SVP 2018: Tooth loss in mysticete whales x5 abstracts

Five SVP abstracts
fumble with the issue of tooth loss preceding the origin of mysticete whales under the invalid assumption that the traditional clade Cetacea is monophyletic. It is not. Whales had two or three (right whales make it three) separate origins, as we learned earlier here.

ABSTRACT 1
Ekdale and Deméré 2018
continue beating a dead horse trying to figure out how Aetiocetus evolved into the clade Mysticeti (Figs. 1-4). In the large reptile tree (LRT, 1038 taxa) mysticetes evolved from desmostylians (Fig. 2-4) while being tested against all prior candidate taxa. Odontocetes evolved from tenrecs, pakicetids and archaeocetids (Fig. 1). Ekdale and Deméré 2018 mistakenly (through taxon exclusion) consider the toothed Aetiocetus a member of the traditional ‘toothed mysticetes’ that they mistakenly think “plays a central role in the debate.”

Figure 5. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

Figure 1. Subset of the LRT focusing on the tenrec/odontocete clade with several whales added.

The authors conclude:
“These results provide critical evidence that the lateral palatal foramina in A. weltoni are
homologous with lateral nutrient foramina in extant mysticetes. As such, the lateral nutrient
foramina in A. weltoni provide strong support for the hypothesis that aetiocetids possessed both teeth and some form of baleen.”
 Unfortunately the authors saw what they wanted to see. They never tested tenrecs or desmostylians and so failed to recover the correct phylogenetic framework upon which their work could proceed. Maybe a similar CT scan will find similar nerve and blood vessel patterns in desmostyians. Only testing will reveal what the cladogram indicates.

Figure 1. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

Figure 2. Subset of the LRT focusing on the mesonyx/mysticete clade showing the split between right whales and all other mysticetes.

ABSTRACT 2
Gatesy et al. 2018 reassess “phylogenetic studies presented over the past dozen years that have variously reconstructed this complex evolutionary sequence. Early work proposed a step-wise transformation in which toothed mysticetes transitioned via ‘intermediate’ forms with both teeth and baleen to toothless filter feeders. Later studies presented alternative scenarios featuring filtration with teeth instead of baleen, loss of a functional dentition before the evolution of baleen, pure suction feeding, and/or convergent evolution of several key mysticete features. We reanalyzed published cladistic matrices in the context of extensive new molecular data, assessed character support for alternative relationships, and mapped six features related to filter feeding in Mysticeti: presence/absence of 1) teeth, 2) baleen, 3) lateral nutrient foramina on the palate (possible osteological correlates of baleen), 4) a broad rostrum, 5) laterally bowed mandibles, and 6) an unsutured mandibular symphysis.”

All for naught.
They could have and should have run a wide gamut phylogenetic analysis like the LRT which separates the ancestors of odontocetes from the ancestors of mysticetes by a wide phylogenetic distance of intervening taxa (Figs. 1, 2). The ancestors of mysticetes are not to be found among the ancestors of odontocetes. This has been online for two years now.

ABSTRACT 3
Geisler, Beatty and Boessnecker 2018
discuss, to no avail, new specimens of Coronodon havensteini, which they say is the most basal mysticete (in the absence of desmostylians and kin) and the LRT nests at the base of the odontocetes and aetiocetes. Surprisingly, the authors report, these specimens support the hypothesis that Coronodon engaged in macrophagy and filter feeding, and underscores the challenges for reconstructing the behaviors of extinct species based on the limited sample provided by the fossil record.” No they have evidence for macrophagy and they have contrived a scenario for filter feeding. 

Figure 1. Taxa in the lineage of the right whale (Eubalaena) include the pygmy right whale (Caperea) and the desmostylian, Desmostylus.

Figure 3. Taxa in the lineage of the right whale (Eubalaena) include the pygmy right whale (Caperea) and the desmostylian, Desmostylus. You don’t have to look for tooth loss in desmostylians. They already have that trait and so many more.

