The paddlefish (Polyodon) and basking shark (Cetorhinus) are closely related

The ‘key trait’: having one gill cover or several gill covers
(as in sharks, Fig. 1) turns out to be a trivial trait in a matrix of 235 traits in the large reptile tree (= LRT, subset Fig. 2). Only one gene has to change to make one type of gill or the other as recently documented (see below).

Figure 1. The basking shark (Cetorhinus) compared to the paddlefish (Polyodon).
Figure 1. The basking shark (Cetorhinus) compared to the paddlefish (Polyodon). Note the gelatinous rostrum in the paddlefish juvenile. That trait is retained in mako sharks, as we learned earlier.

What does ‘closely related’ actually mean?
No other tested taxon shares as many traits with paddlefish (Polyodon) as the basking shark (Cetorhinus, Fig. 1) in the LRT. Someday a taxon might be added that nests between them. At present such taxa remain unknown and untested. Both taxa are derived from the Polyodon hatchling taxon (Fig. 3), which has a shorter rostrum and a more basking shark-like appearance overall. Back in the Silurian, pre-paddlefish hatchlings were likely much smaller and adults were likely the size of present day hatchlings, but that’s not a requirement. No other analysis that I am aware of has ever included paddlefish hatchlings as taxa, but that morphology is key to understanding various lineages within Chondrichthyes. So, here’s a case where adding a taxon is much more important than adding a character.

Figure 6. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.
Figure 2. Adding Debeerius to the LRT helped revise the shark-subset. Note the shifting of the basking shark, Cetorhnus within the paddlefish clade.

Note the gelatinous rostrum
in the paddlefish juvenile (Fig. 1). That trait is retained from mako sharks (Figs. 3, 6, as we learned earlier here. The rostrum of the adult basking shark is likewise filled with gelatin supported by a thin frame of cartilage (Fig. 4). The shark-like appearance of paddlefish has been noted previously. Previously the presence of one enormous gill cover in paddlefish has excluded them form prior shark studies. The LRT minimizes such taxon exclusion by simply adding taxa.

We’ve always known
that ratfish (with one gill cover, Fig. 3) nest with sharks (with several gill covers separating slits). No one has complained about that yet.

Then we learned
that sturgeons and Chondrosteus (with one gill cover, Fig. 3) nest basal to whale sharks and mantas (with several gill covers). The pattern of gill covers was presented and revised recently here.

Figure 3. Shark skull evolution according to the LRT. Compare to figure 1.

Now
paddlefish (Polyodon) nests with basking sharks (Cetorhinus, Fig. 1) in the large reptile tree (LRT, 1785+ taxa, subset Fig. 2). Evolution is full of such trivial exceptions.

Paddlefish inhabit rivers. Basking sharks inhabit the sea.
They both feed the same way. Basking sharks reach 30 feet in length. Paddlefish reach 7 feet in length. The two likely went their separate ways in the Silurian (prior to 420mya), so they had plenty of time to evolve on their own since then.

Figure 2. Skull of Cetorhinus adult and juvenile showing differences in the rostrum and fusion of skull elements in the adult.
Figure 4. Skull of Cetorhinus adult and juvenile showing differences in the rostrum and fusion of skull elements in the adult.

A recent study on gill covers by Barske et al. 2020
“identify the first essential gene for gill cover formation in modern vertebrates, Pou3f3, and uncover the genomic element that brought Pou3f3 expression into the pharynx more than 430 Mya. Remarkably, small changes in this deeply conserved sequence account for the single large gill cover in living bony fish versus the five separate covers of sharks and their brethren.”

Figure 4. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.
Figure 5. Skull of Polyodon from a diagram published in Gregory 1938, plus a dorsal view and lateral photo.

While comparisons to the feeding technique in paddlefish and basking sharks
appear in the literature (Matthews and Parker 1950, Haines and Sanderson 2017), these were presumed to be by convergence based on the single gill cover vs. multiple gill cover difference.

Figure 2. Skull of the dogfish shark, Squalus, superimposed on a graphic of the invivo shark. Yellow areas added to show the extent of the gelatinous material that fills the empty spaces above and below the cartilaginous rostrum (nasal homolog).
Figure 6. Skull of the dogfish shark, Squalus, superimposed on a graphic of the invivo shark. Yellow areas added to show the extent of the gelatinous material that fills the empty spaces above and below the cartilaginous rostrum (nasal homolog).

Relying on one, two or a dozen traits
to trump the other 234, 233 or 213 is called “Pulling a Larry Martin.” You don’t want to do that. Put aside your traditions, add taxa and let the unbiased software figure out where your taxon nests using the widely accepted hypothesis of maximum parsimony (= fewest changes) over a large set of character traits.

The present hypothesis of interrelationships
(Fig. 2) appears to be novel. If not, please advise so I can promote the earlier citation.


References
Barske L et al. (10 co-authors) 2020. Evolution of vertebrate gill covers via shifts in an ancient POU3f3 enhancer. PNAS 117(40):24876–24884.
Integration of swimming kinematics and ram suspension feeding in a model American paddlefish, Polyodon spatula. The Journal of Experimental Biology, 10.1242/jeb.166835, 220, 23, (4535-4547), (2017).
Matthews LH, Parker HW 1950. Notes on the anatomy and biology of the basking shark (Cetorhinus maximus (Gunner)). Proceedings of the Zoological Society of London 120(3):535–576.

