EAVP 2021: Early protostegid turtle more like freshwater turtles

Rabit et al. 2021 studied a new Cretaceous hardshell turtle
and came up with contradictory conclusions.

From the abstract:
“Whether advanced marine adaptations like that of extant sea turtles (Chelonioidea) evolved once or twice in turtles remains unresolved owing to the contested relationships of Protostegidae, a Cretaceous extinct pelagic clade.”

This was resolved in February 2021 when the giant protostegid, Archelon, was added to the large reptile tree (LRT, 1890+ taxa, subset Fig. 1) and nested with fresh water snapping turtles, like Macrochelys, a taxon omitted from prior sea turtle cladograms.

Figure 1. Subset of the LRT focusing on turtle origins.
Figure 1. Subset of the LRT focusing on turtle origins.

The Rabit et al. 2021 abstract continues:
“Fossils of protostegids are globally rare and the absence of species showing a transitional stage between littoral and pelagic adaptation precludes rigorously testing whether this clade is related to extant sea turtles or represents an earlier, convergent marine radiation.”

You don’t have to wait for that transitional fossil to be discovered. Add taxa. Run an analysis. This is exactly why cladograms are useful.

“We report a new protostegid turtle from the Early Cretaceous Aptian Apón Formation of Venezuela based on a single, three dimensionally preserved, near-complete skull. This still unnamed taxon represents one of the oldest protostegids and is characterized by a narrow interorbital space, dorsolaterally oriented and relatively small-sized orbits, anteriorly sloping skull roof, relatively deep lower and upper temporal emarginations, and reduced vomer and cavum tympani. These traits are unlike those of other protostegid or chelonioid sea turtles but approximate the condition seen in freshwater turtles;”

Always wonderful to see new taxa — but wait a minute. The authors say this is “one of the oldest protostegids,” but they also say, “These traits are unlike those of other protostegid or chelonioid sea turtles.” What’s going on here?

“We hypothesize them [= these traits] as plesiomorphic. Parsimony analysis recovers this species as a basal protostegid on the stem-lineage of crown-sea turtles, indicating a single pelagization event during turtle evolution.”

Not a ‘single pelagization event’ according to the LRT. There were at least three entries of turtles into the sea. (Fig. 1). Freshwater turtles are mentioned (above), but snapping turtles are not mentioned in this abstract. Did they miss something? or deliberately holding back? Softshell turtles had their own marine entry, Ocepechelon.

“However, further (less derived) transitional forms are needed to rigorously test the global relationships of Protostegidae. The Venezuelan taxon nevertheless fills a considerable morphological gap in the early evolution of the group, perhaps corresponding to a littoral [=shore dwelling] phase. It represents only the third described protostegid from the Early Cretaceous southwestern Atlantic.”

I wish they hadn’t said,These traits are unlike those of other protostegid or chelonioid sea turtles” and then concluded they had “the third described protostegid“. Confusing and contradictory.

BTW, the “considerable morphological gap” disappears in the LRT with taxon inclusion. Be careful with unwarranted hyperbole. Looking forward to seeing this specimen and its cladogram published.

More details here.

Figure 1. Classic photos of Archelon in ventral and dorsal views.
Figure 2. Classic photos of Archelon in ventral and dorsal views.

References
Rabi M et al. 2021. Plesiomorphic morphology in an early protostegid turtle from the Cretaceous of Venezuela. EAVP 2021 abstracts.

EAVP 2021: You heard it here first: results support a Cretaceous origin for placental mammals

Carlisle, Sivestro and Donoghue 2021 report,
“Recent molecular clock analyses have suggested that placental mammals originated in the mid- to late Cretaceous, before the Cretaceous-Paleogene (K-Pg) mass extinction. However, there are no unequivocal fossils of placental mammals from the Cretaceous to support this.”

Incorrect. The large reptile tree (LRT, 1890+ taxa; subset Fig. 1) recovers several Cretaceous and Late Jurassic mammals as placentals (Fig. 1). Run your own tests. University textbooks must be behind the times if this is what students and workers believe coming out of Bristol.

Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.
Figure 1. Select basal cynodonts and mammals set chronologically. The divergence times for placentals (Eutheria), marsupials (Metatheria) and monotremes (Mammalia) are estimated here.

Carlisle, Sivestro and Donoghue 2021 continue,
“Definitive fossils of placental mammals only appear after the K-Pg boundary, at which point they rapidly radiate leading into the ‘Age of Mammals’.”

This should be the last time this myth is repeated or printed.

“Here we use the Bayesian Brownian Bridge model to estimate the age of origin of placental mammals based on the fossil record. The model uses fossil diversity through time to inform a random walk from the clade’s present-day diversity back to the estimated origin of the clade within a Bayesian framework. This model works well with clades that have poor fossil records, such as the early placental mammals, and does not require a phylogeny, thereby mitigating the lingering uncertainty over the branching pattern at the root of the placental tree of life.”

No reason to estimate. Just create a cladogram. It’s a powerful tool that readily answers many questions like this. Not sure why more students and professionals don’t do this. Leaving issues like this for retired amateurs is no way to run a profession. And don’t borrow someone else’s cladogram. Create your own. You’ll have a powerful tool you can use the rest of your career into retirement.

“Our results support a Cretaceous origin for placental mammals, in agreement with the molecular data, and demonstrate that the group was already present before the K-Pg mass extinction and experienced a radiation during the Paleogene. The Bayesian Brownian Bridge model can therefore help to reconcile paleontological data with molecular data when estimating the origin of clades.”

Who knows what their molecular data recovers? We do know that molecule clades, like Afrotheria and Laurasiatheria, too often deliver false positives. Please use traits, not deep time DNA. The title of this abstract is a wee bit misleading. The authors did not use fossils from Cretaceous and Jurassic strata. They used estimates.

References
Carlisle E, Silvestro D and Donoghue P 2021. The origin of placental mammals according to the fossil record. EAVP abstracts 2021.

Bayesian Brownian Bridge model

The shorebirds (Charadriiformes): traits vs molecules lead to taxon exclusion issues, again

Cerny and Natale 2021 sought to clarify
the ‘time tree’ of shorebirds (= Charadriiformes).

Unfortunately, severe taxon exclusion
(Fig. 2) and the use of genes (Fig. 1), rather than traits (Fig. 2), mars this bird study.

