Read the Beforeitsnews.com story here. Advertise at Before It's News here.

By David Peters
Contributor profile | More stories

Story Views
Now:
Last hour:
Last 24 hours:
Total:

The Fin-to-Finger Transition in one go

Thursday, May 28, 2026 8:01

% of readers think this story is Fact. Add your two cents.

Traditional hypotheses
for the origin of tetrapods (= vertebrates with digits) focused on late Devonian Panderichthys and Elpistostege (Fig 1), two long-torso, wide-rib, small-lobefin taxa on the primitive side of the fin-to-finger transition. On the derived side were Latest Devonian Ichthyostega and Acanthostega (Fig 2), two short-torso, round-rib, large limb, multi-dactyl taxa. These two are also the oldest known tetrapods – but an early Middle Devonian tetrapod trackmaker (Fig 4) was much older.

That’s the first problem.

Figure 1. Convergence demonstrated between flat lobe fin and flat tetrapod taxa.

Second problem:
Most other basal tetrapods had only four fingers and five toes (Fig 6). So it was traditionally assumed that the second wave of Carboniferous tetrapods lost ancestral superfluous digits (Fig 2).

Figure 2. Acanthostega does not have much of a neck.

Third problem:
Some of the most primitive Carboniferous tetrapods are long-torso, wide-body, small limb taxa, (Fig 1) resembling Panderichthys and Tiktaalik, except for the exchange of small lobefins for small limbs with small digits.

Fourth problem:
Late Devonian Tulerpeton (Fig 3) had five slender fingers and five toes with a near-reptile formula of non-ungual phalanges 1-2-3-4-4 on the manus and similarly for the pes.

Figure 3. Manus/Fin diagram from Cloutier et al. The phylogenetic order is wrong and Tulerpeton is not related (in the LRT). Greererpeton is substituted. 4 fingers is the primitive number.

Here the traditional fin-to-finger transition hypothesis is revised
after a phylogenetic analysis that omits fewer taxa. Here basalmost tetrapods, like Pholidogaster and Colosteus (Fig 5), had a long but round (in cross-section) scaly torso with reduced, slender limbs. Here four fingers is the primitive number.

Here five fingers appear in basal Reptilomorpha.
Here Tulerpeton represents an as yet undiscovered Devonian radiation of terrestrial tetrapods, nesting as the proximal outgroup to the Reptilia. Here multi-dactyl taxa with robust limbs (Fig 2) are derived and these few taxa left no Carboniferous descendants.

Introduction
Two short definitions are followed here: Fish = pre-tetrapods have fins and lack digits. Conversely tetrapods have fingers or toes or both. This might seem obvious, but the widely-accepted definition of a stem tetrapod includes vertebrates with lobe fins and the widely-accepted definition of a crown tetrapod excludes many taxa with fingers. There are no known taxa in which one set of lobes/limbs had fins while the other set had digits. Finally, skull-only sister taxa of basal tetrapods are here considered tetrapods ‘by association’.

The focus of this blogpost
is restricted to the one and only fin-to-finger transition recovered in the large reptile tree (LRT, 2340 taxa). The large number of taxa in the LRT minimizes taxon exclusion, an ongoing problem in vertebrate paleontology.

The cladogram
The LRT is the online cladogram recovered after the inclusion of 2340 taxa ranging from Cambrian pre-fish to humans, birds, turtles and long lists of taxa in-between. This experiment began in 2011 with 240 taxa and grew ten-fold in 15 years. 268 pterosaurs and their proximal outgroups are tested separately with a different set of characters in the adjoining large pterosaur tree (LPT). Originally all taxa were on the same matrix, but when the number of taxa reached the software limit of 1500, the matrices had to be divided into overlapping subsets that continued to add taxa. 238 multi-state characters are scored in the LRT. The heuristic search option is used. Resolution is generally good throughout. Taxa colored red in the LRT have been tested, then deleted, generally because they represent only fragments of a skeleton.

Gene studies
Results recovered in the LRT do not match suprageneric results in genomic studies, which cannot test extinct taxa. The reason for this discrepancy is not yet known, but is widely acknowledged.

