Haikouichthys: an Early Cambrian galeaspid in the LRT, not a basal lamprey

Haikouichthys is supposed to be
a lamprey ancestor, but after testing in the LRT nests as an Early Cambrian galeaspid with a small head.

Either way,
Shu et al. reported on the importance of this fossil, “These finds imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, ,555 Myr BP), if not earlier.”

If Haikouichthys is a galeaspid,
ancestral, soft, worm-like chordates, like the more primitive lamprey, emerged in the Ediacaran, “if not earlier.”

Figure 1. Haikouichthys in situ and skull closeup, colors added.

Figure 1. Haikouichthys in situ and skull closeup, colors added. The oral  cavity on both lampreys and galeaspids is ventral.

Haikouichthys ercaicunensis
(Luo, Hu & Shu 1997; Shu et al.1999; HZf-12-127; 2.5cm) is an Early Cambrian galeaspid in the LRT. It has an appropriately much smaller skull than later galeaspids. The pectoral fin (green) is not separate from the body. The gill openings are invisible here, likely beneath the skull, as in galeaspids, not on the sides, as in lampreys. A prominent dorsal fin is present. So is a heterocercal tail. The series of posterior green diamonds are likely armored scales… like those in later sturgeons and osteostracans and those in early thelodonts, like Thelodus (Fig. 3). They are likely not gonads, but overlaid the area where the gonads are in related taxa.

Figure 2. Skull of Dunyu with tetrapod homolog colors applied here.

Figure 2. Skull of Dunyu with tetrapod homolog colors applied here.

The only other tested galeaspid in the LRT,
Dunyu (Fig. 2), is from the Late Silurian andhas a larger skull. We looked at Dunyu earlier here. It is close to the Early Devonian osteostracan, Hemicyclaspis (Fig. 3), which is basal to the extant sturgeon in the LRT. Note that galeaspids arise from soft-bodied thelodonts like Thelodus (Fig. 3), in the LRT.

Figure 3. Subset of the LRT focusing on basal chordates, including Dunyu.

Figure 3. Subset of the LRT focusing on basal chordates, including Dunyu.

Some thelodonts,
like Furcacauda, have a relatively small head, a ventral oral cavity, a dorsal fin and no lateral fins.

Figure 1. Galeaspids from Halstead 1985.

Figure 4. Galeaspids from Halstead 1985.

No prior authors
have attempted to put tetrapod homologs on the skull of Haikouichthys or any other galeaspid (Fig. 4).

Shu et al. 1999 wrote,
The theory of lateral fin folds has had considerable signiificance, but of the fossil agnathans only the anaspids and Jamoytius have such paired fn-folds. The possible occurrence of this condition in these Lower Cambrian agnathans indicates, however, that fin-folds may be a primitive feature within the vertebrates. The occurrence of close-set dorsal fin-radials in Haikouichthys, on the other hand, may be a relatively advanced feature.”


References
Luo H. et al. 1997. New occurrence of the early Cambrian Chengjiang fauna from Haikou, Kunming, Yunnan province. Acta. Geol. Sin. 71, 97-104.
Shu D-G et al. (8 co-authors) 1999. Lower Cambrian vertebrates from China. Nature 402:42-46.

wiki/Haikouichthys

The best ‘Sordes’ uropatagium… is another overlooked wing

This much talked about, but rarely seen ‘Sordes’ specimen
(Fig. 1), has been known for decades. It made a brief appearance some 30 years ago at an SVP talk by David Unwin where it caused quite a stir. I haven’t seen it again since. A scale bar is not shown and the museum number is unknown, but may be one of these three: PIN 104/73, PIN 2585/36, PIN 2585/37.

Today this rare ‘tail-less’ specimen made another brief appearance
in an online Palaeontological Assocation talk “Resolving the pterosaur bauplan using a quantitative taphonomic approach” by Rachel Belben (2012, video link), one of Unwin’s students. We looked at Belben’s nearly identical 2020 abstract here.

Figure 1. Image from Belben's December 2020 talk about the pterosaur bauplan.

Figure 1. Image from Belben’s December 2020 talk about the pterosaur bauplan. That’s Belben inset in red. Click to view video on YouTube.

Not one, but two similar Sordes specimens
were presented by Unwin at SVP decades ago. Both appeared to have a distinct uropatagium stretched bat-like between the sprawling hind limbs (Figs. 1, 2). Everyone wondered whether that membrane was 1) above or below the cloaca, 2) attached or not attached to the tail, and 3) what sort of precursor taxa would gradually develop such a membrane controlled by hyperflexed lateral toes. In bats, of course, the vaguely similar calcar arises from the ankle. The toes are not involved.

Sharov 1971
first described and figured the Sordes holotype (Fig. 2, upper right) with a small drawing that appeared to clearly show a uropatagium stretched between the hind limbs and controlled by those odd Tanystropheus-like elongated lateral toes.

Unwin and Bakhurina 1994
brought this odd bit of flight membrane to a wider audience with a short paper in Nature. Their drawing (Fig. 2 middle right) paid less attention to detail.

Peters 1995
disputed the uropatagium, considering it a displaced wing membrane. That critical hypothesis was presented again in Peters 2002 (Fig. 2, left and bottom).

Elgin, Hone and Frey 2012
sided with Sharov, Unwin and Bakhurina, also paying little attention to the specimen.

Figure 4. Sordes wing drift hypothesis from Peters (2002) which attempted to show that the wings and uropatagia of Sordes were more like those of other pterosaurs than the other way around. The very deep uropatagia are misinterpretations prior to the realization that the left brachiopatagium (main wing membrane) was displaced to the ankle area.

Figure 2. Sordes wing drift hypothesis from Peters (2002) which attempted to show that the wings and uropatagia of Sordes were more like those of other pterosaurs than the other way around. The very deep uropatagia are misinterpretations prior to the realization that the left brachiopatagium (main wing membrane) was displaced to the ankle area.

Back in 2011,
the uropatagium of the Sordes holotype showed up here with another tracing (Fig. 5) that showed the displaced radius + ulna and its displaced membrane.

Figure 6. The PIN 2585/3 specimen of Sordes showing displaced left radius and ulna dragging their membranes along with them. The right wing is articulated.

Figure 3. The PIN 2585/3 specimen of Sordes showing displaced left radius and ulna dragging their membranes along with them. The right wing is articulated and shows a short chord wing membrane. Uropatagia are in red.

