Portunatasaurus almost enters the LRT with dolichosaurs, not mosasaurs

Too few traits are present
for Portunatasaurus (Figs. 1–3) to be entered into the LRT without loss of resolution, but that shouldn’t stop us from figuring out what it is and what it isn’t.

Figure 1. Portunatasaurus compared to stem mosasaur, Aigialosaurus and to marine stem snake, Aphanizocnemus.

From the Mekarski et al. 2019 abstract:
“A new genus and species of plesiopedal mosasauroid, Portunatasaurus krambergeri, from the Cenomanian–Turonian (Late Cretaceous) of Croatia is described.”

Ooops. Taxon exclusion rears its ugly head again. In the large reptile tree (LRT, 1823+ taxa) Portunatasaurus (Fig. 1) is closer to aquatic snake ancestors, like Aphanizocnemus (Fig. 1), than a “plesiopedal mosasaurid.” Even with so few traits to test, moving Portunatasaurus closer to mosasaurs and aigialosaurs adds 4 steps. In the LRT Aphanizocnemus nests as a snake ancestor: a marine varanoid dolichosaur scleroglossan squamate.

Figure 2. Portunatasaurus diagram with corrections. Note the robust ribs, as in dolichosaurs. Mosasaurs and aigialosaurs have gracile ribs, a trait not tested in the LRT.

Mekarski et al. 2019 continue:
“An articulated skeleton, representing an animal roughly a meter long was found in 2008 on the island of Dugi Otok. The specimen is well represented from the anterior cervical series to the pelvis.”

There is no lumbar area in the Mekarsi et al. diagram (Fig. 2). Moving the pelvic area posteriorly to give Portunatasaurus a lumbar area agrees with other clade members. Note the robust ribs in Portunatasaurus, as in dolichosaurs. Mosasaurs and aigialosaurs (Fig. 1) have gracile ribs, a trait not tested in the LRT.

Figure 3. Portunatasaurus manus (right) and reconstructed with PILs (left).

Mekarski et al. 2019 continue:
“Preserved elements include cervical and dorsal vertebrae, rib fragments, pelvic fragments, and an exquisitely preserved right forelimb. The taxon possesses plesiomorphic characters such as terrestrial limbs and an elongate body similar to that of basal mosasauroids such as Aigialosaurus or Komensaurus, but also shares derived characteristics with mosasaurine mosasaurids such as Mosasaurus.”

Note: the authors appear to have omitted dolichosaurs from consideration. Dolichosaurs are not mentioned in the abstract. Let me know if this is an error. I have contacted Mekarski for a PDF.

“The articulated hand exhibits a unique anatomy that appears to be transitional in form between the terrestrially capable aigialosaurs and fully aquatic mosasaurines, including 10 ossified carpal elements (as in aigialosaurs), intermediately reduced pro- and epipodials, and a broad, flattened first metacarpal (as in mosasaurines).

Note: the authors appear to be not looking at dolichosaurs. Whenever an author uses the word “unique” it is a good bet that pertinent taxa have been omitted because nothing in “unique” in evolution. What is unique for one clade is commonplace in another.

“The new and unique limb anatomy contributes to a revised scenario of mosasauroid paddle evolution, whereby the abbreviation of the forelimb and the hydrofoil shape of the paddle evolves either earlier in the mosasaur lineage than previously thought or more times than previously considered.”

Authors rarely consider the number one problem in paleontology: taxon exclusion. They prefer those headline-grabbing words like “unique” so they can postulate newer hypotheses ‘than previously considered.” Well, don’t we all… but these authors/PhDs are paid to do this and not make mistakes in taxon exclusion that an amateur with an online cladogram can pick apart without actually seeing the specimen.

“The presence of this new genus, the third and geologically youngest species of aigialosaur from Croatia, suggests an unrealized diversity and ecological importance of this family within the shallow, Late Cretaceous Tethys Sea.”

I assume it is a coincidence that mosasaur ancestors and unrelated snake ancestors were both found in the earliest Late Cretaceous strata surrounding today’s Mediterranean Sea. Let me know of Mekarski et al. tested dolicohosaurs in their cladogram. I had access only to the abstract and some figures.

The paper [PDF] just arrived.
No phylogenetic analysis is provided. Aphanizocnemus is not mentioned. Other dolichosaurs are compared.

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References
Mekarski MC et al. 2019. Description of a new basal mosasauroid from the Late Cretaceous of Croatia, with comments on the evolution of the mosasauroid forelimb. Journal of Vertebrate Paleontology. 39: e1577872. doi:10.1080/02724634.2019.1577872.

wiki/Portunatasaurus

Cretaceous Aquilolamna nests with Devonian Palaeospondylus in the LRT

Summary for those in a hurry
The authors excluded related taxa that would have helped them identify their strange, new 1.6 m shark with elongate pectoral fins. The authors also failed to identify the correct mouth, eyes, nasal capsules and gill slits.

Vullo et al. 2021 bring us a wonderful new 1.6m Turonian elasmobranch
with graceful, really long, pectoral fins, Aquilolamna milarcae (INAH 2544 P.F.17, Figs. 1, 2). The authors tentatively assigned (without a phylogenetic analysis) their fossil shark to lamniformes, like the mako shark, Isurus, which has a standard underslung mouth and overhanging rostrum. Vullo et al. thought Aquilolamna was a filter-feeder by assuming that it had a wide, ‘near-terminal mouth’ without teeth, as in the manta ray (genus: Manta). That morphology is distinct from lamniformes like Isurus.

This is a difficult fossil to interpret.
More than the fins make Aquilolamna different than most other fossil and extant sharks.

Unfortunately
Vullo et al. put little effort (Fig. 2 diagram) into their attempt to understand the many clues Aquilolamna left us. Those clues are documented here (Fig. 2) by using DGS (= color tracings) and tetrapod homologs for skull bones.

