Guaibasaurus: a theropod! (Not a sauropodomorph)

Just look at it!!
With those very short, sharply-clawed forelimbs, how could anyone misidentify Guaibasaurus as ancestral to sauropods? And yet several big-name paleontologists did exactly that, most recently Baron et al. 2017.

Figure 1. Tiny forelimbs with three sharp-clawed fingers indicate that Guaibasaurus is a theropod, not a sauropodomorph. Shown to scale with related theropods Marasuchus and Procompsognathus.

Figure 1. Tiny forelimbs with three sharp-clawed fingers indicate that Guaibasaurus is a theropod, not a sauropodomorph. Shown to scale with related theropods Marasuchus and Procompsognathus. The posture of this skeleton is similar to the resting position of birds, which are also theropods.

Guaibasaurus candelariensis (Bonaparte et al., 1999, 2007; UFRGS PV0725T; Late Triassic) is known from an articulated skeleton lacking a neck and skull. Originally considered a basal theropod, later studies allied it with basal sauropodomorphs. Here this specimen nests as a basal theropod in a rarely studied clade. In the large reptile tree (LRT, 1018 taxa) Guaibasaurus nests between Segisaurus and Marasuchus + Procompsognathus (Fig. 1).

Wikipedia reports:
José Bonaparte and colleagues, in their 1999 description of the genus, found it to be possible basal theropod and placed it in its own family, Guaibasauridae. Bonaparte and colleagues (2007) found another early Brazilian dinosaur Saturnalia to be very similar to it, and placed the two in the Guaibasauridae which was found to be a primitive saurischian group. Bonaparte found that these forms may have been primitive sauropodomorphs, or an assemblage of forms close to the common ancestor of the sauropodomorphs and theropods. Overall, Bonaparte found that both Saturnalia and Guaibasaurus were more theropod-like than prosauropod-like. However, all more recent cladistic analyses found the members of Guaibasauridae to be very basal sauropodomorphs, except Guaibasaurus itself which was found to be a basal theropod or alternatively a basal sauropodomorph.”

On a similar note, Ezcura 2010 report, 
“A phylogenetic analysis found Chromogisaurus to lie at the base of Sauropodomorpha, as a member of Guaibasauridae, an early branch of basal sauropodomorphs composed of Guaibasaurus, Agnosphitys, Panphagia, Saturnalia and Chromogisaurus.” See Figure 2. We need to realize there are some phytodinosaurs, like Eoraptor, Eodromaeus, Panphagia and Pampadromaeus, that are outside of the Sauropodomorpha and outside the Ornithischia. The greater paleo community has not recognized this yet.

Figure 2. Taxa variously considered members of the Guaibasauridae. Here the top few nest with or closer to Sauropodomorpha. The bottom taxa nest with theropods in the LRT.

Figure 2. Taxa variously considered members of the Guaibasauridae. Here the top few nest with or closer to Sauropodomorpha. The bottom taxa nest with theropods in the LRT. Note the small size of Marasuchus, Agnophitys and Procompsognathus. Evidently phylogenetic miniaturization was taking place here, but in this case we know of no ancestors. Maybe someday we will..

I realize the authors
of the Guaibasaurus Wiki article can’t take a stand nor do they choose to test the hypotheses of PhDs, but I can and do here. Science is all about testing observations, comparisons and analyses. When Baron et al. nested Guaibasaurus with the sauropodomorphs, and Eoraptor + Eodromaeus with theropods, and avoided including a long list of taxa from the only other archosaur clade, Crocodylomorpha. and avoided including a long list of taxa from the outgroup to the Archosauria, the Poposaurs, then their results have to be considered suspect at least and bogus at worst. Headline grabbing is fun and lucrative for paleontologists, but not always good for paleontology. So many mistakes have been chronicled that it’s getting to the point that discoveries need to be put on simmer and only lauded when other studies validate them. On the same note, referees are not being tough enough on manuscripts.

