Chauliodus, the viperfish, enters the LRT

Figure 1. Cheirolepis, a Middle Devonian ancestor to the viperfish.

Figure 1. Cheirolepis, a Middle Devonian ancestor to the viperfish.

Yes, it’s another great grandson
of Cheirolepis (Fig. 1), one of the earliest known bony fish. Earlier we looked at another great, grandson deep sea fish, Malacosteus.

Figure 1. Chauliodus diagram from xxx 1938. Note the convergent loss of cheek bones in this Cheirolepis clade member.

Figure 2. Chauliodus diagram from Gregory 1938. Note the convergent loss of cheek bones in this Cheirolepis clade member.

Chauliodus sloani (Forster in Bloch and Schneider 1801, up to 60cm in length, subset Fig. 2-4) is the extant viperfish. A tiny glowing lure from the anterior dorsal fin lure deep sea fish to the oversized teeth. Scales and maxillary teeth are retained. Apparently the temporal series (intertemporal, supratemporal and tabular) were not retained, which is almost unique among fish. The anterior dorsal fin is new based on comparisons to Cheirolepis (Fig. 1). Note the evolution of the heterocercal tail to a diphycercal tail, only one of many such convergent instances.

Figure 3. Chauliodus, the viperfish, in vivo.

Figure 3. Chauliodus, the viperfish, in vivo.

Biting is a big deal with Chauliodus
as those jaws go through some gymnastics at maximum aperture (Fig. 4).

Figure 3. Viperfish posed as if biting its prey attracted to its first dorsal fin lure.

Figure 4. Viperfish posed as if biting its prey attracted to its first dorsal fin lure.

This nesting
and several others to come are greatly simplifying the fish family tree. I will list the many exciting changes shortly.


References
Forster JR 1801. in Bloch, ME and Schneider JG editors, Systema Ichthyologiae Iconibus cx Ilustratum. Post obitum auctoris opus inchoatum absolvit, correxit, interpolavit Jo. Gottlob Schneider, Saxo. Berolini. Sumtibus Auctoris Impressum et Bibliopolio Sanderiano Commissum. i-lx + 1-584.

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You heard it here in 2011: diadectids are amniotes

Co-author, David S. Berman,
has been saying diadectids are amniotes since the 1990s, but not with a comprehensive taxon list, and, apparently nobody listened. The consensus apparently prefers their diadectids with tadpoles.

Here’s what Wikipedia reports
“Diadectes (meaning crosswise-biter) is an extinct genus of large, very reptile-like amphibians that lived during the early Permian period (ArtinskianKungurian stages of the Cisuralian epoch, between 290 and 272 million years ago[1]). Diadectes was one of the very first herbivorous tetrapods, and also one of the first fully terrestrial animals to attain large size.”

Skeleton of Diadectes. Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Figure 1 Skeleton of Diadectes. Perhaps unnoticed are the broad dorsal ribs of this taxon, basal to Stephanospondylus, Procolophon and pareiasaurs.

Klembara et al. 2019 report
on the inner ear morphology of diadectids and seymouriamorphs. From the abstract:
“Two pivotal clades of early tetrapods, the diadectomorphs and the seymouriamorphs, have played an unsurpassed role in debates about the ancestry of amniotes for over a century, but their skeletal morphology has provided conflicting evidence for their affinities. Both maximum parsimony and Bayesian inference analyses retrieve seymouriamorphs as derived non‐crown amniotes and diadectomorphs as sister group to synapsids.”

Figure 2. Cladogram from Klembara et al. 2019. Green shows reptile taxa in the LRT.

Figure 2. Cladogram from Klembara et al. 2019. Green shows reptile taxa in the LRT.

Dr. David Marjanovic wrote in the DML:
“Amniota is a crown-group; there’s technically no such thing as a “stem-amniote”, because if it’s on the stem, it’s not an amniote.”

Unfortunately, Klembara et al. don’t have enough taxa
to understand that Amniota is a junior synonym for Reptilia. So Repitilomorpha works well for pre-reptiles. More importantly, for the subject at hand, Diadectes (Fig. 1) and kin have been deeply nested within the large reptile tree (LRT, 1583 taxa) since 2011. This is an online resource you can use to double check your taxon list, just to make sure it is up to date. The Klembara et al. taxon list (Fig. 2) is so inadequate it nests several reptiles apart from one another and omits dozens of others pertinent to this issue.

