Rhinochimaera is added to the LRT as another ratfish

Adding taxa continues to clarify hypothetical interrelationships
among all included taxa in the LRT. especially in the shark grade/clade where skull elements are cartilaginous and tend to fuse together leaving fewer clues/landmarks in the more derived taxa.

Didier 1995 reports,
“There are two hypotheses on the origin of Holocephali (Bonaparte 1832). The first and most generally accepted scenario is that holocephalans have evolved from some lineage of bradyodont sharks. The second hypothesis suggests that holocephalans are most closely related to placoderms.”

In the LRT placoderms are not basal to sharks, but nest with bony fish in a clade that reverted to a cartilaginous internal skeleton while keeping a bony dermal skeleton. So the second hypothesis is falsified.

According to Wikipedia, “Most Bradyodonti fossils consist of jaws and teeth. These indicate that Bradyodonti ate mollusks and other shelled invertebrates. Their bodies were probably broad and flattened, like modern rays.”Bradyodonti” can also refer to the present-day Chimaera or ratfish of the order Chimaeriformes, which have an upper jaw fused to the braincase and a flap of skin covering the gill slits.”

So, once again suprageneric taxon labels leave us all a little confused since Bradyodonti = Chimaeriformes in some circles.

Figure 4. Shark skull evolution according to the LRT. Compare to figure 1.

By adding taxa
to the large reptile tree (LRT, 1776 taxa, subset Figs. 1, 2) holocephali (= chimaera, ratfish) arise from taxa near Squalus and Heterodontus (Fig. 8) close to the shark/ray split where marginal teeth become like paving stones.

By adding colors to skulls,
fused and obscure elements may be identified with tetrapod homologs. That makes scoring and identifying errors easier.

Earlier we looked at
a dorsal view of the skull of the dogfish shark, Squalus (Fig. 1) here. You’ll note that there is much more fusion in the skull cartilage of ratfsh (Figs. 5–7) including the fusion of the lacrimal complex (= traditional palatoquadrate) with the neurocranium and dermocranium.

Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.
Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

Didier 1995 reports,
“The adductor muscles of Heterodontus also lie anterior to the eye and superficially they resemble chimaeroid fishes in this respect. I interpret this as a convergent feature of heterodontids and chimaeroids.” That is the only mention of Heterodontus (Fig. 1) in the text. Squalus is the outgroup taxon in Didier’s figure 46 cladogram (Fig. 3).

Figure 1. Cladogram from Didier 1995, colors added to reflect taxon inclusion, exclusion according to the LRT (see figure 2).
Figure 3. Cladogram from Didier 1995, colors added to reflect taxon inclusion, exclusion according to the LRT (see figure 2).

Getting back to Rhinochimaera
(Fig. 4–6). It should come as no surprise that, with its long rubbery snout, Rhinochimaera is among the most derived chimaeras in the LRT (subset Fig. 2). That proboscis is supported by a single slender nasal cartilage articulating on a joint with the rest of the smaller, underlying nasal cartilages (Fig. 6), homologs with similar, smaller elements in Callorhinchus (Fig. 7).

Figure 1. The long-nosed chimaera (Rhinochimaera africana?).
Figure 4. The long-nosed chimaera (Rhinochimaera africana?).
Figure 5. Fused cartilage skull of Rhinochimaera lacking the tactile/sensory probe supports. Compare to diagram in figure 6.
Figure 5. Fused cartilage skull of Rhinochimaera lacking the tactile/sensory probe supports. Compare to diagram in figure 6.
Figure 6. Diagram of Rhinochimaera pacifica from Didier 1995. Inverted area and colors added to show interpretations of element boundaries based on Callorhinchus (Fig. 7) and other related taxa.
Figure 6. Diagram of Rhinochimaera pacifica from Didier 1995. Inverted area and colors added to show interpretations of element boundaries based on Callorhinchus (Fig. 7) and other related taxa.

Rhinochimaera nests with
Callorhinchus (Fig. 6) in the LRT (subset Fig 2), The latter helps identify elements in the former (Figs. 5, 6). Note the lateral rostral rods (l. rost. rod) arises from the lacrimal. The medial rostral rod (m. rost. rod) arises from the nasal.

Figure 7. Callorhinchus milii skull in several views. All the cartilage is fused here, so color identifies elements. Note the tactile rostral elements are smaller and not associated with the premaxilla (contra Didier 1995).
Figure 7. Callorhinchus milii skull in several views. All the cartilage is fused here, so color identifies elements. Note the tactile rostral elements are smaller and not associated with the premaxilla (contra Didier 1995).

Heterodontus
(Fig. 8) likewise helps identify skull elements in chimaeroids prior to the fusion of the lacrimal complex (= traditional palatoquadrate) with the dermocranium and neurocranium.

Figure 8. Heterodontus skull with colors added to identify elements as tetrapod homologs.
Figure 8. Heterodontus skull with colors added to identify elements as tetrapod homologs.

Every added taxon
helps clarify the position of every nested taxon as every included taxon affects every other. Likewise, all included and tested taxa help identify fused elements whenever they appear in taxa like Rhinochimaera (Figs. 4–6). Earlier guesses have been repaired. Current guesses will be repaired as soon as errors are discovered. Sutures may not be visible, but the jaw joint is still the quadrate. The large strut above it is still the hyomandibula. The nasal still extends over the nares. Etc. etc.

Some say I need to look at specimens firsthand.
There’s an answer to that. Although I have examined many specimens firsthand, that’s not my job at present. Precision observations will come, but first a wide-angle view of hundreds of taxa is what is required, because 1) specialists, by definition, are not going to look outside their speciality, and 2) no one has done this before. This one time, just let one guy on the planet do this and the rest of the specialists can benefit from whatever insights are recovered here in this wide-angle view of many taxa at once, the LRT.


References
Bonaparte CL 1832. Iconografia delle fauna italica per le quattro classi degli animali vertebrati. Tomo III. Pesci. Roma. [Issued in puntata (installments), without pagination; total of 556 pp., 78 pls.
Didier DA 1995. 
Phylogenetic Systematics of Extant Chimaeroid Fishes (Holocephali, Chimaeroidei). American Museum Novitates 3119:86pp.
Lund R 1977. New information on the evolution of the bradyodont chondrichthyes. Fieldiana 33(28)521–538.
Venkatesh B et al. 2014. Elephant shark genome provides unique insights into gnathostome evolution. Nature 505:174–179.

