SVP abstracts – JAWS! (+ tooth genesis)

Chen et al. 2019 bring us a new look
at the first teeth and jaws to evolve in the clade Gnathostomata.

A word of caution:
Watch out for, and be able to differentiate between ‘the origin of jaws and teeth’ vs ‘the reduction of jaws and teeth’ here. The two can be confused with one another if you don’t have a good outgroup taxon.

Therefore it is helpful to start with a jawless outgroup
for polarity. In the large reptile tree, (LRT, 1593 taxa; subset Fig. 6) the thelodont, Thelodus (Fig. 1), is that outgroup taxon. In other words, Thelodus is the last common ancestor of all vertebrates with jaws in the LRT. That means some undiscovered taxon or Thelodus itself, documents the genesis of jaws. Since all Thelodus specimens are crushed flat body fossils with no internal details shown or known, we’ll have to wait to find out what is inside some to-be-discovered 3D Thelodus. Perhaps the transition occurs within that genus. Meanwhile…

Figure 4. Manta compared to Thelodus and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes.

Figure 1. Manta compared to Thelodus and Rhincodon. All three have a terminal mouth essentially transverse between the lateral eyes set far forward on the skull. Based on Thelodus, the outgroup, this is the primitive condition.

From the abstract:
“Osteichthyan dentitions are characterized by cyclic tooth replacement and linear tooth rows.”

Not all of them. Whale sharks (Fig. 1; Rhincodon), manta rays (Fig. 1; Manta ) have tooth carpets and no marginal teeth on the jaws (Fig. 1).

Figure 1. Whale shark (Rhincodon) tooth pads, not that much different from catfish tooth pads (Fig. 2).

Figure 2. Whale shark (Rhincodon) tooth pads, not that much different from catfish tooth pads.

Chen et al. continue:
“The acquisition of these characters can be explained by an intimate relationship between the growth of jawbone and the initiation of teeth, supported by substantial evidence from synchrotron microtomography that reveals the 3D pattern of successor teeth, vascular canals, growth arrested and resorption surfaces in various Silurian-Devonian gnathostomes.

Jawbones (premaxilla, maxilla and dentary) are actually the last bones to get teeth. So, according to the LRT, the process of getting marginal teeth was a little more complicated than Chen et al. proposed. Perhaps it happened twice by convergence. Catfish (Fig. 3) show an early version of this in bony fish. Sharks evolved marginal teeth by convergence.

Figure 4. Catfish teeth from Usman et al. 2013, colors added.

Figure 3. Catfish teeth from Usman et al. 2013, colors added. The labeled maxillary teeth are actually premaxillary teeth. Compare these carpets of short teeth with those in figure 2.

Chen et al. continue:
The growing bone provides space for new teeth to attach and the succession of larger teeth maintains the number of teeth as the animal grows.”

OK. Gong with the flow, let’s just focus on jawbones now.

“In non shedding dentitions, whether the spiral addition of acanthodian tooth whorls, the anterior addition of ischnacanthid dentigerous jawbones, or the radial addition of arthrodire gnathal plates, the sequential addition of teeth is synchronized with the appositional growth of bone.”

Figure 2. Onychodus and Ischnacanthus share enough traits to make them sisters, apart from Brachyacanthus + Pteronisculus.

Figure 4. Onychodus and Ischnacanthus share enough traits to make them sisters, apart from Brachyacanthus + Pteronisculus. Circles show the acanthodian tooth whorls mentioned above.

Chen et al. continue:
The most primitive teeth of the most basal stem gnathostome Radotina and Kosoraspis already display the lingual addition of tooth rows shared by the gnathostome crown group.”

The LRT recovers more primitive taxa with teeth on the jaws, like Squatina, the extant angel shark (Fig. 5). It is basically a large Thelodus. You know it has primitive jaws because surrounding the jaws on either side are gill bars. These slowly disappear in all more derived taxa. Radotina and Kosoraspis are both Early Devonian placoderms, a derived gnathostome clade (Fig. 6). Neither preserve lateral gill bars.

On a side note, and regarding placoderms, Vaskaninova and Ahlberg 2017 wrote, “A key development in the understanding of this stem group has been the recognition that the placoderms (armoured jawed fishes of Silurian to Devonian age), which until recently were regarded as a clade branching off the gnathostome stem group, probably form a paraphyletic segment of that stem group. Some groups of placoderms appear to be very primitive and close to jawless vertebrates whereas others possess what were previously regarded as osteichthyan autapomorphies (notably a maxilla, premaxilla and dentary) and are probably close to the gnathostome crown-group node.”

