Pterosaur reproduction and gender identification – SVPCA talks

Two upcoming SVPCA talks worth discussing:
Kellner et al and Unwin + Deeming both discuss pterosaur reproduction, growth and gender.

Key notes from the Kellner et al. (2015) abstract: All eggs show depressions, clearly indicating their overall pliable nature. SEM analysis shows that the eggshell structure is similar to some squamates. SEM analysis of [another] eggshell did not reveal an external calcareous layer suggesting that it was either removed due to taphonomy or not present at all. Histological section of the femur lacks medullary layer, a bone tissue reported in avian dinosaurs during ovulation and egg-laying phase. Those specimens, associated with experimental taphonomic studies, show that pterosaurs had two functional oviducts and laid eggs even smaller than previously thought, indicating that they have developed a reproductive strategy more similar to basal reptiles than to birds.”

Like I’ve been saying since 2007 and before.
Pterosaurs are non-squamate lepidosaurs. Egg shell morphology is just one more clue to this.

Unwin and Deeming abstract:
“Sexual dimorphism is common in extant vertebrates and almost certainly occurred in extinct species as well, but identifying this phenomenon in fossils is difficult. Meeting two key criteria: a large sample size in which all ontogenetic stages are present; and independent evidence of gender, is rarely possible, but has now been achieved for the early Upper Jurassic pterosaur Darwinopterus modularis. This pterosaur is represented by over 20 individuals ranging from hatchlings through juveniles to mature adults (ontogenetic status determined from osteological, histological and morphometric data). One example, ‘Mrs T’, is preserved with two eggs and thus clearly a female. Approximately half the mature individuals of Darwinopterus exhibit a cranial crest and several of these individuals have a relatively narrow pelvis. The remainder lack a cranial crest and in two cases, including Mrs T, have a relatively broad pelvis. All immature individuals lack a crest, an observation that applies to other species of pterosaur in which immature individuals are known. This pattern of morphological variation shows that the cranial crest and pelvis of Darwinopterus modularis are sexually dimorphic. Datasets for other pterosaurs are less complete and/or lack independent evidence of gender, but many species including Ctenochasma gracile, Germanodactylus cristatus and Pteranodon longiceps, exhibit directly, or closely, comparable patterns of anatomical variation to Darwinopterus and are likely to have been sexually dimorphic. We conclude that the spectacular variability in the shape and size of pterosaur cranial crests was likely generated by sexual selection rather than processes such as species recognition.”

Unfortunately
other than with the presence of eggs in association, sexual dimorphism has not been determined in other pterosaurs in which a large sample size is present (Rhamphorhynchus, Pteranodon, Germanodactylus, Pterodactuylus), even without eggs in association. This is widely recognized, hence the excitement level in the abstract for Darwinopterus. Rather speciation of these taxa has been determined through phylogenetic analysis. Speciation has also been determined for the several Darwinopterus specimens. Currently published specimens don’t divide neatly in two. If that changes with the addition of 15 more, I’ll be happy to note that. Unwin and Deeming do not mention phylogenetic analysis in their abstract. If this is a clue to their methods such laziness in skipping phylogenetic analysis is becoming more and more common, especially when it suits a false paradigm. You can’t just eyeball these things. You have to put your data through analysis. Otherwise the work will always be doubted and you’ll be ‘pulling a Bennett’ (assertion of association without cladogram evidence). The purported hatchlings noted by Unwin and Deeming also need to be run through analysis. Are they examples of phylogenetic miniaturization or actual juveniles? Adding hatchlings and embryos along with tiny adults to analysis has been online for more than four years, so there is no excuse for avoiding it.

Tiny wukongopterids are welcome news, by the way. This clade is one of a few that currently lacks any tiny representatives and that lack is the current best reason why wukongopterids left no descendants in the Cretaceous.

The bone originally identified as an ischium on Mrs. T was a misidentified displaced prepubis. The actual ischia were preserved in the counter plate and they were relatively narrow.

Unwin does not support isometric growth during ontogeny, which is otherwise a well established fact in pterosaurs. So he may be accepting dissimilar morphologies as juvenile examples (pulling another Bennett). Very dangerous. As in all other pterosaurs, like Pteranodon, you have to evolve crested derived forms from non-crested basal forms. Unwin and Deeming, if you’re reading this: before you publish your paper, send me your data, if you don’t want to do the analysis yourself. I’ll send back the recovered cladogram. Don’t make the same mistakes again. However, if the juveniles are isometric copies of the adults, then congratulations and remember to give credit where credit is due.

References
Kellner  AWA et al. 2015. Comments on pterosaur reproduction based on recently found specimens from the Jurassic and Cretaceous of China. Among the most spectacular pterosaur finds done in recent years is the bone-bed from the Tugulu Group (Lower Cretaceous) discovered in the Hami area, Xinjiang Uyghur Autonomous Region of China. SVPCA 2015 abstracts.
Peters D 2007. The origin and radiation of the Pterosauria.
Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27
Unwin DM and Deeming CD 2015. New evidence for sexual dimorphism in the basal monofenestratan pterosaur Darwinopterus. SVPCA 2015 abstracts.

More tiny birds and tiny pterosaurs

Earlier we took a peek at a few tiny birds and pterosaurs. Here (Fig. 1) are several more.

Traditional paleontologists
insist that these tiny pterosaurs were babies of larger forms that looked different, (Bennett 1991, 1992, 1994, 1995, 1996, 2001, 2006, 2007, 2012, 2014) ignoring or not aware of the fact that we know pterosaur embryos and juveniles were virtually identical to their adult counterparts (Fig. 2). Bennett (2006) matched two tiny short-snouted pterosaurs (JME SoS 4593 and SoS 4006 (formerly  PTHE No. 1957 52) to Germanodactylus, but they don’t nest together in the large pterosaur tree.

Figure 1. Tiny pterosaurs and tiny birds to scale showing that tiny pterosaurs were generally about the size of the tiny Early Cretaceous bird.

