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More photos of Allosaurus from the AMNH

Greetings friends. In an earlier post from 2014, I put up some photographs which I took of the two Allosaurus skeletons that are on public display in the American Museum of Natural History (or AMNH for short) in New York City. I’ve recently uncovered some other photos which I took during a visit there in March 2019, and so I’m posting them here. Enjoy!

 

 

Allosaurus, revised

Greetings, all. For those who regularly visit this website, you will know that this post has been a long time coming. Years ago, I mentioned that I was planning on re-doing my Allosaurus drawing so that it would be more accurate. However, that project always seemed to be shuffled onto the back-burner in place of other things that I was working on. Well not anymore. I recently completed a detailed drawing of an Allosaurus head (another one of the projects on my to-do list that I never seemed to get around to doing) which you can look at here, and I’m happy to state that after a long delay, I’ve finally completed my updated full-body Allosaurus.

Below is an Allosaurus drawing which I made in July of 2013 and which I posted to this website at that time. This portrays Allosaurus in a color scheme based upon that seen in the 1999 BBC series Walking With Dinosaurs. I must state that, as flawed as this illustration is, this piece was actually itself an updated version of a drawing that I had made a couple of years earlier. Even so, upon reflection, while it was an improvement on my previous work, it still needed more improvement.

And here is my revised Allosaurus drawing, made in July of 2020. This drawing was made in 1:20 scale, which is my preferred scale for illustrating prehistoric animals. From the tip of its nose to the tip of its tail, this drawing measures precisely 21 inches long, which would make the real-life animal 35 feet long; this measurement is regularly given as the maximum size for Allosaurus fragilis. This drawing was made with No.2 pencil on printer paper.

Finally, here is a colorized version of the new drawing. Again, the color scheme is based upon that seen in Walking With Dinosaurs, but the coloration and the color patterns differ slightly from the original image seen at the top. The picture was colored using Crayola colored pencils and No.2 pencil for re-shading.

Nearly everything about my previous drawing was altered in order to make this present artwork. This includes:

  1. The head was changed to be more accurate in appearance. Designing the head took most of the research time.
  2. The shape of the eye’s pupil was changed from a sort of oval slit to being a circle.
  3. The neck was made thicker, more muscular, and not as strongly S-curved.
  4. The body was made deeper.
  5. The arms were slightly enlarged and the hands were changed to be more anatomically accurate.
  6. The legs were thickened to provide extra weight support.
  7. The orientation of the hip bones was shifted.
  8. The tail was thickened to provide better balance to the front of the body. The previous drawing was conspicuously front-heavy.
  9. The tail was slightly elongated.

As you can see, one of the major changes to this drawing was the addition of dermal scutes along its back and sides. Unlike osteoderms, dermal scutes are scales which are enlarged and unusually thick compared to other scales on the rest of the body. There is evidence from preserved skin impressions from stegosaurs and ceratopsians that their skins possessed patterns of dermal scutes, sometimes arranged in lines, and it is therefore possible that theropods had such a feature to their outward appearance as well. It also gives this particular Allosaurus a distinctly reptilian look to it. I decided not to include any type of feathering or some other filamentous structures to the skin.

I also chose to portray this animal in a walking pose rather than running. I think that too many of my drawings of bipedal dinosaurs portray them running Gregory Paul-style, and I wanted to show something more natural. Also, unlike Scott Hartman’s illustrations, the legs are not splayed so widely apart from each other that they’re halfway to performing a split. Mostly, a normal walking stride is about three times the length of the foot. In fact, I actually practiced walking back and forth in front of a mirror, bending my legs theropod-style, in order to get a rough idea of how the leg position on this drawing ought to look.

Keep your pencils sharp, everyone.

Allosaurus head

Hello everyone. Here is a drawing of the head of Allosaurus fragilis, the top predator of the Morrison Formation of Late Jurassic North America. This drawing has been on my to-do list for quite some time, and I’m happy that it’s finally finished. The drawing was made with No. 2 pencil on printer paper.

Evidence of Therizinosaurs in North America during the Late Cretaceous Period

Introduction

For many years, paleontologists have known about the presence of therizinosaurs (formerly classified as segnosaurs) in Asia, especially within what’s now Mongolia and China. However, Asia and North America were linked during a considerable portion of the Cretaceous Period, and this resulted in an interchange of faunas between the two continents, notably ceratopsians, pachycephalosaurs, tyrannosaurs, and maniraptorans. Could therizinosaurs, which had hitherto been exclusively Asian, have lived in North America as well?