ABSTRACT 4
Lanzetti, Berta and Ekdale 2018
looked at fetal mysticetes and reported, “We present new evidence on the ontogeny of the minke whale, which develops a dense tissue dorsal to the rostral canal where the tooth buds are either already absent or clearly undergoing resorption. The identity of this tissue should be confirmed by histological analysis, but it may be the first sign of baleen development, as posited by previous studies of these species. Overall, the GM analyses show that the fossils occupy a different morphospace than modern species, possibly indicating that they had specific feeding adaptations not shared by modern mysticetes.”
Clearly they are not looking at desmostylians, which loose most of their teeth in adults.

Figure 1. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

Figure 41. Rorqual evolution from desmostylians, Neoparadoxia, the RBCM specimen of Behemotops, Miocaperea, Eschrichtius and Cetotherium, not to scale.

ABSTRACT 5
Peredo 2018
thinks tooth loss precedes the origin of baleen in mysticetes by considering an Early Oligocene specimen from Oregon. In his thinking Peredo, like the authors above, is barking up the wrong tree when he reports, “Although living baleen whales are born without teeth, paleontological and embryological evidence demonstrate that they evolved from toothed ancestors that lacked baleen entirely.” However his specimen might be a desmostylian in the lineage of mysticetes when he reports, “This new material includes a transitional fossil mysticete that lacks both teeth and baleen entirely, demonstrating that tooth loss precedes the origin of baleen in mysticetes.”

A toothy Oregon taxon, Salishicetus, was described by Peredo and Pyenson 2018, who nested it basal to other aetiocetids. They reported, “The description of Salishicetus resolves phylogenetic relationships among aetiocetids, which provides a basis for reconstructing ancestral feeding morphology along the stem leading to crown Mysticeti.”

References
Ekdale EG and Deméré TA 2018. Tooth-to-baleen transition in mysticetes: New CT evidence of vascular structures on the palate of Aetiocetus weltoni (Mysticeti, Cetacea). SVP abstract.
Gatesy et al. (4 co-authors) 2018. Contrasting interpretations of the teeth to baleen transition in mysticete cetaceans. SVP abstract.
Geisler J, Beatty BL and Boessenecker RW 2018. New specimens of Coronodon havensteini provide insights into the transition from raptorial to filter feeding in whales. SVP abstract.
Lanzetti A, Berta A and Ekdale EG 2018. Looking at fossils in a new light: teeth to baleen transition in relation to the ontogeny and phylogeny of baleen whales. SVP abstract.
Peredo CM 2018. From teeth to baleen: Tooth loss precedes the origin of baleen in whales. SVP abstracts.
Peredo CM and Pyenson ND 2018. Salishicetus meadi, a new aetiocetid from the late Oligocene of Washington State and implications for feeding transitions in early mysticete evolution. Royal Society Open Science 5: 172336. http://dx.doi.org/10.1098/rsos.172336

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An overlooked trackmaker for Middle Devonian tetrapod tracks

Ahlberg 2018
discusses the quandary of Middle Devonian (397mya) tetrapod tracks (Zalchemie trackway), some with finger and toe impressions, preceding the Late Devonian (360 mya) appearance of body fossils with fingers and toes.

Figure 1. The Early Carboniferous limbed osteolepid, Pholidogaster,  compared to Middle Devonian Zalchemie tracks to scale.

Figure 1. The Early Carboniferous limbed osteolepid, Pholidogaster, compared to Middle Devonian Zalchemie tracks to scale. Would you consider this a tetrapod, a paratetrapod, or just a fish with legs?

Here
the large reptile tree (LRT, 1308 taxa; subset Fig. 2) provides a solution to the problem. Pholidogaster has toes (fingers not preserved, Fig. 1) yet nests basal to Panderichthys, Tiktaalik, Acanthostega and Ichthyostega. Pholidogaster (Fig. 1) is an Early Carboniferous late survivor of a Middle Devonian first attempt at terrestrial locomotion that produced no extant descendants. Essentially Pholidogaster was an osteolepid with fingers and toes that were not homologous with those found in Tulerpeton and all extant tetrapods (including frogs, salamanders, sirens and amniotes). In other words, fingers and toes were re-invented after the Middle Devonian ancestors of Pholidogaster first gave it a try in the first wave of terrestrial locomotion.

