Bird neck length correlated to leg length

Böhmer, et al. 2019 report,
“In contrast with mammals, the length of the cervical vertebral column increases as body size increases and, thus, body size does not constrain neck length in birds. Indeed, neck length scales isometrically with total leg length suggesting a correlated evolution between both modules.”

Unfortunately,
Böhmer et al. employed an invalid cladogram (Hackett et al. 2008) based on genes, not traits. So their cladogram wrongly nests flamingoes with grebes, for instance.

Figure 1. The flamingo, Phoenicopterus, compared to the grebe, Rollandia. DNA says these two are more closely related than any other tested taxa. The LRT reports they are not related.

Figure 1. The flamingo, Phoenicopterus, compared to the grebe, Rollandia. DNA says these two are more closely related than any other tested taxa. The LRT reports they are not related.

We learned earlier
that basal birds, no matter their size, had relatively long neck and legs (Fig. 2) in the LRT, a trait-based analysis. Small birds with shorter legs and necks are derived neotonous clades, retaining chick dimensions and proportions into adulthood. That happened over and over and over again in the large reptile tree (LRT, 1470 taxa, subset Fig. 2).

Figure 4. Subset of the LRT focusing on the crown bird clade. Brown taxa are all long-legged. Neotony produces the smaller, shorter-legged, arboreal taxa.

Figure 2. Earlier subset of the LRT focusing on the crown bird clade. Brown taxa are all long-legged. Neotony produces the smaller, shorter-legged, arboreal taxa. This is the cladogram Böhmer et al. should have used. The pattern is more obvious when the family tree is valid.

We looked at
this cladogram of bird leg length (Fig. 2) a year ago here.


References
Böhmer C, Plateau O, Cornette R and Abourachid A 2019. Correlated evolution of neck length and leg length in birds. Royal Society open science 6: 181588. http://dx.doi.org/10.1098/rsos.181588
Hackett SJ et al. 2008. A phylogenomic study of birds reveals their evolutionary history. Science 320, 1763–1768. (doi:10.1126/science. 1157704)

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