Labial cartilage in sharks and kin

Some, but not all chondrichthyans have labial cartilage,
(Fig. 1) those small, lateral, multi-part strips that bridge the gap between the upper and lower jaws (Fig. 2) and create shark cheeks (Fig. 3). There are no tetrapod homologs for labial cartilage. Megamouth, hammerhead and great white sharks don’t have labial cartilage. Neither do sawfish, skates or tiny Ozarcus.

Figure 1. Subset of the LRT focusing on elasmobranchs. Blue taxa have labial cartilages.
Figure 1. Subset of the LRT focusing on sharks and kin. Blue taxa have labial cartilages. This subset reflects recent additions and changes. The nurse shark, Ginglystoma, is now the basalmost taxon with marginal teeth. Loganiella is by far the oldest taxon with tiny labial cartilages and Manta is a living ancestor with external labial cartilages.

Kilmpfinger and Kriwet 2020 composed a ‘brief historical review’:
“The origin and function of LCs (labial cartilages) have been discussed for almost 150 years.
Gegenbauer 1872: vestiges of pre-mandibular visceral arches,
Pollard 1895: remains of skeletal supports of a primitive set of oral cirrhi as in Amphioxus.
Swertzoff 1916: vestiges of two segments of visceral arches
Goodrich 1930: a secondary structure of no great morphological importance
Smith 1937: strengthen and mobilize the mouth corners.
Veran 1995: “without functional utility” and therefore “in decline”
Motta and Wilga 2001: very important to generate suction forces for ingesting prey items.”

Figure 2. Squatina (angelshark) skull. Note the labial cartilages framing the mouth.

Kilmpfinger and Kriwet 2020 continue:
“Phylogenetic signals or evolutionary pathways for the origin and distribution of LCs among chondrichthyan fishes also have been suggested. For example chimeroids, representing the sister group to all shark-like chondrichthyans and hybodontiforms, which forms the extinct sister group of Elasmobranchii (extant sharks, rays, skates), have five pairs of LCs (Maisey 1983; Didier 1995) that could be considered as the plesiomorphic condition for chondrichthyans and Klug (2010) hypothesized that two dorsal and two ventral pairs of LCs represent the plesiomorphic condition for modern sharks, which would indicate that LCs were reduced during the evolution of sharks.”

That phylogeny is wrong. It is essentially upside-down, according to the large reptile tree (LRT, 1839+ taxa, subset Fig. 1) where chimeroids and hybodontids are derived from other sharks.

Putting things in a phylogenetic context,
(Fig. 1) Chondrosteus, sturgeons and phylogenetically earlier taxa do not have labial cartilages. Tiny external LCs first appear in the flat, wide-mouth and toothless Early Silurian Loganiella. The extant whale shark (Rhincodon; Figs. 2, 3) is the closest living relative and it has internal LCs that create shark cheeks. The whale shark and manta ray demonstrate how Loganiella might have fed, but on a much larger scale (Fig. 3). The original deep open mouth of Chondrosteus turns into a deep closed tube with cheeks in Rhincodon (Fig. 3) due to internal labial cartilages. In the LRT labial cartilages appeared once and disappeared five times.

Imagine what your life would be like
without cheeks…

Basalmost chordates,
like Branchiostoma, Metaspriggina, Arandaspis, and Drepanaspis depend on deep cheeks to process plankton. Sturgeons have tubular mouth parts that extend ventrallly. When jaws first appear in Chondrosteus the tubes / cheeks go away, but quickly return with the appearance of external and internal labial cartilages in Loganiella, Manta and Rhincodon. Some mouths are more efficient with cheeks. Others are not.

Figure 11.  Manta compared to Thelodus (Loganellia) and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of teeth. 
Figure 3.  Manta compared to Loganellia and Rhincodon. All three have a terminal mouth essentially straight across, between the lateral eyes, distinct from most fish. Note the lack of marginal teeth. 
Figure 4. Skull of Rhincodon, the whale shark, from Dennison 1957. The frontal, jugal, squamosal, quadratojugal, supratemporal, tabular, premaxilla, maxilla and dentary had not yet appeared. Other elements are fused as cartilage in chondrichthyans.

When the mouth opens in basal taxa,
like Manta (Fig. 5) flexible external labial cartilages (= cephalic fins) form flexible side walls to funnel plankton-filled water into the shallow mouth and deep gill basket.

Figure 6. Manta ray mouth lacking a barbel. Compare to its living sister, Rhynchodon, the whale shark.
Figure 5. Manta ray mouth showing how well-developed labial cartilages are used to funnel plankton-filled water into the mouth without waste.

In taxa that attack prey larger than themselves,
like Daliatis (kitefin shark, Fig. 4) and Isistius (cookie cutter shark), labial cartilages can be relatively large. When the mouth is open and attached to prey, the labial cartilages and the cheeks they support keep the mouthful of ripped flesh inside the shark’s mouth.

Figure 4. Daliatias, the extant kitefin shark, has relatively large labial cartilages.
Figure 4. Daliatias, the extant kitefin shark, has relatively large labial cartilages (not colored) and thick lips.

