Still working on Diandongosuchus

Sorry for the lack of a regular post today.
On Saturday you’ll see a reconstruction of Diandongosuchus, the new basal phytosaur. We’ll make graphic comparisons to Qianosuchus, poposaurs, phytosaurs, proterochampsids and champsosaurs. So you’ll see why the large reptile tree nests Diandongosuchus with the phytosaurs, not the poposaurs.

Thank you for your patience. It will be rewarded.

In the meantime, there’s a doggone good restoration of Diandongosuchus here.

Where in the World is Rotodactylus?

Rotodactylus ichnites (Peabody 1948, Lower Triassic, Moenkopi Formation, Arizona, Utah; Grès d’Antully Formation, France, Middle Triassic Haizer-Akouker Unit at the Belvédčre (Bkherdous) locality in Algeria; Fig. 1) are distinguished from all others by the impression of pedal digit 5 far behind the other asymmetric digitigrade toes.

Peters (2000) matched Rotodactylus tracks to basal fenestrasaurus, including Cosesaurus (Fig. 2). We can also include a Cosesaurus sister, Langobardisaurus, as a possible trackmaker, following several days of Langobardisaurus news here and here. We can probably also include Pteromimus and Amotosaurus, more sisters to Langobardisaurus and Cosesaurus.

Cosesaurus and Rotodactylus, a perfect match.

Figure 1 Cosesaurus and Rotodactylus, a perfect match. Elevate the proximal phalanges along with the metatarsus, bend back digit 5 and Cosesaurus (left) fits perfectly into Rotodactylus (right).

Here (please check this link) is a good Rotodactylus track along with a model of a  Cosesaurus-like hypothetical trackmaker. Note pedal digit 5 does not include an ungual imprint, as the model indicates it should and Peabody (1948) noted. No, the pedal 5 imprint is a smal round impression, the sort made by the impression of the dorsal side of a flexed interphalanageal joint, as in pterosaurs.

Cosesaurus foot in lateral view matches Rotodactylus tracks.

Figure 2. Cosesaurus foot in lateral view matches Rotodactylus tracks. The center of balance is over the anterior toes. Digit 5 was more like a kickstand bouncing and flexing with each step but distant from the weight-bearing digits.

Amy Barth of Discover magazine reported, “Rotodactylus is believed to be a dinosaur or a surviving dinosaur ancestor that lived just after dinos and crocodilians split into separate branches.” This is the traditional consensus, following the paper by Brusatte et al. (2011) even though no archosaur had an elongated digit 5. She reported, “Footprints in southern Germany, for example, may extend the entire dinosaur lineage back four to five million years. The tracks were formed 240 to 245 million years ago by a cat-size reptile called Rotodactylus, known from its footprints alone; no bone evidence of dinosaurs dates this far back, says paleontologist Hartmut Haubold of Martin Luther University in Halle-Wittenberg, Germany.”

The Triassic World with Rotodactylus areas in pink.

Figure 4. The Triassic World with Rotodactylus areas in pink.

Rotodactylus in white along with other Triassic tracks in red

Figure 3. Rotodactylus in white along with other Triassic tracks in red. Even the manus of this specimen extended posteriorly, but also notice, you see the tip of the digit, unlike the pes.

Thirty years ago Harmut Haubold (1983) reported, “Rotodactylus somewhat resemble those of Lagosuchus (Marasuchus). Trackway pattern shows relatively broad trackways, pes angulation up to 160°, and very long stride from which results overstep of manus by pes  impressions. Stride and trackway pattern show an extremly variable speed, something quite rare in reptilian trackways generally.”

Haubold continues, “The digit group II-IV is subparallel and closed-together. Digits I and V are only impressed as points, V in the characteristic heel-like backward position. The only reasonable interpretation, seems to be that these animals belonged to an ear!y specialised thecodontian group. The pes joint was probably mesotarsal because,  of the very digitigrad impressions and the closed digit group II-IV, but possibly it showed the transitional lacertoid and rabbit-like habit, as in Lagosuchus, the most ‘similar’ genus of Middle Triassic age. Rotodactylus may be characterised as a progressive lacertoid type.”

