Cretaceous Aquilolamna nests with Devonian Palaeospondylus in the LRT

Summary for those in a hurry
The authors excluded related taxa that would have helped them identify their strange, new 1.6 m shark with elongate pectoral fins. The authors also failed to identify the correct mouth, eyes, nasal capsules and gill slits.

Vullo et al. 2021 bring us a wonderful new 1.6m Turonian elasmobranch
with graceful, really long, pectoral fins, Aquilolamna milarcae (INAH 2544 P.F.17, Figs. 1, 2). The authors tentatively assigned (without a phylogenetic analysis) their fossil shark to lamniformes, like the mako shark, Isurus, which has a standard underslung mouth and overhanging rostrum. Vullo et al. thought Aquilolamna was a filter-feeder by assuming that it had a wide, ‘near-terminal mouth’ without teeth, as in the manta ray (genus: Manta). That morphology is distinct from lamniformes like Isurus.

This is a difficult fossil to interpret.
More than the fins make Aquilolamna different than most other fossil and extant sharks.

Unfortunately
Vullo et al. put little effort (Fig. 2 diagram) into their attempt to understand the many clues Aquilolamna left us. Those clues are documented here (Fig. 2) by using DGS (= color tracings) and tetrapod homologs for skull bones.

Figure 1. Aquilolamna in situ from Vullo et al. 2021. Colors added here.

Figure 1. Aquilolamna in situ from Vullo et al. 2021. Colors added here.

For proper identification, it didn’t help that Vullo et al. 

  1. imagined the mouth wide and in front, instead of small and below the occiput
  2. imagined the eyes on the sides, instead of on top
  3. imagined the gill slits on the sides, instead of ventral
  4. did not perform a phylogenetic analysis with a wide gamut of taxa
  5. did not consider Middle Devonian Palaeospondylus (Figs. 3, 4) as a taxon worthy of their time and consideration
  6. did not consider the torpedo ray, Tetronarce (Fig. 5), or the hammerhead, Sphyrna, taxa worth comparing in analysis (as in Fig. 4).
Figure 2. Skull of Aquilolamna and diagram from Vullo et al. 2021. Colors and new labels applied here. The mouth (magenta) appears under the occiput, overlooked by Vullo et al.

Figure 2. Skull of Aquilolamna and diagram from Vullo et al. 2021. Colors and new labels applied here. The mouth (magenta) appears under the occiput, overlooked by Vullo et al. White lines indicate symmetries. The hyomandibulars are small with fused quadrates at the new jaw corners and link to the intertemporals, as in all other vertebrates.

Despite these issues, Vullo et al. thought there was enough of Aquilolamna
that was strange, new and easy to understand to make it worthy of publication. And it is. And that’s okay. In science it’s okay to leave further details to other workers. Keeps us busy and feeling helpful! It’s okay to make mistakes. Others will fix those. That’s all part of the ongoing process.

From the abstract:
“Aquilolamna, tentatively assigned to Lamniformes, is characterized by hypertrophied, slender pectoral fins. This previously unknown body plan represents an unexpected evolutionary experimentation with underwater flight among sharks, more than 30 million years before the rise of manta and devil rays (Mobulidae), and shows that winglike pectoral fins have evolved independently in two distantly related clades of filter-feeding elasmobranchs.”

By contrast, in the LRT filter-feeding manta rays are more primitive than sharks that bite for a living.

Unfortunately the authors omitted important sister taxa recovered by the LRT from their comparison studies. They looked at other elamobranchs, but not the electric torpedo ray, hammerhead and Palaeospondylus (Figs. 3, 4).

By focusing on just a few traits the authors are trying to “Pull a Larry Martin.” Instead they should have performed a wide-gamut phylogenetic analysis with hundreds of traits.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyraena family.

Figure 3. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyrna family, that also includes the electric torpedo ray, Tetronarce.

Figure 4. Palaeospondylus diagram from Joss and Johanson 2007 who mistakenly considered Palaeospondylus a hatchling lungfish.

Figure 4. Palaeospondylus diagram from Joss and Johanson 2007 who mistakenly considered Palaeospondylus a hatchling lungfish.

From the taphonomy section of the SuppData:
“No teeth can be observed in INAH 2544 P.F.17, possibly due to rapid post-mortem disarticulation and scattering affecting the dentition.”

Turns out the authors were looking for teeth in the wrong place. The real jaws with tiny teeth were partly hidden below the occiput, as in Middle Devonian Palaeospondylus (Fig. 4), not at the anterior skull rim of Aquilolamna.

Figure 4. Subset of the LRT focusing on the shark clades related to Aquilolamna and Palaeospondylus.

Figure 4. Subset of the LRT focusing on the elasmobranch clades related to Aquilolamna and Palaeospondylus.

The reported lack of pelvic fins in Aquilolamna
is unexpected in sharks, which otherwise always have pelvic fins. This lack of pelvic fins could turn out to be a synapomporphy of taxa descending from Palaeospondylus. We’ll have to have more taxa for that.

From the Vullo et al. 2021 diagnosis of the ‘family, genus and species’:
“Medium-sized neoselachian shark that differs from all other selachimorphs in having hypertrophied, scythe-shaped plesodic pectoral fins whose span exceeds the total length of the animal. High number (~70) of anteriorly directed pectoral radials. Head short and broad, with wide and near-terminal mouth. Caudal fin markedly heterocercal. Caudal fin skeleton showing a high hypochordal ray angle (i.e., ventrally directed hypochordal rays). Caudal tip slender with no (or strongly reduced?) terminal lobe. Squamation strongly reduced (or completely absent?).”

Figure 1. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m)

Figure 5. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m). Note the robust caudal fin. The hyomandibular links the jaw joint to the braincase.

Aquilolamna has more vertebrae than Palaeospondylus,
but the former is much larger, an adult and geologically younger by 280 million years. We looked at Palaeospondylus just three days ago here. Very lucky timing to have Palaeospondylus for comparison prior to studying Aquilolamna.

