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|Earless Monitor Lizard - Lanthanotus borneensis|
|Tweet Topic Started: Feb 14 2013, 09:29 AM (1,879 Views)|
|Scalesofanubis||Feb 14 2013, 09:29 AM Post #1|
Earless Monitor Lizard - Lanthanotus borneensis
The earless monitor lizard (Lanthanotus borneensis) is a semi-aquatic, brown lizard native to northern Borneo. It is the only species in the family Lanthanotidae, a group related to the true monitor lizards, as well as to the beaded lizards. Earless monitor lizards are around 20cm(7.8in) in snout-ventral length, measuring 40-43cm(15.7-16.9in) in total body length. These animals have reduced eyes and limbs, a thick body, and strongly keeled scales. Despite the name, it is capable of hearing, although it lacks a tympanum or other visible signs of ears. It is a burrowing, nocturnal animal, feeding on earthworms and similar prey. In captivity, it has been known to eat squid, pieces of fish and liver. Like its closest relatives, it is oviparous, although little else is known about its reproduction. This species is very rare, and most known specimens are preserved, though these, also, are rare. The species is primarily of interest to scientists, since it is an evolutionary outgroup for both varanid and helodermatid lizards.
Edited by Ceratodromeus, Feb 9 2016, 08:46 AM.
|Ceratodromeus||Nov 22 2015, 01:23 PM Post #2|
First record of the Borneo Earless Monitor Lanthanotus borneensis (Steindachner, 1877) (Reptilia: Lanthanotidae) in West Kalimantan (Indonesian Borneo)
"The following paper presents the first published record of the cryptic Borneo Earless Monitor (Lanthanotus borneensis Steindachner, 1877) from West Kalimantan (Indonesian Borneo). This sole member of the family Lanthanotidae is endemic to Borneo. Since its description in 1877, all locality records of specimens refer to Sarawak (Malaysian Borneo). The recent discovery of this “living fossil” in an oil palm estate under development in Landak District expands its known distribution southward to Kalimantan. This paper (i) describes the circumstances of the discovery, characteristics of the individual and microhabitat structure in which it was found, (ii) provides results from local community interviews about the local distribution of the species, suggesting it is found more broadly in the Landak District and possibly elsewhere, and (iii) places this information in a broader context of current knowledge and high conservation value of L. borneensis."
Do note how the cryptic coloration and rugosed texture of the dorsal scalature helps this animal blend into its environment -- a very interesting animal!
|Mauro20||Feb 7 2016, 03:35 AM Post #3|
|Is 20 cm the SVL of this lizard, or does this includes the tail?|
|Ceratodromeus||Feb 7 2016, 03:38 AM Post #4|
|i will fix it in the OP, but ~20cm is snout-ventral length. Total body length is around 40-43cm|
|Ceratodromeus||Mar 30 2016, 09:39 AM Post #5|
for those of you have not seen the skull of one of these animals, here are some illustrations, as well as a detailed description of this species' cranial elements from the book The phylogeny of anguinomorph lizards(1980)
"As it has been discussed above, the phylogenetic position of Lanthanotus is still a matter of considerable controversy.
McDowell and Bogert (1954) and McDowell (1967,1972) consider Lanthanotus to be an advanced platynotan
lizard related to the fossil aigialosaur-dolichosaur stock. Russell (1967) believes Lanthanotus to be close to the fossil
saniwine varanids, thus again in an advanced position within the platynotans. The structure ofthe head musculature
indicates a somewhat intermediate position of Lanthanotus between the Helodermatidae and the Varanidae.
A careful consideration of the skull anatomy of Lanthanotus and its comparison to fossil and recent platynotans
becomes now necessary to test the various hypotheses.
On the basis of its skull anatomy (Fig. 24), Lanthanotus appears to be closer to the varanids than it is to the
helodermatids, but on the whole it remains more primitive than the Varanidae. The teeth found on the palatine
and pterygoid bones of Lanthanotus and Heloderma are a primitive feature in comparison with the toothless palate
ofvaranids. The vomerine processes ofthe premaxilla of Lanthanotus and Heloderma are short and blunt much as
in anguinoids (except for Anniella). Those of Varanus are elongate and pointed. The lack of a spiny projection
from the caudal edge of the lacrimal in Lanthanotus and Heloderma may be a primitive feature in comparison with
the Varanidae where this projection is generally present. However, the various species of the Varanidae show a
considerable variability of this character in size and occurence. The dorsal head of the epipterygoid reaches the
descensus parietalis in both Lanthanotus and Heloderma, the primitive condition in comparison with the varanids.
