A naturalist's various thoughts on the frog genus Breviceps, part 1

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ECOLOGICAL DISTRIBUTION OF BREVICEPS IN SOUTH AFRICA:

The extremely aberrant frogs in family Brevicepitidae (https://www.inaturalist.org/observations?place_id=any&taxon_id=64729&view=species and https://en.wikipedia.org/wiki/Brevicipitidae) occur in southern and eastern Africa, as far north as Ethiopia.

Breviceps is a true African speciality, and occurs mainly in southern Africa.

The southernmost tip of Africa is rich in spp. of Breviceps (https://en.wikipedia.org/wiki/Breviceps). These frogs lack any real counterparts at similar latitudes or under mediterranean-type climates on any other continent.

So, I went through the South African spp. in this genus to see which landforms/vegetation types lack Breviceps.
 
The answer is: most of the Karoo (https://en.wikipedia.org/wiki/Karoo) and most of the flat Highveld (https://en.wikipedia.org/wiki/Highveld). Breviceps occurs everywhere else in South Africa.
 
What is remarkable about this finding:

Breviceps spans the full gradient from Namib dunes (Breviceps macrops near the mouth of the Orange River, https://www.inaturalist.org/taxa/25004-Breviceps-macrops) to dense forest (Breviceps fuscus at Knysna, https://www.inaturalist.org/taxa/25003-Breviceps-fuscus).

Yet, it has not penetrated some intermediate environments, such as parts of the Highveld and the Karoo:

• In the Highveld, Breviceps occurs only on slopes at the edges of the biome.
• In the Karoo, Breviceps occurs only at the edge of the Highveld (on flat terrain) and in special parts of the ‘Karoo’ such as Namaqualand (https://en.wikipedia.org/wiki/Namaqualand).

Here are some details:
 
Breviceps verrucosus (https://www.inaturalist.org/taxa/24998-Breviceps-verrucosus) occurs in the Drakensberg (https://en.wikipedia.org/wiki/Drakensberg), Maloti Mountains (https://en.wikipedia.org/wiki/Maloti_Mountains), and the mountains/scarp of Mpumalanga (https://en.wikipedia.org/wiki/Mpumalanga).
 
Breviceps mossambicus (https://www.inaturalist.org/taxa/25002-Breviceps-mossambicus) occurs on the scarp of the Free State (https://en.wikipedia.org/wiki/Free_State_(province)) and Mpumalanga.
 
Breviceps bagginsi (https://www.inaturalist.org/taxa/24996-Breviceps-bagginsi) occurs in the Natal mistbelt (https://en.wikipedia.org/wiki/Forests_of_KwaZulu-Natal#Mistbelt_forest).
 
Breviceps adspersus (https://www.inaturalist.org/taxa/25001-Breviceps-adspersus) occurs on the borders of the Free State (except for the southernmost border and the Maloti border with Lesotho), plus the whole Kimberley area, plus the scarp in Mpumalanga, and high-lying Natal. So it is largely absent from the flat Highveld, although present more or less all around the Highveld.

My interpretation:
If there is a paradox in the ecological distribution of Breviceps in South Africa, it is this:

This genus manages to be virtually the only frog in situations as diverse as the Namib desert and the Knysna forests (away from streams), but is absent from an environment as moderate, mesic, and unremarkable as friable substrates in the flat Highveld.

It would go too far to call Breviceps an afromontane genus (https://en.wikipedia.org/wiki/Afromontane). However, its species-richness is noteworthy in the afromontane environment.

Most of the Karoo and the flat Highveld have no Breviceps at all. However, fynbos and the high-lying slopes of the eastern scarp have various spp. of Breviceps, in some cases with more than one species sharing a given area.

Breviceos adspersus is usually associated with savannas on plains. However, it also occurs at high altitudes, presumably in montane grassland, or nutrient-poor, fire-prone grassland on slopes, in the Highveld.

Do readers see how there is a series of species overlapping each other from west to east, along this belt under temperate climates?