Figure 6. Ontogenetic growth series of an electric torpedo ray. Pectoral fins in green.

Figure 6. Ontogenetic growth series of an electric torpedo ray from Madl and Yip 2000. Pectoral fins in green. Pectoral fins enlarge with maturity. Eyes migrate dorsally. Perhaps the same occurred with Aquilolamna and Palaeospondylus.

Taxon exclusion
continues to be the number one problem in paleontology. Phylogenetic analysis with a wide gamut of hundreds of taxa continues to be the number one solution to nesting all new and enigma taxa. Contra the assertions of dozens of PhDs, first-hand examination of the fossil is not required, nor is a degree or doctorate. This is the sort of profession where you learn on the job with every new taxon that comes along. This one was not in any textbooks, so everyone started like a September freshman with Aquilolamna.

And finally, if you can’t find the mouth where you think it should be,
look somewhere else.


References
Madl P and Yip M 2000. Essay about the electric organ discharge (EOD) in Colloquial meeting of Chondrichthyes head by Goldschmid A, Salzberg, January 2000. Online here.
Vullo R, Frey E, Ifrim C, Gonzalez Gonzalez MA, Stinnesbeck ES and Stinnesbeck W 2021. Manta-like planktivorous sharks in Late Cretaceous oceans. Science 371(6535): 1253-1256. DOI: 10.1126/science.abc1490
https://science.sciencemag.org/content/371/6535/1253

Online Publicity for Aquilolamna:

  1. sciencemag.org/news/2021/03/eagle-shark-once-soared-through-ancient-seas-near-mexico
  2. phys.org/news/2021-03-discovery-winged-shark-cretaceous-seas.html
  3. nationalgeographic.com/science/article/shark-like-fossil-with-manta-wings-is-unlike-anything-seen-before
  4. livescience.com/ancient-shark-flew-through-dinosaur-age-seas.html

Haikouichthys: an Early Cambrian galeaspid in the LRT, not a basal lamprey

Haikouichthys is supposed to be
a lamprey ancestor, but after testing in the LRT nests as an Early Cambrian galeaspid with a small head.

Either way,
Shu et al. reported on the importance of this fossil, “These finds imply that the first agnathans may have evolved in the earliest Cambrian, with the chordates arising from more primitive deuterostomes in Ediacaran times (latest Neoproterozoic, ,555 Myr BP), if not earlier.”

If Haikouichthys is a galeaspid,
ancestral, soft, worm-like chordates, like the more primitive lamprey, emerged in the Ediacaran, “if not earlier.”

Figure 1. Haikouichthys in situ and skull closeup, colors added.

Figure 1. Haikouichthys in situ and skull closeup, colors added. The oral  cavity on both lampreys and galeaspids is ventral.

Haikouichthys ercaicunensis
(Luo, Hu & Shu 1997; Shu et al.1999; HZf-12-127; 2.5cm) is an Early Cambrian galeaspid in the LRT. It has an appropriately much smaller skull than later galeaspids. The pectoral fin (green) is not separate from the body. The gill openings are invisible here, likely beneath the skull, as in galeaspids, not on the sides, as in lampreys. A prominent dorsal fin is present. So is a heterocercal tail. The series of posterior green diamonds are likely armored scales… like those in later sturgeons and osteostracans and those in early thelodonts, like Thelodus (Fig. 3). They are likely not gonads, but overlaid the area where the gonads are in related taxa.

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

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

The only other tested galeaspid in the LRT,
Dunyu (Fig. 2), is from the Late Silurian andhas a larger skull. We looked at Dunyu earlier here. It is close to the Early Devonian osteostracan, Hemicyclaspis (Fig. 3), which is basal to the extant sturgeon in the LRT. Note that galeaspids arise from soft-bodied thelodonts like Thelodus (Fig. 3), in the LRT.

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

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

Some thelodonts,
like Furcacauda, have a relatively small head, a ventral oral cavity, a dorsal fin and no lateral fins.

Figure 1. Galeaspids from Halstead 1985.

Figure 4. Galeaspids from Halstead 1985.

No prior authors
have attempted to put tetrapod homologs on the skull of Haikouichthys or any other galeaspid (Fig. 4).

Shu et al. 1999 wrote,
The theory of lateral fin folds has had considerable signiificance, but of the fossil agnathans only the anaspids and Jamoytius have such paired fn-folds. The possible occurrence of this condition in these Lower Cambrian agnathans indicates, however, that fin-folds may be a primitive feature within the vertebrates. The occurrence of close-set dorsal fin-radials in Haikouichthys, on the other hand, may be a relatively advanced feature.”


References
Luo H. et al. 1997. New occurrence of the early Cambrian Chengjiang fauna from Haikou, Kunming, Yunnan province. Acta. Geol. Sin. 71, 97-104.
Shu D-G et al. (8 co-authors) 1999. Lower Cambrian vertebrates from China. Nature 402:42-46.

wiki/Haikouichthys

Middle Devonian Paleospondylus nests with extant torpedo rays

Summary for those in a hurry:
a traditional enigma fish taxon, Paleospondylus (Figs. 1, 2) nests in the large reptile tree (LRT, 1815+ taxa) with the electric torpedo ray (Fig. 3) genus = Tetronarce), a taxon overlooked by all prior studies.

Before the addition of Paleospondylus,
the closest relative of the torpedo ray in the LRT was the hammerhead shark, Sphyraena. Both contributed to understanding the taxonomy and anatomy of Paleospondylus, a tiny juvenile ray with a relatively big, shark-like tail (Fig. 1). The LRT is the first wide gamut phylogenetic analysis attempt for Paleospondylus. Earlier studies compared only a few traits and few taxa, thereby “Pulling a Larry Martin” in the process.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a ray in the hammerhead shark, Sphyraena family.

Figure 1. A specimen of Palaeospondylus in situ with colors added here. This appears to be a juvenile ray in the hammerhead shark (Sphyraena) family. The torpedo ray, Torpedo, is also a member of this clade. Shown twice life size.

