The manus of Poposaurus revised

Figure 1. Poposaurus manus as originally restored and with digits 1 and 5 switched.

Figure 1. Poposaurus manus as originally restored and with digits 1 and 5 switched.

The manus of basal archosaurs is very rare.
What few clues we have indicate that metatarsals 1-3 aligned distally and digit 5 is a vestige. Revising the manus of Poposaurus to that pattern is demonstrated here (Fig. 1).

References
Gauthier JA, Nesbitt SJ, Schachner ER, Bever GS and Joyce WG 2011. The bipedal stem crocodilian Poposaurus gracilis: inferring function in fossils and innovation in archosaur locomotion. Bulletin of the Peabody Museum of Natural History 52:107-126.
Mehl MG 1915. Poposaurus gracilis, a new reptile from the Triassic of Wyoming. Journal of Geology 23:516–522.

wiki/Poposaurus

MPUM 7039: a pterosaur sternal complex?

Figure 1. MPUM 7039, an isolated Triassic pterosaur sternal complex with parts colorized. The shape is very much like that of Eudimorphodon.

Figure 1. MPUM 7039, an isolated Triassic pterosaur sternal complex with parts colorized. The shape is very much like that of Eudimorphodon (MCSNB 2888) and would have belonged to a powerful flapping flyer with large chest muscles anchored here. This is about 3x life-size at the 72dpi of your monitor screen.

Yes!
MPUM 7039, identified by Dalla Vecchi 2003 as a “relatively large, incomplete and isolated sternal plate “prudently consider it as cf. Eudimorphodon” is indeed that.

Of course, as well all know, a sternal complex includes the interclavicle and clavicles along with the sternal plate, here (Fig. 1) colorized for easy identification. Let’s keep calling this a sternal complex because it’s not just a sternum and sometimes the sternal portion is the smallest part.

This post is part of a Triassic series that follows an earlier one on a gastric pellet containing a pterosaur.

References
Dalla Vecchia FM 2003. A review of the Triassic pterosaur record. Riv. Mus. civ. Sc. Nat. “E. Caffi” Bergamo 22:13-29.

New Mexican Pterosaur Tracks?

Figure 1. I'd like to see 4 toes if this is indeed a pterosaur track. Here three toes points toward a theropod.

Figure 1. I’d like to see 4 toes if this is indeed a pterosaur track. Here three toes suggest a theropod.

Recent announcement of 110 million-year-old pterosaur tracks by Raul Frank Gio Argáez, researcher at the Institute of Marine Sciences and Limnolog , National Autonomous University of Mexico (UNAM ) made the news here.

Unfortunately all pterosaur tracks that I am aware of have four toes.

Here (Fig. 1) the fourth toe appears to be missing, suggesting a misidentification. Looks more like a theropod track. If anyone can see the fourth toe, please let me know.

The Triassic Pterosaur Gastric Pellet – Reconstructed

This is the first in a series of Triassic pterosaur enigmas.

Figure 1 From Dalla Vecchia et al. 1983. Original identification of the pterosaur pellet elements. Scale bar = 1 cm.

Figure 1 From Dalla Vecchia et al. 1983. Original identification of the pterosaur pellet elements. Scale bar = 1 cm. Slightly distorted to match the published photograph. cV= caudal vertebra. Cv = cervical vertebra.

An odd jumble of Triassic bones was identified by Dalla Vecchia, Muscio and Wild (1983) as the remains of Preondactylus (Fig. 2), one of the few Triassic pterosaurs known at that time, in a gastric pellet (aka: vomited bones). The problem is, if you put the bones, as originally identified, on a reconstruction of Preondactylus, you’ll find a few matches and several mismatches (Fig. 1).

Figure 1. The major bones of the Triassic gastric pellet placed upon the skeleton of Preondactylus, a contemporary pterosaur. Note the several mismatches.

