Grouping by Ancestral Time Span

There are over 10,000 species in the current International Ornithological Congress listing. Evolution is a process which takes place over long periods of time, much longer than our own life-times. Some species are a few million years old, quite a few are tens of millions of years old and others have an ancestry which can be traced back at least 90 million years.

Geological time periods.

We have to get used to thinking in terms of millions of years. To do this we can take a broad-brush look at the evolution of birds in relation to the geological time-scale periods in which the process takes place.

Cretaceous - 144 to 65 mya.

The earliest birds, if we go back far enough, date back to about 150 mya. They had a bony tail and clawed fingers. Some say that they had a snout with teeth rather than a beak. People generally accept Archaeopteryx as the ancestor of all other birds but there was probably something else in between. This period ended 65 mya with the K/T event (a large asteroid impacted the earth) in which 75% of the plants and animals (including the dinosaurs) were wiped out. Some bird species survived this event.

Palogene - (Palaeocene, Eocene, Oligocene) – 65 to 23 mya.

Following the K/T event and lasting 42 million years, the Paleogene is notable as being the time in which mammals evolved from relatively small, simple forms into a large group of diverse animals. Birds also evolved considerably during this period, changing into forms that were fairly close to the forms we know today.

Neogene - Miocene, Pliocene, Pleistocene, Holocene – 23 mya to present.

Forests began to reduce in area and open grasslands began to develop. Towards the end of the period human beings evolved. Initially they posed a threat to bird populations but now they tend to confuse the evolutionary issue because their activities provide easy pickings for some birds.

Time of evolution of bird species.

Fossil evidence can provide the latest time of evolution although fossils which have not been found or correctly identified may subsequently indicate an earlier time. Molecular data can provide additional information but should always be viewed with caution.

Fossils from the period 65 to 23 mya can usually be clearly attributed to the group of birds we know today (Neornithes) but tend to exhibit a somewhat primitive appearance. Some show a variety of characteristics associated with two or more families or orders.

Fossils from 23 mya onwards generally resemble the birds we know today quite closely.

Ancient ancestors – evolving before 65 mya.

Three groups, each of which appears to share a common ancestor, may well be the precursors of six types of birds which are in the listing of birds known today.

1. Tinamous and Ratites.

Molecular studies suggest that the Tinamous and the Ratites, Ostrich and Rhea and three extinct groups, the Lithornithiformes (Lithornis), the Dinornithiformes (Moas) and the Aepyornithiformes (Elephant birds), evolved about 110 to 120 mya. A gap in fossil evidence for the period 110 to 65 mya means that this cannot be substantiated by fossil evidence. A well preserved fossil of the extinct flying Lithornis, which may be a common ancestor of Tinamous and Ratites, dates back to at least 65 mya.

2. Guans and Game Birds, Swans, Geese and Ducks.

The Horned Guan is part of a distinct and ancient lineage of Wildfowl. DNA data suggests that Cracidae family, in which this bird is listed, originated before 65 mya.

The discovery of Vegavis iaai, which is an offshoot of an ancient lineage of Waterfowl, demonstrates that this group of birds was already diversifying 65 mya.

Molecular evidence suggests that the common ancestor of these two groups, known as Galloansers, evolved about 77 mya but there is currently no fossil evidence to confirm this claim.

3. Penguins, Albatross and Loons.

A prehistoric seabird, Tytthostonyx, is known from 65 mya. This was closely related to the ancestor of birds in the order in which the Albatross is listed.

Molecular evidence suggests that the common ancestor of Penguins and their sister clade (Albatross and possibly Loons) dates back to around 70–68 mya. By 65 mya the lineage was considered to be evolutionarily distinct. The oldest known fossil Penguin species is Waimanu manneringi, which lived in New Zealand about 62 mya.

The earliest fossil Albatrosses date back to about 45 mya, but are only tentatively assigned to the family and none appear to be particularly close to the living forms.

Loons seem to have originated by 65 mya but modern Loons are only known with certainty since about 55 mya.

Other potential ancestors – evolving 65 to 60 mya.

4. Higher Waterbirds - A group of birds including the Heron, Egrets and Bitterns, Hamerkop and Shoebill, Spoonbill and Ibis appear to belong to a close-knit group which have been called "higher waterbirds". The current International Ornithological Committee classification has Pelicans grouped with the Shoebill (Balaenicipitidae), Hamerkop (Scopidae), Ibises and Spoonbills (Threskiornithidae) and Herons, Egrets and Bitterns (Ardeidae).

