Zhu, Ahlberg and Zhu 2018 discuss the evolution of vertebrate dermal jaw bones
Just found this paper: a chapter in a book.
Let’s take a look at Zhu, Ahlberg and Zhu 2018, with the proviso that it was written four years before the important report of Early Silurian Shenacanthus by co-author Zhu et al 2022.
From the Zhu, Ahlberg and Zhu 2018 abstract:
“The recent discoveries of maxillate placoderms present unique insights into the evolution of osteichthyan dermal jaw bones, previously considered to be an autapomorphy of the Osteichthyes. Here we briefly review the dermal jaw bones in major gnathostome groups, with focus on taxa close to the transition from stem- to crown-group gnathostomes, i.e., various placoderm subgroups (including antiarchs, arthrodires, ptyctodonts, rhenanids) and basal osteichthyans. In particular, we present a detailed description of the dermal jaw components in the two maxillate placoderms, Entelognathus and Qilinyu.”
By contrast, in the large reptile tree (LRT, 2186 taxa, Figs 1, 4) Qilinyu (Figs 1, 2) does not have a maxilla. Entelognathus (Figs 1, 2b) has a maxilla without teeth. In the LRT rhenanids, like Gemuendina, are Manta relatives, not placoderms.
Zhu, Ahlberg and Zhu continue
“In light of the new morphological data and the comparison between these conditions, we propose the homology between the maxillate placoderm dermal jaw bones and arthrodire
gnathal elements.”
This is correct and warranted, but misses a critical point. According to the LRT (subset Fig 4), the appearance of teeth, originally as small tooth pads (Fig 3), precedes or coincides with the appearance of the thin tooth-bearing layers: the premaxilla, maxilla and dentary fused to larger substrate bones: the nasal, prefrontal and lacrimal.
Again: Maginal tooth-bearing bones first appear as thin layers and patches. Entelognathus is an exception with a maxilla (Fig 2b) lacking teeth. Phylogenetically Entelognathus could have lost maxillary teeth either as a reversal or an autopomorphy, because it is surrounded in the LRT with taxa that have small tooth pads.
Zhu, Ahlberg and Zhu continue:
“We suggest that the inner position of gnathal plates in arthrodires might be secondary. The
dermal jaw bones of eubrachythoracid arthrodires show adaptations comparable to those in osteichthyans, in addition to the better-known convergence of ptyctodonts and holocephalans.”
According to the LRT (subset Fig 4), that inner position of the tooth-bearing bones is not secondary, but primary in arthrodires like Coccosteus and the ANU V244 specimen + Shenacanthus. In chondricthyes following Entelognathus in the LRT (Fig 4), a small patch of tooth-bearing bone appears in Early Silurian Loganellia and Middle Devonian Gladbachus (neither mentioned by Zhu, Ahlberg and Zhu 2018).
The authors do discuss tiny Ramirosuarezia,
(Fig 3) “which is resolved phylogenetically close to the gnathostome crown, together with the newly discovered Silurian maxillate placoderms.”
The authors do not ally Ramirosuarezia with Rhincodon, the whale shark. These two nest together in the LRT (subset Fig 4) despite their differences in size and time. Nor do the authors mention a long list of taxa recovered by the LRT at the base of the gnathostomes, both among sharks and acanthodians (which nest basal to bony fish).
Several pertinent basal gnathostome taxa have been documented since 2018,
(Fig 1) especially by co-author Zhu Y-A. More taxa are included in the LRT (subset Fig 4). So knowledge has progressed and insight has refined since 2018 – chiefly by adding taxa.
Science is a moving frontier. Don’t hold it back by omitting taxa.
References
Zhu Y-A, Ahlberg PA and Zhu M 2018. The evolution of vertebrate dermal jaw bones in the light of maxillate placoderms In: Evolution of and Development of Fishes 71–86.
Zhu Y-A et al (10 co-authors) 2022. The oldest complete jawed vertebrates from the early Silurian of China. Nature 609:954–958. online
Source: https://pterosaurheresies.wordpress.com/2022/12/20/zhu-ahlberg-and-zhu-2018-discuss-the-evolution-of-vertebrate-dermal-jaw-bones/
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.
Please Help Support BeforeitsNews by trying our Natural Health Products below!
Order by Phone at 888-809-8385 or online at https://mitocopper.com M - F 9am to 5pm EST
Order by Phone at 866-388-7003 or online at https://www.herbanomic.com M - F 9am to 5pm EST
Order by Phone at 866-388-7003 or online at https://www.herbanomics.com M - F 9am to 5pm EST
Humic & Fulvic Trace Minerals Complex - Nature's most important supplement! Vivid Dreams again!
HNEX HydroNano EXtracellular Water - Improve immune system health and reduce inflammation.
Ultimate Clinical Potency Curcumin - Natural pain relief, reduce inflammation and so much more.
MitoCopper - Bioavailable Copper destroys pathogens and gives you more energy. (See Blood Video)
Oxy Powder - Natural Colon Cleanser! Cleans out toxic buildup with oxygen!
Nascent Iodine - Promotes detoxification, mental focus and thyroid health.
Smart Meter Cover - Reduces Smart Meter radiation by 96%! (See Video).
| Online: | |
| Visits: | 1,603,888,823 |
| Stories: | 8,151,670 |
Whistler Blowers, Insiders