Figure 2. The major bones of the Triassic gastric pellet placed upon the skeleton of Preondactylus, a contemporary pterosaur. Note the several mismatches.

Generally the wing finger elements are too gracile and so is the femur. The dorsals are a bit too long and metacarpal 4, the base of the wing, is not quite large enough.

Putting the originally traced bones together in a different, yet still Triassic way, yields a pre- or proto-pterosaur with some resemblance to Longisquama. Now the more gracile and possibly much shorter wings make some sort of sense, because this was not a flyer, but a running flapper and a glider at best. Of course, in this case, I was able to draw the imagined parts “to fit.”

Freddy Mercury put it best, “Is this the real life? Is this just fantasy?”

Figure 2. With so few bones, and so few of those complete, you can rebuild the gastric pellet into a pre- or proto- pterosaur, something like Longisquama.

Figure 3. With so few bones, and so few of those complete, you can rebuild the gastric pellet bone tracings of Dalla Vecchia et al. into a pre- or proto- pterosaur, something like Longisquama. Now the femur becomes a distal humerus. What was a metatarsal becomes a metacarpal similar in size and thickness to metacarpal 4. The large dorsals are a good fit as Longisquama had a long torso. Minimizing the amount of bone lost from each of the wing/finger phalanges yields a much shorter wing, like Longisquama. Black wiry shapes are completely imagined, as is most of the rest of this restoration. The actual animal shape may never be adequately known.

Wouldn’t it be exciting if the gastric pellet, now known for over 30 years, turned out to be an example of a transitional/basal taxon? Odd that only segments of all four wing phalanges would be preserved.

After producing these images I learned the pellet is under study once again. Hopefully those studies will help resolve this mystery.

When I ran the published images through DGS I was able to identify many other bones and create another much more complete reconstruction that also made sense. It was standard basal pterosaur. But then, the data I was using was poor at best.

Given the mishmash of the in situ fossil, the poor quality of my data and the detailed new study of the gastric pellet specimen to come, I hesitate putting it out early. I will say that the originally identified ‘palatine’ and ‘pterygoid’ are probably the first two dorsal ribs, which were more robust than the others, as in other pterosaurs. And several more ribs are present, which were generally overlooked in the original tracing (Fig. 1).

References
Dalla Vecchia FM, Muscio G and Wild R 1983. Pterosaur remains in a gastric pellet from the Upper Triassic (Norian) of Rio Seazza Valley (Udine, Italy). Gortania – Atti Museo Friul. Storia Naturale 10(88):121-132.

A tiny naris in Guidraco

Figure 1. Closing in on the naris in Guidraco, an Early Cretaceous ornithocheirid from South America. Colors are naris = pink, maxilla = green, jugal = blue, premaxilla = yellow

Figure 1. Closing in on the naris in Guidraco, an Early Cretaceous ornithocheirid from South America. Colors are naris = pink, maxilla = green, jugal = blue, premaxilla = yellow

Guidraco is related to Ludodactylus, another crested ornithocheirid.

And for those who think the fenestra closer to the antorbital fenestra makes a better naris, I say, “good eye!”

References
Frey E, Martill DM and Buchy M-C 2003. A new crested ornithocheirid from the Lower Cretaceous of northeastern Brazil and the unusual death of an unusual pterosaur: In: Buffetaut, E., and J.-M. Mazin, Eds. Evolution and Palaeobiology of Pterosaurs. – London, Geological Society Special Publication 217: p. 55-63.
Wang X-L, Kellner AWA, Jiang S-X and Cheng X 2012. New toothed flying reptile from Asia: close similarities between early Cretaceous pterosaur faunas from China and Brazil. Naturwissenschaften in press. doi:10.1007/s00114-012-0889-1.

wiki/Ludodactylus

wiki/Guidraco

 

Diandongosuchus – another giant younginid

Earlier we looked at Diandongosuchus, which was originally considered a poposaurid (Li et al. 2012). The large reptile tree (now needs to be updated) nested Diandongosuchus at the base of the parasuchians and proterochampsids (including the biped, Lagerpeton). It’s easy to see the resemblance.