A new tracing of the rare specimen
(Fig. 4) shows the purported uropatagium extending far beyond the hind limb. That indicates a problem! This is not a uropatagium. Maybe that’s why we haven’t seen this rare specimen for 30 years. A closer examination reveals a series of pterosaur arm bones beneath the hind limb elements. Arm bones or not, this ‘uropatagium’ is a brachiopatagium, a wing membrane, complete with aktinofibrils (Fig. 5).

Figure 4. Color tracing applied to the rare 'Sordes' specimen reveals another displaced wing (deep blue) along with overlooked wing elements. See figure 5 for a reconstruction.

Figure 4. Color tracing applied to the rare ‘Sordes’ specimen reveals another displaced wing (deep blue) along with overlooked wing elements. See figure 5 for a reconstruction.

Adding what little is known
to the large pterosaur tree (LPT, 256 taxa) nests the rare specimen not with Sordes, but with the tiny flightless anurognathid PIN 2585/4 specimen that shares the plate with the holotype of Sordes, PIN 2585/3 (Fig. 2). We looked at that rarely seen specimen earlier here.

Figure 5. Reconstruction of the specimen in figure 4.

Figure 5. Reconstruction of the specimen in figure 4.

Distinct from the flightless PIN 2585/4 anurognathid specimen,
this one has large, robust wings.

In summary
this rarely seen specimen

  1. is not Sordes
  2. does not present a uropatagium
  3. can now explain why a Sordes-like tail is absent here
  4. evidently has never been carefully examined before
  5. has fooled pterosaur experts for decades
  6. is one source of pterosaur mythology that many pterosaur workers and their minions continue to believe in fifty years after its original description.

Someone please tell Rachel Belben
so she can wash her hands of this decades-old error and start fresh.

The Sordes uropatagium is a misinterpretation.
We need to bury this mistake and forget it. Stop promoting and believing this myth. It has been exposed.


References
Elgin RA, Hone DWE and Frey E 2011. The extent of the pterosaur flight membrane. Acta Palaeonntologica Polonica 56(1): 99-111.
Peters D 1995. Wing shape in pterosaurs. Nature 374, 315-316.
Peters D 2002. A New Model for the Evolution of the Pterosaur Wing – with a twist. Historical Biology 15: 277–301.
Sharov AG 1971. New flying reptiles from the Mesozoic of Kazakhstan and Kirghizia. – Transactions of the Paleontological Institute, Akademia Nauk, USSR, Moscow, 130: 104–113 [in Russian].
Unwin DM and Bakhurina NN 1994. Sordes pilosus and the nature of the pterosaur flight apparatus. Nature 371: 62-64.

wiki/Sordes

https://pterosaurheresies.wordpress.com/2015/03/10/the-evolution-of-the-sordes-wing-and-uropatagia-1971-to-2011/

https://pterosaurheresies.wordpress.com/2015/03/09/how-one-sordes-evolved-into-dorygnathus-via-cacibupteryx/

https://pterosaurheresies.wordpress.com/2014/03/15/variation-in-three-sordes-specimens/

https://pterosaurheresies.wordpress.com/2012/07/17/what-is-happening-between-the-legs-of-sordes/

https://pterosaurheresies.wordpress.com/2020/10/21/svp-abstracts-3-belben-contributes-to-the-bat-wing-pterosaur-myth/

 

An overlooked clade of angel shark-mimics among the lobefins

Long one today:
with lots of pictures (Figs. 1–8) and a large cladogram (Fig. 9).

There is a clade of Early Devonian skate-mimic bony fish
recovered by the large reptile tree (LRT, 1757+ taxa). They are tucked into the lobefin clade and have posteriorly-oriented paddle-like fins where preserved (2x out of 7). The preopercular is gone.

Like lungfish,
the exhalant naris was at or near the jawline. This made some of these taxa (e.g. Kenichthys, Fig. 1) worthy of papers in Nature. The authors reported that this feature was said to relate to tetrapod origins. In the LRT this morphology turns out to be convergent with tetrapods and their proximal ancestors. The noteworthy and distinct anterorventral inhalant naris combined with the lateral jawline exhalant naris is shared by all clade members.

This clade of angel-shark mimics was previously overlooked by fish workers.
Here, skull bone identities were a problem until all seven were studied together and reconstructed in multiple views (Figs. 1–8), including the foreshortening of mandibles set at about 45º to the midline in the wider of the two subclades (see below). Most of these are small taxa.

Figure 1. Kenichthys Images from Zhu and Ahlberg 2004, colors added. The authors made a convincing argument that Kenichthys represented a transitional taxon between Youngolepis and Eusthenopteron. Note the lack of vomer fangs and a distinctly different set of skull sutures in Kenichthys, which does not nest with Eusthenopteron in the LRT.

Figure 1. Kenichthys Images from Zhu and Ahlberg 2004, colors added. The authors made a convincing argument that Kenichthys represented a transitional taxon between Youngolepis and Eusthenopteron. Note the lack of vomer fangs and a distinctly different set of skull sutures in Kenichthys, which does not nest with Eusthenopteron in the LRT.

Members on branch 1 include:

  1. Kenichthys (Fig. 1 Early Devonian) and
  2. Youngolepis (Fig. 2, Early Devonian).

Both have a typical narrow mandible no wider than the skull width.

Members on branch 2 include:

  1. Tungsenia (Fig. 3, Early Devonian),
  2. Stensioella (Figs. 4, 5; Early Devonian),
  3. Styloichthys (Fig. 6; Early Devonian)
  4. Guiyu (Fig. 7, Late Silurian), and
  5. Psarolepis (Fig. 8, Late Silurian).

In this subclade the jaw joints can extend to twice the width of the cranium (Figs. 3, 6, 7), resulting in a wide, flat skull.  Apparently this trait has gone overlooked in prior studies. The most derived of these clade members, Guiyu and Psarolepis, are the oldest. Only Guiyu and Stensioella preserve post-crania of the 7 tested clade members. Only Youngolepis (Fig. 2) preserves a narrow skull morphology with jaws beneath the orbits.

Figure 3. Youngolepis skull. Colors added.

Figure 2. Youngolepis skull. Colors added.