Figure 1. Cladogram from Cerny and Natale 2021 employing too many species and too few genera. See figure 2 for list of missing taxa.
Figure 2. Subset of the LRT focusing on water birds. Here many more genera are included, including hummingbirds, penguins and geese, all missing from the study by Cerny and Natale 2021 (colors match Fig. 1). Colored taxa found in Cerny and Natale are not all related to Charadrius (fourth from top) when based on traits. So genes produce a big mess.

From the abstract:
“Shorebirds (Charadriiformes) are a globally distributed clade of modern birds and, due to their ecological and morphological disparity, a frequent subject of comparative studies.”

Understatement. The large reptile tree (LRT, 1890+ taxa) indicates the morphological disparity of Charadrius relatives was MUCH greater (Fig. 3) than Cerny and Natale imagined.

Figure 2. Balearica compared to its sister in the LRT, Charadrius, the plover/kildeer.
Figure 3. Balearica compared to its close relative in the LRT, Charadrius, the plover/kildeer.

From the abstract:
“While molecular phylogenies have been instrumental to resolving the suprafamilial back bone of the charadriiform tree, several higher-level relationships, including the monophyly of plovers (Charadriidae) and the phylogenetic positions of several monotypic families have remained unclear.”

If you want to clarify relationships, don’t use molecules. Too often they deliver false positives in deep time studies. Cerny and Natale also used WAY too few taxa based on comparisons to the LRT, which employs a wider gamut of birds in order to minimize taxon exclusion.

“The timescale of shorebird evolution also remains uncertain as a result of extensive disagreements among the published divergence dating studies, stemming largely from different choices of fossil calibrations.”

Use traits. Not molecules.

“Here, we present the most comprehensive non-supertree phylogeny of shorebirds to date, based on a total-evidence dataset comprising 336 ingroup taxa (89% of all extant species), 24 loci (15 mitochondrial and 920 nuclear), and 69 morphological characters.”

That’s what they all say. If the Cerny and Natale study is “the most comprehensive” study, how did these authors manage to omit so many taxa published years earlier (Fig. 2)? They were blinkered (= having their blinders on).

“Our node-dating analyses consistently support a mid-Paleocene origin for the Charadriiformes and an early diversification for most major subclades.”

Probably earlier. We have Mid-Paleocene penguins, so penguin ancestors (Fig. 2) needed time to evolve from more primitive charadriformes.

Note
Charadrius (Fig. 2) is a phylogenetically miniaturized version of longer-legged ancestral taxa, like Balearica and Burhinus. Once again, this is neotony at work, creating new taxa, completely overlooked by Cerny and Natale who likely relied on textbooks to determine which birds were traditional charadriiformes and which were not.

Test your textbooks to make sure your textbooks are valid if they repeat results gained from gene studies. This is basic science, so you can find this out for yourself using your own observations. It doesn’t take a PhD or expensive equipment.

References
Černý D and Natale R 2021. Comprehensive taxon sampling and vetted fossils help clarify the time tree of shorebirds (Aves, Charadriiformes) bioRxiv 2021.07.15.452585; doi: https://doi.org/10.1101/2021.07.15.452585

EAVP 2021: Tridentinosaurus soft tissues

From the Rossi et al. 2021 abstract:
“Tridentinosaurus antiquus Leonardi 1959 is a nearly complete reptile-like tetrapod (possibly a member of the Protorosauria group) found in the Early Permian volcanic succession in Trentino Alto Adige, Italy.”

Possibly? Let’s not guess. Let’s find out what it is. In the large reptile tree (LRT, 1890+ taxa) Tridentinosaurus nests far from Protorosaurus, at the base of the Lepidosauriformes, at the base of the pseudo-rib gliding clade (Fig. 2).

Figure 1. Tridentinosaurus at 26.5 cm long is an Earliest Permian ancestor to Late Permian Coelurosauravus and Late Triassic Icarosaurus.
Figure 1. Tridentinosaurus at 26.5 cm long is an Earliest Permian ancestor to Late Permian Coelurosauravus and Late Triassic Icarosaurus.

From the Rossi et al. 2021 abstract:
“Its phylogenetic position is currently uncertain.”

See above. Don’t be lazy. A valid phylogenetic context is essential and, by their own admission, missing from this abstract.

Figure 2. Derived lepidosauriformes. The clade Pseudoribia includes the pseudo-rib gliders
Figure 2. Derived lepidosauriformes. The clade Pseudoribia includes the pseudo-rib gliders

The abstract continues:
“Soft tissues are reported in this specimen but their nature remains unclear. The specimen shows a defined black coloured body outline, alluding that most of the soft tissues are organically preserved. In the proximity of the shoulder and pelvic girdle, three-dimensionally preserved integumentary scales are evident; these are relatively small (ca. 1 x 2 mm) and rhomboidal in shape. Our study reveals that the integumentary scales are in fact osteoderms, formed by apatite with a pitted texture; no ultrastructure of the integument is preserved. The body outline and the abdomen are formed by anhedral crystals of apatite coupled with a small amount of carbon.”

And now, the kicker:
“We suggest that the body outline and the abdomen have been covered with a layer of black paint (e.g., Bone Black) perhaps to consolidate/protect the specimen. Our findings indicate the absence of soft tissues preserved in T. antiquus but the discovery of small rhomboidal osteoderms uncovers a new biological character that will support future phylogenetic studies of this ancient tetrapod.”

Future? There is a current online phylogenetic study (Fig. 2) into which Tridentinosaurus was added based on bone traits (not soft tissue outlines) back in 2016.

Tridentinosaurus antiquus 
(Early Permian, Dal Piaz 1932, Leonardi 1959, 26.5cm long; Museum of Paleontology of the University of Padua 26567). Ronchi et al. described the specimen as “a beautiful but biochronologically useless specimen of which only the out−line of the soft tissues is well preserved.” The volcanic sediments in Sardinia occur in Cisuralian / Sakmarian deposits 291 million years old.


