Piciformes and Phylogenetic Relationships
Recent studies have revealed evidence that the avian order Piciformes has a phylogenetic relationship with the orders Primoscenidae and Sylphornithidae. This has resulted in some taxonomic revisions.
Gerald Mayr wrote an article on this research. It is titled The phylogenetic relationships of the early Tertiary Primoscenidae Sylphornithidae and the sister taxon of crown group piciform birds. This article was published in Ornithologen-Gessellschaft in January of 2004. In this portion of the abstract Mayr says:
The phylogenetic relationships of the early Tertiary Primoscenidae and Sylphornithidae are, for the first time evaluated in a cladistic context. Both taxa include small arboreal birds with a permanently (Primoscenidae) or facultatively (Sylphornithidae) retroverted fourth toe. Primoscenidae were hitherto considered to be most closely related to either woodpeckers and allies (Piciformes) or to songbirds (Passeriformes), whereas the Sylphornithidae were classified into the roller-kingfisher-hornbill assemblage ("Coraciformes"). Analysis of 56 morphological characters supports monophyly of a clade including Sylphornithidae and crown group Piciformes and results in sister group relationship between Passeriformes and a clade including Primoscenidae and the early Miocene Zygodactylidae.
According to Mayr, the results of the research eliminates the idea of a phylogenetic closeness between Primoscenidae and Passeriformes. This excerpt tells of how the conclusion was made:
The systematic position of the Primoscenidae appears to be connected to the identity of the sister taxon of crown group Piciformes, as the primary search indicated Upupiformes (hoopoes and wood-hoopoes) and Bucerotiformes (hornbills) as sister taxa of Piciformes, whereas the constrained search resulted in sister group relationship between Coliiformes (mousebirds) and Piciformes. Songbirds do not show the slightest indication of a zygodactyl foot but in these birds the hindtoe is greatly elongated, an alternative strategy to increase the grasping capabilities of the foot.
This portion of text states further points about Primoscenidae:
Primoscenids are now known from a large number of complete skeletons, and from isolated three-dimensionally preserved bones, and were apparently among the most abundant small arboreal birds in the early Eocene, However, as will be shown below, despite their excellent fossil record, phylogenetic assignment of these birds is not straightforward.
All member of the Primoscenidae had zygodactyl feet, i.e. the fourth toe was permanently retroverted, a derived feature they share with piciform birds (woodpeckers and allies), cuckoos (Cuculiformes), and parrots (Psittaciformes). The distal end of the tarsometatarsus most closely resembles that of the early Miocene Zygodactylidae, which are known from isolated distal tarsometatarsi and tibiotarsi only (Ballman 1969a, 1969b).
After the characters were compared and analyzed, the initial cladistic assignment of Zygodactylidae (as stated in the introduction of the article) was declared to be doubtful. Mayr states the point in this excerpt:
Also, if the Zygodactylidae were the sister taxon of the Pici (Mayr 1998 and Fig.2), it is to be expected tha they would exhibit the apomorphies of crown group Piciformes. Additional skeletal elements of these very incompletely known birds may thus further support or refute the phylogeny in Fig. 2.
Mayr also pointed out that an apparent (though not certain) connection between Piciformes and Colliformes was indicated. He says:
Although an analysis of a combined morphological and molecular data set resulted in sister group relationship between Piciformes and Colliformes (Mayr et al. 2003), there is as yet little morphological evidence for such a grouping.
The article shows that research has resulted in some productive work on Piciformes and their phylogenetic relationships with other order. However, more work will have to be done on the possible connections with some groups. As Mayr said, finding a larger number of Zygodactylidae fossils would be helpful in determining if it is a sister taxon to Piciformes.
Neal Robbins
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