Kenichthys campbelli
(Chang and Zhu 1993; Zhu and Ahlberg 2004; Early Devonian, 395 mya; Fig. 1) was originally considered a basal sarcopterygian demonstrating the migration of the exit nostril to the jaw rim on its way to the palate to become the choana.

Youngolepis praecursor
(Chang and Yu 1981; Early Devonian 410 mya; less than 30 cm in length estimated; ). Distinct from other lungfish, Youngolepis had large eyeballs and retained a large vomer fang. Note the in-naris and out-naris were both ventral in exposure.

Figure 1. Skull of Tungsenia from Lu et al. 2012. Tetrapod skull colors added and restored based on related taxa. Here the tooth-bearing portion of the premaxilla is missing. So are the vomers, which may have had fangs, like those of Youngolepis (Fig. 4),

Figure 3. Skull of Tungsenia from Lu et al. 2012. Tetrapod skull colors added and restored based on related taxa. Here the tooth-bearing portion of the premaxilla is missing. So are the vomers, which may have had fangs, like those of Youngolepis (Fig. 4),

Tungsenia paradoxa
(Lu et al. 2012; Early Devonian; Fig. 3) was originally considered the earliest known stem-tetrapod (= taxa closer to tetrapods than to lungfish). In the LRT it nests with Youngolepis outside of the tetrapods + lungfish.

Figure 7. Stensioella preserves post-crania back to the tail.

Figure 4. Stensioella preserves post-crania back to the tail.

Stensioella heintzi 
(Broili 1933; Emsian, late Early Devonian; 27 cm est.; Fig. 4 is widely considered the most basal placoderm, but here nests outside that clade.  Stensioella would have had a lifestyle like Squatina, the extant angel shark.

Figure 8. Stensioella from nose to tail. Note the large paddle-like pectoral fins, as in Guiyu (Fig. 5).

Figure 5. Stensioella from nose to tail. Note the large paddle-like pectoral fins, as in Guiyu (Fig. 5).

Figure 6. Styloichthys preserves mandibles that greatly widen the dimensions of the skull.

Figure 6. Styloichthys preserves mandibles that greatly widen the dimensions of the skull.

Styloichthys changae 
(Zhu and Yu 2001; IVPP V15542; Early Devonian, 420 mya; Fig. 6) is considered the oldest coelocanth. Here it nests outside that clade.

Figure 7. Guiyu preserves flat, wide, post-crania.

Figure 7. Guiyu preserves flat, wide, post-crania.

Guiyu oneiros 
(Zhu et al. 2009; late Silurian; V17914) was originally considered the earliest articulated bony fish discovered. It was originally given a Eusthenopteron-like reconstruction. The revised restoration differs somewhat from the original in having a flatter oblate cross-section and large Stensioella-type pectoral flippers.

6. Psarolepis skull and mandible. Here the mandibles are spread wider matching sister taxa.

8. Psarolepis skull and mandible. Here the mandibles are spread wider matching sister taxa.

Psarolepis romeri 
(Yu 1998; Zhu et al. 2014; Late Silurian; Fig. 8) is known from parts of its face and a complete mandible.  The upturned and short rostrum includes large in and out nares located higher on the skull. Nearly all the bones of the cranium are fused together. The upturned tip of the mandible lacks teeth. The mandible is likewise largely fused but with deep fovea.

Figure 1. Subset of the LRT focusing on basal vertebrates and highlighting ray fins, spiny sharks and lobe fins. Catfish retain spines on their ray-like pectoral fins.

Figure 9. Subset of the LRT focusing on basal vertebrates and highlighting ray fins, spiny sharks and lobe fins. Catfish retain spines on their ray-like pectoral fins.

References
Broili F 1933. Weitere Fischreste aus den Hunsrickschiefern. Situngsbirechte der bayerischen Akademie der Wissenschaften, Mathematisch-Naturewissenschaftliche Klasse 2: 269–313.
Chang M-M and Yu X-B 1981. A new crossopterygian Youngolepis praecursor gen. et sp. nove.form Lower Devonianof E. Yunna, China. Scientia Sinica 24:89–97.
Chang M and Zhu M 1993. A new Middle Devonian osteolepidid from Qujing, Yunnan. Mem. Assoc. Australas. Palaeontol. 15 183-198.
Cui X, Qiao T and Zhu M 2019. Scale morphology and squamation pattern of Guiyu oneiros provide new insights into early osteichthyan body plan. Nature Scientific Reports 9 (4411).
Lu J, Zhu M, Long JA, Zhao W, Senden TJ, Jia L and Qiao T 2012. The earliest known stem-tetrapod from the Lower Devonian of China. Nature Communications. 3: 1160. doi:10.1038/ncomms2170
Yu X-B 1998. A new porolepiform-like fish, Psarolepis romeri, gen. et sp. nov. (Sarcopterygii, Osteichthyes) from the Lower Devonian of Yunnan, China. Journal of Vertebrate Paleontology. 18 (2): 261–274.
Zhu M and Ahlberg P 2004. The origin of the internal nostril of tetrapods. Nature 432:94-97.
Zhu M, Zhao W, Jia Lu J, Qiao T and Qu Q 2009. The oldest articulated osteichthyan reveals mosaic gnathostome characters. Nature 458:469-474
Zhu M, Yu X, Choo B, Qu Q, Jia L, et al. 2012.  Fossil Fishes from China Provide First Evidence of Dermal Pelvic Girdles in Osteichthyans. PLoS ONE 7(4): e35103. doi:10.1371/journal.pone.0035103
Zhu M, Yu X-B and Janvier P 2014. A primitive fossil fish sheds light on the origin of bony fishes. Nature 287:607–610.

wiki/Tungsenia
wiki/Guiyu
wiki/Psarolepis
wiki/Styloichthys
wiki/Stensioella
wiki/Kenichthys
wiki/Youngolepis

Tiny enigmatic Feralisaurus nests with a giant bizarre sister

Today
another paleo-enigma is confidently nested after those who had direct access to the specimen gave up on it. The authors admitted they didn’t know what they had.

According to the Cavicchini, Zaher and Benton 2020 abstract:
“Phylogenetic analyses, although showing generalized weak support, retrieved Feralisaurus within Neodiapsida or stem-group Lepidosauromorpha: its morphology supports the latter hypothesis.”

