Dunyu [Galeaspida] enters the LRT

According to Wikipedia
“Galeaspida lived in shallow, fresh water and marine environments during the Silurian and Devonian times (430 to 370 million years ago) in what is now Southern China, Tibet and Vietnam. Superficially, their morphology appears more similar to that of Heterostraci than Osteostraci, there being currently no evidence that the galeaspids had paired fins. However, Galeaspida are in fact regarded as being more closely related to Osteostraci, based on the closer similarity of the morphology of the braincase.”

Figure 1. Galeaspids from Halstead 1985.

Figure 1. Galeaspids from Halstead 1985.

“The defining characteristic of all galeaspids was a large opening on the dorsal surface of the head shield, which was connected to the pharynx and gill chamber, and a scalloped pattern of the sensory-lines. The opening appears to have served both the olfaction and the intake of the respiratory water similar to the nasopharyngeal duct of hagfishes.”

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

Figure 2. Skull of Dunyu with tetrapod homolog colors applied here. Note the elongated dorsal opening. In other galeaspids the opining is more oval. On a 72 dpi monitor this image is only slightly smaller than life size.

Dunyu longiforus
(Fig. 2) from the Late Silurian was described by Zhu et al. 2012.

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

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

Here
(Fig. 3) in the large reptile tree (LRT, 1803+ taxa) Dunyu nests between the thelodont, Thelodus, and the osteostracan, Hemicyclaspis (Fig. 3). The resemblance between the three is readily observed. Phylogenetic bracketing (Fig. 3) provides galeaspids with pectoral fins. Closest living relatives are hagfish and sturgeons.


References
Halstead LB 1985. The vertebrate invasion of fresh water. Philosophical Transactions of the Royal Society London B 309:243–258.
Janvier P 1984. The relationships of the Osteostraci and Galeaspia. Journal of Vertebrate Paleontology 4(3):344–358.
Liu YH 1965. New Devonian aganathans from Yunnan. Vertebrata PalAsiatica 9(2):125–134.
Zhu M and Gai Z-K 2006. Phylogenetic relationships of Galeaspids (Agnatha). Vertebrate PalAsiatica 44:1–27.
Zhu M, Liu Y-H, Jia L-T and Gai Z-K 2012. A new genus of eugaleaspidiforms (Agnatha: Galeaspida) from the Ludlow, Silurian of Qujing, Yunnan, Southwestern China. Vertebrata PalAsiatica. 50 (1): 1–7.

wiki/Galeaspida
wiki/Dunyu

Early Silurian Sinacanthus compared to Early Cretaceous Bonnerichthys

Zhu 1998 brought us a peek at Early Silurian vertebrates
represented by distinctive Sinacanthus fin-spines (Fig. 1). These were variously considered acanthodian-like and shark-like.

Zhu argues
“Sinacanths are one of the oldest known chondrichthyans (sharks + ratfish) rather than acanthodians, and their spines are the oldest known shark fin spines.”

Figure 1. Sinacanthus fin spine.

Figure 1. Sinacanthus fin spine. Scale unknown.

No comparable fin spines are currently
documented among the sharks and their kin at ReptileEvolution.com. So I looked at other taxa. After seeing a comparable fin spine that belonged to the Late Cretaceous bony fish, Bonnerichthys (Figs. 2, 3), I wondered if Sinacanthus was similar enough? This time I’ll let you decide because…

Figure 2. Bonnerichthys pectoral fin for comparison.

Figure 2. Bonnerichthys pectoral fin for comparison.

…there is no way
the large reptile tree (LRT, 1720+ taxa) can nest this fin alone given its present set of characters, none of which lump and split fin details.

According to (P’an 1959, 1964)
Sinacanthus wuchangensis (MG.V103a) and its relatives have fins with 15 to 50 ridges per side. Acanthodians have fewer ridges generally, which is why Zhu et al. preferred allying those fins with elasmobranchs rather than acanthodians.

Zhu et al. present a diagnosis
“Sinacanths with long and slender fin spines; spine gradually tapering, recurved posteriorly and dagger-shaped.” 

