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

 

The JZMP embryo and its adult sister taxa

Currently the only known embryo/adult pterosaur pairing is in the genus Pterodaustro. Unfortunately, not much has been made about the allometry/isometry in the growth patterns of this genus, even though the data is available. The best data, unfortunately, is right here, rather than in an academic journal. Adults are 8x larger than hatchlings and ontogeny is chiefly isometric (as shown most clearly in Zhejiangopterus) and other pterosaurs like Ptweety the Pteranodon.

For the other two embryos, the IVPP embryo and the JZMP embryo we currently do not have congeneric adults and have to look to sister taxa or simple isometry to estimate the adult proportions and traits.

Today we’ll look at the sister taxa of the JZMP embryo (Fig. 2).

Figure 1. The closest sisters to the JZMP embryo, a basal ornithocheirid without an adult skeleton known for it.

Figure 1. The closest sisters to the JZMP embryo, a basal ornithocheirid without an adult skeleton known for it. Click to enlarge. This is not the phylogenetic order. Yixianopterus is the most primitive. Then the JZMP embryo followed by the smaller forms. These are followed by the boreopterids. 

Generally what we find at clade bases is a gradual increase in size from tiny ancestors. While we do have a tiny ancestor in Pterodactylus(?) pulchellus, we don’t have a gradual increase from that point forward. Yixianopterus the basalmost ornithocheirid, is large AND primitive. The JZMP embryo as an adult, was similar in size to Yixianopterus, but twice as tall as Haopterus and two Lebanon basal ornithocheirids. Click here to see a phylogenetic lineup of ornithocheirids and their outgroup.

Given these various sizes in basal ornithocheirids, and no gradual increase in size, one wonders if Haopterus and the Lebanon ornithocheirids are juveniles. Finding lots of larger congeneric taxa would be helpful. Checking out the annular rings in their long bones would also give clues.

The alternative, that the small ornithocheirids are adults, might represent the next phase in derived ornithocheirid evolution, in which the wings get longer and the feet get smaller, among other traits, which appears to be the case in the Lebanon ornithocheirids.

References
Ji Q, Ji S-A, Cheng Y-N, You HL, Lü J-C, Liu Y-Q and Yuan CX 2004. Pterosaur egg with leathery shell. Nature 432:572.

A basal ornithocheirid from Lebanon

Several basal ornithocheirids are coming out of Lebanon. This one is more complete than most. It is the most basal form I know of with tiny feet. And it’s pretty small for an ornithocheirid.

Figure 1. a basal ornithocheirid, undescribed, from Lebanon.

Figure 1. A  basal ornithocheirid, undescribed, from Lebanon. Probably a full time flyer, but not very large. The skull is about 4 inches long.

More basal ornithocheirids include the JZMP embryo and Yixianopterusboth of which have more typically sized feet and wings. Earlier we looked at the common ancestors of cycnorhamphids and ornithocheirids, including the tiny pterosaur misnamed Pterodactylus? pulchellus.

Here’s a opportunity to discuss fossil interpretation.

Figure 1. Tracing the coracoid and scapula on the fossil. Note the scapula is way to short. The proximal knob, otherwise just a piece of bone here, is identified.

Figure 1. Tracing the coracoid and scapula on the fossil. Note the scapula is way to short unless extended as shown. The proximal knob of the scapula, the part that goes in the notarium, is identified here. Otherwise, it’s just a piece of bone. This is an instance of an educated guess, one that appears to make sense.

Sometimes fossils are less than complete. Sometimes bones go under other bones. Sometimes chunks of matrix that contain bones do not make it back to the lab. Here’s where best guesses come into play, as in figure 1. I’m pretty sure that small piece of bone over the coracoid is the proximal scapula. Let me know if you think you have a better idea or identification here.

The Evolution of Gigantism in Pterosaurs: The Ancestry of Anhanguera

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

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

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

The ancestry of Anhanguera and Arthurdactylus includes tiny TM 13104.

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

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

The complete TM13104 and the skull of Anhanguera to scale.

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

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

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

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

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

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

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