Elasmosaurus: Beast of the Week

 This week we will be checking out a sea beast who's proportions were so outrageous, it confused even scientists! Check out Elasmosaurus platyurus.

Elasmosaurus was a large reptile that lived in he sea that covered what is now central part of the United States during the late Cretaceous period, between 80 and 77 million years ago.  From snout to tail it would have measured about 34 feet (7.1m) and would have eaten meat when alive.  Its genus name translates to "plate reptile" in reference to how wide and flat some of its hip and chest bones were.  

Watercolor life reconstruction of Elasmosaurus by Christopher DiPiazza.

The first thing you notice about Elasmosaurus is its extremely long neck.  Plesiosaurs, the group of marine reptiles it belonged to, are famous for having long necks, but Elasmosaurus stands out even among them.  Proportionally one of the longest necks of any animal that ever lived, it accounts for more than half of its total body length.  Unlike many other kinds of long-necked animals, like giraffes or the sauropod dinosaurs, which evolved their necks by elongating the individual vertebrae, Elasmosaurus' ancestors appeared to have simply increased the number of vertebra instead, resulting in a whopping seventy two vertebra in just the neck! Because of this, Elasmosaurus' neck would have been relatively flexible, at least when it moved its head side to side.  (I like to compare it to one of those wooden snake toys that you can hold by the tail to make it move around.)  Because the neural arches on the tops of the neck vertebra were pretty tall, Elasmosaurus' vertical range of motion would have been much more limited.  This means that the iconic swan-like neck pose many older depictions of plesiosaurs, as well as most images of the Loch-Ness Monster and other lake cryptids based on plesiosaurs, are anatomically wrong.  

Cheap and surprisingly lifelike, this snake toy has limited movement in an up and down motion but pretty flexible side to side, similar to how Elasmosaurus' neck likely was.

The neck of Elasmosaurus is so unusually long, it even tricked scientists at the time of its discovery.  The first skeletal mount of Elasmosaurus accidentally has the head placed on the end of the tail, instead of the neck, since a reptile with a super long tail seemed more logical at first. (at least to the scientist who drew it)

Drawing of the initial interpretation of Elasmosaurus with the head incorrectly placed at the tip of the tail and has what was really the neck as a long tail.

So why such a long neck?  This is something paleontologists are still contemplating and we may never truly know the answer.  One strong hypothesis is the long neck would have allowed Elasmosaurus to get its head closer to fish, which it would have hunted, without scaring them away with its huge body, essentially tricking them into thinking it was smaller and less threatening, than it really was.  Another idea is the neck may have enabled Elasmosaurus to pursue prey that may have hidden between rocks or other difficult to reach places.  A third idea is that Elasmosaurus evolved such long neck due to sexual selection, being a sign of genetic fitness and therefore attractive as a mate.  Maybe rival Elasmosaurus settled disputes by showing off who had a longer neck?  We may never know for sure.

Elasmosaurus skeletal mount (with the head on the right end) on display at the Academy of Natural Sciences in Philadelphia, USA.

Elasmosaurus had a proportionally tiny head which was flattened top to bottom. Like most long-necked plesiosaurs, its eyes were positioned on the top of its head and its jaws were lined with long cone-shaped teeth that interlocked when its jaws were closed.  The longest teeth were in the front of the mouth, likely an adaptation to hold onto slippery fish prey. 

The body of Elasmosaurus is wide and almost turtle-like in shape and function, with virtually no flexibility, since some parts of its pelvis and shoulder blades were fused together at the midline of its torso, forming wide plate-shaped structures.  This would have made its body stable when swimming at higher speeds.  Like all plesiosaurs, its limbs were modified into long rigid flippers, with upper limb bones and joints suggesting they would have been able to move them like the oars of a boat as they swam for sustained periods of time. Similar to modern sea turtles, Elasmosaurus' front flippers appear to have been where most of its power for swimming came from while the hind flippers would have been more for steering.  It's tail was proportionally short and flattened from side to side like a rudder. 

Elasmosaurus' habitat was a shallow warm sea that existed in the middle of what is now the United States during the late Cretaceous, dividing the continent into two landmasses.  Many marine fossils have been unearthed and studied from there.  When alive Elasmosaurus would have shared its habitat with many kinds of fish, ammonites, turtles, seagoing birds, the pterosaur, Pteranodon, and of course, mosasaurs(marine lizards), including Tylosaurus, Globidens, and Prognathodon.

References

Cope, E. D. (1869). "Synopsis of the extinct Batrachia, Reptilia and Aves of North America, Part I". Transactions of the American Philosophical Society. 14: 44–55. 