Orthocormus: a bony fish with an odd reversal: a shark face

Everyone agrees
that Orthocormus roeperi (Weitzel 1930; Arratia and Schultze 2013; Early Jurassic; 45cm; BSPG 1993 XVIII-VFKO B1) is a pachycormiform fish. In the large reptile tree (1781+ taxa) Orthocormus nests with a more derived, Late Jurassic pachycormiform with a longer snout, Aspidorhynchus (Figs. 3, 4), the famous Rhamphorhynchus nibbler.

For reasons unknown,
Aspidorhynchus (Figs. 3, 4) is not traditionally considered a pachycormiform fish.

Arratia and Schultze 2013 consider 
“The fish described here is the best-preserved pachycormiform from Bavaria, Germany, as well as from the Upper Jurassic worldwide.”

Figure 1. Orthocormus, a small, bony fish with a shark-like face.

Figure 1. Orthocormus, a small, bony fish with a shark-like face. Shown 1/3 actual size on a 72dpi screen.

According to Wikipedia
“Pachycormiformes were characterized by having serrated pectoral fins (though more recent studies demonstrated that fin shape diversity in this group was high, reduced pelvic fins and a bony rostrum.”

Figure 2. The shark-like skull of Orthocormus, a ray-fin bony fish.

Figure 2. The shark-like skull of Orthocormus, a ray-fin bony fish. The extended rostrum is a reversal from shark ancestors.

As you can see, this is less than accurate description.
The pelvic fins are not reduced in Orthocormus nor are the pectoral fins serrated. Pachycormus does not have a bony snout. Wikipedia lists several synapomorphies (“Pulling a Larry Martin“) and does not list Aspidorhynchus as a pachycormiform. Better to just run the analysis and find the last common ancestor to determine clade membership.

Rhamphorhynchus entangled with Aspidorhynchus

Figure 3. Rhamphorhynchus entangled with Aspidorhynchus. Both complete and articulated. Inside the belly of Rhamphorhynchus are several smaller fish. Inside its throat is another. Image from Frey and Tischlinger (2012).

Dentition according to Arratia and Schultze 2013:
“There are small conical teeth on the upper jaw, a large tooth on the posterior part of the premaxilla, and both large and small teeth on the maxilla; the lower jaw carries large teeth anteriorly and smaller ones posteriorly.”

Notochord
“The vertebral column is formed by a persistent notochord without chordacentra,”

The tail
“The scaly caudal apparatus, formed by large modified scales with a precise arrangement, is interpreted as an adaptation to fast swimming comparable to that of modern tunas.”

Spiral valve
Another apparent reversal is the presence of a soft tissue spiral intestine, as found in sharks and several other various taxa without apparent pattern, including sarcopterygians. This is the only time Arratia and Schultze 2013 mention the term, ‘shark’ in their text.

Figure 2. The face of the Wyoming Dinosaur Center CSG 255 specimen of Asphidorhynchus + Rhamphorhynchus with facial bones identified using DGS.

Figure 4. The face of the Wyoming Dinosaur Center CSG 255 specimen of Asphidorhynchus + Rhamphorhynchus with facial bones identified using DGS.

Wkipedia reports on Pachycormiformes,
“Their exact relations with other fish are unclear, but they are generally interpreted as stem-teleosts.”

By adding taxa, the LRT provides exact relations with other fish, in this case, within bony fish, close to the base, not in the stem. Again, a wider view provided by the LRT supplements and aids the more focused view of those describing the fossil firsthand. Reversals and convergent traits can be tricky. Let the unbiased software do the decision-making.


References
Arratia G and Schultze H-P 2013. Outstanding features of a new Late Jurassic pachycormiform fi sh from the Kimmeridgian of Brunn, Germany and comments on current understanding of pachycormiforms. Pp. 87–120 in Mesozoic Fishes 5 – Global Diversity and Evolution, Arratia G, Schultze H-P and Wilson MVH (eds.).
Weitzel K 1930. Drei Riesenfische aus den Solnhofener Schiefern von Langenaltheim. – Abh. Senckenberg. Naturforsch. Ges. 42 (2): 85-113.

wiki/Orthocormus
wiki/Pachycormiformes

The stargazer, Uranoscopus, is a frogfish-mimic

Preview
I am aware and working on a comprehensive comment for the Nature paper that just came out today positing a lagerpetid origin for pterosaurs using a chimaera of specimen bits and pieces while omitting competing complete and articulated candidates with soft tissue (= Cosesaurus and kin). So here is today’s entry as planned. Expect the report on the lagerpetid mish-mash authored by 18 misguided PhDs as soon as it gets done, surely in less than a day.

The marbled stargazer,
Uranoscopus bicinctus (Linneaus 1758), looks and acts like a frogfish/anglerfish. The giant jaws of these half buried ambush predators open dorsally. A small ‘lure’ wiggles over the jaws. Large pectoral fins spread laterally. Smaller ‘chin fins’ are present.

Figure 1. The marbled stargazer, Uranoscopus bicinctus, is an angler-frogfish-mimic, but nests in the LRT with other thread fins.

Figure 1. The marbled stargazer, Uranoscopus bicinctus, is an angler-frogfish-mimic, but nests in the LRT with other thread fins.

The chin fins are thread fins,
homologs to sea robin (Prionotus) fingers and the thread fins of Polydactylus. The pelvic fins of the stargazer are stumpy vestiges. Robust circumorbital bones are present. One is a a palatine/lacrimal. Frogfish and anglers don’t have circumorbital bones.

Figure 2. Skull of Uranoscopus with colors added. Purple elements are chin fins.

Figure 2. Skull of Uranoscopus with colors added. Purple elements are threadfins.