The LRT does not support these placoderm hypotheses. All tested placoderms nest together in the LRT at the base of the lobefin-rayfin split. Some bottom dwelling placoderms revert to a near jawless condition. So do certain catfish, like the kind that cling to aquarium glass.

Figure 5. Squatina skull. Note the gill bars framing the mouth. These are modified in Aetobatus into a digging snout.

Figure 5. Squatina skull. Note the gill bars framing the mouth and the marginal teeth, the most primitive examples in the shark lineage. Heterodontus has the most primitive teeth in the bony fish line, despite the lack of bones in Heterodontus.

Chen et al. continue:
When in situ resorption evolved in osteichthyans, the first-generation teeth of the stem osteichthyan Lophosteus are shed semi-basally forming deeply overlapping tooth rows. As the bone growth slows down at later developmental stages, the succeeding teeth overlap the preceding ones entirely, causing the preceding teeth to be shed basally and replaced in situ. 

“Therefore, tooth replacement may have emerged via a tooth initiation rate higher than the bone growth rate. When a lingual shelf is formed on the marginal jawbones of crown osteichthyans, the lingual growth of bone is restricted, and new tooth rows cannot be added lingually to the previous rows, only apically.”

In the LRT, other than sharks, the most primitive instance of marginal teeth occurs in chimaeras like Falcatus (Fig. 7).

Figure 1. The skull of Falcatus with DGS tracing above.

Figure 7. The skull of Falcatus with DGS tracing above. Note the primitive marginal teeth.

Chen et al. continue:
“The replacement of the marginal linear tooth row of the basal actinopterygian Moythomasia is actually a vertical piling of alternate tooth rows by semi-basal resorption. Thus a single linear tooth row may have transformed from a lingual-labial compressed version of transverse tooth files.”

Moythomasia was added to the LRT, but it nests off a rather derived node, far from the most primitive taxa in the LRT with jaws. Like Falcatus (Fig. 7), Moythomasia has deep jaws that extend to the back of its skull. By contrast the whale shark and other basal taxa have much shallower, more transverse jaws, more like those of Thelodus (Fig. 1).


References
Chen et al.  2019. Development relationships between teeth and jawbones in stem gnathostomes and stem osteichthyans revealed by 3D histology: insights into the evolution of tooth replacement and tooth organization.
Vaskaninova V and Ahlberg PE 2017. Unique diversity of acanthothoracid placoderms (basal jawed vertebrates) in the Early Devonian of the Prague Basin, Czech Republic: A new look at Radotina and Holopetalichthys. PLoS ONE 12(4):eo174794.

SVP abstracts – First largepetid pectorals and forelimbs

McCabe and Nesbitt 2019 present
the first pectorals and forelimbs for Lagerpeton (Fig. 1), a taxon previously known from hind limbs and pelvic region, plus some dorsals, some caudal vertebrae only.

From the abstract:
“The posture of the earliest dinosaurs is thought to be bipedal whereas their
pseudosuchian relatives and stem archosaurs are thought to be typically quadrupedal.”
The large reptile tree (LRT, 1592 taxa) invalidates the traditional clade ‘pseudosuchia.’ All basal archosaurs are bipeds in the LRT. So are some tropidosuchids by convergence. Nesbitt has never tested a large enough taxon list to reveal this. He and others have been traditionally confused by this convergence.
“Therefore, the transition from quadrupedality to bipedality lies somewhere between the origin of Avemetatarsalia (bird-line archosaurs) and Dinosauria.”
The LRT invalidates the traditional clade Avemetatarsalia and shows exactly where quadrupeds became bipeds.
“However, studying this transition is hampered by the lack of forelimb fossils from many of the close relatives of dinosaurs and it is not clear if the morphology of the few dinosauromorphs that have forelimb material are unique or represent the plesiomorphic condition leading to dinosaurs.”
The LRT showed back in 2011 that Lagerpeton is a dinosaur mimic, related to the proterochampsid (Fig. 2) Tropidosuchus, not dinosaurs. So the premise of this abstract is completely wrong, based on invalid Nesbitt 2011 cladogram.
“New forelimb fossils of dinosaur relatives and careful assessments of their osteology is sorely needed to help address this knowledge gap.
We have forelimbs for dinosaur relatives. Pseudhesperosuchus is close. So is Turfanosuchus. We’re glad to see forelimbs for Lagerpeton. Just don’t imagine that they have anything to do with the origin of dinosaurs.
“Here we present the first pectoral (left scapulocoracoid) and forelimb (right humerus) bones of the important early dinosauromorph Lagerpeton chanarensis.”
Not a dinosauromorph.
“The bones were prepared from a concretion that only consisted of Lagerpeton bones and from the cynodont Massetognathus. We identify the bones as belonging to Lagerpeton because the distal end of the femur possesses an inflated crista tibiofibularis – a lagerpetid character state – and the newly recognized pectoral and forelimb bones are generally similar to those of the lagerpetid Dromomeron romeri and Ixalerpeton with tall and
constricted anteroposteriorly narrow scapular blade and a humerus with a highly asymmetrical proximal part of the humerus.”
Sounds good.
Figure 3. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