Without a valid phylogenetic context,
and a last common ancestor, all hypotheses are likely to end up as wrong guesses, no matter how many µCT scans you use.

Klimpfinger and Kriwet conclude
“It is evident that position and dimension of LCs are connected to the shape of the jaws, forming distinct morphological modules.” That’s pretty generic, something that could have been stated prior to their study. Armed with a valid phylogenetic analysis the authors could have found a last common ancestor and traced the expansion, shrinkage and general evolution of labial cartilages among the various chondrichthyan clades (Fig. 1). Instead the authors, armed with a MSc and a PhD, left those tasks to an amateur blog poster working from data discovered on Google. Focused studies are great, but we still need to understand and confirm the systematics a little better. Taxon exclusion remains the number one problem in paleo.

References
Klimpfinger C and Kriwet J 2020. Comparative morphology of labial cartilages in sharks (Chondrichthyes, Elasmobranchii), The European Zoological Journal, 87:1, 741-753, DOI:
10.1080/24750263.2020.1844323

More experts argue the origin(s) of theropod flight

Serrano and Chiappe 2021 seek to "weaken prior evidence"
supporting a multiple origin of powered flight. They wrote, “Feathered dinosaurs discovered during the last decades have illuminated the transition from land to air in these animals, underscoring a significant degree of experimentation in wing-assisted locomotion around the origin of birds. Such evolutionary experimentation led to lineages achieving either wing-assisted running, four-winged gliding, or membrane-winged gliding.”

Oops. They just undermined their argument. No one has yet produced four long bones per forelimb (rather than the typical three found in all limbed tetrapods) in scansoriopterygids like Ambopteryx and Yi qi.

Worse yet, none of these experts are discussing the importance of flapping marked by elongate locked down coracoids, discussed in detail earlier here and here.

“Birds are widely accepted as the only dinosaur lineage that achieved powered flight, a key innovation for their evolutionary success. However, in a recent paper in Current Biology, Pei and colleagues disputed this view. They concluded that three other lineages of paravian dinosaurs (those more closely related to birds than to oviraptorosaurs) — Unenlagiinae, Microraptorinae and Anchiornithinae — could have evolved powered flight independently. While we praise the detailed phylogenetic framework of Pei and colleagues and welcome a new attempt to understand the onset of flight in dinosaurs, we here expose a set of arguments that significantly weaken their evidence supporting a multiple origin of powered flight. Specifically, we maintain that the two proxies used by Pei and colleagues to assess powered flight potential in non-avian paravians — wing loading and specific lift — fail to discriminate between powered flight (thrust generated by flapping) and passive flight (gliding).”

Once again… you heard it here first (“fail to discriminate between powered flight and passive flght” see links above).

Pittman et al. 2021 responded
“In the recent study in Current Biology by Pei and colleagues, we used two proxies “wing loading and specific lift” to reconstruct powered flight potential across the vaned feathered fossil pennaraptorans. The results recovered multiple origins of powered flight. We respectfully disagree with the criticism raised by Serrano and Chiappe that wing loading and specific lift, used in sequence, fail to discriminate between powered flight and gliding. We will explain this in reference to our original conservative approach.”

“Will explain this” does not explain this. So this abstract is more of a tease.

And, of course, a valid phylogenetic context, employing more than one Solnhofen bird, is really all you need (Fig. 1).

References
Pei R et al. 2020. Potential for Powered Flight Neared by Most Close Avialan Relatives, but Few Crossed Its Thresholds. Current Biology online here.
Pittman M et al. (8 co-authors) 2021. Response to Serrano and Chiappe.
Current Biology 31(8): R372-R373 doi: https://doi.org/10.1016/j.cub.2021.03.059
https://www.cell.com/current-biology/fulltext/S0960-9822(21)00432-2
https://www.sciencedirect.com/science/article/pii/S0960982221004322
Serrano FJ and Chiappe LM 2021. Independent origins of powered flight in paravian dinosaurs? Current Biology 31(8): R370-R372
DOI: https://doi.org/10.1016/j.cub.2021.03.058
https://www.sciencedirect.com/science/article/abs/pii/S0960982221004310

PR
eurekalert.org/pub_releases/2021-04/uom-rqw042621.php

Changes to the ray-fin clade of the LRT

A review of taxa, characters and scores
in this bedeviling corner of the large reptile tree (LRT, (1839+ taxa; subset Fig. 1) shifted several taxa to new nodes, resolving many phylogenetic problems and shedding new light on previous anatomical misinterpretations.

Figure 1. Subset of the LRT focusing on changes in the ray-fin subset.

Sauropsis longimanus
is a traditional pachycormiform, but here (Fig. 1) nests alongside Early Cretaceous Calamopleurus and the sea gurnard, Dactylopterus (Fig. 2).

Figure 2. Dactylopterus, the flying gurnard, looks like a sea robin (Prionotus) but nests with other bottom-dwelling, squarish cross-section basal ray fin fish in the LRT.

