Balearica: a unique ‘crane’ with skull bumps

This came with some surprise.
The gray-crowned crane (Balearica regulorum) has beautiful plumage, but under the skin this bird has twin skull bumps on the posterior frontals (Fig. 1).

Figure 1. Balearica regulorum in vivo and two skulls (showing individual variation).

Figure 1. Balearica regulorum in vivo and two skulls (showing individual variation).

Distinct from most cranes,
Balearica has a short rostrum (derived from Charadrius, a neotonous crane with juvenile proportions and size as an adult, based on sister taxa in the large reptile tree, LRT, 1221).

Figure 2. Balearica compared to its sister in the LRT, Charadrius, the plover/kildeer.

Figure 2. Balearica compared to its sister in the LRT, Charadrius, the plover/kildeer.

Balearica regulorum (= Ardea regulorum, Anthropoides regularum, Bennett 1834; extant; 1m tall, 2m wingspan) is the gray crowned crane, and a member of the Gruidae/Gruiformes. In the LRT Balearica is most closely related to the neotenous plovers and kildeers (genus: Charadrius,Fig. 2) and shares with them, a short bill. Twin bumps appear on the posterior frontal. Only four phalanges appear on pedal digit 4, which is as long as pedal digit 3. This trait pops up occasionally, apparently autapomorphic each time.

Using DNA
Prum 2015 nested Balearica with another crane, Grus, the limp kin, Aramus, and the trumpeter, Psophia, which is more closely related to roadrunners and cuckoos in the LRT. Prum 2015 nested Charadrius with Burhinus, close to nestings in the LRT, far from Balearica.

Olson 1985 reports
“From North America there is now a considerable representation of small to medium-sized cranes that are closely related to the modern African crowned cranes of the genus Balearica.” That makes sense with so many plovers and killdeer in North America. I see them all the time on St. Louis parking lots. Never thought they were related the one of the most beautiful birds on the African savanna.

References
Bennett ET 1834. On two new species of Crowned Cranes [Anthropoidea, Vivil.] from Africa. Zoological Society Proceedings pt. 1, 1833:118–119. Oken, Isis, 1835, col. 549–550.
Olson S 1985. The fossil record of birds pp. 80–218 in Farner DS, King JR and Parkes KC (eds.) Avian Biology 8: chapter 2, Academic Press, Inc.
Prum et al. (6 co-authors) 2015. A comprehensive phylogeny of birds (Aves) using targeted next-generation DNA sequencing. Nature 526:569–573. online

wiki/Balearica
wiki/Charadrius

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