Figure 1. Subset of the LRT focusing on basal tetrapods, colorized according to chronology. Note the wide dispersal of Early Carboniferous taxa, suggesting a Late Devonian radiation as yet largely undiscovered.

Figure 1. Subset of the LRT focusing on basal tetrapods, colorized according to chronology. Note the wide dispersal of Early Carboniferous taxa, suggesting a Late Devonian radiation as yet largely undiscovered. Also note the position of Tulerpeton, basal to all extant tetrapods. 

The LRT confirms Ahlberg’s proposition, “As I have previously argued, even Acanthostega may, to some degree, have been secondarily aquatic, descended from more terrestrially competent ancestors.”

The problem may be
that no one has allowed the possibility that osteolepids produced more than one lineage of  limbed and toed descendants. Convergence runs rampant elsewhere. The evidence shows convergence also produced at least two sets of tetrapods, the Tetrapoda and the Paratetrapoda. They existed side-by-side after the first appearance of Tetrapoda until the extinction of the Paratetrapoda.

References
Ahlberg PE 2018. Early vertebrate evolution. Follow the footprints and mind the gaps: a new look at the origin of tetrapods. Earth and Environmental Science Transactions of the Royal Society of Edinburgh, 1–23.

 

 

 

Sphodrosaurus: here identified as a stem soft shell turtle

Known for decades as an enigma,
Sphodrosaurus pennsylvanicus nests here more primitive than Odontochelys and sheds light on the pareiasaur-to-soft shell turtle transition.

FIgure 1. Partial reconstruction of Sphodrosaurus based on tracings in figure 2.

FIgure 1. Partial reconstruction of Sphodrosaurus based on tracings in figure 2. This turtle is more basal than Odontochelys. Lots of loose parts here and no attempt was made to reassemble the manus or pes.

Colbert 1960
described Sphodrosaurus pennsylvanicus (Fig. 1) as, “A new Triassic procolophonid from Pennsylvania” based on North Museum No. 2321, a natural mold in ventral view of a partial skeleton (Fig. 2) resembling Hypsognathus and located less than a mile from the skull of this genus. In the large reptile tree (LRT, 1308 taxa; subset Fig. 3) Sphodrosaurus nests between the tiny pareiasaur Sclerosaurus (Fig. 4) and the basal soft-shell turtle (known only from skull material) Arganaceras.

Based on the appearance of a shape in the mudstone
beneath the ribs (in ventral view, thus dorsal in life), Sphodrosaurus appears to be (by observation and phylogenetic bracketing) the first taxon to have some sort of soft carapace without developing any sort of expanded ribs or any sort of plastron. Thus it informs on the likely appearance of the currently missing post-crania of Arganaceras. Some loose gastralia-like ossifications (in cyan) are apparent. These are plastron precursors (again, based on phylogenetic bracketing). These inform on a previously unknown genesis for the plastron in soft shell turtles. Sclerosaurus lacks them. Odontochelys has massive plastron elements.

Figure 2. Sphodrosaurus in situ with colors added to bones and possible soft carapace impression.

Figure 2. Sphodrosaurus in situ, ventral view, with colors added to bones and possible soft carapace impression overlooked originally. Colbert  1960 tracing also shown here.

Traditionally
Sclerosaurus nests with procolophonids, but that nesting is based on taxon exclusion. Sphodrosaurus is very similar to Sclerosaurus, but a little more derived toward the soft shell turtles.

Figure 3. Sphodrosaurus nests with other soft-shell turtles arising from pareiasaurs.

