Didazoon and Vetulicola: Early Cambrian larvacean and echinoderm ancestors

Urochordates and larvaceans are the relatives
we almost never talk about. Here those long, lost relationships are reestablished.

Didazoon haoae (Figs. 1, 2; Shu et al. 2001; ELI 0000197–0000217) was described as a member of the Ventulicolia, an “enigmatic phylum” of Cambrian deuterostomes of otherwise uncertain affinities. It was a simple, barrel-shaped animal with a line of gill openings dotting a large atrium followed by a down-angled tail. There was no head.

From the Diagnosis:
“Bipartite, cuticularized body, anterior segmented region and voluminous mouth, ventral margin ¯attened, widens posteriorly. On either side the anterior bears fve circular structures, in the form of a cowl with posteriorly directed opening and basin-like interior, apparently connected to interior. A prominent constriction separates dorsal region of anterior from posterior section. The latter, composed of seven segments, tapers in both directions, with rounded posterior termination. Internal anatomy includes alimentary canal, possibly voluminous in anterior, and in posterior narrow intestine, straight or occasionally coiled. Dark strand located along ventral side of anterior section, possibly representing endostyle.”

Figure 1. Didazoon in situ and reconstructed. The 'intestine' may be a notochord remnant because it extends to the tail tip, distinct from Metaspringgina (Fig. 2). The tail was down in all larvaceans.

Figure 1. Didazoon in situ and reconstructed. The ‘intestine’ may be a notochord remnant because it extends to the tail tip, distinct from Metaspringgina (Fig. 2). The tail was down in all larvaceans.

Comparisons to MetasprigginaArandaspis and larvacea
(Fig. 2) were not made by Shu et al. 2001. Here the ‘cuticularized body’ is transitional between Branchiostoma (Fig. 2) and extant larvacea (Fig. 2 which share several traits with these vetulicolians.

In all these taxa, the tail hangs down
and the mouth opens slightly ventrally, beneath what was the rostrum in lancelets. Prior reconstructions at Wikipedia have the tail up and the animal upside-down.

Figure 2. Branchiostoma, Metaspriggina, Didazoon, Vetulicola, Arandaspis and Larvacea to scale. Note the presence of an atrial pore/posterior atrial opening in Branchiostoma and the vetulicolians while Metaspriggina and Arandaspis had fish-like gill openings. The tail of larvaceans hangs down.

Figure 2. Branchiostoma, Metaspriggina, Didazoon, Vetulicola, Arandaspis and Larvacea to scale. Note the presence of an atrial pore/posterior atrial opening in Branchiostoma and the vetulicolians while Metaspriggina and Arandaspis had fish-like gill openings. The tail of larvaceans hangs down.

According to Wikipedia,
Vetulicola (Figs. 2, 3) “is the eponymous member of the enigmatic phylum Vetulicolia, which is of uncertain affinities, but may belong to the deuterostomes. Vetulicola cuneata could be up to 9 cm long (shown at only 6cm in Fig. 2).

Earlier we looked at the parallel development of the enlarged gill chamber in craniates and gnathostomes like the manta ray (Manta) and whale shark (Rhinchodon) that also fed on plankton, but on a much larger scale.

Figure 3. Vetulicola in situ and flipped in vivo configuration.

Figure 3. Vetulicola in situ and flipped in vivo configuration. The shape is transitional to both the larvacea (Fig. 2) and to the crinoid (Fig. 5). Note the four-part separation of the mouth parts, like a budding flower.

According to Wikipedia,
“Vetulicola’s taxonomic position is controversial. Vetulicola cuneata was originally assigned to the crustaceans on the assumption that it was a bivalved arthropod like Canadaspis and Waptia, but the lack of legs, the presence of gill slits, and the four plates in the “carapace” were unlike any known arthropod.”

“Shu et al. placed Vetulicola in the new family Vetulicolidae, order Vetulicolida and phylum Vetulicolia, among the deuterostomes. Shu (2003) later argued that the vetulicolians were an early, specialized side-branch of deuterostomes.”

“Dominguez and Jefferies classify Vetulicola as an urochordate, and probably a stem-group appendicularian (= Larvacea, Tunicata). Like a common tunicate larva, the adult Appendicularia have a discrete trunk and tail.”

“In contrast, Butterfield places Vetulicola among the arthropods.”

“The discovery of the related Australian vetulicolian Nesonektris, from the Lower Cambrian Emu Bay Shale of Kangaroo Island, and the reidentification of the “coiled gut” of vetulicolians as being a notochord affirms the identification as an urochordate.”

Figure 5. Lavacea diagram showing the tadpole organism and the house it builds from cellulose and protein. This is a highly derived organism, based on two parts that originated in the Cambrian with Vetulicola.

Figure 4. Lavacea diagram showing the tadpole organism and the house it builds from cellulose and protein. This is a highly derived organism, with origins in the Cambrian with Vetulicola and close to the salp taxa in figure 3,. Here the larvacea retains the swimming muscles and notochord that extends to the tail tip.

According to Wikipedia:
“Larvaceans have greatly improved the efficiency of food intake by producing a test, which contains a complicated arrangement of filters that allow food in the surrounding water to be brought in and concentrated prior to feeding. By regularly beating the tail, the larvacean can generate water currents within its house that allow the concentration of food. The high efficiency of this method allows larvaceans to feed on much smaller nanoplankton than most other filter feeders.”

“The immature animals resemble the tadpole larvae of ascidians, albeit with the addition of developing viscera. Once the trunk is fully developed, the larva undergoes “tail shift”, in which the tail moves from a rearward position to a ventral orientation and twists 90° relative to the trunk. Following tail shift, the larvacean begins secretion of the first house.”

There are no other chordates that shift the tail 90º relative to the trunk and build an oceanic house of cellulose and protein. Nevertheless Vetulicolia is not a new phylum, but a transitional set of taxa linking lancelets to larvacea and to crinoids. Vetulicolians (Figs. 1–3) demonstrate the down-angled tail appeared in the Early Cambrian pointing to an Ediacaran origin for lancelet-like chordates. That means previously unknown, more active, less benthic (= sea floor) niche full of free-swimming chordates was also present in the Ediacaran.

Figure 7. Vetulicola compared to a fossil crinoid. Note the splitting of the mouth parts into separate 'arms' has only just begun here. The crinoid stalk is the segmented 'tail' of Vetulicola.

Figure 5. Vetulicola compared to a fossil crinoid. Note the splitting of the mouth parts into separate ‘arms’ has only just begun here, starting with four. The crinoid stalk is the segmented ‘tail’ of Vetulicola.

When lips become arms… and tails become stems…
A clade of vetulicolians (former lancelets) also developed a down-hanging ‘tail’ (= stem) that ultimately evolved to become a holdfast: the crinoids within the echinoderms. Remember, adult lancelets also plant their tails in the substrate to become sessile plankton feeders. Crinoids are the ancestors of starfish (Fig. 6), a clade that flips, mouth-side down, and concurrently loses the tail (= stem). Not all echinoderms have a pentagonal morphology. The mouth of Vetucolia has four slightly separating mouth parts. The atrium and tail have just a trace of homologous armor, ringed in the case of the tail and stem.