References
Baron MG, Norman DB, Barrett PM 2017. A new hypothesis of dinosaur relationships and early dinosaur evolution. Nature  543:501–506.
Bonaparte JF;Ferigolo J and Ribeiro AM 1999. 
A new early Late Triassic saurischian dinosaur from Rio Grande do Sol state, Brazil. Proceedings of the Second Gondwanan Dinosaur Symposium, National Science Museum Monographs. 15: 89–109.
Bonaparte JF, Brea G, Schultz CL and Martinelli AG 2007. A new specimen of Guaibasaurus candelariensis (basal Saurischia) from the Late Triassic Caturrita Formation of southern Brazil. Historical Biology, 19(1): 73-82.

Origin of bipedalism in dinosaurs: Overlooking Carrier’s Constraint

Persons and Currie 2017 debunk on old theory
on bipedalism in dinosaurs and introduce a new one that suffers from taxon exclusion while overlooking a very popular theory from the last thirty years: Carrier’s Constraint (Carrier 1987).

From the abstract:
“Bipedalism is a trait basal to, and widespread among, dinosaurs. It has been previously argued that bipedalism arose in the ancestors of dinosaurs for the function of freeing the forelimbs to serve as predatory weapons.”

I never heard of this reason before. Predatory weapons only happen as a result and much later phylogenetically and only sometimes.

“However, this argument does not explain why bipedalism was retained among numerous herbivorous groups of dinosaurs. We argue that bipedalism arose in the dinosaur line for the purpose of enhanced cursoriality.”

The term ‘enhanced’ is pretty vague. Does it mean ‘better’? But can that be proven? The fastest animals on land now are quadrupedal cheetahs. Bipedal Chlamydosaurus does not have greater speed or endurance. Persons and Currie bring up the “tripping on one’s own forefeet” hypothesis and that, IMHO, has some validity.

“Modern facultatively bipedal lizards offer an analog for the first stages in the evolution of dinosaurian bipedalism. Many extant lizards assume a bipedal stance while attempting to flee predators at maximum speed.”

But quadrupedal lizards are just as fast as bipedal ones. Lizards gain no speed when switching to bipedal locomotion as Persons and Currie also note.

Bipedal lizard video marker

Figure 1. Click to play video. Just how fast can quadrupedal/bipedal lizards run? This video documents 11 meters/second in a Callisaurus at the Bruce Jayne lab.

“Bipedalism, when combined with a caudofemoralis musculature, has cursorial advantages because the caudofemoralis provides a greater source of propulsion to the hindlimbs than is generally available to the forelimbs.”

Yes, at first, especially when the forelimbs are lifted from the ground! Persons and Currie stay clear of the bipedal ability of fenestrasaurs including pterosaurs. There, in taxa like Cosesaurus, the driving force switches to the hips.

“That cursorial advantage explains the relative abundance of cursorial facultative bipeds and obligate bipeds among fossil diapsids and the relative scarcity of either among mammals.”

Actually there is no abundance of bipeds anywhere among diapsids, except in the Fenestrasauria (not related to archosaur-line diapsids) and Archosauria + Poposauria. Persons and Currie also stay clear of the inverted bipeds among mammals, the bats, and they are numerous.

None of the so-called ‘reasons’ why are pertinent
without the random evolution of longer hind limbs than forelimbs and the ability to balance over the hind limbs, whether running or standing still. It also helps to have even a small anterior addition to the ilium, according to Shine and Lambeck 1989. The pubic foot of theropods and the prepubis of pterosaurs also provide femoral muscle anchors.

Unfortunately

  1. Persons and Currie do not indicate the node at which bipedalism arose in the last common ancestor of bipedal crocs and dinosaurs: Gracilisuchus and Turfanosuchus at the base of the Poposauria. In the large reptile tree (LRT)  Gracilisuchus (Fig. is the last common ancestor of bipedal crocs, like Scleromochlus, and bipedal pro-dinosaurs, like Lewisuchus.
  2. Persons and Currie subscribe to the outdated hypothesis of “Avemetatarsalia” in which former members, like pterosaurs now nest with lepidosaurs and Lagerpeton now nests with chanaresuchids.
  3. Persons and Currie also avoid the likely bipeds, Arizonasaurus and Postosuchus.
  4. Persons and Currie discuss the the likely biped, Eudibamus, but incorrectly ascribe it to the bolosaurs.
  5. Persons and Currie overlooked Carrier’s Constraint, which holds that,“air-breathing vertebrates which have two lungs and flex their bodies sideways during locomotion find it very difficult to move and breathe at the same time, because the sideways flexing expands one lung and compresses the other, shunting stale air from lung to lung instead of expelling it completely to make room for fresh air.” — but is that the reason to go bipedal? or just the first and biggest advantage narrow-gauge bipedal reptiles enjoy?
Click to enlarge. Squamates, tritosaurs and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

Figure 2. Tritosaurs and fenestrasaurs in the phylogenetic lineage preceding the origin of the Pterosauria.