Figure 1. Aquilolamna in situ from Vullo et al. 2021. Colors added here.

For proper identification, it didn’t help that Vullo et al. 

1. imagined the mouth wide and in front, instead of small and below the occiput
2. imagined the eyes on the sides, instead of on top
3. imagined the gill slits on the sides, instead of ventral
4. did not perform a phylogenetic analysis with a wide gamut of taxa
5. did not consider Middle Devonian Palaeospondylus (Figs. 3, 4) as a taxon worthy of their time and consideration
6. did not consider the torpedo ray, Tetronarce (Fig. 5), or the hammerhead, Sphyrna, taxa worth comparing in analysis (as in Fig. 4).

Figure 2. Skull of Aquilolamna and diagram from Vullo et al. 2021. Colors and new labels applied here. The mouth (magenta) appears under the occiput, overlooked by Vullo et al. White lines indicate symmetries. The hyomandibulars are small with fused quadrates at the new jaw corners and link to the intertemporals, as in all other vertebrates.

Despite these issues, Vullo et al. thought there was enough of Aquilolamna
that was strange, new and easy to understand to make it worthy of publication. And it is. And that’s okay. In science it’s okay to leave further details to other workers. Keeps us busy and feeling helpful! It’s okay to make mistakes. Others will fix those. That’s all part of the ongoing process.

From the abstract:
“Aquilolamna, tentatively assigned to Lamniformes, is characterized by hypertrophied, slender pectoral fins. This previously unknown body plan represents an unexpected evolutionary experimentation with underwater flight among sharks, more than 30 million years before the rise of manta and devil rays (Mobulidae), and shows that winglike pectoral fins have evolved independently in two distantly related clades of filter-feeding elasmobranchs.”

By contrast, in the LRT filter-feeding manta rays are more primitive than sharks that bite for a living.

Unfortunately the authors omitted important sister taxa recovered by the LRT from their comparison studies. They looked at other elamobranchs, but not the electric torpedo ray, hammerhead and Palaeospondylus (Figs. 3, 4).

By focusing on just a few traits the authors are trying to “Pull a Larry Martin.” Instead they should have performed a wide-gamut phylogenetic analysis with hundreds of traits.

Figure 3. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyrna family, that also includes the electric torpedo ray, Tetronarce.

Figure 4. Palaeospondylus diagram from Joss and Johanson 2007 who mistakenly considered Palaeospondylus a hatchling lungfish.

From the taphonomy section of the SuppData:
“No teeth can be observed in INAH 2544 P.F.17, possibly due to rapid post-mortem disarticulation and scattering affecting the dentition.”

Turns out the authors were looking for teeth in the wrong place. The real jaws with tiny teeth were partly hidden below the occiput, as in Middle Devonian Palaeospondylus (Fig. 4), not at the anterior skull rim of Aquilolamna.

Figure 4. Subset of the LRT focusing on the elasmobranch clades related to Aquilolamna and Palaeospondylus.

The reported lack of pelvic fins in Aquilolamna
is unexpected in sharks, which otherwise always have pelvic fins. This lack of pelvic fins could turn out to be a synapomporphy of taxa descending from Palaeospondylus. We’ll have to have more taxa for that.

From the Vullo et al. 2021 diagnosis of the ‘family, genus and species’:
“Medium-sized neoselachian shark that differs from all other selachimorphs in having hypertrophied, scythe-shaped plesodic pectoral fins whose span exceeds the total length of the animal. High number (~70) of anteriorly directed pectoral radials. Head short and broad, with wide and near-terminal mouth. Caudal fin markedly heterocercal. Caudal fin skeleton showing a high hypochordal ray angle (i.e., ventrally directed hypochordal rays). Caudal tip slender with no (or strongly reduced?) terminal lobe. Squamation strongly reduced (or completely absent?).”

Figure 5. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m). Note the robust caudal fin. The hyomandibular links the jaw joint to the braincase.

Aquilolamna has more vertebrae than Palaeospondylus,
but the former is much larger, an adult and geologically younger by 280 million years. We looked at Palaeospondylus just three days ago here. Very lucky timing to have Palaeospondylus for comparison prior to studying Aquilolamna.

Figure 6. Ontogenetic growth series of an electric torpedo ray from Madl and Yip 2000. Pectoral fins in green. Pectoral fins enlarge with maturity. Eyes migrate dorsally. Perhaps the same occurred with Aquilolamna and Palaeospondylus.

Taxon exclusion
continues to be the number one problem in paleontology. Phylogenetic analysis with a wide gamut of hundreds of taxa continues to be the number one solution to nesting all new and enigma taxa. Contra the assertions of dozens of PhDs, first-hand examination of the fossil is not required, nor is a degree or doctorate. This is the sort of profession where you learn on the job with every new taxon that comes along. This one was not in any textbooks, so everyone started like a September freshman with Aquilolamna.

And finally, if you can’t find the mouth where you think it should be,
look somewhere else.

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References
Madl P and Yip M 2000. Essay about the electric organ discharge (EOD) in Colloquial meeting of Chondrichthyes head by Goldschmid A, Salzberg, January 2000. Online here.
Vullo R, Frey E, Ifrim C, Gonzalez Gonzalez MA, Stinnesbeck ES and Stinnesbeck W 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science 371(6535): 1253-1256. DOI: 10.1126/science.abc1490
https://science.sciencemag.org/content/371/6535/1253

Online Publicity for Aquilolamna:

1. sciencemag.org/news/2021/03/eagle-shark-once-soared-through-ancient-seas-near-mexico
2. phys.org/news/2021-03-discovery-winged-shark-cretaceous-seas.html
3. nationalgeographic.com/science/article/shark-like-fossil-with-manta-wings-is-unlike-anything-seen-before
4. livescience.com/ancient-shark-flew-through-dinosaur-age-seas.html

Sinopterus? or Huaxiapterus? It gets confusing…

A kind reader alerted me to a misidentification here.
The grayscale image (Fig. x) is the ZMNH M 8131 specimen of Huaxiapterus. When a higher resolution image becomes available I will return to this specimen and edit the copy. With that in mind… here is the original blogpost, awaiting an edit.

