| Eoalulavis | |
|---|---|
 | |
| Life restoration. | |
Scientific classification | |
| Domain: | Eukaryota |
| Kingdom: | Animalia |
| Phylum: | Chordata |
| Clade: | Dinosauria |
| Clade: | Saurischia |
| Clade: | Theropoda |
| Clade: | Avialae |
| Clade: | †Enantiornithes |
| Genus: | †Eoalulavis Sanzet al., 1996 |
| Species: | †E. hoyasi |
| Binomial name | |
| †Eoalulavis hoyasi Sanzet al., 1996 | |
Eoalulavis (from the Ancient Greek:Éōs, "dawn";alula,"bastard wing";avis, "bird") is amonotypic genus ofenantiornithean bird that lived during theBarremian, in theLower Cretaceous around 125 million years ago. The only known species isEoalulavis hoyasi.[1][2]
Its remains came from theKonservat-Lagerstätte ofLas Hoyas,Cuenca,Spain. Theholotype (LH13500), housed in the collection ofMuseo de las Ciencias de Castilla-La Mancha [es], consists on both slab and counterslab preserving mainly the thoracic region, part of the neck and both almost complete forelimbs of an adult specimen.[1] It also preserves remains of thebody,primary,secondary feathers and abastard wing which have been covered by layers oflimonite as a result of thefossilization process.[1] The preservation is consistent with thetaphonomic processes associated with obruption, stagnation and the action ofmicrobial mats in the locality[3] that have yielded a wide variety of examples of soft-tissue preservation (e.g.,connective tissues in fishes andtheropods[3] or insect wings[4]). Most of the osteological features of theholotype became apparent only after itsacid preparation and transference to aresin cast.[2]
According to its initial description,E. hoyasi was roughly the size of aeuropean goldfinch (Carduelis carduelis), with the bony elements of its wings approximately 17 centimeters (7 inches) in length.[1] Later studies estimated that it had a weight of approximately 45 grams (1.6 ounces) and total wingspan (including feathers) of about 26 centimeters (10 inches), giving it proportions similar to those of acommon kingfisher (Alcedo atthis).[5]
One of the most unusual features of this genus lies in the shape of its bonysternum (breastplate). While most early birds had wide sternums,Eoalulavis had a very thin one, with an expanded front end tapering to a point as well as a rear tip with outward-pointing extensions. This form has been described as "spear-shaped" or "fish-shaped" by some.[1][2]
The morphology of the forelimb inEoalulavis is remarkably primitive compared with that of other genera ofenantiornithean birds.[6] The alular and major digits both bear a largeungualphalanx and the minor one bears twophalanx. Also the alular digit extends until the distal end of the majormetacarpal, which is considered a primitive trait within thecladeEnantiornithes.[6]
At the time of its discovery, it was the earliest bird known to possess analula, a batch offeathers on the alular (first) digit that inmodern birds can be separately moved to improve stability at low flight speeds. Later, moreenantiornithean specimens were discovered withalula[7][8] and this fact has consequently strengthened thehypothesis that these animals were able to develop a highly complex and active flight.[2][6] The wide presence of this trait in bothEnantiornithes andOrnithuromorpha, theclade which comprisesmodern birds along with theirfossil counterparts, suggest that the development of thealula, and the flight capabilities that it implies, occur early in the avianevolution, presumably in the base ofOrnithothoraces.[2][9]
The presence ofalula and a complete set ofaerodynamic asymmetric feathers arranged forming a modern wing,[10] indicate well develop flight capabilities, as in many otherenantiornitheantaxa.[6] Its hindlimb morphology remain uncertain as no material of this kind referable to the genus has been found to date. A 2018 study analyzed the proportions ofEoalulavis andConcornis to determine the optimal flight pattern for those genera. The study found that they likely engaged inbounding flight, a form of flight popular among modern small and short-winged birds. A bird engaging in bounding flight alternates between upward-thrusting flaps and short dives with folded wings. The study also found that they were capable of continuous flapping flight, but were likely unable to glide due to having a high body mass to wingspan ratio. The study concluded thatEolalulavis,Concornis, and likely many other enantiornitheans alternated between the fast bounding flight and the slower but more efficient flapping flight depending on the circumstances, similar to modernsongbirds andwoodpeckers.[5]
Theholotype preserves concentrated remains ofcrustaceancuticles in the area of the abdomen, interpreted as its last meal.[2] It provided the first direct evidence of feeding behaviour inEnantiornithes and inMesozoic birds in general, though, since then, more examples of undigested food associated withenantiornithine specimens have been discovered reporting a wide variety of feeding habits.[6] This fact has been interpreted as evidence of anecological role inEoalulavis similar to that of extantwaders; living mainly in the shore seeking for littleinvertebrates in a similar way of modernturnstones.[4]
The locality ofLas Hoyas was in theBarremian aseasonalsubtropicalwetland ecologically dominated by fully aquatic organisms (e.g.:holostean fishes).[4] The avifauna of the locality includes so far two more enantiornitheantaxa: thesparrow-sizedIberomesornis romerali[11] and thestarling-sizedConcornis lacustris.[12]Eoalulavis hoyasi is believed to be the most linked to a semi-aquatic environment of the three.[12]
Thephylogenetic relationships withinEnantiornithes are largely unsolved so far whilst severalphylogenetic analyses have been performed in the last decades.[13][9] However, some groups of Enantiornithes seem to have fairly strong statistical support.[13] In the last cladistic analysis[13]Eoalulavis groups with the Chinese genusLiaoningornis forming amonophyletic group of derived Enantiornithes. Nevertheless, this concrete grouping has not a high statistical support and the enantiornithean status ofLiaoningornis remains currently controversial.[14][15]
Eoalulavis hoyasi presents numeroussynapomorphies that justifies the inclusion of thetaxon within Enantiornithes and the less inclusivecladeEuenantiornithes.[16] These traits include a groove in the inter-osseous surface ofradius or a conspicuousforamen in the dorsal surface of the strut-likecoracoids.[2]