The authors gave up because they excluded pertinent taxa.
The authors did not reference the large reptile tree (LRT, 1745+ taxa; subset Fig. 6), which minimizes taxon exclusion. Here, having a quantity of taxa really paid off.

The ‘enigmatic Otter Sandstone diapsid’ from 2017 finally has a name:
Feralisaurus corami (Cavicchini, Zaher and Benton 2020; Coram, Radley and Benton 2017; BRSUG 29950-12; Middle Triassic). Cavicchini, Zaher and Benton 2020 provided µCT scans (Fig. 1) from which a reconstruction was created and scored using DGS (digital graphic segregation). They nested aquatic Feralisaurus between the gliding reptile, Coelurosauravus and basal lepidosaurs + another gliding reptile, Icarosaurus (Fig. 5).

Figure 1. Feralisaurus in situ and reconstructed. CT scans (hard colors) from Cavicchini, Zaher and Benton 2020. DGS (soft colors) added here.

Figure 1. Feralisaurus in situ and reconstructed. CT scans (hard colors) from Cavicchini, Zaher and Benton 2020. DGS (soft colors) added here. Shown about 20% larger than life size. Here more cervicals are present, a sternum is present, The tip of the posterior interclavicle is identified along with several skull bones. Creating or attempting to create a reconstruction is the second half of the DGS method and, as you can see, it is so important in understanding all enigmatic specimens.

After DGS, reconstruction and re-scoring in the LRT
(Fig. 6), tiny, flat-headed Feralisaurus nests with the giant, flat-headed macrocnemid tritosaur lepidosaur Dinocephalosaurus. Both are derived from the PIMUZ 2477 specimen of Macrocnemus, nesting apart from the other tested Macrocnemus specimens (Fig. 6).

Figure 6. Dinocephalosaurus skull in situ.

Figure 2. Dinocephalosaurus skull in situ. The maxillary palatal shelf? is not colored here.

The dorsal nares in both Feralisaurus and Dinocephalosaurus
may have emitted stale air as a bubble net to corral fish swimming overhead (Fig. 3), analogous to the feeding strategy of baleen whales. The larger the size, the longer the neck, the greater storage for this stale air. Perhaps that is what drove the transition from tiny Feralisaurus to the much larger Dinocephalosaurus.

Dinocephalosaurus in resting, feeding and breathing modes.

Figure 3. Dinocephalosaurus in resting, feeding and breathing modes. In breathing mode the throat sac would capture air that would not be inhaled until the neck was horizontal at the bottom of the shallow sea. Orbits on top of the skull support this hypothesis.

Coram, Radley and Benton 2017
presented (then nameless) Feralisaurus as a “small diapsid reptile, possibly, pending systematic study, a basal lepidosaur or a protorosaurian.” According to Coram et al. “The Middle Triassic (Anisian) Otter Sandstone was laid down mostly by braided rivers in a desert environment.” 

What was visible to the unaided eye
in the 2017 report suggested a relationship to the basal lepidosaur, Megachirella. The 2020 µCT scans of Feralisaurus data corrected earlier errors. Here (Fig. 4) is the first reconstruction of Feralisaurus based on DGS. The new data nests it with Dinocephalosaurus, despite the great difference in size, the differences in morphology and the niche relocation from braided river in a desert to ocean.

Figure 2. Feralisaurus reconstructed in lateral and dorsal views.

Figure 4. Feralisaurus reconstructed in lateral and dorsal views.

Although Cavicchini, Zaher and Benton 2020 scanned the specimen
those scans were not enough to clarify phylogenetic issues. The authors not only excluded its LRT sister, Dinocephalosaurus, but hundreds of other taxa that would have split basal Reptilia into the new Archosauromorpha and the new Lepidosauromorpha (Fig. 5) as in the LRT. This basal dichotomy following Silvanerpeton in the Viséan (or earlier) is recovered when sufficient pertinent basal taxa are added to a reptile cladogram. Apparently no one wants to add hundreds of taxa when ready-made smaller invalid cladograms are available.

Figure 3. Cladogram from Cavicchini, Zaher and Benton 2020, colors added based on the LRT showing how massive taxon exclusion shuffles convergent taxa.

Figure 5. Cladogram from Cavicchini, Zaher and Benton 2020, colors added based on the LRT showing how massive taxon exclusion shuffles convergent taxa.

The Cavicchini, Zaher and Benton 2020 cladogram
shows what happens when you include too few taxa. As in prior analyses of similar deficit, this one (Fig. 5) shuffles members of the new Archosauromorpha and new Lepidosauromorpha. The Cavicchini, Zaher and Benton 2020 cladogram nests the glider Icarosaurus, with the large plant-eating Trilophosaurus. Note how easily rhynchosaurs (Lepidosauromorpha) nest with protorosaurs (Archosauromorpha) here splitting Protorosaurus from Prolacerta. The LRT adds enough taxa to nest rhynchosaurs with rhynchocephalians and Protorosaurus with the other protorosaur, Prolacerta.

Figure 4. Subset of the LRT with the addition of Feralisaurus (yellow).

Figure 6. Subset of the LRT with the addition of Feralisaurus (yellow).

Feralisaurus was a tiny river predator,
smaller than the PIMUZ 2477 Macrocnemus. Dinocephalosaurus was a giant marine predator with a longer neck, shorter limbs and other extreme traits.

Once again, phylogenetic miniaturization
appears to have preceded a novel morphology.

The apparent lack of maxillary bone
in Feralisaurus (perhaps due to taphonomy) continues as a likely antorbital fenestra in Dinocephalosaurus. What was considered a lateral panel of the maxilla could instead be a maxillary palatal shelf showing through the antorbital fenestra. The broad muzzle and genuine flatness of the Feralisaurus skull continues in Dinocephalosaurus.

Figure 7. Feralisaurus is a phylogenetic miniature nesting basal to Dinocephalosaurus in the LRT.

Figure 7. Feralisaurus is a phylogenetic miniature nesting basal to Dinocephalosaurus in the LRT.

Bottom line: 
Create reconstructions using DGS. Add taxa. These methods solve problems. Workers traditionally say first-hand observation is essential. This case proves, once again, first-hand observation is not essential. A cladogram as large as the LRT is essential.