The ‘spine-brush complex’ of Akmonistion: dorsal fin? or dorsal shield?

A strange taxonomic addition today.
Akmonistion (Figs. 1, 2) nests in the large reptile tree (LRT, 1634+ taxa) between Falcatus (Fig. 3) and Heterodontus (horn shark. Fig. 4), a taxon that nests basal to members of the Holocephali.

So Akmonistion, Falcatus and Iniopteryx are basal members of Chondrichthyes (1880). These are late-surviving, but basal to both Elasmobranchii (1838, sans Rhincodon and Manta) and Holocephali (1832). Clearly a more plesiomorphic, but currently unknown Silurian or Devonian taxon without all the novel secondary sexual traits awaits discovery.

Figure 1. Stethacanthus in situ, diagram and reconstruction from DGS methods.

Figure 1. Akmonistion in situ, diagram and reconstruction from DGS methods. The tan crest portion appears to be the postparietals or at least the dorsal shield.

Traditional paleontology
considers the famous, bizarre ‘spine-brush’ of Akmonistion (Figs. 1,2) an enlarged and specialized dorsal fin. I will present evidence that it is something else.

Figure 2. Akmonistan, a relative of Stethacanthus.

Figure 2. Akmonistion, a relative of Stethacanthus, from Coates and Sequeira 2001.

What is a spine-brush complex?
Phylogenetic bracketing and simple morphology indicate the spine-brush is convergent with the thoracic shield in placoderms or the postparietals in catfish. This is either a completely novel structure or the elaboration of a smaller older structure from ancestral taxa. In any case the spine-brush complex is not a co-opted dorsal fin.

Ordinary dorsal fins
are made of parallel rods with roots that have sharp ventral tips buried deeply into fish flesh.

By contrast, the brush-shield complex
has a one-piece solid root, like a dorsal shield. If a shield, then primitively a low dorsal shield could have been operational at a low height with a few bumps, improving and growing.generationally by sexual selection.

According to Maisey 2009,
in Falcatus the spine appears relatively late in ontogeny and only in males. Unfortunately, we don’t have an ontogenetic series for Akmonistion. I can only imagine a greatly reduced or absent spine-brush when in the egg. Thereafter, if it followed the pattern in male Falcatus, the spine would appear at puberty.

Weighing one spine-brush hypothesis against another,
the “late-appearing, strange-looking anterior dorsal fin with spine” hypothesis competes with “the late-appearing, strange-looking, well-anchored thoracic shield” hypothesis.

The anterior dorsal fin placement patterns
of the few tested taxa in the LRT produce relatively few strong placement patterns. (Here LRT clades are divided by spaces).

  • In Pseudoscaphorhychus, the sturgeon, a series of dorsal shields are present posterior to the skull, anterior to the pectoral fin.
  • In Rhincodon, the whale shark, the dorsal fins are posterior to the pectoral fins
  • In Falcatus (Fig. 2), the spine extends over the skull, rooted largely anterior to the pectoral fin, but directly over the pectoral girdle.
  • In Iniopteryx, one small posterior dorsal fin appeared dorsal to the pelvic fin, but the pectoral fins are rooted dorsally.
  • In Akmonistion (Fig. 2), the spine brush is rooted posterior to the skull, anterior to the pectoral fin. It could be the post parietal.
  • The following taxa are not in the ancestry of Akmonistion and Falcatus.
  • In Heterodontus, the horn shark, the dorsal fins are posterior to the pectoral fins.
  • In Chimaera, the anterior dorsal fin is dorsal to the pectoral fin.
  • In Belantsea, the anterior dorsal fin is dorsal to the pectoral fin.
  • In Cladoselache, the dorsal fins are posterior to the pectoral fin.
  • In Chlamydoselachus, the dorsal fins posterior to the pelvic fin.
  • In Isurus, the mako shark, the dorsal fins are posterior to the pectoral fins.
  • In Sphyrna, the mako shark, the dorsal fins are posterior to the pectoral fins.
  • In all rays, mantas, skates and angel sharks, both dorsal fins are posterior to the pelvic fins
  • In Polyodon, the paddlefish, the dorsal fin is posterior to the pelvic fins.
  • In Hybodus, the the dorsal fins are posterior to the pectoral fins.

Figure 3. Falcatus skull. This taxon is close to Polyodon in the LRT.

Figure 3. Falcatus skull. This taxon is close to Polyodon in the LRT. Note the anterior placement of the antler/spine/dorsal shield just behind the postparietals.

Does the LRT document any Akmonistion ancestors with dorsal shields?
In other words, is the dorsal shield of Akmonistion a reversal? a reappearance of something already in the gene pool? Or is it a novel trait?

FIgure 1. Ratfish (chimaera) and Heterodontus to scale.

FIgure 4. Ratfish (chimaera) and Heterodontus to scale.

We have three armored ancestors, according to the LRT.

  • Jawless Birkenia has dorsal hooks and ossifications
  • Jawless Hemicyclaspis (Fig. 5) is covered in armor.
  • Semi-jawless sturgeons, like Pseudoscaphorhychus (Fig. 5), retain a series of dorsal plates and other armor.

Figure 1. The osteostracan Cephalaspis (above) compared to the sturgeon Pseudoscaphorhynchus (below). The similarities of these armored morphologies have been overlooked previously. In both cases the jawless or tubular mouth is below the skull, the former towards the front, the latter below the eyes.

Figure 5. The osteostracan Cephalaspis (above) compared to the sturgeon Pseudoscaphorhynchus (below). Note the dorsal armor just behind the skull.

Akmonistion zangerli (HMV8246; Coates and Sequeira 2001; Early Carboniferous) had a larger spine-brush complex. Note the great distance between the skull and pectoral girdle along with the short rostrum and large orbit.

Figure F. Basal tetrapods 2020.

Figure 6. Basal vertebrates and tetrapods 2020. Akmonistion nests between Falcatus + Iniopteryx and Heterodontus + the rest of the Chondrichtheys.

Stethacanthus altonensis (St. John and Worthen 1875; Late Devonian to Early Carboniferous; 70cm) has a posterior-leanding brush-spine.