The two cleithrum spines
per side are venomous. Uranoscopus can also produce an electric shock, but does not have electroreceptors.


References
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.

wiki/Uranoscopus

Kryptoglanis: a catfish mimic

Workers wondered, where did those big teeth come from?
Catfish don’t have such long, interlocking teeth. No wonder Vincent and Thomas 2011 called Kryptoglanis shajii (Figs. 1–3; 6cm) an ‘enigmatic’ subterranean catfish. No wonder Britz et al. erected a new clade of catfish to put it in.

Figure 1. The uncatfish-like teeth of Kryptoglanis in anterior view.

Figure 1. The uncatfish-like teeth of Kryptoglanis in anterior view.

According to Wikipedia
“[Kryptoglanis] has also been seen in dense vegetation in paddy fieldsThe species strongly avoids light and feeds on small invertebrates.”

“The morphology of K. shajii differs from all other known species of catfish and includes such features as the absence of dorsal fin; the presence of four pairs of barbels; an upwardly directed mouth, with a distinctly projecting lower jaw with 4 set[s] of teeth; subcutaneous eyes; anal fin completely confluent with the caudal fin; anal and caudal fins together carry 70–74 fin rays; and no spines in any of the fins.”

Figure 2. Kryptoglanis in 3 views. Note the catfish-like barbels.

Figure 2. Kryptoglanis in 3 views. Note the catfish-like barbels.

Figure 3. Skull of Kryptoglanis, a knife fish, not a catfish.

Figure 3. Skull of Kryptoglanis, a knife fish, not a catfish.

Here’s where we put on our lab coats and act like scientists.
Whenever a taxon is described as ‘differs from all other known species’, that’s the time to expand the taxon list. We’ve seen this so many times before. And every time the LRT has found less traditional and more parsimonious sister taxa simply by adding taxa.

Figure x. Gymnotus carapo in vivo.

Figure 4. Gymnotus carapo in vivo.

Figure 8. Skull of Gymnotus.

Figure 5. Skull of Gymnotus.

According to
the large reptile tree (LRT, 1750+ taxa) those catfish-like barbels on Kryptoglanis developed by convergence on an eel-like knife fish, nesting between the eel, Anguilla and two knifefish, Gymnotus and Electrophorus, the electric eel. This clade of fish DO have large interlocking teeth and a long list of other traits shared with Kryptoglanis. They just don’t have barbels. Seems like prior authors were caught “Pulling a Larry Martin” by focusing on the barbels to the exclusion of all the other traits.

Figure 1. Subset of the LRT focusing on the ray fin only clade of bony fish. Fundulus (yellow) is the new taxon. It attracted Anableps. Various convergent eel-like taxa are shown in baby blue.

Figure 1. Subset of the LRT focusing on the ray fin only clade of bony fish. Fundulus (yellow) is the new taxon. It attracted Anableps. Various convergent eel-like taxa are shown in baby blue.


References
Vincent M and Thomas J 2011. Kryptoglanis shajii, an enigmatic subterranean-spring catfish (Siluriformes, Incertae sedis) from Kerala, India. Ichthyological Research. 58 (2): 161–165. doi:10.1007/s10228-011-0206-6.
Britz R, Kakkassery F and Raghavan R 2014. Osteology of Kryptoglanis shajii, a stygobitic catfish (Teleostei: Siluriformes) from Peninsular India with a diagnosis of the new family Kryptoglanidae. Ichthyological Exploration of Freshwaters. 24 (3): 193–207.

wiki/Kryptoglanis_shajii

The Solomon Islands skink (genus Corucia) enters the LRT

Today the extant Solomon Islands skink
(Corucia zebrata, Gray 1855; Figs. 1, 2) enters the large reptile tree (LRT, 1714+ taxa). It nests basal to Gymnophthlamus + Vanzosaura and between Chalcides and Sirenoscincus.

Figure 1. The Solomon Islands skink (Corucia zebrata) is the largest skink on the planet, gives birth with a placenta and lives in communities.

Figure 1. The Solomon Islands skink (Corucia zebrata) is the largest skink on the planet, gives birth with a placenta and lives in communities.

This nesting comes as no surprise.
After all, skeletally Corucia is just another widely recognized skink, albeit with some unique reproductive and social qualities (see below).

Figure 2. The skink, Corucia zebrata with DGS colors added.

Figure 2. The skink, Corucia zebrata with DGS colors added.

Do not confuse Corucia with Carusia
(Fig. 3). The two are not the same, nor are they closely related.

Figure 1. Carusia intermedia, a basal lepidosaur close to Meyasaurus now, but looks a lot like Scandensia. Note the primitive choanae and broad palatal elements. None of the data I have shows the caudoventral process of the jugal, so I added it here from the description. Same with the epipterygoid.

Figure 3. Carusia intermedia, a basal lepidosaur close to Meyasaurus now, but looks a lot like Scandensia. Note the primitive choanae and broad palatal elements. None of the data I have shows the caudoventral process of the jugal, so I added it here from the description. Same with the epipterygoid.

Corucia zebrata
(Gray 1855, Figs. 1, 2) is the extant Soloman Islands skink, the largest known extant species of skink. Long chisel teeth distinguish this herbivorous genus. The tail is prehensile. This is one of the few species of reptile to live in communal groups. Rather than laying eggs, relatively large young are born after developing within a placenta. Single babies are typical. Twins are rare according to Wikipedia.

Removing all Carusia sister taxa in the LRT
fails to shift Carusia from its traditionally overlooked node basal to squamates.