Figure 3. Chordate evolution, changes to Romer 1971 from Peters 1991. Here echinoderms have lost the tail and gills of the free-swimming tunicate larva.

Figure 6. Chordate evolution, changes to Romer 1971 from Peters 1991. Here echinoderms have a stem-like tail with a holdfast, later lost in starfish, similar to the tail and gills of the free-swimming tunicate larva and adult larvaceans.

Garcia-Bellido et al. 2014 concluded
“Phylogenetic analyses resolve a monophyletic Vetulicolia as sister-group to tunicates (Urochordata) within crown Chordata. The hypothesis suggests that a perpetual free-living life cycle was primitive for tunicates. Characters of the common ancestor of Vetulicolia + Tunicata include distinct anterior and posterior body regions – the former being non-fusiform and used for filter feeding and the latter originally segmented – plus a terminal mouth, absence of pharyngeal bars, the notochord restricted to the posterior body region, and the gut extending to the end of the tail.” 

Garcia-Bellido et al. nested tunicates and vetulicolians as sisters to craniates, both derived from lancelets (cephalochordates). That seems to be correct based on the above figures in their tail-down orientation.

Cameron, Garey and Swalla (2000) reported,
“The nesting of the pterobranchs within the enteropneusts dramatically alters our view of the evolution of the chordate body plan and suggests that the ancestral deuterostome more closely resembled a mobile worm-like enteropneust than a sessile colonial pterobranch.”

Actually Peters 1991 (Fig. 6) published that hypothesis earlier… without the use of DNA.

Now we have long-sought evidence in the form of homologous traits that link vetulicolians to chordates (Fig. 2) and to echinoderms (Fig. 5). All have been understood as deuterostomes. The connection between larva was indicated earlier, according to Cameron, Garey and Swalla 2000. Now we have previously overlooked adult homologs to study and compare. This may be a novel hypothesis of interrelationships. If not, please provide a citation so I can promote it here.

Vetulicolians will not enter the LRT.
They diverge from the vertebrate lineage while keeping some basal lancelet traits and feeding patterns. The degree of their divergence indicates an ancient split from lancelets + fish, just as the divergence of starfish indicate a similar ancient split from lancelet deep time ancestors. They no longer resemble lancelets, except for their cirri-lined mouth parts and attendant mucous strands.


References
Aldridge RJ et al. (4 co-authors 2007. The systematics and phylogenetic relationships of vetulicolians. Palaeontology. 50 (1): 131–168.
Cameron CB, Garey JR and Swalla BJ 2000. Evolution of the chordate body plan: New insights from phylogenetic analyses of deuterostome phyla. PNAS 97(9):4469–4474.
Garcia-Bellido DC et al. 2014. A new vetulicolian form Australia and its bearing on the chordate affinities of an enigmatic Cambrian group. BMC Evolutionary Biology 2014, 14:214 http://www.biomedcentral.com/1471-2148/14/214
Peters D 1991. From the Beginning – The story of human evolution. Wm Morrow.
Shu D-G et al. (8 co-authors) 2001. Primitive deuterostomes from the Chengjiang Lagerstätte (Lower Cambrian, China) Nature 414:419–424.

wiki/Didazoon
wiki/Vetulicolia
wiki/Vetulicola
wiki/Larvacea

.https://www.youtube.com/watch?v=ZXCOZ2_blb8

SVP abstract 20: Squamate variability within a single species

Petermann and Gauthier 2020 bring us their views on the 
“potential consequences of our inability to assess intraspecific variability in growth rates.”

From the Petermann and Gauthier abstract:
“An investigation of life-history parameters in the extant iguanian lizard Sauromalus ater (the Common Chuckwalla), a sexually dimorphic species from the SW U.S.A., revealed remarkable intraspecific variability.”

“We found expected differences in growth strategies between males and females, but also within each sex, relating to body size and the timing of sexual maturity. Males and females can grow rapidly to size-at-sexual-maturity, producing above-average adult body sizes. Or, they can grow slowly to size-at-sexual-maturity, yielding adults at or below average body sizes. Neither growth strategy influences longevity. As a result, we found that body size of similar-aged individuals varied by 53% for males and 38% for females, and maximum differences in ‘adults’ of 64% for males and 38% for females.”

Further ranging results were found here earlier in the large pterosaur tree (LPT, 251 taxa) for the lepidosaur pterosaurs, Pteranodon (Fig. 1) and Rhamphorhynchus (Fig. 2). These both became fully resolved in phylogenetic analysis.

Figure 2. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen.

Figure 2. The DMNH specimen is in color, nesting between the short crest KS specimen and the long crest AMNH specimen.

Figure 2. Rhamphorhynchus specimens to scale. The Lauer Collection specimen would precede the Limhoff specimen on the second row.

Figure 2. Rhamphorhynchus specimens to scale. The Lauer Collection specimen would precede the Limhoff specimen on the second row.

Continuing from the Petermann and Gauthier abstract:
“Our results add to previous reports of intraspecific variability in extant and extinct vertebrates. High levels of intraspecific size-variability have multiple implications for vertebrate paleontology.

  1. Morphologically similar specimens from the same locality could belong to the same species even if the size difference among adult individuals exceeds 50%, which is a higher level than previously thought.
  2. Specimens that have been analyzed skeletochronologically and have been found to be similar or identical in chronological age, may not exhibit similar sizes.
  3. Variability in growth strategies may lead to mistaking males and females (especially among sexual dimorphs), or individuals using different growth strategies, as belonging to separate species.”

This is the way evolution works in all vertebrate communities, including humans, where some are taller, some are robust, some are more colorful or sexier, some are brilliant, distinct from the others. In both Rhamphorhynchus and Pteranodon, no two specimens are alike.

“We previously presented evidence that a sequence of sub-terminal skeletal suture fusions relates to maximum body size in squamates, and not to chronological age. This indicates that late-ontogenetic, suture-fusion events could be used to evaluate whether two or more specimens of similar morphology and chronological age are differently-sized conspecifics. Likewise, skeletal suture fusions may aid discerning different growth strategies within a single species, as opposed to the presence of two morphologically similar, but nonetheless separate, species in a single taphonomic assemblage.”

This follows the work of Maisano 2002, who found fusion patterns were phylogenetic in lepidosaurs. a pattern continued in pterosaurs, where fusion patterns are also phylogenetic, distinct form archosaur growth patterns.


References
Maisano JA 2002. 
Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Petermann H and Gauthier JA 2020. Intrespecific variability in an extant squamate and its implications for use in skeletochronology in extinct vertebrates. SVP abstracts 2020.

 

From Berkeley: pterosaur origins and whale evograms

Professor Kevin Padian (U of California, Berkeley)
has been a champion for evolution over the past several decades. In the 1980s I became acquainted with him when he was the science expert for my first book, Giants.

The following one hour video on YouTube caught my eye.
Professor Padian brilliantly discusses how school districts dealt with invading Creationists. Padian has been leading the charge on many fronts regarding evolution. Unfortunately, he has stayed in his tent sipping tea regarding the origin of flight in pterosaurs (Padian 1985), and the origin of whales, as you’ll see below.