Houssaye, A. (January 1, 2013). "Bone histology of aquatic reptiles: what does it tell us about secondary adaptation to an aquatic life?". Biological Journal of the Linnean Society. 108 (1): 3–21.

O'Gorman, J. P. (2016). "A Small Body Sized Non-Aristonectine Elasmosaurid (Sauropterygia, Plesiosauria) from the Late Cretaceous of Patagonia with Comments on the Relationships of the Patagonian and Antarctic Elasmosaurids". Ameghiniana. 53 (3): 245–268.

Sachs, S. (2005). "Redescription of Elasmosaurus platyurus Cope, 1868 (Plesiosauria: Elasmosauridae) from the Upper Cretaceous (lower Campanian) of Kansas, U.S.A". Paludicola. 5 (3): 92–106.

Haolong: Beast of the Week

 This week we'll be checking out a newly described dinosaur that is so unique, it completely changes what we think we knew about dinosaur skin!  Enter Haolong dongi!

Haolong was a plant-eating dinosaur that lived in what is now Liaoning, China, during the Early Cretaceous period, about 112.5 million years ago.  The only specimen on record measures about 8 feet (2.45m) from beak to tail but was a juvenile when it died so the species likely grew larger.  The genus name translates from Chinese to "Spiny Dragon" for a very good reason we are about to get into!

Life reconstruction of Haolong in watercolors by Christopher DiPiazza.

Haolong is an incredibly interesting find because it possesses a feature never before seen in any dinosaur.  like many dinosaur fossils found in this part of China, it includes more than bones, including much of its skin, which was scaly as you might expect for an ornithopod.  What nobody would have predicted, however, is the presence of pointed spines growing out from between the scales.  These spines are relatively short, extremely narrow, and tube shaped.  When examined with a microscope paleontologists were able to see that they were actually hollow with keratin (same material that the outer layer of claws and beaks are made of) outside and bony pulp on the inside.    These strange features are growing out from between the mosaic-like scales on much of the upper part of the dinosaur's body, stopping at the base of the tail.  It is a mystery as to exactly what these spines evolved for.  They very well could have been for protection against predators, similar to what modern hedgehogs have.  Others have suggested they may have also helped keep the dinosaur warm by providing extra insulation.  

Close up image of some of the spines found on Haolong.  These happen to be from the neck.  Image from the paper referenced below by Huang et al. 

In addition to the spines, the skin covering Haolong's tail was also preserved.  It possessed rows of broad overlapping shingle-like scales running down the top and sides of the tail, another feature never before seen in an ornithopod dinosaur.  

Haolong belonged to the iguanodontid family of ornithopod dinosaurs, so it was closely related to the famous Iguanodon, as well as dinosaurs like Mantellisaurus and Tenontosaurus.  Like them it had shorter front limbs than hind limbs and could have likely walked on two and four legs in life.  Each hand had five fingers.  The middle three were fused together into a mitt-like structure, and would have been for supporting its body when standing or walking on all fours.  The pinky jutted out to the side and would have been flexible, possibly to help grab plants.  The thumb claw was in the form of a cone-shaped spike, a trademark feature for iguanodontids.  The thumb spikes could have been for defense against predators but also very well could have been for combat within the species for dominance. (or both?)

Photograph of the complete fossilized skeleton of Haolong dongi. (image credit: Theirry Hubin, Institute of Natural Sciences)

On its skull Haolong possessed a large broad beak backed up by of relatively large blocky teeth in its jaws, which would have been ideal for chopping up plants.    

The environment Haolong lived in when alive would have been warm and humid based on the plant fossils that are found there, like horsetails and ferns, but thanks to paleontologists being able to examine growth rings on fossilized trees from there, we know it also was seasonally quite cold, down to 50 degrees Fahrenheit (10 degrees celsius).  Based on this it would make sense if Yaolong's unusual covering was indeed a way for it to maintain warmth.  Other dinosaurs it would have coexisted with were the therizinosaur, Beipaosaurus, the hawk-sized four-winged dromaeosaur, Changyuraptor, and the large fluffy tyrannosaur, Yutyrannus.  

References

Huang, J.; Wu, W.; Mao, L.; Bertozzo, F.; Dhouailly, D.; Robin, N.; Pittman, M.; Kaye, T. G.; Manucci, F.; He, X.; Wang, X.; Godefroit, P. (2026). "Cellular-level preservation of cutaneous spikes in an Early Cretaceous iguanodontian dinosaur". Nature Ecology & Evolution: 1–8.