Here Lagosuchus nests as a theropod with pedal digit 3 far exceeding digit 4 and digit 5 was absent a far cry from the ichnite Rotodactylus. Cosesaurus and Langobardisaurus are better matches.

Paleontologists see Rotodactylus as digitigrade and consider it archosaurian, close to dinosaurs. They also note that digit 4 is longer than digit 3, which occurs in lizards, proterosuchians and protorosaurs, far from dinosaurs. The presence of pedal digit 5 also knocks archosaurs, out of contention. What we’re looking for is a match on all counts. Such a match occurs in basal fenestrasaurs.

Rotodactylus tracks have been found from the US southwest to central Europe and Algeria (Fig. 3). That’s a large area and it increases hope that more Pteromimus/Langobardisaurs/Cosesaurus-types will be found someday as fossils in this zone.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Brusatte SL Niedźwiedzki G and Butler RJ 2011. Footprints pull origin and diversification of dinosaur stem-lineage deep into Early Triassic. Proceedings of the Royal Society of London, Series B, 278, 1107-1113.
Demathieu G and Gand G 1973 Deux espèces ichnologiques nouvelles des Grès à Empreintes du Trias du Plateau d’Antully [Two new ichnological species from the Triassic Grès à Empreintes of the Antully plateau]. Bulletin Trimestriel de la Société d’Histoire Naturelle et des Amis du Muséum d’Autun 67:11-27
Demathieu G and Gand G 1974. Une nouvelle espèce du genre Rotodactylus découverte dans les grès du Trias moyen du plateau d’Antully: Rotodactylus velox [A new species of the genus Rotodactylus discovered in the Middle Triassic sandstones of the Antully plateau: Rotodactylus velox]. Bulletin Trimestriel de la Société d’Histoire Naturelle et des Amis du Muséum d’Autun 72:9-23
Ellenberger P 1970. Les niveaux paléontologiques de première apparition des mammifères primoridaux en Afrique du Sud et leur ichnologie. Establissement de zones stratigraphiques detaillees dans le Stormberg du Lesotho (Afrique du Sud) (Trias Supérieur à Jurassique) [The paleontological levels of the first appearance of primordial mammals in southern Africa and their ichnology. Establishment of detailed stratigraphic zones in the Stormberg of Lesotho (southern Africa) (Upper Triassic to Jurassic). In: S. H. Haughton (ed.), Second Symposium on Gondwana Stratigraphy and Paleontology, International Union of Geological Sciences. Council for Scientific and Industrial Research, Pretoria 343-370.
Haubold H 1983. Archosaur evidence in the Buntsandstein (Lower Triassic) Acta Palaeontologica Polonica 28 (1-2), 1983: 123-132.
Peabody FE 1948. Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah. University of California Publications, Bulletin of the Department of Geological Sciences 27(8):295-468.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods. Ichnos 7:11-41.

Diandongosuchus. Not a basal poposauroid. A basal phytosaur.

The most recent JVP included a paper by Li et al. (2012) described a new “archosaur” from the marine Triassic of China, Diandongosuchus fuyuanensis. Their phylogenetic analysis, based on Nesbitt (2011) nested their find at the base of the poposauroidea. That was not confirmed by the large reptile tree. Rather Diandongosuchus nested at the base of the Phytosauria.

This was such an open-and-shut case that this poor nesting is a further indictment of the Nesbitt (2011) tree. More details on this very exciting discovery of a VERY basal phytosaur coming soon.

Reference
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.
Nesbitt SJ 2011. The early evolution of archosaurs: relationships and the origin of major clades. Bulletin of the American Museum of Natural History 352: 292 pp.

The Ctenochasma – Pterodaustro transitional taxon

This post has been modified with a new reconstruction, heading and text.
A pre-Solnhofen ctenochasmatid pterosaur has been announced here and here. Please take a look at those links to see the fossil itself. Both sites can be clicked for enlargements.

Figure 1. The new Propterodaustro pterosaur reconstructed. While it nests between Ctenochasma and Pterodaustro, certain traits are distinct from both.

Figure 1. The new Propterodaustro pterosaur reconstructed. While it nests between Ctenochasma and Pterodaustro, certain traits are distinct from both.

The new pterosaur nests here between Ctenochasma and Pterodaustro.