A pair of Tarbosaurus attacking a herd of Therizinosaurus somewhere in Mongolia, approximately 80 million years ago. © Gregory S. Paul (1988). Image used with permission.

 

During the early 2000s, that question was answered with a definitive “yes”. Two genera of therizinosaurs have been described from North America, named Falcarius and Nothronychus. Falcarius represents possibly the earliest stage in therizinosaur evolution, dated to the early Cretaceous Period, while Nothronychus is much larger and more advanced and is dated to the middle Cretaceous. The presence of these two creatures clearly shows that therizinosaurs existed in North America, but so far they have only been found in rocks dated to the early and middle parts of the Cretaceous Period. One wonders if therizinosaurs managed to stay in North America right up until the end of the Mesozoic, 66 million years ago. Would they have kept evolving, becoming larger and more advanced? Would they have lived alongside Triceratops and Tyrannosaurus? (1)

It just so happens that there are a few pieces of evidence here and there which suggest that therizinosaurs did survive past the middle Cretaceous within North America, and that they kept living in North America up to the end of the Cretaceous Period.

 

The Evidence

The idea that there were therizinosaurs in late Cretaceous North America was first proposed by the German paleontologist Hans Sues in 1978. Specifically, he was writing about a particular specimen that had been uncovered in the Dinosaur Park Formation, located in Alberta, Canada, in rocks dated to the Campanian Stage of the Cretaceous Period. The specimen in question was a single “frontal” bone, which forms part of the skull. Today, this specimen is in the collections of the Carnegie Museum of Natural History, categorized as “CMN 12355” (NOT 12349 as you’ll sometimes see in internet searches). In his paper, Sues thought that this frontal bone belonged to a “raptor” dinosaur, and listed it as “gen. et sp. indet.”, which is an abbreviated Latin way of saying “genus and species undetermined” (2).

“CMN 12355”: A frontal bone which may belong to a therizinosaur. Left top: ventral view. Right top: dorsal view. Left bottom: lateral view. Right bottom: medial view. © Tracy Ford. Image from Paleofile.com. Used with permission. http://www.paleofile.com/Dinosaurs/Theropods/Segnosaurincertae.asp

 

Saying that this bone belonged to a raptor is understandable, since the dromaeosaurs and the therizinosaurs are related to each other. Both groups are located in a clade called the “maniraptorans”, which includes the ornithomimids, the oviraptorosaurs, the therizinosaurs, and famously, the dromaeosaurs and troodontids – the so-called “raptors” with their famous killing claws.

The second piece of evidence came in the early to mid 1980s. A single bone called an “astragalus”, which forms part of the ankle, was found in the Hell Creek Formation in rocks dated to the very end of the Cretaceous Period. In 1984, the Canadian paleontologist Dale Russell listed this single peculiar find in a long list of specimens uncovered in the Hell Creek Formation during the middle 1980s. However, this particular specimen has never been analyzed or described in a publication exclusively devoted to this bone. It is simply listed as “therizinosaurid indet.”. In 1992, Kenneth Carpenter looked at this bone, and concluded that it actually belonged to Tyrannosaurus, not a therizinosaur (3).

In 1987, the Canadian paleontologist Philip Currie, who is widely acknowledged as the world’s expert on meat-eating dinosaurs, took a second look at the frontal bone which Sues had examined in the late 1970s, and concluded that Hans Sues had made a mistake. It wasn’t a raptor, but was instead a “segnosaur”, which was the way therizinosaurs were called back then. Currie stated that the bone looked similar to the frontal bone of an Asian therizinosaur called Erlikosaurus, and so he reclassified the bone as “cf. Erlikosaurus” (4).

In 1992, Philip Currie did a more thorough examination of possible therizinosaur finds in Canada. He again wrote about the frontal bone which was initially described in 1978, but he also added two more specimens to the discussion table, both of which were housed in the collection of the Royal Tyrell Museum of Paleontology (RTMP). These specimens were given the identification codes “RTMP 81.16.231” (again, Currie classified this specimen as “cf. Erlikosaurus”) and “RTMP 79.15.1” (a “pedal ungual”, or foot claw, which was classified as “cf. therizinosaurid”) (5).