References
Dal Piaz Gb. 1932 (1931). Scoperta degli avanzi di un rettile (lacertide) nei tufi compresi entro i porfidi quarziferi permiani del Trentino. Atti Soc. Ital. Progr. Scienze, XX Riunione, v. 2, pp. 280-281. [The discovery of the remains of a reptile (lacertide) in tuffs including within the Permian quartz porphyry of Trentino.]
Leonardi P 1959. Tridentinosaurus antiquus Gb. Dal Piaz, rettile protorosauro permiano del Trentino orientale. Memorie di Scienze Geologiche 21: 3–15.
Ronchi, A., Sacchi, E., Romano, M., and Nicosia, U. 2011. A huge caseid pelycosaur from north−western Sardinia and its bearing on European Permian stratigraphy and palaeobiogeography. Acta Palaeontologica Polonica 56 (4): 723–738.
Rossi V et al. 2021. New analyses of the “soft tissues” of the Italian tetrapod Tridentinosaurus antiquus. Insight on taphonomy and conservation history. EAVP abstract 2021.


Joermungandr bolti from the Mazon Creek enters the LRT

Recovered in exquisite detail by splitting a small, round, brown nodule,
tiny Joermungandr bolti (Fig. 1) was recently described by Mann, Calthorpe and Maddin 2021.

Figure 1. Joermungandr bolti from Mann, Calthorpe and Maddin 2021 shown about 2x life size on a 72 dpi monitor. Their diagram matched to their fossil photo and colors around the pectoral area added.
Figure 2. Joermungandr skull in situ and as traced by the authors (above). Colors added here (below). Many differences. Note: The skull is exposed in ventral view, the mandible in dorsal view, just the opposite of what we are used to seeing, but this is what happens when you split a nodule.

The authors did not describe
the skull (Fig. 2) precisely. Nor did they include pertinent sister taxa, like Kirktonecta in their analysis. As a result their cladogram was unable to correctly nest their new discovery. The large reptile tree (LRT, 1890+ taxa) nested tiny Joermungandr correctly and with complete resolution. Rather than assuming expertise, sometimes its better to pretend you don’t know what a taxon is in order to expand your taxon list to minimize the possibility of taxon exclusion. Omitting taxa results in phylogenetic chaos.

From the abstract:
“Here, we describe a new long-bodied recumbirostran, Joermungandr bolti gen. et sp. nov., known from a single part and counterpart concretion bearing a virtually complete skeleton. Uniquely, Joermungandr preserves a full suite of dorsal, flank and ventral dermal scales, together with a series of thinned and reduced gastralia. Investigation of these scales using scanning electron microscopy reveals ultrastructural ridge and pit morphologies, revealing complexities comparable to the scale ultrastructure of extant snakes and fossorial reptiles, which have scales modified for body-based propulsion and shedding substrate. Our new taxon also represents an important early record of an elongate recumbirostran bauplan, wherein several features linked to fossoriality, including a characteristic recumbent snout, are present.

Wikipedia reports, Not all phylogenetic analyses recognize Recumbirostra as a valid grouping.” Worse yet, Kirktonecta is not listed among the Recumbirostra. Worse yet, Joermungandr does not have a recumbi rostrum. If the authors were counting on a certain kind of snout on an elongate taxon, they were “Pulling a Larry Martin” to reduce the number of taxa competing to be sister taxa. Don’t do that.

We used parsimony phylogenetic methods to conduct phylogenetic analysis using the most recent recumbirostran-focused matrix.

The authors borrowed a cladogram. Don’t do that. Use your own.

“The analysis recovers Joermungandr within Recumbirostra with likely affinities to the sister clades Molgophidae and Brachystelechidae.

The published cladogram (their figure 5) has Synapsida and Eureptilia for outgroup taxa. According to the LRT, those are unrelated to Microsauria. According to the LRT, the authors needed more basal tetrapod outgroup taxa, omitted from the authors’ cladoram.

Figure 4. Subset of the LRT focusing on Microsauria and the nesting of Joermungandr with Kirktonecta and Asaphestera platyris.

From the abstract:
“Finally, we review integumentary patterns in Recumbirostra, noting reductions and losses of gastralia and osteoderms associated with body elongation and, thus, probably also associated with increased fossoriality.”

That’s nice, but without a valid phylogenetic context, such studies end up a waste of time. Microsaurs are not reptiles (= amniotes; see publicity title below). Microsaurs are basal tetrapods, not far from Reptilomorpha. The only living microsaurs are caecilians, burrowing, heavily scaled and limbless.

References
Mann A, Calthorpe AS and Maddin HC 2021. Joermungandr bolti, an exceptionally preserved ‘microsaur’ from the Mazon Creek Lagerstätte reveals patterns of integumentary evolution in Recumbirostra. Royal Society Open Science 8(7):

https://royalsocietypublishing.org/doi/10.1098/rsos.210319

Publicity
LiveScience: Tiny ancient reptile named after Thor’s world-ending nemesis

Lancelets and clams compared

Molluscs and chordates are getting closer and closer lately.
Earlier we looked at nautilus and lancelet similarities. Also earlier we looked at garden slug and hagfish similarities.

Today
we look at lancelet (Fig. 1) and clam (Fig. 2) similarities.

Figure 1. Extant lancelet (genus: Amphioxus) in cross section and lateral view. The gill basket nearly fills an atrium, which intakes water + food, sends the food into the intestine and expels the rest of the water. Compare to the clam in figure 2. Pretty much the same.
Figure 2. Clam diagrams modified from Markus Ruchter. As in lophorates, the rectum bends dorsally over the buccal cilia and mouth in clams compared to the straight intestine in lancelets (Fig. 1). The clam foot is homologoous with the lancelet tail. Both are used for digging backwards into the substrate. Both have an atrium for filtering plankton from sea water. Both have a stomach opening posterior to the atrium to collect plankton captured on mucous strands traveling along the atrial walls.

At first clams seem odd and inscrutable,
but when you simplify their structures (Fig. 2), many previously overlooked similarities to lancelets begin to appear. Lancelets (Fig. 1) have a straight intestine terminating below a terminal tail. Clams also have a terminal tail, but it is traditionally called a foot. In clams the stomach and intestine arch dorsally and terminate dorsal to the ciliated mouth (as in lophophorates), expanding to produce a funnel, as in Nautilus (which has a ventral funnel, likely due to a close, but separate ancestry from the clam).

The phylogenetic origin of the bilateral clam shell
remains a mystery at present. Ontogeny (Fig. 3) provides clues. Clam shells develop during the clam’s planktonic (= free-swimming) embryo stage, shortly after feeding commences and prior to settling on or burrowing tail first into the sea floor (like a lancelet, Figs. 1, 2).