The Wikipedia entry
on the ‘clade’ Carusioidea excludes great swathes of taxa relative to the LRT, so it mistakenly suggests that extinct Carusia is a member of the Squamata. Adding pertinent taxa solves that problem, as the LRT demonstrates.


References
Gray JE 1855. (1856). New Genus of Fish-scaled Lizards (Scissosaræ), from New Guinea. Annals and Magazine of Natural History, Second Series 18: 345–346.

wiki/Solomon_Islands_skink
wiki/Carusia
wiki/Carusioidea
http://www.markwitton.com
http://tetzoo.com

https://www.researchgate.net/publication/328388754_A_new_lepidosaur_clade_the_Tritosauria

Manta ray: curious reversals + head fins

Manta rays (= devil rays)
(genus: Manta; Figs. 1, 6; sometimes genus: Mobula) have an odd mixture of derived and primitive traits. We’ll review those today.

Figure 1. The largest manta ray to scale with humans.

Figure 1. The largest manta ray to scale with humans. Note the unique cephalic fins hanging down at lower left.

The manta is different from other rays

  1. Mantas have a unique third set of ‘fins’, the cephalic ‘fins’. These are not connected to the pectoral fins, but originate ventral to the eyes (Fig. 1).
  2. In skates, rays and guitarfish the anterior pectoral fin attaches in front of the orbit, on the prefrontal. In mantas + cownose rays (genus: Rhinoptera (Figs. 4, 5) the pectoral fins attaches further back, near the jaw articulation. This is a reversal going back to Rhincodon, the whale shark (Fig. 3) and Thelodus (Fig. 3), the jawless outgroup taxon of the clade Gnathostomata (jawed vertebrates) in the LRT.
  3. Most sharks, guitarfish, skates and rays have a long nasal bone that gives them a rostrum (which gets really long and toothy in saw fish). A similar elongate nasal is missing in cow nose rays and mantas. This is a reversal, too.
  4. Typical guitarfish, skates and rays have a ventral mouth adapted for bottom feeding (Fig. 2). By contrast, the manta ray mouth opens anteriorly, as in the whale shark, for open water feeding. This is a reversal.
  5. Typical guitarfish, skates and rays have electric prey sensing organs. Manta rays do not. This is also a reversal.
  6. Typical guitarfish, skates and rays cruise sandy sea floors seeking buried hard-shelled prey. Mantas do not. They cruise open waters seeking tiny planktonic and mid-sized oceanic prey they trap using internal gill bars prior to digestion. This is also a reversal going back to whale sharks.
  7. Because their mouths are buried in sediment, typical guitarfish, skates and rays ‘inhale’ through an alternate dorsal opening, the spiracle. The manta ray does not. It ‘inhales’ through its cavernous anterior mouth, like most fish, including the whale shark. This is also a reversal.

    Figure 4. Rhinobatus jaw mechanism animation. This is how skates and rays eat, distinct from the Thelodus/ whale shark/ manta ray method of ram feeding.

    Figure 2. Rhinobatus jaw mechanism animation. This is how skates and rays eat, distinct from the Thelodus/ whale shark/ manta ray method of ram feeding.

  8. Typical guitarfish, skates and rays have eyes essentially on the top of their flattened heads. The eyes of manta and cownose rays are placed laterally, as in the whale shark. This is also a reversal.

With so many reversals
I wondered if Manta might be the taxon that broke the ability of the LRT to lump and separate 1558 taxa based on a small (238) character list originally created to lump and separate reptiles. Fortunately, everything came out okay. We’ve seen reversals several times previously here and elsewhere [use keyword: “reversal” in the search box.]

The cephalic ‘fins’ in Manta 
are not used for propulsion. Instead, these lobes help funnel and gather food. They can curl into a spiral to cut drag while swimming rapidly. A series of flexible cartilage rods, like fins rays, fits inside each one (Fig. 6). The origin of these appendages baffled workers for decades.

Figure 1. Rhincodon typus, the extant whale shark, shares traits with jawless Thelodus, armored Entelognathus, and the walking catfish, Clarias.

Figure 3. Rhincodon typus, the extant whale shark, shares traits with jawless Thelodus, armored Entelognathus, a basal placoderm with bone that informs the identity of the cartilage in Manta. Even Thelodus is not far from Manta.

Swenson et al. 2018 shed new light on the origin of manta cephalic ‘fins’. 
They studied a series of embryo cownose rays (genus: Rhinoptera bonasus) because cownose rays are the closest relatives of the manta. Cownose rays also have movable cephalic lobes (Figs. 4, 5), similar to the cephalic fins of mantas, but completely attached to the head along the long axis, like a tailgate.

Figure 2. Cownose ray lobes open and close like flaps.

Figure 4. Cownose ray lobes open and close like flaps. These are homologous to the cephalic fins seen in Manta. See these in operation in figure 5.

Swenson et al. report, “In cownose rays, cephalic lobes do not develop from independent fin buds emanating from the head; rather, they develop as modifications to the anterior pectoral fins, closely resembling the hooks at the anterior of developing skate and ray pectoral fins (Babel, 1966; Luer et al., 2007; Maxwell et al., 2008). However, unlike the anterior pectoral fins of other batoids, cephalic lobes are distinguished from the rest of the pectoral fin by a small region of reduced tissue outgrowth we call the ‘notch.'” 

With their an ontogenetic series of cownose ray embryos
Swenson et al. documented the disconnection of the anteriormost portion of the pectoral fin from the face in younger embryos and the later fusion to the face prior to hatching. Mantas are similar, but skip this last stage and so retain more flexible anteriormost pectoral fins arising from the lower lateral face.