Figure 1. Tiny pterosaurs and tiny birds to scale showing that tiny pterosaurs were generally about the size of the tiny Early Cretaceous bird. I have, for over a decade, promoted the fact that these tiny pterosaurs were adults, the size of modern hummingbirds and wrens.

One of the most disappointing aspects of modern paleontology
is the refusal of modern pterosaur workers to include in their analyses the small and tiny pterosaurs. They were all the size of living hummingbirds and wrens. Many were similar in size to extinct Early Cretaceous birds (Fig. 1). Those workers don’t want to add these taxa to their lists on the false supposition that the tiny pterosaurs are babies of, so far unknown adults. Note Bennett’s long body of work (see below) indicated otherwise, but never with phylogenetic analysis.

Phylogenetic analysis (Peters 2007) reveals these tiny pterosaurs are adults or can be scored as adults. They are surrounded by adults and they often form transitional taxa in the evolutionary process of phylogenetic miniaturization between larger long-tailed pterosaurs and larger short-tailed pterosaurs.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 2. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen. This is evidence that juveniles were virtually identical to adults, except in size.

More importantly,
earlier we discussed several examples of juvenile pterosaurs morphologically matching adults here, here and here. So young pterosaurs have been shown to match their adult counterparts. They don’t transform like young mammals and dinosaurs do. They were ready to fly upon hatching IF they were the minimum size to avoid desiccation, as discussed earlier here.

The most interesting aspect
to the whole tiny pterosaur story is how small their smallest hatchlings would be. We looked at that earlier here.

References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. 
Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. 
Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Bennett SC 1996. 
Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.
Bennett SC 2001.
 
The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a revision of the genus. Journal of Vertebrate Paleontology 26(4): 872–878.
Bennett SC 2007. A second specimen of the pterosaur Anurognathus ammoni. Paläontologische Zeitschrift 81(4):376-398.
Bennett  SC (2012) [2013] 
New information on body size and cranial display structures of Pterodactylus antiquus, with a revision of the genus. Paläontologische Zeitschrift (advance online publication) doi: 10.1007/s12542-012-0159-8
http://link.springer.com/article/10.1007/s12542-012-0159-8
Bennett SC 2014. A new specimen of the pterosaur Scaphognathus crassirostris, with comments on constraint of cervical vertebrae number in pterosaurs. Neues Jahrbuch für Geologie und Paläontologie, Abhandlungen, 271(3): 327-348.
Peters D 2007. The origin and radiation of the Pterosauria. Flugsaurier. The Wellnhofer Pterosaur Meeting, Munich 27

 

New smallest Pteranodon: Bennett 2014 JVP abstract

Figure 1. Pteranodon ingens. Full size and little Ptweety the baby Pteranodon, not curated.

Figure 1. Pteranodon ingens. Alongside in black is a hypothetical hatchling  and a hypothetical juvnile twice the size of the hatchling. With a 1.5m wingspan, Ptweety is still the smallest, compared to Bennett’s 1.76 m wingspan. The Bennett Pteranodon is not shown.

I was hoping a curated specimen would follow Ptweety, the putative baby Pteranodon (Fig. 1), which turned out to be a Nyctosaurus. It was just a matter of time. Here it is in the 2014 JVP abstracts.

From the Bennett abstract:
“An earlier study of all available specimens of the pterosaur Pteranodon from the
Smoky Hill Chalk Member of the Niobrara Formation found a bimodal size distribution. The small size class with estimated wingspans in life of ~3.1-4.8 m was twice as abundant as the large, with wingspans of ~4.8-6.7 m, and immature specimens formed ~15% of each class suggesting that they cannot be age classes. The bimodal distribution was interpreted as evidence of sexual dimorphism and the absence of specimens smaller than ~3 m wingspan was interpreted as evidence of bird-like parental care during rapid growth to adult size before flying and feeding independently. A new immature specimen of Pteranodon with an estimated wingspan of only 1.76 m demonstrates that juveniles were capable of flying and feeding independently, contradicting the interpretation of parental care during rapid growth. Instead Pteranodon apparently was precocial, flying and feeding independently during several years of growth to adult size as previously observed in Rhamphorhynchus, Pterodactylus, and Pterodaustro. Therefore, the absence of Pteranodon juveniles and a similar absence of Nyctosaurus juveniles from the Smoky Hill Chalk indicates those taxa had multi-niche ontogenies, occupying distinct niches in different locations and environments at different stages of their life history. Thus, the Smoky Hill Chalk represents a pelagic feeding environment of Pteranodon and Nyctosaurus adults whereas hatchlings and juveniles presumably fed on smaller prey in lacustrine, riverine, estuarine, or coastal environments. The pterosaur records of most other Lagerstätten are consistent with multi-niche ontogeny being the norm in pterosaurs. For example, the record of Azhdarcho in the Bissekty Formation consists of hatchlings and adults and represents a breeding ground, that of the Solnhofen Limestone consists primarily of hatchlings and juveniles and represents a nursery environment of juveniles in sheltered lagoons near breeding grounds whereas those of the Romualdo and Cambridge Greensand Formations consist of adults and represent coastal feeding environments of adults. One exception seems to be the record of Pterodaustro in the Lagarcito Formation, which consists of eggs, hatchlings, juveniles, and adults in a single location and environment; however, that may reflect a special environment required to effectively utilize the filter-feeding specializations of the taxon.”

Bennett has been the target of many Pterosaur Heresies blogposts.
And for good reason: (no gender classes, this represent several species evolving from small, small-crest forms to several clades of large, large-crest forms, etc. etc. etc.).

Here Bennett is right on the money
when he agrees to different niches for juvenile and adult pterosaurs, which we discussed earlier here, due to the rarity of juvenile pterosaurs in the fossil record, a topic in which Bennett takes the opposite stance.

Not mentioned in the Bennett abstract
is the fusion of the extensor tendon process to manual 4.1, which occurs in all Pteranodon specimens and no Nyctosaurus specimens except the crested ones. The same goes for scapula and coracoid fusion (fused in Pteranodon, not in Nyctosaurus). I wonder what the data is on his new juvenile Pteranodon?