ON SYMPATRY AND SPECIES-RICHNESS IN BREVICEPS:

It strikes me that, more than any other lineage of southern African frogs, Breviceps has great species-richness at the ‘southern tip of Africa’. This is in the sense of not only the Fynbos Biome, but also the ‘afromontane’ belt that is, in many ways, a biogeographical extension of the temperate-zone South Africa into the tropics.

Heleophryne (https://www.inaturalist.org/observations?place_id=any&taxon_id=24464&view=species) shows a similar pattern, but is far less speciose.

Certain other genera of frogs in southern Africa are speciose, but are concentrated in the most tropical parts of the subcontinent, e.g. Ptychadena (https://www.inaturalist.org/observations?place_id=any&taxon_id=25741&view=species) and Hyperolius (https://www.inaturalist.org/observations?place_id=any&taxon_id=23276&view=species).

The maps in http://frogmap.adu.org.za/ show the distributions of all those spp. of Breviceps that occur anywhere in the Fynbos Biome, or on the scarp from the Eastern Cape to Mpumalanga. All these spp. are roughly associated with fire-prone grassland or fire-free forest patches on mountains, whether near sea level, or in the Drakensberg (https://en.wikipedia.org/wiki/Drakensberg).

A total of nine spp. of Breviceps participate in the pattern I have noticed here.

Breviceps namaquensis occurs on the coastal forelands from the Cederberg area (https://en.wikipedia.org/wiki/Cederberg) south to just north of Cape Town: http://frogmap.adu.org.za/Species_text.php?sp=230.

Breviceps gibbosus is restricted to the western coastal forelands, mainly the ‘Swartland’ (https://en.wikipedia.org/wiki/Swartland): http://frogmap.adu.org.za/Species_text.php?sp=180.

Breviceps rosei occurs along the coast all the way from Klawer (https://en.wikipedia.org/wiki/Klawer) through Cape Town to Mossel Bay (https://en.wikipedia.org/wiki/Mossel_Bay): http://frogmap.adu.org.za/Species_text.php?sp=240.

Breviceps acutirostris occurs in the fynbos mountains from the Hottentots-Holland (https://en.wikipedia.org/wiki/Hottentots_Holland_Mountains) to the Langeberg (https://en.wikipedia.org/wiki/Langeberg):http://frogmap.adu.org.za/Species_text.php?sp=150.

Breviceps montanus occurs in mountain fynbos, as far east as Knysna (https://en.wikipedia.org/wiki/Knysna): http://frogmap.adu.org.za/Species_text.php?sp=210.

Breviceps fuscus is restricted to the southern Cape: http://frogmap.adu.org.za/Species_text.php?sp=170.

Breviceps verrucosus does not reach the Fynbos Biome but picks up in the mountains of the Eastern Cape and proceeds along the scarp of the Drakensberg to reach the northernmost mountains in Mpumalanga (in the Lekgalameetse area, https://en.wikipedia.org/wiki/Lekgalameetse_Provincial_Park):http://frogmap.adu.org.za/Species_text.php?sp=270.

Breviceps mossambicus occurs along the scarp from northernmost Lesotho to the northernmost mountains of the scarp in Limpopo Province (and B. sylvestris occurs in the Soutpansberg area,https://en.wikipedia.org/wiki/Soutpansberg):http://frogmap.adu.org.za/Species_text.php?sp=220/http://frogmap.adu.org.za/Species_text.php?sp=260.

Breviceps adspersus occurs along the scarp of the Drakensberg all the way from Natal to Limpopo Province (https://en.wikipedia.org/wiki/Limpopo), and presumably up through the eastern highlands of Zimbabwe (https://en.wikipedia.org/wiki/Zimbabwe). Its distribution actually begins just east of Plettenberg Bay(https://en.wikipedia.org/wiki/Plettenberg_Bay):http://frogmap.adu.org.za/Species_text.php?sp=160.
 
ANTI-PREDATOR DEFENCES IN BREVICEPS:
  
Two genera of snakes are particularly likely to threaten Breviceps.
 
Both are colubrid genera restricted to southern Africa, and extending to East Africa. They thus mirror the range of Breviceps.

