The sand grouse (genus: Pterocles) revisited

The spark for this blogpost:
A PH reader considered the nesting of the sandgrouse Pterocles with the horned screamer, Anhima, a mismatch. And it is a mismatch in terms of size, color, feet, legs, etc. The thing is… in the LRT, where only skeletal traits are tested, no other tested taxon nested closer to Anhima than Pterocles.

Figure 1. Anhima adult and chick compared to Pterocles adults

Figure 1. Anhima adult and chick compared to Pterocles adults

Earlier I only had skull data (Fig. 4) for the genus Pterocles (Figs. 1–3) and with that heretically nested Pteroclesthe sand grouse, with Anhima, the screamer (Fig. 2). Sand grouse have traditionally been nested with pigeons and chickens, or between pigeons and chickens (Shufeldt 1901), which are not related to one another in the large reptile tree (LRT, 1236 taxa).

Figure 1. Skeleton of Pterocles, the extant sand grouse. Note the 'calcaneal' tubers and manual digit zero, along with the very tiny clavicle/furcula (green).

Figure 2. Skeleton of Pterocles orientalis arenarius, the extant black-bellied sand grouse. Note the ‘calcaneal’ tubers and manual digit zero, along with the very tiny clavicle/furcula (green). This is a different species than the skull shown in figure 3, hence the different mandible ventral margin shape and other differences.

Pterocles is phylogenetically miniaturized
compared to its larger sister, Anhima, the horned screamer (Fig. 2). Even so, and despite the much larger sternum and much smaller feet, Pterocles retains a digit zero process that also includes a spike in Anhima. Both taxa have a large ‘calcaneal heel’ behind the distal tibia, rare to absent in other birds. In Pterocles pedal digit 1 does not reach the substrate and the furcula is much smaller. Both share more traits with each other than with any other taxa among the 1236 taxa in the LRT.

In this case, at least,
the addition of the post-cranial data changed nothing in the LRT tree topology. It would have been less ‘trouble’ to have Pterocles nest with pigeons, or chickens, but a good scientist reports results, no matter how they differ from tradition.

FIgure 2. The larger Anhima compared to its smaller sister, Pterocles.

FIgure 3. The larger Anhima compared to its smaller sister, Pterocles. Note the digit zero spur on the manus along with the ‘calcaneal tuber’ behind the distal tibia.

Back in 1901
Shufeldt reported, “the sand grouse constitute a small assemblage of forms, related on one hand to the gallinaceous (chicken-like) birds, and on the other to the pigeons.” The two clades are not related to one another in the LRT. And that statement was made before the invention of the airplane, computer and PAUP.

Figure 1. Pterocles, the chestnut-bellied sandgrouse is not related to pigeons, despite convergent appearances, but more closely related to the screamer, Anhima.

Figure 4. Pterocles, the chestnut-bellied sandgrouse is not related to pigeons, despite convergent appearances, but more closely related to the screamer, Anhima.

The Fulica, Anhima, Petrolcles clade
is a basal one, probably extending back to the Early Cretaceous. It is a sister clade to the chicken/sparrow/parrot clade, far from the New World vulture/pigeon clade.

References
Shufeldt RW 1901. On the systematic position of the sand grouse (Pterocles: Syrrhaptes). The American Naturalist 35 (409):11–16.

 

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