The presence of hatchling Azhdarcho specimens in a breeding ground comes as something of a surprise. Good news! The literature (Averianov 2010) only refers to a juvenile/immature specimen represented by a notarium (4cm long, compared to a 6.5 notarium for an unrelated adult mid-size Pteranodon adult.)

Bennett does not mention the growth series in Tapejara and Zhejiangopterus. The abstract was probably written before the Caiuajara nesting site. Pterodaustro embryos and hatchlings are well known (Chiappe et al. 2004, Chinsamy et al. 2008, Codorniú and Chiappe 2004). The various growth series described by Bennett (1995, 1996) actually represent individual species if not genera. This he would discover by phylogenetic analysis.

On a side note: 
The blog post on the evolution of frogs is getting an unusually large number of hits. Not sure why. Let me know if there is anything else you want to learn more about.

References
Averianov AO 2010. The osteology of Azhdarcho lancicollis Nessov 1984 (Pterosauria, Azhdarchidae) from the Late Cretaceous of Uzbekistan. Proceedings of the Zoological Institute RAS. 314(3):264–317.
Averianov AO 2013. 
Reconstruction of the neck of Azhdarcho lancicollis and lifestyle of azhdarchids (Pterosauria, Azhdarchidae). Paleontological Journal 47 (2): 203-209. DOI: 10.1134/S0031030113020020
Bennett SC 1995. A statistical study of Rhamphorhynchus from the Solnhofen limestone of Germany: year classes of a single large species. Journal of Paleontology 69, 569–580.
Bennett SC 1996. Year-classes of pterosaurs from the Solnhofen limestones of Germany: taxonomic and systematic implications. Journal of Vertebrate Paleontology 16:432–444.
Bennett, SC 2014. New smallest specimen of the pterosaur Pteranodon and multi-niche ontogeny in pterosaurs. Journal of Vertebrate Paleontology abstracts, Berlin Conference 2014.
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.
Codorniú L and Chiappe LM 2004. Early juvenile pterosaurs (Pterodactyloidea: Pterodaustro guinazui) from the Lower Cretaceous of central Argentina. Canadian Journal of Earth Science 41, 9–18. (doi:10.1139/e03-080)

Pterosaur tails tell tales… Unwin et al. 2014 JVP abstract

Unwin et al. (2014)
describe an increasing number of tail vertebrae in a purported ontogenetic series (hatchling to juvenile to adult in a series of purported Darwinopterus specimens.) Although this is unheard of elsewhere among vertebrates, Unwin et al. link this trait to the origin of pterodactyloid-grade pterosaurs. And it should be mentioned that Unwin et al. are the only workers who nest darwinopterids basal to pterodactyloids. Andres nests anurognathids there. Kellner nests Rhamphorhynchus there. I nest tiny dorygnathids and scaphognathids there by convergence (e.g. Fig. 1) four times.

From the Unwin et al. 2104 abstract:
“The evolution of pterodactyloids from basal pterosaurs in the Early-Middle Jurassic involved a complex series of anatomical transformations that affected the entire skeleton. Until recently, almost nothing was known of this major evolutionary transition that culminated in the Pterodactyloidea, a morphologically diverse and ecologically important clade that dominated the aerial environment throughout the mid-late Mesozoic. The discovery of Darwinopterus, a transitional form from the early Late Jurassic of China, provided the first insights into the sequence of events that gave rise to the pterodactyloid bauplan and hinted at an important role for modularity, but was largely silent regarding the anatomical transformations themselves, or the evolutionary mechanism(s) that underlay them. A series of recent finds allowed us to construct a complete postnatal growth sequence for Darwinopterus. By comparing this sequence with those for Rhamphorhynchus and Pterodactylus, pterosaurs that phylogenetically bracket Darwinopterus, it is possible to map key anatomical transformations such as the evolution of the elongate, complex tail of basal pterosaurs into the short, simple tail of pterodactyloids. In Darwinopterus hatchlings the tail is shorter than the dorsal-sacral series (DSV) and consists of around 18 simple vertebral ossifications. The tail is longer (1-2 x DSV) in juveniles and has a normal complement of about 30 caudals, but only reaches its full length (2-3 x DSV) and complexity in adults. Basal pterosaurs largely conform to this pattern, although some species, including Rhamphorhynchus, have longer tails with up to 40 caudals. Generally, the tail of adult pterodactyloids, including Pterodactylus, resembles that of Darwinopterus hatchlings (≤18 ossified vertebrae; tail ≤0.7 x DSV; vertebrae simple, blocky), but occasionally develops a little further (e.g. in Pterodaustro) corresponding to the condition seen in early juveniles of Darwinopterus and paralleling the developmental pattern observed in long-tailed pterosaurs. The short tail of adult pterodactyloids, and anurognathids, basal pterosaurs that also have relatively short tails, appears to be neotenic, resulting from a sharp decrease in growth rate compared to the rest of the skeleton. This mechanism, heterochrony acting upon a distinct anatomical module to effect a large-scale morphological transformation, can be applied to other modules to generate the derived features (e.g. elongate neck and metacarpus, reduced fifth toe) that typify the pterodactyloid bauplan.”

Problem #1
Among professional pterosaur workers, only Unwin et al. nest Darwinopterus as the stem pterodactyloid. No one else does. Andres nests anurognathids with pterodactyloids. Kellner nests Rhamphorhynchus with pterodactyloids. Readers of this blog and reptile evolution.com know that when you add the sparrow- to hummingbird-sized Solnhofen pterosaurs, you get four clades of pterodactyloid-grade pterosaurs.

Figure 1. Scaphognathians to scale. Click to enlarge.

Figure 1. Scaphognathians to scale. Click to enlarge.

