Overlooked interrelationships document yet another origin of jaws
Taxa like this are what makes fish phylogeny so difficult
based on convergence. Even so, minor discoveries like this are necessary steps toward the ultimate goal of complete resolution and understanding of fish phylogeny.
Today more insights are gained from revised skull labels
that identify tiny jaw elements in Middle Silurian Birkenia (Fig 1) and two specimens of Middle Silurian Lasanius (Figs 2, 3) that link them to Jurassic Leptolepis (Figs 4, 5) and Archaeomene (Fig 6). All these taxa share a very thin (in lateral view) triangular (in ventral view) mandible (= dentary) lacking an articular, prearticular, splenial, angular or any other jaw bone from the more traditional clade of gnathostomes. No presently tested members of this clade remain alive today.
Earlier I made the mistake of not correctly identifying the tiny mandibles of Birkenia (Fig 1) and the larger mandibles of Lasanius (Fig 3) believing toothed mandibles did not develop by convergence with those of placoderm gnathostomes.
The other origin of jaws, the traditional origin of jaws
evolved in placoderms ancestral to sharks, spiny sharks and most bony fish.
Once these fragile jaws had their genesis
two taxa document the continuity of this suite of traits at least into the Latest Jurassic. Little Leptolepis (Figs 4, 5) has a convergent traditional bony fish shape with a single dorsal fin, anal fin and split caudal fin with a heterocercal internal architecture (again, by convergence). Leptolepis has hollow centra (for the notochord) and long curved dorsal ribs. Those ventral elements could be scored as gastralia. The dorsal scutes of Birkenia and Lasanius (Fig 1–3) are reduced-to-missing here.
Archaeomene tenuis
originally Madariscus robustus (Woodward 1895, Bean 2021, Latest Jurassic, 150mya) was originally and traditionally considered a member of the Pholidophorus clade. Here it nests with Leptolepis, Birkenia and Lasanius. Note the tiny premaxilla, convex maxilla, gracile dentary and large orbit.
This appears to be a novel hypothesis of interrelationships.
If not, please provide a citation so I can promote it here.
References
Agassiz L 1843. Recherches sur les poissons fossiles. Imprimerie de Petitpierre et Prince, Neuchâtel.
Bean L B 2021. Revision of the Mesozoic freshwater fish clade Archaeomaenidae. Alcheringa: An Australasian Journal of Palaeontology. 45 (2): 217–259.
Van der Brugghen 2010. New observations on the Silurian anaspid Lasanius problematicus Traquair. Fossil Quarry Articles No. 1.
Woodward AS 1895. The fossil fishes of the Talbragar Beds (Jurassic?). Memoirs of the Geological Survey of New South Wales 9:1-31.
wiki/Archaeomaene
wiki/Archaeomaenidae
wiki/Leptolepis
wiki/Leptolepidae
wiki/Lasanius
Source: https://pterosaurheresies.wordpress.com/2023/10/21/overlooked-interrelationships-document-yet-another-origin-of-jaws/
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.
| Online: | |
| Visits: | 1,641,228,272 |
| Stories: | 8,253,653 |
Whistler Blowers, Insiders