Figure 3. Clam embryo development from fao.org. Though overall similar to the protostomate trochophore, the clam mouth appears at the oral pole surrounded by buccal cilia, as in lancelets, not at the equator, as in other protostomates. Not sure what the single strand arising from the oral pole is yet, but appears to be a swimming organ that is absorbed as the buccal cirri take over that job.

All molluscs are traditionally considered protostomates,
but note a subtle difference: the traditional protostomate trochophore (= early embryo) has a mouth that appears at the so-called equator (Fig. 3). By contrast the clam mouth appears in the middle of buccal cilia, at the oral pole, as in the lancelet. In clams, as in the nautilus, octopus and starfish, the buccal cilia double as organs of locomotion. This is distinct from lancelets that depend on their tail, not their mouth, to swim and dig. By this evidence, this early stage (Fig. 3) is where the switch from one to another took place, if ontogeny recapitulates phylogeny.

Both clams and lancelets have an atrium
for filtering plankton from sea water. Both have a stomach opening posterior to the atrium to collect plankton captured on mucous strands traveling along the atrial walls.

The benthic, burrowing, plankton-feeding lifestyle of a clam
(Fig. 2) remains very much like that of its unarmored ancestor, the lancelet (Fig. 1). The armored body looks extremely different, from the outside, but take away the armor and the similarities become more noticeable.

Lancelets came first.
They are closer in morphology to their elongate nematode ancestors (Fig. 4) and only develop buccal cilia as they near adulthood. In clams the buccal cilia appear early in embryology and take over as swimming organs. Timing is everything. And it looks more and more like the traditional phylum Mollusca is polyphyletic, like traditional diapsids, protorosaurs, pterodactyloids, turtles and whales.

Figure 4. From Mansfield et al. 2015. Lancelets do not go through a trochophore embryo stage, but rather quickly become elongate, like their nematode ancestors, during their planktonic, free-swimming stage. Note the temporary appearance of eyes and a tail better for swimming than digging along with a late appearance of buccal cilia, all key factors in the present hypothesis of interrelationships with molluscs. Lancelets are Ediacaran in origin.

This, too, appears to be a novel hypothesis of interrelationships.
If not please provide an earlier citation so I can promote it here.

References
Mansfield JH, Halaler E, Holland ND and Brent AE 2015. Development of somites and their derivatives in amphioxus, and implications for the evolution of vertebrate somites. EvoDevo 6(21): DOI 10.1186/s13227-015-0007-5

Clam hatchery: http://www.fao.org/3/y5720e/y5720e0a.htm

Lancelets and Nautilus compared

The comparison seems obvious now
The origin of the nautilus links back to the early chordate lancelet (Fig. 1). Details follow.

Figure 1. The lancelet (above) and nautilus (below) still share several traits in common despite their many differences after hundreds of years of evolution. See figure 2 for the correct number of cirri (18 per side) in a lancelet. The nautilus funnel is an extension of the rectum and anus (see figure 3) now exiting anteriorly.

And that’s not all.
Lesser known and less mobile lophophorates (like Phoronis, Fig. 2) are also derived from lancelets. According to Wikipedia, “Molecular phylogenetic analyses suggest that lophophorates are protostomes, but on morphological grounds they have been assessed as deuterostomes.” (More on this issue below).

Figure 2. Lancelets compared to Phoronis the lophophore. Note the migrations of the elongate rectum back to the oral area, as in Nautilus. Don’t overlook the difference. In Lophophorates, which include bryozoans and brachiopods, the rectum is dorsal to the mouth, as in snails. In Nautilus the anus and funnel are ventral to the mouth coincident with 180º torsion of the coiled shell and loss of the tail.

According to Wikipedia,
“Lophophorate, any of three phyla of aquatic invertebrate animals that possess a lophophore, a fan of ciliated tentacles around the mouth. … The lophophorates include the moss animals (phylum Bryozoa), lamp shells (phylum Brachiopoda), and phoronid worms (phylum Phoronida, Fig. 2).”

“The lophophore is a characteristic feeding organ possessed by three major groups of animals: the Brachiopoda, the Bryozoa, and. the Phoronida. The lophophore can most easily be described as a ring of tentacles, but it is often horseshoe-shaped or coiled.”

Here the lophophore is homologous
with the buccal cirri on lancelets, the tentacles of cephalopods, and the feet of echinoderms. In humans the same circum-oral structure, the orbicularis oris, forms the lips.

According to Wikipedia,
“The “tentacles” of the nautili are actually cirri (singular: cirrus), composed of long, soft, flexible appendages which are retractable into corresponding hardened sheaths. Unlike the 8–10 head appendages of coleoid cephalopods, nautiluses have many cirri. In the early embryonic stages of nautilus development a single molluscan foot differentiates into a total of 60–90 cirri, varying even within a species. Nautilus cirri also differ from the tentacles of some coleoids in that they are non-elastic and lack pads or suckers. Instead, nautilus cirri adhere to prey by means of their ridged surface.”

Figure 3. Nautilus external and internal anatomy. Note the migration of the rectum = funnel back to the oral area, as in lophophorates.

According to Wikipedia,
“The mouth consists of a parrot-like beak made up of two interlocking jaws capable of ripping the animal’s food— mostly crustaceans— from the rocks to which they are attached.”

“Unlike many other [all more derived] cephalopods, nautiluses do not have what many consider to be good vision; their eye structure is highly developed but lacks a solid lens. Whereas a sealed lens allows for the formation of highly focused and clear, detailed surrounding imagery, nautiluses have a simple pinhole eye open to the environment which only allows for the creation of correspondingly simple imagery.”

The rectum is dorsal to the mouth,
beneath the mantle (of all places!) in slugs and likewise beneath the coiled shell in snails, as in lophophorates (phoronids Fig. 2, bryozoans and brachiopods, ). By contrast, in Nautilus the rectum and funnel are ventral to the mouth — along with 180º torsion of the coiled shell and loss of the slug and lancelet tail. That shell torsion in free-swimming Nautilus keeps the air-filled empty chambers dorsal to the body for traditional orientation of the preoral lobe (= hood) dorsal to the buccal cirri (= tentacles) and mouth.

The protostomate question.
Molluscs are protostomates (the mouth appears from the first embryonic invaginatiion, then then anus appears later). Chordates and echinoderms are deuterostomates (= anus first, mouth second). Traditionally this has been considered a major division. Both clades arise from nematode (= roundworm) ancestors in which the mouth and anus appear at the same time. Since these all develop in yolk-filled eggs, embryos don’t have to feed, digest and defecate, so the mouth, intestine, rectum and anus are useless and subject to inconsequential genetic timing changes, especially at the planula-grade.