References
Caviccnini I, Zaher M and Benton MJ 2020. An enigmatic neodiapsid reptile from the Middle Triassic of England. Journal of Vertebrate Paleontology e1781143 (18 pages)
Coram RA, Radley JD and Benton MJ 2017. The Middle Triassic (Anisian) Otter Sandstone biota (Devon, UK): review, recent discoveries and ways ahead. Proceedings of the Geologists’ Association in press. http://dx.doi.org/10.1016/j.pgeola.2017.06.007

http://reptileevolution.com/dinocephalosaurus.htm

https://pterosaurheresies.wordpress.com/2017/07/27/what-is-the-enigmatic-otter-sandstone-middle-triassic-diapsid/

wiki/Feralisaurus
wiki/Dinocephalosaurus

Bluefieldius, a tiny Mississippian cheirolepid, enters the LRT

Mickle 2018 described an exquisite, tiny,
Upper Mississippian fish from West Virginia. Bluefieldius mercerensis (Mickle 2018, Late Mississippian, KUVP 155843;  Figs. 1, 2) was originally described without a phylogenetic analysis.

Figure 1. Bluefieldius in situ from Mickle 2018 shown many times larger than life size.

Figure 1. Bluefieldius in situ from Mickle 2018 shown many times larger than life size.

From the abstract
“The description of this new taxon represents the first actinopterygian and the first vertebrate body fossil described from the Bluefield Formation and the second actinopterygian taxon described from the Mauch Chunk Group in West Virginia.”

Figure 2. The skull in situ and diagram of Bluefieldius from Mickle 2018, Colors added here to match tetrapod homologs.

Figure 2. The skull in situ and diagram of Bluefieldius from Mickle 2018, Colors added here to match tetrapod homologs.

Mickle 2018 reports,
B. mercerensis n. gen. n. sp. differs from other Carboniferous fishes in specific cranial characteristics. Lower actinopterygian fishes are characterized by a great deal of anatomic and taxonomic diversity that is not well understood. We have neither a stable classification scheme nor strongly supported hypotheses of relationships for lower actinopterygian fishes.”

That was true back then in 2018. Now that the LRT includes a wide gamut of fish taxa the LRT provides that stable classification scheme.

Figure 5. The genus Cheirolepis by Pearson and Westoll 1979 (line drawing) compared to DGS skull tracing. Evidently these were two different specimens based on scale alone.

Figure 3. The genus Cheirolepis by Pearson and Westoll 1979 (line drawing) compared to DGS skull tracing. Evidently these were two different specimens based on scale alone.

Mickle did not perform a phylogenetic analysis,
but preferred to list traits that marked this taxon. As you know, this is called, “Pulling a Larry Martin,” Some traits were mismarked by Mickle 2018 (Fig. 2) relative to traits traced here based on tetrapod homologs.

Figure x. Subset of the LRT focusing on fish.

Figure x. Subset of the LRT focusing on fish.

Here
in the large reptile tree (LRT, 1742+ taxa, Fig. x) Bluefieldius nests basal to the Cheirolepis (Fig. 3) clade.


References
Mickle KE 2018. A new lower actinopterygian fish from the Upper Mississippian Bluefield Formation of West Virginia, USA. PeerJ 6:e5533; DOI 10.7717/peerj.5533

Beg tse: restoring missing neoceratopsian parts

Yu et al. 2020 bring us
a mostly complete and articulated 3D skull of a new neoceratopsian, Beg tse (Fig. 1; Mid- Cretaceous, Mongolia). Here some restoration, based on comparison to a phylogenetic sister Auroraceratops (Fig. 2), helps us understand the extent of the missing parts of this neoceratopsian.

Figure 1. Most of the skull of the new neoceratopsian, Beg tse. Colors added.

Figure 1. Most of the skull of the new neoceratopsian, Beg tse. Colors added.

Sereno 2005 defined Neoceratopsia as:
The most inclusive clade (Fig. 3) including Triceratops horridus, but not Psittacosaurus mongoliensis.

Figure 2. Beg tse nests with Auroraceratops in the LRT.

Figure 2. Beg tse nests with Auroraceratops in the LRT.

Yu et al. considered
Beg tse the most basal neoceratopsian currently known. That does not quite agree with the results recovered by the LRT (subset Fig. 3). Other taxa (Leptoceratops (Fig. 4), Auroraceratops) also nest in this node.

Figure 3. Subset of the LRT focusing on Ornithischia with the addition of Beg tse.

Figure 3. Subset of the LRT focusing on Ornithischia with the addition of Beg tse.

Figure 1. Leptoceratops in situ 2x. This taxon resolves the headless and head only node at the base of the ceratopsians in the LRT.

Figure 4. Leptoceratops in situ 2x. This taxon resolves the headless and head only node at the base of the ceratopsians in the LRT.

Since Stenopelix (Fig. 5) is almost quadrupedal,
phylogenetic bracketing indicates that Beg tse and Aurorceratops were likely bipeds, like Psittacosaurus (Fig. 5) and Leptoceratops (Fig. 4).

Figure 1. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

Figure 5. Stenopelix reconstructed in lateral and dorsal views to scale with Psittacosaurus. The curved ischium and short tail with short chevrons allies Stenopelix with ceratopsians.

References
Yu C, Prieto-Marquez A, Chinzorig T, Badamkhatan Z and Norell M 2020. A neoceratopsian dinosaur from the early Cretaceous of Mongolia and the early evolution of ceratopsia. Nature Communications Biology 3:499 | https://doi.org/10.1038/s42003-020-01222-7 http://www.nature.com/commsbio

wiki/Beg_tse

Shedding new light (literally!) on Jianianhualong: Li et al. 2020

Li et al. 2020 used various frequencies of light
and spectroscope technology on the holotype bones and feathers of Jianianhualong (Figs. 1, 2; Early Cretaceous, Xu et al. 2020, DLXH 1218) to identify specific elements in the matrix and specimen.

From the abstract:
“Here, we carried out a large-area micro-X-Ray fluorescence (micro-XRF) analysis on the holotypic specimen of Jianianhualong tengi via a Brucker M6 Jetstream mobile XRF scanner.”

Figure 2. Jianianhualong, Serikornis and Jurapteryx to scale.

Figure 1a. Jianianhualong, Serikornis and Jurapteryx to scale.

Figure 1. Jianianhualong tengi in situ. This is the largest among the early birds, a fact overlooked by the Xu et al. 2017. Think of Jianianhualong as a giant Archaeopteryx!