Figure x. Huaxiapterus ZMNH-M-8131 specimen.. 

 

Thank goodness
for museum numbers.

Today the ZMNH M 8131 specimen first attributed to
Huaxiapterus corollatus (Lü et al. 2006) then renamed Sinopterus corollatus (Zhang et al. 2019; Figs. 1, 2) enters the the large pterosaur tree (LPT, 255 taxa) basal to tapejarids, derived from the Sinopterus atavismus specimen nesting basal to dsungaripterids.

Figure 1. Huaxiapterus corollatus ZMNH M 8131 reconstructed. An alternate m4.1 is provided that looks more like a m4.1 than a metacarpal 4.

Sometimes specimens are reassembled slightly wrong.
In this case several long bones were accidentally reversed end-to-end in this otherwise stunning mount. One never knows what the original fossil looked like prior to reassembly. We don’t want to call these ‘fakes’. We do want to be aware of errors and artistic reconstructions as much as is possible.

Figure 2. The ZMNH specimen in situ and somewhat corrected for original perspective issues. The correction makes the wings the same length. Be wary of such wonderful-looking fossils. This specimen appears to have been reassembled. Some long bones are reversed end-to-end, which do not affect scoring.

Sinopterus – Huaxiapterus corollatus (Lü et al. 2006; Early Cretaceous, ZMNH M 8131) is another largely complete specimen with confusing nomenclature. This taxon nests at the base of the Tapejara, basal to the Aathal specimen (below). The pelvis is missing. The sternum is among the largest of all pterosaurs. The cervicals are longer creating a taller pterosaur.

From the Lü et al. abstract:
“A new species of tapejarid pterosaur, Huaxiapterus corollatus sp. nov. is erected on the basis of a nearly complete skull and postcranial skeleton from the Lower Cretaceous Jiufotang Formation of Liaoning Province, China. Huaxiapterus corollatus sp. nov. is characterized by a hatchet-shaped rectangular process on the premaxilla, whose short axis is perpendicular to the anterior margin of the premaxillae. Except for this process, other characters of the skull such as the breadth of the snout between the anterior margin of the nasoantorbital fenestra and the anterior margin of the premaxilla are similar to that of Huaxiapterus jii.”

Figure 3. Huaxiaptrus iii and Huaxiapterus corollatus to scale. These two do not nest next to one another in the LPT.

The Lü et al. abstract continues
“Huaxiapterus and a second Chinese tapejarid, Sinopterus, share several unique cranial characters in common with Tapejara and these three genera appear to be more closely related to each other than to other azhdarchoids.

In the LPT azhdarchids nest with dorygnathids, not tapejarids. Adding these taxa missing from prior studies makes this inevitable.

“The Chinese tapejarids (Sinopterus and Huaxiapterus) have relatively elongate skulls and weakly developed cranial crests and seem to be less derived than Tapejara, with its shorter, deeper skull and large cranial crest. Tupuxuarids (Tupuxuara and Thalassodromeus) have often been associated with tapejarids in the family Tapejaridae, but this relationship is controversial because some phylogenetic analyses have supported the pairing of tupuxuarids with Azhdarchidae.”

Adding taxa moves Azhdarchidae away from tupuxuarids.

Figure 4. Tapejaridae in the LPT.

“We propose that Tapejaridae be restricted to Tapejara, Sinopterus and Huaxiapterus.”

The LPT does not support that proposal (Fig. 4). The Tapejaridae remains a monophyletic clade in the LPT derived from dsungaripterids, shenzhoupterids and earlier, germanodactylids… not azhdarchids.

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References
Lü JC, Jin XS, Unwin DM, Zhao LJ, Azuma Y and Ji Q 2006. A new species of Huaxiapterus Pterosauria: Pterodactyloidea from the Lower Cretaceous of western
Liaoning, China with comments on the system atics of tapejarid pterosaurs. Acta Geol Sinica English 80: 315-326.
Zhang X, Jiang S, Cheng X and Wang X 2019. New material of Sinopterus (Pterosauria, Tapejaridae) from the Early Cretaceous Jehol Biota of China. Anais da Academia Brasileira de Ciencias 91(2):e20180756. DOI 10.1590/0001-3765201920180756.

wiki/Sinopterus
wiki/Huaxiapterus
reptileevolution.com/tapejaridae.htm

Growth pattern of a new large Romualdo pterosaur

Bantim et al. 2020 document
a new “pteranodontoid pterosaur with anhanguerid affinities (MPSC R 1935) from the Romualdo Formation (Lower Cretaceous, Aptian-Albian), is described here and provides one of the few cases where the ontogenetic stage is established by comparison of skeletal fusion and detailed osteohistological analyses.”

Figure 1. Excellent wing finger carpophalangeal joint from the Bantim et al. 2020 paper. Note the unfused sesamoid (extensor tendon process), a phylogenetic trait of lepidosaurs, not an ontogenetic trait of archosaurs, as phylogenetic analysis documents.

Continuing from the abstract
“The specimen … consists of a left forelimb, comprising an incomplete humerus, metacarpal IV, pteroid and digits I, II, III, IV, including unguals. This specimen has an estimated maximized wingspan of 7.6 meters, and despite its large dimensions, is considered as an ontogenetically immature individual. Where observable, all bone elements are unfused, such as the extensor tendon process of the first phalanx and the carpal series. The absence of some microstructures such as bone resorption cavities, endosteal lamellae, an external fundamental system (EFS), and growth marks support this interpretation. Potentially, this individual could have reached a gigantic wingspan, contributing to the hypothesis that such large flying reptiles might have been abundant during Aptian-Albian of what is now the northeastern portion of Brazil.”

Figure 2. Anhanguera.