“The discovery is of similar interest like Archaeopteryx,” says the director of the Bamberg Natural History Museum, Matthias Mäuser. Over 400 teeth were reported. The long teeth are not pointed, but with “small  thickened lobes (Google translated from the original German)” explains Mäuser. He reports, “the food was not chewed or retained, but filtered out of the water – as do baleen whales and flamingos with the slats in the beak.”

“The 155 million year old animal is different in physique from other known species – and its remnants are extremely well preserved. Scientists speak of a major discovery. The specimen had very long arms and long legs, almost like stilts. Fish remains are found in the belly.”

“The Bamberg piece shows that these giant pterosaurs had their origin in the Jurassic period,” reports Dr. Eberhard (Dino) Frey. Such a nesting, at the base of the azhdarchidae, is not confirmed in the present study.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Archosaur Musings link
Der Spiegel link

What Did Langobardisaurus Eat?

Strange body. Strange skull. Strange teeth.

Earlier we looked at the pectoral girdle of this Triassic oddity. The genus Langobardisaurus (Fig. 1) is known from several specimens assigned to two species, L. pandolfii and L. tonelloi. Both have a large skull, large orbit, retracted nares, elongated cervicals, no proximal carpals, a long torso, a great number of gastralia, appressed ulna/radius, appressed tibia/fibula/ and a lizard-like foot with a reduced metatarsal 5 and an elongated p5.1.

Two skulls of Langobardisaurus together with to scale images of them along with sisters Amotosaurus and Pteromimus.

Figure 1. Two skulls of Langobardisaurus together with to-scale images of them along with sisters Amotosaurus and Pteromimus. Note Pteromimus has the most plesiomorphic teeth.

Earlier we also looked at the giant, though still related Tanystropheus, represented by a likely deep water biped with elongated conical teeth feeding on passing cephalopods among elongated crinoids. There are also much smaller specimens with both conical and tricuspid teeth, closer to the dental arrangement in Langobardisaurus, grabbing and crunching, like mammals. Langobardisaurus takes that one step further with an elongated posterior dentary tooth (the result of three fused teeth?). It has a straight processing surface and opposes at least three maxillary teeth.

The orbit was very large, suggesting acute vision (perhaps for night time predation?) The rostrum was narrow, short and pointed, so probably not a fish-eather. There was a possible antorbital fenestra or two, as in its sister Cosesaurus (a small insectivore) and Pteromimus (Fig. 1). The palate is largely, if not entirely, unknown, but in Cosesaurus it is largely open with gracile elements.

What did Langobardisaurus eat?
The small size of Langobardisaurus omits nearly all possible prey items but insects and possibly smaller juvenile reptiles. The tricuspid teeth could have processed the hard exoskeletons of small invertebrates for more rapid assimilation. The rake-like “incisors” would have been good at grabbing tree-crawling insects. The bipedal posture and long neck would have made taller plants harboring insects more available.

Marine Sediments
Like Tanystropheus, Langobardisaurus was found in marine sediments. Was it washed in? Or a denizen of shallow waters? Likely washed in, like the one and only Cosesaurus, found stuck to a jellyfish.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Muscio G 1997. 
Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S and Dalla Vecchia FM 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995 from the Late Triassic of Friuli (Italy)*. Rivista di Paleontologia e Stratigrafia 113(2): 191-201. online pdf

wiki/Langobardisaurus

Now it’s Langobardisaurus and the Origin of the Pterosaur Sternal Complex

Earlier we discussed the evolution of the pterosaurian sternal complex beginning with the plesiomorphic basal tritosaur lizard, Huehuecuetzpalli, and continuing through Cosesaurus (Fig. 1). Though flightless, Cosesaurus had all the elements of a pterosaurian sternal complex in place: 1) strap-like scapula; 2) quadrant-shaped coracoid with stem attached to interclavicle anterior to the transverse processes; 3) cruciform interclavicle; 4) transverse clavicles rimming the broad sternum; 5) sternum and interclavicle layered and coincident. In pterosaurs the clavicles extend posteriorly along an initially triangular sternum and in most pterosaurs the coracoid stem straightens out. So it looks like Cosesaurus was flapping, but not flying.