Figure 2. Cownose ray feeding by dropping their cephalic lobes to increase the suction on their oyster prey.

Figure 5. Cownose ray feeding by dropping their cephalic lobes to increase the suction on their oyster prey. See figure 4 to see these lobes closed like landing gear doors, streamlined prior to swimming.

The Swenson et al. results
showed that the devil ray’s horns are not a third set of fins after all – they’re simply the foremost bit of pectoral fin, modified for a new purpose and separated from the main portion of the pectoral fin. The cownose ray documents a modified transitional phase.

Figure 6. Three views of the skeleton of Manta, colors added. Green represents the maxilla. Note the terminal mouth, distinct from other rays, skates and guitarfish. The pectoral fins do not reach the orbit. The cephalic fins are highly modified maxillae, still gathering food. Note the attachment to the quadrate. The premaxilla extends across the mouth.

Figure 6. Three views of the skeleton of Manta, colors added. Note the near terminal mouth, distinct from other rays, skates and guitarfish. The pectoral fins do not reach the orbit. The cephalic fins are independently mobile extensions of the anterior pelvic fins.

Also added to
the large reptile tree (LRT, 1558 taxa) is one of the basal rays, the guitarfish, Rhinobatos, (Figs. 7, 8). Both taxa enter alongside Isurus, the mako shark. Manta (Figs. 1, 6) is, perhaps, the most derived ray (clade Batoidea). Rhinobatos is, perhaps, one of the most basal batoids, closer to sharks, in morphology. Very likely all the rest of the batoids will nest in the LRT between these two taxa. We’ll test that rather orthodox guess as time goes by.

Figure 2. Rhinobatos, the guitarfish, and Rhina the bowhead guitarfish, are transitional to skates and rays, but not mantas. Note the ventral mouth and pectoral fins extending anterior to the orbits.

Figure 7. Rhinobatos, the guitarfish, and Rhina the bowhead guitarfish, are transitional to skates and rays, but not mantas. Note the ventral mouth and pectoral fins extending anterior to the orbits.

Fun fact: brain size
According to Wikipedia, “The oceanic manta has one of the largest brains (ten times larger than a whale shark) and the largest brain-to-mass ratio of any cold blooded fish.”

Figure 5. Guitarfish (Rhinobatos) skull. Colors, eyeballs and spiracles added.

Figure 8. Guitarfish (Rhinobatos) skull. Colors, eyeballs and spiracles added.

Fun fact #2:
That anterior portion of the pectoral fin lateral to the eye of the guitarfish (Figs. 7, 8) is what evolves to become the flap-like cephalic lobes in cownose rays (Figs. 4, 5) and the anteriorly detached, ever-curling cephalic ‘fins’ in manta rays (Figs. 1, 6).


References
Bancroft EN 1829. On the Fish known in Jamaica as the Sea-Devil. The Zoological Journal. 4: 444–457.
Bloch MC and Schneider JG 1891. Systema anclystoma.
Fisher RA 2010, revised 2012. Life history, trophic ecology, & prey handling by cow nose ray, Rhinoptera bonasus, from Chesapeake Bay.
Garman S 1884. An Extraordinary Shark. Bulletin of the Essex Institute: 47–55.
Linnaeus C 1758. Systema naturæ per regna tria naturæ, secundum classes, ordines, genera, species, cum characteribus, differentiis, synonymis, locis. Tomus I. Editio decima, reformata.
Smith A 1829. Descriptions of new, or imperfectly known objects of the animal kingdom, found in the south of Africa. South African Commercial Advertiser 3: 2.
Rafinesque CS 1810. Caratteri di alcuni nuovi generi e nuove specie di animali e piante della sicilia, con varie osservazioni sopra i medisimi. Per le stampe di Sanfilippo: Palermo, Italy. pp. 105, 20 fold. Pl., online
Swenson JD et al. 2018. How the Devil Ray Got Its Horns: The Evolution and Development of Cephalic Lobes in Myliobatid Stingrays (Batoidea: Myliobatidae). Front. Ecol. Evol, published online November 13, 2018; doi: 10.3389/fevo.2018.00181
White WT et al. 2018. Phylogeny of the manta and devilrays (Chondrichthyes: mobulidae), with an updated taxonomic arrangement for the family. Zoological Journal of the Linnean Society, 2018, 182, 50–75.

wiki/Manta
wiki/Giant_oceanic_manta_ray
wiki/Whale_shark
sci-news.com/biology/manta-rays-cephalic-lobes.html

Megistotherium: Not a gigantic hyaenodont creodont. More like a very basal seal.

Traditionally described as a gigantic hyaenodont creodont,
Megistotherium (Savage 1973; Miocene; Fig. 1) nests in the large reptile tree (LRT, 1544 taxa) at the base of the clade within Carnivora that ultimately produced extant seals and extinct Palaeosinopa (Figs. 1,2). In the LRT creodonts are large marsupial predators, convergent with members of the clade Carnivora.

Therefore 
Megistotherium is also a sister to the Machaeroides clade (which gave rise to Stylinodon) both derived from the Kerbos and Gulo (wolverine) clades (which gave rise to terrifying short face bears, like Arctodus). So, several gigantic, fearless bear-like taxa arise from this branch within Carnivora.

Figure 1. Megistotherium skull in several views. It is 2/3 of a meter in length. Don't overlook the skull of tiny relative, Palaeosinopa with a 10cm skull length.

