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Re: Jeholornis prima discussion



At 9:28 PM -0400 7/27/02, Nicholas Gardner wrote:
From: "Mickey Mortimer" <Mickey_Mortimer111@msn.com>
Reply-To: Mickey_Mortimer111@msn.com
To: <dinosaur@usc.edu>
Subject: Jeholornis prima discussion
Date: Sat, 27 Jul 2002 15:18:44 -0700

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:o(

But what I got was the whole thing, which I reproduce below on the off-chance it might get through. (see also next message) -- Jeff Hecht

At 3:18 PM -0700 7/27/02, Mickey Mortimer wrote:
I've been informed by last attempt to post this was truncated for some reason. Here's a second try....

This newly named bird has been quite a topic of discussion on the DML lately. Here's some information-

Zhou and Zhang unfortunately do not illustrate the whole specimen with line drawings, just the tail, pelvis and distal tibiotarsi. This results in less information being available for most parts of the skeleton, as Yixian fossils are often difficult to interpret from photos.

Holotype- (IVPP V13274) incomplete skull, mandibles, hyoids, five cervical vertebrae, at least three dorsal vertebrae, dorsal ribs, gastralia, last sacral vertebra, twenty-two caudal vertebrae, chevrons, partial scapula, coracoids, partial furcula, partial sternum, forelimbs (humerus 110 mm, ulna 109 mm, metacarpus 47 mm), pelvis (pubis 64 mm), femora (75 mm), tibiotarsi (88 mm), metatarsal fragments (47 mm), pedal phalanges and unguals

The specimen is from the Jiufotang Formation (Early Aptian?) of Liaoning, though Zhou and Zhang say Confuciusornis is an associated fossil, and this genus is from the earlier Yixian Formation.

Apomorphies are- lacrimal with two vertically elongate fossae on shaft; jugal dorsal process angled anteriorly; dentary decurved; distal tip of dentary expanded ventrally; elongation of caudal centra to over three times centrum height starts at fourth vertebrae; two caudals with transverse processes; chevrons contact at distal tips; chevrons all dorsoventrally compressed; fenestra in lateral sternal process; manual phalanges III-1 and III-2 form a bow-shaped structure; proximodorsal process of ischium expanded distally.

The skull seems to be in dorsal view and crushed, with the premaxillae not preserved. The naris is smaller than the antorbital fenestra. The maxilla is said to be reduced and edentulous, with an ascending process not visible laterally. The jugal is elongate and low with an odd dorsal process that projects anterodorsally, forming an acute angle with the anterior process. Zhou and Zhang say the posterior curvature is similar to Sinornithosaurus, but the dorsal process is broken off in that genus (Xu and Wu, 2001). They say the lacrimal has an elongate posterior process, and two distinct dorsoventrally elongate fossae on the shaft. The quadrate has no quadratojugal cotyla and is not pneumatic. Details are hard to observe, but the squamosal, frontal, parietal, palatine, ectopterygoid and pterygoid are also preserved.
The mandibles are well preserved, even with a good medial view of one available. The dentaries are robust, decurved and have a slightly expanded ventral tip. There is a strong symphysis and no external mandibular fenestra or posterior dentary processes. Three dentary teeth are preserved, which lack serrations. What Zhou and Zhang identify as a right surangular really looks like a left splenial to me, as it matches the right splenial in morphology and overlaps the right prearticular medially. The articular is not pneumatic.
The cervicals are coded as having heterocoelous anterior articular ends, and amphicoelous posterior ends. Zhou and Zhang report at least ten cervicals were present, but only five are articulated in the photo, with another possible cervical behind the mandibles. The dorsals lack lateral fossae and have parapophyses placed anteriorly. Gastralia are present. There are twenty-two caudal vertebrae, of which the first two have transverse processes. The first caudal has such expanded transverse processes, I wonder if it's not a sacral. At least 3-22 lack neural spines and they elongate very quickly. The third centrum is about a third as tall as long, and by caudal 17, they are over six times longer than tall. The prezygopophyses start out very short (<20% of the centrum) and reach a maximum length of 37% of central length around caudals 13-18. Thus, they are not unusually elongate compared to most tetanurines. Chevrons extend to the last vertebra and are all dorsoventrally compressed, similar to the eighth and more distal chevrons of Archaeopteryx. They contact each other at the ends, but do not overlap, contra Jaime. Both anterior and posterior ends are forked, making interlocking improbable.
The sternum is said to be short with an unfused lateral process, but it looks only partially preserved to me. A fragment shorter than the coracoid is visible, completely flat with the edge oriented medially straight and the lateral one with two corners. I see nothing to indicate these aren't broken edges, though the fact they coded "coracoid sulci present" might indicate the anterolateral edge is real. The lateral process is very narrow, but expands distally to four times the shaft width. This distal portion has a round fenestra roughly in the center. One furcular arm is well preserved, as is the tip of the other. It shows a roughly Archaeopteryx-like form, though looks straighter to me. It is fairly robust, and is reported to lack a hypocleidium or lateral excavations.
The scapula is straight and tapers to a point distally. It is mobily articulated with the coracoid, though the condition of the joint is unknown. The coracoid is longer than Archaeopteryx and non-avians, comparable to Confuciusornis. It's not strut-like, but has a proximal narrowing and concave lateral edge. There is no procoracoid and the supracoracoid foramen/groove is absent.
The humerus is very primitive, lacking a ventral tubercle, capital incision or the angled distal condyles of enantiornithines. The metacarpus is said to be fused proximally, though it is coded as also being incompetely fused, like Confuciusornis. Metacarpal III is "tightly attached" to metacarpal II distally. It is shorter than the second metacarpal. The first digit is shorter than metcarpal II. Phalanx I-1 is remarkably slender and bowed. Phalanx II-2 is longer than phalanx II-1, which is flattened. The second manual ungual is smaller than the first, but not nearly as much as confuciusornithids. Digit III contains four phalanges, the first very short. The ungual reaches to the middle of phalanx II-2. Interestingly, Zhou and Zhang report new Sapeornis material indicates it has only two reduced phalanges on digit III, like Protopteryx, Longipteryx and Eocathayornis.
The pelvis is weakly opisthopubic, with the pubis angled at 110 degrees. The preacetabular process is elongate and pointed, with hardly any concavity between the pubic peduncle and it, while the postacetabular process is much shorter and also tapered. The pubis is slightly sinusoidal and expanded only posteriorly at its distal end. The authors state "the pubic foot is spoon-shaped as in Archaeopteryx and some enantiornithines", which may refer to a hypopubic cup. Such a structure is absent in Archaeopteryx though (Norell and Makovicky, 1997) and is not found in enantiornithines either (at least in Liaoxiornis, "Cathayornis" caudatus, Concornis and Gobipteryx). The pubic symphysis is described as short. The ischium is about 57% of pubic length. It has both a distally expanded proximodorsal process and a low triangular mid-dorsal process. If present, the obturator process was placed extremely distally.
The femur has a posterior trochantor and the fibula does not reach the tarsus. The astragalus and calcaneum are unfused to each other and the tibia. The ascending process is high (154% of astragalocalcanear transverse width) and arises laterally. The metatarsus is fused proximally, with metatarsal V present. The hallux is said to be reversed, but the phalanges are all disarticulated, making me wonder how they determined this. The second ungual is said to be enlarged, "as in Archaeopteryx and Rahonavis", but Archaeopteryx lacks this character. I do see an ungual perhaps 20% larger than the others that looks rather like a sickle claw.
Despite the fact feathers were found with BPM 1 3-13, Longipteryx and Yixianornis from the type locality, no feathers were preserved with Jeholornis.
Over 50 rounded seeds (8-10 mm) were found in the stomach position. They are referred to Carpolithus.