Here, the epipterygoid abuts against the alar process of the prootic, and it is the latter which articulates with the
lateral surface of the descensus parietalis. The posterior wall of the prefrontal is ventrally in contact with the jugal
in both Lanthanotus and Heloderma, whereas in Varanus the two bones are separated from each other through
a mesioventral extension of the lacrimal."
"Apart from these primitive charactersitics, Lanthanotus shares advanced features with Heloderma which are
lacking in Varanus, such as the contact of the prefrontal with the postfrontal, the lack of the upper temporal arch
and the descensus frontalis which closely approach the dorsal surface of the palatine bones and thus almost
completely separate the orbitae from one another.
Additional features not shared with Heloderma conftrm the assumption that Lanthanotus is more primitive than
In Lanthanotus both lacrimal foramina lie on the suture between the lacrimal and the prefrontal, whereas
in Varanus the lower lacrimal foramen is fully enclosed within the lacrimal bone. In Heloderma, the single lacrimal
foramen lies on the suture between the prefrontal and the lacrimal, as it is commonly observed in other lizards,
too - the primitive condition. Lanthanotus seems to have doubled the lacrimal foramen in its primitive position,
while in Varanus the lower of the two foramina migrated laterally into the lacrimal bone.
In Heloderma the descensus parietalis bears a distinct ventral projection in front of the alar process ofthe prootic
as it does in anguinoids. In Varanus the descensus parietalis bears a straight lower edge. In Lanthanotus, a weak
ventral projection is present which is much smaller than the ventral projection observed in Heloderma.
The shape of the anterodorsal edge of the cephalic condyle of the quadrate of Lanthanotusis again intermediate
between the broad, transverse edge of Heloderma and the narrow, pointed head of Varanus.
Four features are found to be even more primitive in Lanthanotus than they are in Heloderma. Therefore,
Lanthanotus cannot be derived from any helodermatid ancestor. These characters are the variably lesser degree
of posterior elongation of the external naris, since a contact of the prefrontal with the nasal is preserved at least
in the Frankfurt specimen of Lanthanotus (SMF. 66188). This contact is not preserved in the Harvard specimen of
Lanthanotus (MeZ. 8305). The vomers of Lanthanotus retain broad palatal shelves. The palatines retain elongate
and deep choanal grooves. The Meckelian groove is mesially closed in front of the anterior inferior alveolar
foramen due to the contact of the splenial with the dentary.
Shared specialisations of Lanthanotus and Varanus which are lacking in helodermatids include the fused nasals,
the articular socket on the dorsal surface of the cephalic condyle of the quadrate into which ftts the hind end of
the squamosal, and the restriction of metakinetic movement through the broad contact between the supraoccipital
and the parietal, a suture which may even ossifY in large, adult specimens of V. niloticus and V. komodoensis.
Divergent specialisations clearly separate Lanthanotus from the Varanidae, however. Varanids show a marked
elongation of the preorbital portion of the skull which results in an elongation of the tooth row, an adaptation to
capture relatively large prey. The prefrontal remains widely separated from the postfrontal in varanids, but the
two bones meet each other dorsal to the orbit in Lanthanotus. The postorbital bar is incomplete, and the alar
process of the prootic overlaps the descensus parietalis in varanids in contrast to Lanthanotus.
Lanthanotus appears to be specialised in the structure of its septomaxilla which shows a laterally ascending
flange. The lower jaw of Lanthanotus shows the greatest perfection of the lower jaw hinge among extant platynotans.
It is characterised by a straight vertical suture between angular and splenial.
The discussion of the anatomy of the skull shows that Lanthanotus occupies a somewhat intermediate position
between the Helodermatidae and the Varanidae, as it has already been suggested on the basis of the structure of
the head musculature. Many features of the skull of Lanthanotus are clearly of a more primitive nature than they
are in the Varanidae. Some features are even more primitive than they are in Heloderma and thus preclude any
helodermatid ancestry of Lanthanotus. Specialisations shared by Lanthanotus and Varanus demonstrate an advanced
evolutionary level of the two genera versus the primitive helodermatids, however.
Structurally, Lanthanotus is intermediate between Heloderma and Varanus, but phylogenetically the platynotans
must have diverged very early during their evolutionary history and evolved along separate lines of specialisations.
The Helodermatidae may have branched off prior to the dichotomy ofplatynotan evolution which gave rise to the
Lanthanotidae and to the Varanidae. Such an assumption is substantiated by shared specialisations of the skull
of Lanthanotus and Varanus which are lacking in Heloderma. "
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