Eofringillirostrum

Eofringillirostrum; Temporal range: Early Eocene PreꞒ Ꞓ O S D C P T J K Pg N
Scientific classification
Domain:	Eukaryota
Kingdom:	Animalia
Phylum:	Chordata
Class:	Aves
Clade:	Psittacopasseres
Family:	† Psittacopedidae
Genus:	† Eofringillirostrum ; Ksepka, Mayr, & Grande, 2019
Type species
	†Eofringillirostrum boudreauxi; Ksepka, Mayr, & Grande, 2019

Last updated January 02, 2024

Eofringillirostrum is an extinct species of bird known from the Early Eocene Green River Formation of the Western United States and from the Messel Pit in Germany. The genus contains two species, Eofringillirostrum boudreauxi and Eofringillirostrum parvulum. They are the earliest known fossil birds to have a finch-like beak.

Discovery and naming

The holotype of Eofringillirostrum boudreauxi, FMNH PA 793, consists of a complete skeleton preserving impressions of the feathers. It was found in the "sandwich beds" of the Fossil Butte Member of the Green River Formation, near Kemmerer, Wyoming, United States. The holotype of Eofringillirostrum parvulum, IRSNB Av 128a+b, consists of a partial skeleton preserved in slab and counter-slab. The fossil comes from the Messel Formation in Germany. The postcranial remains are poorly preserved in IRSNB Av 128. In 2019, Ksepka, Mayr, and Grande described both species as members of the Psittacopedidae, noting that they were the first birds with finch-like beaks in the fossil record. The generic name Eofringillirostrum comes from the Greek eos, meaning "dawn", Latin fringilla, meaning "finch", and rostrum, meaning "beak", in reference to that anatomical feature. The specific ephitet boudreauxi refers to Terry Boudreaux, who donated the holotype of the American species to the Field Museum. The specific ephitet parvulum is Latin for "small", referring to the size of the bird.^[1]

Description

Eofringillirostrum were small birds, with Eofringillirostrum boudreauxi about as large as a red-breasted nuthatch and Eofringillirostrum parvulum even smaller. They possessed conical, tapering bills with fine tips, much like modern finches, such as the modern American goldfinch. The lower half of the beak curves slightly downward.^[1]

In the postcranial skeleton, the pygostyle is very small. The coracoid has no foramen (opening) for the supracoracoid nerve. The wings are similar to those of other stem group passerine birds, with a short humerus and an ulna that exceeds it in length. The tarsometatarsus is relatively short and is about half the length of the tibiotarsus. On the feet, the trochlea of the fourth metatarsal has an accessory trochlea, separated by the other trochlae by a groove, which indicates that Eofringillirostrum had a zygodactyl foot arrangement, like other Eocene stem passerines. Well-preserved feather impressions allow for measurement of the wings and tail. The wings were relatively narrow, and the tail accounted for about a third of total body length.^[1] The feet were well-adapted for manipulating food items.^[2]

Classification

Eofringillirostrum is similar to the Psittacopedidae, a family of zygodactyl stem-passerines from the early Eocene. Simplified cladogram after Ksepka et al. (2019):^[1]

† Eocuculus

† Psittacopedidae

† Psittacopes

	† Morsoravis sp.

	† Morsoravis sedilis

† Pumiliornis tesselatus

	†Eofringillirostrum parvulum

	†Eofringillirostrum boudreauxi

	† Zygodactylidae

	Passeriformes

A subsequent analysis, published in Mayr (2020),^[2] did not support the positioning of Eofringillirostrum as a psittacopedid and rather placed it as the sister taxon to a clade of Psittacopedidae, Halcyornithidae, and Messelasturidae. Mayr & Kitchener (2022) noted that although there are differences between Eofringillirostrum and unambiguous psittacopedids in foot anatomy, this could be a reuslt of specialised ecology, rather than from a distant relationship.^[3]

Palaeobiology

Eofringillirostrum is the earliest known member of Aves to have specialisations for feeding on small, hard-sheled seeds. Although earlier birds, including taxa from the Cretaceous like Sapeornis and Jeholornis, had a diet including seeds, they do not appear to have possessed adaptations to eat seeds primarily. Indeed, the beak shape shown in Eofringillirostrum is found in modern birds only in groups that feed on seeds. The scarcity of finch-beaked birds in the Eocene apart from Eofringillirostrum suggests that this ecological niche was occupied by relatively few birds in that time period, perhaps because of the small extent of temperate forests and grasslands at the time.^[1]

The last common ancestor of the songbirds is not thought to have consumed seeds, indicating that this ecological niche was filled by different adaptive radiations in the Cenozoic. The diversity of lifestyles among Psittacopedidae, which includes the nectivore Pumiliornis and the thrush-like Morsoravis , are an example of such a radiation. Despite their diversity, the Psittacopedidae, like other zygodactyl stem-passerines, left no living representatives after the Eocene. Ksepka et al. hypothesised that these birds were specialised for cavity nesting, depending on holes in trees for nests. The anisodactyl passerines construct much more varied nests and do not depend on such cavities, and, as such, could have outcompeted other birds with similar feeding specialisations.^[1]

Related Research Articles

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<span class="mw-page-title-main">Lithornithidae</span> Extinct family of birds

Lithornithidae is an extinct, possibly paraphyletic group of early paleognath birds. They are known from fossils dating to the Upper Paleocene through the Middle Eocene of North America and Europe, with possible Late Cretaceous representatives. All are extinct today; the youngest specimen is the currently unnamed SGPIMH MEV1 specimen from the mid-Eocene Messel Pit site.

