Subadult and adult Tropeognathus compared

Holgado and Pegas 2020 name several toothy crested rostral pieces
they assign to Anhangueridae, Coloborhynchinae and Tropeognathinae, subsets of the clade Ornithocheiridae (Seeley 1870).

More interesting due to its completeness,
was the Holgado and Pegas page-wide photo of the BSp 1987 I 47 specimen of Tropeognathus (Fig. 1, Wellnhofer 1987). Here the ’47’ specimen is compared to the larger holotype, BSp 1987 I 46, and to the smaller Scaphognathus holotype (Fig. 1, GPIB 1304, No. 109 of Wellnhofer 1975), a distant ancestor of Tropeognathus in the Large Pterosaur Tree (LPT, 251 taxa).

Quick note to readers after October 19, 2020:
Co-author Pegas sent a comment noting the 47 specimen was a typo and should be 46 instead. I asked about the scale bar differences and am awaiting that reply at present.

Figure 1. A subadult and adult specimen of Tropeognathus compared to a distant relative, Scaphognathus.

Figure 1. A subadult and adult specimen of Tropeognathus compared to a distant relative, Scaphognathus.

Holgado and Pegas provided a cladogram of a clade of pterosaurs
formerly considered Ornithocheiridae, Lanceodontia. Strangely, their outgroup is the derived istiodactylid, Lonchodraco giganteus, which we looked at earlier here and nested with the unnamed SMNS PAL 1136 specimen, which was omitted from their cladogram.

By contrast
In the LPT ornithocheirids arise from small taxa like Yixianopterus, Mimodactylus and before them the Cycnorhamphus clade and before them the tiny Late Jurassic pterosaurs, BM NHM 42735, Gmu10157, TM 13104 and three Scaphognathus specimens (109, SMNS 59395 and 110 and  of descending size. None of these are included in Holgado and Pegas.

There are quite a few nomenclature problems
in the Ornithocheridae that make the taxonomy unnecessarily confusing.

According to Wikipedia,
“Back in 1987, Wellnhofer had named a second species called Tropeognathus robustus, based on specimen BSP 1987 I 47, which is a more robust lower jaw. In 2013 however, T. robustus was considered as a species of Anhanguera, resulting in an Anhanguera robustus.” Comparing the 46 and 47 specimens (Fig. 1) show they are conspecific, or at least congeneric. This clade becomes increasingly confused with every new author or set of authors. Strange that such closely related taxa are generically split while the several dozen variations in Rhamphorhynchus and Pteranodon are ignored.

The first species of Tropeognathus mesembrinus has several synonyms.

  • Anhanguera mesembrinus (Wellnhofer, 1987)
  • Coloborhynchus mesembrinus (Wellnhofer, 1987)
  • Criorhynchus mesembrinus (Wellnhofer, 1987)
  • Ornithocheirus mesembrinus (Wellnhofer, 1987)

Ornithocheiridae Seeley 1870, named when only a few bits and pieces were known

Ornithocheiromorpha Andres et al., 2014, incorrectly nested within Pteranodontoidea.

Pterodactyloidea Plieninger, 1901, adding taxa splits up this traditional clade.

The disappearance of the naris in scaphognathid pterosaurs.

Figure 2. The disappearance of the naris in scaphognathid pterosaurs. Click to enlarge figure 1 to see the tiny naris in the subadult specimen of Tropeognathus, more sealed over in the adult.

The subadult specimen (specimen ’47’)
of Tropeognathus (Fig. 1) documents a vestige, slit-like naris that disappears in the larger ’46’ specimen. If you can’t see it here, click to enlarge.

Rostral crest
Comparing the subadult to the adult specimen (Fig. 1) demonstrates no growth in the size of the rostral crest. Rather the back half of the skull is slightly larger.


References
Holgado B and Pegas RV 2020. A taxonomic and phylogenetic review of the anhanguerid pterosaur group Coloborhynchinae and the new clade Tropeognathinae. Acta Palaeontologica Polonica 65 (X): xxx–xxx.
Wellnhofer P 1975a. Teil I. Die Rhamphorhynchoidea (Pterosauria) der Oberjura-Plattenkalke Süddeutschlands. Allgemeine Skelettmorphologie. Paleontographica A 148: 1-33. 1975b. Teil II. Systematische Beschreibung. Paleontographica A 148: 132-186. 1975c.Teil III. Paläokolgie und Stammesgeschichte. Palaeontographica 149: 1-30.
Wellnhofer P 1987. New crested pterosaurs from the Lower Cretaceous of Brazil. Mitteilungen der Bayerische Staatssammlung für Paläontologie und historische Geologie 27: 175–186; Muenchen

/wiki/Tropeognathus
wiki/Scaphognathus
wiki/Criorhynchus

 

Pterosaur Cervicals: 8 or 9?

Bennett (2004) reported, “The cervical series of the specimen (the third known Scaphognathus, SMNS 59395) consists of 9 vertebrae if the first vertebrae that bears a large rib that articulates with the sternum is interpreted as the first dorsal vertebra.”  This was a break with tradition, in which pterosaurs were considered to have 8 cervicals.

Scaphognathus SMNHS 59395

Figure 1. Scaphognathus SMNHS 59395 with cervicals colored green and orange, dorsal colored purple and blue, sternum in red. Click for more info.

Vertebra number 9 always lies completely within the torso, despite not articulating with the sternum. Hence the traditional number of 8 makes more morphological sense. Vertebra number 9 also shares more traits in common with number 10 than number 8.