According to Wikipedia:
“Palaeospondylus gunni (Gunn’s ancient vertebrae, Traquair 1890) is a mysterious, fish-like fossil vertebrate. The fossil as preserved is carbonized, and indicates an eel-shaped animal up to 6 centimetres (2 in) in length. The skull, which must have consisted of hardened cartilage, exhibits pairs of nasal and auditory capsules, with a gill apparatus below its hinder part, and ambiguous indications of ordinary jaws.”

The phylogeny of this bizarre fossil has puzzled scientists since its discovery in 1890, and many taxonomies have been suggested. In 2004, researchers proposed that Palaeospondylus was a larval lungfish. Previously, it had been classified as a larval tetrapod, unarmored placoderm, an agnathan, an early stem hagfish, and a chimeraThe most recent suggestion is that it is a stem chondrichthyan.”

Palaespondylus diagram from Joss and Johanson 2007, colorized here.

Figure 2. Palaespondylus diagram from Joss and Johanson 2007, colorized here with tetrapod homologs. The authors considered Paleospondylus a larval lungfish. Late Johanson et al. 2017 no longer supported this hypothesis of interrelationships. The lungfish, Dipterus, occurs in the same fossil beds.

From Wikipedia continued,
“Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates.”

Figure 1. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m)

Figure 3. Tetronarce fairchildi (originally Torpedo fairchildi Hutton 1872, 1m)

From Wikipedia continued,
“According to Johnson et al. 2017, “Previously, Palaeospondylus has been assigned to almost every major jawless and jawed vertebrate group and identified as both larval and adult. Most recently, Palaeospondylus has been identified as a stem-group hagfish (Myxinoidea). However, one character questioning this assignment is the presence of three semicircular canals in the otic region of the cartilaginous skull, a feature of jawed vertebrates.”

“Additionally, new tomographic data reveal that the following characters of crown-group gnathostomes (chondrichthyans + osteichthyans) are present in Palaeospondylus: a longer telencephalic region of the braincase, separation of otic and occipital regions by the otico-occipital fissure, and vertebral centra. As well, a precerebral fontanelle and postorbital articulation of the palatoquadrate are characteristic of certain chondrichthyans.”

Johnson et al. 2017 conclude, “the absence/non-preservation of teeth, scales and fins continues to be problematic in determination of Palaeospondylus as a jawed vertebrate. Also problematic with regards to a chondrichthyan association is the composition of the Palaeospondylus cartilaginous skeleton that includes hypertrophied chondrocyte lacunae surrounded by mineralized matrix, previously interpreted as representing an early stage in endochondral bone development, a type of bone found in bony fishes (Osteichthyes).”

Figure 2. Skull of Sphyrna tutus in three views from Digimorph. org and used with permission. Colors added.

Figure 4. Skull of Sphyrna tutus in three views from Digimorph. org and used with permission. Colors added.

When Palaeospondylus was added to the LRT,
it nested with the torpedo ray while retaining many traits (like a precerebral fontanelle) found in hammerhead sharks,  Palaeospondylus lived in the Middle Devonian, so transitional and primitive precursors that look like a ray with a shark tail are to be expected. Lack of fusion in the skull elements, the overall small size and the appearance of several specimens in a small area suggesting a nursery, combine to indicates a juvenile status.

Figure 1. The small hammerhead shark, Sphyrna tutus, is best appreciated in dorsal or ventral view.

Figure 5. The small hammerhead shark, Sphyrna tutus, is best appreciated in dorsal or ventral view.

In the most recent paper on Palaeospondylus
(Johnson et al. 2017) the following taxa were not found in the text, but at times appear in the citations: 1) shark; 2) ray; 3) torpedo. The authors reported, “The presence of
centra within the synarcual of Palaeospondylus is reminiscent of the synarcual in batoid chondrichthyans.” They did not follow up on that clue. Contra tradition, in the LRT members of the traditional batoid clade are split apart and distributed among other chondrichthyans and basal gnathostomes.

In their conclusion Johnson et al. 2017 reported,
“Palaeospondylus gunni has been a perplexing vertebrate fossil since Traquair first described it in 1890; here X-ray tomography provides new data and morphological characters demonstrating that Palaeospondylus is a jawed vertebrate. Characters that associate Palaeospondylus with chondrichthyans are a precerebral fontanelle, foramina for lateral dorsal aorta in the chondrocranium, and the articulation of the palatoquadrate to the ventral postorbital process. Palaeospondylus also lacks bone and instead manifests an entirely mineralized cartilage in the endoskeleton.”

Taxon exclusion is the number one problem affecting paleontology today
and for several prior decades. The LRT minimizes taxon exclusion by testing a wide gamut of extant and extinct taxa in a trait-based phylogenetic analysis. If only prior workers had included hammerheads and torpedos in their own phylogenetic analysis, Paleospondylus would not have been the enigma it remained until today.


References
Hirasawa T, Oisi Y and Kuratani S 2016. Palaeospondylus as a primitive hagfish. Zoological Letters. 2 (1): 20.
Joss J and Johanson Z 2007. Is Palaeospondylus gunni a fossil larval lungfish? Insights from Neoceratodus forsteri development. J Exp Zool B Mol Dev Evol. 2007 Mar 15;308(2):163-71.  https://pubmed.ncbi.nlm.nih.gov/17068776/
Johanson Z et al. 5 co-authors 2017.
Questioning hagfish affinities of the enigmatic Devonian vertebrate Palaeospondylus. Royal Society Open Science. 4 (7): 170214.
Thomson KS 2004. A Palaeontological Puzzle Solved?. American Scientist. 92 (3): 209–211.
Traquair RH 1890. On the fossil fishes at Achanarras Quarry, Caithness. Ann Mag
Nat Hist 6th Ser. 1890;6:479–86.

wiki/Palaeospondylus

Coryphaenoides, the deep-sea rat-tail, is a deep sea cod

No controversy here
as the deep sea rat tail, Coryphaenoides carapinus, enters the large reptile tree (LRT, 1814 taxa) between  the cod, Gadus (Fig. 3) and the mahi-mahi, Coryphaena (Fig. 2) plus its Antarctic relative, Notothenia (Fig. 4).