Today we’ll revise the skull of a tiny Youngina, BPI 2871, which is the basal taxon in this lineage (more primitive than Diandongosuchus). Seems the rostrum of the BPI specimen was probably crushed dorsoventrally, resulting in a false concave rostral profile. The posterior skull is missing, but it can be restored closer to Diandongosuchus now that the phylogenetic analysis shows the close relationship.

Figure 1. The large reptile tree nests these two taxa as sisters despite their size difference. With greater size came the development of an antorbital fenestra, independent of the one developing in other Younginids leading toward archosauriformes beginning with Proterosuchus.

Figure 1. The large reptile tree nests these two taxa as sisters despite their size difference. With greater size came the development of an antorbital fenestra, independent of the one developing in other Younginids leading toward archosauriformes beginning with Proterosuchus.

Evolution works in baby steps.
That’s why maximum parsimony (fewest morphological changes) is still the best route for finding ancestors and descendants and for filling in missing parts by the method of phylogenetic bracketing. Diandongosuchus also gives us clues as to the post-crania of the BPI 2871 specimen of Youngina, with reservations regarding the great size difference.

I’d like to see the BPI 2871 specimen, but the last I heard (several years ago) it was ‘on loan’ and had not been returned.

Some workers, Gow (1975), among them, consider the BPI 2871 specimen congeneric with other Youngina and Younginoides specimens, with all apparent changes in morphology due to crushing. While that is likely true to a certain extent, there are differences that can be scored in phylogenetic analysis to reveal their differences and relationships. And you can always take out the crushing to check out prior hypotheses.

Earlier we looked at Garjainia as another giant younginid.

References
Gow CE 1975. The morphology and relationships of Youngina capensis Broom andProlacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Li C, Wu X-C, Zhao L-J, Sato T and Wang LT 2012. A new archosaur (Diapsida, Archosauriformes) from the marine Triassic of China, Journal of Vertebrate Paleontology, 32:5, 1064-1081.

wiki/Diandongosuchus
wiki/Youngina

Origin of Turtles Update

Earlier we looked at Stephanospondylus (Fig. 1) as the ancestor of turtles like Proganochelys, more primitive than Odontochelys, which represents a splinter off the main line. Unfortunately I never put Stephanospondylus together as a basic silhouette reconstruction, common to all other taxa at reptileevolution.com. Here it is (Fig. 1) along with sister taxa.

Figure 1. Click to enlarge. Stephanospondylus was considered a type of diadectid, but it nests with turtles and pareiasaurs, all derived from millerettids.

Figure 1. Click to enlarge. Stephanospondylus was considered a type of diadectid, but it nests with turtles and pareiasaurs, all derived from millerettids. They all got big and bulky back then. Nyciphruretus is  related, but leads to owenettids and lepidosauriformes. Note the green arrows indicating the angle of the scapula. It leans forward with Stephanospondylus and Proganochelys.

Based on the wide ribs, Stephanospondylus had a low, wide torso, some of which were broadened with costal plates, derived from those in Milleretta and destined to form the carapace in turtles. Here (Fig. 1) you can see the evolution of the pectoral girdle, humerus and femur.

Figure 1. Diadectes phaseolinus showing off those very broad anterior dorsal rib costal plates, by convergence similar in shape to what is found in the pre-pareiasaur/pre-turtle Stephanospondylus and Odontochelys. Diadectids and pareiasaurs grew large by convergence and are not directly related except through tiny ancestral taxa.

Figure 2. Diadectes phaseolinus showing off those very broad anterior dorsal rib costal plates, by convergence similar in shape to what is found in the pre-pareiasaur/pre-turtle Stephanospondylus and Odontochelys. Diadectids and pareiasaurs grew large by convergence and are not directly related except through tiny ancestral taxa.

