Euoscines

Belongs within: Passeriformes.
Contains: Meliphagoidea, Corvides, Passerides, Ptilonorhynchidae.

The Euoscines comprise the songbirds, a major and diverse grouping within the Passeriformes. Euoscines are characterised by the presence of four pairs of intrinsic muscles associated with the syrinx; other Passeriformes have less.

A number of basal lineages within the Euoscines are concentrated in the Australasian region. The sister group to all other Euoscines is a clade uniting the bowerbirds (Ptilonorhynchidae) with the Australasian treecreepers (Climacteridae), small, stout insectivorous birds with slightly down-curved bills and short, robust legs with long toes and claws (Internet Bird Collection) that feed by foraging along bark and on the ground. Other basal taxa include the logrunners Orthonyx, terrestrial foraging birds from eastern Australia with the tail tipped by stiff feathershaft spines (Morcombe 2003). The Australian babblers Pomatostomus are noisy, gregarious birds with long, downcurved bills.

The origins of song

Published 18 March 2021

The world is currently home to roughly ten thousand known species of bird. These come in a significant range of varieties and sizes: ostriches, hummingbirds, penguins, sandgrouse. But one particular clade of birds accounts for roughly half of all living species: the true songbirds of the Euoscines.

Though the name ‘Euoscines’ doesn’t appear to have received a whole lot of usage in the literature, the clade it refers to actually has a long history of recognition. The Euoscines are one of the major subgroups of the well-recognised order Passeriformes, the perching birds. Members of the Euoscines include such familiar animals as finches, crows, wrens, swallows, skylarks, sparrows, and a whole host of others. On a morphological basis, Euoscines are mostly united by the distinctive structure of their syrinx, or voice-box, which is controlled by five pairs of intrinsic muscles (Ericson et al. 2002; by way of contrast, the lyrebirds and scrubbirds that form the clade most closely related to the Euoscines have only three pairs). This complex syringeal structure is doubtless a factor in the elaborate songs that characterise many representatives of the clade and from which the group gets its vernacular name. Molecular data has further strengthened the case for the Euoscines.

Whereas the phylogenetic integrity of the Euoscines is no considered by most researchers to be beyond reproach, its exact origins are a little more mysterious. Outside the Euoscines, the members of the Passeriformes fall into three well supported clades. As noted above, the immediate sister group of the Euoscines is a small Australian clade, the Menurae (the Menurae and Euoscines together form the singing birds, the Oscines). Another very small clade, the New Zealand wrens of the Acanthisittidae, is thought to represent the sister group of all other Passeriformes. The largest clade of Passeriformes outside the Euoscines is the Suboscines, whose members include such examplars as the broadbills and pittas of the Old World tropics, and the antbirds, tapaculos and tyrant flycatchers of the New World. The Suboscines form the sister clade to the Oscines.

We also have a fairly clear idea of basal relationships within the Euoscines, primarily from molecular data. I won’t dwell on details here (I am aware that while litanies of names can hold a lot of interest for myself, others may find them more tedious) but a detail that has garnered attention is that a preponderance of the basal euoscine lineages are enitrely or predominantly Australasian. This, together with the Australasian distribution of two of the other three major passerine clades, has lead to the proposal that Australasia represents the ancestral homeland for the Euoscines as a whole. But when did the Euoscines first make their appearance?

This is where things begin to get fuzzier. The fossil record of Passeriformes, as for many other birds, is very patchy and often difficult to interpret. Possible passerine bones have been identified from the early Eocene of Australia but they are fragmentary and their identity has been questioned. The earliest well-preserved passerines come from the early Oligocene of Europe (Bochenski et al. 2021). These fossils preserve features indicating that at least the oscine and suboscine lineages had diverged by this time. Attempts to apply molecular dating to the passerine phylogeny, however, have lead to proposals that the major lineages of passerines diverged much earlier, during the Cretaceous era in fact. The divergence of the passerines has then been linked to the break-up of Gondwana, beginning with the isolation of the New Zealand wrens as New Zealand separated from Antarctica about 80 million years ago.