Figure 1. The rat tail Coryphaenoides, is close to the cod, Gadus, in the LRT.

Figure 1. The rat tail Coryphaenoides, is close to the cod, Gadus, in the LRT.

Coryphaenoides carapinus (Gunnerus 1765) is the extant rat tail, a deep sea fish close to Gadus with dorsal fins, anal fins and caudal fins merged into a straight tail. Like some sharks, the nasal extends beyond the premaxilla. The circumorbital series is robust. The parietals are unknown in this image.

FIgure 1. Mahi-mahi (Coryphaena) mounted as if in vivo.

Figure 2. Mahi-mahi (Coryphaena) mounted as if in vivo.

Coryphaena hippurus (Linneaus 1758; 1.5m length) is the extant open seas predator mahi-mahi or dolphinfish, here related to the similar, but deeper sea Notothenia (Fig. 4). The dorsal fin starts at the skull. The caudal fin is deeply forked. The teeth are needle-like. Males have a tall fleshy forehead supported by a bony crest. A smaller-crested female is also shown above.

Figure 5. Atlantic cod, Gadus morhua, in lateral view.

Figure 3. Atlantic cod, Gadus morhua, in lateral view.

Gadus morhua (Linneaus 1758) is the Atlantic cod, nesting between the mahi-mahi (Coryphaena) and the cobia, Rachycentron. The anal fin is split in two. The chin has a barbel. The postparietal forms a long crest that divides the parietal. The naris is divided in two by the lacrimal. An antnarial opening precedes the naris. Note the elongate intertemporal and hyomandibular.

Figure 3. Notothenia is a Coryphaena sister of the deepest oceans.

Figure 4. Notothenia is a Coryphaena sister of the deepest oceans.

Notothenia coriiceps (Richardson 1844; 50cm) is the extant Antarctic yellowbelly rockcod. It lacks a swim bladder and the bones are dense, accounting for its reduced buoyancy. The body is adapted to sub freezing temperatures. Here it nests with the mahi-mahi, Corphaena (above), not with traditional perch.


 

References
Gunnerus JE 1765. Efterretning om Berglaxen, en rar Norsk fisk, som kunde kaldes: Coryphaenoides rupestris. Det Trondhiemske Selskabs Skrifter 3: 50-58.
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/Gadus_Atlantic_cod
wiki/Coryphaenoides
wiki/Notothenia_coriiceps
wiki/Mahi-mahi

 

Hollow-cheeked Euchambersia nests alongside puffy-cheeked Charassognathus

Unique among synapsids, Euchambersia
(Broom 1931, Benoit et al. 2017; Fig. 1) had an antorbital fenestra (= maxillary fenestra and fossa, Fig. 1) that may have housed a venom gland posterior to the canine root.

Reported by Brian Switek in Scientific American online,
“Because of the uniqueness of its skull anatomy,” Benoit and coauthors conclude, “Euchambersia mirabilis is and will remain a puzzling species.”

The ability to be unique in a world of gradual accumulations of derived traits 
made this taxon interesting. I wondered, which taxon did Euchambersia nest alongside? And did that taxon have anything like the antorbital fenestra found in Euchambersia?

The two answers are 1) Charassognathus and 2) yes.

Figure 1. Euchambersia skull with colors and shifting bones added.

Figure 1. Euchambersia skull with colors and shifting bones added.

Turns out Euchambersia was not unique among synapsids
for reasons stated above because its sister in the Therapsid Skull Tree (TST, 75 taxa) Charassognathus (Fig. 2) has a skull bulge posterior to the canine root.

Figure 4. Charassognathus does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TT.

Figure 4. Charassognathus (SAM-PK-K10369) does not share more traits with Abdalodon than other taxa, like Bauria and Promoschorhynchops in the TST. Note the bulge posterior to the canine root.

According to Wikipedia, citing Botha, Abdala and Smith 2007
Charassognathus is a basal cynodont.

By contrast, in the TST, Charassognathus is a cynodont-mimic nesting with therocephalians. Given the state of taphonomy documented in Euchambersia, the possibility that the unique maxillary fenestra was in life covered by a thin bulge of bone, as in Charassognathus, should be considered a possibility.

Wikipedia notes,
“Charassognathus has a snout that makes up slightly less than half of the total length of its skull and a long facial process on its septomaxilla. Other than these two features its skull is that of a typical cynodont. The odd shape of its septomaxilla is more typical of therocephalians than other cynodonts indicating that it may be close to a common ancestor between the two groups.”

The same is true of Euchambersia.

Figure 4. Therapid Skull Tree with the addition of Euchambersia and Charassognathus apart from cynodonts.

Figure 4. Therapid Skull Tree with the addition of Euchambersia and Charassognathus apart from cynodonts.

Nomenclature tidbit.
According to Wikipedia, “Broom named the genus Euchambersia, which he considered “the most remarkable therocephalian ever discovered”, after the eminent Scottish publisher and evolutionary thinker Robert Chambers, whose Vestiges of the Natural History of Creation was considered by Broom to be “a very remarkable work” though “sneered at by many.”

Chambers was probably happy to get the honor and compliment from Dr. Broom, while others sneered.


References|
Benoit J, Norton LA, Manger PR and Rubidge BS 2017. Reappraisal of the envenoming capacity of Euchambersia mirabilis (Therapsida, Therocephalia) using μCT-scanning techniques. PLoS ONE 12(2): e0172047. doi:10.1371/journal.pone.0172047
Botha J, Abdala F and Smith R 2007. The oldest cynodont: new clues on the origin and diversification of the Cynodontia. Zoological Journal of the Linnean Society. 149: 477–492.
Broom R 1931. Notices of some new Genera and species of Karroo Fossil Reptiles. Rec Albany Mus. 1931; 41: 161–166.