 

From the Berkeley.edu page on pterosaur flight:
“Pterosaurs are thought to be derived from a bipedal, cursorial (running) archosaur similar to Scleromochlus in the late Triassic period (about 225 million years ago). Other phylogenetic hypotheses have been proposed, but not in the context of flight origins. The early history of pterosaurs is not yet fully understood because of their poor fossil record in the Triassic period. We can infer that the origin of flight in pterosaurs fits the “ground up” evolutionary scenario, supported by the fact that pterosaurs had no evident arboreal adaptations. Some researchers have proposed that the first pterosaurs were bipedal or quadrupedal arboreal gliders, but these hypotheses do not incorporate a robust phylogenetic and functional basis. The issue is not yet closed.”

This comes 20 years after Langobardisaurus, Cosesaurus, Sharovipteryx and Longisquama (Fig. 1) were added to four previously published phylogenetic analyses and all nested closer to pterosaurs than any tested archosaur (Peters 2000). Aspects of this topic were reviewed here in 2011 and here in 2015.

pterosaur wings

Figure 2. Click to enlarge. The origin of the pterosaur wing from Huehuecuetzpalli (B) to Cosesaurus (C) to Sharovipteryx (D) to Longisquama (E) to the basal pterosaur, Bergamodactylus (F and G).

The same webpage notes:
“Pterosaurs also had a bone unique to their clade. It is called the pteroid bone, and it pointed from the pterosaur’s wrist towards the shoulder, supporting part of the wing membrane. Such a novel structure is rare among vertebrates, and noteworthy; new bones are unusual structures to evolve — evolution usually co-opts bones from old functions and structures to new functions and structures rather than “reinventing the wheel.”

This comes 11 years after Peters 2009 showed the pteroid was not unique, but a centralia that had migratred medially in Cosesaurus (like the panda’s ‘thumb’). Likewise, the not-so-unique pteroid was co-opted from old functions, contra the Berkeley evolution page.

The same webpage notes:
“Pterosaurs had other morphological adaptations for flight, such as a keeled sternum for the attachment of flight muscles, a short and stout humerus (the first arm bone), and hollow but strong limb and skull bones.”

We’ve known since Wild 1993 that what Padian 1985 called a keeled sternum is actually a sternal complex composed of a fused interclavicle + clavicle + single lepidosaur sternum (Fig. 3) after migration over the interclavicle.

Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Figure 3. Tritosaur pectoral girdles demonstrating the evolution and migration of the sternal elements to produce a sternal complex.

Backstory…
25 years ago, when I first met Kevin Padian and Chris Bennett, they both impressed upon me, at the same time and during a single conversation, the need for a proper phylogenetic context before making any sort of paleontological hypothesis. That’s when MacClade and PAUP were still ‘newish’. That’s why you might find it ironic that neither Padian nor Bennett have ever tested the addition of the four key taxa in figure 3 to prior published analyses that included pterosaurs, as I did in Peters 2000.

On the second topic of whale evolution:
Padian’s ‘evogram’ (evolution diagram) simply lacks a few key taxa. Odontocetes don’t arise from hippos. Only mysticetes do. Here (Fig. 4) a few missing transitional taxa are added to the existing evogram. Likewise the outgroup for Pakicetus and Indohyus now include overlooked tenrecs and leptictids. They look more like Indohyus than the hippo because microevolution becomes more apparent when pertinent taxa are added. Otherwise it’s a big morphological jump from hippos to Indohyus. Adding taxa makes ‘the jump’ much smaller as the LRT has demonstrated dozens of times. No one should be afraid to simply add taxa.

Figure w. Whale evogram from Berkeley website and what happens when you add taxa based on the LRT.

Figure 4. Whale evogram from Berkeley website and what happens when you add taxa based on the LRT. Two frames change every 5 seconds. It’s not good that the outgroup to the slender Indohyus is the massive Hippopotamus. Frame two repairs that inconsistency with a little microevolution.

As you can see,
the University of California at Berkeley no longer stands at the vanguard of paleontology. Rather it has been promoting traditional myths on its website for the last twenty years.

According to Padian’s online talk (above):
“Just because you have  a degree in science does not mean you’re a scientist. Scientists are people who do research, publish peer-reviewed research as a main part of their living.”

That’s good to know. Of course, it doesn’t help if one suffers from the curse of Cassandra. On that point, I’m not asking anyone to ‘believe the LRT’, but to simply add taxa to your own favorite cladograms, as Peters 2000 did to four different previously published studies that each had their own taxon and character lists. That’s what the large reptile tree has continued to do over the last 9 years. Others who have added taxa and recovered results confirming those recovered by the LRT are listed here. The pair of PhDs who decided those results should be erased are listed here.

Ingroup scientists who attempt to exclude outgroup scientists is a common thread in human history. Here’s a YouTube video trailer for an upcoming Marie Curie biography. I’m sure you all know the story of her pioneering work in radioactive elements.

References
Padian K 1985. The origins and aerodynamics of flight in extinct vertebrates. Palaeontology 28(3):413–433.
Peters D 1989. Giants of Land, Sea and Air — Past and Present. Alfred A. Knopf/Sierra Club Books
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.
Peters D 2009.
A reinterpretation of pteroid articulation in pterosaurs.
Journal of Vertebrate Paleontology 29: 1327-133.
Wild R 1993. A juvenile specimen of Eudimorphodon ranzii Zambelli (Reptilia, Pterosauria) from the upper Triassic (Norian) of Bergamo. Rivisita Museo Civico di Scienze Naturali “E. Caffi” Bergamo 16: 95–120.

https://pterosaurheresies.wordpress.com/2011/09/09/the-origin-of-the-pterosaur-sternal-complex/

https://www.researchgate.net/publication/328388746_The_triple_origin_of_whales

https://evolution.berkeley.edu/evolibrary/article/evograms_02

https://evolution.berkeley.edu/evolibrary/article/evograms_03

https://evolution.berkeley.edu/evolibrary/article/evograms_04

https://evolution.berkeley.edu/evolibrary/article/evograms_05

https://evolution.berkeley.edu/evolibrary/article/evograms_06

https://evolution.berkeley.edu/evolibrary/article/evograms_07

https://ucmp.berkeley.edu/vertebrates/flight/pter.html

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

Several book reviews for ‘The Rise of the Reptiles’ by H-D Sues 2019

Figure 1. Book cover for 'The Rise of Reptiles' by HD Sues.

A new book on evolution,
‘The Rise of Reptiles’ (left), came out last August 2019. Unfortunately, it took this long to come to my attention.  After a short bio on author, Dr. Hans-Dieter Sues, several reviews follow.

According to Amazon.com, author Hans-Dieter Sues is 
“a senior scientist and curator of fossil vertebrates at the Smithsonian’s National Museum of Natural History. He is a coauthor of Triassic Life on Land: The Great Transition.”


Amazon.com called ‘The Rise of the Reptiles’,
“The defining masterwork on the evolution of reptiles.”

John Long, Finders University, called it,
“A valuable reference book―entertaining read and beautifully illustrated―about how reptiles first evolved and diversified into many lineages, including the one leading to us mammals. The Rise of Reptiles is essential reading for every evolutionary biologist.”