By comparison,
coeval Anhanguera has a 4.6m (15 ft) wingspan. The largest complete ornithocheirid, SMNK PAL 1136 has a 6.6m wingspan.

Bone elements fuse and lack fusion
in phylogenetic patterns (rather than ontogenetic patterns) in the clade Pterosauria, as documented earlier here in 2012. That is why you can’t keep pretending pterosaurs are archosaurs and not expect problems like this to accumulate. Your professors are taking your time and money and giving you invalidated information.

Figure 5. Largest Pteranodon to scale with largest ornithocheirid, SMNS PAL 1136.

It is a continuing black mark on the paleo community
that pterosaurs continue to be considered archosaurs by paid professionals when phylogenetic analysis (and Peters 2007 and the LRT) nests pterosaurs with lepidosaurs. That is why pterosaurs have lepidosaur phylogenetic fusion patterns (Maison 2002, 2002) distinct from archosaur ontogenetic fusion patterns. Just add taxa colleagues. The pterosaur puzzle piece does not fit into the archosaur slot… everyone admits that. The pterosaur puzzle piece continues to fit perfectly and wonderfully in the fenestrasaur tritosaur lepidosaur slot.

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References
Bantim RAM et al. (5 co-authors) 2020. Osteohistology and growth pattern of a large pterosaur from the lower Cretaceous Romualdo formation of the Araripe basin, northeastern Brazil. Science Direct https://doi.org/10.1016/j.cretres.2020.104667
Maisano JA 2002. The potential utility of postnatal skeletal developmental patterns in squamate phylogenetics. Journal of Vertebrate Paleontology 22:82A.
Maisano JA 2002.Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.

https://pterosaurheresies.wordpress.com/2013/05/14/phylogenetic-fusion-patterns-in-pterosaurs/

Reconstructing the Cretaceous azhdarchid Keresdrakon

Kellner et al. 2019
presented a new Early or Late Cretaceous (Aptian or Campanian) toothless pterosaur preserved as several 3D bones, far from complete (Fig. 1). Keresdrakon vilsoni (CP.V 2069) was considered an “azhdarchoid pterodactyloid.” Unfortunately, neither clade is monophyletic when more taxa are added in the large pterosaur tree (LPT, 251 taxa). The authors report, “Keresdrakon vilsoni gen. et sp. nov. was recovered as a sister taxon of the tapejaridae.”

Figure 1. All that is known of Keresdrakon layered on top of a Quetzalcoatlus sp. specimen and the same ghosted and reduced to the size of Keresdrakon.

Perhaps too little of Keresdrakon is preserved
to add it to the LPT, but layering elements atop a previously completed image of the six-foot-tall Quetzalcoatlus specimen results in a pretty close match (Fig. 1). Overall Keresdrakon is about 64% the size of Q. sp. Proportionately manual 4.1 is longer than in Q. sp.

Ontogeny
The authors note, “the presence of these growth marks suggests that this bone belongsto an ontogenetically less developed individual compared to others.”

Figure 8 in Kellner et al. 2019 has a few identification errors.

1. a is the left ilium, not the left ischium
2. b and c are ischia, not pubes
3. d and e are pubes, not ischia

The coracoid identified in Kellner et al. 2020
is not co-osified to the scapula and is relatively small (Fig. 1). In pterosaurs ossification or lack thereof is phylogenetic, not ontogenetic. It’s also worth noting that basal taxa in the Azhdarcho clade also have an unfused scapula and coracoid with the coracoid often much smaller than the scapula. The tiny BSPG 1911 I 31 Solnhofen specimen is one such taxon.

Co-author, Alex Kellner, along with Wann Langston
published Q. sp. in 1996, so it’s a bit surprising that Q. sp. was not immediately seen as a close match to Keresdrakon.

Sympatry
Keresdrakon were found close to the tapejarid Caiuajara in desert sandstone.

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References
Kellner AWA and Langston W 1996. Cranial remains of Quetzalcoatlus (Pterosauria, Azhdarchidae) from late Cretaceous sediments of Big Bend National Park, Texas. – Journal of Vertebrate Paleontology 16: 222–231.
Kellner AWA, Weinschütz LC, Holgado B, Bantim RAM and Sayão JM 2019. A new toothless pterosaur (Pterodactyloidea) from Southern Brazil with insights into the paleoecology of a Cretaceous desert. Anais da Academia Brasileira de Ciencias 91: e20190768. DOI 10.1590/0001-3765201920190768

wiki/Quetzalcoatlus
wiki/Keresdrakon

Can the LPT identify a pterosaur known only by its palate (and a few cervicals)?

Updated January 17, 2022
with a new nesting for Hongshanopterus with another Early Cretaceous Hamipterus both derived from Darwinopterus.

Summary for those in a hurry:
Once the phylogeny of this specimen was determined (after considering all options in the LPT), the stratigraphic age of this specimen turned out to be the real surprise.

Wang et al. 2008
described a 22cm pterosaur skull exposed in palatal view (Fig. 1) from the Early Cretaceous Jiufotang Formation of Liaoning, China. Hongshanopterus lacustris (IVPP V14582) was considered a subadult individual. The robust, triangular teeth were flattened inside and out like those of other istiodactylids, but unlike other istiodactylids, the tooth row extended beyond the first third of the skull and in having some premaxillary teeth curved like sharp hooks.

Figure 1. Hongshanopterus in situ compared to Darwinopterus and Wukongopterus. Not an istiodactylid, but a wukongipterid. Here all are shown about half life size.

Witton 2012
nested Hongshanopterus in an unresolved clade with Pteranodon, Coloborhynchus and Haopterus.

Kellner et al. 2019 again
nested Hongshanopterus basal to the clade Istiodactylidae.

Figure x. Revised palate of Hongshanopterus palate.