Dactylopterus volitans,
the flying gurnard (Fig. 2), is typically and traditionally allied with pipefish and seahorses. Earlier the LRT nested it with the similar sea robin, Prionotus, a scorpionfish. Now, after review, Dactylopterus nests with a more similar basal ray-fin fish from the Early Cretaceous, Calamoplerus, famous for its full arcade of long fangs. A peek inside the tail of Dactylopterus reveals a heterocercal tail, a primitive trait retained from shark ancestors.

Esox,
the freshwater muskellunge, now nests with a somewhat similar seawater predator, the needlefish, Tylosurus armed with a longer, tooth-filled rostrum. Transitional taxa remain unknown and untested at present. Traditionally Esox is the sole member of the clade Esociformes.

Satanichthys
was originally and traditionally considered the oldest characiform (= catfish, knifefish, carp). Earlier the LRT nested Santanichthys as a tiny hatchling of a much larger Santana Formation herring, Notelops. After review Satanichthys now nests as a tiny bonefish with the larger Albula and the deepsea barrel-eye, Opisthoproctus.

Figure 3. The threadfin, Polydactylus, also splits the pectoral fin to form threadlike feelers.
Figure 3. The threadfin, Polydactylus, splits the pectoral fin to form threadlike feelers, like unrelated flying gurnard (Fig. 2) and the sea robin.

Polydactylus,
the extant threadfin, has been a constant pain to understand given the present set of taxa. Until recently no others shared a shark-like nasal extending beyond the underslung jaws (Fig. 3). Threadfins are otherwise different from other taxa with pre-pectoral fin rays: sea robins and flying gurnards (Fig. 2). The recent addition of the extant deep sea rat tail (Coryphaenoides) solved that problem. Both are derived from Gadus, the cod. Traditionally threadfins are considered Perciformes (perch-like) fish.

Paleocene Massamorichthys
was originally nested close to similar tuna and mackerel relatives. After review it nests just one node down, basal to Danio, the tiny zebra fish, which is basal to sticklebacks, pipefish and sea horses in the LRT.

Apologies for the earlier mistakes.
I’m learning as I go, trying to be as transparent as possible while adding taxa one at a time in a haphazard (= random) fashion. Each new taxon sheds light on earlier interpretations. So these recent revisions represent progress, like chipping out a recognizable , complex and polished figure from a block of marble. There is no all-knowing paleo teacher to guide any of us. Rather traditional studies are shown to be riddled with errors after testing in the LRT, usually due to taxon exclusion. Research takes scientists into unexplored territories. There are few to no other people on this planet working on these problems in this fashion. Thank you for your readership and patience with the process and the struggle.

Never trust.
Always test.

Your heard it here first: Prorotodactylus trackmaker ‘most likely a lepidosaur,’ not a dinosauromorph

Cosesaurus matched to Rotodactylus from Peters 2000.
Figuure 1. Cosesaurus matched to Rotodactylus from Peters 2000.

Klein and Lucas 2021 wrote:
Trackmaker: Brusatte et al. (2011) and Niedżwiedzki et al. (2013) attributed Prorotodactylus to dinosauromorph trackmakers similar to the trackmaker of Rotodactylus (Haubold, 1999). However, archosauromorph and even lepidosauromorph trackmakers cannot be excluded (see also discussion in Klein and Niedżwiedzki, 2012). Indeed, given the great similarity of Protorodactylus and Rhynchosauroides (one of us SGL, considers both genera to be likely synonyms), a lepidosauromorph trackmaker seems most likely.”

Figure 1. Cosesaurus flapping - fast. There should be a difference in the two speeds. If not, apologies. Also, there should be some bounce in the tail and neck, but that would involve more effort and physics.
Figure 2. Cosesaurus flapping and running bipedally digitigrade, close to life size on a 72 dpi monitor.

Klein and Lucas did not cite Peters 2000, 2011,
who matched Rotodactylus tracks (Peabody 1948; Fig. 1) to the pes of the small lepidosaur precursor to pterosaurs, Middle Triassic Cosesaurus (Figs. 1, 2).

References
Brusatte SL, Niedźwiedzki G and Butler RJ 2010. Footprints pull origin and diversification of dinosaur stem lineage deep into Early Triassic. Proceedings of the Royal Society B. 278 (1708): 1107–1113.
Brusatte S 2018. The rise and fall of the dinosaurs. A new history of a lost world. Wm. Morrow. An imprint of HarperCollins Publishers. 404pp.
Klein H and Lucas SG 2021. The Triassic tetrapod footprint record. New Mexico Museum of Natural History & Science Bulletion 83.
Peabody FE 1948.  Reptile and amphibian trackways from the Lower Triassic Moenkopi formation of Arizona and Utah.  University of California Publications, Bulletin of the  Department of Geological Sciences 27: 295-468.
Peters D 2000. Description and Interpretation of Interphalangeal Lines in Tetrapods.  Ichnos 7:11-41.
Peters D 2011. A Catalog of Pterosaur Pedes for Trackmaker Identification.Ichnos 18(2):114-141. http://dx.doi.org/10.1080/10420940.2011.573605.

mythbusting-prorotodactylus/
rotodactylus-produced-by-an-dinosauromorph-archosaur-or-a-lepidosaur/
what-about-those-really-big-rotodactylus-tracks/
lagerpeton-foot-configurations-modeled-in-cardboard/
reptileevolution.com/cosesaurus.htm

Juvenile Kunpengopterus is an adult Jianchangopterus after analysis

Summary for those in a hurry:
Your pterosaur traditions are going to be upset once again as this small adult pterodactylid with a long tail and a long, bent pedal digit 5 nests apart from the wukongopterid, Kunpengopterus, whenever more taxa are added to compete for its attraction.