Michael J. Benton, University of Bristol, reported,
“The writing style is clear and easy, the illustrations are excellent, and the whole design and print quality highly attractive. There is no other book like it, and this will stand as a useful reference for many years.”

Jeremy B. Stout, Quarterly Review of Biology, called it, 
“The most complete and current compendiumon reptilian evolution and diversity to date… Few (if any) are better suited to have written this volume than Sues. His impressive research record over the past 40 years has dealt directly with many of the taxonomic groups in this volume, including (nonreptile) synapsids, parareptiles, sauropterygians, crocodylomorphs, and dinosaurs.”

After scientifically testing the various hypotheses put forth by Sues
in the Large Reptile Tree (LRT, 1680+ taxa) his book was found to promote many of the traditional myths and misconceptions that have befuddled reptile cladograms for the past decade. Virtually all of the problems in ‘The Rise of the Reptiles’ can be attributed to too few taxa in the various cited phylogenetic analyses.

Starting with outgroups, Sues reports,
“The group generally considered most closely related to amniotes is Diadectomorpha.” He cites papers from 1980, 2003 and 2007.

Using the last common ancestor method, the tested out-group to the clade Reptilia in the LRT (2020) is the Reptilomorpha. This clade includes the long-limbed taxon, Gephyrostegus, a late survivor from an earlier, probably Late Devonian, radiation. When more taxa are added diadectomorphs nest well within the Lepidosauromorpha branch of the Reptilia (Fig. 5), contra Sues 2019.

Dr. Sues “Pulls a Larry Martin” when he reports
on a few traits he notes are present in his short list of stem-amniote ‘outgroups’.

Those outgroups (diadectomorphs, which are ingroups in the LRT) were gleaned from old studies. Look what happens when you don’t have the correct outgroups and correct last common ancestors. The traits you observe are going to be wrong because you’re not even looking at the correct node. Never rely on a few traits to define a clade. Always rely on the ‘last common ancestor’ method to determine clade membership. And don’t exclude pertinent taxa!

Figure x. "Classification" of reptiles according to Sues 2019. Color overlay note differences when more taxa are added, as in the LRT.

Figure 2. “Classification” of reptiles according to Sues 2019. Color overlay note differences when more taxa are added, as in the LRT.

Sues reported on ‘the oldest known reptile, Hylonomus‘ 323-315mya,
but that was based on a pre-cladistic 1964 study. Sues then hedged that ‘undisputed’ report with two ‘recent phylogenetic analyses’ (1988 and 2006) that, “instead found these taxa [Hylonomus + Palaeothyris] closely related to diapsid reptiles.”

Using the last common ancestor method, the oldest known reptile in the LRT (2020) is Silvarnerpeton (346-323 mya). No hedging required here. All descendants laid amniotic eggs.

Figure 3. Reptilia vs. Amniota in Sues 2019 compared to the LRT.

Figure 3. Reptilia vs. Amniota in Sues 2019 compared to the LRT.

Sues cites Tsuji and Müller (2009) who defined ‘Parareptilia’ as
“the most inclusive clade containing Milleretta and Procolophon, but not Captorhinus” and that clade includes such diverse taxa as mesosaurs and pareiasaurs (Fig. 4).

If those two are related, that’s a Red Flag. In the LRT mesosaurs nest with similar pachypleurosaurs and other marine diapsids. Pareiasaurs give rise to turtles. As defined, the clade ‘Parareptilia’ is paraphyletic at worst, and a junior synonym of Reptilia at best in the LRT, which includes a wider gamut of taxa.

Figure x. Parareptilia according to Sues 2019.

Figure 4. Parareptilia according to Sues 2019.

Similar problems
attend the cladogram of ‘Eureptilia’ in Sues 2019 (Fig. 6).

More taxa solve this problem, too.

Figure x. Simplified cladogram of the Reptilia according to Sues 2019 (below in white) compared to a simplified version of the LRT using the same taxa.

Figure 5. Simplified cladogram of the Reptilia according to Sues 2019 (below in white) compared to a simplified version of the LRT using the same taxa. More taxa reveal an earlier dichotomy that creates two diapsid-grade skull morphologies. 

Dr. Sues has no idea how reptiles diverged
from their Viséan (or earlier) initial radiation. This could have been repaired if he had simply added taxa to his own analysis, rather than relying on published academic papers published decades ago with the same flaws.

Figure x. The 'Eureptilia' according to Sues 2019. This is a paraphyletic clade when more taxa are included, as in the LRT.

Figure 6. The ‘Eureptilia’ according to Sues 2019. This is a paraphyletic clade when more taxa are included, as in the LRT. Since the invalid clade ‘Sauria’ includes lepidosaurs and archosaurs it is half colored blue.

Other than cladograms, Sues 2019
also presents photos and diagrams (Fig. 7). Unfortunately some diagrams don’t match the fossils, leading to confusion at best.

Figure x. Figure from Sues 2019 showing Youngina capensis and a diagram of the same, that does not match the fossil. DGS color overlay added for comparison.

Figure 7. Figure from Sues 2019 showing Youngina capensis and a diagram of the same, that does not match the fossil. DGS color overlay added for comparison. What is the specimen number for this specimen?

Exposing and overturning old and new reptile mythology
is what PterosaurHeresies.Wordpress.com is all about as it supports the website www.ReptileEvolution.com and its centerpiece, the growing online cladogram at: www.ReptileEvolution.com/reptile-tree.htm. A wide-gamut cladogram is a powerful tool providing evidence against invalid traditional hypotheses that exclude pertinent taxa.

I cannot recommend this book.


References
Sues HD 2019. The Rise of Reptiles: 320 Million Years of Evolution.
Johns Hopkins University Press, Baltimore. xiii + 385 p.; ill.; index.
ISBN: 9781421428673 (hc); 9781421428680 (eb).

 

Evolution: like explaining the details of a magic trick

Some people really don’t want to know in detail how evolution works.
Unfortunately, this list of people includes some professors and students of paleontology. They prefer to keep a few enigmas and mysteries in their pocket even though all workers employ the number one tool of evolutionary biologists and paleontologists, the cladogram produced by phylogenetic analysis. Their magic trick is to omit certain taxa to get or retain the traditional results they want. Some academics think their fellow workers do this to ensure publication, staying within the current orthodoxy.

Example one:
It has been nearly twenty years since Peters 2000 presented several pterosaur ancestor, each one closer to pterosaurs than the next and each one closer to pterosaurs than any tested archosaur. All traditional archosaur candidates, including Scleromochlus (Benton 1999), were tested by simple taxon addition to four previously published analyses.

  1. Has anyone adopted this hypothesis in the last twenty years? No.
  2. Has anyone tested this hypothesis? Well, Hone and Benton 2007 announced they were going to test this hypothesis, but when tentative results matched those of Peters 2000 (the only study that included all four novel taxa), they decided to delete all data from and all reference to Peters 2000 in their follow up paper (Hone and Benton 2008).
  3. My paper correcting earlier interpretations of several taxa in Peters 2000 was denied publication by referees (members of the pterosaur community). You can read those revisions here at ResearchGate.net. [This update added < 24 hours after yesterday’s post].