Figure 1. The closest kin of Tropidosuchus are the much larger Chanaresuchus (matching Nesbitt 2011) and the smaller Lagerpeton.

McCabe and Nesbitt continue:
“The scapulocoracoid of Lagerpeton has a tall, but anteroposteriorly narrow scapular blade more like Dromomeron romeri than Ixalerpeton.
And more like the omitted Tropidosuchus (based on the above description). McCabe, Nesbitt: why not test Lagerpeton against Tropidosuchus? Novas and Agnolin reported it as a proterochampsian, too. BTW, Ixalerpeton is a protorosaur in the LRT, based on the few bones known.
“The length of humerus and the proportions of the proximal and distal end in Lagerpeton are also more similar to that of Dromomeron romeri. Overall, the scapulocoracoids and humeri of lagerpetids are similar in proportion across taxa, but comparing the length of the forelimbs to the hindlimbs is hampered by the lack of articulated or unambiguously associated individuals of any member of the group. Currently, it is still not clear if the anatomy of the pectoral girdle and forelimb of lagerpetids, and thus posture, is unique for lagerpetids or represents the ancestral condition for dinosauromorphs.”
This pectoral girdle does not represent the ancestral condition for dinosauromorphs. Nor is it unique to lagerpetids (sans Tropidosuchus). McCabe, Nesbitt, look at Tropidosuchus before pushing your hypothesis over the edge.

References
McCabe MB and Nesbitt SJ 2019. The first pectoral and forelimb material assigned to the lagerpetid Lagerpeton chanarensis: comparing to other lagerpetids and other avemetatarsalians. Journal of Vertebrate Paleontology abstracts.
Novas FE and Agnolin FL 2016 Lagerpeton chanarensis Romer (Archosauriformes): A derived proterochampsian from the middle Triassic of NW Argentina. Simposio. From Eventos del Mesozoico temprano en la evolución de los dinosaurios”. Programa VCLAPV. Conferencia plenaria: Hidrodinámica y modo de vida de los primeros vertebrados. Héctor Botella (Universitat de València, España) 2016

Gregorius rexi: not a ratfish in the LRT

Revised November 07, 10 and 17 2019
with a revision to the LRT that moves Gregorius closer to Hybodus, basal to Placodermi.

Talk about a transitional taxon…
Gregorius rexi (Lund and Grogan 2004; 11cm long; Early Carboniferous; CM 35490) is a small fish from the famous Bear Gulch Formation in Montana. Traditionally it is considered a type of ratfish.

By contrast,
in the large reptile tree (LRT, 1593 taxa; Fig. 3), Gregorius is a late surviving member of an Early Devonian genesis representing the most primitive ray-fin fish splitting from Hybodus. Gregorius is the last common ancestor of all bony fish and placoderms. Ratfish are a bit more primitive.

Figure 1. Gregorius rexi enlarged and to to scale with its cousin in the LRT, Robustichthys. Gregorius still has a dorsal spine and an odd soft of diphycercal tail.

Figure 1. Gregorius rexi enlarged and to to scale with its cousin in the LRT, Robustichthys. Gregorius still has a dorsal spine and an odd soft of diphycercal tail.