Results
In the LRT the following taxa are in the ancestral line toward tetrapods: Middle and late Devonian Eusthenopteron, Osteolepis, Glyptolepis, Gooloogongia, Middle Devonian Tinirau and Early Carboniferous Koilops (a skull-only taxon). In the LRT little Koilops gave rise to tetrapods on one branch and on the other branch, long-torso, low-body, small-fin taxa like Tiktaalik, Panderichthys and Elpistostege.

The following Carboniferous taxa are in the basalmost tetrapod clade: Aytonerpeton, Colosteus, Deltaherpeton and Pholidogaster.

The following Carboniferous taxa nested at the bases of the several radiations the followed the appearance of digits: Trypanognathus, giant early Permian Gaiasia and early Carboniferous Greererpeton. Long, low Trypanognathus converges with long, low Panderichthys (with the exception of digits replacing fins). Ichthyostega and Acanthostega arose from the Greerepton clade in the LRT.

Figure 4. The Early Carboniferous limbed osteolepid, Pholidogaster, compared to Middle Devonian Zalchemie tracks to scale.

Tetrapod trackmakers
Early Middle Devonian multi-dactyl tetrapod trackways that can be matched to a multi-dactyl ichthyostegid have been described (Niedźwiedzki et al 2010). So the evolution of fingers from fins preceded the early Middle Devonian.

Before the transition from fins to fingers
Eusthenopteron had no metacarpals. Tiktaalik had three tiny metacarpals, perhaps four, but that lateral area is today taphonomically damaged. Digits are not present. Panderichthys had four larger individually-shaped = dissimilar metacarpals but still lacked phalanges = digits..

Figure 5. Colosteus relatives according to the LRT scaled to a common skull length. Their sizes actually vary quite a bit, as noted by the different scale bars. Only Pholidogaster and Colosteus are taxa in common with traditional colosteid lists.

During the transition from fins to fingers
Colosteus had four small, slender, cylindrical radiating metacarpals and slender digits of laterally increasing length. These tiny ?vestiges were unable to support the weight of the cylindrical body and smaller than ancestral lobes = limbs sans fins.

Aytonerpeton preserved robust pedal digits bones.

Pholidogaster preserved a five-metatarsal pes with mt4 the most robust and digit 4 likely the longest. Distal phalanges and unguals are taphonomically missing. The tarsus had two proximal elements (tibiale and fibular) and three distal elements with a simple hinge joint between them. The robust crus was about half the length of the longer, more slender femur. The fibula was more robust than the tibia. The manus was taphonomically absent. Here again the torso was roughly cylindrical in cross-section, as in Middle Devonian Tinirau.

Figure 6. Origin of fingers according to taxa in the LRT. Trypanognathus is featured as the first tetrapod with fingers.

After the transition from fins to fingers
Trypanognathus had four ‘hourglass’ shaped metacarpals and four long proximal phalanges tipped by four unguals. Digit 3 was the largest. Phalanx 3.1 was the largest. Unguals 3 and 4 were the largest. The flattened wide body and small limbs were convergent with similar traits on members of the Tiktaalk clade.

Greererpeton (Fig 6) had four ‘hourglass’ shaped metacarpals (Fig 6) and four long proximal phalanges. The medial two were tipped by sharp-ish unguals. Digits 3 and 4 had an extra row of phalanges tipped by sharp-ish unguals with the formula 1, 1, 2, 2 (not counting the unguals). Digit 3 was barely the largest. Phalanx 3.1 was the largest. The pes had five digits tipped with sharpish unguals with the following non-ungual number: 1, 1, 2, 3, 3. The body was again flat and wide. The limbs were small and unable to support the weight of the torso. Greerepeton descendants include Ichthyostega (Fig 7) and Acanthostega in the LRT.

Figure 7. Not sure which is more correct, but this Ichthyostega data shows little to no wiggle room for the larger skull, more for the smaller skull.

Multi-dactyl taxa
Ichthyostega (Fig 7) does not preserve a manus. However, pedal digit 1 appears in triplicate, all narrower and shorter than the lateral four robust metatarsals and toes with the following non-ungual number: 2(x3), 2, 3, 3, 2. The pelvis, femur and radius were robust. The scapula and humerus were also robust. The derived torso was short and cylindrical, distinct from the the long, low, small-finned pre-tetrapods.