Figure 3. Sphodrosaurus nests with other soft-shell turtles arising from pareiasaurs without invoking the carapace.

Sphodrosaurus pennsylvanicus (Colbert 1960; North Museum No. 2321; Newark Supergroup, latest Carnian, Late Triassic). Distinct from Sclerosaurus, the femur is longer, the coracoid is smaller. The antebrachium is longer. As in Trionyx, pedal digit 5 is gracile. The specimen was found in mudstones. Note the wide, flat torso, the tall, slender scapula, sigmoidal femur and long-clawed toes… all turtle traits.

Colbert reported,
“The skull seems to have been unusually large in comparison to the size of the postcranial skeleton. The posterior portion of the skull is produced back into a “frill,” as is common in the advanced procolophonids, this frill covering about five cervical vertebrae. There are 25 presacral vertebrae, to which are articulated widely spreading holocephalous ribs. The scapula is rather slender, the ilium seemingly deep. The pubis and ischium are platelike bones, the former being proximally constricted and distally expanded. The hind limbs are large, the extended limb being approximately equal in length to the total length of the presacral series of vertebrae. In total length and in each of its component sections the linear dimensions in the hind limb are about double those in the fore limb. The metatarsals are rather slender, and long. The ungual phalanges of the pes are large, pointed claws.”

Figure 4. Sclerosaurus reconstructed.

Figure 4. Sclerosaurus reconstructed.

Colbert continues,
“Perhaps the most striking differences between this form and the established genera of procolophonids are in the great length and robust size of the hind limb in the Pennsylvania specimen, and the long, sharp claws of the pes. Such characters might lead one to doubt the true procolophonid relationships of Sphodrosaurus, but other characters, such as size, the obviously large skull, the extension of the back of the skull in a sort of frill over the cervical region, the evidently broad vertebral neural arches (as indicated by the separation of the heads of the ribs), and the holocephalous, flaring ribs, are all characters that point to procolophonid affinities for Sphodrosaurus.”

The following paper
was discovered after the reconstruction and phylogenetic analysis were made:

Sues, Baird and Olsen 1993 reexamined Sphodrosaurus
and determined that the specimen was not a procolophonid, but some sort of diapsid or neodiapsid. They note, Baird (1986) suggested rhynchosaurine affinities. They also note “This combination of characters has not been found in any other known diapsid.” 

The authors note
the preservation of the posterior mandibles, rather than a set of dorsal skull bones as Colbert reported. They failed to see the detached retroarticular process. The cervicals and anterior dorsals have a ventral ridge. So do soft-shell turtles, but the authors did not make that connection. What they identify as extremely long cervicals parallel to the spine and apparently coosified are interpreted here as clavicles. They remarked on the “great width of the trunk region,” as in pareiasaurs and turtles, but the authors did not make that connection. They note the scapula has a “slender  blade”, as do turtles, but the authors did not make that connection. They note the femur is sigmoidal, as in turtles, but the authors did not make that connection.

The authors conclude,
“The mode of preservation of the holotype and only known specimen of Sphodorsaurus pennsylvanicus leaves very few anatomical features for assessing its phylogenetic position.” This is true, but phylogenetic analysis over a wide gamut of potential candidates leaves no doubt in the LRT about where this specimen nests, based on the characters that are visible. There is no mention of pareiasaurs or turtles in the Sues, Baird, Olsen 1993 paper.

As in many enigma taxa studied here,
the solution to their nesting problem appears whenever the enigma taxon is permitted to be tested against a wide gamut of taxa. This minimizes initial bias and lets the software do what it was intended to do… keep human preconceptions from interfering in a cold-blooded scientific process.

Added later the same afternoon
Rice et al. 2016 report: “We show that plastron development begins at developmental stage 15 when osteochondrogenic mesenchyme forms condensates for each plastron bone at the lateral edges of the ventral mesenchyme.” In this way ontogenesis recapitulates the phylogenesis demonstrated by Sphodrosaurus.

