Lewisuchus and Pseudolagosuchus

One and the Same?
Recently Nesbitt et al. (2010) attempted to synonymize Lewisuchus admixtus (Romer 1972, Middle Triassic, 235 mya ~70 cm, Fig. 1) and Pseudolagosuchus major (Arcucci 1987, Middle Triassic, 235 mya ~70 cm, Fig. 2). Nesbitt et al. (2010) reported in their supplementary material, “Given that both Lewisuchus and Pseudolagosuchus share apomorphies with other silesaurids, are approximately the same size, and are from the same stratum and locality (Romer, 1972; Arcucci, 1987; Bonaparte, 1997), it is reasonable to suspect that these specimens belong to the same taxon.” They found, “When Lewisuchus and Pseudolagosuchus are placed in a phylogeny as separate taxa, all most parsimonious trees recover both taxa at the base of Silesauridae.” Then reported, “Unfortunately, this lack of overlapping material also means that the two taxa cannot be formally synonymized.”

Figure 1. Lewisuchus, a tiny predecessor to crocs and dinos (including birds).

Figure 1. Lewisuchus, a tiny predecessor to crocs and dinos (including birds).

Romer and Arcucci
Romer (1972) considered Lewisuchus a “thecodont,” but did not delve further.  Arcucci (1987) considered Pseudolagosuchus a basal dinosauromorph.

 Pseudolagosuchus.

Figure 2. Pseudolagosuchus. Gray areas are restored according to Silesaurus. The elongated and gracile posterior ribs are atypical of sister taxa. The ribs were bunched together in situ suggesting they were connected to vertebrae with shorter centra, as shown here, or they could have just drifted closer together during taphonomy.

Non-Overlapping Data
Both Lewisuchus and Pseudolagosuchus shared traits with Silesaurus and and the smaller silesaurid, Asilisaurus, according to Nesbitt et al. (2007) and their analysis (Fig. 3). They were nested as one taxon, which forced them together rather than testing them against other taxa.

Nothing in Common?
Just because Lewisuchus and Pseudolagosuchus share no preserved parts they can still be nested with other, more complete taxa. Here, in the large reptile tree, they don’t nest together.

The Large Study
In the large reptile study Lewisuchus nested with Decuriasuchus and  Pseudhesperosuchus,  two protoarchosaurs outside the Archosauria. Lewisuchus was much smaller than its sisters. This clade was basal to Turfanosuchus and the Archosauria with Trialestes at its base. This is several nodes away from Pseudolagosuchus which nested with Silesaurus nesting within the Paraornithischia within the Dinosauria.

Comparing the Nesbitt (2010) analysis

Figure 3. Comparing the Nesbitt (2010) analysis to a small subset of the large reptile tree, which pretty much follows the pattern of the large tree. See text for details and problems.

Matching the Nesbitt et al. (2012) Taxon List
Decuriasuchus and Pseudhesperosuchus were not included in Nesbitt et al. (2012). I attempted to match the Nesbitt et al. (2012) taxon list (Fig. 3 left) by culling the large reptile taxon list (Fig. 3 right). Five most parsimonious trees were recovered (probably because Pisanosaurus and Pseudhesperosuchus are so incomplete). Most recovered nestings matched the Nesbitt et al. (2012) tree, including nesting the pterosaur with Aetosaurus (ridiculous, isn’t it?). Lewisuchus nested closer to the crocodylomorph Dromicosuchus rather than the silesaurid Pseudolagosuchus, in the absence of Decuriasuchus and Pseudhesperosuchus.

Taxon Exclusion
Please compare the tree on the right in figure 3 to the large reptile tree to gauge the effects of taxon exclusion. Once again, the differences in tree recovery seem to hinge on taxon exclusion, which was minimized in the large reptile tree because it is many times larger than the Nesbitt et al. (2010) tree.

So what happened?
I took data from Romer (1972) while Nesbitt et al. (2012) had access to the specimens. On the other hand, Nesbitt et al. (2012) clearly did not have a large enough taxon list for the gamut of taxa they were testing. I’ll have to see the specimen and Nesbitt et al. (2012) will need to add more taxa before we can come a better understanding here.

Was Asilisaurus the Oldest Known Dinosaur Relative?
Could be. But Lotosaurus may be just as old.

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
Arcucci AB 1987. Un nuevo Lagosuchidae (Thecodontia-Pseudosuchia) de la fauna de Los Chañares (Edad Reptil Chañarense, Triasico Medio), La Rioja, Argentina. .Ameghiniana 24(1-2):89-94.
Nesbitt SJ, Sidor CA, Irmis RB, Angielczyk KD, Smith RMH and Tsuji LMA 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464 (7285):95-98. doi:10.1038/nature08718PMID 20203608.
Romer AS 1972. The Chañares (Argentina) Triassic reptile fauna; XIV, Lewisuchus admixtus, gen. et sp. nov., a further thecodont from the Chañares beds. Breviora 390:1-13.

wiki/Lewisuchus
wiki/Pseudolagosuchus

Isochirotherium and Erythrosuchus

Among the many Triassic tracks made by archosaurs, only one ichnogenus impresses digits 2 and 3 longer than the others and subequal to each other. Lucky for us, among all the many Triassic archosauriform genera only erythrosuchids match that pattern. Case closed?

