The body of Atopodentatus is fairly unremarkable in reconstructions. Other than the hammerhead face of the animal, its body is something we would consider rather typical for a swimming marine reptile. There are basic flippers on the forelimb and hindlimb; show here as early flippers with the digits extending just beyond the edges of the webbing. In appearance these flippers are not unlike the feet of ducks. They are less like the flippers we typically see in marine reptile reconstructions (plesiosaurs and ichtyhosaurs in particular) or in living marine reptiles (think of sea turtles). These flippers likely influence the evolution of the tail as well.

The tail of the animal is not paddle-like, and therefore probably not adapted for powered swimming. Considering the evolving flippers, that tail might not have been used in swimming at all. We could hypothesize that over time and evolution that the tail would become smaller (thinner, shorter, or any combination) like those of turtles or some of the plesiosaurs that we know. The tail would probably aid in turning a very small amount, if at all. However, it is unlikely that this algae grazing reptile needed to turn quickly in its daily life, so the tail not serving as a rudder or a propeller is not unexpected. I cannot speak to its overall speed, and I don't know if there is much study in that area either yet and saying that it likely didn't need to turn quickly is not an indictment of its overall traveling speed. I imagine, just as an off the cuff idea, that Atopodentatus was much closer to a manatee  or a sea turtle than other animals in terms of its swimming speeds. That would allow for short bursts, but overall indicate a nice slow meandering through much of its daily life.

The body itself, in the image below, is fairly average sized. There are reconstructions that show Atopodentatus with a more manatee-like pot belly as well. This imagery meshes well with the increased size we see in many herbivorous animals. One of the reasons for that, many of us know, is the need for increased digestive organ space. In some animals that can include elongated intestinal tracts, multiple stomachs, or organs like gizzards or crops that serve pre-digestive roles and often contain rocks to help grind down plant matter. Could Atopodentatus have had any of these kinds of extra long intestines or accessory organs? It is certainly possible! We would likely need a mummified fossil to be entirely certain, but some of the better preservations of this animal may also have clues. Could those accessory organs then lead to increase abdominal sizes in Atopodentatus? It is likely that they could, and, as noted before, some interpretations of reconstructions have included enlarged abdomens. That idea has permeated to the toy industry as well, so be prepared for young scientists whose first interactions with Atopodentatus are with an elongate, hammerheaded, and pudgy marine reptile.

One More Head Post

In Luoping County in the Yunnan province of China in 2016 the newest fossil of Atopodentatus was discovered. That fossil, as we have seen, offered a very different perspective of the way that the jaws looked in this animal. That change, as we mentioned, required a new interpretation of how Atopodentatus was able to feed and what it fed on. Previously, the initial description described a filter-feeding marine reptile that pushed its head into the muddy bottom of its environment and push out the sediment, filtering that sediment and water in hopes that it would trap small arthropods hiding in the sediments. In the newer description, the change in the dental landscape called for a new interpretation. Instead, the new hypothesis proposed by Chun et al. 2016 (https://advances.sciencemag.org/content/2/5/e1501659) detailed a mechanism in which the the small chisel-shaped teeth were used to scrape algal growths from rocks, plants, and other details of the underwater scenery. The authors also hypothesized that the more posterior teeth were capable of of helping to break up plants so as to be able to retrieve the algae from these materials as well.

As we can see from the paper, two new skulls were described, providing extra information about the organization of the mouth and face of Atopodentatus. These two skulls, in addition to the original (type) specimen allow for a very well defined reconstruction of the skull. Putting those three views of this animal together we end up with a reconstruction that fairly accurately portrays the actual organization of this animal. That allows us to better understand how it fed, how it swam (heads do have an aerodynamic property in all fluids after all), and possibly even how these animals may have interacted with one another. Could they bite each other in territorial disputes? Did they groom themselves, or one another on the beaches? Could they even get to the beaches? Remember, there is evidence of flipper-like digits on their limbs and we have not really determined their ability to "haul out" onto the beach in the first place. The head tells us a lot about behavior, but there is still more to this animal. We will look beyond the head tomorrow, so look at the fossils and reconstructions and consider what we might be able to glean from the bones and the interpretations of those bodies.

Two New Faces

Two Atopodentatus restorations, both by Nobu Tamura. The first was produced shortly after the initial description was published and is, admittedly, quite terrifying in many ways. It turns out that this initial find (published in 2014) was a little crushed, side to side, and the upper and lower jaws (maxillae and mandibulae respectively) were misplaced. The subsequent find (published in 2016) of a differently arranged, and apparently better preserved, skull changed the way that paleontologists, and artists, interpreted the mouth, in particular, of Atopodentatus. This arrangement of teeth (and mouth) is definitely still odd and unique, but helped to better understand the likely feeding habits of this interesting marine reptile.

This fossil, in a short amount of time, shows how new discoveries can change not only how we view an animal, but also how we can, and often need to, change our perspectives and hypotheses due to new discoveries. It also helped to clear up some mysteries about Atopodentatus (e.g. How did it eat with the originally reconstructed mouth? What could it have possibly be eating?)