References
Colbert EH 1960. A new Triassic procolophonid from Pennsylvania. American Museum Novitates 2022:1–19.
Rice R, Kallonen A, Cebra-Thomas J and Gilbert SF 2016. Development of the turtle plastron, the order-defining skeletal structure. PNAS 113 (19):5317–5322.
Sues H-D, Baird D and Olsen PE 1993. Redescription of Sphodrosaurus pennsylvanicus Colbert, 1960 (Reptilia) and a Reassessment of its Affinities. Annals of Carnegie Museum 62(3):245-253

wiki/Arganaceras
wiki/Sclerosaurus
http://reptileevolution.com/arganaceras.htm

North Museum of Nature and Science
Franklin and Marshall College
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Lancaster, PA 17603
717.358.3941

SVP 2018: Reproduction and Growth in Pterosaurs

Unwin and Deeming 2018 report,
“Pterosaur eggshells were pliable and occasionally bounded externally by a thin calcitic layer. Contact incubation seems impractical and eggs were likely buried and developed at ambient temperatures.”

Burial is not only unnecessary, but dangerous
given that pterosaurs are lepidosaurs and therefore able to retain eggs within the mother until just before hatching, something the authors continue to ignore. That’s why the eggs have lepidosaur-like ultra-thin external layers. No tiny fragile pterosaur wants to dig out of a buried situation. Too dangerous for fragile membranes. Unwin and Deeming are clinging to an archosaur hypothesis, ignoring all the data since Peters 2000 that nest them apart from archosaurs.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.

The authors report,
“Near term embryos were well ossified and hatchlings had postcranial proportions and well developed flight membranes that indicate a superprecocial flight ability.” 

As in lepidosaurs, not archosaurs.
Overlooked by the authors, cranial proportions are also adult-like in hatchlings (Fig. 1). Lepidosaurs hatch ready to eat and take care of themselves.

Regarding growth, they report,
“The growth rates recovered for pterosaurs are comparable to those reported for extant reptiles and a magnitude lower than in extant birds.” Here the authors are lumping turtles, lizards and crocs, when lizards will do.

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.

Note,
the authors do not address isometric growth in their abstract, as in lepidosaurs, not archosaurs. Nor do they address sexual maturity at half full growth, which facilitates rapid phylogenetic miniaturization or gigantism whenever needed due to changing environs.

We’ve heard this all before. Years ago.

Respecting the embargo
other SVP abstract posts will show up after the 20th. This one made the news, so its embargo is over. That article featured BMNH 42736 (Fig. 3) labeled as a hatchling or flapling. Actually it’s a hummingbird-sized adult female. We know this because it nests with other phylogenetically miniaturized taxa in the large pterosaur tree (not with a larger specimen) and… it’s pregnant.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

Figure 6. Torso region of BMNH 42736 showing various bones, soft tissues and embryo.

References
Peters D 2000. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Unwin DM and Deeming C 2018. An integrated model for reproduction and growth in pterosaurs. SVP abstracts.

Live Science online

When did T-rex lose its feathers?

There will be two answers here:
1) phylogenetically; and 2) ontogenetically as Bell et al. 2017 discuss changing ideas regarding the integument of tyrannosauroids.

Tradtional taxon exclusion
has given the Bell et al. team a different ancestry of tyrannosaurs than in the large reptile tree (LRT, 1307 taxa). Even so, Early Cretaceous taxa are the last to preserve feathers or filaments in the large and giant members of this clade.

A few facts before we get started:

  1. Mid-sized Early Cretaceous Yutyrannus (from the allosaur clade, Fig. 1) has filaments
  2. Giant Late Cretaceous Tyrannosaurus (a tyrannosauroid, Fig. 1) has scales preserved in small patches and no filaments preserved (Fig. 2).
  3. Small-sized Zhenyuanlong (a stem tyrannosaur, Fig. 2) has flight and contour feathers, but no elongate coracoids for flapping
  4. Bell et al. include Yutyrannus in the ancestry of tyrannosaurs and ignore Zhenyuanlong.
  5. Plucked poultry reveals naked skin, except around the feet
  6. Large dinosaurs of all types also lose their feathers phylogenetically
Figure 1. Late Cretaceous Tyrannosaurus, which has scales, to scale with Early Cretaceous allosaurid, Yutyrannus, which has filaments.