Erythrosuchus matches Isochirotherium

Figure 1. Erythrosuchus matches Isochirotherium (Haubold 1971, Klein and Haubold 2007) and provides data on the manus, which is otherwise lacking.

Data from the manus impression provides the only data known for the manus of erythrosuchids that I am aware of.

Erythrosuchus

Figure 2. Erythrosuchus

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
Broom R 1905. Notice of some new reptiles from the Karoo Beds of South Africa. Records of the Albany Museum 1: 331–337.
Haubold H 1971. Handbuch der Paläoherpetologie [Encyclopedia of Paleoherpetology]. Part 18. Ichnia Amphibiorum et Reptiliorum Fossilium. Gistav Fischer Verlag, Stuttgart 1-124.
Huene F von. 1911. Über Erythrosuchus, vertreter der neuen reptilordnung Pelycosimia. Geologische und Paläontologische Abhandlungen, N.F. 10: 67–122
Klein H and Haubold H 2007. Archosaur footprints – Potential for Biochronology for Triassic Contiental Sequences. In Lucas SG and Spielmann JA eds. The Global Triassic. New Mexico Museum of Natural History Science Bulletin 41. 120-130 online pdf

wiki/Erythrosuchus

Gwyneddichnium and Tanytrachelos

It’s rare when body fossils and ichnites are found in the same fossil beds. Gwyneddichnium (Bock 1952, the ichnite, Fig. 1) and Tanytrachelos (Olsen 1979, the body fossil) are exceptions. Found in the Appalachian valleys of Virginia, these relatively small, middle Triassic specimens both help piece together and integrate the trackmaker and the track itself.

Gwyneddichnium

Figure 1. Comparing the ichnotaxon, Gwyneddichnium to the tritosaur Tanytrachelos. Note the longer penultimate phalanges in digits 3 and 4 in YPM 7540.

We’re seeing some variation in Tanytrachelos
Note the length of the penultimate phalanges in digits 3 and 4 and the relative size of m1.1 in the two bone specimens. Note the relative length of manus digits 3 and 4 between Gwyneddichnium and the bone specimen (YPM 7491).

Tanytrachelos

Figure 2. Tanytrachelos. Click for more info.

Comparing Gwyneddichnium to Rotodactylus
Gwyneddichnium demonstrates that pedal digit 5 in Tanytrachelos was oriented alongside digits 1-4 in a plantigrade configuration. By contrast the pes of Cosesaurus was matched to the digitigrade ichnite Rotodactylus (Peters 2000), which inverts digit 5, impressing far behind digits 1-4 without making a heel impression. online story.

Foot bones attributed to Tanytrachelos

Figure 3. Foot bones attributed to Tanytrachelos. Note the great similarity between these phalangeal proportions and those of YPM 7540. Metatarsal 1 was shorter in this specimen.

Adding the Pes of Tanytrachelos to the Large Ptero Tree
A lone pes attributed to Tanytrachelos from the same formation was added to the pterosaur tree. The foot nested with Tanytrachelos.

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
Bock W 1952. Triassic reptilian tracks and trends of locomotive evolution. Journal of Paleontology 26(3):395-433.
Olsen PE 1979. A new aquatic eosuchian from the Newark Supergroup Late Triassic-Early Jurassic) of North Carolina and Virginia. Postilla 176: 1-14.

What is Qinglongopterus? Perhaps a Junior Synonym.

Lü et al. (2012) erected a new genus and species for a new rhamphorhynchid from the Tiaojishan Formation of China (Mid/Late Jurassic). They reported, “Qinglongopterus is strikingly similar to Rhamphorhynchus and more closely related to this taxon than to any other rhamphorhynchine.”

 

Figure 1. Qinglongopterus? guoi. A new Rhamphorhynchus species. Tracing of photo of specimen modified with wings and leg out, skull reconstructed, sternum flipped.

Figure 1. Qinglongopterus? guoi. A new Rhamphorhynchus species. Tracing of photo of specimen modified with wings and leg out, skull reconstructed, sternum flipped.

Ontogeny
Lü et al. (2012) considered the Qinglongopterus specimen immature due to lack of fusion in the scapula + coracoid, carpals, extensor tendon epiphysis, pubis and ischium, etc. However they noticed, “external bone surfaces appear to be fairly well ossified and do not exhibit the coarse, fibrous texture evident in the rostrum and limb bones of embryos.”