“RTMP 79.15.1”: A foot claw which may belong to a therizinosaur. © Tracy Ford. Image from Paleofile.com. Used with permission. http://www.paleofile.com/Dinosaurs/Theropods/Segnosaurincertae.asp

 

In 2001, Michael Ryan and Anthony Russell conducted their own analysis of North American therizinosaur finds. They confirmed Currie’s claim that the frontal bone found in 1978 did indeed come from a therizinosaur. They also wrote about a neck vertebra found in the Scollard Formation (specimen identification code is “RTMP 86.207.17”), which dates to the very end of the Cretaceous Period, and which they classified as “Therizinosauridae indet.” (6).

Body fossils of therizinosaurs may be rare in North America, but footprints which may belong to therizinosaurs are more abundant. The first footprints were discovered in the 1990s in the Harebell Formation of northwestern Wyoming. According to an article published in 1996, these footprints were unique because they looked like theropod prints except that they had four toes instead of three – unique among theropods, therizinosaurs have four main toes. The authors postulated that the footprints belonged to an animal whose physical remains had not yet been discovered (7).

In 2011, a single therizinosaur footprint was discovered in Denali National Park, Alaska. The rock that the footprint was found in was part of the Cantwell Formation, which spans 80-65 MYA, and the footprint was placed in a layer dated to about 71-69 MYA. Depending upon which source that you read concerning geological dating, this date of 71-69 MYA either marks the boundary between the where the Campanian Stage ends and the Maastrichtian Stage begins, or else it is the earliest phase of the Maastrichtian Stage. In 2012, Anthony R. Fiorillo of the Perot Museum of Nature and Science (located in Dallas, Texas) published an article concerning this peculiar footprint (8). You can see a photo of it here.

In 2013 and 2014, Anthony R. Fiorillo and a team of other researchers returned to the site in Denali National Park and found a total of thirty-one therizinosaur footprints, along with numerous hadrosaur footprints as well. Like the first footprint that had been found in 2011, all of the other footprints were in rock dated to 71-69 MYA. The fact that footprint trackways of both hadrosaurs and therizinosaurs were found together might indicate that these animals traveled together, possibly for mutual protection. An article was published in August 2018 detailing these discoveries (9).

 

Species Identification

As we have seen in the previous section, there is some evidence in the way of footprints and a handful of isolated bones which suggests that therizinosaurs inhabited North America during the late Campanian or early Maastrichtian Stages of the Cretaceous Period. However, is there any way that we can identify which particular genus or species that these fossils belong to?

The subject of identification has been especially contentious concerning the footprints that were found in Wyoming and Alaska. So far, footprints form the majority of finds that are attributed to late Cretaceous therizinosaurs within North America. The problem is that it is difficult to identify a particular genus or species based solely on footprints, unless the shape of the footprint is extremely distinctive. Another problem is that while footprints are abundant, very few body fossils have been found, and none of them are highly diagnostic. Most researchers who examined them determined vaguely that the creature was a therizinosaur, but they couldn’t be more specific than that, with the exception of Philip Currie who proposed that they might belong to Erlikosaurus or a creature very similar to it.

Because it is so difficult to match a footprint with a particular animal, paleontologists often ascribe footprints their own genus and species names. This is what is referred to as an “ichnogenus”, which is a genus of animal known only from trace fossils, such as footprints, rather than actual physical body fossils.

In the 1996 article which discussed the unusual footprints found in Wyoming, the footprints were ascribed to the ichnogenus Exallopus (pronounced as Ex-ALLO-pus, meaning “from different foot” due to its unusual shape) and its species name was given as Exallopus lovei. The type specimen is identified as “DMNH 5989”, and it was identified as a coelurosaur. According to the website Fossilworks, “Its type locality is Whetstone Creek tracksite, which is in a Maastrichtian terrestrial sandstone in the Harebell Formation of Wyoming” (10). The following year in 1997, the genus name was changed from Exallopus to Saurexallopus (SORE-ex-ALLO-pus), because the name Exallopus was already taken by a species of marine worm (11). Another species, Saurexallopus zerbsti, was named in a 2003 article. The type specimen is identified as “CUMWC 224.2”. According to Fossilworks, “Its type locality is Zerbst Ranch Tracksite, which is in a Lancian fluvial sandstone/sandstone in the Lance Formation of Wyoming” (12). In 2014, a third species was named called Saurexallopus cordata based upon a single footprint fount in British Columbia, Canada, and dated to the Wapiti Formation of the late Cretaceous Period (13).

