Cratoavis

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Cratoavis
Artistic reconstruction of Cratoavis cearensis

Artistic reconstruction of Cratoavis cearensis

Temporal occurrence
Aptium
126.3 to 112.9 million years
Locations
Systematics
Archosauria
Birds (aves)
Pygostylia
Ornithothoraces
Enantiornithes
Cratoavis
Scientific name
Cratoavis
Carvalho , Novas , Agnolín , Isasi , Freitas & Andrade , 2015
Art
  • Cratoavis cearensis

Cratoavis is a genus of extinct, tooth-bearing birds from the group of enantiornithes . The only known species of the so far monotypical genus is Cratoavis cearensis from the Crato formation (Santana group) of the Araripe basin of Ceará in northeastern Brazil .

Etymology and history of research

The generic name Cratoavis is derived from the find layer within the Crato formation and the scientific name of the birds (Aves). The additional species “ cearensis ” refers to the locality in the Brazilian state of Ceará.

Genus and type are only documented by a single fossil that was found in the Pedra Branca quarry near Nova Olinda in the state of Ceará. The holotype is available as a plate and counter plate and is kept in the collection of the Department of Geology (DG) at the Universidade Federal do Rio de Janeiro (UFRJ) under the inventory number "UFRJ-DG 031 Av".

The fossil was already described in detail by Ismar de Souza Carvalho , Fernando Novas , Federico Agnolín , Marcelo P. Isasi , Francisco I. Freitas and José A. Andrade in an article in the science journal Nature Communications in May 2015 , but without assignment to it a genus or species. A valid first description by the same group of authors followed a month later in the Brazilian Journal of Geology.

Fossil evidence and age rating

The holotype and so far the only fossil record comprises the largely articulated partial skeleton of a single individual (standing in an anatomical association). Imprints of feathers can also be seen. Parts of the poorly preserved skull , the spine , the shoulder and pelvic girdles as well as the front and rear limbs are exposed from the side. The skull and cervical spine are twisted compared to the trunk and limbs. They are embedded with their right side in the rock, while the rest of the skeleton is mostly with the left side. Only the proximal caudal vertebrae , the pygostyle and the attached tail feathers are exposed in the dorsal view. The small size and some other skeletal features suggest that the individual may have been a juvenile.

The fossil comes from finely laminated, micritic plate limestone (Nova Olinda member ) of the Crato formation . The latter is placed in the aptium ( Lower Cretaceous ; about 126.3–112.9  Ma ) on the basis of palynological findings . At the time of the first description, the fossil provided the most complete record of a representative of birds from the Lower Cretaceous in the area of ​​the former southern continent of Gondwana .

features

The fossil-preserved specimen of Cratoavis cearensis was about 6 cm long, from the snout to the end of the pygostyle, only about the size of a hummingbird . The most outstanding feature of the fossil are two extremely pronounced control springs , the length of which exceeds the body length by 30%. The rachis of these feathers is broadened like a ribbon. A symmetrical spring vane is only formed at the distal end, approximately over the last 15% of the total spring length. The feather flag seems to consist only of feather branches . There are no indications of barbulae . Feathers of this type do not occur in modern birds, but are known from several other representatives of the enantiornithes, such as Protopteryx , Bohaiornis , Dapingfangornis or Junornis as well as from some of the Confuciusornithidae that do not belong to the enantiornithes .

Another characteristic of the species are the slender and very elongated phalanges of the third toe. This makes the third toe much longer than the corresponding metatarsal bone . The claw of the first toe is much more curved than that of the other toes.

Teeth are not fossilized, but the corresponding alveoli indicate that at least the maxilla was dentate during its lifetime. The conical pygostyle has two nearly parallel longest ridges ventrolaterally . The medial edge of the cavernous bone is clearly concave, while the lateral edge is convex in shape. The raven bone itself is connected to a corresponding socket of the shoulder blade via a pivot pin . The distal end of the third metacarpal bone extends beyond the second metacarpal bone. The distal tarsal bones are fused with the proximal ends of the metatarsals to form the tarsometatarsus . The distal ends of the metatarsal bones, on the other hand, are free and the first metatarsal bone is curved backwards in a "J-shape" at the distal end. All these features show Cratoavis as a typical representative of the enantiornithes.

Systematics

The first descriptors interpreted Cratoavis as a representative of the Euenantiornithes ( sensu Chiappe & Walker , 2002) within the Enantiornithes. However, there is still no general consensus on the internal systematics of the enantiornithes. In particular, the taxon of the Euenantiornithes is not accepted as valid by all authors and has been heavily criticized by David William Steadman and Paul Sereno , among others .

Paleecology

Location and geological map of the Araripe Basin in northeastern Brazil. Nova Olinda Member and Crato Formation are part of the Santana group (dark blue).

The rocks of the Nova Olinda member within the Crato Formation were deposited in an extensive lake or lagoon in the northeastern area of ​​the Araripe Basin. The current distribution of the finely laminated, micritic limestone shows an extent of the water body of at least 75 × 50 km. The lithology and geochemistry of the plate limestone suggest a stably stratified body of water with a well-aerated, near-surface freshwater layer and stagnant, anoxic and / or hypersalinous deep waters.