Phylogeny
Lü et al. (2012) considered their find an archosaur. They used Euparkeria for an outgroup taxon. While noting similarities to Rhamphorhynchus and considering the specimen immature, oddly Lü et al. (2012) did not test their find against any so-called “immature” Rhamphorhynchus specimens. Their analysis of 37 taxa recovered 550 trees and nested Qinglongopterus with R. muensteri.

That’s 549 Red Flags
IMHO, that’s way too many MPTs for so few taxa.

Testing All the Above
Qinglongopterus was inserted into the matrix of the large pterosaur study, which included eleven Rhamphorhynchus specimens of all sizes. Having so many possible nesting partners covers more contingencies and minimizes problems with taxon exclusion. Here, employing 183 taxa, one MPT (most parsimonious tree) was recovered. That’s complete resolution and inspires high confidence that this tree mirrors nature’s own. Qinglongopterus was recovered as a successor to the BMM Rhamphorhynchus and a predecessor to Wellnhofer’s (1975) No. 10 and No. 11, three Rhamphorhynchus specimens generally and traditionally considered juveniles. But they were not juveniles. They were small adults as demonstrated earlier using phylogenetic analysis. Small specimens are typically found at the bases of all major pterosaur clades as size reduction accompanies major morphological changes in the Pterosauria. Even their feet were distinct (Fig. 2)

Is Qinglongopterus a Rhamphorhynchus?
You decide. If the phylogenetic predecessors of Qinglongopterus were Rhamphorhynchus and its phylogenetic successors were Rhamphorhynchus, what is Qinglongopterus? This is an awkward nomenclature situation akin to the nesting of Nesodactylus within Campylognathoides and Eosipterus within Germanodactylus.

Taxon Exclusion Restricts Nesting Possibilities
Unfortunately Lü et al. (2012) did not test for the possibility that Qinglongopterus might have nested within Rhamphorhynchus by restricting their taxon list to only one Rhamphorhynchus despite a wide gamut of morphological variation within that genus. Adding a few small specimens of Rhamphorhynchus would have tested their ontogenetic and phylogenetic concerns.

Is Qinglongopterus a new Species of Rhamphorhynchus?
Yes. Distinct from sister taxa in the present study manual 2.2 was longer than m2.1. Manual 3.3 was not as long as m3.1 + m3.2. The pes/tibia ratio was relatively smaller than in sisters. Pedal 2.1 was longer than p3.1. The sternal complex was wider than long. Otherwise Qinglongopterus retains certain plesiomorphic traits retained from the BMM specimen and displays certain derived traits not found in the BMM specimen but found in No. 10 and No. 11, like the pointed jaws. The pes of Qinglongopterus is similar to the pes in the BMM specimen (Fig. 2) and the pes of No. 11 .

 

Sample feet of Rhamphorhynchus

Figure 1. Sample feet of Rhamphorhynchus in phylogenetic order. Note the differences in metatarsal and phalanx proportions. These are distinct species, not a growth series of a single species. Figure 2. Rhamphorhynchus pedes demonstrating variation and speciation. The pes of Qinlongopterus is most similar to the BMM specimen and that of No. 11. Click to enlarge.

Is Qinglongopterus Immature?
All sister taxa share the same lack of fusion enjoyed by Qinglongopterus. Earlier we discussed lack of fusion as a phylogenetic trait, not an ontogenetic one. It’s important to remember that pterosaurs do not follow archosaur ontogenetic patterns because they are not archosaurs. Maisano (2002) spelled out the “rules” for lepidosaurs, and pterosaurs follow them.

Fusion Patterns in Pterosaur Ontogeny
Three pterosaur embryos (IVPP specimen, JZMP specimen and Pterodaustro) all have an unfused scapula and coracoid. So do sister taxa (Dimorphodon? weintraubi and Boreopterus) and adults (Pterodaustro). The less developed and largely unossified embryo Darwinopterus had an unfused scapula and coracoid. It’s mother and all sister taxa back to Pterorhynchus fused those elements.

When does fusion take place in taxa with a fused scapulocoracoid?
Maybe at hatching. Maybe later. We don’t know at present.

By the way…
I wrote to Drs. Lü and  Unwin asking why they did not test any purported juvenile Rhamphorynnchus specimens against Qinglongopterus. When  I hear from them, I’ll update this blog.

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
Lü J, Unwin DM, Zhao B, Gao C and Shen C 2012. A new rhamphorhynchid (Pterosauria: Rhamphorhynchidae) from the Middle/Upper Jurassic of Qinglong, Hebei Province, China. Zootaxa 3158:1-19. online first page
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.

wiki/Qinglongopterus

Basal Dinosaur Footprints in the Early Triassic? Not Yet.