Zhu documented the histology of sinacanths.
Given today’s observations, perhaps the histology of Bonnerichthys will be worth looking into and comparing it to Sinacanthus. There’s another project for a grad student!

Zhu goes on to say in their Remarks:
“Since the phylogeny of early elasmobranchs remains obscure, the diagnosis given above is more descriptive than phylogenetic.”

Actually the phylogeny of early elasmobranchs is clear in the LRT. Nevertheless, nothing quite like this fin spine has shown up yet in tested elasmobranchs,

Chronology
in the LRT Late Cretaceous Bonnerichthys phylogenetically precedes some derived Late Silurian taxa (e.g. Entelognathus, Qilinyu, Romundina and Guiyu). So maybe this chronology jump is another opportunity to explore for that grad student.

Figure 1. Bonnerichthys parts from Friedman et al. 2010 and colorized here.

Figure 3. Late Cretaceous Bonnerichthys parts from Friedman et al. 2010 and colorized here.

Apparently the earliest radiation of fish clades
occurred during the Ordovician. Unfortunately only a few ‘armored lancelet’ fossils, like Arandaspis, have been found in Ordovician strata so far. The LRT indicates there are more fish and more derived fish waiting to be found in that early stratum.

Figure x. Subset of the LRT focusing on fish.

Figure x. Subset of the LRT focusing on fish. Spiny sharks are related to osteoglossiformes here.

A little housekeeping note…
the skull of Pachycormus (Figs. 4, 5) has been reviewed, overhauled and this taxon is now happier in its new home (Fig. x) with Bonnerichthys, the extant arowana, Osteoglossum (Fig. 6) and two extinct pseudo-swordfish, Protosphyraena and Aspidorhynchus.

Figure 1. Pachycormus fossil. Pelvic fins vestigial near vestigial anal fin. See figure 2 for closeup of the skull.

Figure 4. Pachycormus fossil. Vestigial pelvic fins seem to appear near the vestigial anal fin. See figure 2 for closeup of the skull. Note the extra set of spines medial to the spiny pectoral fins.

Still wondering if
those slender curved spines medial to the pectoral fins are pelvic fins or new structures? Normal pelvic fins are absent, but a long set of dorsal ribs suggests the anus is still just anterior to the anal fin, as in all related taxa. Osteoglossum (Fig. 6) seems to have posterior pelvic fins, but the skeleton does not show them. So the situation is confusing at present.

Figure 8. Pachycormus macropterus has a new skull reconstruction. Originally I did this without template or guidance. Now osteoglossiformes provide a good blueprint.

Figure 5. Pachycormus macropterus has a new skull tracing and reconstruction. Originally I did this without template or guidance. Tinkering. Now osteoglossiformes provide a good blueprint.

These osteoglossiformes/pachcormiformes
arise from spiny sharks, a novel hypothesis of phylogenetic relationships recovered by the LRT earlier.

Figure 1. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.

Figure 6. The arowana (Osteoglossum) an Amazon River predator has posterior pelvic fins and no mid pectoral fins in life, but the skeleton does not show that. Confusing.

This fish phylogeny recovered by the LRT,
including certain taxa not traditionally included with certain other taxa (Fig. x), is a novel hypothesis of interrelationships awaiting confirmation from an independent study with another character list, but a similar taxon list.


References
P’an K 1959. [Devonian fish fossils of China and their stratigraphic and geographic distributions.] Monographic summary of basic data on Chinese geology 1:1–13 [in Chinese].
Zhu M 1998. Early Silurian sinacanths (Chondrichthyes) from China. Palaeontology 41(1):157–171.

Fish cladogram: Cambrian period to the present day

When one layers established time periods
over the fish portion of the large reptile tree (LRT, 1673+ taxa; Fig. 1) the surprising length of certain ghost lineages and the ability of several clades to survive several hundred million years becomes apparent.

Figure 1. Subset of the LRT focusing on basal vertebrates (= fish). Colors indicate time periods. This chart documents the lack of fossils for several clades and genera in the Silurian and Devonian.

Figure 1. Subset of the LRT focusing on basal vertebrates (= fish). Colors indicate time periods. This chart documents the lack of fossils for several clades and genera in the Silurian and Devonian.