Sometimes I wonder if anyone else would have tested these four taxa sometime over the last twenty years if I had not done so. The odds and circumstances, I fear, don’t support that vague hope. Dr. John Ostrom also lamented this sort of situation, noting that Archaeopteryx linked theropod dinosaurs to birds a hundred years before his Deinonychus and the proliferation of feathered Chinese taxa that finally sealed the deal for most of the paleo community.

 

Example two:
Genetic studies keep coming up with odd sister taxa that don’t look like one another. Nevertheless, workers have put their faith in their parade of illogical results without batting an eyelash. They think their results reveal previously unconsidered relationships, creating greater gulfs between sister taxa that will hopefully, someday be filled by future paleo discoveries. They seem to ignore, or don’t wish to examine the bones in their cabinets, preferring instead the invisible, hopeful results of DNA codes, while publicly recognizing that genomic results rarely duplicate phenomic results.

Examples three through eighteen:

  1. In turtle studies, you won’t find Niolamia, Odontochelys, Sclerosaurus and Elginia in the same cladogram.
  2. In whale studies, you won’t find tenrecs, elephant shrews, mesonychids, hippos and desmostylians in the same cladogram.
  3. In bat studies you won’t find pangolins and their ancestors in the same cladogram.
  4. In Jurassic placental studies you won’t find rodents, carpolestids, Daubentonia and multituberculates in the same cladogram.
  5. In ichthyosaur studies you won’t find mesosaurs and pachypleurosaurs in the same cladogram.
  6. In dinosaur studies you won’t find a list of basal bipedal crocodlyomorphs in the same cladogram.
  7. In synapsid/mammal studies you won’t find a long list of amphibian-like reptiles in the same cladogram.
  8. In caseid studies you won’t find millerettids, Aclestorhinus and a long list of amphibian-like reptiles in the same cladogram.
  9. In basal mammal studies, you won’t find arboreal didelphids in the same cladogram.
  10. In Vancleavea studies, you won’t find thalattosaurs in the same cladogram.
  11. In basal archosauriform studies, you won’t find a long list of terrestrial younginid and proterosuchid specimens in the same cladogram.
  12. In pterosaur studies, you won’t find every well-known specimen, including tiny Solnhofen pterosaurs, in the same cladogram.
  13. In bird origin studies, you won’t find all 13 Solnhofen birds and pre-birds in the same cladogram.
  14. In lepidosaur studies you won’t find pterosaurs and their fenestrasaur and tritosaur ancestors in the same cladogram.
  15. In placoderm studies you won’t find catfish in the same cladogram.
  16. In snake origin studies you won’t find the quadrupedal Jurassic ancestors that link to basalmost geckos in the same cladogram.
  17. The list goes on…

If you want to see all the above omitted taxa in the same cladogram,
all you have to do is click here for the large reptile tree (1558+ taxa) where the last common ancestors of all included clades are documented and validated all the way back to Silurian jawless fish. Here taxon exclusion is minimized adding confidence to the results vs. prior studies that continue to omit key taxa.


References
Benton MJ 1999. Scleromochlus taylori and the origin of the pterosaurs. Philosophical Transactions of the Royal Society London, Series B 354 1423-1446.
Hone DWE and Benton MJ 2007. An evaluation of the phylogenetic relationships of the pterosaurs to the archosauromorph reptiles. Journal of Systematic Palaeontology 5:465–469.
Hone DWE and Benton MJ 2008. Contrasting supertree and total evidence methods: the origin of the pterosaurs. Zitteliana B28:35–60.
Peters D 2000a. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2000b. A Redescription of Four Prolacertiform Genera and Implications for Pterosaur Phylogenesis. Rivista Italiana di Paleontologia e Stratigrafia 106 (3): 293–336.

The other clade descending from speedy jacks includes slower eels and anglers

Earlier, and with fewer taxa,
the large reptile tree (LRT, 1535 taxa, subset Fig. 1) nested European eels (Anguilla) with pikes (Esox) and barracuda (Sphyraena). With the addition of new taxa the transitions between the earlier forms become smoother, easier to understand and more complete.

Figure 1. Subset of the LRT focusing on basal vertebrates (fish) and the clade that gave rise to eels and frogfish.

Figure 1. Subset of the LRT focusing on basal vertebrates (fish) and the clade that gave rise to eels and frogfish.

You might ALSO remember,
earlier we looked at a species of amberjack, Seriola rivoliana, which nests basal to pufferfish, molas, triggerfish and mudskippers. Another species of speedy Seriola (Fig. 2) is the focus of today’s blogpost.

Figure 2. Seriola zonata, the banded rudder fish, is basal to cusk eels and frogfish in the LRT.

Figure 2. Seriola zonata, the banded rudder fish, is basal to cusk eels and frogfish in the LRT.

Today, with additional taxa
European eels are moved away from pikes with intervening, transitional taxa, including a second species of amberjack, the banded rudder fish, Seriola zonata (Valenciennnes 1833). In the LRT S. zonata is basal to eels, frogfish, anglers, knife fish and electric eels (Fig. 1). Notably, none of these derived taxa are speedy, open-water predators distinct from S. zonata. Aparently all derived taxa have slower lifestyles and thus many became bottom dwellers. Note the almost identical skulls shown in figures 2 and 3, despite their postcranial differences.

Seriola zonata (Valenciennnes 1833; commonly 50cm, up to 75cm) is the extant banded rudderfish. Here it nests basal to the European eel (Fig. 4) and cusk eel (Fig. 3). Large individuals (over 10 inches) have no bands. This fish, though commonly caught, is rarely identified. Large ones, with a raccoon-stripe on the eye and an iridescent gold stripe on the side, are usually called amberjacks when caught, and juveniles are called pilotfish.

Figure 3. Dicrolene, the cusk eel, nests close to S. rivoliana in the LRT.

Figure 3. Dicrolene, the cusk eel, nests close to S. rivoliana in the LRT.

Dicrolene nigracaudis (Goode and Bean 1883, Alcock 1899, Dicrolene introniger shown below) is a rare species of deep sea cusk eel, family Ophidiiformes. Distinct from true eels, cusk eels have pelvic fins transformed into barbels below the pectoral fins. The lower half of each long pectoral fin is transformed into a set of bottom feeling rays.

European eels
are longer-skulled versions of cusk eels in the LRT.

 

Figure 2. The skull of Anguilla from Gregory 1936, with bones colored here and matched to an invivo photo. This is a revised illustration.

Figure 5. The skull of Anguilla from Gregory 1936, with bones colored here and matched to an invivo photo. This is a revised illustration.

Anguilla anguilla (Linneaus 1758; up to 80cm in length, 1.5 exceptionally) is the extant European eel, a sister to the cusk eel in the LRT. Like DicroleneAnguillal acks several facial bones, pelvic fins and the tail has reverted to a straight tail. The life cycle includes breeding and young hatching in the mid-Atlantic with migration back to European rivers before the adults return to the mid-Atlantic. Bones are relabeled here based on sister taxa.

This appears to be a novel hypothesis of interrelationships
that links previously unlinked taxa. If I missed a citation that predates this one that supports this hypothesis of interrelationships, please send me the citation.