Gregorius is not far from catfish,
still tucked inside the placoderms. Thunnus, the tuna, is the most primitive extant ray-fin fish among taxa derived from a sister to Gregorius.

FIgure x. Gregorius rexi with articulated bones in vivo.

Figure 2. Gregorius rexi with articulated bones in vivo. This taxon is basal to the clade Placodermi. 

In the meantime,
I’ve been learning more about ray fin fish. Some taxa have moved around as mistakes are discovered and corrections are made. The four-eyed fish now nests with the mudskipper, as an example. The general topology of the tree has otherwise stayed much the same as the Bootstrap scores get better. When that portion is complete, we’ll review the changes.

Figure 9. Subset of the LRT focusing on fish. The two nominal Gemuendia specimens are highlighted.

Figure 9. Subset of the LRT focusing on fish. The two nominal Gemuendia specimens are highlighted.


References
Lund R and Grogan E 2004. Five new euchondrocephalan Chondrichthyes from the Bear Gulch Limestone (Serpukhovian, Namurian E2b) of Montana, USA. Recent Advances in the Origin and Early Radiation of Vertebrates 505-531.

https://people.sju.edu/~egrogan/BearGulch/pages_fish_species/Gregorius_rexi.html

SVP abstracts – Silurian gnathostome

Zhu et a. 2019 bring us
a new Silurian fish they claim is close to the origin of jawed vertebrates (= Gnathostomata).

From the abstract:
“Modern jawed vertebrates or crown-group gnathostome include the last common ancestor of living bony and cartilaginous fishes and all its descendants. The gross morphology of the earliest modern jawed vertebrates, and how they arose from stem gnathostomes, were previously unknown due to a lack of articulated fossils.”

These taxa are not unknown in the large reptile tree (LRT, 1592 taxa). Put enough taxa in an analysis and one will end up close to the origin of gnathostomes. There will be a last common ancestor. In the LRT Thelodus, a ?jawless (phylogenetic bracketing indicates some sort of transverse jaws are present) Silurian fish is the current proximal outgroup to all tested taxa with jaws. In LRT the extant whale shark (Rhincodon), angel shark (Squatina) and horn shark (Heterodontus) are basal members of the Gnathostomata and the first taxa with primitive tooth carpets.

“The recent discovery of the Xiaoxiang Fauna from the Silurian of South China revolutionarily adds to the diversity of Silurian jawed vertebrates. However, considerable morphological gap is still present between stem- and crown-group gnathostomes.”

Not so, when appropriate taxa are included.

“Here, we report a new bony fish very close to the crown-group gnathostome node, also from the Xiaoxiang Fauna. The attributed specimens include a head, jaws and an articulated postcranial skeleton.”

“The new fish displays a unique suite of characters: the dermal pectoral girdle condition transitional between Entelognathus and osteichthyans, the braincase profile recalling the condition in Janusiscus and early chondrichthyans, and the premaxillae and lower jaw largely showing osteichthyan features. This mosaic character combination suggests the tentative phylogenetic position of this new taxa in the most basal segment of the osteichthyan stem, possibly forming a quintessential component of the evolutionary transition between placoderms and osteichthyans.”

In the LRT taxa between placoderms and osteichthyans are either acanthodians (spiny sharks) on one branch, or catfish (also with spiny fins) on the other branch. Catfish are whales-shark mimics with regard to their jaws and teeth, likely representing some sort of reversal to that basal condition.

“For the first time, we are able to look into a near-complete bony fish close to the last common ancestor of all the living jawed vertebrates, and reconstruct the acquisition sequence of osteichthyan characters based on a series of fossils in morphological proximity. The fact that most of these fossils are from the Silurian Xiaoxiang Fauna, suggests that this fauna is unprecedentedly close to the initial radiation of jawed vertebrates.” 

Figure 2. Updated subset of the LRT focusing on basal vertebrates (fish). Arrow points to Hybodus. This tree does not agree with previous fish tree topologies.

Figure 1. Updated subset of the LRT focusing on basal vertebrates (fish). Arrow points to Hybodus. This tree does not agree with previous fish tree topologies. Check out the LRT for a slightly updated version of this cladogram.

This is all very interesting, and welcome, but let them look at the structure of Rhincodon as it relates to Thelodus at least once before settling down with the Zhu et al. hypothesis.

Figure 4. Manta compared to Thelodus and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes.