By contrast
the large pterosaur tree (LPT, 251 taxa then, 261 taxa in 2022) nested Hongshanopterus with Hamipterus and Darwinopterus, far from any istiodactylids. It takes 5 extra steps to force fit Hongshanopterus in the base of the Istiodactylidae (and that’s using just the few characters visible in Hongshanopterus).

That makes Hongshanopterus the largest and latest surviving
wukongopterid (Fig. 2), a clade otherwise restricted to the Middle to Late Jurassic and a clade famous for having a ‘pterodactyloid’-grade skull with a more primitive long-trailed post-crania.

Figure xx. Hongshanopterus palate compared to Hamipterus and Darwinopterus. Added June 16, 2022.

A clade member,
Darwinopterus, was considered a transitional taxon leading to pterodactyloid-grade pterosaurs. Adding more taxa, as in the LPT, does not support that hypothesis. At present Darwinopterus is a terminal taxon leaving no descendants. Hongshanopterus is the only wukongopterid (so far) to make it into the Early Cretaceous… and it has the largest skull.

Figure 3. Click to enlarge. Anurognathids to scale. The adult of the IVPP embryo is 8x the size of the embryo, as in all other tested adult/embryo pairings.

Only a few basal pterosaurs survived into the Cretaceous.
The giant anurognathid embryo, IVPP V13758  (Fig. 3) is the only other basal pterosaur known at present to survive into the Cretaceous.

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References
Kellner AWA et al. (6 co-authors) 2019. First complete pterosaur from the Afro-Arabian continent: insight into pterodactyloid diversity. Nature.com/ScientificReports 9:17875. PDF
Wang X, de Almeida Campos D, Zhou Z and Kellner AWA 2008. A primitive istiodactylid pterosaur (Pterodactyloidea) from the Jiufotang Formation (Early Cretaceous), northeast China. Zootaxa. 1813: 1–18.
Witton MP 2012. “New Insights into the Skull of Istiodactylus latidens (Ornithocheiroidea, Pterodactyloidea)”. PLoS ONE. 7 (3): e33170.

wiki/Hongshanopterus
wiki/Wukongopteridae

Albian South Korean tracks do not match Monjurosuchus

Lee et al. 2020 describe
“a new quadrupedal trackway found in the Lower Cretaceous Daegu Formation (Albian) in the vicinity of Ulsan Metropolitan City, South Korea, in 2018. A total of nine manus-pes imprints show a strong heteropodous quadrupedal trackway (length ratio is 1:3.36). Both manus and pes tracks are pentadactyl with claw marks. The manus prints rotate distinctly outward while the pes prints are nearly parallel to the direction of travel. The functional axis in manus and pes imprints suggests that the trackmaker moved along the medial side during the stroke progressions (entaxonic), indicating weight support on the inner side of the limbs. There is an indication of webbing between the pedal digits. These new tracks are assigned to Novapes ulsanensis, n. ichnogen., n. ichnosp., which are well-matched not only with foot skeletons and body size of Monjurosuchus but also the fossil record of choristoderes in East Asia, thereby N. ulsanensis could be made by a monjurosuchid-like choristoderan and represent the first possible choristoderan trackway from Asia.”

Not sure why they say they have a “well-matched”
foot skeleton and body size for Monjurosuchus. That does not appear to be true (Fig. 1). Other coeval mammal-mimic trackmakers, like Repenomamus, appear to match better (Fig. 1).

Figure 1. Novapes tracks from Lee et al. 2020 matched to little Monjurosuchus (lower left) and Repenomamus (upper right) and Repenomamus overall. Croc tracks are similar but the pes lacks digit 5.

Images provided by Lee et al.
indicate digits of nearly equal length on both manus and pes. Unfortunately the choristoderan, Monjurosuchus (Fig. 1) is too small and digit 4 on both manus and pes the longest on a sprawling (not erect) hind limb. Not a good match.

A better match can be found
in the mammal-mimic Repenomamus. It is the correct size, shape and coeval with the trackmaker of Novapes. Repenomamus is not mentioned by Lee et al. 2020. A Repenomamus relative, Liaoconodon, better preserves the extremities, but the manus and pes are similar in size.

Repenomamus and Liaoconodon are found in
the nearby Yixian Formation, NE China, Albian, late Early Cretaceous, 125 mya. Novapes is also from the Albian, late Early Cretaceous, nearby in South Korea.

Novapes diagnosis from Lee et al. 2020:
Monjurosuchus (M: yes, no); Repenomamus (R: yes, no)

1. Quadrupedal tracks with a pronounced heteropody; (M no; R yes)
2. Pentadactyl manus impression with claw marks and semi-symmetrical outline (M yes; R yes)
3. Manus wider than longer (M no; R yes)
4. Divergence between digit I and V imprints ranges 180° to 210°; (M no; R yes)
5. Digit IV imprint slightly longer than digit II; (M yes; R yes)
6. Entaxonic manus (medial digits more robust than lateral digits); (M no; R no; Novapes no)
7. Pentadactyl pes impression with claw marks and asymmetrical outline (i.e., lateral digits are more developed) (M yes; R yes)
8. Longer than wide; (M yes; R yes)
9. Webbing between the proximal portion of slender digits; (M ?; R?)
10. The subequal digits III and IV imprints longer than others (M 4>3; R 4=3)
11. Digit I imprint only 30% in length of the digit IV imprint); (M yes; R yes)
12. The sole pad impression is elongate with a U-shaped “heel”; (M no; R yes)
13. Entaxonic pes (M no; R no; Novapes no)

Ichnites are sometimes difficult to match to trackmakers, 
but some trackmakers can be eliminated. The possibility of a mammal-mimic trackmaker, like Repenomamus, should not be omitted from consideration.