References
Bonaparte 1832. Iconografia della fauna italica, per le quatro classi degli animali vertebri. Rome, 78 pp.
Coates MI and Sequeira SEK 2001. A new stethacanthid chondrichthyan from the lower Carboniferous of Bearsden, Scotland. Journal of Vertebrate Paleontology. 21 (3): 438–459.
Maisey JG 2009. The spine-brush complex in Symmoriiform sharks (Chondrichthyes: Symmoriiformes), with comments on dorsal fin modularity. Journal of Vertebrate Paleontology, 29(1), 14-24.
St. John OH and Worthen AH 1875. Palaeontology of Illinois. Descriptions of fossil fishes. Geological Survey of Illinois, 6: 245–488.
Zangerl R 1984. On the microscopic anatomy and possible function of the spine-“brush” complex of Stethacanthus (Elasmobranchii: Symmoriida). Journal of Vertebrate Paleontology. 4 (3): 372–378.

wiki/Stethacanthus
wiki/Stethacanthidae
wiki/Akmonistion

Hybodus enters the LRT as one of our direct ancestors

Updated January 27, 2020
with new interpretations of Hybodus and many dozen addition taxa helping to settle Hybodus in a node basal to the basal dichotomy that splits most bony fish (see cladogram below, Fig. 3).

It should come as no surprise
that Hybodus (Figs. 1, 2) was basal to the spiny sharks (Acanthodii), but the surprise is there are several intervening taxa between these nodes. Hybodus is also transitional from chimaeras to lobefins + humans in the LRT. So this is a ‘key players’.

Figure 1 (added 01/27/2020 with a current interpretation of skull bones on Hybodus, plus a reconstruction. Note the retention of external gill bars.

Figure 1 (added 01/27/2020 with a current interpretation of skull bones on Hybodus, plus a reconstruction. Note the retention of external gill bars.

Figure 1. Diagram of Hybodus in vivo and skeleton plus teeth.

Figure 2. Diagram of Hybodus in vivo and skeleton plus teeth.

Traditionally considered an odd sort of shark with dorsal spines,
Hybodus (Fig. 1) nests in the large reptile tree (LRT, 1583 (now 1643) taxa; Fig. 2) between sharks + chimaeroids and placoderms leading + two large clades of bony fish. Apparently this hypothesis of interrelationships has been overlooked until now, but it answers so many long-standing questions. Hybodus also greatly resembled the basal placoderm, Coccosteus (Fig. 1) another overlooked hypothesis of interrelationships. And catfish, too.

FIgure 3. Taxa highlighted in today's blog are highlighted here in this subset of the LRT.

FIgure 3. Taxa highlighted in today’s blog are highlighted here in this subset of the LRT.

Hybodus basanus (Agassiz 1837; H. reticulatus (Early Jurassic skull); 2m in length, Permian –Late Cretaceous) nests between sharks + chimaeroids and spiny sharks + bony fish. This relationship was overlooked until now. Note the spines on the dorsal fins. These are homologous with spines on spiny sharks like Diplacanthus (below). Spines are transitional betwen fleshy shark fins and transparent ray fins. The skull is also transitional between sharks and bony fish, despite the presence of large gill bars (yellow) lateral to the jaws.

Figure 3. Diplacanthus, a Mid-Devonian acanthodian with proportions similar to those of a young Hybodus, shorter with longer spines.

Figure 4. Diplacanthus, a Mid-Devonian acanthodian with proportions similar to those of a young Hybodus, shorter with longer spines.

Diplacanthus crassisimus (Miller 1841; Duff 1842; 13cm ; holotype NMS G.1891.92.333, widespread in the Middle Devoinian; Fig. 4). Skull details are vague, so it was not added to the LRT.

According to Davis et al. 2012:
“Acanthodians, an exclusively Palaeozoic group of fish, are central to a renewed debate on the origin of modern gnathostomes: jawed vertebrates comprising Chondrichthyes (sharks, rays and ratfish) and Osteichthyes (bony fishes and tetrapods)… These new data contribute to a new reconstruction that, unexpectedly, resembles early chondrichthyan crania. Principal coordinates analysis of a character–taxon matrix including these new data confirms this impression: Acanthodes is quantifiably closer to chondrichthyans than to osteichthyans. However, phylogenetic analysis places Acanthodes on the osteichthyan stem, as part of a well-resolved tree that also recovers acanthodians as stem chondrichthyans and stem gnathostomes.”

The LRT nests two acanthodians in the stem lobefin clade (Fig. 2).
Earlier we looked at the central nesting of acanthodians between basal taxa and bony fish. Hybodus further confirms this hypothesis of interrelationships now seeking confirmation or refutation from an independent study using a similar taxon list and a new character list.

With more taxa,
and more knowledge of the 137 taxa at hand, note that catfish no longer nest with placoderms, but transitional between placoderms and ray fin fish (Fig. 2).


References
Agassiz L 1837 in Agassiz L. 1833-1843. Recherches sur les Poissons fossiles-I, I, III, Neuchatel, pp 1420.
Burrow C, Blaauwen J, Newman M and Davidson R 2016. The diplacanthid fishes (Acanthodii, Diplacanthiformes, Diplacanthidae) from the Middle Devonian of Scotland. Palaeontologia Electronica 19.1.10A: 1-83.
Davis SP, Finarelli JA and Coates MI 2012. Acanthodes and shark-like conditions in the last common ancestor of modern gnathostomes. Nature 486:247–250.
Duff P 1842. Sketch of the Geology of Moray. Forsyth and Young, Elgin
Maisey JG 1983. Cranial anatomy of Hybodus basanus Egerton from the Lower Cretaceous of England. American Museum Novitates 2758:1–64.
Miller H 1841. The Old Red Sandstone. (first edition). Thomas Constable and Sons, Edinburgh.

wiki/Hybodus
wiki/Diplacanthus

Remora adhesion disc: origin, evolution and ontogenetic development

Figure 1. The head of a remora showing in three views of the adhesion disc that make this fish the one and only 'shark-sucker.'

Figure 1. The head of a remora showing in three views of the adhesion disc that make this fish the one and only ‘shark-sucker.’ Suction is created by raising the Venetian blind-like strips shown here once the seal is made with the rim of the disc.