Psittacopes is an extinct genus of bird from Middle Eocene. One species is recorded from Messel, Germany, and other three possible species are from London Clay, England, one named ?Psittacopes occidentalis in 2022, and the other two unnamed. Its phylogenetic placement within Aves is uncertain; it was originally interpreted as a parrot, but the phylogenetic analysis conducted by Mayr (2015) recovered it as more closely related to the passerines and the extinct family Zygodactylidae.

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Halcyornithidae is an extinct family of telluravian birds thought to be related to the Psittaciformes (parrots), Passeriformes (songbirds), and to the extinct Messelasturidae. Halcyornithids have been found in various Eocene formations in Europe and North America. Widespread and diverse in the Early Eocene of North America and Europe, halcyornithids are not found in locales later than the Middle Eocene. Halcyornithids were small, arboreal birds with zygodactyl feet, with two toes facing forwards and two facing back, a trait shared with other tree-dwelling families of Eocene birds like the Zygodactylidae and the messelasturids. The skull of halcyornithids features a ridge of bone above the eye called the supraorbital process, similar to birds of prey. The relationships of the halcyornithids to other birds remain uncertain. Halcyornithids have been proposed as relatives to owls and as a lineage closer to parrots than to songbirds. Most recently, halcyornithids have been identified as the sister group of the clade including parrots and songbirds. It is also possible that Halcyornithidae is paraphyletic with respect to the Messelasturidae.

Morsoravis is an extinct genus of neoavian bird from the Early Eocene Fur Formation of Denmark. It contains a single named species, Morsoravis sedilis. Fossils of Morsoravis have also been found in the Green River Formation of Wyoming and possibly the Nanjemoy Formation of Virginia.

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Charadriisimilis is an extinct genus of charadriiform birds from the Early Eocene (Ypresian) London Clay of Walton-on-the-Naze, United Kingdom. The genus contains a single species, Charadriisimilis essexensis, known from partial postcranial remains.

Cyrilavis is an extinct genus of halcyornithid bird from the Early Eocene Fossil Butte Member of the Green River Formation, United States. The genus contains two species, Cyrilavis olsoni and Cyrilavis colburnorum.

Pseudasturides is an extinct genus of halcyornithid bird from the Middle Eocene Messel pit in Hesse, Germany, and possibly the Isle of Sheppey, United Kingdom. The genus is represented by a single species, Pseudasturides macrocephalus.

Serudaptus is an extinct genus of halcyornithid bird from the Middle Eocene Messel pit in Hesse, Germany. The genus contains one species, Serudaptus pohli, and is known for long, raptorial claws on its zygodactyl feet.

Parapsittacopes is an extinct genus of psittacopedid bird from the Early Eocene London Clay, United Kingdom. The genus contains one species, Parapsittacopes bergdahli.

Sororavis is an extinct genus of bird from the Early Eocene London Clay of Walton-on-the-Naze, United Kingdom. It contains a single named species, Sororavis solitarius. It is a member of the Morsoravidae.

Morsoravidae is a family of extinct birds known from the Early Eocene of Europe and North America, related to the Psittacopasseres, the clade containing parrots and songbirds. They have specialised feeding ecologies, and one morsoravid, Pumiliornis tesselatus, fed on nectar. The family contains the genera Morsoravis, Pumiliornis, and Sororavis.

References

1 2 3 4 5 6 Ksepka, Daniel T.; Grande, Lance; Mayr, Gerald (2019-02-18). "Oldest Finch-Beaked Birds Reveal Parallel Ecological Radiations in the Earliest Evolution of Passerines". Current Biology. 29 (4): 657–663.e1. doi: 10.1016/j.cub.2018.12.040 . ISSN 0960-9822.
1 2 Mayr, Gerald (2020-11-16). "A remarkably complete skeleton from the London Clay provides insights into the morphology and diversity of early Eocene zygodactyl near-passerine birds". Journal of Systematic Palaeontology. 18 (22): 1891–1906. doi:10.1080/14772019.2020.1862930. ISSN 1477-2019.
↑ Mayr, Gerald; Kitchener, Andrew C. (2022-11-14). "Psittacopedids and zygodactylids: The diverse and species-rich psittacopasserine birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)". Historical Biology: 1–24. doi: 10.1080/08912963.2022.2141629 . ISSN 0891-2963.

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[ksepka-2019-1] 1 2 3 4 5 6 Ksepka, Daniel T.; Grande, Lance; Mayr, Gerald (2019-02-18). "Oldest Finch-Beaked Birds Reveal Parallel Ecological Radiations in the Earliest Evolution of Passerines". Current Biology. 29 (4): 657–663.e1. doi: 10.1016/j.cub.2018.12.040 . ISSN 0960-9822.

[mayr-2020-2] 1 2 Mayr, Gerald (2020-11-16). "A remarkably complete skeleton from the London Clay provides insights into the morphology and diversity of early Eocene zygodactyl near-passerine birds". Journal of Systematic Palaeontology. 18 (22): 1891–1906. doi:10.1080/14772019.2020.1862930. ISSN 1477-2019.

[mayr-2022-3] Mayr, Gerald; Kitchener, Andrew C. (2022-11-14). "Psittacopedids and zygodactylids: The diverse and species-rich psittacopasserine birds from the early Eocene London Clay of Walton-on-the-Naze (Essex, UK)". Historical Biology: 1–24. doi: 10.1080/08912963.2022.2141629 . ISSN 0891-2963.

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