Most spp. of Breviceps are likely to coexist with these snakes, which are particularly common in the range of Breviceps, including fynbos (https://en.wikipedia.org/wiki/Fynbos). (Note that both Breviceps and the mole snake occur on Robben Island (https://en.wikipedia.org/wiki/Robben_Island).)

The circumstantial evidence is suggestive.
 
The first snake is the mole snake Pseudaspis cana (https://www.inaturalist.org/taxa/28948-Pseudaspis-cana), which is capable of digging down to the subterranean refuges of Breviceps (using the loosely filled track of the frog as it submerges), as well as taking them at the surface during the day.

Adults are too large-bodied to bother with Breviceps. However, juveniles look and behave like a separate species of snake. They possibly eat these frogs, although this does not seem to have been recorded.

I realise that the mole snake is normally regarded as a rodent-eater. However, juveniles eat lizards, and all ages eat eggs by swallowing them whole.

I infer that, although the mole snake may find it hard to get the space to constrict its prey underground, it does behave as a constrictor above-ground.

So, it is plausible that a major predator of Breviceps, throughout the range of this genus, is juveniles of the mole snake.

What is worth bearing in mind:

Adults of the mole snake eat rodents. However, there are two facts that make this species important for Breviceps.

Firstly, the mole snake is abundant in southern Africa, because of the abundance of mole-rats. Thus, even if just juveniles attack Breviceps, that would still constitute major predatory pressure.

And secondly, the mole snake is extremely fecund, with up to 95 live-borne young per litter.
 
The second snake is skaapstekers, Psammophylax (https://www.inaturalist.org/observations?place_id=any&taxon_id=28951&view=species), of which there are five spp., but only two relevant to Breviceps.

Between them, these two spp. cover - as in the case of the mole snake - the whole range of Breviceps from the Cape Peninsula (https://en.wikipedia.org/wiki/Cape_Peninsula) to southern East Africa.

As in the case of the mole snake, Psammophylax is one of the commonest snakes in fynbos and grassland. Psammophylax is less specialised on rodents than is Pseudaspis, and this genus is certainly known to eat frogs (although I have not seen any records of Breviceps in particular).

Again, it is likely to be mainly juveniles that eat frogs. However, again this would be a considerable factor, because these snakes are so common in fynbos and other environments in which Breviceps is common.

Pseudaspis is non-venomous, and may rely on constriction of Breviceps. Psammophylax is venomous, and I suspect that it does not rely on constriction when predating this genus of frogs.

Here is footage of Psammophylax rhombeatus subduing prey: https://www.youtube.com/watch?v=u1NxjBRFs-Y and https://www.youtube.com/watch?v=JqydZk6m6X0.
 
The teeth of the mole snake are noteworthy, and so is the venom of skaapstekers.
 
This what Alexander and Marais (2007) wrote:
“...some of the teeth of the Mole Snake’s lower jaw have a cutting edge along their inner curve. Once a Mole Snake bites onto a finger, it is able to pull the lower jaw backwards using the upper jaw as a lever, slicing the teeth of the lower jaw through the flesh to make two parallel cuts. If not immediately removed, it will rotate its head right around the finger, causing lacerations that can encircle a finger. This unique method of biting probably aids Mole Snakes in dispatching dangerous mole-rats underground, where the physical limitations of the burrow prevent the snake from constricting its prey in the conventional way...Mole Snakes are very unusual in that males fight rivals by biting them viciously. Most adult male Mole Snakes bear scars from previous fights that tend to be concentrated either on their necks or tails. Cuts may encircle the tail completely, and bites on the body often expose ribs. Males appear, remarkably, to recover from these injuries, which often appear to be very serious.”

We should perhaps consider

• what this unusual slicing ability might mean in the case of inflated frogs. and
• whether it is possessed by juveniles of these snakes, which could conceivably have a different dentition.

In the case of the venom of skaapstekers:
What is odd is that this is produced in small quantities, and is harmless to humans. (I infer that the effects of a bite are less than that of a bee sting.)

This suggests that perhaps the main function of the venom is to subdue reptiles and/or amphibians, skaapstekers relying on constriction when they eat rodents.