Jiang et al. 2021 had the right idea, but did not see it through.
They wrote: “It is worth noting that Jianchangopterus zhaoianus, first published as a rhamphorhynchid pterosaur, may represent a young wukongopterid (Witton 2013, Wu et al. 2017). The only specimen of Jianchangopterus should have been housed at Yizhou Museum (Lü & Bo 2011), but none of the staff knew the whereabouts of this specimen when two of our authors (JS & CX) checked in the museum in 2019. Without observation of the holotype, especially the confluent condition of the nasoantorbital fenestra, it is impossible to confirm whether Jianchangopterus is a wukongopterid. Here, we described the first small-sized wukongopterid pterosaur to show some skeletal changes during ontogeny and revised the diagnosis of Kunpengopterus sinensis.”

There is no phylogenetic analysis in Jiang et al.
Evidently they didn’t feel the need to do so. After analysis in the large pterosaur tree (258 taxa, 183 characters) the ‘Kunpengopterus juvenile’ (STM 19-59) nests between the pterodactylids, Douzhanopterus (not mentioned in the Jiang et al. text) and Jianchangopterus (see paragraph above). These are basal pterodactylids close to the Painten pterosaur (privately owned and cited in Jiang et al.). Contra Jiang et al., it is not “impossible to confirm whether Jianchangopterus is a wukongopterid.” It is not a wukongopterid in the LPT and never was. 23 additional steps are needed to move STM 19-59 to Kunpengopterus.

Don’t freak out
over the long tail and bent pedal digit 5 in the pterodactylid, STM 19-59. Some traditions have exceptions and reversals when tested. These are things you learn by testing, not out of current textbooks, videos and lectures. So, put away your favorite traditions and test this for yourself.

Figure 1. The STM 19-59 specimen (lower left) compared to scale to related taxa in the LPT. Note the fragility of the cranial area of Jianchangopterus. That’s matched in the STM 19-59 specimen.

From the Jiang et al. 2021 abstract:
“The Wukongopteridae is a transitional clade between the long- and short-tailed pterosaur groups, and at least ten specimens have been studied without a determined juvenile specimen.

Actually, after testing in the LPT, Wukongopteridae is a clade without descendants in the Cretaceous. Pterosaur workers, all PhDs with reputation to lose if found to be wrong, have been cherry-picking and omitting taxa, including outgroup taxa, to perpetuate the myths they have been teaching at their universities and museums. No one has been brave enough to match the 250+ taxon list in the LPT, now ten years old, first discussed in front of a gathering of PhDs and chronicled in Peters 2007.

“Here, we described a small-sized Kunpengopterus sinensis, less than half the size of the holotype, which is the smallest specimen in wukongopterids. Based on unossified small elements, unfused cranial and postcranial elements, and grooves on the bone surface, this specimen is thought to be at least an early juvenile or even a late hatchling.”

If so, STM 19-59 should nest with an adult Kunpengopterus, since pterosaurs matured isometrically, like other lepidosaurs (Maisano 2002a, b), not like archosaurs. In the LPT STM 19-59 nests within an expanded Pterodactylidae. Clade members have a long tail and and elongated pedal digit 5. In paleontology we call this a reversal.

“By comparing the juvenile and subadult specimens of K. sinensis, we have found that the mid region of the upper and lower jaws had a higher growth rate than the anterior part, and that the growth rates were similar in most postcranial elements except for a higher rate in the caudal vertebrae.”

That does not sound like isometry. So this observation by Jiang et al. should be a red flag. This is where phylogenetic analysis comes in handy. Don’t assume. Test. You might be surprised by the results. Juveniles nest with adult pterosaurs in analysis.

Figure 2. The STM 19-59 specimen is not a juvenile Kunpengopterus, but a full size adult sister to Jinchangopterus, a pterodactylid with a long tail and long pedal digit 5. The orbital portion of the skull is composed of extremely gracile elements.

The Jiang et al. 2021 abstract concludes:
“We revised the previous diagnosis of K. sinensis and specified that two characteristics, nasoantorbital fenestra approximately 40% of the skull length and a thin and relatively short maxillary process of the jugal, should be diagnostic in subadult or adult specimens. We have also found that pedal features are stable during ontogeny and can be diagnostic in juvenile, subadult or adult specimens in K. sinensis.”

So now new myths and false traditions enter the world of pterosaurs.

Stable is the word you want to hear as it indicates isometry, but the authors actually found convergence.