It’s not often that all the references fall within the range of one letter. The odds against that are approximately one in 26 cubed or 17.576.

https://blogs.scientificamerican.com/laelaps/did-this-protomammal-have-a-venomous-bite/

wiki/Euchambersia
wiki/Charassognathus
wiki/Akidnognathidae

From Tapanila et al. 2020: Edestus, a scissors ‘shark’, enters the LRT

Among the oddest fish in the late Paleozoic seas,
are relatives of Helicoprion, famous for its buzz saw teeth (Fig. 3) that grew in a single spiral set in the mid-line of the jaws. Unfortunately not enough is known of the skull to attempt a nesting in the large reptile tree (LRT, 1812+ taxa) at present.

Figure x. Shark skull evolution diagram.

Earlier
Harpagofututor (Figs. 2, 3), a Carboniferous relative of today’s moray eel (Gymnothorax), was tentatively allied with the buzz-saw clade because it shared a small medial tooth row.

Today
Edestus heinrichi (Leidy 1856; Fig. 1; FMNH PF2204; 25cm skull length; Pennsylvanian) joins this clade with its scissors-like medial jaws (Fig. 1) and enough skull to work with.

Figure 1. Skull of Edestus from Tapanila et al. 2018 and reconstructed here using DGS methods.

From the Tapanila et al. 2020 abstract
“Sharks of Late Paleozoic oceans evolved unique dentitions for catching and eating soft bodied prey. A diverse but poorly preserved clade, edestoids are noted for developing biting teeth at the midline of their jaws. Helicoprion has a continuously growing root to accommodate >100 crowns that spiraled on top of one another to form a symphyseal whorl supported and laterally braced within the lower jaw. Reconstruction of jaw mechanics shows that individual serrated crowns grasped, sliced, and pulled prey items into the esophagus.”

Figure 2. Harpagofututor skull colored and reconstructed here. Compare to Gymnothorax in figure 4.
Figure 2. Harpagofututor skull colored and reconstructed here. Compare to Edestus in figure 1

From the abstract, continued.
“A new description and interpretation of Edestus provides insight into the anatomy and functional morphology of another specialized edestoid. Edestus has opposing curved blades of teeth that are segmented and shed with growth of the animal. Set on a long jaw the lower blade closes with a posterior motion, effectively slicing prey across multiple opposing serrated crowns.

Figure 5. Harpagofututor male and female skulls. Added here is the best partial skull of the buzz tooth shark, Helicoprion.
Figure 3. Harpagofututor male and female skulls. Added here is the best partial skull of the buzz tooth shark, Helicoprion.

Tradtionally
Edestus and Helicoprion are portrayed with a shark-like body, but phylogenetic bracketing gives it a moray eel-type body (Fig. 5), like Harpagofututor.

Figure 4. From Tapanila et al. 2020, animated here to show the biting cycle of Edestes.
Figure 4. From Tapanila et al. 2020, animated here to show the biting cycle of Edestus.

From the abstract, continued:
“The symphyseal dentition in edestoids is associated with a rigid jaw suspension and may have arisen in response to an increase in pelagic cephalopod prey during the Late Paleozoic.”

Note that Gymnothorax, the extant moray eel (Fig. 6), also has large palatal teeth along the symphysis (= midline) by homology.

Figure 1. Harpagofututor female from Lund 1982.
Figure 5. Harpagofututor female from Lund 1982.
Figure 2. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.
Figure 6. The skull of the moray eel, Gymnothorax, in 3 views. Colors added as homologs to tetrapod skull bones. The nares exit is above the eyes.

Pulling prey deeper into the jaws
is a trait shared with the moray eel (Gymnothorax, Fig. 6), though done with an extra set of esophageal jaws (Fig. 7), distinct from the buzz-saw and scissors sharks.

Figure 7. GIF animation showing the dual bite of the dual jaws in moray eels. Both are derived from gill bars.
Figure 7. GIF animation showing the dual bite of the dual jaws in moray eels. Both are derived from gill bars.

Special thanks to reader JeholornisPrima
who sent a link to the Tapanila et al. 2020 paper on Edestus this morning to get this ball rolling.


References
Leidy J 1856. Indications of five species, with two new genera, of extinct fishes. Proc Acad Nat Sci Philadelphia 7:414.
Tapanila L, Priuitt J, Wilga CD and Pradel A 2020. Saws, Scissors, and Sharks: Late Paleozoic Experimentation with Symphyseal Dentition. The Anatomical Record 303:363–376. https://doi.org/10.1002/ar.24046

wiki/Edestus

Short-faced, big-eyed taxa at the base of all bony fish

The origin of bony fish 
is a traditional enigma. Apparently no one before the LRT derived bony fish from specific hybodontid sharks. Perhaps this is so due to a lack of effort. Evidently no prior workers applied tetrapod homologs to all vertebrate skulls, including sharks and sturgeons. Applying those homologs was required here in the large reptile tree (LRT) in order to score all taxa using a common set of traits.

According to Arratia 2010,
“Traditionally, fossils have played little role in most studies of the phylogenetic relationships of teleosts. The usual approach is to study only recent fishes and when fossils are considered their position is assumed in the cladogram. During the last few years this approach has been challenged by the inclusion of both fossil and recent species in phylogenetic studies.”

Unfortunately Arratia did not include enough fossil species. No sharks, No placoderms. No spiny sharks. No placoderms. No Gregorius (Fig. 1).

According to Arratia 2010,
“When fossil and recent taxa are included in phylogenetic analyses, the elopomorphs stand as the most plesiomorphic group among extant teleosts.”

Elopomorphs are not basal bony fish in the LRT where more taxa are included. Prohalecites (Fig. 1) and spiny sharks like Homalacanthus (Fig. 1) are basal taxa to their respective bony fish clades following the first great dichotomy of bony fish. Gregorius (Fig. 1) is their last common ancestor (LCA). Note the shorter rostrum and large eyes close to the anterior margin are juvenile traits retained into adulthood, as we discussed earlier.