The evolutionary leap from Huehuecuetzpalli to Cosesaurus was great, but not insurmountable. Now we find a transitional taxon between these two to better bridge that gap and provide data on the order of changes.  Some surprises and unexpected wonders are here that should open all new chapters on the origin of vertebrate flapping and flight.

langobardisaurus-pectoral-girdle

Today we reexamine Langobardisaurus tonelloi (Figs. 1-3), a close relative of Cosesaurus, Tanytrachelos and the long-necked giant, Tanystropheus. Langobardisaurus demonstrates a transitional phase in the evolution of the fenestrasaurian/pterosaurian pectoral girdle. 

The anterior dorsal area of Langobardisaurus tonneloi with original designations noted in black and new interpretations in color overlays.

Figure 2. Click to enlarge. The anterior dorsal area of Langobardisaurus tonelloi with original designations noted in black and new interpretations in color overlays. The original clavicle is now rib #9. The original coracoid is now the broad clavicle. The original scapula is now the coracoid. The original rib #10 (on the right) is now the strap-like scapula. Rib #10 (on the left) and the sternum were identified correctly. See below for a reconstruction and comparison.

New Interpretations of the Langobardisaurus pectoral elements
Renesto’s tracing of L. tonelloi (Fig. 2) included his interpretations based on what was known of sister taxa at the time, all of which were thought to have a Tanystropheus/Macrocnemus-like pectoral girdle with short broad, elliptical elements. Now Cosesaurus (Fig. 1) offers new possibilities. Here colorized to re-identify the elements (Fig. 2), the original coracoid is now the broad clavicle. The original scapula is now the coracoid. The original rib #10 (on the right) is now the strap-like scapula. Rib #10 (on the left) and the sternum were identified correctly. See below for a reconstruction and comparison.

Langobardisaurus tonneloi reconstructed. Note the cosesaur-like pectoral girdle.

Figure 3. Langobardisaurus tonelloi reconstructed. Note the cosesaur-like pectoral girdle. Click to learn more. The pes is also fenestrasaurian/pterosaurian in character.

Distinct from Cosesaurus
The coracoid in L. tonelloi did not develop an elongated stem. Otherwise the Cosesaurus and Langobardisaurus shared many pectoral shapes and arrangements.

The Shift
In order for the fenestrasaur pectoral girdle to develop, the coracoids had to move anterior to the interclavicle transverse processes. Langobardisaurus gives us that transitional mid-point. Remember the sternal complex was chiefly transverse in orientation while the the scapula/coracoid was largely parasagittal.

Bipedalism Frees up the Forelimbs
How the muscles shifted and why they shifted is still to be determined. A study by Renesto, Dalla Vecchia and Peters (2002) described the bipedal abilities of Langobardisaurus. When the forelimbs rise off the substrate, they are free to do other tasks. There’s the opportunity.

The coracoids do not appear to be locked in place in Langobardisaurus as they were in Cosesaurus, so pterosaur-like, bird-like flapping was not so well developed.

Chlamydosaurus, the Austrlian frill-neck lizard

Fig. 4 Chlamydosaurus, the Austrlian frill-neck lizard with an erect spine and elevated tail. Click to see a YouTube movie.

Hypothesis
As small insectivores, langobardisaurs and cosesaurs might have made tasty meals for larger predators. If similar in their bipedal abilities to the living lizard, Chlamydosaurus (Fig. 4), then bluff and charge might have been in their repertoire. Lacking expanding neck skin, langobardisaurs and cosesaurs might have charged bipedally frantically waving their forelimbs. This might have also impressed the girl langobardisaurs and if that’s deemed sexy, well, folks, you just get more of the same generation after generation.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Muscio G 1997. 
Preliminary note on a specimen of Prolacertiformes (Reptilia) from the Norian (Late Triassic) of Preone (Udine, north-eastern Italy). Gortania – Atti del Museo Friulano di Storia Naturale 18:33-40
Renesto S 1994. A new prolacertiform reptile from the Late Triassic of Northern Italy. Rivista di Paleontologia e Stratigrafia 100(2): 285-306.
Renesto S and Dalla Vecchia FM 2000. The unusual dentition and feeding habits of the Prolacertiform reptile Langobardisaurus (Late Triassic, Northern Italy). Journal of Vertebrate Paleontology 20: 3. 622-627.
Renesto S and Dalla Vecchia FM 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995 from the Late Triassic of Friuli (Italy)*. Rivista di Paleontologia e Stratigrafia 113(2): 191-201. online pdf
Renesto S, Dalla Vecchia FM and Peters D 2002. Morphological evidence for bipedalism in the Late Triassic Prolacertiform reptile Langobardisaurus. Senckembergiana Lethaea 82(1): 95-106.