Problem #2
Are the specimens truly juvenile Darwinopterus? Or do they represent smaller genera or species, perhaps closely related, or not? Currently no two Darwinopterus specimens are conspecific. No two are identical. See them here. By comparing purported Rhamphorhynchus and Pterodactylus juveniles to putative adults I’m afraid Unwin et al. are playing with a pack of Jokers. Those smaller specimens are distinct species and genera, as recovered in the large pterosaur tree. Everyone should know by now that pterosaur juvenile pterosaurs are isometric matches to their adult counterparts, from several well-known examples. Any differences in Darwinopterus likewise mark phylogenetic, not ontogenetic differences.

Problem #3
Rhamphorhynchus and Pterodactylus only phylogenetically bracket Darwinopterus if the inclusion set is reduced to these three taxa. Otherwise they nest several nodes away from each other with lots of intermediate taxa as you can see here.

Problem #4
Unwin et al. claim the caudal count increases with maturity in Darwinopterus (18 in hatchlings, 30 in juveniles and adults). Put these into a cladogram and they probably become disparate taxa. Where else does the vertebral count nearly double during ontogeny? Nowhere. Those caudal counts for the larger specimens have to be estimates. Not every tail is complete. It appears as if the caudal count could vary among the larger specimens as well.

Problem #5
I see no mention of a phylogenetic analysis with regard to the various Darwinopterus specimens. This is a problem as Unwin et al. do not want to test their observations with the only method known to lump and split taxa. In the large pterosaur tree IVPP V 16049 nests with YH2000. 41H111-0309A nests with ZMNH M 8782. All four Darwinopterus taxa nest as a sister clade to Kunpengopterus + Archaeoistiodatylus and this combined clade is a sister to Wukongopterus, then the PMOL specimen of Changchengopterus, then Pterorhynchus. This major clade nests between Dorygnathus and Scaphognathus, both of which ultimately give rise to the two pairs of basalmost pterodactyloids.

Possible Solution 
I noted earlier that the Darwinopterus clade left no descendants. They also did not produce any small taxa like Dorygnathus and Scaphognathus did. Other workers thought the smaller Scaphognathus specimens were juveniles, despite the morphological differences. I can only wonder if the same situation is happening in the Darwinopterus clade? Perhaps what the Unwin team found are the smaller specimens previously missing from their clade branch. Even so, and sadly, this clade was not able to survive into the Cretaceous, small or not, because no known Cretaceous pterosaurs share darwinopterid traits. They are all accounted for with presently known tiny ancestors.

References
Unwin D, Lü J-C, Pu H-Y, Jim X-S  2014. Pterosaur tails tell tails of modularity and heterochrony in the evolution of the pterodactyloid bauplan. JVP 2014 abstracts

Caiuajara dobruskii – new tapejarid pterosaur bone bed

We’ll call this:
“When discovery confirms heretical hypotheses.”

Figure 1. Caiuajara adult skull. Color bones added.

Figure 1. Caiuajara adult skull. Color bones added. Their premaxillary crest also includes the nasal. Blue = jugal. Yellow = missing teeth. Fo = foramina. Wonder if those represent ancient tooth sockets? For now they are blood vessel holes. Exp = ventral expansion of premaxilla, but it’s really the nasal. That’s where the descending process drops on certain other pterosaurs.

Another pterosaur bone bed,
this time with subadults and juveniles (no eggs or hatchlings) of a new tapejarid, Caiuajara dobruskii (Manzig et al. 2014). Contra traditional paradigms, there is no indication of a large orbit and short rostrum in juveniles (confirming earlier posts here and at reptileevolution.com. Yes, the crest developed in adults, because it wouldn’t have fit inside the eggshell! At least 47 individuals here. Smallest were twice the size of hatchlings, one quarter the size of adults.

Also,
you can’t tell the females from the males. All had crests.

Figure 2. from Manzig et al. 2014. Note the lack of change in the size of the orbit vs rostrum in Caiuajara.

Figure 2. from Manzig et al. 2014. Note the lack of change in the size of the orbit vs rostrum in Caiuajara.

Bone beds are great for individual bone size comparisons, but difficult for creating reconstructions as small individuals are mixed in with large ones. From Manzig et al. (2014) “The presence of three main levels of accumulation in a section of less than one meter suggests that this region was home to pterosaur populations for an extended period of time. The causes of death remain unknown, although similarities with dinosaur drought-related mortality are striking. However, it is also possible that desert storms could have been responsible for the occasional demise of these pterosaurs.”

Figure 2. Typical portion of bone bed of Caiuajara.

Figure 3. Typical portion of bone bed of Caiuajara.

The size of the crests, both below and above the jaws, became larger with age. Most of the individuals were young with only a few adults present.

Figure 4. Caiuajara skulls to scale.

Figure 4. Caiuajara skulls to scale.

The authors found no allometry during ontogeny in post-cranial elements, but adults appear to be more robust and the scapula fused to the coracoid in adults only. This confirms what I’ve found in the fossil record in Zhejiangopterus, Pteranodon, Pterodaustro and generally in phylogenetic analysis. Now, after so much evidence, I hope the naysayers will give the hypothesis of isometry during ontogeny in pterosaurs its day in court.

Figure 5. Caiuajara post crania. Hypothetical hatchlings added at 1/8 adult size.

Figure 5. Caiuajara post crania, a. humerus, b. femur, c. coracoid and scapulocoracoid, d. sternal complex. Hypothetical hatchling elements added at 1/8 adult size. Finally, a fused adult coracoid along with an unfused juvenile and subadult coracoid. Scale bars = 1 cm.

Caiuajara is a small tapejarid, very similar to other tapejarids. This brings up the subject of lumping and splitting with nomenclature, whether a new genus is warranted or not. Is Caiuajara just another species of Tapejara? If not then we need to start splitting up other genera clades containing a wide variety of morphologies as in Rhamphorhynchus, Pteranodon, Germanodactylus, Darwinopterus and other pterosaurs, in which essentially, no two are identical. I’ll leave that to the experts. It’s going to take more than consensus.

Figure 6. Caiuajara size comparisons. There is quite a variety of tapejarids, approaching the variety in Pteranodon, Rhamphorhynchus and other pterosaurs. Note that in the larger Tapejara there is still a suture in the scapulocoracoid.