Genes determine the timing of trait appearances.
Genes both evolve and reverse. Though still helpful, this makes the timing of the first appearance of the mouth or anus in embryos not the big deal they teach in universities. Long time readers will be expecting this: “Don’t pull a Larry Martin!” Look at the entire organism, not just one, two or a dozen traits — especially embryo traits — no matter how traditional or established in text books and lectures.

Why did someone not see this before?
Perhaps because most workers are trained in universities where they have rules students must follow or risk displeasing their professors and failing tests. We’ve already seen how a support system among academics keeps myths alive while keeping out disruptive hypotheses.

The antiquity of hagfish and lancelets
extends into the Ediacaran (= the Pre-Cambrian). On hindsight it seems rather exceptional that such ancient and primitive creatures should traditionally lead, like a simple ladder, only toward vertebrates. Instead, now consider the idea that a wider range of taxa evolved from hagfish and lancelets, creating more of a topological bush, which would be more typical of evolutionary events in other lineages.

The connection between lancelets and nautiloids
appears to be a novel hypothesis of evolutionary interrelationships. If not, please provide a citation so I can promote it here.

[I found one with citations for others. The more recent citations discuss convergence, not homology and do not mention lancelets. See below].

Shigeno et al. 2010 wrote:
“In 1830, two young naturalists, Meyranx and Laurencet, attempted a comparison of the anatomy of vertebrates and cephalopods, speculating that they have the same basic structural principle. While Geoffroy St. Hilaire adopted the idea as proof of his theory, on the unity of body plan that is composed of shared components of all animals, Georges Cuvier rejected it using questionable results of his anatomical study of an octopus (Figure 1; Appel, 1987; Le Guyader, 2004 for reviews). Ever since this pre-Darwinian academic debate, many zoologists have indulged in a long lasting discussion of how the cephalopod body plan and their organ systems can be linked to those of vertebrates (e.g. Packard, 1972; O’Dor and Webber, 1986).”

PS
Shigeno et al. 2008 document the origin of the hood + eye separate from the mantle without an operculum with this image of a 3-month-old Nautilus embryo. Note the posterior funnel = anus, prior to the U-turn it takes in adults with the funnel beneath the mouth. Here the yolk sac is the mouth, not a gastropod-like foot. So the tentacles and funnel both rotate to the front during embryological ontogeny as the yolk sac is absorbed.

References
O’Dor RK and Webber DM 1986. The constraints on cephalopods: Why squid aren’t fish. Canadian Journal of Zoology 64: 1591–1605.
Packard A 1972. Cephalopods and fish: The limits of convergence. Biological Review vol. 47, p. 241-307.
Shigeno S, Sasaki T, Moritaki T, Kasugai T, Vecchione M, Agata K 2008. Evolution of the cephalopod head complex by assembly of multiple molluscan body parts: Evidence from Nautilus embryonic development. J Morphol 269(1):1-17. doi: 10.1002/jmor.10564. PMID: 17654542.
Shigeno S, Sasaki T and von Boletzky S 2010. The origins of cephalopod body plans: A geometrical and developmental basis for the evolution of vertebrate-like organ systems. Pp. 23-34 in Tanabe K., Shigeta Y., Sasaki T and Hirano H (eds) 2010. Cephalopods – Present and Past Tokai University Press, Tokyo.

wiki/Nautilus
wiki/Lancelet
wiki/Phoronis
wiki/Lophophore = buccal cilia
wiki/Lophophorata

For an opposing view:
A giant cephalopod (Endoceras) with a straight shell has ‘tripartite operculum’ homologous with the ‘hood’ of Nautilus in figure 1, thanks to Tyler Greenfield, whose cladogram does not include lancelets, but just goes back to the suprageneric taxon, “Cephalopoda’. Details here:

https://incertaesedisblog.wordpress.com/2020/02/16/reconstructing-fossil-cephalopods-endoceras/

Microleo: another possible sister to Thylacoleo

Microleo is a small fossil
marsupial taxon known from teeth and jaw fragments. So it will not enter the LRT— unless more of it becomes known someday. Microleo gathers minor fame by being related to a large, carnivorous marsupial, Thylacoleo (Fig. 1), featured in the video below.

Like the video, a recent Microleo paper
(Gillespie, Archer and Hand 2018) failed to include a number of taxa related to Thylacoleo, including Petaurus (Figs. 1, 2), the extant sugar glider. Petaurus nests as a sister to Thylacoleo whenever the two are tested in the same analysis (Fig. 3).

Figure 2. Thylacoleo skeleton compared to Petaurus skeleton to scale.
Figure 1. Thylacoleo skeleton compared to Petaurus skeleton to scale.

Turns out
the sugar glider is the only living omnivore in an otherwise herbivorous clade, as noted in the video. Thylacoleo was not only larger, but less herbivorous (= more carnivorous). Which wraps up this matter rather neatly.

Figure 1. Petaurus breviceps skeleton in two views, plus a skull with mandible, lacking in the skeleton.
Figure 2. Petaurus breviceps skeleton in two views, plus a skull with mandible, lacking in the skeleton.

The authors report,
“Marsupial lions are the only carnivorous vombatiform marsupials as well as the only vombatiforms that have bunodont molars.”

These taxa are not wombats, as confirmed by the authors of the Microleo paper, who did not test any taxa related to sugar gliders.

Taxon exclusion mars this otherwise complete study.
As we learned earlier (in 2018) marsupial lions (Thylacoleo) are sugar gliders (Petaurus) and members of a marsupial clade apart from wombats. This clade includes all the weird-o taxa: Adalatherium, Paedotherium, Groberia, Vintana, along with some wonderful, but more ordinary extant taxa, including Balbaroo, Phalanger and Dactylopsia, all herbivores.

Figure 7. Subset of the LRT focusing on Metatheria (marsupials) including Paedotherium and Adalatherium.
Figure 3. Subset of the LRT focusing on Metatheria (marsupials) including Paedotherium and Adalatherium.