wiki/Langobardisaurus

“Renestosaurus” rossii and the DGS Method

Updated with a new reconstruction July 2, 2014.

Bizzarini and Muscio (1995) and Bizzarini, Muscio and Rossi (1995) introduced MFSN 19235 (Fig. 1) as a new species (L. rossii) of Langobardisaurus, the long-necked tritosaur (then wrongly considered a protorosaur). The fossil is represented by part and counterpart of more than a dozen broken pieces. Most of the skull pieces are missing and replaced with putty. Other bones are decayed. Bizzarini, Muscio and Rossi (1995)  considered the broken mandible a series of elongated neck vertebrae with the skull curled back.

MFSN 19235, Renestosaurus

Figure 1. Click to enlarge. This image updates an earlier one. MFSN 19235, once considered Langobardisaurus rossii and here renamed Renestosaurus rossii. The torso was actually flatter than shown here with ribs transverse as in Dalinghosaurus (fig. 3). Note that the long ventral torso bone tentatively identified as the interclavicle by Renesto and Dalla Vecchia (2007) is the left humerus. The rest of the left arm extends dorsally and is disarticulated. Higher resolution enabled better identification of elements. The nesting on the large reptile tree did not change, between Gephyrosaurus and basal squamates.

This post has been updated with the reception of an image of higher resolution.

 

Figure 2. Langobardisaurus(?) rossii (MFSN 19235) reconstructed. Here it nests between basal sphenodontids and basal tritosaurs + squamates.

Figure 2. Langobardisaurus(?) rossii (MFSN 19235) reconstructed. Here it nests between basal sphenodontids and basal tritosaurs + squamates.

 

Renesto and Dalla Vecchia (2007) redescribed the skeleton, concluding that it did not exhibit any “protorosaurian” characters, but all evidence supported attribution to the Lepidosauromorpha with some skull traits possibly supporting a sphenodontian affinity. They re-identified the former neck vertebrae as dentary fragments and noted the actual cervicals were short and small. They found the pisiform, which suggested inclusion within the Lepidosauromorpha. Renesto and Dalla Vecchia (2007) noted what remains of the skull suggested affinity with the Sphenodontia, but preservation was “too poor to allow a firm assignment to this group.”

Homoeosaurus

Figure 2. Homeosaurus, a sister to Dalinghosaurus and Renestosaurus at the base of the Squamates, not far from the Sphenodontia.

Here (Fig. 1), using DGS (digital graphic segregation), reconstruction and phylogenetic analysis permits a firm assignment of MFSN 19235 to the base of the small clade that also includes Homoeosaurus (Fig. 2) and Dalinghosaurus (Fig. 3), both nesting at the base of the Squamates and derived from a sister to Gephyrosaurus. MFSN 19235 may someday be considered a species of Homoeosaurus, but let’s call it Renestosaurus rossii until someone comes along and writes a paper on this clade. This species is a sister to Marmoretta + Megachirella and  Gephyrosaurus at the base of the Sphenodontia, somewhat supporting the tentative conclusions of Renesto and Dalla Vecchia (2007).

Reconstruction of Dalinghosaurus

Figure 3. Reconstruction of Dalinghosaurus, note the larger girdles and more asymmetrical manus and pes.

Note that the long ventral torso bone tentatively identified as the interclavicle by Renesto and Dalla Vecchia (2007) is the other femur extending anteriorly. The other tibia, fibula and pes are mixed in with the anterior dorsal ribs. A higher resolution image should resolve these similar elements better than done here (Fig. 1). A smaller interclavicle matching a smaller pectoral girdle is identified here (Fig. 1).

The DGS method permitted identification of nearly every post-cranial bone. Phylogenetic analysis nested Renestosaurus with the homoeosaur clade. Traits are indeed similar.