Figure 1. Gregorius descends from Hybodus, the shark and is ancestral to Prohalecites at the base of the ray-fin bony fish. Gregorius is also ancestral to Homalacanthus at the base of the spiny sharks leading to lobefins, placoderms, catfish and a variety of other taxa.

Figure 1. Gregorius descends from Hybodus, the shark and is ancestral to Prohalecites at the base of the ray-fin bony fish. Gregorius is also ancestral to Homalacanthus at the base of the spiny sharks leading to lobefins, placoderms, catfish and a variety of other taxa. See figure 2 for a to scale view.

Figure 2. Representatives from the Early Devonian radiation that gave us bony fish, including Prohalecites and Homalcanthus.

Figure 2. Representatives from the Early Devonian radiation that gave us bony fish, including Prohalecites and Homalcanthus. Harpagofututor is close to living moray eels.

A short face and large orbit
characterize both branches of basal bony fish in the LRT, derived from Gregorius, a late survivor ion  the Late Carboniferous of an Late Silurian radiation.

Figure 1. Taxa from the LRT on one branch of the bony fish. Doliodus is one of these.

Figure 3. Taxa from the LRT on one branch of the bony fish. Doliodus is one of these.

Figure 1. Click to enlarge. Acanthodians and their spiny and non-spiny relatives in the LRT (subset Fig. 2), not to scale.

Figure 4. Acanthodians and their spiny and non-spiny relatives in the LRT (subset Fig. 2), not to scale.

Due to taxon exclusion,
Arratia 2010 lists the moray eel, Gymnothorax, and the gulper eel, Eurypharynx (Fig. 5), as elopomorphs. By contrast, when more taxa are added, as in the LRT, both nest closer to Gregorius and hybodontid sharks, both basal to the bony fish first dichotomy.

Figure 6. Eurypharynx evolution. This clade split from Gregorius prior to the major split in bony fish.

Figure 5. Eurypharynx evolution. This clade split from Gregorius prior to the major split in bony fish.

Some taxa (e.g  spiny sharks) at basal nodes in the LRT
are not mentioned by Arratia 2010. Some elops relatives (e.g. the swordfish, Xiphias) are not mentioned by Arratia 2010. Osteoglossum (Fig. 6) nests in the other bony fish clade, the one that includes placoderms, catfish, lobe fins and spiny sharks, and not at the base.

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

Figure 6. The arowana, an Amazon River predator, nests with Late Jurassic Dapedium in the LRT.

After spending several months 
with ninety+ ray fin fish, trying to shuffle and reshuffle them into their evolutionary order in the LRT (correcting hundreds of mistakes along the way) only a relative few LRT characters turn out to be important for lumping and splitting bony fish. And many of these recur as reversals and convergent trait, making the task more difficult.

  1. Orbit close to the tip of the rostrum, in the middle of the skull vs. close to the rear margin. Sometimes a sword can lengthen the rostrum
  2. Sagittal crest or not
  3. Maxilla either with teeth and a butt joint with the premaxilla, or loosely overlapping the premaxilla without teeth, or other variations
  4. Circumorbital bones absent, or present as a gracile ring, or present as large plates extending toward the preopercular, or as a gracile ring extending to the preopercular
  5. Rostral profile convex or cornered or straight or concave
  6. Coracoid short or long or essentially absent
  7. Parietals meet medially or split by an intervening postparietal
  8. Naris separate from the orbit or confluent
  9. Etc., etc.

Earlier we looked at the various radiations of bony fish
from a variety of spiny sharks in their ancestry (Fig. 4). Since then more taxa have been added, especially on the ray-fin clade. Please see the LRT for the latest cladogram.


References
Arratia G 2010. Critical analysis of the impact of fossils on teleostean phylogenies, especially that of basal teleosts. In: Morphology, Phylogeny and Paleobiogeography of Fossil Fishes Elliott DK, Maisey JG, Yu X and Miao D (eds.): pp. 247-274, 15 figs., 6 tabs. Verlag Dr. Friedrich Pfeil, München, Germany – ISBN 978-3-89937-122-2

https://pterosaurheresies.wordpress.com/2020/05/08/an-unexpected-resolution-to-the-spiny-shark-problem/

Didazoon and Vetulicola: Early Cambrian larvacean and echinoderm ancestors

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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

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


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

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

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

Flying squirrels and aye-ayes: convergent with multituberculates

For those in a hurry, a two-part summary:
1. By convergence, basal multituberculates in the Jurassic (Figs. 1, 4), had a distinct  flying squirrel (Glaucomys, Figs. 2, 3)-like patagial (= gliding membrane) morphology.
2. Also by convergence, multituberculates in the Jurassic had a short post-dentary skull length with a sliding jaw joint and a nearly absent angular process as seen in the extant aye-aye (Daubentonia, Figs. 5, 6).

Figure 2. The paratype specimen of Arboroharamiya HG-M018, in situ. DGS color tracing added. The skull is in poor shape.

Figure 1. The paratype specimen of Arboroharamiya HG-M018, in situ. DGS color tracing added. The skull is in poor shape.

Today’s blogpost had its genesis
when I finally noticed several basal multituberculates that preserved soft tissue had flying-squirrel-like patagia preserved in the sediment (Fig. 1)… and squirrels nested more or less close to the origin of multituberculates. So, I added a flying squirrel, Glaucomys (Fig. 1) to the large reptile tree (LRT, 1810+ taxa) to see what would happen.

It should come as no surprise
that Glaucomys nested with the extant red squirrel Sciurus, NOT any closer to multituberculates. Thus, the ability to glide in the manner of a flying squirrel turned out to be by convergence in basal multituberculates of the Jurassic.

Figure 2. Glaucomys gliding.

Figure 2. Glaucomys gliding.

Figure 2. Multituberculates to scale. Carpolestes is the proximal outgroup taxon.