As reported at NationalGeographic.com
The remora is so ridiculous that no one would try to make it up. The top of its head is a giant, flat suction cup. It uses the cup to lock onto the bodies of bigger animals, such as sharks, sea turtles, and whales. As the big animal swims for miles in search of a meal, the remora hangs on for the ride. When its host finds a victim, the remora detaches and feasts on the remains.”

“Remains”? According to Williams et al. 2003, 
remora diets are composed primarily of host feces.

FIgure 1. The origin of the remora starts here with the swift, open water predator, the barracuda (Sphyraena). Note the long body, jutting lower jaw and flat top skull.

FIgure 2. The origin of the remora starts here with the swift, open water predator, the barracuda (Sphyraena). Note the long body, jutting lower jaw and flat top skull.

As reported at NationalGeographic.com
“Their closest relatives include Mahi-Mahi and amberjacks, neither of which has anything on their head that even faintly resembles the remora’s sucker.”

According to the Friedman et al. 2013,
and the large reptile tree (LRT, 1556 taxa) the closest relatives of remoras include the barracuda (Sphyraena, Fig. 2), the cobia (Rachycentron, Fig. 3) and Opisthomyzon (Figs. 4, 5). Basal to these nests the open seas predator, mahi-mahi (Coryphaena) and its sister, the cave-dwelling wolffish (Anarhichas) and prior to these, the shorter-bodied carp and perch, derived from the more primitive piranha. Amberjacks, like Seriola revoliana, are more derived, basal another list of slower-moving taxa.

As reported at NationalGeographic.com
“Britz and Johnson’s research indicates that the remora suction disk started out, improbably enough, as a dorsal fin.” (Fig. 9)

That statement requires a bit of explanation
because outgroup taxa, like the barracuda (Fig. 2) and the cobia (Fig. 3) don’t have a traditional dorsal fin near the skull. The latter taxon does have a series of tiny hooks with spine bases (Fig. 9) and it is this structure that spreads laterally, develops a surrounding lip and moves forward over the flat skull during the ontogeny of remoras (Fig. 9), one step of which is tentatively shown in the early Oligocene pre-remora, Opisthomyzon (Fig. 4, 5). Those tiny little hooks could barely attach themselves to a larger host, a little like Velcro, not well and not often, but those fish that were better at it due to various morphological modifications (mutation), survived and reproduced better in their chosen niche, ultimately evolving to become full-fledged remora.

FIgure 2. The remora transition starts here: with the cobia (Rachycentron). Note the overall resemblance, lacking an adhesion disc. Instead six to nine tiny spine-hooks appear where an anterior dorsal fin appears on other fish.

FIgure 3. The remora transition starts here: with the cobia (Rachycentron). Note the overall resemblance, lacking an adhesion disc. Instead six to nine tiny spine-hooks appear where an anterior dorsal fin appears on other fish. Those little hooks could barely attach themselves to a larger host, but not well. Improvements led to more hooks, wider plates, then suction as the adhesion disc evolved.

Rachycentron canadum (Kaup 1826; 2m; Fig. 3) is the extant cobia. Like the remora but without the adhesion disc, this fish also follows larger hosts (Fig. 8) seeking bits and pieces of the detritus and excrement. The first ‘dorsal fin’ has 6 to 9 short sharp spines. Females spawn 30 times a season, producing thousands of planktonic eggs 1.2mm in diameter.

Figure 3. The early Oligocene pre-remora, Opisthomyzon, with a small adhesion disc at the back of the flat skull.

Figure 4. The tiny  early Oligocene pre-remora, Opisthomyzon, with a small adhesion disc at the back of the flat skull. Note the smaller dorsal fin and elevated pectoral fins.

Opisthomyzon glaronensis (Friedman et al. 2013; early Oligocene) is a small prehistoric remora with only a small posterior sucker. This specimen indicates that the adhesion disc originated in a postcranial position, and that other specializations (including the origin of pectination, subdivision of median fin spines into paired lamellae, increase in segment count and migration to a supracranial position) took place later in the evolutionary history of remoras.

Figure 4. The skull of Opisthomyzon in situ and reconstructed. Note the small adhesion disk at the back of the skull, essentially replacing the postparietals.

Figure 5. The skull of Opisthomyzon in situ and reconstructed. Note the small adhesion disk at the back of the skull, essentially replacing the postparietals.

This phylogenetic sequence of transformation
finds some parallels in the order of ontogenetic changes to the disc documented for living remoras (Britz and Johnson 2012).

Figure 2. A remora attached to a much larger shark with an adhesion disc atop its head. Gone are the 6 to 9 dorsal spines.

Figure 6. A remora attached to a much larger shark with an adhesion disc atop its head. Gone are the 6 to 9 dorsal spines.

Remora remora (Rafinesque 1810; 75cm) is the extant remora or shark-sucker. A flexible Venetian blind-like membrane rises due to blood flow atop the skull to produce suction (Flammang BE and Kenaley 2017). Hatchlings are less than a centimeter in length. At 3cm juvenile Remora has a fully formed 2mm sucking disc. Like its phylogenetic sister, the barracuda, the skull roof is otherwise flat and the lower jaw juts out beyond the upper one. Remoras eat the ectoparasites and feces of their host.

Figure 5. Skull of Remora with a large adhesion disc extending forward to the premaxilla.

Figure 7. Skull of Remora with a large adhesion disc extending forward to the premaxilla.

Notably
remoras lack a swim bladder. And they are more likely than not to attach themselves in an inverted or angled position on their host (Fig. 6). Most fish (Fig. 8) swim upright.

FIgure 7. Cobia and remora surrounding a whale shark. Cobia have to work harder to keep up. Remora rather easily hitches a ride instead.

FIgure 8. Cobia and remora surrounding a whale shark. Free-swimming cobia have to work harder to keep up. Shark-sucking remora rather easily hitch a ride instead.

Recent studies on disc origin
Britz and Johnson 2012 report: “We compared the initial stages of development of the disc with early developmental stages of the spinous dorsal fin in a representative of the morphologically basal percomorph Morone.” (Fig. 9)

Morone is a sea bass, not related to Remora. It is not long, like a barracuda and it has two dorsal fins, unlike a barracuda.

“We demonstrate that the “interneural rays” of echeneids are homologous with the proximal‐middle radials of Morone and other teleosts and that the “intercalary bones” of sharksuckers are homologous with the distal radials of Morone and other teleosts.”