Figure 1. Late Cretaceous Tyrannosaurus, which has scales, to scale with Early Cretaceous allosaurid, Yutyrannus, which has feather-like filaments. This is the largest theropod, so far, to have such filaments.

Bell et al. report
“Recent evidence for feathers in theropods has led to speculations that the largest
tyrannosaurids, including Tyrannosaurus rex, were extensively feathered. We describe fossil integument from Tyrannosaurus and other tyrannosaurids (Albertosaurus, Daspletosaurus, Gorgosaurus and Tarbosaurus), confirming that these large-bodied forms possessed scaly, reptilian-like skin. These new findings demonstrate that extensive feather
coverings observed in some early tyrannosauroids were lost by the Albian, basal to Tyrannosauridae. This loss is unrelated to palaeoclimate but possibly tied to the evolution of gigantism, although other mechanisms exist.”

And they conclude,
“Gigantism (i.e. increased body mass) affords greater heat retention: a thermodynamic by-product of the square-cube law and linked to reductions in hair in large modern terrestrial mammals.”

Figure 2. Tyrannosaurus (without feathers) to scale and directly compared to Zhenyuanlong (with feathers).

Figure 2. Tyrannosaurus (without feathers) to scale and directly compared to Zhenyuanlong (with feathers). Integument patches shown from Bell et al. 2017. Note the reduction of the forelimbs and hind limbs as tyrannosaurs grow in size phylogenetically. For those who don’t like the LRT phylogeny, this GIF animation shows just how similar tiny Zhenyuanlong and Tyrannosaurus really are.

A modern analogy: small furry hyrax ~ large naked elephant
Just as baby elephants can have a bit more vestigial hair than their parents do, baby giant theropods might have had more vestigial filaments. And considering the small patches of scales found for giant theropods so far, small patches of vestigial filaments might still have been present elsewhere, perhaps trailing the forelimbs, for instance. We just don’t know yet.

Figure 4. The small furry hyrax is in the lineage of the large naked elephant, analogous to small feathery theropods and large naked theropods. The fingers and incisors already show similarities.

Figure 4. The small furry hyrax is in the lineage of the large naked elephant, analogous to small feathery theropods and large naked theropods. The fingers and teeth already show similarities here.

The authors discuss hatchling tyrannosaurs
as they report, “Finally, the presence of epidermal scales in a large adult individual does not rule out the possibility that younger individuals possessed feathers—a developmental switchover that, to our knowledge, would be unprecedented at any rate.” No birds have more feathers as hatchlings than as adults.

What are tyrannosaur scales? And did birds lose their scales?
According to bird studies (Dhouailly 2009) theropod scales may be [phylogenetically] derived from feathers. (Remember chickens and other birds are naked underneath.) Scales and scutes can develop at any place and at any time from naked skin. Consider the ankylosaurs, as an extreme example. Naked and/or furry skin can develop from scales. Consider the scaly tail of the opossum ancestral to the tail of a hamster or lemur, as examples.

This topic was inspired by the following video on YouTube:

References
Bell PR, Campione NE, Persons WS, Currie PJ, Larson PL, Tanke DH, Bakker RT 2017. Tyrannosauroid integument reveals confllcting patterns of gigantism and feather evolution. Biology Letters 13: 20170092. http://dx.doi.org/10.1098/rsbl.2017.0092
Dhouailly D 2009. A new scenario for the evolutionary origin of hair, feather, and avian scales. Journal of Anatomy 214:587-606.

the-origin-of-feathers-and-hair-part-3-feathers/

Mistralazhdarcho: a new pterosaur, but not an azhdarchid

Vullo et al. 2018 bring us a new small ‘azhdarchid’
known from a few 3D bones. In the large pterosaur tree (LPT, 236 taxa) Mistralazhdarcho nests with tiny Nemicolopterus and mid-sized Shenzhoupterus (Fig. 1). Mistralazhdarcho is more than twice as tall as Shenzhoupterus with similar gracile cervicals, a longer radius and shorter metacarpus. Distinct from Shenzhoupterus, the mandible is gracile, more like that of Nemicolopterus.