What fenestrasaurs gain by a bipedal configuration

  1. height dominance over conspecific rivals for mating privileges. This is emphasized in Langobardisaurus with its long neck. This is emphasized by Cosesaurus by flapping and leaping, both working to increase height.
  2. Ability to breathe while running for added endurance
Chlamydosaurus, the Austrlian frill-neck lizard

Fig. 3. Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. At one time some paleontologists did not believe what you can see here, that this lizard can stand bipedally. Such was their bias.

What the lizard, Chlamydosaurus, gains by bipedal configuration

  1. combined with their frightfully opening frill neck, dominance over rivals and interlopers, which they charge bipedally.
  2. better ability to survey the local area for rivals (principally) and predators while on the ground, — but Chlamydosaurus is primarily (90%) arboreal for the same reason and 90% bipedal while on the ground, not just while running, which some paleontologists are not aware of or did not believe (Hone and Benton 2007, 2009).
Figure 1. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Herrerasaurus, Tawa and Eoraptor.

Figure 4. The origin of dinosaurs to scale. Gray arrows show the direction of evolution. This image includes Decuriasuchus, Turfanosuchus, Gracilisuchus, Lewisuchus, Pseudhesperosuchus, Herrerasaurus, Tawa and Eoraptor. Note the phylogenetic miniaturization.

What Gracilisuchus gained by a bipedal configuration

  1. Gracilisuchus is not much taller bipedally. Remember, archosaurs had no scales at this point. Feather quills would appear on dino backs. Osteoderms appeared along croc backs to support their longer spinal columns. So, standing erect might have just been sexy at first.
  2. Overcoming Carrier’s Constraint: greater endurance by not having to undulate while breathing and so continue breathing while running.

What do bipedal reptiles have in common?

  1. Other than sauropods and other reptiles that adopt a tripodal pose bipedal reptiles are generally small, having experienced phylogenetic miniaturization.
  2. Other than Tanystropheus, bipeds are terrestrial and/or arboreal
  3. Longer hind limbs than forelimbs
  4. Anterior process of the illiim, no matter how small
  5. Typically stronger or more sacral connections to the ilium
  6. Typically a long neck and short torso (but Longisquama (Fig. 2), as a lemur analog, and lemurs themselves break that rule).
Figure 1. The ancestry of Scleromochlus going back to Lewisuchus, Saltoposuchus, Terrestrisuchus, SMNS 12591 and Gracilisuchus.

Figure 1. The ancestry of Scleromochlus going back to Lewisuchus, Saltoposuchus, Terrestrisuchus, SMNS 12591 and Gracilisuchus.

It’s easy to overlook the most obvious.
I have a feeling that this will not be the first time Persons and Currie are going to be reminded of Carrier 1987.

References
Carrier DR 1987. The evolution of locomotor stamina in tetrapods: circumventing a mechanical constraint. Paleobiology (13): 326–341.
Clemente CJ, Withers PC, Thompson G, Lloyd D 2008. Why Go Bipedal? Locomotion and Morphology in Australian Agamid Lizards.J. Exp. Bio. 211: 2058-2065
Peters D 2000b. A reexamination of four prolacertiforms with implications for pterosaur phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106: 293–336.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.
Persons WS and Currie PJ 2017. The functional origin of dinosaur bipedalism: Cumulative evidence from bipedally inclined reptiles and disinclined mammals. Journal of Theoretical Biology, 2017; 420: 1 DOI: 10.1016/j.jtbi.2017.02.032
Shine R and Lambeck R 1989. Ecology of Frillneck Lizards, Chlamydosaurus kingii (Agamidae), in Tropical Australia. Aust. Wildl. res. Vol. 16: 491-500.
Snyder RC 1954. The anatomy and function of the pelvic girdle and hind limb in lizard locomotion. American Journal of Anatomy 95:1-46

Baby Limusaurus had teeth!

