An ancient bird with an extraordinarily long toe

There’s a new paper in Current Biology that details the finding of a very unusual bird in Burmese amber—a bird with one huge toe and weird bristles on its feet. You can read it with UnPaywall by clicking on the screenshot below (pdf here, reference at bottom).

The specimen, uncovered by amber miners five years ago, consists of a lower right leg and foot, as well as some feathers (both those attached to the leg and flight feathers free in the amber). It dates back about 99 million years, to the middle Cretaceous, when flying birds had already evolved from reptiles. Since it was a new species (the first ever described from amber), the authors gave it the binomial Elektorornis chenguangi, with the genus name meaning “amber bird”.  Phylogenetic analysis places the species in the Enantiornithes, a bird family that went extinct without descendants at the K/T boundary—about 66 million years ago when the dinosaurs also began to die out. (All modern birds belong to the clade Neornithes, a group within the subclass Aves.)

Briefly, there are two remarkable features of this bird—features that may be connected.

The first is that the third digit on the foot is much longer than the second and fourth digits: about 41% longer. It’s also more curved than the other toes. That disproportionality is unique among all known birds, living or extinct. (The specimen was at first thought to belong to an extinct lizard, but it was immediately clear to experts that this was a bird.)

You can see the long claw in the Figure below, both to the left and in the drawing in the center. On the right you can see the second unusual feature: the scutellae scale filaments (SSFs), bristly feathers on the feet and legs.

(From paper) A) HPG-15-2 overview, with inset providing greater detail on foot, arrowheads marking different apices of unguals and ungual sheathes where visible, and red arrow marking base of mt III 4 shared with (D). (B and C) Osteological details. (D) Tuft of elongated SSFs near apex of mt III ph 3, with horizontal arrowhead marking edge of reticulae from digital pad, inclined arrowhead marking edge of scute, white arrow marking sloughed reticulae, and red arrow marking base of ungual in (A). (E) Detail of lowermost SSFs in (D), showing hollow cores (arrowheads) and mottled outer walls, presumably due to feather oils. Fe, femur; fi, fibula; lc, lateral condyle; mc, medial condyle; mt, metatarsal and corresponding digit; ph, phalanx; tb, tibia. Scale bars, 5 mm in (A); 1 mm in (A) inset; 0.5 mm in (D); and 0.25 mm in (E). See also Figures S1, S2, and S4.

The authors conclude that the configuration of the foot itself indicates that it was a perching (“arboreal”) bird. But what about that toe? When I first saw the figure, I thought the toe must have been for extracting prey (probably insects) from bark and tree holes, sort of like what the aye-aye (Daubentonia madagascariensis—a bizarre lemur with an elongated digit—does. And the possible sensory nature of the foot bristles would help with that task. Great minds think alike, for that is the authors’ own suggestion.

The figure below is of lesser interest to us; it shows some of the flight feathers from the wing that were also preserved in the amber. What is most important is that the feathers are asymmetrical, with the leading filaments (“vanes”) being less than half as long as the trailing filaments. That is an indication of flight, as shown in these modern bird feathers from Quora, which also explains the aerodynamic reason for the asymmetry.

Here’s a figure showing the feathers, which still bear brown pigmentation in the amber:

(From paper): (A) Overview of primary and secondary feather exposure at polished edge of amber piece, with inclined arrows marking primary rachises (P1 and P2 weakly distinguished from secondaries and marked in red); vertical arrows mark secondaries; horizontal arrows mark pale areas in wing; and lettered circles mark positions of (B) and (C). (B) Weakly pigmented reduced barbules from primary barbs in leading edge of wing. (C) Dark brown barbules from primary barbs in base of posterior vane of primary. Scale bars, 2 mm in (A); 0.25 mm in (B) and (C). See also Figures S1 and S2.

The authors are a bit waffle-y about this third toe, saying “the function of the elongated third toes is uncertain”. And indeed, it is uncertain. But in the abstract they are a bit more certain, saying “we suggest that the elongated third digit was employed in a unique foraging strategy,” i.e., extracting food (probably insects) from trees. And, given the presence of what are likely sensory bristles on the toes, similar to sensory bristles around the mouths in some New Zealand birds, including the kiwi, that makes sense. Here are the sensory bristles on a kiwi’s face, which undoubtedly help it forage and navigate at night, since the species are nocturnal:

Photo from BirdEden.

Here, for comparison with the new bird, is the thin but long middle finger of an aye-aye:

Photo from Jenman Safaris

Finally, here’s an aye-aye using its elongated finger to probe for insects. (That finger has a ball and socket joint and can swivel 360°.) I suspect that Elektorornis chenguangi did a similar thing.

