SVP 2025 abstracts of interest 6

It’s SVP abstracts season!
Here we start the second half of the bunch with part 6 of 10.

Evolutionary history of limb regeneration in lissamphibians: new evidence from two paleozoic stem-group species

Fröbisch NB et al (p251)
“Unlike amniotes, salamanders and frogs (i.e., limbed lissamphibians) can fully regenerate their limbs.”

“In this study, we show that limb abnormalities indicative of regeneration are also present in Apateon pedestris and Sclerocephalus haeuseri, two temnospondyl species that coexisted with Micromelerpeton. The evidence presented here further supports the idea that limb regeneration is ancestral to lissamphibians.”

For context, in the LRT Micromelerpeton is an early, but not basal member of the Lissamphibia. So is Apateon (Fig 1). By contrast, Sclerocephalus is a basal member of the Temnospondyli.

Consider this: frogs and toads are like marsupials. Their young hatch from ‘eggs’ at a premature stage. Tadpoles, like newborn marsupials, are limbless embryos that have to wiggle to where the food is. Unlike marsupials, tadpoles are free-swimming and can fend for themselves as they develop limb in their little ponds, a pouch analog.

On the current topic, one wonders if the gene that released precocious limbless swimming hatchlings had something to do with the continuing ability to grow lost limbs during the rest of their ontogeny? In other words, did they embryo state and chemistry continue into adulthood in this clade?

“Instead, the idea that lissamphibians can regenerate limbs due to self-organizational properties characteristic of their late limb development is consistent with the lack of limbs in the smallest known Apateon”

In the Apateon specimen scored in the LRT (Fig 1) neotony is present based on the lack of ossification of the carpals and tarsals, the short ribs and simply shaped phalanges despite the fully ossified skull.

“Finally, given that the preaxial polarity of limb development characteristic of salamanders has also been documented in Micromelerpeton, Apateon, and Sclerocephalus, the evidence of regeneration in these species supports the hypothesis of a pleiotropic link between these two features, which would be plesiomorphic for lissamphibians and would have been decoupled later in the anuran lineage.”

Note the lack of carpls and tarsals in Apateon (Fig 1), indicating neotony in the adult.

The anatomy of galeaspids (stem gnathostomes) and its evo-devo implications.

Gai, Zhu and Donoghue (p255)
“The galeaspid is an armored jawless stem gnathostome group to understand the sequential evolutionary origin of the gnathostome body plan.”

In the LRT galeaspids do not nest close to any of the gnathostomes. With their dorsal oral cavities (Fig 2) they are, instead, the most different clade from the other fish.

“we have shown that the paired nasal sacs and hypophyseal duct in galeaspid Shuyu are independent of each other, as in gnathostomes, but different from cyclostomes or osteostracans, which is the condition that current developmental models regard as a prerequisite for the development of jaws. The cranial anatomy of Shuyu also shows the first fossil evidence for a complete gillfunctional hyomandibular pouch (aphetohyoidean condition) in stemgnathostomes, an observation that sheds new light on the origin of the spiracle of jawed vertebrates.”

No new light is shed here on the topic of the spiracle unfortunately. Add taxa.

“The articulated galeaspid remains of Tujiaaspis and Foxaspis provide the details of the postcranial anatomy of galeaspids and reveal a pair of skeletal ventrolateral fin folds, which are compatible with aspects of the fin-fold hypothesis for the origin of vertebrate paired appendages.”

The authors are unaware that fish arose several times by convergence in the LRT.

“Therefore, the cylindrical branchial chamber in jawless ostracoderms probably represents an intermediate condition between the lateral in lampreys and medial location of gills aches in gnathostomes.”

The authors are unaware that jaws arose several times by convergence in the LRT.

In the LRT galeaspids left no descendants.

Taxonomic and ecological diversity of middle Eocene protocetids from Togo

Gay et al (p262)
“The evolutionary history of cetaceans is documented by a rich fossil record tracing their origin to the early Eocene of the Indo-Pakistani region, which is considered the cradle of the group.”

By contrast in the LRT baleen whales originated around the Pacific rim.

There is no such thing as a ‘cetacean’ anymore.
That label is not monophyletic in the LRT.

“Protocetids were the first to reach Western Africa and the Americas and their retention of an amphibious lifestyle holds significant ecological importance. Here, we present the
anatomical description of a newly discovered large protocetid from Togo. This new form is
represented by several individuals, including nearly complete cranio-dental remains. One
specimen is remarkably well preserved, featuring a complete skull and numerous
postcranial elements.”

Good news! More specimens!

The cranial and mandibular anatomy of softshell turtles (Trionychidae): a revised character list and phylogenetic analysis

Girard and Joyce (p270)
“Soft-shell turtles (Pan-Trionychidae) are an early branching clade of hidden-necked turtles (Cryptodira) with a rich fossil record extending back to the Upper Cretaceous.”

Not according to the LRT. Turtle analyses need a revised taxon list, not a revised character list. In the LRT softshell turtle ancestors extend back to the Permian with the small, horned pareiasaur, Sclerosaurus, followed by Odontochelys in the Triassic.

“The evolutionary history of softshell turtles is still unclear, mostly because phylogenetic relationships remain unresolved.”

Not true. See above. Apparently no one in academia is curious enough to add taxa.

“We assembled a revised list of characters focused on the skull anatomy of extant and extinct trionychids through the reassessment of pre-existing characters and the exploration of new characters, including phrasing of morphometric characters. To better assess the polymorphism present in soft-shell turtle skulls, we assembled a sample of 334 specimens of extant trionychids representing most extant species.”

Add more extinct taxa. Don’t omit them. That way you won’t waste your time with the wrong outgroup taxa.