Without a valid phylogenetic context, don’t even attempt to try to understand ontogenetic patterns. In this case the authors were attempting to force the adoption of an adult Jinchangopterus on unsuspecting Kunpengopterus parents.

Yes, the STM 19-59 specimen
has a long tail and a long, bent pedal digit 5. These are traditional rhamphorhynchoid (= pre-pterodactyloid-grade traits). Workers make the mistake of drawing a line in the systematic sand because these traits have been traditions for centuries. Test all traditions. Some of them have exceptions and reversals you may not be aware of. Don’t end up ‘Pulling a Larry Martin‘. Don’t base your decisions on a few traits, even a few famous traits. Several pterodactyloid pterosaurs have a surprisingly long tail. And that’s okay! Test the entire taxon against a wide gamut of competing candidates. Then your cladogram will model actual evolutionary events, including reversals without adding to the mythology that PhDs have been putting on your favorite pterosaurs.

PS. For those new to this blog:
The traditional clade ‘Pterodactyloidea‘ has been demoted to a grade. In the LPT four pterodactylod grades arise from various basal pterosaurs.

PPS.
An email from lead author S Jiang suggested running the analysis without Jianchangopterus. So let’s do that (and more) to see how many taxa must be deleted to move the STM 19-59 specimen to the wukongopteridae.

Deletion of Jianchangopterus: no topology change
Plus deletion of Douzhanopterus: no topology change
Plus deletion of the Painten private specimen: shift to Wukongopteridae, but not with Kunpengopterus.
Deletion of only the Painten private specimen: no topology change

Remember, skull shape does not lengthen with maturity, as all other juvenile/adult pairings in pterosaurs demonstrate (contra Jiang et al. 2021).

References
Jiang S et al. 2021. An early juvenile of Kunpengopterus sinensis (Pterosauria) from the Late Jurassic in China. An. Acad. Bras. Ciênc. [online]. 2021, vol.93, suppl.2, e20200734. Epub Apr 19, 2021. ISSN 1678-2690.  https://doi.org/10.1590/0001-3765202120200734.
Maisano JA 2002a. The potential utility of postnatal skeletal developmental patterns in squamate phylogenetics. Journal of Vertebrate Paleontology 22:82A.
Maisano JA 2002b.
Terminal fusions of skeletal elements as indicators of maturity in squamates. Journal of Vertebrae Paleontology 22: 268–275.
Peters D 2007. The origin and radiation of the Pterosauria. In D. Hone ed. Flugsaurier. The Wellnhofer pterosaur meeting, 2007, Munich, Germany. p. 27.

wiki/Kunpengopterus
researchgate.net First_juvenile_Rhamphorhynchus_recovered_by_phylogenetic_analysis

wiki/Pterodactyloidea – this is the traditional, untested view

Whale experts consider the origin of the cetacean brain without a valid phylogenetic context

Orliac and Thewissen 2021
looked at the brain endocast of the tenrec-to-pakicetid transitional taxon, Indohyus (Figs. 1, 2), but omitted comparisons to extant tenrecs. Instead they held on to the myth of an artiodactyl ancestry for all whales. Sadly, these whale experts did not realize that: 1) Indohyus is a tenrec (Fig. 4) and: 2) baleen whales (mysticetes) had an entirely different ancestry arising from hippos (= mesonychids, not artiodactyls), anthracobunids and desmostylians (Figs. 3–5). This has been online for five years and at ResearchGate for three years.

Figure 3. Indohyus skeletal elements nest between tenrecs and whales.
Figure 1. Indohyus skeletal elements nest between tenrecs and whales. Note the assymetry in the yellow ear bones at lower right.

The authors also overlooked
the cranial torsion (= assymmetry, Fig. 1) found here in tenrecs that echolocate, a trait retained by living odontocetes like Orcinus (Fig. 2), and not found in mysticetes.

Figure 8. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.
Figure 2. Odontoceti (toothed whale) origin and evolution. Here Anagale, Andrewsarchus, Sinonyx, Hemicentetes, Tenrec Indohyus and Leptictidium precede Pakicetus. Maiacetus and Orcinus are aquatic odontocetes.

From the Orliac and Thewissen 2021 abstact:
“We present the first description of the endocranial cast of the small raoellid artiodactyl Indohyus indirae.”

Indohyus is not an artiodactyl. It is a tenrec in the large reptile tree (LRT, 1838+ taxa; subsets Figs. 4, 5), which minimizes taxon exclusion by its wide gamut of included taxa.

“Raoellidae are sister group to Cetacea and the new morphological observations allow for outlining some of the early steps of the evolutionary history of the cetacean brain.”

Cetacea is not a monophyletic clade as discussed in a paper here in 2018 and first hypothesized here in 2016.

“The combination of primitive artiodactyl features and typical cetacean characters is unique about the Indohyus endocast. The fact that it presents the symplesiomorphic brain pattern observed in earliest Artiodactyla indicates that the cetacean brain derives from a very simple, plesiomorphic brain, with simple neocortical folding pattern, widely exposed midbrain, and concurrent small neocortex expansion.”