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References
Lee Y-N, Kong D-Y and Jung SH 2020. The first possible choristoderan trackway from the Lower Cretaceous Daegu Formation of South Korea and its implications on choristoderan locomotion. Nature Scientific Reports 10:14442 https://doi.org/10.1038/s41598-020-71384-1

More details on Parahesperornis

Bell and Chiappe 2020
provide additional insight and valuable photos of Parahesperornis alexi (Martin 1984; Fig. 1; Late Cretaceous ~90 mya) a smaller sister/ancestor to Hesperornis (Fig. 1) with more plesiomorphic traits.

Figure 1. Parahesperornis (from Bell and Chiappe 2020) compared to Hesperornis (Marsh 1890) to scale and not to scale. Everything is exaggerated in the derived taxon, Hesperornis.

Backstory
According to Bell and Chiappe, “The Hesperornithiformes constitute the first known avian lineage to secondarily lose flight in exchange for the evolution of a highly derived foot-propelled diving lifestyle, thus representing the first lineage of truly aquatic birds. First unearthed in the 19th century, and today known from numerous Late Cretaceous (Cenomanian-Maastrichtian) sites distributed across the northern hemisphere, these toothed birds have become icons of early avian evolution.”

Figure 2. Hesperornis cladogram from Bell and Chiappe 2020. Compare to LRT results in figure 3 where more taxa are tested and nested. Gansus should be closer to Hesperornis. Many taxa are omitted between Archaeopteryx and Asparavis here.

Figure 3. Click to enlarge. Toothed birds of the Cretaceous to scale. Compare to figure 2. See the difference when more taxa are added.

Cladistics
Bell and Chiappe and the Large Reptile Tree (LRT, 1694+ taxa, illustrated in figure 3) are in broad agreement regarding the phylogenetic nesting of Parahesperornis (Fig. 2). Unfortunately, Bell and Chiappe don’t include enough taxa to understand the nesting of toothed birds within the clade of toothless birds, as recovered by the LRT (Fig. 3).

And what the heck 
are Gallus, the chicken, and Anas, the duck, doing in figure 2 nesting together? They are not related to one another in the LRT, but… (and here’s the key)… absent ANY pertinent transitional taxa, figure 2 is actually correct, a match with the LRT. Taxon exclusion delivers this oversimplified and misinforming cladogram (Fig. 2). More taxa, not more characters, makes a cladogram more and more accurate.

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References
Bell A and Chiappe LM 2020. Anatomy of Parahesperornis: Evolutionary Mosaicism
in the Cretaceous Hesperornithiformes (Aves). Life 2020, 10, 62; doi:10.3390/life10050062
Marsh, OC 1880. Odontornithes, a Monograph on the Extinct Toothed Birds of North America. Government Printing Office, Washington DC.
Martin L 1984. A new Hesperornithid and the relationships of the Mesozoic birds. Transactions of the Kansas Academy of Science 87:141-150.

wiki/Hesperornis

Plesiosaur necks: not so flexible after all

With a neck WAAAYYY longer than half the total length
elasmosaurs, like Albertonectes (Figs. 1, 2), have been traditionally referred to as ‘a snake threaded through a sea turtle’ (going back to the Buckland lectures 1832, full story online here). Snakes have no trouble swimming, but so far, paleontologists have not considered the long, minimally flexible neck of elasmosaurs a propulsive organ, as in sea snakes. That might change a little today.

Figure 1. A weak attempt at making sea snake-like sine waves in the neck of Albertonectes. Note the minimum of bending through effort. Relaxation realigned the neck.

Earlier a vertical configuration was suggested
to explain the weird and extreme morphology of elasmosaurs, entering fish and squid schools from below, distinct from all other oceanic predators. While the flippers were powerful propulsive organs for long distance, when it came to fine tuning while hovering, perhaps the increasingly longer (Fig. 2), snake-like necks helped some. It also moved the bulky flapping torso further from the mouth, so the school of fish would be less and less  likely to notice the intruder in the middle.

Figure 2. Click to enlarge. Albertonectes reconstructed. This 11 m elasmosaur is the longest thusfar recorded. This may be the breathing pose, swallowing air, then submerging the neck. When horizontal the air could be passed back to the lungs, as hypothesized for Dinocephalosaurus.

By contrast, Noe, Taylor and Gomez-Perez 2017 reported,
“Based on the anatomy of the articular faces of contiguous cervical vertebral centra, neural arches, and cervical ribs, the plesiosaur neck was mainly adapted for ventral bending, with dorsal, lateral and rotational movements all relatively restricted. A new model is proposed for the plesiosaur bauplan, comprising the head as a filter, straining, sieve feeding or sediment raking apparatus, mounted on a neck which acted as a stiff but ventrally flexible feeding tube, attached to the body which acted as a highly mobile feeding platform.”

“The neck increased drag due to its form and large surface area, but was also potentially part of an integrated locomotor system, for instance affecting steering (as it lies in front of the locomotor apparatus) and because the rear of the neck acted as anchorage for musculature from the anterior limb girdles. Hence, any explanation of neck function should consider both slow speed locomotion and more rapid movement during respiration, feeding and predator avoidance.”

Their study looked at
Muraenosaurus (Figs. 3, 4), Cryptoclidus and Tricleidus (none if these yet in the LRT) as exemplars of long-necked plesiosaurians. All are related to one another, not to elasmosaurs. Noe, Taylor and Gomez-Perez presented a history of plesiosaur neck interpretation and presented their own interpretation (ventral flexion, Fig. 5). Given that comprehensive review, apparently no prior workers envisioned a sea-snake analog for the long neck of elasmosaurs, nor have any envisioned a vertical feeding orientation.

Figure 2. Muraenosaurus in dorsal and lateral views. Compare to figure 1.