The manus of Acanthostega preserves three short straight digits (again in triplicate) where digit 1 is otherwise located in other taxa. Digit 2 is aligned with the axis of the antebrachium. Fingers 3–6 radiate laterally with digit 4 the longest. So digits 1, 2 and 6-8 appear to be novel in appearance after 4-fingered ancestral taxa. The pes had a vestige digit 1, a short digit 2, digits3-5 equally long, digit 6 shorter and digit 7 shorter still. Digit 8 was a vestige no longer than mt7. These traits are not found in Carboniferous taxa, indicating that Ichthyostega and Acanthostega were derived, not primitive, as they nest in the LRT some distance from the origin of digits.

The earliest and most derived Reptilomorph
Late DevonianTulerpeton nested at the base of the Reptilia = Amniota in the LRT. Viséan Silvanerpeton is the last common ancestor of all extant mammals, reptiles and birds. ‘Amniota’ is a junior synonym in the LRT. The right hand of Tulerpeton had only five fingers. The purported sixth finger was the emerging, but otherwise buried tip of the left fourth finger.

Speculation on the advantage of digits over lobe fins
Tiny digits tipping small, slender limbs in Colosteus and Pholidogaster (Fig 5) ancestors apparently deep in the Early Devonian must have provided some niche advantage not afforded to their lobe-fin ancestors and sister taxa. Primitive tiny limbs and relatively weak girdles would have been less able to lift the relatively large torso off the substrate, so the terrestrial option seems to be untenable – that is unless one considers the present activity of finless moray eels as they hunt for crabs on rocky shorelines. YouTube video here.

Compared to lobe fins, digit tips might have providedindividual points of sensory input, perhaps for navigation along shallow water bottoms cluttered with detritus. Digits can wrap around objects, preventing the rest of the body from drifting in weak currents. Thus digits could have been anchors, not paddles. Digits can cling to or lodge against the substrate when traversing through shallow waters. Perhaps limbs were useful during exaggerated sinusoidal motions of the torso that provided the mail thrust, as in moray eels.

References
Ahlberg PE, Clack JA and Blom H 2005. The axial skeleton of the Devonian tetrtrapod Ichthyostega. Nature 437(1): 137-140.
Beznosov PA, Clack JA, Lufsevics E, Ruta M and Ahlberg PE 2019. Morphology of the earliest reconstructable tetrapod Parmastega aelidae. Nature 574:527–531.(971):29-101.
Boisvert CA, Mark-Kurik E and Ahlberg PE 2008. The pectoral fin of Panderichthys and the origin of digits. Nature 456:636–638.
Clack JA 1994. Silvanerpeton miripedes, a new anthracosauroid from the Visean of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences 84 (for 1993), 369–76.
Clack JA 2006. The emergence of early tetrapods. Palaeogeography Palaeoclimatology Palaeoecology. 232: 167–189.
Clack et al. (14 other authors) 2016. Phylogenetic and environmental context of a Tournaisian tetrapod fauna. Nature ecology & evolution 1(0002):1-11.
Cloutier R, Clement AM, Lee MSY, Noël R, Béchard I, Roy V and Long JA 2020. Elpistostege and the origin of the vertebrate hand. Nature https://doi.org/10.1038/s41586-020-2100-8
Daeschler EB, Shubin NH and Jenkins FA, Jr 2006. A Devonian tetrapod-like fish and the evolution of the tetrapod body plan. Nature. 440 (7085): 757–763.
Godfrey SJ 1989. The postcranial skeletal anatomy of the Carboniferous tetrapod Greererpeton burkemorani Romer, 1969. Philosophical Transactions of The Royal Society B Biological Sciences 323(1213):75-133.
Gross W 1941. Über den Unterkiefer einiger devonischer Crossopterygier (About the lower jaw of some Devonian crossopterygians), Abhandlungen der preußischen Akademie der Wissenschaften Jahrgang.
Jarvik E 1952. On the fish-like tail in the ichthyostegid stegocephalians. Meddelelser om Grønland 114: 1-90.
Jarvik E 1996. The Devonian tetrapod Ichthyostega. Fossils and Strata. 40:1-213. Niedźwiedzki G, Szrek P, Narkiewicz K, Narkiewicz M and Ahlberg PE 2010. Tetrapod trackways from the early Middle Devonian period of Poland Nature 463, 43-48.
oi:10.1038/nature08623
Ruta M, Jeffery JE and Coates MI 2003. A supertree of early tetrapods. Proc. R. Soc. Lond. B (2003) 270, 2507–2516 DOI 10.1098/rspb.2003.2524 online pdf Säve-Söderbergh G 1932. Preliminary notes on Devonian stegocephalians from East Greenland. Meddelelser øm Grönland 94: 1-211.
Ruta M and Clack, JA 2006 A review of Silvanerpeton miripedes, a stem amniote from the Lower Carboniferous of East Kirkton, West Lothian, Scotland. Transactions of the Royal Society of Edinburgh: Earth Sciences, 97, 31-63.
Schoch RR and Voigt S 2019. A dvinosaurian temnospondyl from the Carboniferous-Permian boundary of Germany sheds light on dvinosaurian phylogeny and distribution. Journal of Vertebrate Paleontology. DOI: 10.1080/02724634.2019.1577874.
Schultze H-P and Arsenault M 1985. The panderichthyid fish Elpistostege: a close relative of tetrapods? Palaeontology 28, 293–309 (1985).
Smithson TR 1982. The cranial morphology of Greererpeton burkemorani Romer (Amphibia: Temnospondyli). Zoological Journal of the Linnean Society 76(1):29-90.
Swartz B 2012. A marine stem-tetrapod from the Devonian of Western North America. PLoS ONE. 7 (3): e33683. doi:10.1371/journal.pone.0033683
Watson DMS 1929. Croonian Lecture. The evolution of the Amphibia. Philosophical Transactions of the Royal Society, London B 214:189-257.
Westoll TS 1938. Ancestry of the tetrapods. Nature 141, 127–128 (1938).