Figure 1. Mistralazhdarcho compared to reconstructions of Shenzhoupterus and Nemicolopterus.

Figure 1. Mistralazhdarcho compared to reconstructions of Shenzhoupterus and Nemicolopterus. A longer antebrachium is found in Mistalazdarcho.

A downturned dentary
is a trait found in this clade of pterosaurs, and to a lesser extent in sister sinopterids.

The small prominence at the ‘bend’ of the mandible
in Mistralazhdarcho is a curious trait not visible in Shenzhoupterus due to closed jaws in situ. Nemicolopterus might preserve that trait, but a humerus is under the mandible exactly at that point, making it difficult to determine in photos.

A warped deltopectoral crest,
like the one found in Mistalazdarcho (Fig. 1), is not found in azhdarchids. And look at the size range in this clade!

Having reconstructions for direct comparisons,
and a large cladogram that is regularly adding new taxa are tools the LPT and www.ReptileEvolution.com offer freely online to paleontologists worldwide. Best to test here rather than trust your hunch elsewhere.

References
Vullo R, Garcia G, Godefroit P, Cincotta A, and Valentin X 2018. Mistralazhdarcho maggii, gen. et sp. nov., a new azhdarchid pterosaur from the Upper Cretaceous of southeastern France. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2018.1502670.

The origin of the open acetabulum in dinosaurs: Egawa et al. 2018

Egawa et al. 2018
bring us “a morphogenetic mechanism of the acquisition of the open dinosaur-type acetabulum.” Using embryos, they found, “the avian perforated acetabulum develops via a secondary loss of cartilaginous tissue in the acetabular region.” 

Figure 2. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocritta.

Figure 2. The genesis of the Archosauria embodied in PVL 4597 to scale with a modern archosaur, Cyanocritta.

Phylogenetically
the open acetabulum develops as a semi-perforation (slight erosion of the inner wall) in PVL 4597 (Fig. 1), close to the last common ancestor of all archosaurs in the large reptile tree (LRT, 1308 taxa). It closes in all crocs (except Terrestrisuchus and Trialestes). It opens more (but not completely) in basal dinos. It opens completely in basal phytodinosaurs and theropods. It closes slightly in the ProcompsognathusMarasuchus clade of theropods. It also closes slightly in the paleognath (basal flightless bird theropod, Fig. 1) clade…

Figure 1. Acetabulum of Struthio.

Figure 1. Acetabulum of Struthio.

… and many other birds (Fig. 2).

Figure 2. Unidentified bird pelvis. Note the semi-closed acetabulum.

Figure 2. Unidentified bird pelvis. Note the semi-closed acetabulum.

The authors conclude,
“We hypothesize that during the emergence of dinosaurs, the pelvic anlagen became susceptible to the Wnt ligand, which led to the loss of the cartilaginous tissue and to the perforation in the acetabular region.”

Not sure why
the authors did not consider a comparison with phylogeny. It’s more interesting and visual.

On the same note…
certain aquatic taxa, like derived ichthyosaurs also have an open acetabulum due to the embryonic development of small, almost useless pelvic bones that fail to suture and close at the acetabulum.

References
Egawa S, Saito D, Abe  G ande Tamura K 2018. Morphogenetic mechanism of the acquisition of the dinosaur-type acetabulum. Royal Society Open Science 5(10): 180604 DOI: 10.1098/rsos.180604. http://rsos.royalsocietypublishing.org/content/5/10/180604