This is pretty remarkable.
Wang et al. 2016 reported on a growth series for Limusaurus (Xu et al. 2009; Jurassic, Oxfordian; 1.7m in est. length; IVPP V 15923; Figs. 1-5,) “the only known reptile to lose its teeth and form a beak after birth.”  

You might remember
Limusaurus became famous earlier for its tiny forelimbs complete with a digit 0 medial to digit 1, that made theropod workers go bonkers because they assumed the digits present were 1-4, not 0-3.

Figure 2. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Figure 1. Limusaurus also has four fingers and a scapula with a robust ventral area, like Majungasaurus, but those four fingers are not the same four fingers found in Majungasaurus.

Wang et al. report,
“The available data are important for understanding the evolution of the avian beak.” Except… Limusaurus is not close to the avian line of ancestry anyway you look at it. The LRT nests Limusaurus, with or without teeth, with Khaan, a toothless, beaked oviraptorid. Wang et al. nest Limusaurus with Elaphrosaurus (Fig. 3) even though Khaan is part of their taxon list. So something is not scored right. Not sure about the discrepancy, but some of that could be due to the misidentification of manual digits 0-3.

Figure 3. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Figure 2. Khaan, an oviraptorid that nests with Limusaurus in the large reptile tree AND the repaired Cau, Brougham and Naish tree.

Wang et al. report,
“The ontogenetically variable features (e.g. teeth/no teeth, etc.) have little effect on its phylogenetic position.” The LRT agrees. Wang et al. report that no matter which ontogenetic stage is tested for Limusaurus, it always nests with or near the ceratosaur, Elaphrosaurus (Fig. 3).The LRT disagrees.  In other words, with or without teeth, the topology does not change. In the LRT  toothed juvenile Limusaurus also nested with Khaan. Toothed Juravenator and Sinosauropteryx nest as sisters to that clade. The large Compsognathus specimen CNJ79 (Fig. 6) was a basal taxon. All of these sisters are closer to Limusaurus in size and morphology than is Elaphrosauru (Fig. 3).

Figure 3. Elaphrosaurus is known from a partial skeleton lacking a skull.

Figure 3. Elaphrosaurus is known from a partial skeleton lacking a skull. Adult Limusaurus added to scale. Wang et al. consider these two to be sister taxa among basal theropods, which is not confirmed by the LRT.

The ontogenetic series of Limusaurus
is shown in figure 4. Not all the specimens are complete. None are shown to scale. All are portrayed as tiny rough tracings. I think this lack of detail is one shortcoming of the paper.

Figure 4. Specimens attributed to Limusaurus, not to scale.

Figure 4. Specimens attributed to Limusaurus, not to scale, from Wang et al. 2016.

Wang et al. also provided
reconstructions of a juvenile and adult Limusaurus (Fig. 5). Unfortunately, Wang et al. filled in all the missing bones and gave both reconstructions something of a generic theropod character, lacking some of the traits unique to this genus.

Limusaurus reconstructions from Wang et al. 2016, to scale and not to scale.

Figure 5. Limusaurus reconstructions from Wang et al. 2016, to scale and not to scale. The angle of the pubis is difficult to determine.

That Limusaurus juveniles had teeth
and adults did not, tells us less about the avian line and more about the oviraptorid line of theropod dinosaurs.

Figure 1. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

Figure 6. The large (from Peyer 2006) and small Compsognathus specimens to scale. Several different traits nest these next to one another, but at the bases of two sister clades. Note the differences in the forelimb and skull reconstructions here. There may be an external mandibular fenestra. Hard to tell with the medial view and shifting bones.

References
Wang S, Stiegler J, Amiot R, Xu W, Du G-H, Clark JM, Xu X 2016. Extreme ontogenetic changes in a ceratosaurian theropod. Currently Biology 27:1-5 plus SupData.

Full scale models from the vault

Back in the day
when I was writing and illustrating dinosaur books (1988~1992) I also built a few full scale models that I intended to use as subjects for paintings and museum displays. Here are most of them. Other models include the pterosaur skeletons you can see here.

Figure 1. Brachiosaurus skull, carved out of wood. Full scale.