Taxon exclusion is present here. Note how whale authors never find a sister for Indohyus within the Artiodactyla. That’s because it isn’t there. In like fashion authors never find a sister for pterosaurs within Dinosauria, but keep insisting the two clades are somehow related.

“On the other hand, the Indohyus endocast shows characters that also occur in early cetaceans. These include modifications of the olfactory tract with narrow, elongated olfactory bulbs and peduncles, accompanied by a posterior location of the braincase in the cranium.”

Which other overlooked taxa have an elongate olfactory bulbs? Tenrecs (Fig. 2).

“The derived endocranial cast features of Indohyus mainly reflect changes in cranial architecture and these are most probably associated with modifications of the masticatory apparatus and a shift in diet.”

The authors overlook the echolocation abilities of tenrecs and Indohyus, their ability to send out signals through the nasal area, as in odontocetes, along with a torsioned skull for receiving signals slightly out of phase for more accurate 3D imagery.

“Indohyus meninges (= the three membranes that envelop the brain and spinal cord) were very thin like in most terrestrial artiodactyls and it had no extensive rostral or lateral retia mirabilia (= a complex of arteries and veins lying very close to each other). It however shows a branching pattern of ramification of intraosseous blood sinuses above the cerebellum that might represent the initial development of the caudal venous rete mirabile that would have colonized the endocranial cavity later on, in early archaeocetes.

Good to know, but take a look at tenrecs.

Figure 6. Isanacetus compared to sisters recovered in the LRT. Balaeonoptera is much reduced.
Figure 3. Isanacetus compared to sisters recovered in the LRT. Balaeonoptera is much reduced.

Some definitions according to Wikipedia:
Raoellidae are an extinct family of semiaquatic digitigrade artiodactyls in the clade Whippomorpha. An exceptionally complete skeleton of Indohyus from Kashmir suggests that raoellids are the “missing link” sister group to whales (Cetacea).”

In the LRT Indohyus is basal only to pakicetids, archaecetids and odontocetes, not to mysticetes. ‘Cetacea’ is not a monophyletic clade (Figs. 4, 5).

Whippomorpha is a group of animals that contains all living cetaceans (whales, dolphins, etc.) and hippopotamuses, as well as their extinct relatives. All Whippomorphs are descendants of the last common ancestor of Hippopotamus amphibius and Tursiops truncatus. This makes it a crown group.

In the LRT this definition includes edentates (=xenarthrans), uintatheres, rhinos, macrauchenids, chalicotheres, elephants and horses, taxa not intended for inclusion when originally defined.

Figure 4. Subset of the LRT focusing on the odontocetes and their ancestors.
Figure 4. Subset of the LRT focusing on the odontocetes and their ancestors.
Figure 3. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT
Figure 5. The oreodont-mesonychid-hippo-desmoystlian-mysticete clade subset of the LRT

Choosing to exclude taxa
is a common trait among established PhDs in paleontology. That’s why it is the number one problem in paleontology. PhDs got into paleontology to make discoveries, but when others make discoveries that change or challenge their hypotheses, a less welcoming attitude ensues.

References
Orliac MJ and Thewissen JGM 2021. The Endocranial Cast of Indohyus (Artiodactyla, Raoellidae): The Origin of the Cetacean Brain. Journal of Mammalian Evolution (advance online publication) DOI: https://doi.org/10.1007/s10914-021-09552-x
https://link.springer.com/article/10.1007/s10914-021-09552-x

wiki/Raoellidae
wiki/Whippomorpha

The garden eel, Gorgasia, enters the LRT apart from other eels

Apparently there are far too many traditional fish clades
and they are disordered according to results recovered in the LRT. The traditional and academic phylogenetic lumping and splitting of fish, as in mammals, birds, reptiles and amphibians, needs a major overhaul.

Figure 1. Garden eels (Gorgasia) in vivo arising from the burrows to feed on arriving plankton. Note the ability to bend the neck, rare for any fish except the salamander fish, Lepidogalaxias (Fig. 4).

Gorgasia punctata (Meek and Hildebrand 1923; 50cm; Figs. 1–3) is the dotted garden eel. This basal rayfin fish is a lancelet mimic, burrowing tail first in soft sand, rising to feed on plankton currents, never leaving its burrow. Reproduction is by external fertilization. Juveniles swim freely for the first year. Colonies burrow together. Like its ancestor, the salamander fish, Lepidogalaxias (Fig. 4), the garden eel can bend its neck, a rare trait in fish.

Figure 2. Line drawing of the garden eel, Gorgansia, overall and focused on the head and pectoral region. Upper, complete view about 1/2 actual size. Lower view about 1.5x actual size.
Figure 3. Skull of the garden eel, Gorgasia punctata, from Rosenblatt

Here
in the large reptile tree (LRT, 1837+ taxa) the garden eel, Gorgasia, nests among basal ray-fin fish between the salamanderfish, Lepidogalaxias, and the viperfish, Chauliodus. These three form a tight little clade in the LRT, but not in traditional fish systematics:

Lepidogalaxias – family: Lepidogalaxiidae, order: Lepidogalaxiiformes
Gorgasia – family: Congridae, order: Anguilliformes
Chauliodus – family: Stomidae, order: Stomiformes

Fig. 4. Cladogram of basal ray fin fish at full scale.