Psammophylax also has a small head, and thus a rather small mouth. From this, I infer that inflation would slow down the snake greatly in swallowing the frog. This in turn would expose the snake to its own predators, which are many in southern Africa.
 
I suggest that the glue of Breviceps, if it is indeed secreted under threat of predation or immediately following a strike by a snake, could work particularly well in combination with inflation.

This would, come to think of it, work well w.r.t. both slowing down swallowing and glueing the coils of the snake together, in both ways compromising the ability of the snake to flee its own enemies. If Breviceps produced a distress call, that would also work well, in conjunction.
 
I wonder: what is it about the lungs of Breviceps that prevents snakes from puncturing the inflation as they swallow the frog?

INSIGHT INTO DEFENCES OF BREVICEPS:
 
This video clip (https://www.youtube.com/watch?v=VYT9Oniwbh4) shows that Bitis schneideri (https://www.inaturalist.org/taxa/30859-Bitis-schneideri) can take up to 1.5 hours to swallow Breviceps, owing to the defensive inflation of the frog.

Furthermore, the fangs of this adder, although no doubt having killed the frog early in the sequence, were never able to puncture the frog enough to deflate its body.

Does this indicate that a major tactic for Breviceps is to remain inflated even when dead, slowing down its consumption by snakes, and thus exposing the snakes to their own predators?
 
There is no evidence of any secretion on the frog in the above video, sticky or otherwise. This could possibly be because it died quickly when bitten by this venomous snake.

Alternatively, it is possible that Breviceps uses its glue only in amplexus (https://en.wikipedia.org/wiki/Amplexus), as opposed to anti-predator defence.

Certainly I have seen a photo of an inflated specimen of Breviceps with plenty of latexy-looking secretion oozing out of the skin on its back. However, this secretion cannot be assumed to be gluey.

The following show B. rosei with minimal inflation of the body. All spp. of Breviceps tend to be in inflated mode when photographed, hinting at their ‘hyper-defensiveness’. 
https://hardakerwildlife.files.wordpress.com/2012/10/011-20120909melkbos-sandrainfrog.jpg
http://biodiversityfocused.co.za/wp-content/uploads/2015/02/Sand-Rain-Frog-Breviceps-rosei-6.jpg.

Despite the sheer number of species and the diversity of the environments, Breviceps is consistent in its body form, reproductive habits and seasonal emergences.

It is essentially a single, distinctive kind of frog, probably adapted to extreme predation and differentiated into various species and habitats but without modification of its basic strategy of life.
 
Is there any frog in South or North America that is comparable with Breviceps?

In the case of Australia there is Notaden. However, Notaden breeds in pools like a ‘normal’ frog, and does not enter the cool southern regions of Australia at all.

Both Breviceps and Notaden inhabit tropical savannas and semi-arid interiors. However, where they differ is in penetrating the temperate climate: Notaden does not do so at all (except in the dry interior of e.g. southern New South Wales, https://en.wikipedia.org/wiki/New_South_Wales), whereas such penetration is the hallmark of the ecological distribution of Breviceps in southern Africa.

Breviceps namaquensis:
https://www.tyroneping.co.za/amphibians-of-southern-africa/breviceps-namaquensis-namaqua-rain-frog/
 
Breviceps gibbosus:
https://www.tyroneping.co.za/amphibians-of-southern-africa/breviceps-gibbosus-cape-rain-frog/
 
Breviceps rosei:
https://www.tyroneping.co.za/amphibians-of-southern-africa/breviceps-rosei-rosei/

Breviceps acutirostris:
https://www.tyroneping.co.za/amphibians-of-southern-africa/breviceps-acutirostris-strawberry-rain-frog/

Breviceps montanus:
https://www.tyroneping.co.za/amphibians-of-southern-africa/mountain-rain-frog-breviceps-montanus/

Breviceps fuscus:
https://www.oneearth.org/species-of-the-week-black-rain-frog/
 
Breviceps verrucosus:
https://www.tyroneping.co.za/amphibians-of-southern-africa/breviceps-verrucosus/