Figure 1. Brachiosaurus skull, carved out of wood. Full scale.

At this point in my life
(1990s) the work (paintings / illustrations) was considered ‘acceptable.’ Even my papers were ‘acceptable.’ Unfortunately, when I started applying phylogenetic analysis to taxa and discovering new and overlooked relationships (published at ReptileEvolution.com, ) my work and manuscripts were no longer considered ‘acceptable,’ despite the fact that early discoveries made here are being re-discovered and validated years later by PhDs.

FIgure 2. Camarasaurus baby model. Full scale.

FIgure 2. Camarasaurus baby model. Full scale.

This Dimorphodon
(Fig. 3) was among the first of the models, based on Kevin Padian’s 1983 running illustrations.

Figure 3. Dimorphodon skull with dog hair for pycnofibers.

Figure 3. Dimorphodon skull with dog hair for pycnofibers.

Not sure why I produced this plesiosaur
because it took up a bunch of garage space and only entertained the mailman. Ultimately it was purchased by the AMNH, but never put on display. Where it is now is anyone’s guess.

Figure 4. Plesiosaur model. Full scale.

Figure 4. Plesiosaur model. Full scale. See figure 5 for the face.

Much of this plesiosaur
was fashioned at the late Bob Cassilly studios, who was a famous St. Louis sculptor and founder of The City Museum. Bob contacted me after seeing my book, Giants, because he had been commissioned to produce some of the giant marine animals pictured therein. Through that friendship in the 1990s, I was able to study specimens, including Sharovipteryx and Longisquama, from the traveling Russian Dinosaur Exposition that came to the City Museum for their first stop.

Figure 5. Plesiosaur model head detail. Full scale. Teeth are tree thorns.

Figure 5. Plesiosaur model head detail. Full scale. Teeth are tree thorns.

Among the smaller full scale models
is this sparrow-sized Pterodactylus in a bipedal pose (Fig. 6), ready to take flight.

FIgure 6. Pterodactylus scolopaciceps (n21) model. Full scale.

FIgure 6. Pterodactylus scolopaciceps (n21) model. Full scale. Later I learned that this genus was plantigrade (flat-footed), when quadrupedal. This one is about to take flight from a bipedal configuration. Digitigrady at this instance would have given Pterodactylus a bit more power in its initial leap during take-off.

And based on the evolution book

From the Beginning, these three (Fig. 7) are fleshed out steps in the evolution of tetrapods, cynodonts, mammals and man. Ichthyostega is a bit out of date now.

Figure 7. Ichthyostega, Osteolepis and Thrinaxodon, all more or less ancestral to humans. Full scale.

Figure 7. Ichthyostega, Osteolepis and Thrinaxodon, all more or less ancestral to humans. Full scale.

References
Padian K 1983. Osteology and functional morphology of Dimorphodon macronyx (Buckland) (Pterosauria: Rhamphorhynchoidea) based on new material in the Yale Peabody Museum, Postilla, 189: 1-44.

A Dinosaur Year 1989 Calendar

This ‘blast from the past’ by request: 
Click here or on image to download all 13 lorez images from my 1989 Dinosaur Year calendar, published by Alfred A. Knopf, New York. Thanks for the request, Leo!

I see two copies are presently available from Amazon.com here.

Click to download PDF of cover + 12 months of 1989 Dinosaur Year Calendar pix by David Peters at 72 dpi. It's over 25 years old and you'll find mistakes here. It was a product of its time.

Click to download PDF of cover + 12 months of 1989 Dinosaur Year Calendar pix by David Peters at 72 dpi. It’s over 25 years old and you’ll find mistakes here. It was a product of its time.

The calendar is over 25 years old
and you’ll find mistakes galore. It was a product of its time and the first time I ever painted dinosaurs in settings.

This followed
the book GIANTS and A Gallery of Dinosaurs, which illustrated dinosaurs on white backgrounds, all to the same scale. Both books are available as pdf files here and as used books at several online sites.

Where are the originals?
Collectors purchased all the originals except for the Brachiosaurus family in a pond (December) because it has a razor knife cut in the sky over the mountain top, inflicted upon opening the package at the publisher. It’s hanging on the wall over my monitor as I type this and I never notice the slit.