Why are these three taxa
not all recognized as members of the order Lepidogalaxiiformes? Apparently there are too many traditional fish clades and some that are not yet recognized other than in the LRT.

Not all ‘eels’
are members of the European eel clade, Anguilliformes. The eel-like morphology arose several times by convergence. The moray eel (Gymnothorax) is not related to either the garden eel or European eel in the LRT. Neither is the electric eel (Electrophorus).

Deep sea taxa,
like the viperfish (Fig. 5), have shalllow sea ancestors, like the salamanderfish (fig. 4) and garden eel (Figs. 1–3).

Figure 3. Chauliodus, the viperfish, in vivo.
Figure 5. Chauliodus, the viperfish, in vivo.

Paleontology and ichthyology students
and professors have been overspecializing, looking at individual taxa without understanding their trait-based relationships to one another in a general sense. The overall view of fish interrelationships needs a thorough house-cleaning according to results recovered by the LRT and exemplified by the garden eel problems noted above. Sorry to have to bring you such results, especially if you’re paying tuition in a paleontology major, but this is what happens when you minimize taxon exclusion, as in the LRT.

The presented hypothesis of interrelationships
(above and in the LRT) appears to be novel. If you run across a prior citation, please bring it to my attention so I can promote it.

References
Meek SE and Hildebrand SF 1923. The marine fishes of Panama. Part I. Field Museum of Natural History, Publications, Zoölogical Series 15 (publ. 215): i-xi + 1-330, Pls. 1-24.
Rosenblatt RH 1967 (1989). The osteology of the congrid eel Gorgasia punctata and the relationships of the Heterocongrinae. Pacific Science 21(1):91–97.

wiki/Gorgasia

Benoit et al. 2021 wonder if varanopids may in fact belong to Diapsida

Answer:
Varanopids are basal to synapsids AND non-lepidosaur diapsids. We’ve known this for about a decade in the large reptile tree (LRT, 1837+ taxa, subset Fig. 1).

Figure 4. Subset of the LRT focusing on basal Archosauromorpha including Vaughnictis and Cabarzia nesting at the base of the Protodiapsid-Synapsid split. Note all the large varanopids nest together here in the Synapsida, separate from small varanopids in the Protodiapsida.
Figure 1. Subset of the LRT focusing on basal Archosauromorpha including Vaughnictis and Cabarzia nesting at the base of the Protodiapsid-Synapsid split. Note all the large varanopids nest together here in the Synapsida, separate from small varanopids in the Protodiapsida.

The Benoit et all 2021 study suffers from taxon exclusion
and from trying to ‘Pull a Larry Martin’ by examining only the maxillary canals of several cherry-picked taxa using µCT scans without a valid phylogenetic context (Fig. 1). These authors had no idea that lepidosaur diapsids are NOT related to archosauromorph diapsids.

References
Benoit J, Ford DP, Miyamae JA and Ruf I 2021. Can maxillary canal morphology inform varanopod phylogenetic affinities? Acta Palaeontologica Polonica 66 (x): xxx?xxx, 2021. https://doi.org/10.4202/app.00816.2020

Diapsida
Archosauromorpha – Lepidosauromorpha split in the Viséan

A tiny, ancient, African river fish, Cromeria, enters the LRT alongside an ancient Amazon river fish, Anableps (four-eyed fish)

Contra tradition and textbooks
the tiny fish pictured here (Fig. 1) are all basal taxa in the clade of bony ray fin fish. Their presumed origin and radiation in the Silurian is based on the presence of known, more derived taxa in the Late Silurian. Perhaps the small size of these taxa has helped them avoid detection in Silurain strata. Prohalecites, the basalmost taxon, is known from Middle Triassic strata. The rest are late-surviving extant taxa.

Figure 1. Small taxa from the base of the ray-fin bony fish clade shown at full scale. Cromeria is the sixth taxon down and the third illustration down. Taxa not shown are generally much larger in size.

The physical and phylogenetic separation of Anableps and Cromeria,
both freshwater taxa, occurred before South America separated from Africa in the Jurassic Period 180 mya.

Cromeria nilotica
(Boulenger 1901; 4.5cm; Figs 1-3) is an extant tiny African naked shellear previously not associated with Anableps (Fig. 4). They must have split apart prior to the South America – Africa rift. Two species are shown below (Fig. 3). Note the subterminal mouth, as in Anableps. The scaleless body lacks a lateral line. Like other clade members, the caudal fin extends anteriorly both dorsally and ventrally.

Figure 2. From Gregory 1933, diagram of Cromeria. Colors added here. Note the odd caudal fin extending anteriorly to the dorsal and anal fins.
Figure 3. Two species of Cromeria, the African naked shellear shown several times life size.
Figure 2. Anableps skull CT scan images from Michel et al. 2015.
Figure 4. The four-eyed fish Anableps skull CT scan images from Michel et al. 2015. Compare to Figs 1–3.