Wish they had compared Remora to Rachycentron?

“The “intercalary bones” or distal radials develop a pair of large wing‐like lateral extensions in echeneids, not present in this form in any other teleost. Finally the “pectinated lamellae” are homologous with the fin spines of Morone and other acanthomorphs. The main part of each pectinated lamella is formed by bilateral extensions of the base of the fin spine just above its proximal tip, each of which develops a row of spinous projections, or spinules, along its posterior margin. The number of rows and the number of spinules increase with size, and they become autogenous from the body of the lamellae.”

And that’s the story, told both in ontogeny and phylogeny.

Figure 8. From Britz and Johnson 2012 showing a hatchling remora, focusing on the tiny spines in the cervical region that ultimately become the adhesion disc.

Figure 9. From Britz and Johnson 2012 showing a hatchling remora, focusing on the tiny spines in the cervical region that ultimately become the adhesion disc. Compare to Rachycentron (Fig. 3). Like a very primitive form of Velcro, such backward pointing spines dig in deeper whenever the host is accelerating relative to the hitchhiker and dislodged whenever the reverse is initiated.

Finally let’s return to the Devonian – Carboniferous
and the chimaera-like clade Iniopterygidae (Fig. 10), which share with remoras the trait of large elevated pectoral fins. 

Figure 2.I The Iniopterygidae include Iniopteryx, Promexyele, Iniopera and Sibyrhynchus. These reconstructions are from Zangerl and Case 1973 and the captions label them "tentative."

Figure 10. Imagine these Iniopterygidae (Iniopteryx, Promexyele, Iniopera and Sibyrhynchus) attaching their prickly fins to larger hosts. Remoras also have elevated pectoral fins, but without the tiny hooks.

Distinct from remoras,
members of the Iniopterygidae (= Iniopterygiformes, 15-46cm in length) have pectoral fins with tiny hooks. Now we can wonder if these fins and hooks enabled iniopterygids to hitch a ride on larger hosts. Something about that hypothesis makes sense in light of what we’ve learned about the evolution of remoras. Let me know if anyone has promoted this idea before and I will publish the citation.

Figure 1. The skull of the barracuda (genus: Sphyraena) with bones identified with colors.

Figure 11. The skull of the barracuda (genus: Sphyraena) with bones identified with colors.

PS
Before reading Britz and Johnson 2012, and after nesting Remora with the barracuda, Sphyraena (Fig. 11), I wondered if the subdivided adhesion disc of Remora might be evolved from the similar area in Sphyraena. Most fish postparietals are flat to gently convex. By contrast the barracuda postparietal (Fig. 11) is absent… AND the similar adhesion disc of Opistomyzon (Fig. 5) essentially replaces the missing postparietal in shape, size and position. Sphyraena deserves a closer look.


References
Britz R and Johnson GD 2012. Ontogeny and homology of the skeletal elements that form the sucking disc of remoras (Teleostei, Echeneoidei, Echeneidae). Journal of Morphology https://doi.org/10.1002/jmor.20105 online here.
Flammang BE and Kenaley 2017. Remora cranial vein morphology and its functional implications for attachment. Scientific Reports 7(5914). https://www.nature.com/articles/s41598-017-06429-z
Friedman M, et al. 2013. An early fossil remora (Echeneoidea) reveals the evolutionary assembly of the adhesion disc. Proc. R. Soc. B 280.1766 (2013): 20131200.
Williams EH, et al. (6 co-authors) 2003. Echeneid-sirenian associations, with information on sharksucker diet. Journal of Fish Biology. 63 (5): 1176.

nationalgeographic.com/what-good-is-half-a-sucker/

scientificamerican.com/how-the-sharksucker-got-its-suction-disc/

https://en.wikipedia.org/wiki/Remora

https://en.wikipedia.org/wiki/Common_remora

Untangling the Sclerothorax chimaera

Tough one today
with many puzzle pieces.

The genus Sclerothorax
was first named by Huene 1932 based on two giant salamander-sized Early Triassic specimens. One was a torso and anterior tail lacking a skull and ventral pectoral girdle (HLD-V 608; Fig. 1). The other was a skull and ventral pectoral girdle (HLD-V 607; Fig. 1). Apparently there were no bones in common. Both are shown here at about one-quarter natural size.

Figure 1. Sclerothorax holotypes (two specimens) described by Huene 1932. Colors added. The NMK specimens (at right) are traced from new specimens added by Shoch et al. (2007, Fig. 3), but newly traced here.

Figure 1. Sclerothorax holotypes (two specimens) described by Huene 1932. Colors added. The NMK specimens (at right) are traced from new specimens added by Shoch et al. (2007, Fig. 3), but newly traced here.

The 608 specimen torso and tail are notable
for their exceedingly tall neural spines topped by spine tables, like those of Eryops, and overlapping ribs, like those of Eryops, Sclerocephalus, Mastodontsaurus (Fig. 2) and Petobatrachus.

The 607 skull is notable
for being shorter than the interclavicle like no other basal tetrapods.. Schoch et al. 2007 report, “At first sight, this (second) specimen seemed so different from the first find that Huene himself was struck. Yet his efforts in further preparing the second specimen revealed the morphology of the dorsal spines which he found similar to the first specimen, albeit affected by compaction and consequently distorted.”

Figure 2. Click to enlarge. The largest amphibians of all time include Mastodonsaurus, Prionosuchus, Koolasuchus, Siderops, Crassigyrinus and the extant Andrias, the giant Chinese salamander.

Unfortunately
those purported high dorsal spines on the 607 skull specimen are not visible with the present data, nor were they illustrated (Fig. 1). No doubt the torso with overlapping ribs also resembles that of the hippo-sized Mastodontsaurus (Fig. 3). To that point, Shoch et al. nested Sclerothorax with Mastodonsaurus in their phylogenetic analysis.

Figure 2. NMK-S118 and 117 specimens assigned to Sclerothorax. Colors added.

Figure 3. NMK-S118 and 117 specimens assigned to Sclerothorax. Colors added. Snout restored two ways. Trying to identify sutures in such a textured skull with lateral line canals is fraught with difficulties. Note the dorsal ribs on the 117 specimen. They do not appear to overlap and appear to be laterally oriented, creating a broad, flat torso, but we are seeing them in ventral aspect.