How is this specimen important in combating ABSRD?
The tail is not deinonychosaur-like enough to matter. The pubis being only slightly opisthopubic might be good, though it seems disarticulated and ABSRDists have ignored better evidence from Archaeopteryx for years. The most important feature may be the ascending process, which very clearly arises from the astragalus, while ABSRDists claim birds' is associated with the calcaneum (and is thus a non-homologous feature they call the pretibial bone). This should quash that theory, if Feduccia et al. are even taken seriously by anyone anymore.


What's Jeholornis related to?
A good question. Zhou and Zhang added it and Rahonavis to Norell and Clarke's Apsaravis matrix, and deleted hesperornithiformes for some reason. Doing the latter amusingly made pygostylians primitively toothless, with Gobipteryx as the most basal enantiornithine because of this. Jeholornis came out in a trichotomy with Rahonavis and Sapeornis+pygostylians. As this study did not include Yandangornis, Protopteryx, Jibeinia or several other important taxa, this result should be viewed with caution.
Judging by some quick comparisons, it's more derived than Archaeopteryx based on the semi-heterocoelous cervicals, less than twenty-three caudals, less than eight caudals with transverse processes, elongate lateral sternal processes, more elongate coracoid, scapulacoracoid joint mobile, proximally fused metacarpus, manual digit I shorter than metacarpal II, flattened manual phalanx II-1, fibula does not contact tarsus. More primitive characters are- no lateral dorsal fossae (also in Sapeornis), distal caudal prezygopophyses not reduced. It shares the mobile scapulocoracoid joint and fibula that does not contact the tarsus with Rahonavis, as well as the sickle claw (though that is probably symplesiomorphic). The elongate proximal caudals and universally dorsoventrally compressed chevrons are shared with Microraptor. Compared to Yandangornis, it is more derived in having semi-heterocoelous cervicals. The two genera share several characters- toothless maxilla, maxilla reduced in size compared to premaxilla, less than six caudals with transverse processes, elongation of caudal centra to over three times centrum height starts at at least fifth vertebrae, fibula does not reach tarsus. I very provisionally refer Jeholornis to the Yandangornithidae until my coelurosaur analysis is completed.


Mickey Mortimer

-- Jeff Hecht, science & technology writer jeff@jeffhecht.com; http://www.jeffhecht.com Boston Correspondent: New Scientist magazine Contributing Editor: Laser Focus World, WDM Solutions 525 Auburn St., Auburndale, MA 02466 USA v. 617-965-3834; fax 617-332-4760