Diadectes (Fig. 2) had similar large costal ribs, but these were smooth, not highly textured as in Stephanospondylus. We don’t know where the costal ribs were located in Stephanospondylus. In Proganochelys and Odontochelys the anterior ribs are narrow, not provided with large costal plates (Fig. 1). Stephanospondylus also had a broad, textured interclavicle, the starting point for the plastron.

Note that Stephanospondylus did not have a central neural spine as did Diadectes and Milleretta. That spine, as you know, anchors back muscles. Not having that spine indicates that back muscles were on the way out for Stephanospondylus, one more sign that it was developing a carapace, as in turtles, which also, obviously, lack back muscles.

References
Broom R 1924. On the classification of the reptiles. Bulletin of the American Museum of Natural History 51:39-45.
Geinitz HB and Deichmüller JV 1882. Die Saurier der unteren Dyas von Sachsen. Paleontographica, N. F. 9:1-46.
Gregory WK 1946. Pareiasaurs versus placodonts as near ancestors to turtles. Bulletin of the American Museum of Natural History 86:275-326
Kissel R 2010. Morphology, Phylogeny, and Evolution of Diadectidae (Cotylosauria: Diadectomorpha). Toronto: University of Toronto Press. pp. 185. online pdf
Li C, Wu X-C, Rieppel O, Wang L-T, Zhao L-J 2008. An ancestral turtle from the Late Triassic of southwestern China. Nature 456: 497-501.
Lyson TR, Sperling EA, Heimberg AM, GauthierJA, King BL, and Peterson KJ 2011.MicroRNAs support a turtle + lizard clade. Biol Lett 2011 : rsbl.2011.0477v1-rsbl20110477. abstract online news story
Reisz RR and Head JJ 2008. Turtle origins out to sea. Nature 456, 450–451.
Rieppel O and deBraga M 1996. Turtles as diapsid reptiles. Nature 384:453-454.
Rieppel O and Reisz RR 1999. The Origin and Early Evolution of Turtles. Annual Review of Ecology and Systematics 30: 1-22.
Romer AS 1925. Permian amphibian and reptilian remains described as Stephanospondylus. Journal of Geololgy 33: 447-463.
Stappenbeck R 1905. Uber Stephanospondylus n. g. und Phanerosaurus H. v. Meyer: Zeitschrift der Deutschen Geologischen Gesellschaft, v. 57, p. 380-437.
Williston SW 1917. The phylogeny and classification of Reptilies. Journal of Geology 28: 41-421.
wiki/Stephanospondylus

You Must See: Your Inner Fish with host Neil Shubin

PBS presented part 1 of 3 last night of Your Inner Fish, a new TV series hosted by and based on Neil Shubin’s book of the same name. I recommend this highly. It’s wonderfully done and, it goes without saying, this subject is close to my heart. Shubin is an excellent host and his presentation is clear, true and entertaining.

Figure 1. Click to go to the website. Your Inner Fish is Neil Shubin's 3-part series based on his book of the same name. This the best presentation on human evolution I have seen on TV.

Figure 1. Click to go to the website. Your Inner Fish is Neil Shubin’s 3-part series based on his book of the same name. This the best presentation on human evolution I have seen on TV.

The book, Your Inner Fish, came out in 2008. Here’s the Amazon.com synopsis.
Why do we look the way we do? Neil Shubin, the paleontologist and professor of anatomy who co-discovered Tiktaalik, the “fish with hands,” tells the story of our bodies as you’ve never heard it before. By examining fossils and DNA, he shows us that our hands actually resemble fish fins, our heads are organized like long-extinct jawless fish, and major parts of our genomes look and function like those of worms and bacteria. Your Inner Fish makes us look at ourselves and our world in an illuminating new light. This is science writing at its finest—enlightening, accessible and told with irresistible enthusiasm.”