While all of the scientific articles concerning Saurexallopus identify it as a theropod, there has been some dispute as to what particular type of theropod it is. The original article which was written in 1996 identified it as a coelurosaur. In 2012, Anthony Fiorillo and Thomas Adams identified Saurexallopus as a therizinosaur (14). In an article written in 2015, Saurexallopus was identified as an oviraptorid (15). In an article written in 2018, Saurexallopus was simply identified as a theropod without any specific affinity (16). The website Fossilworks identifies Saurexallopus as a therizinosaur (17).

 

Reconstructing Saurexallopus

During the late 1980s and early 1990s, Philip Currie made comparisons between the various finds in North America with the Asian species Erlikosaurus. According to a phylogenic analysis of therizinosaur genera which was conducted in 2019, Erlikosaurus was closely related to Nothronychus, a therizinosaur which lived in North America during the middle Cretaceous Period. Since Saurexallopus is believed to be physically similar to Erlikosaurus, it is likely that it was genetically related as well, and as such would have been genetically related to Nothronychus. It is therefore quite possible that Erlikosaurus, Nothronychus, and Saurexallopus would have been similar in appearance (18).

Erlikosaurus skull and foot.jpg

Upper jaw and right foot of the Asian therizinosaur Erlikosaurus. Saurexallopus was probably similar in appearance to this genus. Illustration from Rinchen Barsbold and Altangerel Perle (1980) “Segnosauria, a new infraorder of carnivorous dinosaurs”. Acta Palaeontologica Polonica, 25 (2): pages 187-195. https://www.app.pan.pl/article/item/app25-187.html. Creative Commons Attribution License.

 

We can guess that Saurexallopus reached a similar length to Erlikosaurus, measuring about fifteen to twenty feet long (Holtz claims that Erlikosaurus was smaller than other authors do, although his estimate of Nothronychus is in fitting with the size bracket mentioned above) (19). Unlike the eponymous Therizinosaurus, which possessed long scythe-like finger claws (hence its name, which translates to “scythe lizard”), Nothronychus possessed shorter hook-shaped claws, which looked very similar to the stereotypical talons that are seen on carnivorous dinosaurs like Allosaurus and Torvosaurus. These claws were only one-third the size of the claws of Therizinosaurus, but they were well-suited for pulling down branches, for digging (if they could pronate their hands, but that’s a whole other argument), and for smacking the daylights out of any would-be predator. Thomas R. Holtz Jr. has compared therizinosaurs to the large ground sloths of the Cenozoic Era, and the analogy has some merit (20). Saurexallopus and other therizinosaurs likely lived a similar lifestyle and occupied a similar ecological niche, with the possible exception of Falcarius, which may have had a more cursorial lifestyle similar to early coelurosaurs like Ornitholestes.

Based upon their place within the dinosaur family tree, as well as from fossil finds, we are fairly certain that therizinosaurs were feathered. Therefore, it is almost certain that Saurexallopus would have had some form of feather covering as well, although whether it was over the entire body or only partially cannot be determined.

Below is a drawing that I made of Saurexallopus, based upon Erlikosaurus and Nothronychus. The erect mane running down the middle of its neck, back, and tail are just artistic conjecture.

Saurexallopus. © Jason R. Abdale. May 7, 2020.

 

Conclusions

So where does all of this information lead us? So far, there is some evidence which suggests that therizinosaurs were living in Alberta, Canada and Alaska, USA during the late Campanian Stage or early Maastrichtian Stage of the late Cretaceous Period up until about 70 MYA or thereabouts. As such, they would have lived side-by-side with creatures such as Albertosaurus, Edmontosaurus, and Hypacrosaurus. There is only one piece of evidence, a single neck vertebra, which suggests that therizinosaurs existed in North America during the Maastrichtian Stage of the Late Cretaceous. However, no specimens that can be definitely and unquestionably identified as belonging to a therizinosaur have been found in the Hell Creek Formation. Therefore, as far as our current evidence goes, it is unlikely that therizinosaurs lived side-by-side with Triceratops and Tyrannosaurus. However, this may change in the future if more body fossils are discovered.