Like its sisters the tarsus is no co-ossified. The torso is wide. The scapula is anteriorly embayed.

Unlike its sisters the pectoral and pelvic girdles were relatively small. Metacarpal 2 was longer than the others. The manus and pes were relatively more symmetrical.

To those looking for an example of the DGS method, this is one. All challenges are accepted. If you find something wrong, let’s fix it. So far,  not getting too many brave enough to step forward, but lots of bitchin’ as expected.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Bizzarini F and Muscio G 1995. Un nuovo rettile (Reptilia, Prolacertiformes) del Norico di Preone (Udine, Italia Nordorientale). Nota Prelimininare. Gortania – Atti Mus. Friulli. Sti. Nat., 16 (1994): 67-76, Udine.
Bizzarini F, Muscio G and Rossi IA 1995. Un nuovo rettile fossile Langobardisaurus? rossiin. sp. Prolacertiformes (Reptilia) della val Preone (UD), Prealpi Carniche Italine. 1-35 Grafiche Tipo, Catelgomberto.
Renesto S and Dalla Vecchia F 2007. A revision of Langobardisaurus rossii Bizzarini and Muscio, 1995, from the Late Triassic of Friuli (Italy)*

re: Adding Taxa

A new phylogenetic study by Wiens and Tiu (2012) concluded: “We show that adding taxa that are highly incomplete can improve phylogenetic accuracy in cases where analyses are misled by limited taxon sampling. These surprising empirical results confirm those from simulations, and show that the benefits of adding taxa may be obtained with unexpectedly small amounts of data. These findings have important implications for the debate on sampling taxa versus characters, and for studies attempting to resolve difficult phylogenetic problems.”

Nice to hear. I agree.
All three of my trees (reptiles, pterosaurs and basal therapsids) include incomplete taxa. Some with skulls. Some without. Some just bits and pieces. Most, however, are complete. It’s important to include odd and incomplete taxa, just to know where they belong. Problems come when skull only taxa nest with skull-less taxa. Even so, that can be overcome with complete sisters.

Interestingly:
The Wiens and Tiu (2012) study found turtles closer to archosaurs than lizards with mammals the outgroup. Not sure why turtle DNA is closer to archosaurs when their morphology says otherwise. And I wonder why mammal DNA doesn’t nest closer to archosaurs when their morphology says otherwise. Bottom line: the morphology has to support the DNA and vice versa. Since prehistoric taxa will never give us DNA, we’re stuck with morphology, so long as a sufficient number of taxa are included. The more the better. 500+ taxa is not a bad start.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Wiens JJ, Tiu J 2012. Highly Incomplete Taxa Can Rescue Phylogenetic Analyses from the Negative Impacts of Limited Taxon Sampling. PLoS ONE 7(8): e42925. doi:10.1371/journal.pone.0042925

What Goes On Inside a Pregnant Pterosaur?

Earlier we looked at the Darwinopterus and egg association (Fig. 1). We noted that the embryo inside that egg had virtually the same proportions as the mother, matching the situation of other pterosaur embryos. Now let’s put that egg back inside the mother (Fig. 2) to learn what we can from a pregnant pterosaur.

Darwinopterus and associated egg.

Figure 1. Darwinopterus and associated egg.

A Pregnant Pterosaur
Prior to the moments before death, the Darwinopterus egg was within the mother. It was not full term. The embryo was not well ossified nor was it large enough to fill its shell. Here then is that egg placed back within the mother (Fig. 2).

Placing the egg back into the pregnant mother pterosaur.

Figure 2. Placing the egg back into the mother pterosaur. The egg fills up the pelvic canal  and is partially supported by the prepubes. The egg, as shown, is crushed with a very flexible coating, not a thicker ellipitical crackling shell. That flexibility allowed it to pass out of the narrower pelvic opening.

Support from the Prepubes
Acting a pubic extenders, the prepubes of pterosaurs were anchors for important thigh adductor muscles, helping pull those slightly-to-greatly splayed legs inward for a more-or-less erect stance. Inside the prepubes would have supported the intestines, but when an egg was developing inside the mother, even they had to move out of the way (Fig. 2).