Figure 2. Subset of the LRT focusing on basal lepidosauromorphs and Diadectes.

Figure 3. Subset of the LRT focusing on basal lepidosauromorphs and Diadectes.

Bottom line, when you add enough taxa
diadectomorphs are not close to synapsids, but arise from millerettids.

At least the Klembara team
moved diadectomorphs inside the Amniota. That’s a minor victory. Add the above taxa to your cladogram (Fig. 2) and see where Diadectes nests. That’s what the LRT is here for… to help workers avoid taxon exclusion.


References
Klembara J, Hain M, Ruta M, Berman DS,  SEPierce and Henrici AC 2019. Inner ear morphology of diadectomorphs and seymouriamorphs (Tetrapoda) uncovered by highâresolution xâray microcomputed tomography, and the origin of the amniote crown group. Palaeontology (advance online publication) Future publication date: August 5, 2020
doi: https://doi.org/10.1111/pala.12448
https://onlinelibrary.wiley.com/doi/full/10.1111/pala.12448

wiki/Diadectes

Spiny sharks (Acanthodii) transitional to lobefins in the LRT

The most recent changes
to the large reptile tree (LRT, 1583 taxa, subset Fig. 1) resolve earlier problems and place two spiny sharks (clade: Acanthodii, Fig. 1) at the base of the newly expanded pre-lobefin clade, all arising from catfish + placoderms, some of which also have spiny pectoral fins.

Figure 1. Classic reconstruction of Cladoselache, a shark-like taxon basal to sturgeons and catfish+placoderms in the LRT.

Figure 1. Classic reconstruction of Cladoselache, a shark-like taxon. Note the robust pectoral fin skeleton. A Silurian sister is the genesis for the spiny sharks, catfish and placoderms.

These in turn
arise from taxa like Cladoselache (Fig. 1), which had strongly supported pectoral fins along with robust anterior spines on the two dorsal fins, homologs of dorsal spines on spiny sharks.

Figure 1. Subset of the LRT focusing on fish. Note the position of two spiny sharks, basal to the lobefin clade and arising from catfish, which also have spiny fins.

Figure 2. Newly revised subset of the LRT focusing on fish. Note the position of two spiny sharks, basal to the lobefin clade and arising from catfish, which also have spiny fins.

The tiny size of the basal acanthodian, Brachyacanthus, 
(Fig. 3) documents phylogenetic miniaturization at the genesis of a new major clade. If large eyes, a high forehead and a short rostrum indicate ‘cuteness’ and neotony, then Brachyacanthus is an early example of this. Cladoselache (Fig. 1) has two out of three of these traits.

According to Wikipedia
“Acanthodii or acanthodians (sometimes called spiny sharks) is a paraphyletic class of teleostomefish, sharing features with both bony fish and cartilaginous fish. In form they resembled sharks, but their epidermis was covered with tiny rhomboid platelets like the scales of holosteans (gars, bowfins). They represent several independent phylogenetic branches of fishes leading to the still extant Chondrichthyes.” In the LRT spiny sharks don’t lead to sharks, rays and chimaera, but diverge away from them.

Figure 2. The placoderm/catfish to spiny shark/lobe fin transition. We need more taxa, but here's how the LRT recovers it.

Figure 3. The placoderm/catfish to spiny shark/lobe fin transition. We need more Silurian taxa, but here’s how the LRT recovers it. Brachyacanthus, once again, documents phylogenetic miniaturization at the genesis of new major clades.

So, what is it about the spine fin
that made it a key trait?

Figure 1a. Cheirolepis fossils.

Figure 4. Cheirolepis fossils. Both have a spiny pectoral fin leading edge.

On the ray fin side of the cladogram
basal taxa include Pholidophorus (Fig. 5) and Coccocephalichthys (Fig. 6). This clade embraced open water speedy swimming and predation as their niche from the start. The extant tuna (Thunnus) is an extant relative of these two. Later taxa, like the frogfish (Antennarius) and sea robin (Prionotus), reverted to bottom-dwelling.