Source: https://pterosaurheresies.wordpress.com/2026/05/28/the-fin-to-finger-transition-in-one-go/

Before It’s News® is a community of individuals who report on what’s going on around them, from all around the world.

Anyone can join.
Anyone can contribute.
Anyone can become informed about their world.

"United We Stand" Click Here To Create Your Personal Citizen Journalist Account Today, Be Sure To Invite Your Friends.

Before It’s News® is a community of individuals who report on what’s going on around them, from all around the world. Anyone can join. Anyone can contribute. Anyone can become informed about their world. "United We Stand" Click Here To Create Your Personal Citizen Journalist Account Today, Be Sure To Invite Your Friends.

LION'S MANE PRODUCT

Try Our Lion’s Mane WHOLE MIND Nootropic Blend 60 Capsules

Mushrooms are having a moment. One fabulous fungus in particular, lion’s mane, may help improve memory, depression and anxiety symptoms. They are also an excellent source of nutrients that show promise as a therapy for dementia, and other neurodegenerative diseases. If you’re living with anxiety or depression, you may be curious about all the therapy options out there — including the natural ones.Our Lion’s Mane WHOLE MIND Nootropic Blend has been formulated to utilize the potency of Lion’s mane but also include the benefits of four other Highly Beneficial Mushrooms. Synergistically, they work together to Build your health through improving cognitive function and immunity regardless of your age. Our Nootropic not only improves your Cognitive Function and Activates your Immune System, but it benefits growth of Essential Gut Flora, further enhancing your Vitality.

Our Formula includes: Lion’s Mane Mushrooms which Increase Brain Power through nerve growth, lessen anxiety, reduce depression, and improve concentration. Its an excellent adaptogen, promotes sleep and improves immunity. Shiitake Mushrooms which Fight cancer cells and infectious disease, boost the immune system, promotes brain function, and serves as a source of B vitamins. Maitake Mushrooms which regulate blood sugar levels of diabetics, reduce hypertension and boosts the immune system. Reishi Mushrooms which Fight inflammation, liver disease, fatigue, tumor growth and cancer. They Improve skin disorders and soothes digestive problems, stomach ulcers and leaky gut syndrome. Chaga Mushrooms which have anti-aging effects, boost immune function, improve stamina and athletic performance, even act as a natural aphrodisiac, fighting diabetes and improving liver function. Try Our Lion’s Mane WHOLE MIND Nootropic Blend 60 Capsules Today. Be 100% Satisfied or Receive a Full Money Back Guarantee. Order Yours Today by Following This Link.

Comments

Visits:	1,808,903,780
Stories:	8,647,441