The Triassic and associated taxa and ichnotaxa

Figure 1. The Triassic and associated taxa and ichnotaxa (in black boxes)

Brusatte et al. (2011) reported, “the earliest phase of dinosaur history remains poorly understood…Here, we report footprints from the Early–Middle Triassic of Poland… which shifts the origin of the dinosaur stem lineage back to the Early Olenekian (ca 249–251 Ma, Fig. 1), approximately 5–9 Myr earlier than indicated by body fossils, earlier than demonstrated by previous footprint records, and just a few million years after the Permian/Triassic mass extinction (252.3Ma).” The two featured ichites included Prorotodactylus and Sphingopus.

Problems
Unfortunately, Prorotodactylus ichnites (Fig. 2) did not belong to dinosaur stem taxa.  According to the large tree, no dinosaur sisters had digit 4 longer than 3 going back to Proterosuchus and Garjainia. Brusatte et al. (2011) considered Lagerpeton (another taxon with an elongated digit 4) a dinosaur stem taxon, but the large tree nests Lagerpeton with the chanaresuchid Tropidosuchus, unrelated to the DinosauriaProrotodactylus ichnites more closely match Macrocnemus sisters (Fig. 3) with pedal digit 4 longer than 3. Brusatte et al. (2011) ignored these candidates. Klein and Haubold (2007) discussed Rotodactylus tracks, attributing them to a Lagosuchus (Marasuchus)-grade of stem dinosaurs, despite differences in relative toe length and ignoring earlier published matches to Cosesaurus (Peters 2000), as blogged earlier.

Porotodactylus pes

Figure 2. Prorotodactylus pes and manus ichnites. Latest Early Triassic. Here digit 5 typically does not make an impression.

Tritosaur pedes.

Figure 3. Tritosaur pedes. Compare these to Porotodactylus ichnites. From left: Huehuecuetzpalli, a basal Macrocnemus, a more derived Macrocnemus, Langobardisaurus, Cosesaurus. Note the shorter metacarpal 1 in M. fuyuanensis and the short toe 4 in Langobardisaurus. These taxa were overlooked as possible trackmakers by Brusatte et al. (2011).

The pes of Sphingopus.

Figure 3. The pes of Sphingopus. Typical of rauisuchian pedes, digit 4 was shorter than 3.

Sphinogopus
Brusatte et al. (2011) also presented Sphingopus, a much larger ichnite created by a rauisuchid. The distal phalanges were shorter and pedal digit 4 was shorter than 3. Note digits 2-4 bore most of the weight as in  basal and theropod dinosaurs. Digit 5 was offset from the others by a large hook. See more on functionally tridactyl pedes here.

And Yet…
Since two derived paraornithischian dinosaurs, Lotosaurus (and perhaps Ctenosauriscus) are from the latest early Triassic, somewhere on planet Earth dinosaur stem taxa were taking their first bipedal steps earlier in the Early Triassic. Asilisaurus (Nesbitt et al. 2010) was a contemporary. With so much variation occuring in the relatively short Olenekian (early Triassic) period, the middle and late Triassic now appear to be, by comparison, a time of relative evolutionary stasis and geographical radiation in dinosaur evolution.

Then There’s the Late Arrival of Dinosaur Precursors…
Pseudhesperosuchus and Trialestes phylogenetically nest before dinosaurs, but chronologically nest after them. We can only assume that both represented late surviving lineages of earlier radiations, part of the evolutionary stasis mentioned above.

Pedal digit 4 vs. 3
In basal reptiles pedal digit 4 was typically longer than 3. Generally, derived taxa with less than a sprawling configuration reduce digit 4 relative to 3. Exceptions include on the lepidosauromorph branch: 1. turtles; 2. Icarosaurus; 6. certain Jurassic and Cretaceous pterosaurs; and on the archosauromorph side: 7. certain higher placodonts; 8. certain higher pararchosauriforms with a reversal in Lagerpeton; , and 9. most Erythrosuchia (ErythrosuchusEuparkeria and higher taxa). Digit 4 and 3 were subequal in drepanosaurs, langobardisaurs, therapsids, plesiosaurs and the Ornithosuchidae, among others.

 

References
Brusatte S, 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.
Klein H and Haubold H 2007. Archosaur footprints – Potential for Biochronology for Triassic Contiental Sequences. In Lucas SG and Spielmann JA eds. The Global Triassic. New Mexico Museum of Natural History Science Bulletin 41. 120-130 online pdf
Nesbitt SJ, Sidor CA, Irmis RB, Angielczyk KD, Smith RMH and Tsuji LMA 2010. Ecologically distinct dinosaurian sister group shows early diversification of Ornithodira. Nature 464 (7285):95-98. doi:10.1038/nature08718PMID 20203608.
Peters D 2000. 
Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.

Does a Big Crest Make a Nyctosaurus Mature?