Figure 6. Caiuajara size comparisons. There is quite a variety of tapejarids, approaching the variety in Pteranodon, Rhamphorhynchus and other pterosaurs. Note that in the larger Tapejara there is still a suture in the scapulocoracoid.

A little speculation
Here we have a large number of juveniles (not hatchlings) and only a few adults in a sandy environment sometimes flooded by rising waters from a nearby lake. What does this mean?

A little backstory:
Pterosaur eggs are large enough that only one could be produced at a time, and held within the mother until just prior to hatching. So the large number of juveniles in this case (no hatchlings here) huddling together, did not belong to a single set of parents. The authors were right, pterosaurs of a certain size (perhaps hatchlings, but up to twice the size of hatchlings in this case) were able to fly. Since they were hatched individually the hatchlings/juveniles sought each other out at an early age, and sought out the company of older, larger tapejarids. Those crests made identification easy. It did not matter that the adults were their parents or not (distinct from the nuclear family illustration at Nat Geo) because the numbers don’t match up. Now IF the adults were found in a distinct layer from the juveniles, the speculation about the adult influence has no basis in evidence.

References
Manzig PC et al. 2014. Discovery of a Rare Pterosaur Bone Bed in a Cretaceous Desert with Insights on Ontogeny and Behavior of Flying Reptiles. Plos ONE 9 (8): e100005. doi:10.1371/journal.pone.0100005.

Cope’s Rule in Pterosaurs Revisited in 2014

A new article (Benson et al. 2014) in Nature Communications seconds the notion put forth by Hone and Benton (2006) that Cope’s Rule was in force throughout the Mesozoic, ultimately creating giant pterosaurs at the end of the Cretaceous. And birds were the likely culprits.

From their abstract:
“Here we show 70 million years of highly constrained early evolution, followed by almost 80 million years of sustained, multi-lineage body size increases in pterosaurs. These results are supported by maximum-likelihood modelling of a comprehensive new pterosaur data set. The transition between these macroevolutionary regimes is coincident with the Early Cretaceous adaptive radiation of birds, supporting controversial hypotheses of bird–pterosaur competition, and suggesting that evolutionary competition can act as a macroevolutionary driver on extended geological timescales.”

Of course,
you can’t get to giant without first going through small, medium and large. So it helps their cause to have Quetzalcoatlus northropi appear at the very end of the Cretaceous.

Figure 1. From Benson et al. 2014. Sure the slope goes up from beginning to end. It also does so with mammals. But the actual trip is more like a roller coaster. And the data does not include dozens of really tiny pterosaurs from the Solnhofen, deleted because they were not tall enough.

Figure 1. From Benson et al. 2014. Sure the slope goes up from beginning to end. It also does so with mammals. But the actual trip is more like a roller coaster. And the data does not include dozens of really tiny pterosaurs from the Solnhofen, deleted because they were not tall enough. Color and questions added to original art.

However,
from their own data, their latest example in the Pteranodontia clade was smaller than their earlier example. And in the mid-Cretaceous there was a trendy drop in size. So, those counter their thesis which only works with one clade, the Azhdarchidae, and only because the Mesozoic ended when it did, with big Q on stage.

And are we forgetting that small to medium pterosaur fossils have been found (so far) only  in Lagerstätten localities, like Jehol and Solnhofen? How many of those are known from the Late and Latest Cretaceous? None. That’s something that I wish wasn’t so. The present phylogenetic analysis indicates that we’re not likely to see them either. Everything progresses without noticeable gaps.

So the paper was a nice exercise, repeating an experiment, skewed by the ringer at the end. Take away one data point and sure the Cretaceous pterosaurs are on average larger than the Triassic and Jurassic pterosaurs, but the trend is not up at the end.

And I don’t trust straight lines in evolution because then only the beginning and end dots contribute to create the line. The middle ones mean nothing when a straight line is drawn.

Earlier Hone and Benton (2006) also invoked Cope’s Rule for pterosaurs. They did so by deleting all tiny Solnhofen pterosaurs. Likewise, there were no tiny Solnhofen pterosaurs listed in the Benson et al. 2014 spreadsheet.

References
Benson RBJ et al. 2014. Competition and constraint drove Cope’s rule in the evolution of giant flying reptiles. Nat. Commun. 5:3567 doi: 10.1038/ncomms4567.
Hone and Benton 2006. Cope’s Rule in the Pterosauria, and differing perceptions of Cope’s Rule at different taxonomic levels. Journal of Evolutionary Biology 20(3): 1164–1170. doi: 10.1111/j.1420-9101.2006.01284.x

NOT a new Zhenyuanopterus: XHPM1088

Very, very close, but no cigar.

And not a juvenile either.
A new paper by Teng et al. (2014) reports on a small partial Zhenyuanopterus (XHPM1088, Fig. 1) that does quite fit the morphology of the holotype. No worries. They said it was a juvenile with some odd sorts of allometry going on.

I hate to say it, but we can blame Chris Bennett for this bit of wishful thinking as his 1995 and 1996 papers on Solnhofen pterosaurs opened the doors to letting almost any small specimen become the juvenile of any somewhat similar, but much larger specimen based on the false notion of allometry during ontogeny. Several specimens falsify that little fantasy, including all the embryos now known.

Phylogenetic analysis would have put a stop to such nonsense, but no analysis was undertaken, either in 1995, 1996 or 2014.

Figure 1. XHPM1088 in situ. Only the posterior half is preserved here.

Figure 1. XHPM1088 (mistakenly referred to Zhenyuanopterus) in situ. Only the posterior half is preserved here.