The size of the egg compared to the internal portion of the mother devoted to laying it, appears to indicate that there would have been room for only one egg at a time.

Pterodaustro adult with embryo and egg all to scale.

Figure 3. Pterodaustro adult with embryo and egg all to scale.

Then There’s Pterodaustro
Pterodaustro adults and eggs are known from the same formation, just not in intimate association — yet. When we place the embryo Pterodastro up against the most complete specimen known to date we get a 1:7 size ratio, a little larger than the 1:8 ratio seen in other pterosaurs. This may be due to the fact that the most complete specimen was not the largest specimen so far documented. Half-sized specimens were sexual according to Chinsamy et al. (2008), so we’re at least in the ballpark.

 Putting the egg back inside the mother Pterodaustro demonstrates the egg fills up the inner pelvic area and was supported by the prepubes.

Figure 4. Putting the egg back inside the mother Pterodaustro demonstrates the egg fills up the inner pelvic area and was supported by the prepubes.

A Hypothetical Pregnant Pterodaustro
When we put the Pterodaustro egg back inside the mother (Fig. 4) we get a similar situation as in Darwinopterus (Fig. 2). There’s room for only one egg and the prepubes help support it.

In fenestrasaurs, including pterosaurs, the anterior pubes separate creating a wider embayment between them. The prepubes bridge that gap, becoming virtual pubic extensions, deepening the abdomen. Could it be that prepubes were as much tied into reproduction as to locomotion?

Prepubes (epipubic bones) on basal mammals are convergent structures that appear to support the pouch but may have other functions.

The only thing I find surprising is the lack of more pregnant female pterosaurs in the fossil record. We might look harder. Ossified embryo wing bones might be about the same size as gastralia. It may be that ossification and shell formation happened only during the last few days prior to laying, with the necessary minerals being leached from the inside walls of the mother’s own store of calcium, her bony skeleton.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Chiappe LM, Codorniú L, Grellet-Tinner G and Rivarola D. 2004. Argentinian unhatched pterosaur fossil. Nature, 432: 571.
Lü J, Unwin DM, Jin X, Liu Y and Ji Q 2009. Evidence for modular evolution in a long-tailed pterosaur with a pterodactyloid skull. Proceedings of the Royal Society London B  (DOI 10.1098/rspb.2009.1603.)
Lü J, Unwin DM, Deeming DC, Jin X, Liu Y and Ji Q 2011a. An egg-adult association, gender, and reproduction in pterosaurs. Science, 331(6015): 321-324. doi:10.1126/science.1197323
Lü J, Xu L, Chang H and Zhang X 2011b. A new darwinopterid pterosaur from the Middle Jurassic of Western Liaoning, northeastern China and its ecological implicaitions. Acta Geologica Sinica 85: 507-514.

wiki/Darwinopterus

The Evolution of Gigantism in Pterosaurs: The Ancestry of Anhanguera

Earlier we followed up on a National Geographic article on how many generations it takes to create a blue whale and an elephant. Yesterday we looked at the evolution of the giant pterosaur Quetzalcoatlus. Today we’ll examine two ornithocheirids.

Others consider toothy ornithocheirids, like Arthurdactylus and Anhanguera (Fig. 1), to be related to toothless Pteranodon based on the shared trait of a warped deltopectoral crest. The large pterosaur tree did not recover that relationship, but found that humerus warp to be a convergence.

The beauty of the large reptile tree and the large pterosaur tree is the ability to trace the ancestry of any listed taxon back to the basal tetrapod, Ichthyostega. Today we won’t go that far back. Rather we’ll start with one of the smallest pterosaurs from the first Late Jurassic in the lineage of Anhanguera and Arthurdactylus. That pterosaur is a tiny specimen inaccurately referred to Pterodactylus? micronyx? TM 13104 (Winkler 1870, No. 34 in the Wellnhoger 1970 catalog), Fig. 1).

The ancestry of Anhanguera and Arthurdactylus includes tiny TM 13104.

Figure 1. The ancestry of Anhanguera and Arthurdactylus includes tiny TM 13104 (no. 34 in the Wellnhofer 1970 catalog).