Some reporters would include Penguins and Albatross and related birds in this group. These lineages appear to have originated around 65 mya. This might imply that this group of birds might be related back to Tytthostonyx, the ancient seabird ancestor in 3 above.

5. Cormorants - are an ancient group; fossilised remains suggest that their ancestors may date back as far as 65 mya. It appears likely that these ancestors were already a distinct group undergoing evolutionary radiation by about 65 mya.

6. Owls - genera Berruornis and Ogygoptynx suggest that Owls were already present as a distinct lineage about 60 mya implying that they may have evolved prior to the K/T event.

7. Parrots – are generally assumed to have shared a common ancestor with various related bird orders, as yet unidentified, which were present around 65 mya.

Birds evolving more recently than 60 mya.

8. Passerines – probably evolved in Gondwanaland around 60 to 50 mya. They apparently evolved out of a fairly close-knit group of "Near Passerines" including the Piciformes (Woodpeckers etc) and Coraciiformes (Rollers and Kingfishers). Claims from molecular studies suggest that these birds evolved as early as 82 mya but this date does not seem to be supported. The following items suggest that 55 mya is a likely evolution date for this group of “Near Passerines”.

9. Trogons - the earliest formally described fossil specimen was found in Denmark and is dated at 54 mya. Other fossils have been found in Germany dated 49 mya. They might constitute a member of the basal radiation of the Coraciiformes or could be closely related to Mousebirds and Owls.

10. Woodpeckers, Toucans and related birds – are listed in order Piciformes. There are some extinct ancestral Piciformes known from fossils which have been difficult to place but at least in part probably belong here. Neanis is an extinct genus probably related to Woodpeckers and Toucans known from 52 mya. The earliest known modern Picids were Piculet-like forms about 25 mya.

11. Birds of prey – Caracaras and Falcons may have evolved 55 mya. Kites, Hawks and Eagles in family Accipitridae have links dating back to about 50 mya with genera we know today being well established by 30 mya.

12. Swifts – appear to have evolved about 50 mya. Fossil Aegialornis is dated at 48 mya.

13. Rails – date back to about 50 mya according to fossil evidence. DNA studies suggest that they diverged from the Gruiformes lineage as long ago as 86 mya but there is so far no evidence to substantiate this. Fossils dated 20 to 30 mya suggest a morphology not greatly different from Rails we know today.

14. Rollers – are listed in order Coraciiformes which is fairly closely related to the Piciformes. The ancestor of these birds may well be a member of the Eocoraciidae family which is very basal. Eocoracias brachyptera is known from fossils in Germany and France dating back to 49 mya.

15. Kingfishers – diverged from the lineasge after the Rollers. Fossil Kingfishers have been described from rocks in Germany, around 40–30 mya.

16. Storks - seem to have arisen about 40–50 mya and were distinct and possibly widespread by 34 mya.. Fossils of living genera date to about 15 mya.

17. Flamingo and Grebe - Flamingos are well attested in the fossil record, with the first unequivocal member of the extant family Phoenicopteridae, Elornis known from 34 mya. The fossil Palaelodids can be considered intermediate between Flamingos and Grebes.

18. Cuckoos – seem to have evolved about 34 mya.

19. Shorebirds, Plovers, Sandpipers – fossils of undisputed Charadriiforms are known only from 35-30 mya. Claims that they originated 65 mya or more do not appear to be substantiated. Fragmented fossil finds often seem to be confused with Waterfowl and Flamingos and it has been suggested that they are part of the “Higher Waterbirds” mentioned in 4 above.

It appears very likely that Waders originated around 40-30 mya. No Vanellinae fossils known before 2.6 mya. Sandpipers probably originated about 34 mya with Gulls appearing slightly later about 33 to 30 mya.

20. Pigeons and Doves – surprisingly the fossil record is poor. A study in 2002 indicated that the ancestors of the Rodrigues Solitaire and the Dodo diverged from the lineage around 23 mya implying that their ancestors were in existence before this date.

Summary by Ancestral time-span.

In the following table I list the time period in mya in which some of the well known Non-Passerine ancestors are believed to have evolved:-

65 60 55 50 45 40 35 25
Tinamou Albatross Roller Falcon Stork Kingfisher Flamingo Pigeon
Ostrich Loon Trogon Swift Cuckoo
Guan Cormorant Woodpecker Rail Sandpiper
Waterfowl Heron Gull
Penguin Owl