Figure 1b. Jianianhualong tengi in situ. This is the largest among the early birds, a fact overlooked by the Xu et al. 2017. Think of Jianianhualong as a giant Archaeopteryx!

From the abstract:
“Jianianhualong tengi is a key taxon for understanding the evolution of pennaceous feathers as well as troodontid theropods, and it is known by only the holotype, which was recovered from the Lower Cretaceous Yixian Formation of western Liaoning, China.” 

What they didn’t do is to rerun their phylogenetic analysis with more taxa (Fig. 2).

What they didn’t do is to create a reconstruction, perhaps using DGS to precisely trace and segregate the bones to rebuild the skeleton (Figs. 1, 3, 4).

Figure 2. Subset of the LRT focusing on Pennaraptora 2014 = Tyrannoraptora 1999. Here Khaan and Velociraptor substitute for Oviraptor and Deinonychus.

Figure x. Subset of the LRT focusing on birds and their ancestors. Jianianhualong nests within Aves (five taxa from the bottom).

By contrast,
in the large reptile tree (LRT, 1730+ taxa) Jianianhualong nests within Aves (five taxa from the bottom of Fig. 2) even though it was clearly not volant due to its much larger size and smaller forelimbs. Close relatives include Archaeopteryx (= Jurapteryx) recurva (= Eichstätt specimen, Fig. 3) and the privately held #11 specimen of Archaeopteryx.

The authors think Jianianhualong is a troodontid.
According to Wikipedia“A number of characteristics allow Jianianhualong to be identified as a member of the Troodontidae. These include:

  1. the long forward-projecting branch and flange of the lacrimal bone; [✓]
  2. the foramina on the nasal bone; [?]
  3. the smooth transition between the eye socket and the backward-projecting branch of the frontal bone; [✓]
  4. the ridge on the forward-projecting branch of the jugal bone; [✓]
  5. the triangular dentary bearing a widening groove; [✓]
  6. the robust forward-projecting branch of the surangular bone; [✓]
  7. the relatively large number of unevenly-distributed teeth; [✓]
  8. the flattened chevrons with blunt forward projections and bifurcated backward projections; [✓]
  9. and the broad and flat “pubic apron” formed by the pubic bones.” [?]
Figure 3. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Figure 2. The Eichstätt specimen, Jurapteryx recurva, nests with the living ostrich, Struthio, presently in the LRT.

Professor Larry Martin would be so proud!
Why? Because the Wikipedia author (above) is using a list of traits to support an hypothesis of interrelationships rather than using a cladogram to support that hypothesis.  Checkmarks [✓] indicate traits Jurapteryx shares. Question marks [?] indicate traits not shown in Jianianhualong or Jurapteryx. Or did I miss something?

The problem is,
various authors add taxa to the Troodontidae that don’t belong there in the LRT, as we learned earlier here. The LRT; subset Fig. x) recovers Jiaianhualong as the largest known member of the Sapeornis/Jurapteryx clade of birds. Several flightless birds are in this clade. These could be confused with troodontids for that reason. In the LRT the clade Troodontidae include Sinornithoides + Sauronithoides their LCA and all derived taxa. None of these are direct bird ancestors.

Getting back to chemistry
“The bone in Jianianhualong is, as expected rich in calcium and phosphorus, corresponding mineralogically to apatite. The regions where feather remains can be observed show an enrichment and correlation pattern of several elements including manganese, titanium, nickel and copper.”

FIgure 2. GIF animation of the skull of Jianianhualong showing original tracing in line art and colorized bones (DGS) used to create a reconstruction (Fig. 3).

FIgure 3. GIF animation of the skull of Jianianhualong showing original tracing in line art and colorized bones (DGS) used to create a reconstruction (Fig. 3).

Jianianhualong is a troodontid-like bird,
not a bird-like troodontid. Note the odd scapula shape, like that in Sapeornis. Note the retrovered pedal digit 1, showing this taxon was derived from perching birds. The tall naris and long tibia are autapomorphies.

Xu et al. 2014 made a headline out of
the asymmetric feathers found with Jianianhualong. In the present context, Jianianhualong is derived from volant ancestors. So asymmetry is expected, not exceptional. This is the earliest known large flightless bird, not an example of the invalid hypothesis of ‘mosaic’ evolution.

Figure 3. Reconstruction of the skull of Jianianhualong based on DGS tracings in figure 2.

Figure 4. Reconstruction of the skull of Jianianhualong based on DGS tracings in figure 2.

Liaoningventor curriei (Shen et al. 2017; DNHM D3012; Early Cretaceous) was also originally described as a non-avian troodontid, but nests with Jianianhualong as a flightless bird.


References
Li J, et al. (8 co-authors 2020. Micro-XRF study of the troodontid dinosaur Jianianhualong tengi reveals new biological and taphonomical signals. bioRxiv 2020.09.07.285833 (preprint) PDF doi: https://doi.org/10.1101/2020.09.07.285833
https://www.biorxiv.org/content/10.1101/2020.09.07.285833v1
Shen C-Z, Zhao B, Gao C-L, Lü J-C and Kundrat 2017. A New Troodontid Dinosaur (Liaoningvenator curriei gen. et sp. nov.) from the Early Cretaceous Yixian Formation in Western Liaoning Province. Acta Geoscientica Sinica 38(3):359-371.
Xu X, Currie P, Pittman M, Xing L, Meng QW-J, Lü J-C, Hu D and Yu C-Y 2017. Mosaic evolution in an asymmetrically feathered troodontid dinosaur with transitional features. Nature Communications DOI: 10.1038/ncomms14972.

wiki/Sapeornis
wiki/Jianianhualong
wiki/Liaoningvenator

Enigmatic Jamoytius enters the LRT

Sansom et al. 2010 studied and discussed
Jamoytius kerwoodi (White 1946; Early Silurian; Fig. 1) an early eel-like taxon originally considered to be the most primitive known vertebrate, then a sister to lampreys, then a sister to Euphanerops (the subject of yesterday’s post). Turns out, it is none of these.

Sansom et al write:
“The study of the anatomy of problematic organisms can be aided by the use of a methodology designed to separate topological and morphological reconstruction from anatomical interpretation and to gather as much information as possible about the preserved features through taphonomic analyses.”