 

Sources

  1. Utah’s Dino Graveyard; When Dinosaurs Roamed America.
  2. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172.
  3. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172; Dinosaur Mailing List. “Re: Yet even more questions (and I’m sure there’ll be more…)”, by Mickey Mortimer (June 22, 2002). http://dml.cmnh.org/2002Jun/msg00369.html; Theropod Database. “Therizinosauroidea”. http://theropoddatabase.com/Therizinosauroidea.htm.
  4. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172.
  5. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172; Dinosaur Mailing List. “Re: Yet even more questions (and I’m sure there’ll be more…)”, by Mickey Mortimer (June 22, 2002). http://dml.cmnh.org/2002Jun/msg00369.html.
  6. Lindsay Elizabeth Zanno. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008. Page 172.
  7. J. D. Harris, K. R. Johnson, J. Hicks and L. Tauxe (1996). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming”. Cretaceous Research, 17: 381-401.
  8. Anthony R. Fiorello and Thomas L. Adams (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400.
  9. Anthony R. Fiorello and Thomas L. Adams (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400; “The Lower Cantwell Formation and Its Fossils”; “Therizinosaur: prehistoric predator set standard for ‘weird’ in Alaska”; “First North American co-occurrence of Hadrosaur and Therizinosaur tracks found in Alaska”.
  10. Fossilworks. “Saurexallopus lovei”. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=65844.
  11. J. D. Harris, K. R. Johnson, J. Hicks and L. Tauxe (1996). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming”. Cretaceous Research, 17: 381-401; J. D. Harris (1997). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming: a correction”. Cretaceous Research, 18: 139.
  12. Martin G. Lockley, G. Nadon, and Philip J. Currie. (2003). “A diverse dinosaur-bird footprint assemblage from the Lance Formation, Upper Cretaceous, eastern Wyoming; implications for ichnotaxonomy”. Ichnos, 11: 229-249; Fossilworks. “Saurexallopus zerbsti”. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=81011.
  13. R. T. McCrea, L. G. Buckley, A. G. Plint, Philip J. Currie, J. W. Haggart, C. W. Helm, and S. G. Pemberton (2014). “A review of vertebrate track-bearing formations from the Mesozoic and earliest Cenozoic of western Canada with a description of a new theropod ichnospecies and reassignment of an avian ichnogenus”. In Lockley Martin G.; Lucas, Spencer G., eds. New Mexico Museum of Natural History & Science. Bulletin 62: Fossil Footprints of Western North America. Albuquerque: New Mexico Museum of Natural History & Science, 2014. Page 87.
  14. Anthony R. Fiorello and Thomas L. Adams (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400.
  15. R. T. McCrea, D. H. Tanke, L. G. Buckley, M. G. Lockley, J. O. Farlow, L. Xing, N. A. Matthews, C. W. Helm, S. G. Pemberton and B. H. Breithaupt (2015). “Vertebrate ichnopathology: pathologies inferred from dinosaur tracks and trackways from the Mesozoic”. Ichnos, 22 (3–4): 235-260.
  16. Martin Lockley, Gerard Gierlinski, Lidia Adach, Bruce Schumacher, and Ken Cart (2018). “Newly Discovered Tetrapod Ichnotaxa from the Upper Cretaceous Blackhawk Formation, Utah”. In Spencer G. Lucas and Robert M. Sullivan, eds. New Mexico Museum of Natural History and Science. Fossil Record 6, Volume 2: Bulletin 79. Albuquerque: New Mexico Museum of Natural History and Science, 2018. Pages 469-480.
  17. Fossilworks. “Saurexallopus”. http://fossilworks.org/bridge.pl?a=taxonInfo&taxon_no=65843.
  18. Scott Hartman, Mickey Mortimer, William R. Wahl, Dean R. Lomax, Jessica Lippincott, and David M. Lovelace (2019). “A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight”. PeerJ, 7: e7247. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626525/.
  19. David Lambert, The Dinosaur Data Book (New York: Avon Books, 1990), page 61; Don Lessem and Donald F. Glut, The Dinosaur Society Dinosaur Encyclopedia (New York: Random House, 1993), page 184; Peter Dodson, The Age of Dinosaurs (Lincolnwood: Publications International Ltd., 1993), page 142; Thomas R. Holtz Jr, Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of All Ages (New York: Random House, 2007), page 382.
  20. Thomas R. Holtz Jr, Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of All Ages (New York: Random House, 2007), page 147.

 

Bibliography

Books:

  • Dodson, Peter. The Age of Dinosaurs. Lincolnwood: Publications International Ltd., 1993.
  • Holtz Jr., Thomas R. Dinosaurs: The Most Complete, Up-To-Date Encyclopedia for Dinosaur Lovers of All Ages. New York: Random House, 2007.
  • Lambert, David. The Dinosaur Data Book. New York: Avon Books, 1990.
  • Lessem, Don; Glut, Donald F. The Dinosaur Society Dinosaur Encyclopedia. New York: Random House, 1993.