Figure 4. Manta compared to Thelodus and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes.


References
Zhu et al. 2019. A new Silurian bony fish close to the common ancestor of crown gnathostomes.

SVP abstracts – Earliest avemetatarsalian?

Patellos et al. 2019 brings us
news of the earliest archosaur in the lineage of birds (rather than crocs).

Okay. That’s already wrong. In the large reptile tree (LRT, 1592 taxa) only crocs and dinos make up the Archosauria. Nesbitt et al. does not understand that hypothesis of interrelationships due to taxon exclusion and poor scoring going back to Nesbitt 2011. The purported clade, ‘Avemetatarsalia’ (= Ornithodira) was invalidated by the LRT.

From their abstract:
“Understanding of the evolution of the earliest avemetatarsalian (bird-line) archosaurs and the morphology of the hypothetical common ancestor of Archosauria is hampered by a poor fossil record.”
Incorrect. The common ancestor of Archosauria has been identified in the LRT as the PVL 4597 specimen wrongly attributed to Gracilisuchus. After that: Turfanosuchus (Fig. 1).
Figure 2. Skull of Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Figure 1. Skull of Turfanosuchus compared to Herrerasaurus, the basalmost dinosaur.

Patellos et al. 2019 continue:
“The earliest-diverging avemetatarsalians known, such as Teleocrater, are separated from the earliest diverging pseudosuchian (crocodylian-line) archosaurs, and the closest outgroups of Archosauria by a clear morphological gap.”
The LRT invalidates the traditional clade, ‘Pseudosuchia.’ Crocodylian-line archosaurs are Crocodylomorphs, distinct from bird-line archosaurs, dinosaurs. Remember, these authors consider the lepidosaurian pterosaurs to be closely related to dinosaurs, a theory with as much evidence as tail-dragging dinosaurs.
“Here we describe a potential early-diverging avemetatarsalian from the Middle Triassic (~ 230 Ma) “Basal Isalo II” beds of Madagascar, which appears to bridge these gaps. This new taxon is represented by a well-preserved partial skeleton including articulated cervical
vertebrae with articulated osteoderms; a scapulocoracoid; a partial femur; isolated trunk, sacral, and caudal vertebrae; and an ilium.”
“Noteworthy features of the neck region include: anteroposteriorly elongated vertebrae with laterally expanded dorsal ends of the neural spines, and an articulated set of osteoderms dorsal to the vertebrae. The cervical osteoderms, three pairs per vertebra, arranged in paramedian row, and bear tapering anterior processes.” 
“Potential synapomorphies of this specimen with avemetatarsalians include: femur with an incipient anterior trochanter, 1st sacral vertebra with a dorsoventrally expanded sacral rib, and ilium possessing a notch on the articulation surface with the ischium. This combination of features places the new taxon represented by this specimen at the base of Avemetatarsalia, outside aphanosaurs + dinosaurs, but this position is poorly supported.”
The best known members of the invalid Aphanosauria include Yarasuchus and Teleocrater (Fig. 2), taxa nested with a long line of non-Aphanosauria by the LRT between Rauisuchia and Archosauria.
Figure 3. Yarasuchus, Qianosuchus and Turfanosuchus nest together in Nesbitt et al. 2017 after rescoring.

Figure 2. Yarasuchus, Qianosuchus and Turfanosuchus nest together in Nesbitt et al. 2017 after rescoring.

Patellos et al. 2019 continue:
“More broadly, this new specimen indicates that cervical osteoderms were present in the earliest avemetatarsalians and were soon lost in the lineage.”
There’s no need for such phylogenetic gymnastics in the LRT.
“The generally plesiomorphic morphology of the new taxon also underscores the difficulty of identifying early avemetatarsalians from incomplete skeletons. Presence of an early diverging avemetatarsalian together with a lagerpetid and silesaurid in the “Basal Isalo II” beds of Madagascar documents the co-occurrence of multiple avemetatarsalian subgroups in Gondwana during the Triassic.”
They wish. The LRT resolves all such problems with high resolution. Blame S. Nesbitt for relying on his own poorly scored cladogram, inventing the ‘Aphanosauria’ and supporting the ‘Avemetatarsalia.’ Blame M. Benton for inventing the clade ‘Avemetatarsalia’.
Don’t trust those clades. Don’t trust the LRT. Run your own tests so you’ll know. In science this is the first, last and best option to resolve all such disagreements.