Figure 4. Antennarius, the frogfish, nests basal to anglerfish, derived from S. rivoliana.

Figure 4. Antennarius, the frogfish, nests basal to anglerfish, derived from S. rivoliana.

Antennarius sp. (Daudin 1816) is the extant frogfish, a bottom-dwelling sit-and-wait predator with a lure and an enormous gape. The pelvic fins are anterior to the pectoral fins. Both are used to walk on the sea floor. Note the separation of the parietals by the postparietals. Although Antennarius superficially resembles an angler, it is as sister to Seriola zonata (above).

Earlier we looked at the connection between the remaining clade members: anglers, cave fish and electric eels.

Figure 7. Lophius, the anglerfish, nests between frogfish and electric eels in the LRT.

Figure 5. Lophius, the anglerfish, nests between frogfish and electric eels in the LRT.

Lophius americanus (Rafinesque 1810; up to 1.5m in length) is the extant goosefish or monkfish. The closest relative in the LRT is the electric eel, Electrophorus. The pelvic fins are small and anteroventral to the pectoral fins.

The LRT continues to bring diverse clades of fish together,
reducing the number of clades and illuminating interrelationships.

Figure 5. Skull of the electric eel (Electrophorus) distinct from the moray eel (Fig. 4) and European eel (Fig. 2).

Figure 6. Skull of the electric eel (Electrophorus) distinct from the moray eel (Fig. 4) and European eel (Fig. 2).

Electrophorus electricus (originally Gymnotus electricus, Linneaus 1766; Gill 1864; up to 2m in length) is the extant electric eel, an obligate air breather nesting between Lophius and Gymnotus (Fig. 7). Electric organs that deliver shocks to enemies and prey make up 80% of the body.

Figure 6. Gymnotus, the knife fish.

Figure 7. Gymnotus, the knife fish.

Gymnotus carapo (Linneaus 1758; up to 100cm in length) is the extant banded knifefish, a nocturnal small prey predator with essentially no dorsal, caudal or pelvic fins. The anal fin undulates for slow propulsion. The electric signal is weak.

Figure 8. Skull of Gymnotus.

Figure 8. Skull of Gymnotus.

I never knew fish could be so fascinating.
And I never thought I would be among the first to employ phylogenetic skeletal traits to recover this branch of the tree of life. There has been too much dependence on gene studies, which likewise don’t produce a gradual accumulation of derived traits for all sister taxa for other vertebrate clades over deep time. Soon we will take a look at the differences between a genomic fish tree and a phenomic fish tree. You’ll see.


References
Alcock AW 1899. A descriptive catalogue of the Indian deep-sea fishes in the Indian Museum. International Publisher, USA 87 pp.
Cubelio SS, Joseph J, Venu S, Deepu AV and Kurup BM 2009. Redescription of Dicrolene nigracaudis (Alcock, 1899) a rare species of deep sea cusk eel (Ophidiiformes; Ophidiidae) from Indian EEZ. Indian Journal of Marine Sciences 38(2):166–169.
Daudin FM 1816. Antennarius. In: Dictionaire des sciences naturelles.
Goode GB and Bean TH 1883. Reports on the results of dredging under the supervision of Alexander Agassiz, on the east coast of the United States, during the summer of 1880, by the U. S. coast survey steamer Blake, C, Bulletin of the Museum of Comparative Zoology at Harvard College 10 (5), pp. 183-226: 202 .
Linnaeus C von 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Valenciennnes A in Cuvier G and Valenciennes A 1833. Histoire naturelle des poissons. Tome neuvième. Suite du livre neuvième. Des Scombéroïdes. 9: i-xxix + 3 pp. + 1-512. Pls. 246-279.,

wiki/Seriola
wiki/Amberjack
wiki/Antennarius

wiki/Cusk-eels
wiki/Dicrolene
wiki/European_eel

Guiyu and Psarolepis enter the LRT together

Today’s study confirms
the phylogenetic analyses of prior workers, like Zhu et al. 2012 and others cited therein. They considered Guiyu (Silurian, 419 mya) the earliest articulated bony fish. Zhu and Zhau 2009 described it as a basal lobe-finned fish with some ray-finned traits.

Figure 1. Guinyu in situ, as originally restored and as restored here based on the in situ data. Psarolepis shares the median spike seen here.

Figure 1. Guinyu in situ, as originally restored and as restored here based on the in situ data. Psarolepis shares the median spike seen here.

Today’s study offers a new reconstruction
for Guiyu: less like a sarcopterygian (Fig. 1) and more like the placoderm, Stensioella, from which it arises in the large reptile tree (LRT, 1480 taxa). So Guiyu documents the transition from placoderms to most bony fish (except catfish and sturgeons). Zhu et al. 2012 did not report the placoderm connection, perhaps because their reconstruction did not look like a placoderm. They did not notice the armored pectoral and pelvic fins were separate from the torso and tail.

Figure 2. Guiyu in situ, DGS colors added here and used to create the flatter, wider reconstruction with paddles preserved.

Figure 2. Guiyu in situ, DGS colors added here and used to create the flatter, wider reconstruction with paddles preserved. This rather complete taxon provides phylogenetic bracketing clues to the lateral skull and post-crania missing in a sister taxon, Psarolepis (Fig. 3). This taxon documents the transition from placoderms to bony fish.

Zhu et al. 2012 reported,
“Guiyu and Psarolepis have been placed as stem sarcopterygians in earlier studies, even though they manifested combinations of features found in both sarcopterygians and actinopterygians (e.g. pectoral girdle structures, the cheek and operculo-gular
bone pattern, and scale articulation). When Guiyu was first described based on an exceptionally well-preserved holotype specimen, it also revealed a combination of osteichthyan and nonosteichthyan features, including spine-bearing pectoral girdles and
spine-bearing median dorsal plates found in non-osteichthyan gnathostomes as well as cranial morphology and derived macromeric squamation found in crown osteichthyans. In
addition, Guiyu provided strong corroboration for the attempted restoration of Psarolepis romeri based on disarticulated cranial, cheek plate, shoulder girdle and scale materials.”

FIgure 2. Psarolepis skull restored from published data.

FIgure 2. Psarolepis skull restored from published data. Hypothetical opercula are not present, based on Guiyu.

Most of the cranial bones of Psarolepis are fused to one another.
Unfortunately that provides few clues to figure out bone outlines. Here (Fig. 2) Psarolepis is restored based on patterns found throughout the clade. The colors applied to each bone makes this restoration challenge a bit easier and certainly easier to convey to readers.

FIgure 3. Guiyu skull reconstruction in closer view. Mandibles in dorsal view.

FIgure 3. Guiyu skull reconstruction in closer view. Mandibles in dorsal view.