From the abstract
“Microleo attenboroughi, a new genus and species of diminutive marsupial lion
(Marsupialia: Thylacoleonidae), is described from early Miocene freshwater limestones
in the Riversleigh World Heritage Area, northwestern Queensland, Australia. A broken
palate that retains incomplete cheektooth rows demonstrates that this new, very small
marsupial lion possessed the elongate, trenchant P3 and predominantly subtriangular
upper molars characteristic of thylacoleonids, while other features of the premolar support
its placement in a new genus.”

Step 1. Understand the complete taxa. Step 2. Slowly sprinkle in the incomplete taxa.

“Phylogenetic analysis suggests that Microleo attenboroughi is the sister taxon to all other thylacoleonids, and that Thylacoleonidae may lie outside Vombatomorphia as the sister taxon of all other wombat-like marsupials including koalas.”

Just add taxa to find out.

“However, given limited data about the cranial morphology of M. attenboroughi, Thylacoleonidae is concluded here, conservatively, to be part of the vombatomorphian clade.”

No. Don’t do that! Don’t blame Microleo. Don’t just guess and don’t guess wrong. Don’t give up. Test more complete taxa. Then add incomplete taxa, like Microleo, more confidently.

“This new thylacoleonid brings to three the number of marsupial lion species that have been recovered from early Miocene deposits at Riversleigh and indicates a level of diversity previously not seen for this group. It is likely that the different size and morphology of the three sympatric taxa reflects niche partitioning and hence reduced competition. Thylacoleonids may have been the dominant arboreal predators of Cenozoic Australia.”

Figure 5. Dactylopsila skull and in vivo. This taxon bears a strong resemblance to Apatemys by convergence.
Figure 5. Dactylopsila skull and in vivo. This taxon bears a strong resemblance to Apatemys by convergence, but nests basal to Petaurus and Thylacoleo.
Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider.
Figure 4. Thylacoleo skull. Many times larger than Petaurus, with fewer larger teeth, this is a giant sugar glider.

References
Gillespie AK, Archer M and Hand SJ 2018. A tiny new marsupial lion (Marsupialia, Thylacoleonidae) from the early Miocene of Australia. Palaeontologia Electronica 19.2.26A: 1-26.

wiki/Microleo

Several pterosaur myths get a boost from Naish, Witton and Martin-Silverstone 2021

Naish, Witton and Martin-Silverstone 2021 team up
to promote just about every pterosaur myth out there. Roll up your sleeves if you want to continue through this mucky paper. Longtime readers will be familiar with the usual issues.

From the abstract:
“Competing views exist on the behaviour and lifestyle of pterosaurs during the earliest phases of life. A ‘flap-early’ model proposes that hatchlings were capable of independent life and flapping flight, a ‘fly-late’ model posits that juveniles were not flight capable until 50% of adult size, and a ‘glide-early’ model requires that young juveniles were flight-capable but only able to glide.”

Competing views? 1) There is no view that hatchlings were able to glide without flapping. Flapping precedes flight in pterosaur precursors. due to a locked-down, elongate coracoid. 2) The authors omit tiny adult pterosaurs with fly-sized hatchlings (Fig. 8). Tiny pterosaurs had to wait to fly due to surface area-to-volume constraints that would result in desiccation whenever removed from a damp leaf litter environment, as in extant tiny lizards. Four pterodactyloid-grade clades had their genesis with phylogenetic miniaturization.

“We argue that a young Sinopterus specimen has been mischaracterised as a distinct taxon.”

They are talking about Nemicolopterus, which is a tiny pterosaur more closely related to Shenzhoupterus (Fig. 1). There is no phylogenetic context in this paper. Shenzhoupterus is not mentioned in text.

Figure 1. Germanodactylus cristatus and members of the Shenzhoupteridae, Nemicolopterus and Shenzhoupterus.
Figure 1. Germanodactylus cristatus and members of the Shenzhoupteridae, Nemicolopterus and Shenzhoupterus.

Naish et al. continue,
“We further show that young juveniles were excellent gliders, albeit not reliant on specialist gliding.”

No. Not reliant. Gliding evolves after flapping in taxa capable of both.

“The wing forms of very young juveniles differ significantly from larger individuals, meaning that variation in speed, manoeuvrability, take-off angle and so on was present across a species as it matured.”

This is false. Late-stage embryos and hatchlings had adult proportions (Figs. 1, 3, 4, 8, 9).

See if you can find the internal conflict in these two abbreviated sentences
from the Naish et al. introduction. 1) “very young pterosaurs can be identified on the basis of both skeletal proportions and… osteological immaturity. 2) Even embryonic pterosaurs were well-ossified and adult-like in skeletal proportions.”

See if you can find the internal conflict in this sentence:
“Overall, their development recalls that of precocial sauropsids rather than the altricial offspring of neoavian birds.” (Hint: birds are traditional sauropsids, an invalid taxon not recovered by the LRT).

Naish et al. cite other authors who mix up phylogeny with ontogeny

Naish et al. cite authors who mix up early embryos with full-term embryos.

Naish et al. wander into an imaginary scenario
when they report, “It could be argued that a late development of flight in pterosaurs is consistent with the fact that the majority of extant volant vertebrates are incapable of flight in early life.” Stay with the evidence. Don’t wander.

Naish et al. have no idea what pterosaurs are.
Pterosaur egg shells are lizard-like because pterosaurs are lepidosaurs. The authors eschew a phylogenetic context. The keyword, “lepidosaur” does not appear in their text.

Throwing phylogeny out of the window,
the authors cite “Hone et al. [who] showed how skeletal proportions present across the ontogeny of Rhamphorhynchus are indicative of precociality and adult-like flight behaviour in hatchlings.” Hone et al. mixed phylogenetically miniaturized taxa with larger, later taxa. Whatever happened to ‘adult proportions’? Naish either want to have it both ways and hope nobody notices, or they don’t want to upset their firend. I don’t see any critical thinking or editing in this paper.

See if you can find the internal conflict in this sentence:
“Firstly, we modelled the gliding ability of hatchlings to assess whether their wing skeletons were sufficiently developed to support flight.” Gliding (like some squirrels) and flying (like birds and bats) should not be discussed in the same sentence. Those taxa able to glide and fly always flap first, glide later.

So far,
this paper is a prime example of looking for details when the overall setting is wrong to begin with. In other words, this paper is like trying to straighten a picture hanging on the wall while the whole house is being rapidly swept downstream in raging flood waters. The authors do not understand what pterosaur is before trying to understanding what their hatchlings were capable of. A valid phylogenetic context is needed here.