Bennett (2003) reported on two Nyctosaurus discoveries made by fossil collector Kenneth Jenkins. Both (Fig. 1) had the largest crests, relative to skull length and body size, of any known pterosaur. This came as even more of a surprise to paleontologists because no other Nyctosaurus specimens show any hint of a crest.

Late in Ontogeny?
Bennett (2003) reported in his abstract, “Despite the large crest, the specimens do not differ significantly in morphology from previously known specimens of Nyctosaurus, and do not represent a new species of Nyctosaurus. The specimens suggest that the cranial crest was developed late in ontogeny, which is consistent with the interpretation of pterosaur cranial crests as intraspecific display structures.” Unfortunately, these statements have been taken as gospel and have been uncritically repeated. For instance, here’s an online pdf of an article by Greg Paul from the Prehistoric Times.

Nyctosaurus clade

Figure 1. The clade of Nyctosaurus and kin. Click to enlarge.

Actually the Variations is Easy to See
Bennett (2003) did not make reconstructions of the clade for comparison. One look at reconstructions of several known Nyctosaurus specimens shows that none are conspecific (Fig. 1). There ARE many significant differences in morphology (contra Bennett 2003, details in reptileevolution.com starting here). Even the two crested Nyctosaurus specimens have distinct differences in crest shape and wing length.

In Pterosaurs More Mature = Larger
If the crested specimens were indeed more mature, then one would expect them to be larger, following the study by Chinsamy et al. (2008) on the growth series documented in Pterodaustro, the only pterosaur with a varifiable growth series. That study found that sexual maturity occurs at half the largest size attained by individuals, a pattern also found in certain lizards like Iguana (Kaplan 2007)  and Varanus (Pianka 1971). The crested specimens are actually smaller than some, similar in size to other Nyctosaurus (not counting the largest known Nyctosaurus specimens known from a pelvis and disassociated scraps.) Nyctosaurus nanus (known from a humerus and pectoral girdle) is the only Nyctosaurus that is genuinely smaller than the others pictured here.

Is the Crest a Sexual Signal?
Sure. It appears that the crest is a secondary sexual characteristic. If so one would expect a crest to appear at sexual maturity (half the final size). There is only one pair of crested pterosaurs that I am aware of that appear to be conspecific and those are a pair of tupuxuarids that have identical crests, identical rostral lengths and identical orbit sizes relative to their overall size. The smaller specimen is less than half the size of the larger one, so it was prepubescent, which falsifies the notion of a sexual signal. No, the crests appear to have identified species, not gender, maturity or sexual fitness (mutual selection). Other sorts of secondary sexual characters must have been present in crested and crestless specimens, such as wattles, coloration or behavior.

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
Bennett SC 2003. New crested specimens of the Late Cretaceous pterosaur Nyctosaurus.Paläontologische Zeitschrift 77: 61-75.
Chinsamy A, Codorniú L and Chiappe LM 2008. Developmental growth patterns of the filter-feeder pterosaur, Pterodaustro guinazui. Biology Letters, 4: 282-285.
Kaplan M 2007. Iguana Age and Expected Size. iguana/agesize online
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Pianka E 1971.
Notes on the Biology of Varanus tristis. West. Aust, Natur, 11(8):80-183.

wiki/Nyctosaurus

Ontogeny: Pteranodon vs. Diomedea

The Albatross (Diomedea exulans) and Pteranodon ingens (Fig. 1) were two large soaring reptiles, the former a bird, the latter a pterosaur. Insight into the ontogeny, maturity and lifespan of the extant Diomedea may shed some light on the extinct Pteranodon.

Pteranodon and the albatross

Figure 1. Left: Pteranodon. Right: Diomedea (albatross).

Widest Wingspan Among Birds
The albatross has a wingspan that reaches an extreme of 12 feet and averages 9 feet. The pterosaur Pteranodon had a similar wing plan with an enlarged wingspan up to 20 feet. Thus, and for little other reason, the albatross is the closest living analog to Pteranodon.

Albatross: Latest Maturation Among Birds
Most birds reach maturity in less than a year and many (crow, ostrich) do so in two years. By contrast, albatross males begin breeding at age 7, females at age 10. Some wait until 13. The life expectancy of an albatross is 30 years. According to Couzens (2008) it takes years for the albatross to become proficient at finding enough food for itself and more to take on the extra task of feeding a chick. The albatross also takes a long time to establish a pair bond.

Lizards vs Birds: Traditional Views
Most workers follow the paradigm that cold-blooded lizards mature more slowly than warm-blooded birds and mammals. Often, but not always, this is the case. However, more than mere physiology, size is typically an overriding factor. As everyone knows, mice mature faster than dogs, which mature faster than elephants and humans. The blue whale, which matures at 5 (females) or 8+ (males), does not follow this pattern. Among cold-blooded reptiles, iguanas are sexually mature at 50% of maximum size before the end of the second year (Kaplan 2007). Varanus hatchlings triple in size to sexual maturity and reach maximum size by the end of the first year (Pianka 1971). However some may continue growing thereafter, reaching up to 50% longer.