Breviceps mossambicus:
https://www.tyroneping.co.za/amphibians-of-southern-africa/breviceps-mossambicus/
 
Breviceps adspersus:
https://www.flickr.com/photos/cowyeow/4884400121

SIMILARITIES AND DIFFERENCES, NOTADEN OF AUSTRALIA VERSUS BREVICEPS OF AFRICA:
 
Breviceps of southern Africa is an extremely specialised genus of frogs, not so much dietarily but in terms of body form and anti-predator strategy. This genus has the flattest face of any frogs worldwide, along with extreme inflation of the body to virtually spherical shapes (backed up by secretion of glue from the skin, which complicates swallowing by a predator), something aided by the shortness of the legs.

Despite the flatness of the face, the eyes are large and distinguished by markings on the face.

Breviceps has not only direct development (lacking a conventional tadpole stage) but subterranean development with subterranean parental care.
 
The only frogs worldwide that somewhat resemble Breviceps are four spp. of Notaden in Australia. These belong to a different family: Limnodynastidae.

Notaden also

• has a rather flat face,
• spends most of its life underground,
• inflates its body to some extent with threatened by predators, and
• secretes glue from its skin.

There are few genera of frogs worldwide that secrete glue. However, Breviceps and Notaden are the best-known of them, a strong point of convergence.
 
However, there are also important differences, beyond the lesser specialisation of body form in Notaden than in Breviceps.
 
Notaden has conventional development via a tadpole stage, in pools on the surface during the rainy season. This contrasts with the much more specialised reproduction seen in Breviceps.

Both genera spend most of their time underground, penetrating arid areas but not restricted to them. However, they have quite different reproductive habits. In this way they parallel the point I have made about Ranoidea, which is reproductively conservative.
 
Breviceps can make a distress call. I do not know whether Notaden can do this.
 
Notaden bennettii has aposematic colouration (https://en.wikipedia.org/wiki/Aposematism), in contrast with all its congeners, and all spp. of Breviceps.
 
Notaden can perhaps be described as a myrmecophagous genus of frogs, because it eats mainly termites and ants. Several spp. of Breviceps depend on termite alates, but the genus as a whole is not myrmecophagous.
 
The ecological distributions are different. Breviceps occurs widely in southern Africa, with gaps in the Karoo and the Highveld; it is particularly speciose at the southern tip of Africa. By contrast, Notaden does not reach the southernmost parts of Australia at all (collective distribution of all four spp. of Notaden: http://upload.wikimedia.org/wikipedia/commons/thumb/d/d4/Notaden_distribution.png/220px-Notaden_distribution.png).
 
The most Breviceps-like species of Notaden, namely N. weigeli (https://www.frogid.net.au/frogs/notaden-weigeli), has by far the most restricted distribution, being confined to a small part of northernmost Western Australia, in tropical savanna.
 
This leads me to the following thought:
 
In some ways, Breviceps is the antithesis of the pelodryadid genus Ranoidea.

Ranoidea is extremely speciose in Australia, with much sympatry and differentiation in adult body form, but little departure from a classic, conservative larval stage.

Breviceps is one of the most speciose genera of frogs in southern Africa, with much sympatry in the southwestern Cape and the eastern scarp particularly.

However, in contrast with Ranoidea, the adult body form is remarkably conservative for the wide range of environments occupied, from desert to forest, and from low altitudes to high altitudes. And, true enough, the reproductive strategy of Breviceps is extreme: subterranean direct development with parental care.
 
Hence my growing realisation that a major difference between Australian and southern African frogs is that the latter are far more shaped by predation pressures than the former.
 
Looking at the overall distribution of the genus Notaden, it is easy to think that the main factor determining this might be the availability of ants and termites in the rainy season, i.e. there is a central specialisation on food, a secondary specialisation on dormancy for most of the year underground, and a conservative (ancient) reproductive mode.

In Breviceps, the organising principles seem different:
Food and habitat vary far more greatly than in Notaden, but body form is always extreme in terms of flat face, short legs and spherically inflatable body, while the reproductive mode is extremely specialised in a way consistent with minimising predation.