Unfortunately the authors did not trace the skull bones (Fig. 1) and those of several related taxa (Figs. 3, 4) and so missed the ability to score Jamoytius more completely and accurately.

“Interpretations of paired fins remain equivocal. Analyses of the phylogenetic affinity of Jamoytius identify a sister taxon relationship with Euphanerops. This clade, the Jamoytiiformes, is a primitive group of stem-gnathostomes and does not form a clade with the Anaspida.”

By contrast, the large reptile tree (LRT, 1718+ taxa, subset Fig. 2) nests Jamoytius not with lampreys, nor with Euphanerops, but between Birkenia (Fig. 3) and Thelodus (Fig. 4), taxa ignored by Sansom et al.

Figure 1. Jamoytius photo and diagram from Sansom et al. 2020. Colors and new labels added here.

Figure 1. Jamoytius photo and diagram from Sansom et al. 2020. Colors and new labels added here. Note the lack of skull bone tracings on the diagram. It looks like each gill opening has a little opercular flap. Note the new identification for the left eye. The ‘notochord’ is here a dorsal ridge, a precursor to dorsal armor.

Jamotius kerwoodi (White 1946, Sansom et al. 2010; Early Silurian; 10+cm in length) shares a tiny circular mouth and naris at the tip of its short snout with closely related taxa along with a similar set of skull bones, plus a dorsal ridge!

Figure 2. Subset of the LRT focusing on basal chordates and Jamoytius.

Figure 2. Subset of the LRT focusing on basal chordates and Jamoytius.

 With a small circular oral cavity,
Jamoytius and its sisters could not have been open sea predators, or blood suckers, but likely scoured sea muds and lake sands for tiny buried prey, like young lancelets and This extant sturgeons. Sturgeons (Fig. 4) feed on a spectrum of small benthic prey. Larger  sturgeons are known to suck in larger prey, like salmon, into their toothless, nearly jawless oral cavity.

BTW,
these taxa are all buried deep in the human lineage. So, say ‘hello’ to your ancestors.

Figure 3. Birkenia skull for comparison to Jamoytius.

Figure 3. Birkenia skull for comparison to Jamoytius.

Paleontologists of all stripes are fond of saying,
‘first-hand examination of the fossil is essential’. Sansom et al. had several fossils to look at firsthand and did not trace skull bones (Fig. 1). As I’ve been saying for nine years, the computer monitor and a digitally scanned photo can be superior to a binocular microscope because the monitor can trace elements in color, thereby reducing the apparent chaos into discrete segregated units. That opens up a whole new world of data that can be used to confidently nest enigmatic taxa, like Jamoytius (Fig. 2).

Figure 7. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

Figure 4. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

Taxon exclusion, once again. 
Sansom et al. did not mention, trace and test either Birkenia (Fig. 3) or Thelodus (Fig. 4). So taxon exclusion is also an issue resolved here by the LRT using character traits originally designed for reptiles and still working in basal chordates. It’s that simple. Just add taxa and enigmas get confidently nested.


References
Sansom RS, Freedman K, Gabbott SE, Aldridge RJ and Purnell MA 2010. Taphonomy and affinity of an enigmatic Silurian vertebrate, Jamoytius kerwoodi White. Palaentology 53(6):1393–1409.
White EI 1946. Jamoytius kerwoodi, a new chordatefrom the Silurian of Lanarkshire. Geological Magazine, 83, 89–97.

wiki/Jamoytius

Euphanerops: basal to sturgeons with tiny new pelvic fins

Janvier and Arsenault 2007 took another look at
Euphanerops longaevus (Woodward 1900; Late Devonian, Figs. 1, 2) comparing it uncertainly to living lampreys and extinct jawless, finless fish. They report, “The anatomy of Euphanerops longaevus is reconstructed here on the basis of 17 specimens, 14 of which were hitherto undescribed. Practically all the mineralized elements that can be observed in the largest individuals of E. longevous display the same structure, which strikingly recalls that of lamprey cartilage, despite the uncertainty as to the origin of its mineralization.”

Elongated and confluent paired fins
“The new material of E. longaevus described here provides strong support for the presence of ventrolateral, ribbon-shaped, paired fins armed with numerous parallel radials. These fins extend from the anus to the anterior part of the branchial apparatus anteriorly, and are the first instance of paired fins with radials, whose anteroposterior extension largely overlaps that of the branchial apparatus in a vertebrate.”

Mostly true, but let’s not forget in manta rays and guitarfish, skates and rays, paired pectoral fins indeed do overlap the branchial apparatus (= gill basket), IF that is happening in Euphanerops (see below).

From the abstract
“Owing to the uncertainty as to the biogenic or diagenetic nature of the anatomical features described in E. longevous, no character analysis is proposed. Only a few possible homologies are uniquely shared by euphaneropids and either lampreys or anaspids, or both.”

Phylogenetically, the authors note:
“Euphanerops longaevus has been referred to as an anaspid, chiefly because of its distinctive hypocercal tail and anal fin. However, since it apparently has no mineralized dermal skeleton, E. longaevus lacks evidence for the tri-radiate postbranchial spine, which Forey (1984) proposed as the defining character of the Anaspida. Consequently, it is now often treated in recent phylogenetic analyses as a separate terminal taxon, alongside other scale-less (or “naked”) jawless vertebrate taxa also once regarded as anaspids, namely Endeiolepis and Jamoytius.”

Figure 1. Several basal chordates: Branchiostoma, Euphanerops, Jamoytius and Birkenia. The middle image of Euphanerops is the tracing. The others are freehand interpretations not supported here.

Figure 1. Several basal chordates: Branchiostoma, Euphanerops, Jamoytius and Birkenia. The middle image of Euphanerops is the tracing. The others are freehand interpretations from Janvier and Arsenault 2007.

Here 
(Fig. 2) individual skull bones and tiny overlooked pectoral and pelvic fins are identified. Adding a missing (unossified?) rostrum (= nasal) restores the original profile. In the large reptile tree (LRT, 1717+ taxa) Euphanerops nests basal to sturgeons, like Pseudoscaphirhynchus (FIg. 3), a clade not mentioned by Janvier and Arsenault 2007. A previously enigmatic element in front of the mouth is here identified as a pair of barbels, as in sturgeons. The tiny dorsal spines of Euphanerops are also found as larger dorsal armor in Birkenia, osteostracans and sturgeons.