References
Patellos E et al. 2019. A new reptile from the ?Middle Triassic of Madagascar may represent the earliest-diverging avemetatarsalian (Archosauria). Journal of Vertebrate Paleontology abstracts.

SVP abstracts – Perleidus joins the LRT

Argyriou and Romano 2019
study an Early Triassic fish, Perleidus woodwardi (Fig. 1).

Figure 1. Perleidus woodwardi in situ and with skull reconstructed.

Figure 1. Perleidus woodwardi in situ and with skull reconstructed. The new reconstruction differs from the traditional one in Gregory 1938.

From the abstract:
“Despite decades of research, the deep-time origins and ancestral morphologies of crown actinopterygian evolutionary lineages remain obscure, with the membership of late Paleozoic-Triassic taxa being particularly fluid with respect to the actinopterygian crown group. Lack of data on the endoskeleton of important fossil groups, and a disjunction among phylogenetic matrices aimed at resolving different branches of the actinopterygian tree of life, are the major causes of this gap of knowledge.”

The large reptile tree (LRT, 1592 taxa) solved this problem over the last few months by including more taxa than in prior studies without much data from the endoskeleton of fish.

The abstract continues:
“The Triassic ‘perleidids’ have been historically viewed as early members of Neopterygii, the most successful group of modern actinopterygians.”

That is confirmed in the LRT.

“Yet, recent research has cast  doubts not only on their evolutionary affinities, but also their monophyly, though no stable phylogenetic alternatives have been provided. Based on previously undescribed material in museum collections in Paris and Zurich, we reappraise ‘Perleidus’ woodwardi, from the early Olenekian (Early Triassic) of Spitsbergen. Exquisitely preserved exoskeletons provide novel data on the osseus constituents of the ethmoid region, and the anatomy of the tail fin, which is now shown to lack obvious epaxial rays. In addition, using μCT, we studied a recently collected, three-dimensionally preserved cranium and pectoral girdle, which revealed a wealth of phylogenetically important information.”

“The braincase and endocast of ‘P’. woodwardi broadly resemble those of Australosomus, with the presence of a posteriorly elongate parasphenoid in the former being a notable difference between the two.” 

Australosomus is another Early Triassic ray-fin fish. The rest of the abstract provides various skeletal traits of interest without making additional comparisons.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Perleidus (Fig. 1) nests between this Triassic fish and the bronze featherback, Notopterus (Fig. 3).

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Perleidus (Fig. 1) nests between this Triassic fish and the bronze featherback, Notopterus (Fig. 3).

In the LRT
Perleidus nests between the tuna-like Triassic ray-fin, Pholidophorus (Fig. 2) and the derived extant bronze featherback, Notopterus, taxa not mentioned in the Arygriou and Romano abstract.

Figure 3. Perleidus shares many traits with the extant knife fish, Notopterus, a taxon not mentioned in the abstract.

Figure 3. Perleidus shares many traits with the extant bronze featherback, Notopterus, a taxon not mentioned in the abstract.

Earlier
the LRT was able to nest Pholidophorus with the distinctively different NotopterusPerleidus provides the perfect transitional taxon. In fact, it is so midway between the two sister taxa that there is complete loss of resolution between the three.


References
Arygriou T and Romano C 2019. New fins or old fins? Skull and pectoral girdle of Early Triassic ‘Perleidus’ woodwardi revisited using µCT. Journal of Vertebrate Paleontology abstract.

SVP abstracts – Origin of aquatic reptiles?

Sobral and Schoch 2019
bring us news on a taxon at the genesis of aquatic reptiles.

I presume that means
no sea turtles, no marine iguanas, no mosasaurs, no sea crocs, no penguins. If so, the LRT already provides a long list of diapsid taxa at the base of the Enaliosauria (Fig. 1; including mesosaurs, ichthyosaurs, thalattosaurs, placodonts, pachypleurosaurs and plesiosaurs) along with other basal aquatic marine younginiforms (Fig. 2), a monophyletic clade distinct from terrestrial younginiforms that gave rise to protorosaurs and archosauriforms.

Figure 3. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

Figure 1. Aquatic younginiform subset of the LRT demonstrating relationships within the Enaliosauria (=Sauropterygia + Ichthyosauria)

From the abstract:
“The Middle Triassic was a time of major changes in terrestrial tetrapod faunas, but the fossil record of this interval is largely obscure.”