We’re often taught that as organisms grow larger they also become more robust, with stronger, thicker bones to withstand the effects of their greater mass and weight. Here, there’s more —  and less — of a case for that. Giant Arthurdactyulus was more robust, especially in the wings than, no. 34. However the scapula + coracoid were not. The hind limb was ever so slightly more gracile (certainly not more robust). The torso was shorter with taller vertebral spines. Unfortunately the head and neck are unknown, but sister taxa, like Haopterus and Coloborhynchus, had a more robust neck and a longer skull (which may explain the more robust neck). The feet of Arthurdactylus were comparatively tiny! What a strange combination evolution has wrought here: more wing and head, less body and feet!

The complete TM13104 and the skull of Anhanguera to scale.

Figure 2. The complete TM13104 and the skull of Anhanguera to scale. Also shown in gray is a hypothetical skull of Arthurdactylus based on a stretched out Haopterus.

What can we learn here?
Between no. 34 (which was reduced from early Scaphognathus specimens) and basal ornithocheirds like Arthurdactylus and Haopterus, the proportions changed rather starkly. This is likely due to a distinctively different mode of flight. Over time and millions of generations, the lineage of Arthurdactylus gradually grew and reengineered itself to withstand the increasing stresses imposed by that growth. The wing became more robust. Here the time frame is only from the Late Jurassic, 150 mya to the Early Cretaceous Crato Formation, 112 mya, a time span of 38 million years.

Then Along Comes Anhanguera
Anhanguera was more derived than Arthurdactylus and it shows the “evolution engineers” were hard at work further lightening this aerial predator. Much larger than Arthurdactylus, Anhanguera had a relatively smaller diameter humerus, reduced to not much thicker than the femur at both of their smallest diameters. The rest of the wing followed suit. The pectoral girdle was reengineered with elongated processes to route the wing muscles more efficiently and provide larger areas for their insertion.

Forelimb Take-Off
Dr. Mike Habib (2008) has noted the greater size of the humerus vs femur in Quetzalcoatlus and other large pterosaurs. He didn’t mention no. 34, which does not have a humerus greater in diameter than the femur. Habib considered the more robust humerus a sign that pterosaurs used a vampire bat-like forelimb launch sequence demonstrated here, rather than a bird-like hind limb launch demonstrated here. Unfortunately, its all math at present. We know of no pterosaur take-off tracks, nor any that document the implantation of the wing metacarpal into the substrate. Rather only the fragile first three digits make any impression. Perhaps the increased size of the humerus in Arthurdactylus is a sign that the pectoral engine for wing flapping is much larger to drive the larger wings. The reduced size of the humerus in Anhanguera indicates a reengineered solution to flight: lighter and stronger.

As always, I encourage readers to see specimens, make observations and come to your own conclusions. Test. Test. And test again.

Evidence and support in the form of nexus, pdf and jpeg files will be sent to all who request additional data.

References
Campos, D de A and Kellner AW 1985. Un novo exemplar de Anhanguera blittersdorffi(Reptilia, Pterosauria) da formaçao Santana, Cretaceo Inferior do Nordeste do Brasil.” In Congresso Brasileiro de Paleontologia, Rio de Janeiro, Resumos, p. 13.
Frey E and Martill DM 1994. A new Pterosaur from the Crato Formation (Lower Cretaceous, Aptian) of Brazil. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen 194: 379–412.
Habib M 2008. Comparative evidence for quadrupedal launch in pterosaurs. Pp 161-168 in Buffetaut E, and DWE Hone, eds. Wellnhofer Pterosaur Meeting: Zitteliana B28
Kellner AWA and Tomida Y 2000. Description of a New Species of Anhangueridae (Pterodactyloidea) with Comments on the Pterosaur Fauna from the Santana formation (Aptian-Albian), Northeastern Brazil. National Science Museum, Tokyo, Monographs, 17: 1-135.
Wang X and Lü J 2001. Discovery of a pterodactylid pterosaur from the Yixian Formation of western Liaoning, China. Chinese Science Bulletin 46(13):1-6.
Wellnhofer P 1970. Die Pterodactyloidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Abhandlungen der Bayerischen Akademie der Wissenschaften, N.F., Munich 141: 1-133.
wiki/Arthurdactylus
wiki/Haopterus