The antiquity of Silurian members in the highly derived lungfish clade
(Guiyu and Psarolepis) helps one understand the coeval Silurian appearances of so-called primitive fish, like acanthdians and placoderms (Entelognathus). Traditional cladograms assumed early taxa must be more primitive, not realizing that phylogenetic analysis indicates a vast undiscovered radiation of taxa in the Silurian (Fig. 1). Most of these are still waiting to be discovered.

What do Silurian and Early Devonian fossil fish in the LRT have in common?
Many were flat bottom dwellers with small eyes.

By contrast, coeval spiny sharks had large eyes and were free-swimmers. Even so they lost their flexible fin rays, they lost large teeth, they kept a large mouth, and they had vestigial skeletons. Such traits are associated today with slow-moving deep sea fish.

So known Silurian fish were not open sea visual predators with great swimming skills. Their ecological absence must have a reason. I wonder if such taxa were gobbled up before they could drift to muddy or silty anoxic regions of the sea floor where they could wait undisturbed to be buried for fossilization? Even a few exceptions are lacking. Very puzzling…

According to Google:
“In North America geologic activity over the last 417 million years has removed or covered up most Silurian rocks. Well-preserved fossils from Silurian reefs can be found in the Great Lake States of Minnesota, Wisconsin, Michigan, and Illinois.” So Silurian exposures are comparatively rare.

How do left column fish differ from right column (Fig. 1) fish?
As a general rule (allowing for many exceptions) left column fish do not appear to be the fast, open water swimmers seen in the majority of primitive right column fish in the Silurian and Devonian. It is noteworthy that not one taxon in the right column has a Silurian through Permian representative. I will add them as they come to my attention. It is also noteworthy that the left column has very few living representatives. I count nine.

Traditional cladograms
put more emphasis on time and exclude extant taxa. That’s why traditional cladograms often nest spiny sharks and placoderms near the base of the basal vertebrates, prior to sharks and bony fish. And they attempt to add tube-feeding sturgeons somewhere in the middle of bony fish. In the LRT taxon exclusion is minimized and more natural evolutionary patterns are recovered based on phenomics (traits).

Some previously unrecognized relationships recovered by the LRT include:

  1. The wide radiation of clades in the Silurian.
  2. Devonian taxa take us rapidly to tetrapods, documented by Middle Devonian tracks
  3. Note the proximity of Silurian lobefins to Viséan (Early Carboniferous) tetrapods, including reptiles.
  4. Note the unbalanced fossil record with regard to the major dichotomy splitting bony fish
  5. Proamia is known from the Devonian while a sister taxon, Amia, is known from extant taxa, separated by 360 million years. This is the closest we get to a right column fish fossil in the Silurian or Devonian.
  6. The time span between tiny Silurian Loganiella and giant extant sisters Rhincodon + Manta is about 430 million years.
  7. A similar time span splits Hemicyclaspis from living sturgeons.
  8. A longer time span (~500 my) splits Branchiostoma from its Cambrian precursors.
  9. When comparing the LRT to traditional cladograms, check to make sure they have similar outgroup taxa. Too often taxon exclusion is an unaddressed issue in those papers, which make them fitting subjects for the next few blogposts.

Cautionary note:
The choosing of fish taxa for the LRT has not been random, but was made on the basis of availability and possible importance. At present the fossil record is skewed toward left column fish prior to the Permian. As more taxa are discovered and added, the subjective second reason will hopefully pale to become less of a factor.

 

A catfish with barbels from the Silurian

Finally
a catfish from the Silurian with preserved barbels (Figs. 1, 2).

Ironically
catfish are members of the order Siluriformes (from ‘silurus’ Latin = large river fish). Previous oldest member of this clade: Late Cretaceous, 100mya.  Sir Roderick Murchison (1792–1871), a wealthy Scottish aristocrat, named the Silurian Period after an ancient Welsh Celtic tribe, the Silures. Appears to be a coincidence. The slow genesis of plants and arthropods on land occurred in the Silurian, along with a rise in oxygen levels, a rise in temperature and a rise in sea levels after the massive glaciation of the Ordovician.