Articles:

  • Fiorello Anthony R.; Adams Thomas L. (2012). “A therizinosaur track from the Lower Cantwell Formation (Upper Cretaceous) of Denali National Park, Alaska”. Palaios, 27: 395-400.
  • Fiorillo, Anthony R.; McCarthy, Paul J.; Kobayashi, Yoshitsugu; Tomsich, Carla S.; Tykoski, Ronald S.; Lee, Yuong-Nam; Tanaka, Tomonori; Noto Christopher R. (August 3, 2018). “An unusual association of hadrosaur and therizinosaur tracks within Late Cretaceous rocks of Denali National Park, Alaska”. Scientific Reports, 2018; 8 (1) DOI: 10.1038/s41598-018-30110-8. https://www.nature.com/articles/s41598-018-30110-8.
  • Harris, J. D.; Johnson, K. R.; Hicks, J.; Tauxe; L. (1996). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming”. Cretaceous Research, 17: 381-401.
  • Harris, J. D. (1997). “Four-toed theropod footprints and a paleomagnetic age from the Whetstone Falls Member of the Harebell Formation (Upper Cretaceous: Maastrichtian), northwestern Wyoming: a correction”. Cretaceous Research, 18: 139.
  • Hartman, Scott; Mortimer, Mickey; Wahl, William R.; Lomax, Dean R.; Lippincott, Jessica; Lovelace, David M. (2019). “A new paravian dinosaur from the Late Jurassic of North America supports a late acquisition of avian flight”. PeerJ, 7: e7247. https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6626525/.
  • Lockley, Martin G.; Nadon, G.; Currie, Philip J. (2003). “A diverse dinosaur-bird footprint assemblage from the Lance Formation, Upper Cretaceous, eastern Wyoming; implications for ichnotaxonomy”. Ichnos, 11: 229-249.
  • Lockley, Martin; Gierlinski, Gerard; Adach, Lidia; Schumacher, Bruce; Cart, Ken (2018). “Newly Discovered Tetrapod Ichnotaxa from the Upper Cretaceous Blackhawk Formation, Utah”. In Spencer G. Lucas and Robert M. Sullivan, eds. New Mexico Museum of Natural History and Science. Fossil Record 6, Volume 2: Bulletin 79. Albuquerque: New Mexico Museum of Natural History and Science, 2018. Pages 469-480.
  • McCrea, R. T.; Buckley, L. G.; Plint, A. G.; Currie, Philip J.; Haggart, J. W.; Helm, C. W.; Pemberton, S. G. (2014). “A review of vertebrate track-bearing formations from the Mesozoic and earliest Cenozoic of western Canada with a description of a new theropod ichnospecies and reassignment of an avian ichnogenus”. In Lockley Martin G.; Lucas, Spencer G., eds. New Mexico Museum of Natural History & Science. Bulletin 62: Fossil Footprints of Western North America. Albuquerque: New Mexico Museum of Natural History & Science, 2014. Pages 5-94.
  • McCrea, R. T.; Tanke, D. H.; Buckley, L. G.; Lockley, Martin G.; Farlow, James O.; Xing, L.; Matthews, N. A.; Helm, C. W.; Pemberton, S. G.; Breithaupt, B. H. (2015). “Vertebrate ichnopathology: pathologies inferred from dinosaur tracks and trackways from the Mesozoic”. Ichnos, 22 (3–4): 235-260.
  • Zanno, Lindsay Elizabeth. A Taxonomic and Phylogenetic Reevaluation of Therizinosauria (Dinosauria: Theropoda): Implications for the Evolution of Maniraptora. PhD dissertation, submitted to the University of Utah. December 2008.

Websites:

Videos:

  • Utah’s Dino Graveyard. The Discovery Channel, 2005.
  • When Dinosaurs Roamed America. The Discovery Channel, 2001.

 

Ceratosaurus Osteoderms: A Revised Perspective

Ceratosaurus is an iconic dinosaur due to numerous physical attributes that distinguish it from other theropod species: the horn on the end of its nose, the massive teeth, the tiny hands with the four fingers, the wide tail, etc. However, the main focus of this article are its osteoderms – the bony bumps that were on its back. What were they, where exactly on the body were they, and what did they look like?

Despite its instantly recognizeable profile, Ceratosaurus fossils are surprisingly rare. Only a handful of skeletons have been found, and all of them are incomplete. Of these specimens the things which are especially unlikely to be preserved are its osteoderms. These small bony lumps (there’s really no other way to describe them) occured in a row running down the middle of its back, and it is one of this animal’s more distinctive features. It is one of only two theropod species (the other being Carnotaurus) which are known to have possessed body armor. Yet “armor” is hardly the word that I would use to describe this anatomical attribute, as we shall see later.