Will we ever know? I don’t see how, but speculation is fun, and may lead to some testable predictions.

___________

Xing, L., J. K. O’Connor, L. M. Chiappe, R. C. McKellar, N. Carroll, H. Hu, M. Bai, and F. Lei. 2019. A New enantiornithine Bird with unusual pedal proportions found in amber. Current Biology. Published:July 11, 2019. DOI:https://doi.org/10.1016/j.cub.2019.05.077

 

 

16 Comments

  1. BJ
    Posted July 14, 2019 at 9:43 am | Permalink

    The aye-aye (or Why Aye, for the Mark Knopfler fans like me out there) was my immediate thought. The big question is whether the bird could straighten the finger, or if it was always that curved; if it’s the latter, it makes it more difficult to believe it’s for foraging specifically in the way the aye-aye does, but it could still be for foraging in some other ways.

    The picture of the aye-aye’s finger just made me think of E.T.

  2. Posted July 14, 2019 at 9:50 am | Permalink

    The aye aye fishing for bugs with its elongated digit reminds me of a chimpanzee fishing for termites with a twig. The aye aye comes equipped with its own fishing “tool.”

    Perhaps I lack imagination, but I can’t think what else the amber bird’s elongated toe would be good for. Grasping a branch while roosting?

  3. Roger
    Posted July 14, 2019 at 9:55 am | Permalink

    Very selfish bird. He should save some of that toe for the other birds.

  4. DrBrydon
    Posted July 14, 2019 at 10:17 am | Permalink

    Coke? Thanks for the write-up, Jerry. I skip this stuff in the general media, and wait for you.

  5. Bruce E Lyon
    Posted July 14, 2019 at 11:04 am | Permalink

    Thanks for this Jerry. Interesting writeup about an interesting bird. A very picky taxonomic point–calling this an extinct ‘family’ of birds is probably not technically correct. The opposite birds were a completely different (and I believe independent) evolution of birds compared to all living birds. It is pretty interesting that birds were invented twice! I am not sure what taxonomic status to call but I am sure there might be readers who know the taxonomy of the various extinct lineages.

  6. Posted July 14, 2019 at 11:18 am | Permalink

    Reblogged this on The Logical Place.

  7. Liz
    Posted July 14, 2019 at 11:20 am | Permalink

    My first thought was of the Elektorornis chenguangi using the longer digit to tap on a clam or mussel and then taking the meat out. This is very interesting. I also find the Cretaceous-Paleogene boundary interesting. It was most likely the meteorite that was responsible for the mass extinction? I remember learning about a few other proposed reasons.

  8. Posted July 14, 2019 at 1:25 pm | Permalink

    As I was reading (with great interest), it seemed likely to me as well that this bird was specialized for extracting grubs like the aye-aye.

    Another possibility is for extracting snails from their shell. The curved toe would be helpful for that, but I suspect the sensory bristles demotes that idea a bit.

  9. grasshopper
    Posted July 14, 2019 at 4:14 pm | Permalink

    My thoughts are that such a long and delicate toe could be a handicap if it was used for probing. It could easily break if it was deeply inserted in a hole and the bird got startled and turned sharply. Depending on the size of the hole, of course. Perhaps it was more attuned to fossicking about in leaf litter.

  10. phar84
    Posted July 14, 2019 at 4:26 pm | Permalink

    “The specimen, uncovered by amber miners”

    Didn’t know there were amber miners. Should they be somewhat educated about fossils as amber tend to hold well preserved specimen?

  11. grasshopper
    Posted July 14, 2019 at 4:33 pm | Permalink

    The toe on each foot seems equally developed, so can we assume the bird was amber-dextrous?

    • Roger
      Posted July 14, 2019 at 10:48 pm | Permalink

      That pun really resin-ates with me.

  12. C.
    Posted July 14, 2019 at 4:55 pm | Permalink

    The foot looks quite lizard-like, or more specifically to my amateur eyes anolis-like, and somewhat like the feet of the tree-climbing/hopping/spiraling American brown creeper, Certhia americana. I’m not convinced the elongated toe need be a tool for extraction, but perhaps very helpful in grasping and climbing trees. Just throwing that out there since we are speculating.

  13. grasshopper
    Posted July 14, 2019 at 7:04 pm | Permalink

    The toe could be an encumbrance when roosting on a thin branch, but might actually allow better purchase when roosting on thicker boughs.

  14. ThyroidPlanet
    Posted July 16, 2019 at 6:36 am | Permalink

    Sub

    By the way, I have been clicking the link in the email since it arrived in my inbox. The link opened a page on WordPress that said something like “page not found”. Today at last, I figured it might be found by manually going through posts – and voila.


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