Rather than a flexible ball-and-socket joint
between cervicals, each plesiosaur vertebra consisted of a spool-shaped centrum with flat or slightly concave articular surfaces (Fig. 4). Most cervical centra are wider than deep. according to Noe, Taylor and Gomez-Perez, but that is largely due to a dorsal indentation for the neural spine. Cervicals preserved in situ indicate no intervening cartilage between centra. So, think of plesiosaur centra as Incan wall stones. There are no spaces between either. This compaction between vertebrae greatly restricts movement between individual cervicals and restricts cervical movement overall. Even so, even half a degree per centrum magnified by 76 cervicals can add up (Fig. 1) permitting some movement. Short, L-shaped cervical ribs are fused to each centrum.Their distal processes do not articulate with one another, but hypothetical ligaments extending from anteroposteriorly-oriented distal tips may have done so.

Figure 4. Muraenosaurus cervical sections from Noe et al. 2017 alongside a ghosted diagram of a complete Muraenosaurus neck. The space between centra can be compared to the space between Incan wall stones. In other words: none. That is not shown in the ghosted reconstruction.

Noe, Taylor and Gomez-Perez conclude,
“The consistent presence of numerous cervical segments that lack bony stiffening adaptations, however, is also strong evidence that flexibility was an important functional element in plesiosaur necks (Evans 1993), and gives the potential for a considerable range of movement in the living animal (cf. Zarnik 1925–1926).” The authors compare plesiosaurs to stiff-necked tanystropheids (with only 12 cervicals) to emphasize their point. They overlooked the tight articulations of each centrum with its neighbors. 

From a historical perspective, Noe, Taylor and Gomez-Perez report, 
“Previous workers have considered the degree of neck flexibility in plesiosaurs to range from: extreme mobility (Hawkins 1840; Zarnik 1925–1926; Welles 1943; Welles and Bump 1949), including the ability to arch the neck like a swan (Conybeare 1824; Andrews 1910; Brown 1981b); through relative inflexibility (Hutchinson 1897; Williston 1914; North 1933; Shuler 1950; Storrs 1997); to almost complete rigidity (Buckland 1836; Watson 1924, 1951; Cruickshank and Fordyce 2002; Figs. 3, 9); although some of this variation in interpretation may be due to differences between the species studied (Watson 1924, 1951).”

Clearly some of these workers were right and others were wrong.
But which ones? Zoe, Taylor and Gomez-Perez conclude, to their credit, “Overall, the range of movement available to the plesiosaur neck was strictly limited.”

Figure 5. Illustration from Noe, Taylor and Perez-Gomez showing their view of plesiosaur feeding and escape configurations. Usually paleo illustrations are more anatomically accurate than this.

Elasmosaurs were morphologically different than anything else in the sea. 
And they became more and more different as time went by (Fig. 2). So, something was working better and better as evolution selected for more extreme neck lengths.

Once again, let’s broaden our scope and look at the environs,
including coeval predators. All of these were robust, fast, streamlined, short-neck predators that swam horizontally preceding an attack from outside in. All of this is the opposite of elasmosaurs who hypothetically loitered below schools of fish unobtrusively rising to slip only their head in from below with minimum turbulence in order to remove fish or squid at leisure from the inside out.

Plesiosaur respiration at the surface
had to take place horizontally due to air pressure constraints. Alternatively, elasmosaurs could have gulped air, then assumed a horizontal or diving orientation to let the air bubble travel back through their long neck back or up to their lungs. With such tiny nostrils, gulping air seems more reasonable than narial inhalation.

Exhalation could have been more leisurely
and might have involved producing a ‘bubble net’ from stale air stored in the long trachea and released through the tiny nares. Extant baleen whales sometimes produce a bubble net to herd fish and plankton as they rise to feed on them. Perhaps elasmosaurs did the same, again based on their vertical orientation.

Fins at all four corners
Noe, Taylor and Gomez-Perez report, “With limbs at the four corners of the body, plesiosaurs could potentially produce vectored thrust from different limbs, to provide fine control of movement in all directions, and around all axes. This is more useful in slow swimming or hovering animals than simple shark-like control fins, which require movement in order to generate a current over the control surfaces.” Exactly. Unfortunately, these authors did not consider plesiosaurs to have a vertical orientation. Instead they focused on the ability of the neck to flex ventrally from a horizontal orientation.

Stomach stones
Noe, Taylor and Gomez-Perez report, “Swimming efficiency was further impaired by the mass of the neck, and the stomach stones commonly preserved in plesiosaurs. This stone ballast was probably needed to establish trim control and longitudinal stability to enable the animal to swim slowly horizontally and to hover, especially when diving in shallow water when the animal was positively buoyant.” The other explanation is that stomach stones helped weight the body below the more buoyant neck (filled with stagnant air), again supporting a vertical orientation when not swimming to other locations.

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References
Noe LF, Taylor MA and Gomez-Perez M 2017. An integrated approach to understanding the role of the long neck in plesiosaurs. Acta Palaeontologica Polonica 62 (1): 137–162.

Mononykus and Shuvuuia: Cretaceous tickbirds

Traditionally
the small, but extremely robust hand claws of Mononykus and Shuvuuia (Figs. 1, 2) were considered digging tools. If so, their forelimbs would have been distinctly different from the digging forelimbs of all other fossorial tetrapods based on size alone, not to mention the rest of the bird-like morphology that does nothing to support a digging hypothesis.

Figure 1. Forelimb of Mononykus. Large deltopectoral crest pulls humerus toward the sternum like a clasp.

Maybe there’s another answer.
For a moment, let’s not focus on Mononykus and Shuvuuia. Let’s broaden our view to see what related taxa are doing with their forelimbs. Let’s see if phylogenetic bracketing and environment can provide clues to the Mononykus forelimb mystery.

Figure 2. Shuvuuia and Mononykus to scale in various poses. The odd digit 1 forelimb claws appear to be retained for clasping medial cylinders, like tree trunks and dinosaur backs. The forelimb is very strong. Click to enlarge.

Outgroup taxa
include Haplocheirus (Fig. 3) and, more distantly, Velociraptor (Fig. 3). These two have forelimbs more typical of theropods with three digits and digit 2 longer than 1. Both come with a reputation and ability to jump on large dinosaurs (Fig. 4).