Anableps tetrophthalmus
(originaly Cobitis anableps Linnaeus 1758, Scopolis 1777; Michel et al. 2015; 32 cm) is the extant four-eyed fish (aka: cuatro ojos), a surface predator of insects falling into Amazonian fresh waters or shallow shores where Anableps beach themselves to eat them. The underslung jaw enables this behavior.

Females are much larger than males.
Internal fertilization (with a modified tubular anal fin) leads to live birth (viviparity) of up to 14 young. The vertebral number is higher than typical for most ray-fin fish.

Traditionally Anableps is a member
of the pupfish (guppy, killifish, topminnow, Danio) family. Here, in the LRT, Anableps nests with basalmost ray fin fish like Lepidogalaxias (Fig. 1) and tiny Cromeria (Fig. 1) from Africa, close to the origin of ray fin bony fish and far from the more highly derived guppies and pupfish.

References
Boulenger GA 1901. Diagnoses of new fishes discovered by Mr. W. L. S. Loat in the Nile. Annals and Magazine of Natural History, Including Zoology, Botany and Geology, Being a Continuation of the ‘Magazine of Botany and Zoology’, and of Louden and Charlesworth’s ‘Magazine of Natural History’, Series 7 8: 444-446.

Schoch 2018 tries to figure out Dissorophoids

Schoch 2018
recovered a cladogram he considered ‘dissorophoid temnospondyls’, and considered them putative lissamphibian precursors. This study closely follows a similar one by Pérez-Ben, Schoch and Báez 2018 that we looked at earlier here.

Schoch 2013 defined Dissorophoidea
as “The least inclusive clade containing Micromelerpeton credneri and Dissorophus multicinctus” (Fig. 2). In the the large reptile tree (LRT, 1837+ taxa, subset Fig. 1, non-ghosted taxa) that clade also includes Microsauria, Seymouriamorpha, Reptilomorpha and Reptilia, which was not Schoch’s intention. And it excludes several taxa Schoch included. This was all due to taxon exclusion and following tradition.

Laurin 1998 defined Temnospondyli
to include “all choanates more closely related to Eryops than to amniotes.” This is a poor definition because it doesn’t have a last common ancestor. Moreover, in the LRT no relatives of Eryops are related to Dissorophus (Fig. 2) and the dissorophoids (Fig. 1).

Figure 1. Subset of the LRT focusing on basal tetrapods (ghosted). Cherry-picked taxa from Schoch 2018 are shown in green. The least inclusive clade is not ghosted. Much better to let your cladogram tell you which taxa are putative lissamphibian stem-group taxa, than to gerrymander your own taxon list.

Unfortunately
taxa exclusion mars the Schoch 2018 study. He did not see the microsaur and reptile connection to this clade (Fig. 1). It is much better and more scientific to let your cladogram tell you which taxa are putative lissamphibian stem-group taxa, than for you to tell your claogram what the taxon list will be.

Figure 2. Dissorophus nests with Stegops among basal lepospondyls in the LRT.
Figure 2. Dissorophus nests at the base of the Dissorophidae in the LRT. And that clade is basal to Seymouria, Reptilomorpha, Microsauria, Reptilia and Lissamphibia.

Shoch 2018 reported,
“This study aims to resolve or constrain the following major questions of dissorophoid phylogeny:

  1. What does the large-scale phylogeny of Dissorophoidea look like?
  2. What is the position of the enigmatic taxon Perryella?
  3. Do Micromelerpetidae form a clade and where do they nest?
  4. Do Branchiosauridae form a clade and where do they nest?
  5. What is the relationship of Doleserpeton and Gerobatrachus to Lissamphibia/Batrachia?
  6. What is the most likely evolutionary scenario for the origin of the Dissorophoidea
  7. and the origin and early diversification of Lissamphibia/Batrachia?
  8. The goal of the phylogenetic analysis was to cover as wide a range of well-studied dissorophoid taxa as possible, with the focus on the origin and diversification of this clade and the in-group relationships of amphibamids.

The LRT confidently handles all these questions
(Fig. 1) simply by employing a wider range of taxa. Adding taxa in the LRT recovers a different origin and diversification of this clade, but agrees with the origin of frogs and salamanders. Caecilians have a separate ancestry arising from Microsauria (Fig. 1), so, “Goodbye Lissamphibia!” It’s not a monophyletic clade unless it includes a much wider gamut of taxa, including the Dissorphoidea. We looked at the origin of modern amphibians in the LRT here back in 2018.

References
Pérez-Ben CM, Schoch RR and Báez  AM 2018. Miniaturization and morphological evolution in Paleozoic relatives of living amphibians: a quantitative approach
https://doi.org/10.1017/pab.2017.22Published online: 23 January 2018
Schoch RR 2018. The putative lissamphibian stem-group: phylogeny and evolution of the dissorophoid temnospondyls. Journal of Paleontology 93(1):1-20. 0022-3360/15/0088-0906
doi: 10.1017/jpa.2018.67