#enatiornithine

[harpagornis]

Enantiornithean Earth

Yungavolucris and Halimornis by midiaou and xenopleurodon respectively. Both are real life Cretaceous taxa, showing that these birds were already diversifying into aquatic ecologies.

Enantiornithes are a group of extinct flying theropod dinosaurs that you could reasonably call birds, being the sister group of Euornithes (the group that includes modern birds). However, they differ from our birds in a variety of ways (their name literally means “opposite birds” for a reason):

Several skeletal details, including a tarsometatarsus that is either unfused or half-fused (beginning at the top rather than at the bottom, the opposite than in modern birds), an articulation of the scapula and coracoid that is oppositely shaped (hence the name; the coracoid joint is convex and the scapula joint is concave shaped in enantiornitheans, while the opposite happens in modern birds), a shallower sternum keel with bizarre antler-like projections (which, combined with large crests in their humerus, suggests the muscles lifting the wing were attached to the back as in bats and pterosaurs, rather than all flight muscles being attached to the keel as in modern birds), and a large, rod-shaped pygostyle (which will be relevant later).

Usually toothed jaws instead of beaks, though some taxa did become toothless. Even then, these weren’t capable of cranial kinesis like modern birds (i.e. watch a duck or your pet parrot yawn and you can see them moving their upper jaw; enantiornitheanss are many things but they’re not that abominatory).

All known taxa thus far seem to have been superprecocial: ample sites show buried eggs like those of megapodes, and the hatchlings were already fully flight capable soon after birth.

Unlike modern birds, enantiornitheans lacked a tail fan. They either had contour feathers on their butt like in the rest of the body or had long, streamer-like display feathers, also found in other Cretaceous bird groups but not in modern birds. Some species did have retrices, but they were arranged along the rod-like pygostyle and were not a movable fan, so essentially they were a variation of the tail fronds seen in Archaeopteryx and kin. Note that this did not make flight harder; even modern birds can fly reasonably well without a tail.

Why the opposite birds died out at the end of the Mesozoic while ours survived is unclear. Often, a bias towards arboreal niches is cited, as many enantiornitheans were in fact arboreal, but as the examples above show they also occured in marine and terrestrial niches alongside the ancestors of modern birds. Another possibility is their supreprecocial habits, meaning a more complex ecology as the birds matured since they were already functionally independent since birth, and this did hinder reptiles like lizards so the answer might lay there.

Or, most likely, it was just dumb luck.

Anyways:

Senmuruy hvare by Dave García. A four meter wingspan predator vaguely analogous to the golden eagle and cinnereous vulture, soaring across the northern hemisphere for corpses to dig its long snout into or live mammals and birds to sink its talons into.

Many Cretaceous enantiornitheans were already suspected of being raptorial, so it is only natural that, once pterosaurs were gone, they’d increase in size. Some reach wingspans of fiver meters, but most are more moderately sized at 1.5-3 meter adult wingspans. Smaller sizes are handled by the young, which like all enantiornithes can already fly since birth and occupy distinct ecological niches. Most species protect the nest and moderate its temperature like our megapodes, and a few even display mild parental care, allowing the young to remain in the vicinity until they’re large enough to be competition.

Euodontopteryx anatosuchus, a six-meter wingspan pelagic soarer that occurs in tropical and temperate waters, using its massive wings to ride on thermals like frigatebirds while landing to feed like albatrosses. Males sport streamer-like display feathers. By Dave García.

As noted above, some Cretaceous enantiornitheans were already aquatic, so this trend continued. Some species became divers, mostly wing propelled and some even flightless like our penguins, while others inversely invested in supreme gliding abilities, able to either ride thermals like frigatebirds or wave winds like albatrosses.

The most impressive species are reccord beaters. Divers can be as tall as a man when on land, while soarers can reach wingspans of over 7 meters, competing with flying multituberculates for largest living flying animals. Both groups tend to have long, toothy maws, the teeth alloted into a single row rather than individual sockets; this condition is known in both extinct sea birds and reptiles as well as some living cetaceans, and is known as aulacodonty.