Here’s the problem
The new specimen has a relatively long and robust tail (15 caudals) and a more robust forelimb than hindlimb, plus a Yixian Formation (Early Cretaceous) locality. These facts identified this pterosaur as Zhenyuanopterus to its authors. With identical length ratios between the humerus and femur, Teng et al. thought growth was isometric in these bones, but not others. The scapula has an odd sort of shape otherwise found only in Zhenyuanopterus. However the coracoid was not the same shape or size ratio (Fig. 1). They thought the length of the coracoid would slow dramatically during growth compared to other bones, not realizing that taxa just outside of Zhenyuanopterus (i.e. Boreopoterus, Arthurdactylus, Fig. 2) had a similar long, straight coracoid. They also blamed the coracoid length problem on the holotype of Zhenyuanopterus, saying it was not well-preserved and giving it a longer redicted length based on XHPM1008. That’s not good Science, especially when the coracoids are well preserved and articulated in the holotype.

Unfortunately
Teng et al. thought one of the unique characters of Zhenyuanopterus was its small feet, but the reality is ALL ornithocheirids (more derived than the JZMP embryo) had tiny feet.

Figure 2. The partial pterosaur XHPM1088 to scale with Boreopterus and Zhenyuanopterus and also scaled up to a similar humerus length with Zhenyuanopterus.  Note the coracoids don't match. This is one of the few pterosaurs in which the tibia is shorter than the femur. Boreopterus is similar in this regard.

Figure 2. Click to enlarge. The partial pterosaur XHPM1088 to scale with Boreopterus and Zhenyuanopterus and also scaled up to a similar humerus length with Zhenyuanopterus. Note the coracoids don’t match. This is one of the few pterosaurs in which the tibia is shorter than the femur. Boreopterus is similar in this regard.

A beautiful illustration of Zhenyuanopterus is included in the paper (Fig. 3) sadly flawed by bat-like, deep chord wing membranes and an odd sort of hanging posture for a pterosaur, especially one with such small feet. Some traditions are very hard to kill.

Zhenyuanopterus-illustration

Figure 3. Zhenyuanopterus illustration by Zhao Chuang, a very talented artist. Sadly the wing membranes are wrong and the hanging posture is unlikely based on the tiny feet.

I encourage pterosaur workers
to start putting bones together in reconstructions, then adding new taxa to good phylogenetic analyses before assigning a juvenile status to a small pterosaur that doesn’t match a large one. Here’s a new genus that Teng et al. could have named, but didn’t.

Reference
Teng F-F, Lü J-C, Wei X-F, Hsiao Y-F and Pittman, M 2014. New Material of Zhenyuanopterus (Pterosauria) from the Early Cretaceous Yixian Formation of Western Liaoning. Acta Geologica Sinica (English) 88(1):1-5.

Juvenile? Tapejarid – Rio Ptero Symposium

Figure 1. XHPM 10009 specimen in situ and here colorized with DGS.

Figure 1. XHPM 10009 specimen in situ and here colorized with DGS. the dorsal and sacral are are tucked beneath the other elements. Looks like a possible sacrum in the antorbital fenestra. I have less confidence in the femora as both are beneath other elements.

Another Rio Ptero abstract came with a wonderful little halftone picture that captured a ton of data on a purported juvenile tapejarid (Lü and Teng 2013, Fig. 1). Talk about a paradigm buster! Check out that little skull.

Figure 1. Sinopterus and purported juvenile, but note the skull is relatively smaller with smaller eyes in the smaller specimen. The feet are also distinct. This appears to be a smaller adult of another species, not a juvenile.

Figure 2. Sinopterus and purported juvenile, XHPM 1009, but note the skull is relatively smaller with smaller eyes in the smaller specimen. The feet are also distinct, more like Noripterus, a dsungaripterid.. This appears to be a smaller adult of another species, not a juvenile.

Tapejarids reached their acme in Early Cretaceous South America. They appear in a variety of sizes (Fig. 2) and they had their origin in China with sinopterids, shenzhoupterids and dsungaripterids. These had origins in Europe with Germanodactylus (Fig. 2).

The new skull compared to other tapejarids. Click to enlarge.

Figure 3. Click to enlarge. The rising size of the tapejaridae.

Lü and Teng report on what they considered a juvenile based on its size (Fig. 1, Fig. 2 left, Fig. 3 second from left), smaller than Sinopterus with wingspan only 2/3 as wide and a skull half the size of the Sinopterus skull. In a clade of increasing skull and crest size, to find one with a smaller skull is a real oddity. And it reminds me of one other pterosaur with the small skull, Eosipterus, which we looked at earlier.

Look at the foot of Sinopterus and you’ll see toes about equal in length to the metatarsals. In the XHPM specimen (Fig. 1) the toes are much smaller. The femur is relatively longer in the XHPM specimen. Folks, this is a different species.

To their credit,
Lü and Teng note, “the premaxillary crest…is not influenced by ontogeny,” even though this is not a juvenile. They also report, “the humeri of the young individuals grew faster than the wing metacarpals and femora of the adult or sub-adult.” Unfortunately these distinct proportions more accurately reflect phylogenetic differences, not ontogenic differences. Germanodactylus (Fig. 3) is the baseline taxon here.

I contacted Dr. Lü with this data. Still waiting to hear from him with feedback.

References
Lü J-C and Teng F-F 2013. A juvenile tapejarid pterosaur fromt he Early Cretaceous of Liaoning Province and its ontogenetic implications. Rio Ptero Symposium 2013: 81-82.

Ontogenetic crest development in Tupuxuara

Let’s set the stage
Earlier we looked at the isometric growth of the azhdarchid pterosaur, Zhejiangopterus and the juvenile Pteranodon. Earlier we falsified unsupported claims that tiny Solnhofen pterosaurs were allometric juveniles of larger forms. Earlier we reported on four pterosaur embryos that demonstrated isometric growth. None had the larger eyes and shorter rostrum that typify hatchling and newborn mammals, birds and crocs (contra Bennett 2006). Even so, Witton 2013 continues to promote the false hypothesis of allometric growth during ontogeny in pterosaurs (Fig. 1).

But we haven’t yet touched on the crest size question
Today we’ll show evidence that yes, crest size does increase during ontogeny. And, really, how else would you ever expect to get such big crests inside an eggshell? However, rostrum length and eye size does not change during ontogeny, no matter how much Bennett and Witton want that to happen. Witton unwittingly demonstrates this himself with a juvenile Tupuxuara (Fig. 1).