Figure 3. Multituberculates to scale. Carpolestes is the proximal outgroup taxon.

Based on the phylogenetic position
of squirrels and other rodents as sisters to multituberculates, either flying squirrels were also gliding from tree-to-tree during the Mesozoic, or they took their time and only appeared after the Mesozoic. That is the current paradigm based on present evidence.

End of part 1. Scroll down for part 2.

Figure 1. Subset of the LRT focusing on basal placentals, including multituberculates.

Figure 4. Subset of the LRT focusing on basal placentals, including multituberculates.

Part 2.
By convergence, the aye-aye, Daubentonia

(Fig. 5) has a multituberculate-like mandible lacking an angular process along with a large circumference, sliding jaw joint and reduced post-dentary skull.

Figure 1. Taxa in the lineage of Daubentonia and multituberculates.

Figure 5. Taxa in the lineage of Daubentonia and multituberculates. Note the loss of the angular process and the sliding jaw joint.

By convergence, Carpolestes
has an enlarged posterior lower premolar, as in multituberculates. So, lots of convergence surrounds the multituberculates.

The aye-aye is a traditional basal primate,
based on gene studies (Dene et al1980; Rurnpler et al 1988; Del Pero et al 1995; Porter et al 1995).

By contrast
the large reptile tree (LRT, 1810+ taxa; subset Fig. 4) nests the aye-aye (Daubentonia) with rodents, plesiadapiformes, carpolestids and multituberculates. We’ve seen how genomic studies produce false positives. Add Daubentonia to that list of flubs. Note that both lemurs and aye-ayes are both from Madagascar, lending more evidence to the hypothesis that geography and geology (e.g. Afrotheria, Laurasiatheria) affect genomics to a greater degree than professionally realized over deep time.

Like rodents:
The aye-aye does not have mammary glands on the chest, as in primates, but along the groin, as in non-primates. The aye-aye has a large diastema between the incisors and molars, as in plesiadapiformes and rodents, distinct from primates.

Like primates:
The aye-aye has a postorbital bar, stereoscopic vision and an opposable hallux. Owen 1863 considered such traits ‘must be ordained’ in arguments for God and against Darwin’s then novel hypothesis of natural selection and evolution.

Like rodents,
Perry et al. 2014 report: “the single pair of incisors consists of continuously growing, elongate, open-rooted chisels, both upper and lower incisors.”

Based on the LRT
mutltuberculates are netonous rodents, growing to adulthood without ontogenetically incorporating post-dentary bones into the tympanic and periotic (inner ear enclosing bones), as we learned earlier here.

Figure 6. The aye-aye, Daubentonia in vivo. This is the closest living relative of multituberculates and is itself a plesiadapiform member of Glires, close to rodents, not primates.

Figure 6. The aye-aye, Daubentonia in vivo. This is the closest living relative of multituberculates and is itself a plesiadapiform member of Glires, close to rodents, not primates.

By convergence
the aye-aye (Daubentonia. Fig. 6) likewise reduces the tympanic and periotic along with the angular process of the dentary, producing a sliding joint that would have interfered with the ear bones if allowed to develop as in most placentals.

Carter 2009 notes
(while mistakenly assuming a lemur affinity for Daubentonia), “The overall dimensions of the D. madagascariensis auditory ossicles are large and they have a unique morphology.” Carter also reports on the elongate manubrium of the malleus (the former articular). This is in accord with similar structures in the neotonous (not primitive!) multituberculate auditory bone chain you can see here.

What does the angular process of the plancental dentary do?
According to Meng et al. 2003, a huge angular process was present in Rhombomylus, an extinct gerbil. Meng et al. mapped insertions for the deep masseter and superficial masseter externally. Then they mapped insertions for the medial pterygoid and superficial masseter internally. The Rhomboylus glenoid has a small diameter and rotates. It does not slide.

Meng et al. write: “As the major muscle to move the mandible forward, the superficial masseter must be long enough so that it can work to bring the jaw forward at least the minimum working distance. In general, the action line of the anterior deep masseter is nearly perpendicular to the moment arm of the mandible, while the posterior one has an acute angle to the moment arm and, therefore, less mechanical advantage. the deep masseter must have been sizable and supplies the main force for mastication as in rodents.”

The point of which is: multituberculates and the aye-aye reduce and eliminate the angular process. So we can imagine the muscles listed by Meng et al. either migrate or are lost in multituberculates and the aye-aye.

Figure 1. Maiopatagium in situ in white and UV light. The X marks an area surrounded by fur lacking proptagial data. Is the propatagium wishful thinking?

Figure 7. Maiopatagium in situ in white and UV light. The X marks an area surrounded by fur lacking proptagial data. Is the propatagium wishful thinking? Yes. Those are long guard hairs, precursors to porcupine quills. There is no patagium here.

We can’t leave Jurassic flying squirrels
without a quick review of Maiopatagium (Early Jurassic, Fig. 7, Meng et al. 2017), which was hailed ever since as a gliding mammal or mammaliaform.

Contra Meng et al. 2017
phylogenetic analysis nested Maiopatagium with the extant porcupine (Coendou), not with gliding multituberculates, like Vilevolodon. Maiopatagium has long straight hairs and lacks any trace of a patagium. Those long straight hairs are the precursors to porcupine quills according to the LRT.

Phyogenetic analysis puts rodents and all their precursors
(Tupaia, Henkelotherium, Nasua) squarely and clearly in the earlier part of the Early Jurassic, though not yet recovered in fossils.

The myth about the patagium surrounding Maiopatagium
seems to have had its genesis in the fact that Vilevolodon was described at the same time,  by the same authors, in the same publication. Vilevolodon (Fig. 1) has a no-doubt, flying sqirrel-like patagium. Maiopatagium (Fig. 7) was described with a misidentified patagium and a misidentified bat-like calcar. No patagium is present, but long straight hairs are. As noted above, these are precursors to porcupine quills. Getting taxa into a proper phylogenetic context is the key to understanding soft tissue and taxonomy.