Figure 5. Pholidophorus ghosted to highlight the fins.

Figure 5. Pholidophorus fossil ghosted to highlight the fins and eyes.

By contrast, lobefins and their predecessors
appear to have preferred a slower swimming, bottom-dwelling lifestyle. That’s how they readily transitioned into shallow waters, swampy waters, swampy land and dry land in that order.

Figure 2. Coccocephalichthys (formerly Coccocephalus) is a Late Carboniferous transitional taxon between Devonian Strunius and Cretaceous Saurichthys.

Figure 6. Coccocephalichthys (formerly Coccocephalus) is a Late Carboniferous transitional taxon between Devonian Strunius and Cretaceous Saurichthys.

Even so,
some highly derived lobefins learned how to climb trees, fly, and even speed through open waters, with or without fins (Homo, Orcinus, Pavo).

New paper on Plesiadapis suffers from taxon exclusion

Boyer and Gingerich 2019
bring us an excellent and comprehensive review of Plesiadapis (Figs. 1-3), a rodent relative (clade: Glires, Figs. 4, 5) traditionally and wrongly considered a basal primate with rodent-like teeth.

Figure 1. From Boyer and Gingerich 2019, Plesiadapis skeleton and in vivo.

Figure 1. From Boyer and Gingerich 2019, Plesiadapis skeleton and in vivo.

This primate-mimic
nests with another primate mimic, Daubentonia (Fig. 3), the extant aye-aye, a taxon barely mentioned and not analyzed by Boyer and Gingerich.

Plesiadapis

Figure 2. Plesiadapis, formerly considered a basal primate, is here considered a member of Glires close to Carpolestes and Daubentonia. See figure 3.

From the abstract
“Plesiadapis cookei is a large-bodied plesiadapiform euarchontan (and potential stem primate) known from many localities of middle Clarkforkian North American Land Mammal age, late Paleocene epoch, in the Clarks Fork Basin of northwestern Wyoming.”

Figure 1. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

Figure 3. Ignacius and Plesiadapis nest basal to Daubentonia in the LRT.

From the abstract
“On a broader scale, cladistic analysis of higher-level taxa… indicates that plesiadapids and carpolestids exhibit a greater number of identical character states than previously thought … Even so, analysis of combined data from dentition, cranium, and postcrania still robustly support a link between plesiadapids, saxonellids, and carpolestids (Plesiadapoidea) and does not contradict previous hypotheses suggesting a special relationship of plesiadapoids to euprimates (Euprimateformes).”

Figure 4. From Boyer and Gingerich 2019, cladograms nesting Plesiadapis.

Figure 4. From Boyer and Gingerich 2019, cladograms nesting Plesiadapis. Too few taxa. Where is Daubentonia? Where are the derived rodents and multitubercuates? Compare to figure 5.

Too few taxa,
alas is the one obvious issue with Boyer and Gingerich 2019 (Fig. 4).

Figure 1. Subset of the LRT focusing on Glires and subclades within.

Figure 5. Subset of the LRT focusing on Glires and subclades within.

Not much else to say.
The large reptile tree (LRT, 1583+ taxa; subset Fig. 5) is an online resource that can and should be employed. Current traditions and textbooks are out of date on this subject. At least consider the taxon list in your more focused studies so you don’t overlook any obvious taxa. Test them yourselves. Don’t make the same mistake.


References
Boyer DM and Gingerich PD 2019. Skeleton of Late Paleocene Plesiadapis cookei (Mammal, Euarchonta): life history, locomotion, and phylogenetic relationships. University of Michigan Papers on Paleontology 38:269pp.

wiki/Plesiadapis

Anableps, the four-eyed fish, enters the LRT

Another oddball fish today
and a short report on it.

Figure 1. Anableps skull and in vivo drawing from Gregory 1938, colored here.

Figure 1. Anableps skull and in vivo drawing from Gregory 1938, colored here.