Contra earlier studies,
in the large reptile tree (LRT, 1443 taxa) the NMK S-118 posterior skull referred specimen nested with the similarly-sized Early Permian Trimerorhachis (Fig. 6), a flat-head, flat-torso taxon without overlapping dorsal ribs or high dorsal spines. Distinct from most basal tetrapods, the jugal does not contribute to the orbit rim. The HLD-V 608 torso and tail holotype specimen nest at the base of Peltobatrachus + Sclerocephlaus, and between the Ossinodus clade and the Eryops clade. So the two specimens are not congeneric in the LRT and that skull does not belong with that torso and tail (Fig. 4). (As always, I am willing to be convinced otherwise with better data.)

Figure 3. Images from Schoch et al. 2007 combining various specimens to create a Sclerothorax chimaera.

Figure 4. Images from Schoch et al. 2007 combining various specimens to create a Sclerothorax chimaera. Note the small size of the limbs relative to the torso.

When it used skull traits from Schoch et al. (2007)
(Fig. 5) the LRT lost resolution. I also discovered the lateral view of the reconstructed skull  did not match the dorsal view with regard to the placement of nares, orbits and certain sutures. A repair of the lateral view is presented here (Fig. 5).

Figure 4. Sclerothorax skull in 4 views from Schoch et al. 2007, colors added. A second skull is shown in lateral view to match the elements and proportions of the dorsal view.

Figure 5. Sclerothorax skull in 4 views from Schoch et al. 2007, colors added. A second skull is shown in lateral view to match the elements and proportions of the dorsal view.

The change in the skull sutures
presented here (Fig. 3) and the subsequent nesting of the 607 skull specimen with Trimerorhachis (Fig. 6) is supported by the preservation of long, only slightly curved and laterally oriented ribs in the NMK S-117 specimen (Fig. 3), like those of Trimerorhachis (Fig. 6).

Figure 1. Trimerorhachis was considered a dvinosaurian temnospondyl. Here both Trimerorhachis and Dvinosaurus nest low on the basal tetrapod tree, close to the fin/finger transition.

Figure 6. Trimerorhachis. Like Sclerothorax and distinct from other basal tetrapods the jugal does not contact the orbit rim. 


Fossils typically come to rest

with their major axis parallel to the bedding plane. In this way taxa with a wide, flat, skull and torso will usually be preserved in dorsal aspect. By contrast, taxa preserved in lateral view are more likely to have a deeper than wide torso, as in the Sclerothorax holotype (Fig. 1).

Eryops also had tall neural spines,
overlapping ribs and a deep pelvis in common with Sclerothorax. Perhaps Sclerothorax had a large skull and strong limbs, like Eryops, suitable for terrestrial locomotion.

By contrast
the 607 skull retains lateral line canals, like those of Trimerorhachis, so we might expect shorter limbs and an aquatic environment for the 607 skull specimen.

Figure 7. Subset of the LRT focusing on basal tetrapods. The two Sclerothorax taxa are highlighted in separate clades.

Figure 7. Subset of the LRT focusing on basal tetrapods. The two Sclerothorax taxa are highlighted in separate clades.

Phylogenetically separating
the 607 skull from the holotype torso resolves the lateral line canal issue when the skull was joined to the torso as a chimaera.


References
Huene F v 1932. Ein neuartiger Stegocephalen−Fund aus dem oberessischen Buntsandstein. Palaönontologische Zeitschrift 14: 200–229.
Schoch RR, Fastnacht M, Fichter J and Keller T 2007. Anatomy and relationships of the Triassic temnospondyl Sclerothorax. Acta Palaeontologica Polonica 52 (1): 117–136.

wiki/Sclerothorax

Procompsognathus – What does it look like?

The small Late Triassic archosaur Procompsognathus (~60 cm length, von Huene 1921, Fig. 1) was earlier and convincingly revealed to be a chimaera by Sereno and Wild (1992). The croc skull (Figs. 2,3) did not belong to the dino post-crania. Unfortunately no reconstruction was provided. Here (Fig. 1) is a Procompsognathus reconstruction , along with Segisaurus (~1 m length, Camp 1933) an early Jurassic dinosaur, to which it was allied.

Figure 1. Procompsognathus (below) along with Segisaurus (not to scale). We don't have the actual skull of Procompsognathus, but it was likely small, but taller than wide.

Figure 1. Procompsognathus (below) along with Segisaurus (not to scale). We don’t have the actual skull of Procompsognathus, but it was likely small, but taller than wide.

Procompsognathus post-crania
The post-cranial portion of the specimen (SMNS 12591) was considered close to Segisaurus (Fig. 1) and here nests close to it, but closer to the tiny Middle Triassic theropod, Marasuchus.  Pedal digit 1 rides a little higher on the metatarsus in Procompsognathus and Marasuchus among only a few distinguishing traits.

Distinct from Segisaurus, Procompsognathus has longer, more robust hind limbs and essentially vestigial forelimbs. It is also half as large with a much longer pubis, longer cervicals with smaller cervical ribs, a higher metatarsal 1 and shorter, more robust phalanges on pedal digit 4, which also has a very long ungual.

Figure 2. SMNS 12591a, a basal croc skull close to the ancestry of dinosaurs.

Figure 2. SMNS 12591a, a basal croc skull close to the ancestry of dinosaurs. The premaxilla is unknown and has been restored here. The palatine appears in the antorbital fenestra.

SMNS 12591a – the croc skull
A basal croc, the SMNS 12951a skull, is twice as wide as tall. The quadrate leans anteriorly. Phylogenetically the skull nests in the large reptile tree at the base of the Gracilisuchus + Scleromochlus clade and next to the Terrestrisuchus + Saltoposuchus clade. So there is a good chance that the SMNS 12951a skull was attached to gracile bipedal crocodylomorph post-crania, along the morphological lines of Procompsognathus, and not too far from the base of the Archosauria.

Figure 3. The SMNS 12591a skull reconstructed. It is twice as wide as tall, a croc feature.

Figure 3. The SMNS 12591a skull reconstructed. It is twice as wide as tall, a croc feature.