A Short Video for your Sunday

1) Minor correction, I had a typo in the name of Atopodentatus yesterday, it has been fixed though!

2) Now, please enjoy some background info on the world of Atopodentatus and then some more on the animal itself in this video.

Vegetarian Hammerheads

We typically write about dinosaurs here. We then branched into mammals at different points. We sometimes even talked about birds, small reptiles, varied reptiles (turtles, snakes, etc.), and amphibians from time to time. We have discussed traditional looking animals (i.e. animals that we expect to look a certain way as in T. rex always looks kind of like we expect T. rex to look). We have also looked at very odd looking animals (Megacerops and Ceratosaurus, I'm thinking immediately of you). I think we ought to restart with an animal that is different looking and from one of the interesting fringe groups that we have discussed. To top things off, this somewhat recently described animal looks like pretty much none of its closest living relatives, making it far from what we might expect to see.

Enough intrigue and vagueness, we will start off this month by discussing Atopodentatus unicus. An herbivorous pantestudine (a group that includes the living turtles, testudines, and their ancestors the extinct "stem-turtles") marine reptile that has been assigned as a possible primitive (basal) member of the sauropterygia (the "lizard flipper" group that includes long and short-necked plesiosaurs). This classification follows the Schoch and Sues 2015 phylogeny that places sauropterygia within pantestudines (one can find other arrangements of the family tree that make this description hard to accept). Regardless, this animal appears to be related to turtles, but also has a long neck and long limbs with elongate digits that appear to be situated into primitive flippers. It also has a long tail and many ribs and gastralia ("belly ribs"). Despite all of these "normal" sounding bodily descriptions of a large marine reptile that make it sound like a very typical swimming air-breather of the Triassic, its head is anything but normal.

The name Atopodentatus translates to "Unusual toothed" and, with a "zipper-like" smile of teeth, it is unicus ("unique"). The anterior part of the skull can best be described as "hammerheaded", with the teeth forming their "zipper-like" pattern at the front of the mouth. The entire head is not hammer head shaped, only the mouth. This formation is very interesting. It looks almost like a hadrosaur ("duck-billed" dinosaur) mouth, but filled with small peg-like teeth. Approximately 8 million years older than any other herbivorous marine reptile, Atopodentatus is thought to have fed on algae embedded in the sea floor.

An Exciting Opportunity

From the Facebook page of Julius Csotonyi:

A twist! On Sunday, join me in a drawing lesson on a rare modern-day survivor of the last ice age: the arctic ground squirrel or ᓯᒃᓯᒃ (pronounced "siksik") (Urocitellus parryii). Yukon paleontologist Dr. Grant Zazula will provide scientific commentary on this interesting (and large!) species of ground squirrel while I demonstrate its illustration, in an online event hosted by the Yukon Beringia Interpretive Centre at 1 pm Pacific Time on Sunday, June 14.

Penguins Part II

Inkayacu, was approximately the same size as Palaeeudyptes

 

Fossil penguins were not always penguin "shaped", as we saw with Waimanu, but they became more distinctively penguin-like over time, as we saw with Kumimanu. Intermediate family members like Perudyptes and Anthropornis continue this "penguinification" trend of the overall body plan throughout the Eocene era and, by the times of Icadyptes, Palaeeudyptes, and Inkayacu, penguins look like the animals we think of when we hear the name penguin. There is one rather enormous exception to their recognizable penguin form: these are very tall penguins. Additionally, some of these penguins were likely still using their feet, in some capacity, in propulsion for swimming. Though we mentioned that it appeared as though Kumimanu may not be using its feet anymore to swim, it has been noted that the feet and ankles of some of these larger penguins indicate that they may have still played a role in swimming.The Eocene was an age of giant birds. Whereas the "Terror Birds" ruled portions of South America terrestrially, the giant penguins were taking to the ocean and at least terrorizing fish populations. Sharks were still apex predators in the ocean. Whales were in the process of fully transitioning from land to water. Enormous penguins could have been filling a niche that is now occupied by small whales and dolphins (and even smaller sharks like the reef sharks). Whatever their absolutely exact role, they were clearly highly successful birds that transitioned back from a terrestrial lifestyle to a nearly fully aquatic lifestyle. They did so as large animals that, over time, became increasingly efficient swimmers with streamlined bodies. Even if whales, dolphins, and smaller sharks (possibly seals and sea lions as well) pushed them into a finer definition of a niche, one which they currently occupy as pursuit predators. The nuances of penguin evolution, locomotion, diet, and the life histories of individual species are all complex topics that span the careers of scientists. Hopefully these two discussions are helpful in a very general sense to understanding penguins and their history.