At this point, Naish et al. argue for the youth of Nemicolopterus.
Indeed, Nemicolopterus is much smaller than related taxa (Fig. 1). Phylogenetic analysis in the large pterosaur tree (LPT) nests Nemicolopterus with Shenzhoupterus, an adult taxon and possible parent. Shenzhoupterus is not mentioned by Naish et al. Instead they decide (without a cladogram) that Nemicolopterus is a juvenile Sinopterus… AND that various larger Sinopterus and Huaxiapterus taxa represent more mature specimens of a single species. When you play such phylogenetic games, making up relatives as you please, the concept of hard science has clearly left the building.

Figure 2. This comes from figure 2 in Naish et al. 2021 in which they mix up phylogeny with ontogeny. Remember when they said hatchlings had adult proportions? Here they forgot they said that.

Remember when Naish et al. said hatchlings had adult proportions?
Here (Fig. 1) they forgot they said that. They double down in their caption, which reads, “Note progressive change in skull shape and exaggeration of cranial crest in larger specimens, a feature consistent with cranial growth in other pterosaur species.”

At this point it is probably appropriate to remind readers
that hatchings and juveniles had adult proportions. See Pterodaustro (Fig. 3) and Zhejiangopterus (Fig. 4) for documentation of these examples.

Figure 1. The V263 specimen compared to other Pterodaustro specimens to scale.
Figure 3. The V263 specimen compared to other Pterodaustro specimens to scale. This demonstrates that hatchlings and juveniles from the same bone bed had adult proportions.
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 4. There are several specimens of Zhejiangopterus, all with adult proportions. Also shown is a hypothetical hatchling, 1/8 the size of the largest specimen.

Morphological changes in pterosaurs come via phylogeny and embryology.
Pteranodon arising from Germanodactylus is an easily seen example of this (Fig. 5).

Figure 2. The Tanking-Davis specimen compared to other forms. Specimen w and specimen z appear to be the closest to the Tanking-David specimen. Specimen 'w' = Pteranodon sternbergi? USNM 12167 (undescribed). Specimen 'z' = Pteranodon longiceps? Dawndraco? UALVP 24238. Click to enlarge.
Figure 5. Pteranodon skulls showing phylogenetic differences in phylogenetic order, not ontogenetic differences. Primitive taxa AND some derived taxa, had smaller crests.

At this point Naish et al. break out
their precise measurements and calculations and finish with a chart of gliding tetrapods, all adults other than the ‘hatchling pterosaurs’. No where on this chart do they include birds or bats. Nor do they include adult pterosaurs. We call that, “taxon exclusion.”

Naish et al. report,
“Our gliding calculations emphasise differences between gliding animals and hatchling pterosaurs, and thus raise the possibility that hatchlings were powered fliers.” No where do Naish et al spell out the single trait shared by powered fliers: an elongate, locked down coracoid (or clavicle in the case of bats). Gliders that never had powered flyer ancestors, lack this trait.

Naish et al. report,
“The robustness of pterosaur humeri has been linked to the demands of forelimb-assisted launch, and the exceptionally high humeral bending strengths of hatchlings leaves little doubt about launch capacity.”

We covered the extreme danger of the hypothetical and invalid forelimb-assisted launch earlier here (Fig. 6), along with the morphological errors (Fig. 7) ignored by its creator, Michael Habib and embraced by Naish, Witton and Martin-Silverstone.

Unsuccessul Pteranodon wing launch based on Habib (2008).
Figure 6. Unsuccessul Pteranodon wing launch based on Habib (2008) in which the initial propulsion was not enough to permit wing unfolding and the first downstroke.
Figure 9. Quad launch hypothesis from Habib's SciAm article. He cheats the position of metacarpals 1-3 and does not show what happens after the leap.
Figure 7. Quad launch hypothesis from Habib’s SciAm article. He cheats the position of metacarpals 1-3 (they should not appear on the dorsal surface, but anterior to digit 4) and does not show what happens after the leap. Metacarpal 4 never makes an impression in pterosaur tracks.
The smallest known pterosaur, bird and lizard.
Figure 8. The smallest known adult pterosaur, bird and lizard to scale. Behind no. 6 is a hypothetical hatchling, no larger than a housefly and the IVPP embryo, larger than the adult no. 6.

Some things are difficult if not impossible for Naish et al. as they report,
“It is difficult if not impossible to state precisely when hatchling pterosaurs began to fly given that presently unknowable factors—possible parenting behaviours, hatchling coordination, last-minute soft-tissue development, the nature of nesting environments and so on—likely influenced this, as they do in living megapodes.”

Sadly, these three pterosaur experts do not attempt a reconstruction of the IVPP embryo (Fig. 8), or the JZMP embryo (Fig. 9) or cite those who have done this already. These embryos were definitely ready to fly without the need for ‘last minute soft-tissue development.’

JZMP-03-03-2
Figure 9. The JZMP-03-03-2 embryo reconstructed at bottom, restored to an 8x larger adult and compared with related taxa. This embryo was ready to fly immediately after hatching. There was no need for parental care.

Over and over Naish et al. 2021 give the impression
that they don’t like to include more taxa, that they don’t like cladograms, that they don’t like tracing bones (their caption 2 confesses, “Skulls redrawn from the literature”), that they are often 15 years behind the times when they embrace then deny the fact that pterosaur hatchlings and embryos are identical to their parents (Figs. 3, 4).

When Naish et al. 2021 report,
“Our results are further evidence of pterosaur hatchlings being highly precocial and potentially capable of living independently of their parents.” It’s okay if you’re not excited. We’ve known this for 16 years.

Naish et al. report their thoughts on parenting,
when they have no evidence for it, or against it. They just wander through it. With a valid phylogenetic context, they could have said, “The hatchlings of the tuatara receive no parental care and have to fend for themselves.” They could also have said, “As in other lepidosaurs, pterosaur mothers retained her pterosaur egg(s) within her uterus until ready for hatching.” That explains the Hamipterus assemblage where empty eggs and skeletons were found swept together after asphyxiation during pregnancy and later decay.

Naish et al. report,
With reduced flight speeds and lesser glide performance (Table 2), hatchling Sinopterus and Pterodaustro would not have been as efficient as their parents at long-distance travel.”