Sereno and Wild (1992) described postfrontals (blue in Fig. 2), but strangely did not illustrate them (Fig. 3). Gracilisuchus and Scleromochlus also retain postfrontals but most other crocs do not. What appears to be a post dividing the antorbital fenestra in situ is actually the displaced palatine, as described by Sereno and Wild (1992).

References
Camp C 1936. A new type of small bipedal dinosaur from the Navajo sandstone of Arizona. Univ. Calif. Publ., Bull. Dept. Geol. Sci., 24: 39-56.
Huene F von 1921.
Neue Pseudosuchier under Coelurosaurier aus dem württembergischen Keuper. Acata Zoologica 2:329-403.
Sereno P and Wild R 1992. Procompsognathus: theropod, “thecodont” or both? Journal of Vertebrate Paleontology 12(4): 435-458.

LACM Pteranodon – Chimaeras and Fakes – Part 7

Is the neck too big?

Figure 1. the Los Angeles County Natural History Museum specimen LACM 50926, famous for having a shark tooth embedded in the anterior cervical. But does the neck belong to the rest of the specimen?

Figure 1. the Los Angeles County Natural History Museum specimen LACM 50926, famous for having a shark tooth embedded in the anterior cervical. But does the neck belong to the rest of the specimen? or is it a chimaera?

According to Bennett (2003), the Los Angeles County Natural History Museum specimen of Pteranodon, LACM 50926, includes the following bones:

  1. Fragmentary skull, including a deformed mandible ramus.
  2. right radius and ulna, tibia;
  3. left scapula, coracoid, humerus, radius, metacarpal 4;
  4. both m4.1, m4.2, m4.3, femur

Absent from this list is the cervical series, represented on the mount with a series of five bones, one with the famous embedded shark tooth. So the cervicals are not on “the list,” yet there they are. Did they come from another Pteranodon? Is this another chimaera? Good question. If anyone has the answer, please let me know.

Figure 2. Reconstruction of LACM 50926 with painted and questionable material in light red. Here the cervicals look too big for this mid-sized specimen.

Figure 2. Reconstruction of LACM 50926 with painted and questionable material in light red. Here the cervicals look too big for this mid-sized specimen.

At present and by comparison
A reconstruction (Fig. 2) demonstrates the cervicals appear to be a little too big for the rest of the skeleton. They don’t look too bad on the mount because the museum staff only employed 5 of the 8 cervicals that are supposed to be there. Here (fig. 3)are more complete Pteranodon specimens for comparison:

Figure 3. The Triebold specimen and UALVP 24238, the two most complete Pteranodon known. Neither has quite the neck length exhibited by the LACM specimen.

Figure 3. The Triebold specimen and UALVP 24238, the two most complete Pteranodon known. Neither has quite the neck length exhibited by the LACM specimen.

It’s hard to say, but the clues point to a chimaera here. Perhaps someone has the answer. The pelvis of the LACM specimen, also not on the Bennett 2003 manifest, looks odd too.

References
Bennett SC 2003. A survey of pathologies of large pterodactyloid pterosaurs. Palaeontology 46(1):185-198.

Human and Dinosaur Tracks Together – Chimaeras and Fakes – Part 6

Creationists jumped all over the Archaeoraptor chimaera. Then they came up with this piece of carved artwork (Fig. 1, and others) they claimed was genuine. It appears on the Creation Evidence Museum website masthead. It’s a crying shame when these Christians associate themselves with acts of deception like this. They make all Christians look bad. Luckily we have scientists like Glen Kuban who fight the good fight for the rest of us.

Figure 1. The Alvis Delk print purporting to show a three-toed dinosaur intersecting with a human print. IT was "discovered" near the Paluxy River in Texas, a  Cretaceous locality.

Figure 1. Click to enlarge. The Alvis Delk print purporting to show a three-toed dinosaur intersecting with a human print. It was “discovered” near the Paluxy River in Texas, a Cretaceous locality. Both prints show evidence of being carved and neither conform to known anatomy. Note the extreme depth of the human medial toe. No pad impressions appear in the dino track, as shown in figure 2 and it lacks good morphology.

Poor Creationist artistry is the giveaway.
The human big toe is too deep and too short. The dinosaur track has no pad impressions and extends through several layers, rather than compressing them. There is no displacement of sediment from either track.

Glen Kuban has made an extensive study of the Paluxy River tracks. Here’s his take on them. The Alvis Delk Print is reported on here. Kuban reports, “a number of its features are so unrealistic that some have described it as cartoon-like. To be more specific, the hallux (big toe) of the “human” print is exceedingly deep compared to the rest of the print. The lesser toe depressions are on a plane considerably higher than the rest of the print, and jut out at an unnatural angle. The middle three toe marks are also unusually long (or overly separated from the ball area).  Also, the margin of the print lacks the “mud up-push” and other evidence of deformation usually seen on distinct prints. In the 1970’s, Glen Rose resident Wayland “Slim” Adams, explained to a group of creationists how his uncle George Adams, who carved human tracks on loose blocks and sold them to tourists during the Great Depression, usually did start with existing (but not human) depressions. George’s granddaughter recently confirmed this, as well as her grandfather’s use of acid to blur chisel marks.(Kennedy, 2008).”

Figure 2. Conmparing the alleged theropod track to a genuine theropod track. Poor Creationist artistry is the giveaway.

Figure 2. Conmparing the alleged theropod track to a genuine theropod track. Poor Creationist artistry is the giveaway. From Glen Kuban’s website, referenced below.  The A/B line intersects the claws of digits 2 and 4. Digits 1 adn 5 do not make impressions.

Then there are problems with the purported theropod track, too. Kuban reports, “a number of the Delk print’s features conflict with those of typical “Acro” tracks. A series of odd holes appears to run down the length of the middle toe and into the main body of the track. Moreover, the digits on the Delk print show little if any indications of individual digit pads which are normally detectable on real dinosaur tracks with such a distinct outline. However, it does resemble a number of other likely carvings that were made decades ago, as well as some that have come out of the Glen Rose and Stephenville area in more recent years, and which were sold to tourists.

“Unlike real tracks that show deformational lines corresponding to the print depression, the subsurface features of these loose tracks were truncated by the depressions, strongly indicating a carved origin.”