 

Author Neil Shubin along with this discovery, Tiktaalik.

Figure 2. Author Neil Shubin along with his discovery, Tiktaalik.

How the book came to be as told by author Neil Shubin
“This book grew out of an extraordinary circumstance in my life. On account of faculty departures, I ended up directing the human anatomy course at the University of Chicago medical school. Anatomy is the course during which nervous first-year medical students dissect human cadavers while learning the names and organization of most of the organs, holes, nerves, and vessels in the body. This is their grand entrance to the world of medicine, a formative experience on their path to becoming physicians. At first glance, you couldn’t have imagined a worse candidate for the job of training the next generation of doctors: I’m a fish paleontologist.

It turns out that being a paleontologist is a huge advantage in teaching human anatomy. Why? The best roadmaps to human bodies lie in the bodies of other animals. The simplest way to teach students the nerves in the human head is to show them the state of affairs in sharks. The easiest roadmap to their limbs lies in fish. Reptiles are a real help with the structure of the brain. The reason is that the bodies of these creatures are simpler versions of ours.

During the summer of my second year leading the course, working in the Arctic, my colleagues and I discovered fossil fish that gave us powerful new insights into the invasion of land by fish over 375 million years ago. That discovery and my foray into teaching human anatomy led me to a profound connection. That connection became this book.”

Figure 1. From the Beginning - The Story of Human Evolution was published by Little Brown in 1991 and is now available as a FREE online PDF from DavidPetersStudio.com

Figure 3. From the Beginning – The Story of Human Evolution was published by Little Brown in 1991 and is now available as a FREE online PDF from DavidPetersStudio.com

If you are interested in human evolution and want to see more details on the development of human body parts and — when — they came to be, see “From the Beginning, the Story of Human Evolution” free online pdf here.

Only a few updates to this 1991 book are needed based on more recent discoveries. Updates can be found at reptileevolution.com where you can also read about the evolution of any reptile, from snakes to pterosaurs to whales, dinosaurs and bats, from their fishy genesis through all their transitional taxa.

Congratulations
to Neil Shubin for work well done!

 

 

Osmolskina – a basal ornithosuchid

Figure 1. Osmolskina was a euparkeriid that was basal to the ornithosuchids, Ornithosuchus and Riojasuchus. Note the scale bars.

Figure 1. Osmolskina was a euparkeriid basal to the ornithosuchids, Ornithosuchus and Riojasuchus. Note the scale bars. Osmolskina was quite tiny relative to its descendants.

Ornithosuchids are often just a footnote.
Only three taxa are known, Ornithosuchus, Venaticosuchus and Riojasuchus (Fig. 1). And nobody pays much attention to them because they’re, frankly, off the beaten track.

Now,
thanks to phylogenetic analysis (and the large reptile tree) we can add one more, the much smaller basal form, Osmolskina. Sure it doesn’t have all the traits of the classic ornithosuchids, but among the 378 taxa now included, no others come closer.

References
Borsuk-Bialynicka M and Evans SE 2009. Cranial and mandibular osteology of the Early Triassic archosauriform Osmolskina czatkowicensis from Poland. Palaeontologia Polonica 65, 235–281.

 

 

 

Evidence for a flightless Quetzalcoatlus northropi

Quetzalcoatlus northropi (Fig. 1, Lawson 1975) is well known as the largest pterosaur of all time. It is known chiefly from most of the wing, which dwarves that of the more complete specimen of Q. sp. (Kellner and Langston 1996), which was found a mere 40km away from sediments of a similar age (Latest Cretaceous). Other giant azhdarchid pterosaurs competing for “the largest pterosaur of all time” are known from less complete remains.

Figure 1. Quetzalcoatlus specimens to scale.

Figure 1. Click to enlarge. Quetzalcoatlus specimens to scale. Here Q. northropi is 2.5x taller than Q. sp, if nothing else changed other than size. 