Zhu et al. 2014 followed tradition in their abstract:
“Living gnathostomes (jawed vertebrates) include chondrichthyans (sharks, rays and chimaeras) and osteichthyans or bony fishes. Living osteichthyans are divided into two lineages, namely actinopterygians (bichirs, sturgeons, gars, bowfins and teleosts) and sarcopterygians (coelacanths, lungfishes and tetrapods). [1] It remains unclear how the two osteichthyan lineages acquired their respective characters and how their common osteichthyan ancestor arose from non-osteichthyan gnathostome groups. [2] Here we present the first tentative reconstruction of a 400-million-year-old fossil fish (Psarolepis) from China; this fossil fish combines features of sarcopterygians and actinopterygians and
yet possesses large, paired fin spines previously found only in two extinct gnathostome groups (placoderms and acanthodians). [3] This early bony fish provides amorphological link between osteichthyans and non-osteichthyan groups. It changes the polarity of many characters used at present in reconstructing osteichthyan interrelationships and offers new insights into the origin and evolution of osteichthyans.” [4]

The following notes answer issues raised above:

  1. The LRT separates actinopterygians into several ray-fin clades. Sturgeons, bichirs, and catfish nest apart from bowfins, gars and teleosts.
  2. That lack of clarity is resolved in the LRT.
  3. They are forgetting bichirs, sturgeons, sticklebacks, and Guiyu.
  4. All the more so if they had only included Entelognathus and Guiyu.
  5. Adding Tinirau and LRT taxa helps separate Eusthenopteron and kin from their traditional, and now offshoot link to Tetrapoda.

Zhu et al. 2014 also reported, 
“Psarolepis was first placed within sarcopterygians, as a basal member of Dipnormorpha or among the basal members of Crossopterygii. The new features revealed by the shoulder girdle and cheek materials reported here indicate that Psarolepis may occupy a more basal position in osteichthyan phylogeny.” The LRT resolved this historical issue by including pertinent and key taxa.

Zhu et al. 2014 produced two cladograms
when they introduced Psarolepis, neither of which included Guiyu. In cladogram A Zhu et al. nested Psarolepis between the spiny sharks (acanthodians) and ray-fin fish beginning with the bichir, Polypterus + lungfish. In cladogram B Zhu et al. nested Psarolepis between Polypterus and lobe-fin fish beginning with coelacanths. The placoderms, Entelognathus (Zhu et al. 2013) and Stensioella (Broilli 1933) were not mentioned or included. Both are ougroups to Guiyu and Psarolepis in the LRT. Acanthodians are not primitive or basal to bony fish. They are derived bony fish in the LRT as we learned earlier here. Contra traditions, the most interesting taxa that transition to tetrapods are all slow-moving bottom feeders, not swift open water predators.

Figure 4. Subset of the LRT updated with new basal vertebrates.

Figure 4. Subset of the LRT updated with new basal vertebrates.

Dr. Zhu Min
is the lead author on several of these new discoveries and publications shedding light on key taxa at the origin of bony fish, tetrapods and ultimately humans.


References
Broili F 1933. Weitere Fischreste aus den Hunsrickschiefern. Situngsbirechte der bayerischen Akademie der Wissenschaften, Mathematisch-Naturewissenschaftliche Klasse 2: 269–313.
Zhu M and Zhau W-J 2009. The Xiaoxiang Fauna (Ludlow, Silurian) – a window to explore the early diversification of jawed vertebrates. Abstract from: Rendiconti della Società Paleontologica Italiana. 3 (3): 357–358.
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, Ahlberg PE, Choo B and 8 others 2013. A Silurian placoderm with osteichthyan-like marginal jaw bones. Nature. 502:188–193.
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/Psarolepis
wki/Stensioella

Karaurus and the origin of frogs + salamanders

Figure 1. Karaurus in situ. About the size of a living salamander.

Figure 1. Late Jurassic Karaurus in situ. About the size of a living salamander.

Karaurus sharovi (Ivachnenko 1978; Late Jurassic; Figs. 1, 2) nests with Celtedens (Fig. 3) in the large reptile tree (LRT, 1467 taxa; Fig. 4)  and resembled living salamanders (Fig. 5) in size, shape and lifestyle. Here (Fig. 2) certain skull bones are reidentified. The orbit was confluent with an upper + lateral temporal fenestra that appeared by the loss of the posterior circumorbital bones.

Figure 2. Karaurus drawing from Carroll 1988, originally from Ivanchenko 1978, photo of same, DGS of same. Colors standard. Some re-identify bones. Hypothetical eyeball added. It does not have to fill the orbit, but it could.

Figure 2. Karaurus drawing from Carroll 1988, originally from Ivanchenko 1978, photo of same, DGS of same. Colors standard. Some re-identify bones. Hypothetical eyeball added. It does not have to fill the orbit, but it could. The former squamosal is a tabular + supratemporal. The lacrimal and prefrontal are not fused. Postparietals are present.

Post circumorbital bones are also missing,
in Celtedens (Fig. 3). distinct from frogs, like Rana, and salamanders, like Andrias (Fig. 5).

Figure 3. Celetendens is the closest relative to Karaurus in the LRT.

Figure 3. Celetendens is the closest relative to Karaurus in the LRT.

FIgure 2. Subset of the LRT focusing on lepospondyls including salamanders and frogs.

Figure 4. Subset of the LRT focusing on lepospondyls including salamanders and frogs.

The previous illustration of the giant Chinese salamander skull
(genus: Andrias; Fig. 5) is here updated based in new understandings of homologous bumps and sutures.

Figure 3. Revised skull of Andrias japonicas, the giant Chinese salamander. This was informed by recent studies of the mudpuppy, Necturus.

Figure 3. Revised skull of Andrias japonicas, the giant Chinese salamander. This was informed by recent studies of the mudpuppy, Necturus.


References
Ivanchenko KF 1978. Urodelans from the Triassic and Jurassic of Soviet Centra Asia. Paleontological Journal 12(3):362–368.

Strunius: transitional between lobe fins and ray fins

Not sure why this one was overlooked for so long…
… but then again, so many phylogenetic relationships have been overlooked by taxon exclusion.

Earlier the large reptile tree (LRT, 1155 taxa, subset Fig. 4) indicated a novel origin for many (not all) ray-fin fish arising from the lobe fin, Gogonasus (Fig. 1). Today another transitional taxon was added to the LRT, Strunius (Fig. 1). Described as the sarcopterygian with ray fins, Strunius cements that earlier hypothesis.

Figure 1. Transitional taxa from the lobe fin Osteolepis to the ray fin Xiphactinus, including tiny Strunius at the transition.

Figure 1. Transitional taxa from the lobe fin Osteolepis to the ray fin Xiphactinus, including tiny Strunius at the transition. Note, Cheirolepis retains lobe fins on the pectoral set, not the pelvic set.

Once again,
phylogenetic miniaturization played a part in clade origins as Strunius is much smaller than both its ancestors and descendants (Fig. 2).

Figure 2. Tiny Strunius to scale with Cheirolepis.

Figure 2. Tiny Strunius to scale with Cheirolepis.

The earlier question about
the second origin of the dual (in-out) external naris is answered with Strunius (Fig. 3). The naris appears to be split in two (at least in this drawing), creating a new dual naris. The palate remains unknown, so whether Strunius retained a choana or not is not yet known.

Figure 3. Strunius enlarged to show detail. Inset shows the second origin of the dual external naris as the original apparently splits by the addition of a skin bridge creating two openings. A reminder, this is a late-survivor of an earlier radiation.

Figure 3. Strunius enlarged to show detail. Inset shows the second origin of the dual external naris as the original apparently splits by the addition of a skin bridge creating two openings. A reminder, this is a late-survivor of an earlier radiation.