In order to make an accurate picture of Ceratosaurus, I needed to get as much information as I could about its osteoderms. So far, nobody has done a comprehensive study of Ceratosaurus osteoderm morphology – there’s a paleontology Master’s thesis that’s just begging to be picked up by someone. There wasn’t much information to go on because written descriptions of the osteoderms are rather scant. Only a few mounted specimens of Ceratosaurus include the osteoderms as part of the display, and I’m not aware of any museum having Ceratosaurus osteoderms housed in its collections departments.

Charles W. Gilmore says the following in his description of Ceratosaurus fossils:

“Several dermal ossifications were found with the type specimen of Ceratosaurus nasicornis, and some of these were so retained in the matrix as to indicate their exact position in relation to the internal skeleton of the living animal. Reference is made here to the row of elongate, irregularly shaped, bony ossicles present above the spinous processes of caudals (fig. 1, pl. 22) 4 to 10 inclusive, and above cervicals 4 and 5 (0, pls. 29 and 30). The position of these ossicles would appear to indicate a continuous row of dermal ossifications, extending along the median line of the back from the base of the skull well down on the tail, if not the greater part of its length…The ossifications above the tail are from 25 to 38 mm above the tops of the spinous processes of the vertebrae, evidently indicating the thickness of the skin and muscles between them and the tops of the spines. Those on the neck are much closer to the vertebrae, and in one instance appears to rest on the spine (figs. 1, 2, and 3, pl. 20). That there were other dermal ossifications is shown by the presence of a small skin plate found with the bones of this skeleton. It had been freed from the matrix when it came into my hands, so there is no evidence as to its probable position in the skin. It is a relatively small subquadrangular plate of bone 58 by 70 mm., with a comparatively smooth ventral and a roughened dorsal surface. The under surface is gently concave in the direction of its shortest diameter, with a low longitudinal swelling extending through the middle of its longest diameter. The roughening of the external surface is without definite pattern” (Charles W. Gilmore, Smithsonian Institution-United States National Museum, Bulletin 110 – “Osteology of the Carnivorous Dinosauria of the United States National Museum, with a Special Reference to the genera Antrodemus (Allosaurus) and Ceratosaurus”. Washington: Government Printing Office, 1920. Pages 113-114).

Unable to examine these osteoderms in person, I did the next best thing – I looked at as many pictures of Ceratosaurus osteoderms as I possibly could, and I made the following observations:

  1. There was only one row of osteoderms running along the middle of its back.
  2. The osteoderms are all fairly small.
  3. The osteoderms are irregularly shaped.
  4. From overhead, the osteoderms appear to be diamond or lozenge-shaped, elongated anteriorally-posteriorally.
  5. The osteoderms were smooth underneath, but they had a rugose texture on their upper surface.
  6. Some osteoderms seem to come to a point on their upper surface, while others come to a low ridge, and others don’t have any raised features at all. This might be due to the fossilization process.

The appearance of the osteoderms was somewhat perplexing to me. In numerous examples of paleo-art, these bony knobs were shown as pronounced features, more or less uniform in shape, often being exposed bone or bone covered with a thin scute. However, the physical evidence doesn’t look anything like the commonly-portrayed iconography. If the osteoderms themselves were used for display purposes (as they likely were, since the use of a single row of small pieces of bone as armor would only be minimally protective), then they would have been much larger, much more pronounced, more uniform in appearance, and would have had a more “finished” look to them in order to make them more visually apparent. As they are, these formless bony lumps would have made a poor sight, and they certainly would have been of little use as armor.

The rough texture of the osteoderm’s dorsal surface implies that they had a covering of keratin atop them. Due to the irregular shape of the osteoderms, it is also implied or inferred that the osteoderms themselves were not the visual focus, but rather, what was on top of the osteoderm was. It’s possible that each of these small osteoderms served as the anchor point for a large keratinous scute which extended upwards from the dorsal surface of the osteoderm, possibly for a considerable distance. The image that comes to mind is that of the spines which are seen running along the backs of some lizards like a crest, such as the iguana.

In 1990, a specimen of Diplodocus was discovered with skin impressions, and among these were a series of iguana-like keratinous spines running along the top of the animal’s vertebrae. It’s therefore possible that Ceratosaurus might have had a similar appearance.