Penguins Part I

Waimanu manneringi ©Nobu Tamura

We know a lot about fossil penguins. Partly, this is because we have a fairly large number of fossils from penguins, which is a rarity for birds as a group in general. It's also a bit of a blessing. There are a number that are a little more well-known for various reasons (mostly to do with publication and news cycles) like Waimanu, Inkayacu, and Perudyptes; all penguins described since 2006. However, we have been recovering and describing penguin fossils since much earlier times: Pachydyptes (Oliver, 1930), Paraptenodytes (Ameghino, 1891), and Palaeosphenicus (Morino and Mercerat, 1891) are notable examples. Not all penguins are the same, so lumping them together is not really fair. However, their overall body plans are fairly conservative. Most members of the penguin family are recognizably penguin-like though ancestral members of the family are not exceptionally penguin-like. This includes Waimanu, an early member of the penguin family that has some penguin-like traits, but looks less like a penguin than we would imagine even an early penguin might appear. Waimanu has a longer tail and more wing-like upper limbs than we would expect a penguin to possess. However, its bill does look very much like the bill that we associate with fish catching birds and is reminiscent of that we see in penguins. The legs of Waimanu are more like those of a loon or a grebe and do not appear to be very useful for walking on land (just like those of loons and grebes). The position of the legs are better for swimming than for walking, to be honest, and from what we know about penguins, this makes a lot of sense.

Kumimanu biceae ©Nobu Tamura

Penguins do not swim with their legs though, they swim with their fins, their wings, providing propulsion underwater. So how does a penguin transition from leg power to wing power? The next oldest penguin we know (currently) from fossils, Kumimanu is decidedly more penguin-like. The feet look more like penguin feet. The tail is shorter than Waimanu's tail. The bill is still rather large and fish catching; not entirely penguin-like yet. We do have more flipper-like wings with Kumimanu, likely indicating that the legs are no longer propulsive and the flippers have taken over this function. The wings are not entirely like flippers that we see in modern day penguins though. Also, as we can see in Nobu Tamura's illustration, Kumimanu was a rather large early penguin. There are larger penguins that we know of, but rather than attempting to discuss all of the very important penguin fossils in one post, we will continue tomorrow with other notable penguins, some of which may be the largest penguins that ever lived.

Long Distance Hugs

We could probably all use some kind of interaction from outside our family these days. While we cannot really pat one another on the back and continue social distancing, there are animals that could have done so. One such animal was the ornithomimosaur Deinocheirus mirificus. Originally, a pair of arms and their shoulders were described in 1970 by Osmólska & Roniewicz, and Deinocheirus was originally thought to be some kind of carnosaur. The description was amended after some time to assign Deinocheirus to the ornithomimosaurs, but new material to even more thoroughly describe the dinosaur was unknown for nearly 50 years. In 2014 (49 years after the initial dig that found Deinocheirus remains) new remains were found in Mongolia (later they were stolen but then returned to the country) from two individuals of the species. At an estimated 11 m and 6.4 t, this was a large and heavy ornithomimosaur of the Late Cretaceous.

The enormous hands and long arms are thought to have been well adapted for digging, which, given the duckbill-like head that seems adapted for water and grass foraging, appears to be at odds with the hypothesized diet. A large number of gastroliths associated with Deinocheirus support a vegetation heavy diet, as the dinosaur would have used these to help break down the fibrous plant matter. It has been reported that fish vertebrae were also discovered along with the gastroliths, meaning that it is likely that Deinocheirus was eating fish as well. Could oversized hands be useful for catching fish? There is a possibility for this as a use, but digging and manipulation of vegetation remains a good hypothesis.

Digging, with large hands, could help efficiently find supplemental dietary items like insects and burrowing lizards; there is no known evidence for this behavior currently. Also unknown is the nesting behavior of these animals. Could hands good at digging make very good nesting mounds? This is also a potential hypothesis. Holding vegetation to crop (or chop) small amounts of food could also be plausible. Defense could also be a plausible explanation for the namesake "horrible hands". Injuries to the holotype digit joints and bitemarks in the coracoids near the shoulder indicate manipulation of the digits (important for dexterous activities noted above) and unsuccessful predation. These predation events are attributed to one of the largest predators on Earth during the Cretaceous, Tarbosaurus bataar.

©Abelov2014
Adapted by Wiki users from the original at (https://www.deviantart.com/abelov2014)

Talk to me on Twitter!

Hello all!

You're stuck at home. You're loved ones are stuck at home. I'm stuck at home. I'll be working on lectures and moving my class (and helping colleagues move online) all week. However, if you, your friends, or those lovely students you've suddenly been locked in with are looking for dinosaur or ornithology information over the coming weeks I'd like to offer what I can.

From 9am - 12pm EST during the weekdays I'll leave my Twitter feed (@ornithanatomist) open to questions. Maybe I'll get a lot of questions, maybe I won't! If you have questions, though, ask and I'll answer, find an answer (if I can), or point you to a good source to find the answer.

Stay tuned here and on Twitter. As I'm able I may be able to work out themed question days. I may (time permitting) be able to set up live Q & A sessions as well. Stay tuned everyone.