Figure 1. Megistotherium skull in several views. It is 2/3 of a meter in length. Don’t overlook the skull of tiny relative, Palaeosinopa with a 10cm skull length.

Megistotherium osteothlastes (Savage 1973; Miocene, 23mya; 66cm skull length) was originally considered a giant hyaenodontid creodont based on tooth data. Here, because it nests basal to Palaeosinopa and seals it was probably semi-aquatic. Premaxillary teeth were weak and disappearing. The jaw muscles were enormous judging by the widespread cheek arches and tall cranial crest. The large diameter canines were housed in large, laterally expanded maxillae. The braincase was narrow. Note the prefrontal and lacrimal are no longer fused to one another.

Earlier mistakes in nesting Megistotherium
may be assigned to an over reliance on dental traits, which tend to converge more often than traditionally realized, and to taxon exclusion, something the LRT tends to minimize due to its wide gamut, getting bigger every week.

Figure y. Palaeosinopa in situ with tail reconstructed from disturbed elements.

Figure 2. Palaeosinopa in situ with tail reconstructed from disturbed elements. This taxon provides clues to the post-crania of Megistotherium by way of phylogenetic bracketing.

Side note:
In overall size and general features, the skull of Megistotherium was similar, by convergence, to the giant Eocene elephant shrew, the mighty Andrewsarchus.

Figure 1. Harpagolestes macrocephalus compared to sisters Sinonyx and Andrewsarchus to scale.

Figure 1. Harpagolestes macrocephalus compared to sisters Sinonyx and Andrewsarchus to scale. Compare these elephant shrews to Megistotherium (Fig. 1)/

In the past,
several mammal taxa achieved gigantic proportions not found in today’s relatives.


References
Savage RJ 1973. Megistotherium, gigantic hyaeonodont from Miocene of Gebel Zelten, Libya. Bulletin of the British Museum (Natural History) Geology 22(7):483–511.

wiiki/Megistotherium

The deep-sea gulper eel (Eurypharynx) also arises from Gregorius

Updated April 22, 2020
with the addition of taxa Gymnothorax and Eurypharynx are both derived from Gregorius prior to the major dichotomy that splits bony fish in two (see updated cladogram

Earlier we resurrected an ‘extinct’ clade of rhizodont lobefin fish,
when the moray eel, Gymnothorax (Fig. 2) entered the large reptile tree (LRT, 1521 taxa) along with the the rhizodont, Barameda. Today the deep sea gulper eel, Eurypharynx (Figs. 1,2), nests with Gymnothorax. 

Update: Both are now derived from the pre-bony fish, Gregorius

Figure 1. The skull of Eurypharynx from Gregory 1936 with colors added. Compare to Gymnothorax in figure 2.

Figure 2. The skull of Eurypharynx from Gregory 1936 with colors added. Compare to Gymnothorax in figure 2.

Eurypharynx pelecanoides (= Gastrostomus Vailiant 1882; up to 75cm long) is the extant deep sea pelican eel or gulper eel. Like its sister, the moray eel (Gymnothorax, Fig. 2), the naris, antorbital fenestra, orbit and temporal fenestra are confluent. Pectoral fins are barely present. Distinctly the jaw joint is far behind the occiput and hyperelongated hyomandibular and quadrate. The stomach can stretch to accomodate large prey. The muscle segments are V-shaped, not W-shaped, as in most bony fish. The lateral line system projects from the body, rather than lying in a groove.

This appears to be a novel hypothesis of interrelationships.
If someone else has published on this earlier, please let me know so I can cite them properly.

The YouTube video (above)
shows the slender, oversized jaws can balloon with water AND the dorsal half above the skull does, too! This is done, evidently, as a threat display, to appear much larger than ordinary, and to feed — convergent with the blue whale (Balaenoptera) and other rorqual mysticetes.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.

Figure x. Subset of the LRT focusing on basal vertebrates. This represents the latest hypothesis of interrelationships and includes several changes from prior versions of this section.


References
Bloch ME 1795. Naturgeschichte der ausländischen Fische. Berlin. v. 9. i-ii + 1-192, Pls. 397-429.
Valliant LL 1882. Sur un poisson des grandes profondeurs de l’Atlantique, l’Eurypharynx pelecanoides. Comptes Rendus Hebdomadaires des Séances de l’Académie des Sciences, Série D, Sciences Naturelles 95: 1226-1228.

wiki/Gogonasus
wiki/Onychodus
wiki/moray eel
wiki/Barameda
wiki/Rhizodus
wiki/Eurypharynx

Restoring and re-nesting Murusraptor

Traditional megaraptorans,
like Megaraptor namunhuaiquii (Novas 1998, Fig. 1) and Murusraptor barrosaensis (Coria and Currie 2016; Rolando, Novas and Agnolin 2019; MCF-PVPH-411; Fig. 1), are currently only known from bits and pieces. Perhaps for these reasons Wikipedia reports, “the clade Megaraptora (Benson, Carrano and Brusatte 2010 ) has controversial relations to other theropods.”

According to Wikipedia
“Murusraptor is a megaraptoran, one of a group of large predatory dinosaurs whose exact classification remains disputed. Once believed to be dromaeosaurids, they have since been classified as either allosauroid carnosaurs or as tyrannosauroid coelurosaurs. While the discovery of Murusraptor does not clarify as of yet the placement of this group of theropods, the specimen does add further clarity to some aspects of megaraptoran anatomy and potentially, eventual classification of the Megaraptora within the theropod evolutionary tree.”