Personally, I find this completely incredible. Firstly, it implies a gap of at least 25 million years or so at the beginning of the passerine fossil record (if we accept the Australian fossils as passerines). I’ve already noted that passerines do not have a great fossil record overall, particularly in the Southern Hemisphere where they are supposed to have originated, but other small birds do have a decent fossil record in the Northern Hemisphere during this time period. The absence of passerines from Europe and North America in the Palaeocene and Eocene does seem likely to be genuine. Secondly, it implies the survival through the devastation of the end-Cretaceous extinction event of not just at least three lineages of passerines but also those bird lineages that diverged before the passerines. At a bare minimum, that requires at least ten clades of birds surviving the Cretaceous and more than likely requires significantly more, most of those lineages also having no recognisable Cretaceous fossil record. Meanwhile, all other non-bird dinosaurs that we do know were around, many of them ecologically very similar, were completely wiped out. Thirdly (and this is perhaps the one that really gets me), it requires that these passerine lineages divided by continental drift then failed to disperse enough over the next eighty million years to obscure the imprint of said drift. Need I remind you that birds can fly? Hand-waving explanations such as the members of many of these early-diverging lineages being poor fliers, or the northern and southern continents being further apart at the time, just don’t cut it in my opinion. Why should we assume that if modern Acanthisittidae or Menurae are poor fliers, their extinct relatives also had to be? Eighty million years seems like more than enough time for variation in flight strength to evolve. And are Suboscines even any more prone to being poor fliers than Euoscines? As for the greater distance between continents, passerines have made their way to isolated oceanic islands (such as those in the mid-Atlantic) that were never close to any landmass. Phylogenetic evidence suggests that some modern passerine groups are indeed the descendants of long-distance dispersals, such as the South American vireos being apparently descended from Asian ancestors, or Hawaiian honeycreepers originating from near the Arctic. And of the previously mentioned European Oligocene passerines, some such as Wieslochia weissi were possibly not part of the Suboscines + Oscines clade (Manegold 2009), indicating that passerines of this grade could indeed make the ocean crossing. So no, the idea of Cretaceous songbirds is just not something I buy right now.

Basal Australasian songbirds

Published 24 September 2025

As described in the above section, current songbird phylogenies suggest an Australo-Papuan origin for the group, with many early-diverging lineages endemic to that area. Among these are three phylogenetically isolated families that I thought I would go into some more detail on today: the Climacteridae, Pomatostomidae and Orthonychidae.

The Climacteridae, Australasian treecreepers, are two genera of small, stocky passerines with medium-length, slightly decurved bills and short but strong legs (Noske 2007). As their vernacular name indicates, climacterids forage for the insects that make up most of their diet by climbing on the surface of tree trunks. Their characteristic position in this activity is head upwards with one foot typically in front of the other. The tongue of climacterids has a fringed tip that presumably aids in extracting insects from concealed locations under bark. Unlike many trunk-climbing birds, however, climacterids lack stiffened tail feathers, and primarily support themselves on the trunk surface by their feet only. Said feet have long toes and claws, and a system of extensors that is unique among passerines: the hind toe lacks the ligaments that couple it to the fore toes in other songbirds, so climacterids are able to raise and rotate the hind toe independently in order to improve its grip on uneven surfaces.

Like many other trunk-climbing passerines, climacterids were historically included in the family Certhiidae with the Holarctic treecreepers. However, though the two groups are similar in external appearance, it was recognised as early as the 1960s that they exhibited significant morphological differences. Nevertheless, it took until the advent of molecular phylogenetics to firmly recognise the currently accepted position of climacterids as the sister group to the bowerbirds at the base of the Euoscines. The two genera of climacterids are distinguished by the longer legs and stouter bill of Climacteris species, and the presence of a terminal notch on the upper mandible in Cormobates. The wings of Cormobates species contain nine secondaries whereas those of Climacteris contain six. Climacteris species are often found in drier forest habitats than Cormobates.

The Pomatostomidae, Australasian babblers, are five species of medium-sized terrestrial birds with long tails and strong legs (Matthew 2007). The bill is relatively long and decurved, and primarily used to collect insects and other arthropods at ground level. Pomatostomids are highly social, and typically found in groups of two to fifteen individuals. They are also vocal, producing a wide variety of sometimes loud calls. One species, the grey-crowned babbler Pomatostomus temporalis, produces antiphonal calls, in which the primary breeding pair (and only the primary pair) of a group performs a ‘ya-hoo’ duet, the female producing the ‘yah’ in response to the male’s ‘awoo’.

Pomatostomids bear a strong resemblence to the Asian scimitar babblers of the genus Pomatorhinus, even to the presence in most species of a prominent white stripe above the eye. Nevertheless, molecular phylogenetics confirms that the two groups are not closely related; scimitar babblers are part of the broad sylvioid radiation with the true warblers and babblers. Authors have differed on whether the pomatostomid species should be included in a single genus Pomatostomus, or whether the New Guinea babbler P. isidorei should be assigned to its own genus Garritornis. This species differs from other pomatostomids in its overall rufous coloration and yellow rather than black bill.