Anableps tetrophthalmus (Scopoli 1777; Anableps anableps Linneaus 1758; 32 cm max length) is the extant four-eyed fish, a slow-moving surface predator with eyes often exposed above the surface of slow-moving fresh and brackish waters where they seek nearby insects. The eyes have divided or dual pupils, one for aerial vision and one for the denser medium of aqueous vision. A close relative of the flying fish, which also is found near the surface and has large eyes.

Anableps brings to mind
the vision issue facing other fish that sometimes expose their face to the air, like the mudskipper and our pre-tetrapod ancestors among the lobe fin fish.


References
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Scopoli GA 1777. Introductio ad historiam naturalem sistens genera lapidum, plantarum, et animalium. Wolfgang Gerle, Pragae 3-506.

wiki/Four-eyed_fish

Multiple origins for the preopercular

Yesterday we looked at the origin of the quadratojugal in tetrapods arising from the split of the long, deep maxilla in Gogonasus (Fig. 1). But wait! There’s more!

Figure 1. Gogonasus skull demonstrating the genesis of the split between the toothy maxilla and the toothless quadratojugal.

Figure 1. Gogonasus skull demonstrating the genesis of the split between the toothy maxilla and the toothless quadratojugal.

Gogonasus also gives us
the origin of the preopercular arising from an anterior/posterior split of the squamosal (Fig. 1). This type of preopercular shrinks and disappears in Late Carboniferous tetrapods.

Figure 1. The lizardfish, Trachinocephalus with colors added. Diagram from Gregory 1936. This taxon nests with Devonian Cheirolepis, a basal ray-fin fish.

Figure 2. The lizardfish, Trachinocephalus with colors added. Diagram from Gregory 1936. This taxon nests with Devonian Cheirolepis, a basal ray-fin fish.

By convergence,
the preopercular appears in Trachinocephalus (Fig. 2) and in no other taxa derived from that clade. Since this is an extant taxon with a convergent loss of cheek/facial bones it would be good to find out what happened in fossil ancestors here.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Compare the one on the left to figure 2. No tested fish in the LRT is closer to Robustichthys than Pholidophorus.

Figure 3. Pholidophorus in situ and two skulls attributed to this genus. Compare the one on the left to figure 2. No tested fish in the LRT is closer to Robustichthys than Pholidophorus.

By a third convergence
the preopercular has yet another genesis in Pholidophorus (Fig. 3), a trait that continues in all descendant taxa among the remaining ray-fin fish. Is this the same preopercular as in Trachinocephalus? At this point, no. However just a few fossil added intervening taxa would solve this issue.

Figure 4. Skull of Lepisosteus in dorsal and lateral views. Several cheek bones were lost earlier and refilled here creating another solid cheek without a lateral temporal fenestra

Figure 4. Skull of Lepisosteus in dorsal and lateral views. Several cheek bones were lost earlier and refilled here creating another solid cheek without a lateral temporal fenestra

Note
in Lepisosteus (Fig. 4) the preopercular (light green) has evolved to be like those in pipefish and sea horses: completely horizontal, ventral to the jugal, with the anterior end following the jaw joint (quadrate) as it migrates anterior to the orbit.

Figure 2. Subset of the LRT focusing on basal lobefin fish and kin.

Figure 5. Subset of the LRT focusing on basal lobefin fish and kin.

Catfish
also develop a preopercular (Fig. 5).

Figure 1. Synodontis skull with bones colored as homologs to tetrapod bones. Note the wrapping of the postparietals around the dorsal fin and the posterior extension of the pectoral girdle (cleithrum) to protect the  flank. 

Figure 1. Synodontis skull with bones colored as homologs to tetrapod bones. Note the wrapping of the postparietals around the dorsal fin and the posterior extension of the pectoral girdle (cleithrum) to protect the  flank.

Bottom line:
traits can converge. The same new bone can appear more than once. Or disappear more than once.

 

No longer an enigma: Kudnu mackinlayi

I live for discoveries like this one,
which started as a Facebook post of the tiny specimen. This is what the LRT (Fig. 3) was built for.