A cladogram of tested taxa
(Fig. 4) shows three separate origins for ray-fin fish:

  1. sturgeons and spoonbills arising from placoderms;
  2. bichirs arising from lungfish;
  3. the rest of the ray-fins arising from Strunius
Figure 4. Subset of the LRT focusing on the three origins of ray-fin fish.

Figure 4. Subset of the LRT focusing on the three origins of ray-fin fish.

Including the outgroup taxon
Entelognathus (Zhu et al. 2013) might make all the difference between traditional cladograms (Fig. 5) and the LRT (subset Fig. 4). In the basal fish cladogram by Bemis, Findels and Grande 1997 (Fig. 5) Cheirolepis nests with the distinctly different Polypterus at the base. This does not show a gradual accumulation of derived traits.

Figure 5. Traditional cladogram of sturgeon origins from Bemis, Findels and Grande 1997. They did not have Entelognathus as an outgroup, which might make all the difference.

Figure 5. Traditional cladogram of sturgeon origins from Bemis, Findels and Grande 1997. They did not have Entelognathus as an outgroup, which might make all the difference. Note the huge morphological gap between the first two taxa.

Some authors
have championed the lungfish clade as tetrapod ancestors. Others have championed the rhipidistian clade (Osteolepis and kin). The present cladogram indicates both were offshoots with convergent traits. Here (Fig. 4), the tetrapod lineage arose more directly from basalmost bony fish, before the Devonian radiation of lungfish and rhipidistians.

So
Eusthenopteron and Osteolepis turn out to have a different set of living representatives than earlier workers once thought — IF this hypothesis of relationships pans out. I will keep adding taxa, but the topology is not changing, so far.

Strunius rolandi (Jessen 1966; originally Glyptomus rolandi Gross 1956; 10 cm in length; Late Devonian) was considered a lobe-fin fish with ray fins. Here it nests with Cheirolepis, a traditional and transitional ray fin fish. The origin of the double naris in this lineage appears here as a split dividing the original single in two. The palate and possible choana are not known. The maxilla and quadratojugal are fused relative to more primitive taxa.


References
Gross W 1956. Über Crossopterygier und Dipnoer aus dem baltischen Oberdevon im Zusammenhang einer vergleichenden Untersuchung des Porenkanalsystems paläozoischer Agnathen und Fische. Stockholm Almqvist & Wiksell.
Jessen H 1966. Die Crossopterygier des Oberen Plattenkalkes (Devon) der Bergisch-Glabach-Paffrather Mulde (Rheinisches Schiefergebirge) unter Berücksichtigung von amerikanischem und europäischem Onychodus-Material. Arkiv für Zoolgi 18:305–389.

wiki/Gogonasus
wiki/Cheirolepis
wiki/Strunius

Where do sea horses come from?

A little off topic,
but I was curious to see how the odd morphology of the sea horse came to be, who its ancestors were and what transitional taxa went through on their evolutionary journey through deep time. Hope you find this interesting.

The relationship between sticklebacks and sea horses
has been known for many decades. Both are members of the clade Gasterosteiformes, which is in the clade of spiny finned fish, Acanthopterygii, which is in the clade of bony ray-finned fish, Actinopterygii.

A helpful guide
is Gregory 1933, available online as a PDF. Most of the images below come from that book.

No phylogenetic analysis was performed here,
so think of the following images as broad evolutionary brush strokes, not a narrow ladder of succession. Few details are offered because most are apparent at first glance. Precise last common ancestors remain unknown. These are rare derived representatives of deep time radiations.

Even so,
the early appearance of body armor in the stickleback, G. aculeatus; the diminution of the tail (except in the pipefish/fantails, Dunckerocampus and Solenostomus); the gradual loss of the fusiform shape; the elongation of the rostrum and the reduction of the mouth are all apparent in this series of illustrations.

Figure 1. Stickleback to sea horse evolution through pipefish. Sticklebacks have some of the body armor that overall encases and stiffens sea horses and sea dragons like Hippocampus and two species of Phyllopteryx. The ghost pipeish Solenostomus, is distinct from the more slender, elongate types of pipefish.

Figure 1. Stickleback to sea horse evolution through pipefish. Sticklebacks have some of the body armor that overall encases and stiffens sea horses and sea dragons like Hippocampus and two species of Phyllopteryx. The ghost pipeish Solenostomus, is distinct from the more slender, elongate types of pipefish.

The skulls of the taxa shown above
(Fig. 2) detail other changes, such as how far anteriorly the quadrate and palate bones shift on these fish with an ever longer rostrum and ever smaller mouth losing tiny teeth. The hyomandibular (hy) is the stapes in tetrapods. Not sure about the homology of the squamosal and the labeled preopercular, but the following is offered. Sometimes fish and tetrapods have different names for the same bones, as we learned earlier here.

Figure 2. Most of the bones of the tetrapod skull are also found in sea horses with some odd changes, like the placement of the quadrate well anterior to the orbit. Hippocampus illustration from Franz-Odendaal and Adriaens 2014. Not the parasphenoid passing midway through the orbit, while in tetrapods the orbit is typically raised above this anteriorly-directed splint-like bone arising from the basicranium. Everything below it is mouth cavity.

Figure 2. Most of the bones of the tetrapod skull are also found in sea horses with some odd changes, like the placement of the quadrate well anterior to the orbit. Hippocampus illustration from Franz-Odendaal and Adriaens 2014. Not the parasphenoid passing midway through the orbit, while in tetrapods the orbit is typically raised above this anteriorly-directed splint-like bone arising from the basicranium. Everything below it is mouth cavity.

So many bones
are displaced or lost in sea horses distinct from their basal vertebrate locations (e.g. Cheirolepis, Fig. 3) that an evolutionary series illustration (Fig. 2) proves helpful in understanding the lumping and splitting of clade members. Sarcopterygians, like Osteolepis (Fig. 3), split off early from other ray-finned fish, which is why they appear share more traits and proportions with Cheirolepis. Note the jaw hinge remains posterior to the orbit in these two.

Figure 2. Cheirolepis skull (left) with skull bones colorized as in Osteolepis (right) and Enteognathus, figure 1. Colors make bone identification much easier. Note the post opercular bone differences between Osteolepis and Cheirolepis indicating separate and convergent derivation, based on present data.

Figure 3. Cheirolepis skull (left) with skull bones colorized as in Osteolepis (right) and Enteognathus, figure 1. Colors make bone identification much easier. Note the post opercular bone differences between Osteolepis and Cheirolepis indicating separate and convergent derivation, based on present data.

Understanding where we came from,
and where our cousins went in their evolutionary journeys are the twin missions of this blogpost in support of ReptileEvolution.com.


References
Franz-Odendaal TA and Adriaens D 2014. Comparative developmental osteology of the seahorse skeleton reveals heterochrony amongst Hippocampus sp. and progressive caudal fin loss. EvoDevo 2014, 5:45
Gregory WK 1933. Fish skulls: a study of the evolution of natural mechanisms. American Philosophical Society. ISBN-13: 978-1575242149 PDF

wiki/Seahorse
diverosa.com/Syngnathidae