They ignore the simple fact that relative distances for tiny hatchlings are 8x greater AND hatchlings have proportionally smaller body stores. Moving deeper into conjecture, the authors report, “these attributes might have rendered juvenile pterosaurs more dynamic fliers than their parents, better able to switch between aerial and terrestrial locomotion, better suited to executing sudden changes in direction and velocity, and capable of nimbler flight in complex environments.”

No comparisons can be made with arctic terns, who raise altricious plover-like hatchlings for several weeks before fledging. But shortly after doing so, young terns are able to migrate from pole to pole twice a year.

Naish et al. report,
“The changes in wing form that pterosaurs underwent during growth might not be viewed as strictly adaptive because much of their effect on flight reflect unavoidable laws of scaling.”

This is false and contradicts earlier text. As shown above (Figs. 3, 4, 8, 9), pterosaur embryos and hatchlings all have adult proportions from skull to wing form and elsewhere. Only the size changes.

Naish et al. report the obvious,
“many pterosaurs were large animals with small offspring, creating large intraspecific size ranges and the potential for multiple potential niches.”

All adult pterosaurs are 8x larger from available data. You bet they are going to go after different prey.

Naish et al. confess:
“We stress that the concepts outlined here are hypothetical.” Usually Nature doesn’t get into such hypothetical studies, preferring instead to document new exciting fossil discoveries that break new ground. As you can see, it’s not always good to have friends who support your ideas. Chris Bennett is still out there. He is listed as one of those who provided “comments that improved the manuscript substantially.”

With all the above disregard for morphology and phylogeny by Naish et al.,
you might ask yourself, why was this paper published in Nature? Answer: The authors have academic friends who are editors and referees who like what they are saying, just like any other paper. That doesn’t mean they are correct. Nature has published a long list of paleo mistakes all listed and chronicled here, only a few of which they have owned up to.

Congratulations to Naish, Witton and Martin-Silverstone
Nature has never published such a raft of conjecture, fantasy and misinformation.

References
Naish D, Witton MP and Martin-Silverstone E 2021. Powered flight in hatchling pterosaurs: evidence from wing form and bone strength. Sci Rep 11, 13130 (2021). https://doi.org/10.1038/s41598-021-92499-z

ResearchGate.org: First juvenile Rhamphorhynchus

This just in
from Tetzoo.com, Darren Naish’s website. “The novelty of our study, is that we use specific tests to better establish these models [pterosaur superprecociality or ontogenetic niche partitioning] over others that have been presented, and that we propose more finely honed ideas on the ways in which hatchlings and young juveniles might have differed from older juveniles and adults.”

Naish also provides “a ridiculous backstory.” According to him the project has been on the burner since 2008. Naish writes, “The problem with doing science in your ‘spare time’ (neither myself, Mark or Liz are salaried research scientists: any scientific writing or research we do happens in ‘spare time’), is that it’s very hard to find time to do things like deal with the rewrites and new tests demanded by peer review.” So there you have it, a little insight into the process.

Figure w. Pterosaur egg data from Naish, Tetzoo.com. The authors, both artists, refuse to dive in and attempt a tracing of the elements. Compare to figures x, y and z.
Figure 2. Original interpretations (2 frames black/white) vs. new interpretations (color).
Figure 2. Original interpretations (2 frames black/white) vs. new interpretations (color).

Click here to go to the Pterodaustro embryo page.

Figure y. The JZMP embryo traced here. Compare to figure w.

Click here to go the JZMP embryo tracing and reconstruction pages.

Figure z. IVPP embryo in situ, segregated into parts.
Figure z. IVPP embryo in situ, segregated into parts.

Click here to go to IVPP embryo page with links to the egg enlargement page.

Two plesiosaurs: Plesiopleurodon and Luskhan, enter the LRT

This post had its genesis
with a viewing of a YouTube video hosted by paleontologists Valetin Fischer re-describing two plesiosaurs, Luskhan (Fig. 1), and Plesiopleurodon, (Fig. 2), using µCT scanning techniques. He labeled the former a polycotlid-like pliosaurid, and the latter a pliosaur-like polycotylid. Both apt.

My beef today
is with the presentation technique of Fischer et al. 2017, who took a perfectly good dorsal view photograph of a specimen and inked in the sutures they identified. That provided no opportunity to wonder if they got it all right or not. A better solution would be to provide a photograph and a side-by-side diagram, or to colorized a photograph in which the sutures remain visible. The authors’ attempt at improving their presentation had the opposite effect.

Figure 1. The nearly complete skeleton of Luskhan, a less dangerous relative to Kronosaurus in the LRT. Top: the published tracing of the dorsal skull is what NOT to do. The authors took a perfectly good photo and ruined it with pen lines (top), obscuring the sutures from proper view. If you’re going to outline bones with ink, keep the diagram separate from the photo. Or use transparent colors without outlines on the bones. Below the original is a revision with standardized colors applied. The overall diagram is modified here from the original.

Luskhan itilensis
(Fischer et al. 2017, YKM 68344/1 262, Early Cretaceous, 6.5m in length) nests as a sister to Kronosaurus in the LRT, but with a slender snout and short teeth not adapted to large prey.

Figure 2. Plesiopleurodon skull in several views, here colorized.

Plesiopleurodon wellesi
(Carpenter 1996; 71cm skull length; NHMUK R4058; Late Cretaceous) is a traditional enigma, here nesting at the base of the pliosaurids, derived from Plesiosaurus. Note the elongate snout and longer premaxilla. The prefrontals contact the premaxilla, separating the nasals from the frontals.

Figure 3. Subset of the LRT focusing on plesiosaurs. There is little to no strangeness or convergence here. Plesiopleurodon is the first of the plesiosaurs with a longer skull.

Here
in the large reptile tree (LRT, 1889+ taxa, subset Fig. 3) Luskhan nests with Kronosaurus. Pliesiopleurodon nests at the base of the short-neck pliosaurs, derived from long-necked Plesiosaurus.

References
Carpenter K 1996. A review of short-necked plesiosaurs of the Western Interior, North America. Neues Jahrbuch fur Geologie und Palaontologie, Abhandlungen 201(2):259-287.
Fischer et al., (8 co-authors) 2017. Plasticity and Convergence in the Evolution of Short-Necked Plesiosaurs, Current Biology, http://dx.doi.org/10.1016/j.cub.2017.04.052

wiki/Luskhan
wiki/Plesiopleurodon