With all of this being considered, I decided to revise my Ceratosaurus drawing that I had made in April 2012. In the original drawing, the animal has a single row of osteoderms that form a line of low semi-circular bumps, looking very much like crocodilian armored scutes. You can see that drawing below.

Now, I changed the animal’s appearance by extending the osteoderms with the addition of a keratinous scute, shaped like the spines of a lizard (although my impression was that they actually looked more like theropod teeth). I also took the time to touch up the drawing’s overall color and smoothness. You can see the updated drawing below.

When I decided to alter the shape of the osteoderms with the addition of the erect spines, I noticed two important changes to the animal’s overall appearance. Firstly, it made the animal taller. In real life, the addition of a few inches of height would have made the animal seem bigger and more imposing than it actually was. Secondly, it gave the animal a much more intimidating appearance, like a “razorback” wild boar. This might have been helpful in disputes over carcasses or competition for mates. It is unknown whether both male and female Ceratosaurus possessed this feature because so few fossils have been found that a sexual compare-and-contrast cannot yet be performed. However, it is almost certain that the males were ornamented in this way.

I hope that you found all of this interesting. Keep your pencils sharp.

Tyrannosaurus rex juvenile, two years old

Hello everyone. This is  drawing which I made of a juvenile Tyrannosaurus rex, two years old. The anatomy is based upon the skeletons of juvenile Tarbosaurus (a tyrannosaur from Asia which is closely related to Tyrannosaurus) as well as from bones found in North America which may/may not belong to T. rex. There is a theory that the young were covered in a full or partial coating of feathery fuzz, and gradually lost it as they aged. Therefore, I have shown this 2 year old T. rex with a mottled camouflage coloring similar to that seen on wild boar piglets and some species of birds. This drawing was made with No. 2 pencil on printer paper.

Revising my Troodon drawing

Hello everyone. Time to kick off the new year with some much belated paleo-art. One of the projects on my to-do list was to re-do my old and very out-dated 2012 drawing of Troodon. Seven years ago, this drawing was my first attempt at making modern up-to-date paleo-art by featuring theropods with feathers, something that I’d never done before. However, I soon realized that my illustration was utterly pitiful, and I needed to make a new one that was not only more scientifically accurate but also more artistically pleasing. Below is my revised drawing that I made recently. I hope that you’ll agree it’s a distinct improvement. The old drawing has been deleted, partly because I was embarrassed by it, and partly because I don’t what people to get incorrect ideas about what Troodon would have looked like.

Some Quickie Drawings of Late Triassic Life

Hi everybody. As many of you already know, I occasionally volunteer at the Garvies Point Museum in Nassau County, New York. One day, I decided to hash out some drawings of Late Triassic creatures when I had a few moments of spare time, and I stuck them on the wall over the bulletin board. Recently, I went back to the museum for their annual Native American Feast, and to tell you the truth, I had completely forgotten about these pictures. I decided to take some photos of them while I was there. I’m hoping that the museum staff uses them for coloring activities with the children that visit the museum every week.

Coelurus

This is a little-known theropod from the Morrison Formation named Coelurus. You don’t see Coelurus very often in Jurassic paleo-art, but I think it’s an interesting creature. It had a much thinner build than its Morrison coelurosaurid counterpart, Ornitholestes, and it was also bigger. Ornitholestes measured 6 feet long and scarcely 2 feet tall, while Coelurus measured 8 feet long and 3 feet tall. Note the unusually long metatarsal bones. With its long lanky legs, Coelurus was probably a very good runner. I imagine it having the same ecological niche as a Secretary Bird today on the African Savannah.

There are two images here. The first is an uncolored pencil drawing, and the second is a colored drawing that I made using Prismacolor colored pencils. I don’t like coloring my drawings because it tends to wash out the detail. Black and white is more my “thing”.

 

Dakotaraptor

Hi everybody. Here is my latest Hell Creek paleo-art. Say hello to Dakotaraptor steini, a large dromaeosaurid raptor that lived in South Dakota at the end of the Cretaceous Period. How large? We don’t have an exact measurement because this animal is known only from partial remains. However, enough was recovered to give a ballpark estimate that the creature measured somewhere around 15 to 20 feet long. Not as big as Utahraptor, but still pretty impressive.

Dakotaraptor steini. © Jason R. Abdale. May 26, 2018.

This drawing was made with No. 2 pencil, Crayola and Prismacolor colored pencils, a black felt-tipped marker, and A LOT of touch up work on the computer in order to make the scanned image as bold and vivid as it is in real life.