References
Carter Y 2009. Monkey Hear: A morphometric analysis of the primate auditory ossicles. Master of Arts thesis, The U of Manitoba.
Del Pero M et al (4 co-authors) 1995. Phylogenetic relationships among Malagasy lemuls as revealed by mitochrondrial DNA sequence analysis. Primates 36: 43I-440.
Dene H, Goodman M and Prychodlco V 1980. Immunodiffusion systematics of the primates. Mamalia 44:27-31.
Luo Z-X, (6-co-authors) 2017. New evidence for mammaliaform ear evolution and feeding adaptation in a Jurassic ecosystem. Nature. in press (7667): 326–329. doi:10.1038/nature23483
Meng et al. 2003. The osteology of Rhombomylus (Mammalia, Glires): Implications for phylogeny and evolution of Glires. Bulletin of the American Museum of Natural History 275: 1–247.
Meng Q-J, Grossnickle DM, Liu D, Zhang Y-G, Neander AI, Ji Q and Luo Z-X 2017.
New gliding mammaliaforms from the Jurassic. Nature (advance online publication)
doi:10.1038/nature23476
Owen R 1863. On the characters of the aye-aye as a test of the Lamarckian and Darwmian hypothesis of the transmutation and origin of the species. Rep Br Assoc Adv Sci 1863: 114-116.
Perry JM et al. (4 co-authors) 2014. Anatomy and adaptations of the chewing muscles in Daubentonia (Lermuriformes). The Anatomical Record 297:308–316.
Porter CA et al (5 co-authors) 1995. Evidence on primate phylogeny from e-globin gene sequences and flanking regions. Journal of Molecular Evolution 40: 30-55.
Rurnpler Y et al (4 co-authors) 1988. Chromosomal evolution of the Malagasy lemurs. Folio Primatologica 50 124-129.
Sterling EJ 1994. Taxonomy and distribution of Daubentonia madagascariensis: a historical perspective. Folio Primatologica 62: 8-I3.

wiki/Maiopatagium
wiki/Coendou
wiki/Multituberculata

https://pterosaurheresies.wordpress.com/2019/01/06/a-post-dentary-reversal-between-rodents-and-multituberculates/

The lancet fish (Alepisaurus): a swordfish with fangs and no sword

According to Wikipedia
The lancet fish (Alepisaurus) is a traditional member of the Aulopiformes, the clade of lizardfish and their allies. Lizardfish, as you might remember, have eyeballs as far anteriorly as possible, the opposite of lancet fish.

Figure 1. Alepisaurus, the lancet fish nests with swordfish and eels in the LRT.

Figure 1. Alepisaurus, the lancet fish nests with swordfish and eels in the LRT.

By contrast,
in the large reptile tree (LRT, 1810+ taxa) the lancet fish nests close to European eels (Anguilla), but closer to swordfish (Xiphias). All three have similar skulls with a straight rostrum and very little (if any) post-orbital region anterior to the massive hyomandibular. Of course, neither eels nor swordfish have anything like those massive fangs found in the lancet fish. All three had a last common ancestor (LCA) distinct from other fish, and each evolved from that LCA their own special way leaving few clues, other than a similar skull, as evidence of their relationship to one another. That’s the way the LRT recovered it.

Figure 1. Extant swordfish (Xiphias) to scale with Eocene swordfish (Blochius).

Figure 2. Extant swordfish (Xiphias) to scale with Eocene swordfish (Blochius), which looks more like Alepisaurus overall.

That’s why we run all taxa through phylogenetic analysis. 
To do otherwise, to cherry-pick one trait or a dozen, is to “Pull a Larry Martin” which we are cautioned (for good reason) never to do. Professor Martin taught us well.

Figure 5. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Figure 3. Skull of Anguilla, the European eel, compares well with that of Bavarichthys. Note the loss and reduction of preorbital bones.

Alepisaurus ferox
(Lowe 1833, 1835a b, 215cm) is the extant lancetfish. Traditionally considered a aulopiform (= lizard fish. likeTrachinocephalus) here Alepisaurus nests as a swordfish sister without a rostrum sword, but with giant fangs and vestigial pelvic fins. During prey capture the fangs pierce swimming muscles, stopping the struggle. This hermaphrodite taxon can descend more than a mile into deep unlit seas.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins.

Figure 4. Swordfish ontogeny (growth series). Hatchings have teeth, a short bill and an eel-like body still lacing pelvic fins.

It’s worth noting
that swordfish hatchlings have teeth and a long dorsal fin, like lancet fish. So the resemblance is closer in younger swordfish. It’s also worth noting that fossil swordfish precursors, like Blochius (Fig. 4, Eocene; 60-150cm) also had proportions closer to lancet fish.

Fierstine 2006, in his history of billfishes,
mistakenly included the convergent sailfish, Istophorus, and excluded the European eel and the lancet fish. This is what I mean when we talk about “Pulliing a Larry Martin.” It looks right. It feels right. It gets published. However, whenever you cherry-pick taxa, you are less likely to get the big picture you are chasing: an accurate hypothesis of interrelationships that models real evolutionary events. Instead you should  employ lots and lots of taxa. Then the big picture (= the accurate model) will come to you. The cladogram will recover the correct tree topology.


References
Fierstine HL 2006. Fossil history of billfishes (Xiphoidei). Bulletin of Marine Science 79(3):433–453.
Lowe RT 1833. Description of a new genus of acanthopterygian fishes, Alepisaurus ferox. Proc. zool. Soc. Lond ,1:104.
Lowe RT 1835a. Description of a new genus of acanthopterygian fishes, Alepisaurus ferox. Trans. zool. Soc. Lond., 1: 123-128, pl. 19.
Lowe RT 1835b. Additional observations on Alepisaurus ferox. Trans. zool. Soc. Lond., 1: 395-400, pl. 59.

wiki/Aulopiformes
Alepisaurus_ferox