References (from Glen Kuban’s web site)
Baugh CE 2008.  Creation Museum website article: “Alvis Delk Cretaceous Footprint article here
Darrell E 2008. “Fred Flintstone waded here: Hoaxsters ready to teach creationism to Texas kids” Millard Fillmore’s Bathtub blog here.
Godfrey L 1985. “Footnotes of an Anatomist,” Creation/Evolution, Issue 15, Volume 5, Number 1 (Winter 1985)
Hurd G. Stones and Bones website blog.
Juby I  2008. “Examining the Delk Track,” August, 2008 website article.
Kennedy B  2008 (Aug 10), Fort Worth Star-Telegram“Human Footprints Along with Dinosaur Tracks?”
Ketcham RA and Carlson WD 2001. “Acquisition, optimization and interpretation of X-ray computed tomographic imagery: Applications to the geosciences.” Computers and Geosciences, 27, 381-400.
Kuban GJ 2006. On the Heels of Dinosaurs. Website article here
Kuban GJ and Wilkerson G 1989. The Burdick Print at here.
Lines D 2008. web links here
May D 2008a Rock-solid Proof? Mineral Wells Index. On line version
May D 2008b. One Step at a Time. Mineral Wells Index. On line here
Snelling AA., 1991. Website article here Originally published in: Creation 14 (1):28-33, December 1991.

Support for the Alvis Delk track is here and here.

Glen Kuban’s Paluxy track page is here and here.

Yixianopterus – Chimaeras and Fakes – Part 6

Yixianopterus jingangshanensis JZMP-V12 (Lü et al. 2006) ~20 cm skull length, Barremian/Aptian Early Cretaceous ~125 mya, was correctly considered an ornithocheirid pterosaur like Haopterus. With a keen eye, Lü et al. (2006) reported, “The posterior portion of the skull is a forgery, which was made by glueing together some fragments to create a composite “complete” skull.”

Chinese farmers have found many fabulous fossils, but they have also made certain fossils even more fabulous by adding bones (a skull in this case) or rearranging the bones to increase its value.

Yixianopterus. The white boxed area is where the forgers attempted to create a complete skull from disassociated fossil bones.

Figure 1. Yixianopterus. Click to enlarge. The white boxed area is where the forgers attempted to create a complete skull from disassociated fossil bones. Roadkill fossils like this are typically not reconstructed, but DGS permits the identification of most traits. The colors are applied here using DGS to help identify bones and to make sure none are duplicated more than left/right.

Surprised to see I haven’t featured this specimen earlier.
Despite its roadkill appearance and lack of outstanding traits, Yixianopterus turns out to be a very important taxon because it nested at the base of the ornithocheirid family tree close to the JZMP embryo and not far from large and small basal cycnorhamphids and tiny derived scaphognathids from which it evolved. See the pterosaur family tree here.

Other pterosaur workers have apparently ignored this taxon in their phylogenetic trees — and that’s a problem. As I’ve said on many occasions, these plain-looking roadkill fossils are the ones that open most of the doors that answer the mysteries of paleontology. They should not be overlooked.

Figure 2. Reconstruction of Yixianopterus. Roadkill fossils really need at least this much reconstruction to make then intelligible. And don't ignore them in phylogenetic studies. Nothing spectacular here, which means it is more likely to be phylogenetically important.

Figure 2. Reconstruction of Yixianopterus. Roadkill fossils really need at least this much reconstruction to make then intelligible. And don’t ignore them in phylogenetic studies. Nothing spectacular here, which means it is more likely to be phylogenetically important.

References
Lü J, Ji S, Yuan C, Gao Y, Sun Z and Ji Q 2006. New pterodactyloid pterosaur from the Lower Cretaceous Yixian Formation of Western Liaoning. In J. Lü, Y. Kobayashi, D. Huang, Y.-N. Lee (eds.), Papers from the 2005 Heyuan International Dinosaur Symposium. Geological Publishing House, Beijing 195-203.

wiki/Yixianopterus

Dendrorhynchoides – Chimaeras and Fakes – Part 4

Dendrorhynchoides curvidentatus (Ji and Ji 1998 – originally Dendrorhynchus preoccupied) Tithonian, Late Jurassic or Barremian-age Lower Cretaceous, ~150 -130 mya (later considered Middle Jurassic), ~13 cm in length [GMV 2128] was originally considered a rhamphorhynchid due to its long, robust tail. Later that long tail was considered a forgery added from another specimen (making this fossil a chimaera) to increase its value on the fossil market. Ironically, as we learned earlier, the real tail has been overlooked, bent under the left uropatagium (Fig. 1). The real tail is slightly longer, just not so robust.

Dendrorhynchoides after DGS (digital graphic segregation).

Figure 1. Dendrorhynchoides after DGS (digital graphic segregation). Click to enlarge. Here the doctored tail is outlined in brown. The real tail is identified with an arrow. Contra published reports and Wikipedia, the sternal complex and m4.4 are both present and all the parts of the skull can be identified. See figure 2 for a reconstruction.

Speaking of the tail…
A second specimen attributed to Dendrorhynchoides was named, and it nests as a close relative, but nests just a little closer to the flathead anurognathid. The second specimen, undoubtedly a distinct genus that needs a new name, has a long tail, too. The long tail came as a surprise to Hone and Lü (2010), but confirmed my studies in which longer tails are routinely found in anurognathids.

These are the only skeletal reconstructions of either Dendrorhynchoides. Obviously they are distinct genera and the second needs a new name. Shunning DGS, professional paleontologists consider the task too daunting or time consuming to make anurognathid reconstructions. When one attempt was made at reconstructing an anurognathid skulls, as in the curious case of the flathead anurognathid (Bennett 2007) major mistakes were made.

The holotype of Dendrorhynchoides

Figure 1. Click to enlarge. (Left) The holotype of Dendrorhynchoides compared to (right) the new ?Dendrorhynchoides, that actually nests with the flat-head pterosaur and the two nest alongside Dendrorhynchoides, so, not far off. These both have a long tail.

References
Hone DWE and Lü J-C 2010. A New Specimen of Dendrorhynchoides (Pterosauria: Anurognathidae) with a Long Tail and the Evolution of the Pterosaurian Tail. Acta Geoscientica Sinica 31 (Supp. 1): 29-30.
Ji S-A and Ji Q 1998. A New Fossil Pterosaur (Rhamphorhynchoidea) from Liaoning. Jiangsu Geology 4: 199-206.

wiki/Dendrorhynchoides