But wait! There’s more!
Click here to connect to a FREE build-it-yourself paper Pteranodon model.
And click here to connect to a FREE build-it-yourself paper Thalassomedon model.
All you need is 8.5×11″ bristol (stiff) paper, some glue or tape and a scissors or knife. Have fun, kids!

Feathered T-rex video: Excellent!*

The best video* I’ve seen on feathered dinosaurs.
*But note: their gliding Anchiornis forgot how to flap. Flapping came first. Then flapping with bipedal climbing. Then flapping with flying. Birds don’t come by gliding except to rest while airborne. Same with bats (if any glide ever). Same with pterosaurs. Let’s take gliding out of the equation for the origin of flight. That’s widespread antiquated thinking not supported by evidence. If you glide you do not flap. If you flap, some of your ancestors may learn to glide.

Click here or on the image to play.

Hypsibema missouriensis – a Late Cretaceous Appalachia duckbill dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Figure 1. Model of Hypsibema missouriensis, a hadrosaurid dinosaur

Hypsibema missouriensis
(Cope 1869; Gilbert and Stewart 1945; Gilbert 1945; Baird and Horner 1979; Darrough et al. 2005; Parris 2006; Campanian, 84-71 mya, Late Cretaceous) is a fairly large hadrosaurid dinosaur discovered in 1942, at what later became known as the Chronister Dinosaur Site near Glen Allen, Missouri. At present this literal pinprick in the map of Missouri is the only site that preserves dinosaur bones.

Figure 2. Where the Hypsibema maxilla chunk came from on the skull of Saurolophus.

Figure 2. Where the Hypsibema maxilla chunk (Figure 3) came from modeled on the skull of Saurolophus.

Small pieces of broken bone and associated caudals and toes
were first discovered when digging a cistern. They had been found about 8 feet (2.4 m) deep imbedded in a black plastic clay. The area is in paleokarst located along downdropped fault grabens over Ordovician carbonates.

Gilmore and Stewart 1945 described a series of Chronister caudal centra (now at the Smithsonian) as sauropod-like, reporting, “The more elongate centra of the Chronister specimen, with the possible exception of Hypsibema crassicauda Cope, and the presence of chevron facets only on the posterior end appear sufficient to show that these vertebral centra do not pertain to a member of the Hadrosauridae.”

First named Neosaurus missouriensis,
the caudals were renamed Parrosaurus missouriensis by Gilmore and Stewart 1945 because “Neosaurus” was preoccupied. The specimen was allied to Hypsibema by Baird and Horner 1979.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Figure 3. Back portion of a Hypsibema maxilla showing tooth root grooves and cheek indention close to jugal.

Back in the 1980s
I enjoyed going to the Chronister site with other members of the local fossil club, the Eastern Missouri Society for Paleontoogy. I was lucky enough to find both a maxilla fragment (Fig. 3) and a dromaeosaurid tooth. I remember the horse flies were pesky and  one morning, before the other members got there, I was met by a man with a shot gun who relaxed when I identified myself. A friend found a series of hadrosaur toe bones, each about as big as a man’s hand (sans fingers). The bone was so well preserved you could blow air through the porous surfaces.

References
Baird D and Horner JR 1979. Cretaceous dinosaurs of North Carolina. Brimleyana 2: 1-28.
Cope  ED 1869.
Remarks on Eschrichtius polyporusHypsibema crassicaudaHadrosaurus tripos, and Polydectes biturgidus“. Proceedings of the Academy of Natural Sciences of Philadelphia 21:191-192.
Darrough G; Fix M; Parris D and Granstaff B 2005.
 Journal of Vertebrate Paleontology 25 (3): 49A–50A.
Gilmore CW and Stewart DR 1945. A New Sauropod Dinosaur from the Upper Cretaceous of Missouri. Journal of Paleontology (Society for Sedimentary Geology 19(1): 23–29.
Gilmore CW 1945. Parrosaurus, N. Name, Replacing Neosaurus Gilmore, 1945. Journal of Paleontology (Society for Sedimentary Geology 19 (5): 540.
Parris D. 2006. New Information on the Cretaceous of Missouri. online

wiki/Hypsibema_missouriensis
bolinger county museum of natural history
More info and links