FUNCTION OF CROSSING OUT OF EYE IN BREVICEPS:
 
Breviceps, a southern African speciality, and one of the most familiar frogs in the Cape Town area, is the flattest-faced frog on Earth.

By flattest-faced, I mean having the eyes right above the mouth, with no rostrum (muzzle) to speak of.

There are other small-mouthed and short-snouted frogs out there (e.g. southwestern Australian Myobatrachus, https://www.inaturalist.org/taxa/25298-Myobatrachus-gouldii).

However, what is odd about Breviceps is that it combines a small mouth with a short muzzle and large eyes.

This means the eyes bear the same sort of relationship to the nose and mouth, and the nose bears the same sort of relationship to the mouth, as in the human face.

It is this humanlike, flat-faced appearance that accounts more than anything else for the viral success of this video clip (https://www.youtube.com/watch?v=qwKak-r74k8). This is despite the alien-looking (and even rather diabolical) eyes of this frog, which detract from its human appeal.

All Breviceps have horizontal, goat-like pupils. However, this species has a particularly pale iris, and this individual has the pupil nearly closed because of the bright illumination. The unappealing eyes are outweighed by the flat face. This frog comes over as cute, because of its overall resemblance to a human infant.
 
The closest to Breviceps, worldwide, is Notaden in Australia. The formula for the face is similar, but not taken to the extremes seen in Breviceps.
 
The main point of this section of this Post – and an original observation – is that most spp. of Breviceps have the eye crossed out with dark pigmentation on the nearby skin, DESPITE the flatness of the face.

This is one of the few frogs in which the bar, which crosses out the eye, runs diagonally back from the eye, rather than

• horizontally (extremely common among frogs), or
• vertically (seen in rather weak form in e.g. Ranoidea novaehollandiae and Notaden spp.).

There are so many lineages of frogs, around the world, with the eyes crossed out with dark markings on the face (usually longitudinal) that this pattern is almost a 'default' for frogs. It seems to have re-evolved innumerable times among frogs.

What is odd about Breviceps mossambicus, B. adspersus, and most congeners, is that there is no ‘longitude’ to speak of in such a small face, and the dark bar runs obliquely downwards from the eye, instead of straight towards the neck.

What this really means is that the bar that crosses out the eye has changed course in keeping with the main plane of the flat face.

It would be interesting to see if any fishes (a group in which crossed-out eyes are extremely common) also show this shift from horizontal to vertical, in keeping with a particularly short face.
 
Also odd is my observation that, in some individuals of at least one species, B. mossambicus, the pattern on the face is so stark that it actually seems to increase, not decrease, the conspicuousness of the frog (http://calphotos.berkeley.edu/imgs/512x768/0000_0000/0612/1425.jpeghttp://www.jacobsjungle.com/wp-content/uploads/2014/01/The-Mozambique-rain-frog-Breviceps-mossambicus.jpghttp://static.inaturalist.org/photos/806834/medium.jpg?1398300653http://40.media.tumblr.com/1a21d6b76d1392d7ae99829237aecc36/tumblr_n65u9qTMih1qb8vfjo2_500.jpg).
 
Breviceps spends most of its time underground. It can therefore be expected to lack crossing out of the eyes, because they are not seen in bright illumination often enough for the conspicuousness of the eyes to attract predators much.

Even during their brief period of activity, in the early summer when the termite alates swarm, they spend the days under cover and only come out at night.

So, I suspect that the advantage of the disruption of the eyes is somewhat different between Breviceps and other frogs.

In most frogs, it prevents the animal being noticed in the first place. Such a function is unlikely in Breviceps because of its habits.

Instead, I suspect that the function in Breviceps is after the frog is spotted by the predator, and the frog has already inflated its body. The bars then tend to confuse the anterior pole of the body with the posterior pole, making it hard for the predator to locate the head for a lethal strike. Breviceps, when inflated, becomes closer to a sphere than does any other frog on Earth.

Please note from the photos below that, when the frog is inflated, the dark band running from the eye tends to follow the circumference of the sphere. This may disrupt the eye more than would be the case were this band horizontal.
 