Potentially related to the pomatostomids are the three species of logrunner in the genus Orthonyx. These are medium-sized, stocky birds with short bills bearing terminal maxillary notches (Boles 2007). The feathers of the relatively short tail bear stiffened shafts that protrude beyond the ends of the vanes. Like pomatostomids, logrunners are terrestrial foragers on small invertebrates. They have a distinctive manner of foraging by clearing leaf litter with the strong feet, using the alternate foot and stiffened tail to support the body while one foot is engaged in this manner. Food items disturbed by this behaviour are eaten by the logrunner; other small birds and mammals may follow foraging logrunners to collect invertebrates that the logrunner misses. Their vigorous scratching results in the production of clear rounded patches up to twenty centimetres in diameter on the forest floor. So extensive is the degree of litter turn-over produced in this way that the largest logrunner species, the chowchilla O. spaldingii, has been observed to have a significant impact on the survival of tree seedlings.

Systematics of Euoscines

<==Euoscines [Accentorinae, Corvida, Liotrichidae, Phyllorninae, Phyllornithidae, Polymyodi]
    |--+--MeliphagoideaJF11
    |  `--+--+--CorvidesOF19
    |     |  `--PasseridesOF19
    |     `--+--Orthonychidae [Ornythoncidae]OF19
    |        |    |--Sphenostoma Gould 1838 [Sphenostomidae]B94
    |        |    |    `--S. cristatum Gould 1838 [incl. S. cristatum occidentale Mathews 1912]WS48
    |        |    `--Orthonyx Temminck 1820 [=Ornythoncus (l. c.)]B94
    |        |         |  i. s.: O. kaldowinyeriOF19
    |        |         |         O. spinicaudaR66
    |        |         |--O. temminckiiBKB15
    |        |         `--+--O. novaeguineaeBKB15
    |        |            `--O. spaldingiiBKB15
    |        `--Pomatostomidae [Pomatostominae]OF19
    |             |--Garritornis isidoreiAP21
    |             `--Pomatostomus Cabanis 1851B94
    |                  |--P. isidoreiBKB15
    |                  `--+--+--P. halliBKB15
    |                     |  `--P. temporalis (Vigors & Horsfield 1827)BKB15, WS48 [=Pomatorhinus temporalisWS48]
    |                     |       |--P. t. temporalisWS48
    |                     |       `--P. t. rubeculus (Gould 1839) (see below for synonymy)WS48
    |                     `--+--P. ruficepsBKB15
    |                        `--P. superciliosus (Vigors & Horsfield 1827)JT12, WS48 (see below for synonymy)
    `--+--PtilonorhynchidaeJF11
       `--ClimacteridaeJF11
            |--CormobatesJF11
            |    |--C. leucophaeus (Latham 1802) [incl. Climacteris scandens Temminck 1824]CC10
            |    |    |--C. l. leucophaeus [incl. C. l. grisescens, C. l. metastasis]M03
            |    |    |--C. l. intermediusM03
            |    |    `--C. l. minorM03
            |    `--C. placensJF11
            `--Climacteris Temminck 1820B94
                 |  i. s.: C. affinis Blyth 1864WS48
                 |           |--C. a. affinisWS48
                 |           `--C. a. superciliosa North 1895 [incl. C. erythrops neositta Mathews 1912]WS48
                 |         C. leucophaea (Latham 1801)MW91
                 |         C. melanurus Gould 1842JT12, WS48
                 |           |--C. m. melanurusWS48
                 |           `--C. m. wellsi Ogilvie-Grant 1909 [incl. Whitlocka wellsi straita Mathews 1923]WS48
                 |         C. pyrrhonotaR87
                 |--C. erythropsBKB15
                 `--+--C. picumnusBKB15
                    |    |--C. p. picumnusM03
                    |    `--C. p. melanotaM03
                    `--C. rufus Gould 1840BKB15, WS48 [incl. C. rufa obscura Carter 1910WS48]

Pomatostomus superciliosus (Vigors & Horsfield 1827)^{JT12, WS48} [=Pomatorhinus superciliosus^WS48; incl. Pomatorhinus superciliosus ashbyi Mathews 1911^WS48, Pomatorhinus superciliosus gwendolenae Mathews 1912^WS48]

Pomatostomus temporalis rubeculus (Gould 1839) [=Pomatorhinus rubeculus; incl. Pomatorhinus temporalis nigrescens Mathews 1912]^WS48

*Type species of generic name indicated

References

[AP21] Arlott, N., & B. van Perlo. 2021. Collins Birds of the World. William Collins.

