Blind and sighted clades derived from lancelets
When eyes first developed beneath the skin of early chordates
one lineage stopped and stayed blind (Fig 1). That led to several extinct Cambrian filter feeders known from extraordinary soft tissue preservation including Haikouella and Yunnanozoon (Fig 1). Hou et al 2021 considered these ‘Bilateria of uncertain affinity.’
Actually, they’re not of uncertain affinity anymore. Just start with simple ancestors, = outgroups, like Enoplus and Branchiostoma (Fig 1). Build on their Bauplan. Take away their eyes. And everything else becomes understandable. Tunicates and salps are extant examples of blind lancelet descendants.
Traditional cladograms too often get this order upside down, due to the simple Bauplan of tunicates and salps.
Figure 1. At the genesis of eyes in chordates, these filter-feeders found no selective pressures to continue seeing things. Only lancelets are still living. Yunnanozoon and Haikouella are among these.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/blind_lancelets_compared588.jpg?w=92″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/blind_lancelets_compared588.jpg?w=315″ tabindex=”0″ role=”button” class=”size-full wp-image-87861″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/blind_lancelets_compared588.jpg” alt=”Figure 1. At the genesis of eyes in chordates, these filter-feeders found no selective pressures to continue seeing things. Only lancelets are still living. Yunnanozoon and Haikouella are among these. ” width=”584″ height=”1896″ />
Figure 1. At the genesis of eyes in chordates, these filter-feeders found no selective pressures to continue seeing things. Only lancelets are still living. Yunnanozoon and Haikouella are among these.
The other clade of lancelet descendants evolved better eyes
that rose from the brain and broke through the epidermis. We humans are in that clade of sighted lancelet descendants. Here (Fig 2) the lineage that led to modern sturgeons is presented. Other lineages, like our own, are longer and much more complex = more transitional taxa.
Figure 2. Several basal lancelet descendants that kept their eyes and improved on them. These were bottom feeders, predators of essentially immobile prey they swept up with ventral oral openings, tubes and eventually, jaws. The appearance of pectoral, pelvic and other fins in this clade is convergent with those same developments in other clades, according to the LRT.
” data-medium-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/sighted-lancelets_compared588-1.jpg?w=134″ data-large-file=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/sighted-lancelets_compared588-1.jpg?w=456″ tabindex=”0″ role=”button” class=”size-full wp-image-87870″ src=”https://pterosaurheresies.wordpress.com/wp-content/uploads/2024/07/sighted-lancelets_compared588-1.jpg” alt=”Figure 2. Several basal lancelet descendants that kept their eyes and improved on them. These were bottom feeders, predators of essentially immobile prey they swept up with ventral oral openings, tubes and eventually, jaws. The appearance of pectoral, pelvic and other fins in this clade is convergent with those same developments in other clades, according to the LRT.” width=”584″ height=”1310″ />
Figure 2. Several basal lancelet descendants that kept their eyes and improved on them. These were bottom feeders, predators of essentially immobile prey they swept up with ventral oral openings, tubes and eventually, jaws. The appearance of pectoral, pelvic and other fins in this clade is convergent with those same developments in other clades, according to the LRT.
Evolution is fascinating the more it is understood.
And the story is not yet completely known. Build your own LRT to confirm, refute or modify these newly recovered interrelationships. Figure out what errors earlier authors made and figure out for yourself what they left for us as enigmas to be resolved.
Allow for convergence. That makes everything simple to understand.
References
Hou X-G et al (9 co-authors) 2003. Bilateria of Uncertain Affinity. In: The Cambrian Fossils of Chengjiang, China: The Flowering of Early Animal Life. researchgate.net/Bilateria_of_Uncertain_Affinity
“The Chengjiang biota is one of the most remarkable fossil discoveries ever made. The Cambrian Fossils of Chengjiang is the first book in English to provide fossil enthusiasts with an overview of the fauna. 100 superb full color plates.”
Source: https://pterosaurheresies.wordpress.com/2024/07/29/blind-and-sighted-clades-derived-from-lancelets/
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