[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Kokartus (stem salamander) bone histology + turtle ribs + Nyctisoma, new heron from Mongolia

Ben Creisler

A number of recent non-dino papers that may be of interest to some:

Pavel Skutschas and Koen Stein (2015)
Long bone histology of the stem salamander Kokartus honorarius
(Amphibia: Caudata) from the Middle Jurassic of Kyrgyzstan.
Journal of Anatomy (advance online publication)
DOI: 10.1111/joa.12281

Kokartus honorarius from the Middle Jurassic (Bathonian) of Kyrgyzstan
is one of the oldest salamanders in the fossil record, characterized
by a mixture of plesiomorphic morphological features and characters
shared with crown-group salamanders. Here we present a detailed
histological analysis of its long bones. The analysis of a growth
series demonstrates a significant histological maturation during
ontogeny, expressed by the progressive appearance of longitudinally
oriented primary vascular canals, primary osteons, growth marks,
remodelling features in primary bone tissues, as well as progressive
resorption of the calcified cartilage, formation of endochondral bone
and development of cartilaginous to bony trabeculae in the epiphyses.
Apart from the presence of secondary osteons, the long bone histology
of Kokartus is very similar to that of miniaturized temnospondyls,
other Jurassic stem salamanders, miniaturized seymouriamorphs and
modern crown-group salamanders. We propose that the presence of
secondary osteons in Kokartus honorarius is a plesiomorphic feature,
and the loss of secondary osteons in the long bones of crown-group
salamanders as well as in those of miniaturized temnospondyls is the
result of miniaturization processes. Hitherto, all stem salamander
long bong histology (Kokartus, Marmorerpeton and ‘salamander A’) has
been generally described as having paedomorphic features (i.e. the
presence of Katschenko's Line and a layer of calcified cartilage),
these taxa were thus most likely neotenic forms. The absence of clear
lines of arrested growth and annuli in long bones of Kokartus
honorarius suggests that the animals lived in an environment with
stable local conditions.


Ritva Rice, Paul Riccio, Scott F. Gilbert and Judith Cebra-Thomas (2015)
Emerging from the rib: Resolving the turtle controversies.
Journal of Experimental Zoology Part B: Molecular and Developmental
Evolution (advance online publication)
DOI: 10.1002/jez.b.22600

Two of the major controversies in the present study of turtle shell
development involve the mechanism by which the carapacial ridge
initiates shell formation and the mechanism by which each rib forms
the costal bones adjacent to it. This paper claims that both sides of
each debate might be correct—but within the species examined.
Mechanism is more properly “mechanisms,” and there is more than one
single way to initiate carapace formation and to form the costal
bones. In the initiation of the shell, the rib precursors may be kept
dorsal by either “axial displacement” (in the hard-shell turtles) or
“axial arrest” (in the soft-shell turtle Pelodiscus), or by a
combination of these. The former process would deflect the rib into
the dorsal dermis and allow it to continue its growth there, while the
latter process would truncate rib growth. In both instances, though,
the result is to keep the ribs from extending into the ventral body
wall. Our recent work has shown that the properties of the carapacial
ridge, a key evolutionary innovation of turtles, differ greatly
between these two groups. Similarly, the mechanism of costal bone
formation may differ between soft-shell and hard-shell turtles, in
that the hard-shell species may have both periosteal flattening as
well as dermal bone induction, while the soft-shelled turtles may have
only the first of these processes.


Andrzej Elzanowski & Nikita V. Zelenkov (2015)
A primitive heron (Aves: Ardeidae) from the Miocene of Central Asia.
Journal of Ornithology (advance online publication)
DOI: 10.1007/s10336-015-1164-y

Free pdf:

A robust quadrate from the Middle Miocene of Mongolia represents a new
genus of Ardeidae that combines the similarities to Nycticorax and
Tigrisoma, both of which have been recovered in basal positions in
recent phylogenies of the Ardeidae, and to cf. Pikaihao from the
Middle Miocene of Africa. The confluence of mandibular facets on the
medial condyle and pterygoid condyle in the new genus, Nycticorax, and
cf. Pikaihao is likely to be symplesiomorphic, as it is shared with
nearly all other waterbirds (except for the Ciconiidae), including the
immediate outgroup (Threskiornithidae). However, the medial
supraorbital crest is a likely synapomorphy of the new genus and cf.
Pikaihao. The similarities to Trigrisoma support its basal position,
as recovered from molecular sequences and proposed by a pre-cladistic
morphological analysis. Since both the night herons and Tigrisoma have
heads that are proportionally much larger than those of the large day
herons, it appears that the Ardeidae started their evolution with
relatively heavy heads, which may have contributed to the origins of
the family-specific head retraction in flight.