That’s similar to
what extant tickbirds (oxpeckers) do to large African mammals (Fig. 4), though not with the intention of ripping into their flesh with a wicked pedal digit 2.

Figure 3. Haplocheirus sollers traced from several photos. This specimen is 15 million years older than Archaeopteryx and tens of million years older than dromaeosaurs and alvarezsarids. Click to enlarge. Note the robust pedal digit 2 and manual digit 1.Haplocheirus sollers (Choiniere et al. 2010 Late Jurassic, 150 mya, 2m long) is a a theropod dinosaur from the Jurassic that nests at the base of the alvarezsaurids (including Mononykus and Shuvuuia) and also basal to the Cretaceous dromaeosaurids (including Velociraptor), ~and~ basal to Jurassic proto-birds (including Aurornis, Fig. 2).

In modern day Africa
tickbirds are often seen happily perching atop rhinos and other larger mammals (Fig. 5), cleaning them of parasites and riding them like passengers on a bus… yet always able to fly away or jump off and run away.

To scale with other dinosaurs of their time and place
(Fig. 3) it becomes clear that alvarezsaurids and Mononykus were relatively about the size of tickbirds and able to do the same job (plucking off parasitic insects) for their mutual benefit.

Figure 4. Giant Deinocheirus, a contemporary of Mononykus, might have served as the host and dining room for a series of ever smaller and more specialized parasite eaters.

Clearly Mononykus and Shuvuuia are highly specialized
taxa leaving no descendants. In the large reptile tree (LRT, 1692+ taxa) these alvarezsaurids evolve from larger theropods like Hapolocheirus. As the ancestors of Mononoykus and Shuvuuia grew smaller, so did their forelimbs, pelvis, killer toe and teeth. These tiny theropods became more and more specialized for their insect-plucking, hitchhiking niche. As they became phylogenetically-miniaturized, smaller alvarezsaurids were able to hitch rides on smaller and smaller dinosaurs.

Figure 5. Tickbirds (oxpeckers) sitting atop a pair of rhinos, perhaps a modern analog for mononykids.

So the little adducting forelimbs of Mononykus and Shuvuuia
acted like little hair clips, keeping these little dinosaurs attached to the skin and feathers of their hosts. That’s really all they were good for. Not flying. Not flapping. Not digging. Not display. Just mighty adduction. Those tiny forelimbs with big thumbs were perfect for clipping to giant host dinosaurs. The long legs of Mononykus would have been just long enough to walk through high feathers, like a human walks through tall grass. Or to run and hop on one new dinosaur after another. Active and highly coordinated, alvarezsaurids would have had the same agility as modern birds when they cavort on tree branches, tree trunks and rhino backs, all without using their ‘hands.’

This may be a novel hypothesis.
If not, please provide a citation so I can promote it.

Added a day later in response to the above promise:
Thank you, Tyler. From the abstract: “I propose that bizarre structures may have served to defend against parasitic dorsal attacks from riding dromaeosaurs. Frequent dismounts from large living dinosaurs may explain the origin of feathers, gliding and avian flight.”

Fraser G 2014. “Bizarre Structures” Point to Dromaeosaurs as Parasites and a New Theory for the Origin of Avian Flight. The Journal of Paleontological Sciences: JPS.C.2014.01 PDF

In counterpoint, Fraser was postulating the origin of larger wings and feathers for dismounting dromaeosaurs. He also discussed the origin of frills, plates and spikes on large host herbivores to dissuade dromaesaurs from mounting in the first place. Unfortunately, nowhere does he discuss the alvarerzsaurids or Mononykus and the development of its bizarre tiny forelimbs. Evidently they were not on his ‘radar’. Even so, thank you for bringing this paper to my attention. A good read!

A few more data points and citations:

Velociraptor mongoliensis (Osborn 1924; Late Cretaceous, 75 mya; 6.8m long) The tail was long and stiffened with elongate chevrons and zygapophyses. The deep pubis was oriented posteriorly with a large pubic ‘boot’.

Haplocheirus sollers (Choiniere et al. 2010 Late Jurassic, 150 mya, 2m long) The tail was not stiffened with elongate accessory processes.

Mononykus olecranus (Perle et al, 1993; Late Cretaceous ~70 mya, 1 m in length) Only digit I remained full size on the stunted hand. The proximal ulna (the elbow)  was enlarged. The pubis was shorter and lacked a pubic boot.

Shuvuuia deserti (Chiappe, Norell and Clark 1998, Late Cretaceous) was smaller and retained digits 2 and 3 as vestiges.

Halszkaraptor escuilliei (Cau et al. 2017; Late Cretaceous) was originally considered an aquatic dromaeosaur related to Mahakala, but here nests with Shuvuuia. A distinctly different manual digit 3 was the longest, but the gracile thumb retained the largest claw. The hands did not act like hair clips.

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References
Cau A, et al. 2017. Synchrotron scanning reveals amphibious ecomorphology in a new clade of bird-like dinosaurs. Nature. doi:10.1038/nature24679
Chiappe LM, Norell MA and Clark JM 1998. The skull of a relative of the stem-group bird Mononykus. Nature, 392(6673): 275-278.
Choiniere JN, Xu X, Clark JM, Forster CA, Guo Y, Han F 2010. A basal alvarezsauroid theropod from the Early Late Jurassic of Xinjiang, China. Science 327 (5965): 571–574. Perle A, Norell MA, Chiappe LM and Clark JM 1993. Flightless bird from the Cretaceous of Mongolia. Nature 362:623-626.
Perle A, Chiappe LM, Rinchen B, Clark JM and Norell 1994. Skeletal Morphology of Mononykus olecranus (Theropoda: Avialae) from the Late Cretaceous of Mongolia. American Museum Novitates 3105:1-29.

wiki/Mononykus
wiki/Halszkaraptor
wiki/Shuvuuia

Here’s the blogpost that inspired this one.