Pterodaustro Ontogeny
The only pterosaur for which a complete record of growth is known is the filter-feeder Pterodaustro. Chinsamy et al. (2008) reported: “…upon hatching, Pterodaustro juveniles grew rapidly for approximately 2 years until they reached approximately 53% of their mature body size, whereupon they attained sexual maturity. Thereafter, growth continued for at least another 3–4 years at comparatively slower rates until larger adult body sizes were attained.” So, this pterosaur’s growth rate, despite an apparent warm-blooded metabolism and active lifestyle, was not dissimilar to that of other lizards, reaching sexual maturity at 50% of the ultimate size. However, Pterodaustro took twice as long as Varanus, a cold-blooded lizard. Apparently, growth was not so rapid in pterosaurs — more along the lines of Iguana.

Pteranodon
If we add in the factor of increased size to what we know of Pterodaustro, we can imagine that Pteranodon might have had a maturation rate similar to that of the albatross (sexually mature at 7 to 10) along with a similar lifespan (30 years). However, if Pteranodon was more like Pterodaustro we get 2 years until half-grown, 5 to 6 years until fully grown.

Where Are the Juvenile Pterosaurs?
A long maturation brings up a problem. Where are the juveniles and immature forms (ages 0 to 6)? The Pterodaustro bone beds (nesting sites) provide the only evidence. There we find all sizes of Pterodaustro.

Ptweety the Only Juvenile Pteranodon
We know of only one juvenile Pteranodon. All others are adults that fit neatly into a phylogenetic framework of increasing size and crest size originating with a specimen of Germanodactylus (SMNK-PAL 6592) as an outgroup. This falsifies the current paradigm presented by Bennett (1991, 2001) and followed by others (Hone et al. 2011) of gender and maturation variation in most known specimens of Pteranodon. Here there is evidence of speciation leading to the largest crested forms (that in one clade only preceded a continuing clade of smaller crested, smaller forms.)

Bone Histology
The age of sexual maturity in Pteranodon has not yet been determined. Neither has the lifespan. Bone histology in Pteranodon has not provided the data needed due to crushing and resorption of the inner walls of the extremely thin long bones. At present we can only guess using extant analogs, like the albatross, and extinct analogs, like Pterodaustro.

Then There’s the Tiny Pterosaur Hypothesis
Tiny pterosaurs giving birth to fly-sized hatchlings were likely terrestrial until reaching adult-size due to desiccation problems, as discussed earlier. Larger pterosaur hatchlings, like Pteranodon (and all known, apparently flight ready pterosaur embryos), did not have a problem with desiccation — but they may have retained some sort of non-flying lifestyle living in environments not conducive to fossilization. This may explain the lack of immature pterosaurs in the fossil record (contra all traditional studies that considered tiny adults to be juveniles and embryos to be flight ready).

Not ready to jump on the flightless hatchling hypotheses quite yet, but it’s something to consider when faced with current and future evidence.

Just a Reminder
Maisano (2002) provides guidance on lizard ontogeny that can be applied to pterosaurs. That is: fusion can precede maturation and ultimate size or fusion may never take place in the oldest individuals, depending on their phylogeny. Recent work by Lü et al. (2012) show that the archosaur model continues to be wrongly applied to pterosaur studies.

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.
Couzens D 2008. Extreme Birds: The world’s most extreme and bizarre birds. Firefly Books.
Hone DWE Naish D and Cuthill IC 2011. Does mutual sexual selection explain the evolution of head crests in pterosaurs and dinosaurs? Lethaia, DOI: 10.1111/j.1502-3931.2011.00300.x
Kaplan M 2007. Iguana Age and Expected Size. iguana/agesize online
Lü J, Unwin DM, Zhao B, Gao C and Shen C 2012. A new rhamphorhynchid (Pterosauria: Rhamphorhynchidae) from the Middle/Upper Jurassic of Qinglong, Hebei Province, China. Zootaxa 3158:1-19. online first page
Maisano JA 2002. Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Pianka E 1971.
 
Notes on the Biology of Varanus tristis. West. Aust, Natur, 11(8):80-183.

How Did Pteranodon Walk?

Earlier we looked at terrestrial locomotion in pterosaurs, discriminating a basal bipedal taxon from the quadrupedal track makers that can be matched to tracks attributed to ctenochasmatid, pterodactyloid (check out the animation!) and maybe even ornithocheirid pterosaurs (Peters 2000, 2010, 2011). We also looked at the many potential problems that surround the wing launch hypothesis and presented an alternative or two.