Definition
Megaraptora (Benson et al 2010) “The most inclusive clade comprising Megaraptor namunhuaiquii, but not Chilantaisaurus tashuikouensis.” 

Wikipedia reports,
“Megaraptorans were most diverse in the early Late Cretaceous of South America, particularly Patagonia. However, they had a widespread distribution. Fukuiraptor, the most basal (“primitive”) known member of the group, lived in Japan. Megaraptoran material is also common in Australia, and the largest known predatory dinosaur from the continent, Australovenator, was a megaraptoran.” 

Taxa traditionally included within Megaraptora:

  1. Megaraptor (known from a long maxilla and forelimb, Figs. 1, 2)
  2. Fukuiraptor (known from jaw fragments, coracoids, humeri, femur, acetabulum, two vertebrae
  3. Australovenator (known from a dentary, a few dorsal ribs, distal forelimbs and nearly complete hind limbs)
  4. Murusraptor (known from several skull elements and other bones Figs. 1, 2)

Of these, only two, Megaraptor and Murusraptor, are tested in the LRT.

Other megaraptoran traits according to Wikipedia

  1. “Their forelimbs were large and strongly built,
  2. The ulna bone had a unique shape (except Fukuiraptor).
  3. The first two fingers were elongated, with massive curved claws ,
  4. The third finger was small. 
  5. Megaraptoran skull material is very incomplete, but a juvenile Megaraptor described in 2014 preserved a portion of the snout, which was long and slender. 
  6. Leg bones referred to megaraptorans were also quite slender and similar to those of coelurosaurs adapted for running. 
  7. Although megaraptorans were thick-bodied theropods, their bones were heavily pneumatized, or filled with air pockets. The vertebrae, ribs, and the ilium bone of the hip were pneumatized to an extent which was very rare among theropods, only seen elsewhere in taxa such as Neovenator
  8. Other characteristic features include opisthocoelous neck vertebrae
  9. and compsognathid-like teeth.” 

Several of the above traits
are shared with other taxa. The LRT employes a suite of 231 shared, unique and often convergent traits to lump, split and ultimately nest all taxa. Surprisingly, even the poorly preserved, disarticulated and incomplete Megaraptor and Murusraptor found secure nodes.

Araciaga, Rolando, Novas and Agnolin 2019
bring us ‘new evidence about the phylogenetic relationships of Megaraptora.’ They report, “The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affilation with Tyrannosauroidea (supported by > 20 synapomorphies).”

From their abstract:
“Murusraptor is particularly similar to juvenile specimens of tyrannosaurids; both share: 1) lacrimal with a long anterior prosess; 2) corneal process and; 3) lateral pneumatic fenestra; 4) square and dorsoventrally low frontals; 5) parietals with well-developed sagittal and nuchal crests, among other features. The current study lends further support to the hypothesis that megaraptorans are basal members of Coelurosauria (supported by 20 synapomophies), with strongest affilation with Tyrannosauroidea (supported by > 20 synapomorphies).”

“Murusraptor is unique in having several diagnostic features that include anterodorsal process of lacrimal longer than height of preorbital process, and a thick, shelf-like thickening on the lateral surface of surangular ventral to the groove between the anterior surangular foramen and the insert for the uppermost intramandibular process of the dentary.

“Other characteristic features of Murusraptor barrosaensis n.gen. et n. sp. include a large mandibular fenestra, distal ends of caudal neural spines laterally thickened into lateral knob-like processes, short ischia distally flattened and slightly expanded  dorsoventrally. Murusraptor belongs to a Patagonian radiation of megaraptorids together with Aerosteon, Megaraptor and Orkoraptor.”

A little backstory with links for more details:
Aerostean is a giant (9m) Late Cretaceous theropod with no skull material known. Orkorpator is a large (6m) Latest Cretaceous theropod includes only a post-orbital and quadratojugal for skull material and bits and pieces otherwise.

Figure 1. Murusraptor compared with related taxa to scale.

Figure 1. Murusraptor compared with related taxa to scale. Ghosted rostrum of Guanlong added to missing rostrum of Mururaptor.

Phylogenetic analysis
In the large reptile tree (LRT, 1415 taxa; Fig. 4) Megaraptor (Fig. 1) nests with the basal theropod, Sinocalliopteryx. Murusraptor (Fig. 1) nests between long-snouted Dilong and the long-snouted Guanlong / Spinosaurus clade.

One problem comes from
the hypothesis of relationships published by Coria and Currie 2016 that nests long-snouted Xiongguanlong, Dilong, Proceratosaurus and Guanlong with robust-snouted Tyrannosaurus, rather than with long-snouted spinosaurs. Even so, Coria and Currie 
nest Murusraptor with Megaraptor. The closest theropod also tested in the LRT is the finback allosaurAcrocanthosaurus. So, the Coria and Currie cladogram is different in most respects from the LRT. Coria and Currie also nest the giant horned theropod, Ceratosaurus, as a basalmost/outgroup taxon. In the LRT (Fig. 4) Ceratosaurus has no descendants.

Figure 2. Megaraptor, Murusraptor and Sinocalliopteryx. See figure 1 for revised restoration of Murusraptor. Not to scale.

Figure 2. Megaraptor, Murusraptor and Sinocalliopteryx. See figure 1 for revised restoration of Murusraptor. Not to scale. The Rolando et al. restoration draws more on Megaraptor and Dilong.

In counterpoint to Coria and Currie 2016,
Novas et al. 2016 reported, “megaraptorids retained several of the manual features present in basal tetanurans, such as Allosaurus. In this regard, Megaraptor and Australovenator are devoid of several manual features that the basal tyrannosauroid Guanlong shares with more derived coelurosaurs (e.g., Deinonychus).” 