Figure 2. Witton 2013 promotes the myth that small Rhamphorhynchus specimens were juveniles of larger specimens. Actually the small ones were ancestral to the larger ones as recovered in phylogenetic analysis.  Below: An actual juvenile Tupuxuara, matched to another species of Tupuxuara with a longer rostrum. Note the juvenile eyes are not large. Crest size does increase with ontogenetic age.

Figure 1. Witton 2013 promotes the myth that small Rhamphorhynchus specimens were juveniles of larger specimens. Actually the small ones were ancestral to the larger ones as recovered in phylogenetic analysis.
Below: An actual juvenile Tupuxuara, matched to another species of Tupuxuara with a longer rostrum. See figure 3 for a better match to an adult. Note the juvenile eyes are not large. Crest size does increase with ontogenetic age.

Today
we have three size of Tupuxuara (Fig. 2) based on the Goshura specimen including two likely juveniles morphologically close to it. Each has a distinct skull showing some variation, but together they shed some light on crest development with maturation in these large Cretaceous pterosaurs. Note that none have the traditional short rostrum and large eyes Bennett (2006) predicted. Neither the juveniles nor the adult have the long rostrum of the Tupuxuara longicristatus specimen that Witton (2013) substituted (Fig. 1) for an adult version of this species. Note that the middle colorized specimen has a relatively longer rostrum than the Goshura specimen. This may represent individual variation grading into speciation.

Figure 1. Ontogenetic skull and crest development in Tupuxuara. Note the eyes are small and the rostrum is long in juveniles. Only the crest expands and only posteriorly.

Figure 2. Ontogenetic skull and crest development in Tupuxuara. Note the eyes are small and the rostrum is long in juveniles and adults, even longer in the middle juvenile. Only the crest expands  posteriorly.

TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It's a close match to that of Tupuxuara, otherwise known only from Early Cretaceous South American strata.

Figure 3. TMM 42489-2, the tall crested Latest Cretaceous large rostrum and mandible. It’s a close match to that of Tupuxuara longicristatus, otherwise known only from Early Cretaceous South American strata. Note the big difference in rostral length is a phylogenetic difference, not an ontogenetic one. If you were hell bent on proving allometric growth, this is the skull I would use, like the one Witton did. 

We also have a juvenile Tapejara with a crest
And the crest not much smaller than an adult crest. Skull proportions are virtually the same between adult and juvenile. And yet, look, there’s another long rostrum adult, just another variation on a theme.

Figure 4. Juvenile Tapejara with two adults of distinct species. Note the rather large crests on the juvenile, but otherwise the skull had adult proportions.

Figure 4. Juvenile Tapejara with two adults of distinct species. Note the rather large crests on the juvenile, but otherwise the skull had adult proportions.

Along the same lines:
Witton 2013 also attempted to promote the Bennett (1995) idea that small Rhamphorhynchus specimens were actually juveniles (Fig. 1). Neither worker used phylogenetic analysis which demonstrates that known small Rhamphorhychus specimens were actually primitive, closer to the outgroup taxon, Campylognathoides.

You’ll recall
Bennett (1991, 2000) said that short-crested, smaller specimens of Pteranodon represented juveniles and females. That was falsified using phylogenetic analysis that recovered short-crested Pteranodon specimens closer to short-crested outgroup taxa, such as Germanodactylus.

Nevertheless, it’s obvious that long and tall-crested pterosaur specimens could not have fit such long and tall crests into an eggshell. So there must have been some sort of crest growth during ontogeny in large crested specimens. And this, so far, is the evidence for it.

References
Bennett SC 1991. Morphology of the Late Cretaceous Pterosaur Pteranodon and Systematics of the Pterodactyloidea. [Volumes I & II]. Ph.D. thesis, University of Kansas, University Microfilms International/ProQuest.
Bennett SC 1992. Sexual dimorphism of Pteranodon and other pterosaurs, with comments on cranial crests. Journal of Vertebrate Paleontology 12: 422–434.
Bennett SC 1994. Taxonomy and systematics of the Late Cretaceous pterosaur Pteranodon (Pterosauria, Pterodactyloidea). Occassional Papers of the Natural History Museum University of Kansas 169: 1–70.
Bennett SC 2001. The osteology and functional morphology of the Late Cretaceous pterosaur Pteranodon. Part I. General description of osteology. Palaeontographica, Abteilung A, 260: 1–112. Part II. Functional morphology. Palaeontographica, Abteilung A, 260: 113–153
Bennett SC 2006. Juvenile specimens of the pterosaur Germanodactylus cristatus, with a review of the genus. Journal of Vertebrate Paleontology 26:872–878.SMNS
Witton M. 2013. Pterosaurs. Princeton University Press. 291 pages.

Extremely rare juvenile pterosaurs: no cute little baby faces here!

Contra traditional thinking (Witton 2013, Unwin 2005), there are very few pterosaur juveniles known and certainly there are no “cute” ones. The term “cute” here means having a baby face = short rostrum and big eyes, as in baby mammals, crocs and bird, distinct from the longer faces with relatively smaller eyes found in adults.

Among those verified pterosaur juveniles are Pterodaustro (see embryo and hatchling, we’re still waiting to see mid-size juveniles published, but we hear (Chinsamy et al. 2008) they are known) and Zhejiangopterus (Fig. 1, Cai and Wei 1994). We also know of four other embryos: Darwinopterus, the IVPP basal anurognathid embryo, the JVMP basal ornithocheirid embryo and the aborted embryo of Anurognathus.

None of these have a short rostrum and large eyes when compared to adults of the same genus. Rather, they are virtually identical to adults, only smaller. Note, however, the IVPP specimen and the Anurognathus embryo both have a short rostrum because that is typical for adult anurognathids. Even so, their eyes remain small.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured  in figure 2 are the two smallest above at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Figure 1. Click to enlarge. There are several specimens of Zhejiangopterus. The two pictured in figure 2 are the two smallest ones at left. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen. The skull is unknown in the largest specimens, but it is difficult to envision any skull longer than those shown here. Known bones from each specimen are shown in white.