Although some of the other underground frogs of the world do have some crossing out of the eyes, I suspect that Breviceps is the only lineage in which the crossing out functions mainly in inflated mode.

In summary, I suggest that the pattern of colouration about the eyes in Breviceps functions not to hide the whole frog (as is usual among thousands of spp. of frogs worldwide), but instead to confuse the anterior with the posterior in inflated mode.
 
Brevicepitidae:

Breviceps adspersus:
https://c1.staticflickr.com/5/4141/4885007478_a8f5f48554_b.jpg
http://i27.photobucket.com/albums/c175/fooble182/Middelrus%20Herping%2015-07-2012/Breviceps%20adspersus/Breviceps-adspersus-Middelrus-By-Tyrone_Ping-Watermark3.jpg
http://calphotos.berkeley.edu/imgs/512x768/0000_0000/0612/1430.jpeg
http://www.sabisabi.com/images/21Feb12-Bushveld-Rain-Frog---Wim-Vorster.jpg

Breviceps mossambicus:
see above

Breviceps rosei:
https://www.inaturalist.org/observations/59858090
https://www.inaturalist.org/observations/12006777
https://www.inaturalist.org/observations/51072382
https://www.inaturalist.org/observations/52510009

Breviceps sylvestris:
https://www.inaturalist.org/observations/68514153
https://www.inaturalist.org/observations/60397418

TESTING WHETHER MOST UNDERGROUND FROGS LACK CROSSED-OUT EYES:
  
I wondered whether most frog lineages that spend most of their lives underground lack the ‘eye crossed out’ pattern so common in frogs that are active above ground for most of their lives.
 
In Ranoidea, some species do have crossed-out eyes, but no species in this genus is extremely specialised for underground life.

In a large-bodied species, Ranoidea novaehollandiae (https://www.inaturalist.org/taxa/517099-Ranoidea-novaehollandiae), there is a noteworthy pattern, in which the horizontal dark bar is joined by a vertical dark bar ventral to the eye. However, this pattern is not strong.
 
In Neobatrachus (https://www.inaturalist.org/observations?place_id=any&taxon_id=22067&view=species), Scaphiopus (https://www.inaturalist.org/observations?place_id=any&taxon_id=26689&view=species), and Pelobates (https://www.inaturalist.org/observations?place_id=any&taxon_id=25309&view=species), there seems to be no crossing out of the eyes.
 
Notaden (https://www.inaturalist.org/observations?place_id=any&taxon_id=22078&view=species) is particularly worthy of scrutiny because this is the genus, of all frog genera worldwide, that most resembles southern African Breviceps.

Notaden does not really have a crossed-out pattern about the eyes. The closest thing is a pattern that is fairly weak, and found only in certain soecies, in which there is something of a dark bar extending ventrally from the eyes.
  
Limnodynastidae:

Notaden bennettii:
https://www.inaturalist.org/taxa/22082-Notaden-bennettii
http://calphotos.berkeley.edu/imgs/512x768/0000_0000/0412/2182.jpeg

Notaden nichollsi:
https://www.inaturalist.org/taxa/22080-Notaden-nichollsi

Notaden melanoscaphus:
http://i720.photobucket.com/albums/ww206/froggerowl/Notadenmelanoscaphus-NorthernSpadef.jpg
 
Pelobatidae:

Pelobates fuscus:
http://www.naturephoto-cz.com/photos/sevcik/common-spadefoot--pelobates-fuscus-4.jpg
 
Scaphiopodidae:

Scaphiopus couchii:
http://tolweb.org/tree/ToLimages/204405806_400dd43616_o.300a.jpg

Limnodynastidae:

Neobatrachus pictus:
http://frogs.org.au/img/450/0512-SE-frog-Neobatrachus_pictus-Hattah.jpg

to be continued in https://www.inaturalist.org/journal/milewski/69046-a-naturalist-s-various-thoughts-on-the-frog-genus-breviceps-part-2#...

Publicado el 13 de agosto de 2022 por milewski