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.

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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 1. 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.

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

Giant Mesozoic flat heads: Siderops and Koolasuchus

Little Gerrothorax has a new giant sister, Siderops,
(Fig. 1) in the large reptile tree (LRT, 1440 taxa). This is a traditional nesting recovered by prior workers.

We’re still missing those poorly ossified fingers and toes.
Or did this clade have lobefins (Fig. 2)? Nothing past the wrist is known for any clade members (that I’ve seen). Could go either way with available data… so, don’t assume fingers and toes.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale.

Figure 1. Siderops in several views from Warren and Hutchinson 1983, colors added. The related giant Koolasuchus and small Gerrothorax are added for scale. Are these lobefins or did they have feet? And look at the size of those palatal fangs!

Speaking of clades,
both Siderops and Gerrothorax are traditionally considered temnospondyls, which all have fingers and toes. Here they nest prior to traditional temnospondyls, closer to flathead lobefin tetrapods, like Tiktaalik, in the LRT (subset Fig. 2).

Figure 1. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Figure 2. Subset of the LRT focusing on basal tetrapods and showing those taxa with lobefins (fins) and those with fingers and toes (feet). Inbetween we have no data.

Siderops kehli (Warren and Hutchinson 1983; Early Jurassic, 180mya; skull 50cm long, overall 2.5m long) was traditionally considered a chigutisaurid temnospondyl or a brachyopoid. Here Siderops nests with the much smalller Gerrothorax. No branchials and scales were reported. The back of the skull and the extremities are unknown, so modifications were made to reflect that lack of data here.

Koolasuchus cleelandi was a late surviving Early Cretaceous giant from this clade, presently known from just a few bones, like the mandible (Fig. 2).

Tomorrow we’ll take a look
at several giant ‘amphibians’ (= anamniote tetrapods) all to scale.


References
Warren A and Hutchinson M 1983. The last labyrinthodont? A new brachyopoid (Amphibia, Temnospondyli) from the Early Jurassic Evergreen Formation of Queensland, Australia. Philosophical Transactions of The Royal Society B Biological SciencesB 303:1–62.

wiki/Gerrothorax
wiki/Siderops