Some workers (Henderson 2010) have questioned the flying abilities of Q. northropi. Others (Witton and Habib 2010) have given it tremendous flying abilities, able to soar between continents. Both have relied on scaling the small specimen up to the size of the giant.

I was curious
to compare the large and small specimens. Several years ago I took photos of the large specimen wing at the Langston lab in Austin, Texas. The tracings of the large specimen were scaled down to the size of the small specimen (Fig. 2). They are — almost  – identical.

Figure 1 Quetzalcoatlus sp. compared to the large specimen wing, here reduced. I lengthened the unknown metacarpus to match the Q. sp. and other azhdarchid metacarpi. I offer the wing finger has reconstructed by the Langson lab and with filler reduced. Note m4.2 is narrower on the larger specimen, which doesn't make sense if Q. northropi was volant.

Figure 2. Quetzalcoatlus sp. compared to the large specimen wing, here reduced to match that of the smaller specimen. I lengthened the unknown metacarpus to match the Q. sp. and other azhdarchid metacarpi. Note m4.2 is narrower and shorter on the larger specimen, which doesn’t make sense if Q. northropi was volant. It might have been shorter still if Option 1 is valid. At this point, either is possible. 

Scaling pterosaurs helps one understand some of the “big” questions. Everyone knows that to double the height of the animals is to cube its weight. The same holds true for pterosaurs. So then we might ask, if the larger specimen had higher wing loading, why wasn’t the wing spar more robust? As you can see, the wing elements were not more robust in the giant — AND — m4.2 was more gracile (Fig. 2).

The answer to that question is not so obvious, as we learned before. The proportions of giant azhdarchids were quite similar to those of the tiniest proto-azhdarchids, as you can see below (Fig. 3).

We also see distal wing phalanx reduction in the evolution of the flightless pterosaur, Sos 2428 from tiny ancestors, n42, and n44 (from the Wellnhofer 1970 catalog, Fig. 3) with longer wings.

Figure 2. The flightless pterosaur, Sos 2428, along with two ancestral taxa, both fully volant. Note the reduction of the wing AND the expansion of the torso. We don't know the torso of Q. northropi. It could be small or it could be very large.

Figure 3. The flightless pterosaur, Sos 2428 to scale along with two ancestral taxa, both fully volant. Note the reduction of the wing AND the expansion of the torso. We don’t know the torso of Q. northropi. It could be small or it could be very large.

Here in the flightless pterosaur (Fig. 3), perhaps more importantly, the torso expanded greatly in every direction during the evolution of flightlessness. The pelvis was also much larger in Sos 2428.

We don’t have enough torso material from the Quetzalcoatlus northropi specimen to understand its volume. While it is possible that the torso remained small, as in Q. sp. (Fig. 1), it is equally possible that it could have expanded to become voluminous, as in Sos 2428.

Until we know, we can only guess, but the relative reduction of the distal wing elements, beyond what we see in the smaller specimen, adds weight to the argument that flight was more difficult for the giant.

More data would help settle this issue.
We take our clues wherever we can. Don’t overlook the little stuff.

References
Henderson DM (2010). Pterosaur body mass estimates from three-dimensional mathematical slicing. Journal of Vertebrate Paleontology 30(3):768-785.
Kellner AWA and Langston W 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from late Cretaceous sediments of Big Bend National Park, Texas. – Journal of Vertebrate Paleontology 16: 222–231.
Lawson DA 1975. Pterosaur from the latest Cretaceous of West Texas: discovery of the largest flying creature. Science 187: 947-948.
Witton MP and Habib MB 2010. On the Size and Flight Diversity of Giant Pterosaurs, the Use of Birds as Pterosaur Analogues and Comments on Pterosaur Flightlessness. PlosOne 5(11): e13982. doi:10.1371/journal.pone.0013982

wiki/Quetzalcoatlus