Pteranodon and especially Nyctosaurus (Fig. 1) were two special cases united by extremely long metacarpals coupled with relatively short hind limbs that prevented them from walking in the same manner as pterosaurs having shorter metacarpals.

 

Nyctosaurus reconstruction

Figure 1. Nyctosaurus reconstruction according to Bennett (1997) and Peters, both based on UNSM 93000. Click to enlarge.

Bennett’s Take on Nyctosaurus
Bennett (1997) provided a great illustration of Nyctosaurus “essentially bipedal” (Fig. 1) because the forelimbs could only touch the substrate on the “back” of the folded wing finger, so far in front of the jaw tips that they were unable to provide a thrust vector to the elbow and shoulder. The fingers were greatly reduced, perhaps because they were no longer in use. See Muzquizopteryx and  Nyctosaurus bonneri for extreme proportions within this clade. Even shorter metacarpals on pterosaurs don’t appear to contribute thrust, only support, especially when nosing around for food items buried in the substrate or swimming around their submerged ankles in the shallows.

Pteranodon
The Triebold specimen of Pteranodon NMC41-358 is the most complete one known (Fig. 2). Others had larger wings and shorter legs. In the Triebold specimen it appears difficult for the free fingers (especially fingers 1 and 2) to contact the substrate as in other pterosaurs due to the great length of the metacarpus relative to the hind legs.

Pteranodon walking animated

Figure 2. Pteranodon walking. Click to animate. Note the femur is drawn and moves in the parasagittal plane for ease of animation. When properly sprawled the butt would drop a wee bit. The feet may have been plantigrade. They are not well preserved in this specimen. Other Pteranodon have digitigrade pedes. Those closer to UALVP 24238 had plantigrade pedes.

Too Erect?
If the above animation was configured too erect, then imagine it with lower shoulders (Fig. 3). That moves the free fingers even further forward, further unable to contact the substrate (despite the cheating on finger placement here by ignoring the configuration of the metacarpals). In any configuration the forelimbs were more like adult crutches on a little kid, my friends: very awkward on land. And, obviously, secondarily evolved, interrupted by a bipedal phase in pre-pterosaurs and basal pterosaurs. 

Walking pterosaur according to Bennett

Figure 3. Click to animate. Walking pterosaur according to Bennett (1997). Note the forelimbs provide no forward thrust, but merely act as props. They probably provided braking in this configuration and would have compressed (flexed) on contact with the substrate, rather than extending to provide thrust as in all other tetrapods. Compare this reconstruction to the Bennett reconstruction of Nyctosaurus.

Send alternatives if you have them!

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
Bennett SC 1997. Terrestrial locomotion of pterosaurs: a reconstruction based on Pteraichnus trackways. Journal of Vertebrate Paleontology, 17: 104–113. online pdf
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D. 2010. In defence of parallel interphalangeal lines. Historical Biology 22:437-442.
Peters David 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification. Ichnos, 18: 2, 114 —141

Introducing the Pararchosauriformes

Traditional studies (eg. Nesbitt 2011) nest all Archosauriformes in a ladder of taxa that  includes a major split between the so-called “Pseudosuchia” (aetosaurs, poposaurs, rauisuchids, crocodylomorphs and several individual genera) and the so-called “Avemetatarsalia” (pterosaurs and dinosauriforms).

The Pararchosauriformes. Lagerpeton is the most derived taxon.

Figure 5. The Pararchosauriformes. Lagerpeton is the most derived taxon.

The present large heretical study, that includes many times more taxa, recovers a major split at the grade of Youngina and Youngoides. One branch includes the taller, narrower skull forms descending from sisters to Proterosuchus. The other branch includes the wider, lower skull forms that include choristoderes, phytosaurs and chanaresuchids along with related taxa.

Taxon Exclusion is the Problem 
Traditional studies do not include dozens of key taxa due to a priori exclusion policies based on tradition and prejudice. The present heretical study minimizes those prejudices by including specimens from every corner of the reptile family tree.

Pararchosauriformes.

Figure 1. The Pararchosauriformes. Only the larger taxa are visible here.

It All Begins with Youngoides
Youngina and Youngoides (Fig. 2) have been recognized for decades as basal taxa to the Archosauriformes. That’s absolutely correct. What hasn’t been recognized is that the variety in Youngina is real. The skulls look crushed and distorted, but some really are taller than wide or wider than tall. Basically, that’s what sets euarchosauriforms (Proterosuchus and descendants) apart from pararchosauriforms (choristoderes and desendants). The nares drift dorsally. The rostrum becomes elongated. The orbits either are or are not elevated above the rostrum. After those basal traits, evolution produced bipeds, croc-like forms and pachypleurosaur-like forms, along with at least one plant-eater in both branches of the Archosauriformes.