The vertebrate fauna of the Nova Olinda member is dominated by fish, especially small fish of the genus Dastilbe . Remains of pterosaurs are amazingly the second most common group of vertebrate fossils. Fossils of other vertebrates are much rarer and include various amphibians, the crocodile Susisuchus or the snake-like scaled reptile Tetrapodophis .

Shell remnants from molluscs are not present in the Nova Olinda member. On the other hand, well-preserved plant remains and fossils of mostly land-living arthropods are often found .

With the exception of the fish, a large part of the animal and plant remains were transported via rivers or as wind cargo to the dump of the Nova Olinda member. Accordingly, they represent fauna and flora in the hinterland, which can be characterized as an arid area with a chaparral- like vegetation cover.

With a few exceptions, the representatives of the enantiornithes can generally be interpreted as tree-dwelling insectivores and an illustration attached to the first description shows Cratoavis accordingly. The function of the extra-long control springs has not been fully clarified. Obviously, the springs are not particularly suitable for aerodynamic purposes or otherwise for stabilizing the body balance. It is believed that it is a secondary sex characteristic .

Individual evidence

  1. ↑ a b c d e f g h I. de Souza Carvalho, FE Novas, FL Agnolín, MP Isasi, FI Freitas & JA Andrade: A new genus and species of enantiornithine bird from the Early Cretaceous of Brazil. In: Brazilian Journal of Geology , Volume 45, Number 2, 2015, pp. 161-171, doi : 10.1590 / 23174889201500020001 .
  2. ↑ a b c d e f g h i j k I. de Souza Carvalho, FE Novas, FL Agnolín, MP Isasi, FI Freitas & JA Andrade: A Mesozoic bird from Gondwana preserving feathers. In: Nature Communications , Volume 6, 2015, Article No. 8141, doi : 10.1038 / ncomms8141 .
  3. ↑ a b U. Heimhofer, D. Ariztegui, M. Lenniger, St. P. Hesselbo, DM Martill, AM Rios-Netto: Deciphering the depositional environment of the laminated Crato fossil beds (Early Cretaceous, Araripe Basin, North ‐ eastern Brazil ). In: Sedimentology. Volume 57, number 2, 2010, pp. 677-694, doi : 10.1111 / j.1365-3091.2009.01114.x .
  4. ↑ E. Frey, DM Martill, M.-C. Buchy: A new crested ornithocheirid from the Lower Cretaceous of northeastern Brazil and the unusual death of an unusual pterosaur. In: E. Buffetaut, J.-M. Mazin (Ed.): Evolution and Palaeobiology of Pterosaurs. In: Geological Society of London - Special Publications. Volume 217, 2003, pp. 55-63 ( preview ).
  5. ^ D. Liu, LM Chiappe, F. Serrano, M. Habib, Y. Zhang & Q. Meng: Flight aerodynamics in enantiornithines: Information from a new Chinese Early Cretaceous bird. In: PLoS ONE , Volume 12, Number 10, 2017, e0184637, doi : 10.1371 / journal.pone.0184637 .
  6. ↑ LM Chiappe & CA Walker: Skeletal Morphology and Systematics of the Cretaceous Euenantiornithes (Ornithothoraces: Enantiornithes). In: LM Chiappe & LM Witmer (eds.): Mesozoic Birds: Above the Heads of Dinosaurs , University of California Press, Berkeley / Los Angeles / London, 2002, ISBN 0-520-20094-2 , pp. 559-588, ( Digitized version ).
  7. ↑ DW Steadman: Mesozoic Birds: Above the Heads of Dinosaurs. In: The Auk , Volume 120, Number 4, 2003, pp. 1206-1208, ( online ).
  8. ↑ P. Sereno: Euenantiornithes. In: TaxonSearch: Stem Archosauria 1.0. PC Sereno, July 11, 2005, accessed October 20, 2019 .
  9. ↑ a b c DM Martill, RF Loveridge, JA Ferreira Gomes de Andrade, AH Cardoso: An unusual occurrence of amber in laminated limestones: The Crato Formation Lagerstätte (Early Cretaceous) of Brazil. In: Palaeontology. Volume 48, Number 6, 2005, pp. 1399-1408 ( digitized version ).
  10. ↑ St. W. Salisbury, E. Frey, DM Martill, M.-C. Buchy: A new crocodilian from the Lower Cretaceous Crato Formation of north-eastern Brazil. In: Palaeontographica. Section A: Palaeozoology - Stratigraphy, Volume 270, 2003, pp. 3–47 ( digitized version ).
  11. ↑ DM Martill, H. Tischlinger, NR Longrich: A four-legged snake from the Early Cretaceous of Gondwana. In: Science. Volume 349, number 6246, 2015, pp. 416-419, doi : 10.1126 / science.aaa9208 ( digitized version ).
  12. ^ MP Witton: A new Azhdarchoid Pterosaur from the Crato Formation (Lower Cretaceous, Aptian?) Of Brazil. In: Palaeontology. Volume 51, Number 6, 2008, pp. 1289-1300, doi : 10.1111 / j.1475-4983.2008.00811.x .
  13. ^ Z. Li, Z. Zhou, M. Wang & JA Clarke: A new specimen of large-bodied basal Enantiornithine Bohaiornis from the Early Cretaceous of China and the inference of feeding ecology in Mesozoic birds. In: Journal of Paleontology , Volume 88, Number 1, 2014, pp. 99-108, ( digitized ).

Web links

Commons : Cratoavis  - collection of images, videos and audio files