Figure 1. Originally considered another Silurian Thelodus, this specimen nests with catfish in the LRT.

Figure 1. Originally considered another Silurian Thelodus, this specimen nests with catfish in the LRT. Here’s where DGS tracing helps pick out the details from a ‘fish silhouette’ fossil.

Not sure what the museum number is on this one.
In the large reptile tree (LRT, 1602 taxa; subset Fig. A) this taxon is labeled ‘unnamed Sil. catfish‘ (in the purple clade). In the LRT the new taxon is not as primitive as the armored catfish, Hoplosternum. Worthy of note, basal catfish in the LRT are air breathers employing the intestine or modified gill arches, not their air bladder, which they need to swim upright. Clarias is the famous walking catfish (Figs. 3–5) able to traverse land in search of other ponds. The spiny pectoral fins (Fig. 4) keep it upright and act as ground undulates as it wriggles from pond to pond.

Figure A. Subset of the LRT focusing on basal vertebrates (fish).

Figure A. Subset of the LRT focusing on basal vertebrates (fish). The base of the LRT will change by the next time you see it with the addition of several jawless fish. 

The identity of this specimen
might have been overlooked because it appears like a silhouette, offering little detail. Digital Graphic Segregation (DGS) enables details to be colored, identified and later scored in the LRT.

Figure 3. Silurian catfish face

Figure 2. Silurian catfish face. Note the left barbel is aligned with a crack.

Extant velvet catfish,
members of the clade Diplomystidae, are considered primitive.

Figure 6. Clarias head with barbels in vivo.

Figure 3. Clarias head with barbels in vivo.

Clarias batrachus (Linneaus 1758, up to 50 cm in length) is the extant walking catfish. The skull bones are nearly identical to those in the placoderm, Entelognathus. The spiny pectoral fins keep the walking catfish upright as it wriggles from pond to pond. No scales or bones appear on the surface. The teeth are short bristles on pads. The maxilla is absent.

FIgure 1. Clarias, the walking catfish is a living placoderm with skull bones colorized as homologs of those in Entelognathus (Fig. 2). Here the mandible shifts forward and the opercular shifts backwards relative to Entelongnathus in the Silurian.

Figure 4. Clarias, the walking catfish skull bones identified. Note the ossified spines at the leading edge of the pectoral fin. 

Figure 3. Clarias batrachus, the walking catfish, in vivo. The pelvic fin is tiny. The single dorsal fin is elongate. The anal fin is also elongate. The skull is flat and provided with sensory barbels.

Figure 5. Clarias batrachus, the walking catfish, in vivo. The pelvic fin is tiny. The single dorsal fin is elongate. The anal fin is also elongate. The skull is flat and provided with sensory barbels.

Generally recognized fossil catfish
include Qarmoutus hitanensis from the same Eocene North African beds as the early whale, Basilosaurus. Reported by NatGeo.com (citation below): Even though the fossil is relatively old in the way we ordinarily think of ages in millions of years, it is still essentially anatomically modern and directly comparable to living catfishes,” says John Lundberg of Drexel University’s Academy of Natural Sciences. “It’s one of the best preserved and oldest of its family.”

Afterthought about fish with spines in their fins
Spiny sharks (Acanthodii), like Brachyacanthus (Fig. 6), also briefly appeared in the Silurian and Devonian. Since the walking catfish uses its spiny fins to ‘walk’ on land, I wonder if spiny sharks, especially those with longer, thinner pectoral and pelvic spines, did the same, perhaps on the sea floor, not on land?

Figure 1. Surprising homologies in Pteronisculus and Brachyacanthus indicate a close relationship, despite the spiny fins.

Figure 6. Brachyacanthus has short, thick spiny fins, distinct from the long spines found in the walking catfish.

That might explain
why those extra spines appeared between the pectoral and pelvic fins, as extra hooks in the substrate?


References

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

https://www.nationalgeographic.com/news/2017/03/ancient-egypt-catfish-fossil-palaeontology-science/

https://pubs.geoscienceworld.org/gsa/geology/article-abstract/5/4/196/195354/Fossil-catfish-and-the-depositional-environment-of?redirectedFrom=fulltext