Figure 7. Transitional Euphanerops is more sturgeon-like, but the location of the operculum and/or gill openings are not apparent here. The nasal is missing from both the plate and counter plate.

Figure 7. Transitional Euphanerops is more sturgeon-like, but the location of the operculum and/or gill openings are not apparent here. The nasal is missing from both the plate and counter plate.

According to Wikipedia
Euphaneropidae have, “greatly elongated branchial apparatus which covers most of the length of the body.”

Here that area is identified as a typical subdivided and flattened ventral surface, as in Birkenia, sturgeons and osteostracans.

Figure 2. Skull of Pseudoscaphorhynchus. Note the mouth is created by the lacrimal and angular, not the maxilla and dentary, which are tooth-bearing bones in more derived fish.

Figure 2. Skull of Pseudoscaphorhynchus. Note the mouth is created by the lacrimal and angular, not the maxilla and dentary, which are tooth-bearing bones in more derived fish.

The hypocercal tail of Euphanerops
has heterocercal elements and this taxon nests between taxa with a heterocercal tail. With an Ordovician genesis, Late Devonian Euphanerops likely developed a dipping tail and larger propulsive dorsal fin secondarily, as a reversal. An ancestor, Birkenia, has a similar dipping tail.

Figure 4. Euphanerops caudal fin with elements re-identified.

Figure 4. Euphanerops caudal fin with elements re-identified.

Small enigmatic squares of rod-like elements near the cloaca
are here identified as primitive pelvic fins or vestiges of the same. More primitive taxa do not have pelvic fins. More derived taxa do.

Figure 3. Euphanerops with elements here identified as tiny pectoral fins just anterior to the cloaca.

Figure 5. Euphanerops with elements here identified as tiny pectoral fins just anterior to the cloaca and posterior to the ventral armor. Images from Janvier and Arsenault 2007.

Primitive pectoral fins
are known in ancestral and descendant taxa, so Euphanerops should have them, too. Here (Fig. 6) they are identified as vestiges.

Figure x. Euphanerops plate and counter plate with colors added identifying elements.

Figure 6. Euphanerops plate and counter plate with colors added identifying elements.

Traditionally sturgeons have not been tested with osteostracans
(Fig. 7) and other jawless fish. The LRT tests a wide gamut of competing candidates and nests sturgeons prior to the advent of jaws and teeth in vertebrates, close to osteostracans and Euphanerops. Do not let one or two traits, like a dipping (hypocercal) tail, steer you off course in your wide-gamut analysis.

Figure 7. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

Figure 7. Top to bottom: Thelodus a soft jawless fish with a ventral oral opening and gill slits, perhaps a hint of diamond-shaped armor laterally. Hemicyclaspis, adds extensive armor. Euphaneropsps, a late survivor of an Ordovician radiation basal to sturgeons. Acipenser, a sturgeon with a protrusible tube for a mouth and reduced armor. Chondrosteus, a fish with jaws, but no marginal teeth.

The ‘paired fin ridges’ observed by Janvier and Arsenault
may be ray-like ossifications that gathered to produce the ventrolateral armor on sturgeons (Fig. 7) or were vestiges thereof. Additionally, that’s where basal chordate gonads are located.

A set of lamprey-like gill openings appear near the skull
of Euphanerops. This appears to be a retention of or reversal back to similar multiple openings seen in Birkenia (Fig. 1). Again, don’t judge a taxon by one or two traits. Test them all against a wide gamut of taxa, like the LRT. We may be seeing what happens a the transition from multiple gill openings to a sturgeon-like operculum here.


References
Janvier P, Desbiens S, Willett JA and Arsenault 2006. Lamprey-like gills in a gnathostome related Devonian jawless vertebrate. Nature 440:1183–1185.
Janvier P and Arsenault M 2007. The anatomy of Euphanerops longaevus Woodward, 1900, an anaspid-like jawless vertebrate from the Upper Devonian of Miguasha, Quebec, Canada. Geodiversitas 29 (1) : 143-216.
Woodward AS 1900. On a new ostracoderm fish (Euphanerops longaevus) from the Upper Devonian of Scaumenac Bay, Quebec, Canada. Magazine of Natural History ser. 7, 5: 416-419.

wiki/Euphaneropidae

Platysomus sheds new light on placoderms

Short one today.
One more fish enters the LRT. Some changes (like a prefrontal) are added to previously nested taxa.

Adding the Carboniferous fish,
Platysomus (Fig. 1) , to the large reptile tree (LRT, 1713+ taxa; Fig. 2) to no one’s surprise nests it with Cheirodus (= Chirodus, Amphicentrum; Fig. 1), a less stretched-out version.

The heresy is
these two taxa nest with catfish and placoderms (Fig. 2) when allowed to do so by taxon inclusion, as we’ve seen previously. Placoderms evolve from ordinary fish.

Figure 1. Platysomus and Cheirodus are both platysomids, related to catfish and placoderms. All these taxa lack maxillae.

Figure 1. Platysomus and Cheirodus are both platysomids, related to catfish and placoderms. All these taxa lack maxillae. Note the relabeling on Platysomus.

None of these taxa
have a maxilla and they share a long list of other synapomorphic traits.

Figure 3. Subset of the LRT focusing on fish and updated here.

Figure 3. Subset of the LRT focusing on fish and updated here. Catfish and placoderms are located in the center of this diagram.

Another traditional platysomid, 
Eurynotus (Fig. 4), is even closer to the placoderms Coccosteus (open sea predators) and Entelognathus (bottom dwellers).

Figure 2. Eurynotus is another platysomid, basal to the placoderms Coccosteus and Entelognathus.

Figure 2. Eurynotus is another platysomid, basal to the placoderms Coccosteus and Entelognathus. Sharp-eyed readers will notice several skull identity changes in placoderms based on what was learned from this taxon.

Platysomus parvulus (Agassiz 1843, Carboniferous to Permian; 18cm long) is a taller, more disc-like fish related to Cheirodus. Note the reduction of the mandible. Considered a plankton eater.

Apologies for the bone ID changes.
I’m learning as I go and revising the naming system so homologies with tetrapods can be more readily understood. Someone had to do it. Why wait until 2021 or thereafter?


References
Agassiz L 1833, 1837 in Agassiz L 1833-1843. Recherches sur les Poissons fossiles-I, I, III, Neuchatel, pp 1420.