“We carried out numerous parsimony analyses under several parameters and compared the results with a reference tree built from molecular data”

Forget molecules. Add fossils.

“Use of early fossil trionychids or Carettochelys insculpta as outgroups not only affects internal relationships but also character evolution. Despite progress relative to previous analyses, the use of a backbone is still recommended.”

Side note: “The backbone phylogeny serves as the reference to locate where single tips or entire clades extracted from the source.”

In the LRT Carettochelys is derived hardshell turtle close to the extant leatherback sea turtle, Dermochelys. Neither are related to softshell turtles. So… another academic barking up the wrong phylogenetic tree wasting their time because their cladogram was not correct with too few pertinent taxa.

A new bizarre basilosaurid from the Pisco Basin of Peru displaying unexpected primitive features challenges the major trends in cetacean evolution

Giuffra, Uhen and Benites Palomino (p276)

“Basilosaurid whales are the first truly marine mammals ever to evolve.”

Basilosauridae (Fig 5) began in the Middle Eocene with smaller marine ancestors.

“how they derived from a protocetid ancestor are still unclear”

Very clear in the LRT where there are enough transitional taxa (Fig 5). Here again paleontologists like to ignore and dismiss prior studies so they can be heroes in their discoveries and abstracts.

“Here, we present a nearly complete and well-preserved specimen collected from the mid Eocene of the Pisco Basin in Ica, Peru that possesses a mosaic of protocetid and basilosaurid characteristics and expand the known ecological disparity of archaeocete cetaceans.”

Good news! New taxa.
I’m not a fan of the word ‘mosaic’ when ‘transitional’ is avaiable and reflects gradual evolution, rather than a bit of this and abit of that cobbled magically together.

“The animal retains a big pelvis and functional hind limbs that appear to articulate with differentiated sacral vertebrae. It also retains a short tail, low vertebral count and shows no evidence of caudal flukes. The anterior part of its body, however, shows more derived anatomical features, such as a basilosaurid-like humerus, denticles in the cheek teeth and the acquisition of the basilosaurid tooth formula.”

“Surprisingly, an initial phylogenetic analysis using implied weights parsimony has placed this specimen within Basilosauridae, in a nesting more closely related to the Pachycetinae than to Dorudon and Basilosaurus.”

According to /wiki/Pachycetinae  “They differ from other basilosaurids in having pachyostotic and osteosclerotic vertebrae and ribs, making them denser and heavier by comparison.”

Pakicetus is not considered a clade member.

Here comes the mysterious part. 

“This implies that our specimen is not plesiomorphic to the clade but instead exhibits a secondary enlarged pelvis and hind limbs, accompanied by a reduced vertebral count compared to a more elongated ancestor, and therefore possibly occupying an ecological niche not previously documented among Pelagiceti.”

According to Wikipedia, Pelagiceti: “includes the common ancestor of Basilosauridae and all of its descendants, including Neoceti, the living cetaceans.”

Unfortunately this is an invalid = not monophyletic definition because in the LRT baleen whales are not related to toothed whales.

New giant protocetid pelves from the middle Eocene of Egypt: implications for hindlimb evolution in early whales

Gohar et al (p272)
“Here, we report on two exceptionally large innominates (= pelves, MUVP 832 and MUVP 833) from the Lutetian Midawara Formation in the Fayum Depression, Egypt. Recovered from the same stratigraphic level and ~2 km apart near the type locality of Phiomicetus anubis, the specimens likely represent two individuals of the same species, potentially referable to Phiomicetus. If confirmed, they would constitute the first pelvic material attributable to this taxon.”

Phiomicetus (Fig 6) is a giant prehistoric Tenrec (Fig 6) in the LRT.
Extant tenrecs are much smaller.

“Although the anterior ilium is missing, the preserved elements exhibit exceptional robustness and exceed the dimensions of all known protocetid pelves by 25–65%, ranking among the largest for any archaeocete.”

Phiomicetus is the outgroup for pakicetids + archaeocetids + odontocentes in the LRT.

“Overall, these pelves highlight a previously undocumented pelvic morphology within Protocetidae, supporting semi-aquatic propulsion via pelvic paddling and reinforcing the evolutionary diversity of hindlimb function among middle Eocene cetaceans.”

Please compare the new giant pelves to those of tenrecs. Don’t omit taxa.
BTW, tenrecs can swim.

Phylogenetic machine learning predicts cryptic aquatic habits and soft-tissue features in extinct amniotes.

Gordon (p279)
“I developed a novel phylogenetic supervised machine-learning approach to test the validity of previously proposed osteological correlates for both (1) webbing/flippers and (2) highly or fully aquatic habits within an extant bracket encompassing crown amniotes. I compared the proportions and shapes of the major limb regions and phalanges among webbed, unwebbed, and flippered species of differing aquatic affinities.”

“I ultimately found that simple limb region proportions predict amniote flippers and highly/fully aquatic habits with >90% accuracy.”

“These predictions… confirm that no Paleozoic stem reptiles were fully aquatic, support multiple origins for fully aquatic habits in sauropterygians and mosasaurs, and clarify that a semi-aquatic ichthyosauromorph has yet to be found.”

The LRT recovered ichthyosaur ancestors back to Ediacaran worms.

“More broadly, this work offers a versatile new method for reconstructing cryptic functional phenotypes (such as powered flight and bipedality) from sparse fossil remains in extinct species.”

I like that Gordon is discovering new ways to look at limbs.
PILs (parallel interphalangeal lines) were described about twenty years ago.

Source: https://pterosaurheresies.wordpress.com/2025/11/19/svp-2025-abstracts-of-interest-6/