In the LRT,
(Fig. 4) Guanlong is closer to Allosaurus than to Tyrannosaurus.

Figure 4. Megaraptor also preserves a complete and distinct manus, here compared to Sinocalliopteryx, which also has a digit 4, and Suchomimus has a robust ungual 1.

Figure 3. Megaraptor also preserves a complete and distinct manus, here compared to Sinocalliopteryx, which also has a digit 4, and Suchomimus has a robust ungual 1. According to the LRT, Suchomimus is not related to Megaraptor, but is shown here to demonstrate the convergence.

According to the writers of Wikipedia,
the large compsognathid, Sinocallioteryx (Figs. 1-3) is not related to megaraptorids, despite the many similarities in the skull. Curiously, other long-snouted theropods with massive curved claws on their forelimbs, like Suchomimus (Fig. 3), are also not traditionally considered related to megaraptorids. I wish they were. Everyone wishes they were. However, I have to report results, no matter how controversial, as I have for the last eight years. That way, if I made mistakes, someone will tell me. If someone has forgotten certain taxa, perhaps next time they will add them.

Figure 4. Subset of the LRT focusing on basal theropods. Megaraptor and Murusraptor are highlighted.

Figure 4. Subset of the LRT focusing on basal theropods. Megaraptor and Murusraptor are highlighted.

In conclusion
Murusraptor barrosaensis
  (Coria and Currie 2016; Rolando, Novas and Agnolin 2019; Late Cretaceous) was originally considered a sister to Megaraptor and close to tyrannosaurs. Here (Fig. 4) Murusraptor nests between Dilong and Guanlong closer to spinosaurs. Megaraptor nests with Sinocalliopteryx, a basal theropod, not close to Murusraptor. Wherever other traditional megaraptorans (see list above) nest has not yet been tested in the LRT. We looked at the relationship of long-snouted theropods with spinosaurs, rather than tyrannosaurs earlier here.


References
Rolando AMA, Novas FE and Agnolin FL 2019. A reanalysis of Murusraptor barrosaensis Coria & Currie (2016) affords new evidence about the phylogenetical relationships of Megaraptora. Cretaceous Research. https://doi.org/10.1016/j.cretres.2019.02.021
Benson RBJ, Carrano MT and Brusatte SL 2010. A new clade of archaic large-bodied predatory dinosaurs (Theropoda: Allosauroidea) that survived to the latest Mesozoic.
Naturwissenschaften 97(1): 71–78.
Coria RA and Currie PJ 2016. A New Megaraptoran Dinosaur (Dinosauria, Theropoda, Megaraptoridae) from the Late Cretaceous of Patagonia. PLoS ONE 11(7): e0157973. doi:10.1371/journal.pone.0157973
Novas FE 1998. Megaraptor namunhuaiquii, gen. et sp. nov., a large-clawed, Late Cretaceous theropod from Patagonia. Journal of Vertebrate Paleontology. 18: 4–9. doi:10.1080/02724634.1998.10011030
Novas FE, Rolando AMA and Agnolín FL 2016. Phylogenetic relationships of the Cretaceous Gondwanan theropods Megaraptor and Australovenator: the evidence afforded by their manual anatomy. Memoirs of Museum Victoria. 74: 49–61.
Porfiri JD, Novas FE, Calvo JO.; Agnolín FL.; Ezcurra MD and Cerda IA. 2014. Juvenile specimen of Megaraptor (Dinosauria, Theropoda) sheds light about tyrannosauroid radiation. Cretaceous Research. 51: 35–55.

wiki/Megaraptor
wiki/Murusraptor
wiki/Megaraptora

Allactaga and Pedetes enter the LRT

Those leaping rodents from Africa,
jerboas (genus: Allactaga) and jumping hares (genus: Pedetes, Fig. 1), are more closely related to chinchillas and guinea pigs (Cavia), than to the marsupial kangaroos (Macropus) they converge with.

Allactaga major (Cuvier 1836; Late Miocene to present; snout-vent length 5–15cm; Fig. 1) is the extant jerboa, a nocturnal bipedal rodent that burrows into sand during the day. The long hind limbs help it hop, like a kangaroo, zig-zagging over long distances, and avoid attacking owls. They can hurdle several feet in a single bounce. Some have short ears, others have giant ears for cooling. Closest relatives in the LRT include Pedetes and Chinchilla, not the traditional Mus.

Figure 1. Skeletons of Pedetes and Allactaga to scale.

Figure 1. Skeletons of Pedetes and Allactaga to scale. Not sure yet if the jerboa is a miniature spring hare, or if the spring hare is a giant jerboa.

Figure 3. The spring hare (Pedetes) nests with the jerboa (Allactaga) in the LRT.

Figure 2. The spring hare (Pedetes) nests with the jerboa (Allactaga) in the LRT.

Pedetes capensis (Illiger 1811; snout-vent length: 35-45cm; Figs. 1, 2) is the extant South African springhare, a diurnal burrower and a nocturnal hopper native to South Africa. Pedal digit 1 is absent. Young are born with fur and are active within days.


References
Cuvier F 1836. Proceedings of the Zoololgical Society of London 1836:141.
Illiger 1811. Prodromus systematis mammalium et avium additis terminis zoographicis utriusque classis, eorumque versione germanica. Sumptibus C. Salfeld, Berolini [Berlin]: [I]-XVIII, [1]-301.

wiki/Allactaga
wiki/Pedetes