Benton 1985 wrote:
“Bartholomai (1979) has described Kudnu [QMF8181], a partial snout from the early Triassic of Australia, as a paliguanid. The exact relationships of these forms to each other, and to other early ‘lizard-like’ forms are unclear (Carroll, 1975a, b, 1977; Currie, 1981c: 163-164; Estes, 1983: 12-15). Indeed, the group cannot be defined by any apomorphy, and the genera must be considered separately. As far as can be determined, all of these genera are lepidosauromorphs. Kudnu lacks the lepidosaur character X4 and the squamate character Y 1, but none of the others may be determined. Blomosaurus and Kudnu are classified here as Lepidosauromorpha, incertae sedis.”

Figure 1. Kudnu colorized using DGS and slight restored postcranially.

Figure 1. Kudnu colorized using DGS and slight restored postcranially, shown 10x natural size at a 72 dpi standard screen resolution. Here’s a taxon basal to Stephanospondylus, pareiasaurs and turtles. Prior workers excluded Stephanospondylus from their studies.

Contrad 2008 wrote:
“Other authors have followed this opinion and have described new ‘‘paliguanids’’, including Blomosaurus (Tatarinov, 1978) and Kudnu (Bartholomai, 1979). Even so, ‘‘Paliguanidae’’is widely regarded as a paraphyletic taxon and, unfortunately, the preservation of specimens constituting the known ‘‘paliguanid’’ genera (including Paliguana, Palaeagama, and Saurosternon) makes it impossible to characterize them except through plesiomorphy (Benton, 1985; Gauthier et al., 1988a; Rieppel, 1994). Thus, their position within Lepidosauromorpha is currently impossible to ascertain with any kind of precision.”

Evans and Jones 2010 wrote:
Kudnu (Australia, Bartholomai, 1979) and Blomosaurus (Russia, Tatarinov, 1978) are too poorly preserved to interpret with confidence but are probably also procolophonian.”

Figure 1. Click to enlarge. Stephanospondylus was considered a type of diadectid, but it nests with turtles and pareiasaurs, all derived from millerettids.

Figure 2.  Stephanospondylus was considered a type of diadectid, but it nests with turtles and pareiasaurs, all derived from millerettids,.. next to diadectids.

All that being said,
what does the LRT recover? In the large reptile tree (LRT, 1583 taxa, subset Fig. 3) Kudnu nests basal to Stephanospondylus (Fig. 2), a late survivor from deep in the lineage of pareiasaurs + turtles, not far from bolosaurids + diadectids + procolophonids. These clades are derived from Milleretta (Fig. 2) which was  2 to 3x larger.

Due to its small size,
Kudnu
can be considered phylogenetically miniaturized, the kind of taxon we often find at the base of many major reptile clades.

Sadly, earlier workers (see above)
were looking at the wrong candidates for sister taxa, excluding the right taxa. This is a problem that is minimized by the LRT due to its large number of taxa over a wide gamut.

Figure 4. Subset of the LRT focusing on the the clade that includes Kudnu.

Figure 3. Subset of the LRT focusing on the the clade that includes Kudnu.

Once again,
you don’t need to see the fossil firsthand in a case like this. What you need is a wide gamut phylogenetic analysis like the LRT, to figure out how an enigma like Kudnu  nests with other reptiles.

If
Kudnu was earlier associated with Stephanospondylus, let me know and I will publish the citation. Otherwise, this is a novel hypothesis of interrelationships that inserts Kudnu without disturbing the rest of the LRT tree topology.


References
Bartholomai A 1979. New lizard-like reptiles from the Early Triassic of Queensland. Alcheringa: An Australasian Journal of Palaeontology 3:225–234.
Benton MJ 1985. Classification and phylogeny of the diapsid reptiles. Zoological Journal of the Linnean Society 84:97–164.
Conrad JL 2008. Phylogeny and systematics of Squamata (Reptilia) based on morphology.  Bulletin of the American Museum of Natural History 310: 182pp.
Evans SE and Jones MEH 2010. Chapter 2 The Origin, Early History and Diversification of Lepidosauromorph Reptiles in Bandyopadhyay S (ed.), New Aspects of Mesozoic Biodiversity, Lecture Notes in Earth Sciences 132, DOI 10.1007/978-3-642-10311-7_2 Springer-Verlag Berlin Heidelberg 2010