Bennett (2004) reported that Pterodactylus had 7 cervicals and large [unspecified] pterodactyloids had 9 cervicals, the latter resulting from the cervicalization of the anterior two dorsal vertebrae.” Unfortunately, I can find no examples of either. Large or small, all pterosaur specimens in reptileevolution.com have 8 cervicals.

The skull of the SMNS 59395 specimen of Scaphognathus

Figure 2. The skull of the SMNS 59395 specimen of Scaphognathus with bones color coded. Note there were 4 premaxillary teeth, as in most other pterosaurs and all sister taxa, not 2 as Bennett (2004) reported.

On a side note, Bennett (2004) reported there were only two teeth in the premaxilla of SMNS 59395. I found four (Fig. 2) as in most other pterosaurs and all known sisters. I saw the specimen before it was prepared. But I was able to “see” four teeth in photos. Here Bennett (2004) might have made a different determination if he had realized that two teeth would have been autapomorphic, but no phylogenetic analysis was performed.

Prepared and unprepared images of the SMNS 59395 specimen of Scaphognathus.

Figure 4. Prepared and unprepared images of the SMNS 59395 specimen of Scaphognathus. Click to enlarge.

There’s a nice articulated wing ungual present in this undisturbed completely articulated specimen.

Finally, Bennett (2004) considered SMNS 59395 a “juvenile with unfused girdles, carpals, and tarsals.” No phylogenetic analysis was offered. Here, after phylogenetic analysis, the smaller SMNS specimen was found to be distinct in several traits from the larger No. 109 specimen, and derived taxa were smaller still. So SMNS 59395 was likely a precocious small adult, not a juvenile. A juvenile should have been virtually identical to the adult, only smaller, because that’s the pattern we see in embryos, the only pterosaurs for which we have an exact ontogenetic age – zero.

This data was gleaned from photos. Bennett (2004) had the specimen in hand. Some of these conclusions, like whether vert #9 was a cervical or a dorsal goes back to the choices we make as paleontologists. Phylogenetic analysis helps.

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 2004. New information on the pterosaur Scaphognathus crassirostris and the pterosaurian cervical series. Journal of Vertebrate Paleontology, 24(Suppl. to #3):38A.

What is Jianchangnathus?

A recent paper by Cheng et al. (2012) introduced a new basal pterosaur, Jianchangnathus robustus (IVPP V 16866). Middle Jurassic in age, Jianchangnathus shared several characters with Scaphognathus from the Late Jurassic, according to the authors. It was also compared to Fenhuangopterus, a basal dorygnathid from the same deposits at Jianchangnathus.

Jianchangnathus

Figure 1. Jianchangnathus was allied with Scaphognathus, but retains many traits of its ancestors within Dorygnathus.

A Basal Nesting in the Second Half of the Pterosauria
Here Jianchangnathus nested at the base of the Scaphognathia, essentially the second half of the Pterosauria. In this important phylogenetic site Jianchangnathus was derived from a sister to the Donau specimen of Dorygnathus, itself at the very base of the Dorygnathia and not far from Sordes, the outgroup taxon (Fig. 2). Pterorhynchus and the wukongopterids (= darwinopterids) were sister taxa.

A phylogenetic sequence that includes Jianchangnathus

Figure 2. A phylogenetic sequence that includes Jianchangnathus at the transition point between a basal Dorygnathus and Pterorhynchus + Scaphognathus. All are to scale. This is a rare instance of morphological transition in which a tiny pterosaur did not intervene.

Jianchangnathus was not originally subjected to a phylogenetic analysis, nor was it reconstructed.

The skull of Jianchangnathus with bones identified using the DGS method.

Figure 3. The skull of Jianchangnathus with bones identified using the DGS method. Here the nasal is in pink (anteriorly) and purple (posterior to the break).

Redescription Using DGS
Cheng et al. (2012) reported fusion between the premaxilla and maxilla. Here (Fig. 3) the suture is between the 4th and 5th tooth as in sister taxa. The first fang was the first maxillary tooth, as in the SMNS 55886 specimen of Dorygnathus. The dentary did not extend to the quadrate but extended posteriorly beneath posterior jugal as in sister taxa. The nasal extended to mid orbit as in sister taxa. The jugal extended to the pmx/mx suture as in sister taxa. The prefrontals were longer than originally reported. The vomers, ectopalatine and pterygoid were rod-like elements, as in sister taxa. The tip of the mandible is a double-tooth morphology.

Dorygnathus Was Barely Mentioned
The upturned premaxilla and anteriorly-oriented teeth are traits of Dorygnathus, but that taxon was not mentioned by Cheng et al. (2012) in comparison. The relatively large skull is a trait shared with Pterorhynchus and the wukongopterids. The manual and pedal element proportions are shared with sister taxa.

Maturity
Cheng et al. (2012) observed the non-fusion of the scapula and coracoid and mistakenly considered Jianchangnathus immature. In this case fusion, or a lack thereof, is a matter of phylogeny, not ontogeny. Because pterosaurs are lizards that do not follow archosaur growth patterns as discussed earlier. Sister taxa likewise do not fuse the scapula and coracoid and Jianchangnathus was similar in size to them (Fig. 2).

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
Cheng X, Wang X-L, Jiang S-X and Kellner AWA 2012. A new scaphognathid pterosaur from western Liaoning, China. Historical Biology iFirst article available online 29 Nov 2011, 1-11. doi:10.1080/08912963.2011.635423

wiki/Jianchangnathus