All other purported juveniles (small to tiny chiefly Solnhofen pterosaurs), phylogenetically nest with a variety of other small to tiny pterosaurs succeeding larger primitive taxa and preceding larger derived taxa. Since this pattern repeats itself a half dozen times within the Pterosauria, this appears to be the most common method by which certain pterosaurs evolved smaller to genetically survive whatever was killing their unreduced brethren.

The other well known azhdarchid
Earlier we guessed what the embryo of another azhdarchid, Quetzalcoatlus, might look like and we restored the skull of Q. sp. based on all known specimens. Here (Fig. 1) we do the same with a hatching Zhejiangopterus. It’s easy because hatchlings and juveniles were virtual copies of adults. We call this method of maturation isometric development.

Isometry: the growth rates in different parts of a growing organism are the same. This is appropriate for pterosaurs. They hatch ready to fly.

Allometry: the growth rates in different parts of a growing organism are not the same. This is appropriate for mammals, birds and crocs who are fed by their parents and are stimulated to do so by their “cute” appearance.

Today’s focus
will be on a family of Zhejiangopterus individuals Figs. 1-4) that were described together (Cai and Wei 1994).

Figure 2. Zhejiangopterus juveniles. Neither of these two juveniles has a short rostrum or large eyes. Note the soft tissue impressions. Rostrum restored on M1324 based on M1330 by simple enlargement.

Figure 2. Click to enlarge. Zhejiangopterus juveniles to scale (see figure 1). Neither of these two juveniles has a short rostrum or large eyes. Green = maxilla. Yellow on skull = premaxilla. Note the soft tissue impressions. Rostrum restored on M1324 based on M1330 by simple enlargement. In M1324 the ascending process of the premaxilla is displaced.

Here (Figs. 1, 2) it is plain to see (we call this “evidence” in paleontology) that even young juveniles of Zhejiangopterus had a long skull and tiny eyes. And, wonder of wonders, this follows in the pattern of all other known pterosaur juveniles and embryos (listed above), rare though they are. The evidence in Zhejiangopterus also falsifies any claims made by traditional researchers that pterosaur young had “cute” features.

Moreover, we determined, through phylogenetic analysis, that skeletal bones did not co-ossify with maturity. Rather all the evidence indicates that bone fusion was a phylogenetic, rather than an ontogenetic signal.

Many of the small, chiefly Solnhofen specimens belong to clades of adults, like Scaphognathia, that also feature a short rostrum and large eyes. These traits were emphasized in ever smaller descendants by allometric development within the eggshell. That’s the only explanation that fits the evidence for morphological change (evolution) when juveniles display isometric ontogeny. Note, however, many other tiny pterosaurs had a long rostrum and small eyes, matching the traits of their clade and sisters, as demonstrated earlier.

There’s one other issue:
Cai and Wei (1994, Fig. 3) published a reconstruction of the small Zhejiangopterus skull that is inaccurate with regard to skull sutures. Unwin and Lü (1997) reprinted the same image without commenting on the problem.

Figure 3. Zhejiangopterus according to Cai and Wei 1994. No other pterosaur and no other azhdarchid has such a deep premaxilla. The back of the skull is more difficult to reconstruct. A better reconstruction, based on DGS, is shown in figure 4.

Figure 3. Zhejiangopterus according to Cai and Wei 1994. No other pterosaur and no other azhdarchid has such a deep premaxilla with such a long ventral margin. Moreover, no pterosaur has such a short maxilla.  The back of the skull is more difficult to reconstruct due to crushing. A better reconstruction, based on DGS, is shown in figure 4.

Cai and Wei 1994 gave Zhejiangopterus a huge premaxilla (Fig. 3) and a tiny maxilla, both atypical for azhdarchids and pterosaurs in general. Unwin and Lü (1997) accepted this error without comment.

The actual premaxilla (Figs. 2, 4) is a small strip along the dorsal rim (Fig. 4) and it extends along the jawline just a short length. The maxilla actually comprises the great majority of the rostrum with the nasal and jugal adding laminated layers (Fig. 4). This may be yet another example of how experts have disfigured pterosaurs and how DGS has brought more accuracy to tracings than experts have provided with the fossil in front of them. More precision in tracing along with referencing other closely related taxa would have solved such problems.

Figure 4. Zhejiangopterus skull. Two scale bars are shown for the large and small specimens.

Figure 4. Reconstructed Zhejiangopterus skull. Two scale bars are shown for the large and small specimens, but the reconstruction is based on the two smallest juveniles (Figs. 1, 2). Here the premaxilla is a small strip on the dorsal rim of the rostrum. The nasal and jugal laminate the large maxilla . The nasal is much larger here and the postorbital is more traditionally triangle shaped.

All that aside, if you have evidence for errors or more precision, please send them along.

The Independent Hatchling Issue
In Zhejiangopterus and Pterodaustro various size specimens were found together. So at least some pterosaurs enjoyed families or flocks, despite being able to fly independently shortly after hatching.

References:
Cai Z and Wei F 1994.
 On a new pterosaur (Zhejiangopterus linhaiensis gen. et sp. nov.) from Upper Cretaceous in Linhai, Zhejiang, China.” Vertebrata Palasiatica, 32: 181-194.
Hwang K-G, Huh M, Lockley MG, Unwin DM and Wright JL 2002. New pterosaur tracks (Pteraichnidae) from the Late Cretaceous Uhangri Formation, southwestern Korea. Geology Magazine 139(4): 421-435.
Unwin D and Lü J. 1997. On Zhejiangopterus and the relationships of Pterodactyloid Pterosaurs, Historical Biology, 12: 200.

wiki/Zhejiangopterus

PS an update was just added to the pterosaur wings as gills hypothesis with reference to gas exchange in bat wings here.