Ghaltavis rex, a three meter tall predator that stalks African and Asian savannas. An apex predator of its own right, an echo of the distant unrelated tyrannosaurs in the form of a bird. By Dave García.

At least one real life enantiornithean, Elsornis, appears to have been flightless. It’s descendents were quick to occupy roles previously taken by non-avian theropods, from ratite-like herbivores to formidable predators that look like the fusion of a terror bird and a tyrannosaur, using their powerful jaws to crush bone.

The relatively long enantiornithean pygostyle allowed them to balance their pelvis/femur joints (a known size inhibittor in our birds) and grow to sizes larger than our timeline’s birds, though species above a ton are fairly rare seeing as mammals got their footing as well.

Bennu seti, a filter-feeding bird from Africa, Eurasia and Australia. Like flamingos it metabolizes carotenoids, giving it an orange colouration. By Dave García.

The Cretaceous Lectavis had long legs in some aspects convergent with those of flamingos. Thus, several enantiornitheans developed wading ecologies, ironically more associated with their euornithean competitors. Some became probers, dipping their maws (or toothless beaks) into the subtrate, while others became piscivores like herons or aquatic plant specialists like some cranes and magpie geese.

Most spectacular is a filter-feeding clade, Bennuidae. These birds modified their teeth into thin, delicate strands like some Cretaceous pterosaurs, and feed by swallowing water and expelling it, trapping prey in the teeth and keratinous spikes in the tongue. Having the nostrils still at the end of the snout, these birds usually feed in a different position from flamingos: rather than upside down, the lower jaw is submerged, in a manner similar to avocets.

Like most opposite birds the young are superprecocial, starting as plover-like birds before transitioning into a filter feeding lifestyle months later. Though some taxa form protective creches like flamingos, though unlike them they do not feed the young.

Like many of our shorebirds, these are continuous flappers, displaying remarkable endurance as they fly non-top for days in their migrations.

#enantiornithes #enantiornithean #enatiornithine #bird #birds #dinosaur #dinosaurs #paleoblr #palaeoblr #speculative zoology #speculative evolution #speculative biology #spec evo

[a-dinosaur-a-day]

Halimornis thompsoni

By Scott Reid on @drawingwithdinosaurs

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Name: Halimornis thompsoni

Name Meaning: Sea Bird

First Described: 2002

Described By: Chiappe, Lamb & Ericson

Classification: Dinosauria, Theropoda, Neotheropoda, Averostra, Tetanurae, Orionides, Avetheropoda, Coelurosauria, Tyrannoraptora, Maniraptoriformes, Maniraptora, Pennaraptora, Paraves, Eumaniraptora, Averaptora, Avialae, Euavialae, Avebrevicauda, Pygostylia, Ornithothoraces, Enantiornithes, Cathayornithiformes

Halimornis was an Enantiornithine from the Mooreville Chalk Formation of Alabama, which was on the coast of the Western Interior Seaway, which is what lead to this Enatiornithine’s name. It lived about 80 million years ago, in the Campanian age of the Late Cretaceous, and it was a small bird with an extensively long wingspan - a body length of 17 centimeters, but a wingspan of 40 centimeters. This ocean going species probably used its large wings to fly above the ocean and search for food there, given that its fossil was found very far away from the nearest shoreline; this is another unique adaptation for an Enantiornithine into a typically Euornithine niche. It had unique knees which probably would have allowed it to be good at swimming as well. It probably fed primarily on fish, and maybe other small birds on the ocean. 

Sources:

Martyniuk, M. P. 2012. A Field Guide to Mesozoic Birds and other Winged Dinosaurs. Pan Aves; Vernon, New Jersey.

https://en.wikipedia.org/wiki/Halimornis

Shout out goes to @tiniest-jo!

#halimornis #halimornis thompsoni #bird #dinosaur #palaeoblr #birblr #tiniest-jo #paleontology #prehistory #prehistoric life #dinosaurs #biology #a dinosaur a day #a-dinosaur-a-day #dinosaur of the day #dinosaur-of-the-day #science #nature #factfile #Dìneasar #דינוזאור #डायनासोर #ديناصور #ডাইনোসর #risaeðla #ڈایناسور #deinosor #恐龍 #恐龙 #динозавр