Why do paleontologists always paint themselves into a corner like this? To make their discoveries more newsworthy?

“This is unfortunate, since many modern groups originated or diversified during this time. However, recent excavations in the upper Middle Triassic of Germany have revealed several new taxa, most of which are much smaller than those found in other tetrapod-bearing basins of similar age.”

Here’s Galesphyris (Fig. 2) at the base of the aquatic younginiforms in the LRT.

Figure 3. Spinoaequalis and descendant marine younginiformes.

Figure 3. Spinoaequalis and descendant marine younginiformes. These give rise to plesiosaurs, placodonts, mesosaurs, ichthyosaurs and thalattosuchians. Click to enlarge.

Sobral and Shoch continue:
“Here, we report a new taxon from the Vellberg limestone quarry comprised of skull bones distinct from other diapsids from this locality. It is diagnosed by a long maxilla with a far posteriorly reaching tooth row; a long and stout ventral process of the postfrontal; exclusion of the postorbital from the lower temporal fenestra due to a contact between the anteroventral process of the squamosal and the dorsal process of the jugal; and a tall quadrate + quadratojugal complex.”

“Some anatomical aspects of the new taxon are similar to stem diapsids such as Elachistosuchus huenei from similar deposits of Northern Germany and of uncertain phylogenetic affinity.”

In the LRT Elachistosuchus (Fig. 3) nests certainly between proterosuchids and choristoderes (Fig. 4). Neither are related to aquatic younginiforms.

Figure 1. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 3. Elachistosuchus (Janensch 1949, Sobral et al. 2015) is a sister to BPI 2871, a basal choristodere.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

Figure 4. This is where Elachistosuchus nests, next to BPI 2871, at the base of the Choristodera.

“A phylogenetic analysis retrieved both taxa in an “ichthyosauromorph” clade, included in an almost exclusively aquatic group. The new taxon, Hupehsuchus, and Elachistosuchus appear as successive sister-taxa to Ichthyopterygia.”

This is not supported by the LRT where Hupehsuchus (Fig. 5) and Elachistosuchus (Fig. 3) are not related  to one another. The outgroups to the Ichthyopterygia (Fig. 1) are the Thalattosuchia, Mesosauria and basal Sauropterygia (pachypleurosaurs).

Figure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

Figure 5. Basal Ichthyosauria in the LRT, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and ThesaurusFigure 2. Basal Ichthyosauria, including Wumengosaurus, Eohupehsuchus, Hupehsuchus and Thaisaurus

“It is interesting to note that many of the autapomorphic characters of the new taxon pertain to elements related to the lower temporal fenestra. In particular, the contact between the jugal and squamosal is unusual, but is also found in sauropterygians, saurosphargids, Hupehsuchus, and Wumengosaurus, as well as in rhynchocephalians.”

Oh, why did they have to add rhynchocephalians? They were doing so well! Readers beware, convergence is rampant (= everywhere) in the Reptilia. Don’t rely on one, two or a dozen traits. If you do, you’ll be pulling a Larry Martin. Only rely on the last common ancestor in a valid cladogram to determine relationships.

“Derived ichthyosaurs show the typical jugal-quadratojugal contact, but via an unusual dorsal contact between the two. The jugal–squamosal contact may thus represent a transitional state to the anatomy observed in later ichthyosaurs, reinforcing the interpretation of the ‘ventral cheek embayment’ of basal ‘euryapsids’ as a ventrally open lower temporal fenestra.”

“Thus, the new taxon has implications for the origin of secondarily aquatic groups, and therefore also paleobiogeographic significance. The appearance of placodontians has been traced to central Europe, but ichthyopterygians are believed to have originated in the Eastern Tethys. The new taxon indicates that the earliest evolutionary history of these groups may have occurred in the Western Tethys, associated with the Germanic Basin. This new material emphasizes the importance of sampling small-bodied taxa in the understanding of reptile evolution.”

The Lower Keuper is Carnian, early Late Triassic. Galesphyris is older. It comes from the Late Permian, perhaps representing an early Early Permian genesis.


References
Sobral G and Shoch R 2019. A small diapsid from the Lower Keuper of Germany and the origin of aquatic reptiles. Journal of Vertebrate Paleontology abstracts.