Bochenski, Z. M., T. Tomek, M. Bujoczek & G. Salwa. In press 2021. A new passeriform (Aves: Passeriformes) from the early Oligocene of Poland sheds light on the beginnings of Suboscines. Journal of Ornithology.

[B94] Bock, W. J. 1994. History and nomenclature of avian family-group names. Bulletin of the American Museum of Natural History 222: 1–281.

Boles, W. E. 2007. Family Orthonychidae (logrunners). In: Hoyo, J. del, A. Elliott & D. A. Christie (eds) Handbook of the Birds of the World vol. 12. Picathartes to tits and chickadees pp. 338–347. Lynx Edicions: Barcelona.

[BKB15] Burleigh, J. G., R. T. Kimball & E. L. Braun. 2015. Building the avian tree of life using a large-scale, sparse supermatrix. Molecular Phylogenetics and Evolution 84: 53–63.

[CC10] Checklist Committee (OSNZ). 2010. Checklist of the Birds of New Zealand, Norfolk and Macquarie Islands, and the Ross Dependency, Antarctica 4^th ed. Ornithological Society of New Zealand and Te Papa Press: Wellington.

Ericson, P. G. P., L. Christidis, M. Irestedt & J. A. Norman. 2002. Systematic affinities of the lyrebirds (Passeriformes: Menura), with a novel classification of the major groups of passerine birds. Molecular Phylogenetics and Evolution 25: 53–62.

[JT12] Jetz, W., G. H. Thomas, J. B. Joy, K. Hartmann & A. Ø. Mooers. 2012. The global diversity of birds in space and time. Nature 491: 444–448.

[JF11] Jønsson, K. A., P.-H. Fabre, R. E. Ricklefs & J. Fjeldså. 2011. Major global radiation of corvoid birds originated in the proto-Papuan archipelago. Proceedings of the National Academy of Sciences of the USA 108 (6): 2328–2333.

Manegold, A. 2009. The early fossil record of perching birds (Passeriformes). Palaeontologia Africana 44: 103–107.

Matthew, J. S. 2007. Family Pomatostomidae (Australasian babblers). In: Hoyo, J. del, A. Elliott & D. A. Christie (eds) Handbook of the Birds of the World vol. 12. Picathartes to tits and chickadees pp. 322–336. Lynx Edicions: Barcelona.

[MW91] Millener, P. R., & T. H. Worthy. 1991. Contributions to New Zealand’s late Quaternary avifauna. II: Dendroscansor decurvirostris, a new genus and species of wren (Aves: Acanthisittidae). Journal of the Royal Society of New Zealand 21: 179–200.

[M03] Morcombe, M. 2003. Field Guide to Australian Birds 2^nd ed. Steve Parish Publishing.

Noske, R. A. 2007. Family Climacteridae (Australasian treecreepers). In: Hoyo, J. del, A. Elliott & D. A. Christie (eds) Handbook of the Birds of the World vol. 12. Picathartes to tits and chickadees pp. 642–660. Lynx Edicions: Barcelona.

[OF19] Oliveros, C. H., D. J. Field, D. T. Ksepka, F. K. Barker, A. Aleixo, M. J. Andersen, P. Alström, B. W. Benz, E. L. Braun, M. J. Braun, G. A. Bravo, R. T. Brumfield, R. T. Chesser, S. Claramunt, J. Cracraft, A. M. Cuervo, E. P. Derryberry, T. C. Glenn, M. G. Harvey, P. A. Hosner, L. Joseph, R. T. Kimball, A. L. Mack, C. M. Miskelly, A. T. Peterson, M. B. Robbins, F. H. Sheldon, L. F. Silveira, B. T. Smith, N. D. White, R. G. Moyle & B. C. Faircloth. 2019. Earth history and the passerine superradiation. Proceedings of the National Academy of Sciences of the USA 116 (16): 7916–7925.

[R66] Ramsay, E. P. 1866. Remarks upon the new species of Atrichia and on A. clamosa of the west coast. Proceedings of the Zoological Society of London 1866: 439–440.

[R87] Ramsay, E. P. 1887. Descriptions of Australian birds’ eggs. Proceedings of the Linnean Society of New South Wales, series 2, 1 (4): 1141–1152, pl. 19.

[WS48] Whittell, H. M., & D. L. Serventy. 1948. A systematic list of the birds of Western Australia. Public Library, Museum and Art Gallery of Western Australia, Special Publication 1: 1–126.