Several choristoderes

Figure 3. Several choristoderes (in white), their predecessor and sisters (in yellow).

Choristodera
Basal pararchosauriforms, like Doswellia and the Choristodera (Fig. 2), did not have an antorbital fenestra. These enlarged descendants of Youngoides elongated the snout and moved the naris dorsally.  Lazarussuchus lost the lateral temporal fenestra and further elongated the pre-narial premaxilla.

Proterochampsa
Currently known from a single published skull and an unpublished post-crania, Proterochampsa (Figs. 1, 2) is the most basal pararchosaur to sport an antorbital fenestra and no fossa surrounded it. This flat-skulled form was probably aquatic and short-legged like its sisters.

Phytosuchia/Parasuchia
The croc-like phytosaurs are a distinct clade sharing a long list of character traits. Even basal taxa have a longer rostrum than Proterochampsa.

Chanaresuchidae
Chanaresuchus and Tropidosuchus comprise the Chanaresuchidae, a clade of increasingly terrestrial forms culminating in the biped, Lagerpeton, a taxon commonly and mistakenly associated with dinosaurs by traditional workers.

Strangely, members of the Phytosauria and Chanaresuchidae have nested in traditional studies with pterosaurs, but this is patently ridiculous, a result of improper taxon inclusion and exclusion as demonstrated by the results of the large 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
Broom R 1914. A new thecodont reptile. Proceedings of the Zoological Society of London, 1914:1072-1077.
Gardner NM, Holliday CM and O’Keefe FR 2010. The braincase of Youngina capensis(Reptilia, Diapsida): New insights from high-resolution CT scanning of the holotype. Paleonotologica Electronica 13(3):online PDF
Gow CE 1975. The morphology and relationships of Youngina capensis Broom and Prolacerta broomi Parrington. Palaeontologia Africana, 18:89-131.
Olsen EC 1936. Notes on the skull of Youngina capensis Broom. Journal of Geology, 44 (4): 523-533.

Mecistotrachelos, the Walking Stick “Rib” Glider

Among the Permo/Triassic so-called “rib” gliders is an oddball with a walking-stick sort of torso with fused ribs no wider than its centra. The oddball is Mecistotrachelos from the Late Triassic and it was a sister to Coelurosauravus of the Late Permian.

Mecistotrachelos

Figure 1. Mecistotrachelos, the walking stick "rib" glider in lateral view except for the dorsal series and pseudoribs, which are seen in dorsal view. pseudoribs folded above, and extended below. The tail length is unknown.

Mecistotrachelos apeoros (Fraser et al. 2007) Late Triassic ~210 mya, demonstrates variety in later derived clade members with fewer dorsal vertebrae and fewer pseudoribs. The body was extremely slender, almost stick-like, with hyper-elongated cervicals and greatly reduced ribs fused to each centrum. The limbs were more gracile and the tail length is unknown. The fibula was fused or closely adhered to the tibia.

The long neck would have made Mecistotrachelos an unstable glider according to Fraser (2007). Coelurosauravus had a long neck and a larger skull. Were the dermal struts deployed for gliding? For display? Or both? Like other kuehneosaurs, Mecistotrachelos had small teeth and was likely an insectivore. Fraser (2007) wondered if his find was an archosauromorph. It is not. Here Mecistotrachelos nested with Coelurosauravus among the lepidsauromorpha, within the lepidosauriformes.

Not Like Draco the Extant Glider
Fraser (2007) reported, “The new form is characterized by the presence of extremely elongate thoracolumbar ribs that presumably supported a gliding membrane in life.” Fraser (2007) notes kuehneosaurs had “ribs forming hinge joints with the markedly elongate transverse processes on the dorsal vertebrae.” This is wrong. No Mecistotrachelos sister taxa had elongated transverse processes. The apparent transverse processes ARE the ribs, fused to the vertebrae, derived from the condition seen in the short ribs of Coelurosauravus (Fig. 2). The pseudoribs were actually elongated dermal ossicles described as “bundles of rodlike neomorph ossifications,” by Fraser (2007) quoting Frey et al. (1997). By contrast, in Draco the gliding struts are indeed elongated dorsal ribs.

The Triassic gliders and their non-gliding precursors.

Figure 2. Click to enlarge. The Triassic gliders and their non-gliding precursors.

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
Fraser NC, Olsen PE, Dooley AC Jr and Ryan TR 2007. A new gliding tetrapod (Diapsida: ?Archosauromorpha) from the Upper Triassic (Carnian) of Virginia. Journal of Vertebrate Paleontology 27 (2): 261–265.

Frey E, Sues H-D and Munk W 1997. Gliding Mechanism in the Late Permian Reptile Coelurosauravus. Science Vol. 275. no. 5305, pp. 1450 – 1452
DOI: 10.1126/science.275.5305.1450